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1
Boon, Calvin, and Thomas Dick. "Mycobacterium bovis BCG Response Regulator Essential for Hypoxic Dormancy." Journal of Bacteriology 184, no. 24 (December 15, 2002): 6760–67. http://dx.doi.org/10.1128/jb.184.24.6760-6767.2002.
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ABSTRACT Obligately aerobic tubercle bacilli are capable of adapting to survive hypoxia by developing into a nonreplicating or dormant form. Dormant bacilli maintain viability for extended periods. Furthermore, they are resistant to antimycobacterials, and hence, dormancy might play a role in the persistence of tuberculosis infection despite prolonged chemotherapy. Previously, we have grown dormant Mycobacterium bovis BCG in an oxygen-limited Wayne culture system and subjected the bacilli to proteome analysis. This work revealed the upregulation of the response regulator Rv3133c and three other polypeptides (α-crystallin and two “conserved hypothetical” proteins) upon entry into dormancy. Here, we replaced the coding sequence of the response regulator with a kanamycin resistance cassette and demonstrated that the loss-of-function mutant died after oxygen starvation-induced termination of growth. Thus, the disruption of this dormancy-induced transcription factor resulted in loss of the ability of BCG to adapt to survival of hypoxia. Two-dimensional gel electrophoresis of protein extracts from the gene-disrupted strain showed that the genetic loss of the response regulator caused loss of the induction of the other three dormancy proteins. Thus, the upregulation of these dormancy proteins requires the response regulator. Based on these two functions, dormancy survival and regulation, we named the Rv3133c gene dosR for dormancy survival regulator. Our results provide conclusive evidence that DosR is a key regulator in the oxygen starvation-induced mycobacterial dormancy response.
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Allen, Phil S., and Susan E. Meyer. "Ecological aspects of seed dormancy loss." Seed Science Research 8, no. 2 (June 1998): 183–92. http://dx.doi.org/10.1017/s0960258500004098.
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AbstractAdvances in seed biology include progress in understanding the ecological significance of seed dormancy mechanisms. This knowledge is being used to make more accurate predictions of germination timing in the field. For several wild species whose seedlings establish in spring, seed populations show relevant variation that can be correlated with habitat conditions. Populations from severe winter sites, where the major risk to seedlings is frost, tend to have long chilling requirements or to germinate very slowly at low temperatures. Populations from warmer sites, where the major risk is drought, are non-dormant and germinate very rapidly under these same conditions. Seed populations from intermediate sites exhibit variation in dormancy levels, both among and within plants, which spreads germination across a considerable time period. For grasses that undergo dry after-ripening, seed dormancy loss can be successfully modelled using hydrothermal time. Dormancy loss for a seed population is associated with a progressive downward shift in the mean base water potential, i.e., the water potential below which half of the seeds will not germinate. Other parameters (hydrothermal time requirement, base temperature and standard deviation of base water potentials) tend to be constant through time. Simulation models for predicting dormancy loss in the field can be created by combining measurements of seed zone temperatures with equations that describe changes in mean base water potential as a function of temperature. Successful validation of these and other models demonstrates that equations based on laboratory data can be used to predict dormancy loss under widely fluctuating field conditions. Future progress may allow prediction of germination timing based on knowledge of intrinsic dormancy characteristics of a seed population and long-term weather patterns in the field.
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Soltani, Elias, Sabine Gruber, Mostafa Oveisi, Nader Salehi, Iraj Alahdadi, and Majid Ghorbani Javid. "Water stress, temperature regimes and light control induction, and loss of secondary dormancy in Brassica napus L. seeds." Seed Science Research 27, no. 3 (June 6, 2017): 217–30. http://dx.doi.org/10.1017/s0960258517000186.
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AbstractThis study investigated the induction and loss of dormancy in oilseed rape (Brassica napus). Twenty genotypes were preliminary screened; from these, two genotypes, RGS003 and Hayola 308, which possess high potential for dormancy induction (HSD) and medium potential to induce secondary dormancy (MSD), were selected. The stratification of seeds at alternating temperatures of 5–30°C (in dark) significantly relieved secondary dormancy, but dormancy was not fully released. The ψb(50) values were −1.05 and −1.06 MPa for the MSD and the HSD before dormancy induction. After inducing dormancy, the ψb(50) values for the MSD and the HSD were increased to −0.59 and −0.01 on day 0 stratification at 20°C. The hydrothermal time (θHT) value was low for one-day stratification for HSD in comparison with other stratification treatments. Water stress can induce dormancy (if the seeds have the genetic potential for secondary dormancy) and warm stratification (in dark) can only reduce the intensity of dormancy. The seeds with a high potential of dormancy induction can overcome dormancy at alternating temperatures and in the presence of light. It can, therefore, be concluded that a portion of seeds can enter the cycle of dormancy ↔ non-dormancy. The secondary dormant seeds of B. napus cannot become non-dormant in darkness, but the level of dormancy may change from maximum (after water stress) to minimum (after warm stratification). It seems that the dormancy imposed by the conditions of deep burial (darkness in combination with water stress and more constant temperatures) might be more important to seed persistence than secondary dormancy induction and release. The dormancy cycle is an important pre-requisite in order to sense the depth of burial and the best time for seed germination.
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Walck, Jeffrey L., Carol C. Baskin, and Jerry M. Baskin. "Seeds of Thalictrum mirabile (Ranunculaceae) require cold stratification for loss of nondeep simple morphophysiological dormancy." Canadian Journal of Botany 77, no. 12 (February 20, 2000): 1769–76. http://dx.doi.org/10.1139/b99-149.
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Seeds of the eastern North American herbaceous polycarpic perennial Thalictrum mirabile Small have differentiated but underdeveloped (small) embryos that are physiologically dormant at maturity in September. Physiological dormancy was broken effectively by cold stratification at 1°C, but embryos required temperatures [Formula: see text]15:6°C for growth after physiological dormancy was broken. Gibberellic acid substituted for cold stratification. Breaking of physiological dormancy in seeds exposed to natural temperatures in a greenhouse occurred during winter, and embryo growth and germination occurred in late winter - early spring. Furthermore, seeds in the greenhouse remained viable until the second and third (spring) germination seasons. Thus, T. mirabile seeds have the capacity to form a short-lived persistent soil seed bank. Buried seeds of T. mirabile apparently go through an annual dormancy-nondormancy cycle. Seeds buried in September 1994 were nondormant when exhumed in April 1995 and April 1996 and incubated in light at 25:15°C for 2 weeks, but they were dormant in June 1995 and September 1995. Seeds of T. mirabile have nondeep simple morphophysiogical dormancy. This is the first report of nondeep simple morphophysiological dormancy being broken by cold, and not by warm, stratification.
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Tuttle, Keiko M., Shantel A. Martinez, Elizabeth C. Schramm, Yumiko Takebayashi, Mitsunori Seo, and Camille M. Steber. "Grain dormancy loss is associated with changes in ABA and GA sensitivity and hormone accumulation in bread wheat,Triticum aestivum(L.)." Seed Science Research 25, no. 2 (March 9, 2015): 179–93. http://dx.doi.org/10.1017/s0960258515000057.
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AbstractKnowledge about the hormonal control of grain dormancy and dormancy loss is essential in wheat, because low grain dormancy at maturity is associated with the problem of pre-harvest sprouting (PHS) when cool and rainy conditions occur before harvest. Low GA (gibberellin A) hormone sensitivity and high ABA (abscisic acid) sensitivity were associated with higher wheat grain dormancy and PHS tolerance. Grains of two PHS-tolerant cultivars were very dormant at maturity, and insensitive to GA stimulation of germination. More PHS-susceptible cultivars were less sensitive to ABA inhibition of germination, and were either more GA sensitive or germinated efficiently without GA at maturity. As grain dormancy was lost through dry afterripening or cold imbibition, grains first gained GA sensitivity and then lost ABA sensitivity. These changes in GA and ABA sensitivity can serve as landmarks defining stages of dormancy loss that cannot be discerned without hormone treatment. These dormancy stages can be used to compare different cultivars, seed lots and studies. Previous work showed that wheat afterripening is associated with decreasing ABA levels in imbibing seeds. Wheat grain dormancy loss through cold imbibition also led to decreased endogenous ABA levels, suggesting that reduced ABA signalling is a general mechanism triggering dormancy loss.
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Jones, Steve K., Richard H. Ellis, and Peter G. Gosling. "Loss and induction of conditional dormancy in seeds of Sitka spruce maintained moist at different temperatures." Seed Science Research 7, no. 4 (December 1997): 351–58. http://dx.doi.org/10.1017/s0960258500003755.
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AbstractPretreatment of moist seeds at certain temperatures can reduce seed dormancy, but such observations represent the net effect of pretreatment. Seeds of Sitka spruce (Picea sitchensis [Bong.] Carr.) were raised to 30% moisture content and pretreated at five different temperatures between 5 and 30°C for up to 24 weeks (168 d). Subsequent ability to germinate at 10°C and viability were then determined in order to investigate the effects of pretreatment on seed dormancy and survival. There was a curvilinear, negative semi-logarithmic relationship between seed longevity and pretreatment temperature, such that Q10 for loss in viability increased from 2.6 between 10 and 20°C to 2.8 between 20 and 30°C. Simple multiplicative models combining cumulative normal frequency distributions for each of loss in viability and loss in dormancy were able to describe the changes in ability to germinate at 10°C, after pretreatment at 5, 10 and 30°C. However, in order to quantify the changes in ability to germinate observed at 10°C after pretreatment at 15°C, it was necessary also to invoke a model of dormancy reimposition, while for the results at 20°C it was necessary to postulate both dormancy reimposition and the further loss of this reimposed dormancy. It is concluded that moist seeds of Sitka spruce held at 15 and 20°C cycle between the dormant and non-dormant condition.
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Hawkins, K. K., P. S. Allen, and S. E. Meyer. "Secondary dormancy induction and release inBromus tectorumseeds: the role of temperature, water potential and hydrothermal time." Seed Science Research 27, no. 1 (January 10, 2017): 12–25. http://dx.doi.org/10.1017/s0960258516000258.
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AbstractSeeds of the winter annualBromus tectorumlose primary dormancy in summer and are poised to germinate rapidly in the autumn. If rainfall is inadequate, seeds remain ungerminated and may enter secondary dormancy under winter conditions. We quantified conditions under which seeds enter secondary dormancy in the laboratory and field and also examined whether contrastingB. tectorumgenotypes responded differently to dormancy induction cues. The study also extends previous hydrothermal time models for primary dormancy loss and germination timing inB. tectorumby using similar models to account for induction and loss of secondary dormancy. Maximum secondary dormancy was achieved in the laboratory after 4 weeks at –1.0 MPa and 5°C. Seeds in the field became increasingly dormant through exposure to temperatures and water potentials in this range, confirming laboratory results. They were released from dormancy through secondary after-ripening the following summer. Different genotypes showed contrasting responses to dormancy induction cues in both laboratory and field. To examine secondary dormancy induction and release in the field in terms of hydrothermal time parameters, we first created a model that allowed mean base water potential (Ψb(50)) to vary while holding other hydrothermal time parameters constant, as in models for primary dormancy loss under dry conditions. The second model allowed all three model parameters to vary through time, to account for changes (e.g. hydrothermal time accumulation) that could occur simultaneously with dormancy induction in imbibed seeds. Shifts in Ψb(50) could explain most changes in dormancy status for seeds retrieved from the field, except during the short period prior to dormancy induction, when hydrothermal time was accumulating. This study illustrates that hydrothermal modelling, and specifically changes in Ψb(50), can be used to characterize secondary dormancy induction and loss inB. tectorum.
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Barboza, Perry S., Sean D. Farley, and Charles T. Robbins. "Whole-body urea cycling and protein turnover during hyperphagia and dormancy in growing bears (Ursus americanus and U. arctos)." Canadian Journal of Zoology 75, no. 12 (December 1, 1997): 2129–36. http://dx.doi.org/10.1139/z97-848.
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Subadult bears were studied during their autumn hyperphagia (n = 3) and winter dormancy (n = 6). Urea kinetics were measured with 14C- and 15N-urea, protein turnover was estimated with 15N-glycine, and body composition was assessed with 3H-water. Reduced amino acid degradation in winter was indicated by declines in plasma urea and aminotransferase activities, and lower urea production than in autumn (4.7 vs. 27.5 mmol urea-N∙kg−0.75∙d−1). Only 7.5% of urea produced in hyperphagic bears was degraded and just 1.1% of the degraded N reutilized as amino-N. Dormant bears reutilized 99.7% of urea produced, indicating thorough microbial ureolysis and urea-N resorption. Low rates of body N loss during dormancy suggested losses of non-urea N as creatinine. Protein turnover rates (15.2–21.5 g∙kg−0.75∙d−1) were similar between seasons and reflected the apparent maintenance of hepatic, intestinal, and muscular functions through dormancy. Protein synthesis accounted for 32% of energy expended in dormancy, which was mainly (91.5%) derived from fat oxidation. Consistent organ function and body temperature in dormant bears enables recycling of urea-N, which minimizes body protein loss and conserves mobility. In comparison with heterothermic hibernation, ursid dormancy would provide greater flexibility during winter and facilitate rapid resumption of foraging and growth in spring.
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Buczacki, Simon J. A., Semiramis Popova, Emma Biggs, Chrysa Koukorava, Jon Buzzelli, Louis Vermeulen, Lee Hazelwood, Hayley Francies, Mathew J. Garnett, and Douglas J. Winton. "Itraconazole targets cell cycle heterogeneity in colorectal cancer." Journal of Experimental Medicine 215, no. 7 (May 31, 2018): 1891–912. http://dx.doi.org/10.1084/jem.20171385.
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Cellular dormancy and heterogeneity in cell cycle length provide important explanations for treatment failure after adjuvant therapy with S-phase cytotoxics in colorectal cancer (CRC), yet the molecular control of the dormant versus cycling state remains unknown. We sought to understand the molecular features of dormant CRC cells to facilitate rationale identification of compounds to target both dormant and cycling tumor cells. Unexpectedly, we demonstrate that dormant CRC cells are differentiated, yet retain clonogenic capacity. Mouse organoid drug screening identifies that itraconazole generates spheroid collapse and loss of dormancy. Human CRC cell dormancy and tumor growth can also be perturbed by itraconazole, which is found to inhibit Wnt signaling through noncanonical hedgehog signaling. Preclinical validation shows itraconazole to be effective in multiple assays through Wnt inhibition, causing both cycling and dormant cells to switch to global senescence. These data provide preclinical evidence to support an early phase trial of itraconazole in CRC.
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Cochrane, Anne. "Are we underestimating the impact of rising summer temperatures on dormancy loss in hard-seeded species?" Australian Journal of Botany 65, no. 3 (2017): 248. http://dx.doi.org/10.1071/bt16244.
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Short duration dry heat shock similar to the heat of fire is known to be effective in alleviating physical dormancy in seeds, but are we underestimating the impact of the cumulative heat dose of summer soil temperatures on dormancy loss in hard-seeded species in the context of a changing climate? This study investigated short and long duration dry heat treatments in seeds of four Acacia species (Fabaceae) from South-West Western Australia. Seeds were treated at 90, 100, 110 and 120°C for 10 and 180 min (‘fire’) and at fluctuating temperatures of 30/20, 55/20, 65/20°C for 14, 28, 56 and 112 days (‘summer’). The non-dormant seed fraction of each species was low, but seeds were highly viable after scarification. The results indicate the presence of species-specific temperature thresholds for dormancy loss with duration of heating slightly less important than temperature for dormancy break. Seeds remained highly viable after all long duration treatments but short duration heat shock treatments above 110°C resulted in increased seed mortality. Although cumulative periods of lower fluctuating temperatures were less effective in breaking physical dormancy than the heat of fire in three of the four species, more than 40% of seeds of Acacia nigricans (Labill.) R.Br. lost dormancy after 28 days at 65/20°C. These potentially disturbing findings suggest that long hot summer conditions may compromise soil seed bank longevity over time and may be detrimental to the bet-hedging ability afforded by a hard seed coat in some species in the face of climate warming forecasts for the region.
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Vitetta, Ellen S., Thomas F. Tucker, Emilian Racila, Yi-Wu Huang, Radu Marches, Nancy Lane, Richard H. Scheuermann, Nancy E. Street, Takeshi Watanabe, and Jonathan W. Uhr. "Tumor Dormancy and Cell Signaling. V. Regrowth of the BCL1 Tumor After Dormancy Is Established." Blood 89, no. 12 (June 15, 1997): 4425–36. http://dx.doi.org/10.1182/blood.v89.12.4425.
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Abstract The majority of BALB/c mice immunized with the BCL1 lymphoma-derived idiotype (Id+) IgM and subsequently challenged with BCL1 tumor cells develop a state of tumor dormancy. The vast majority of dormant lymphoma cells are in cell cycle arrest, but there are also residual replicating cells. In the present studies, we attempted to define features of both the dormant lymphoma cells and the host that lead to escape from dormancy. Escape from dormancy occurs at a steady rate over a 2-year period, suggesting that it is a stochastic process. We found that, in the majority of mice, escape was due to the emergence of genetic variants that were no longer susceptible to the anti-Id–mediated induction of dormancy. Ten percent of these variants were Id−; the remainder were Id+ but could grow in the presence of anti-Id antibodies, suggesting that there were mutations in molecules involved in one or more mIg-mediated negative-signaling pathways. In two of five such escapees, alterations in either Syk, HS1, and/or Lyn were observed. In a small percentage of mice, a low titer of circulating anti-Id antibody before tumor challenge correlated with a subsequent, more rapid loss of dormancy.
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FRÉGEAU, JUDITH A., and VERNON D. BURROWS. "SECONDARY DORMANCY IN DORMOATS FOLLOWING TEMPERATURE TREATMENTS: FIELD AND LABORATORY RESPONSES." Canadian Journal of Plant Science 69, no. 1 (January 1, 1989): 93–99. http://dx.doi.org/10.4141/cjps89-011.
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Partially after-ripened seeds of three dormoat lines (Avena sativa L. × A. fatua L.) were treated to induce secondary dormancy before field planting in the fall. The objectives of this experiment were to evaluate the dormancy response of the treated seeds and to determine if field performance, in terms of both survival and emergence, was improved by the treatments. Treatments consisted of imbibition and incubation of seeds at two temperatures: 4 °C for 3 wk or 30 °C for 2 wk. Both treatments increased dormancy, but differences were also noted in the type of relative dormancy expressed by each seed population under laboratory conditions. Treated seeds and the appropriate untreated control seeds were sown in the field, in fiberglass mesh bags, either in early or late fall depending on the treatment. Levels of dormant seeds retrieved from the field, at the end of the fall season, varied for each dormoat line and did not reflect the induced secondary dormancy measured before field planting. The fate of these dormant seeds after exposure to winter stresses was assessed on field-retrieved material in the spring. In relation to a late sowing of untreated seeds, the treatments were effective in improving levels of viable seeds (dormant or germinating) remaining in the ground, in the spring. However, the best performance, both in survival and emergence, was obtained with an early fall planting of untreated seeds. High loss of viability was common to both treated and untreated seeds of the three dormoat lines. The major shortcoming of dormoats seems to be in the area of cold resistance of the fall dormant seeds since damage during winter played an important role in survival.Key words: Secondary dormancy, relative dormancy, dormoats, emergence
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Cao, Hong, Yi Han, Jingyi Li, Meng Ding, Yu Li, Xiaoying Li, Fengying Chen, Wim Jj Soppe, and Yongxiu Liu. "Arabidopsis thaliana SEED DORMANCY 4-LIKE regulates dormancy and germination by mediating the gibberellin pathway." Journal of Experimental Botany 71, no. 3 (October 23, 2019): 919–33. http://dx.doi.org/10.1093/jxb/erz471.
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Abstract The molecular mechanisms underlying seed dormancy and germination are not fully understood. Here, we show that Arabidopsis thaliana SEED DORMANCY 4-LIKE (AtSdr4L) is a novel specific regulator of dormancy and germination. AtSdr4L encodes a protein with an unknown biochemical function that is localized in the nucleus and is expressed specifically in seeds. Loss of function of AtSdr4L results in increased seed dormancy. The germination of freshly harvested seeds of the Atsdr4l mutant is insensitive to gibberellin (GA). After-ripened mutant seeds are hypersensitive to the GA biosynthesis-inhibitor paclobutrazol but show unaltered sensitivity to abscisic acid. Several GA biosynthesis genes and GA-regulated cell wall remodeling genes are down-regulated in the mutant in both dormant and after-ripened seeds. These results suggest that the Atsdr4l mutation causes both decreased GA biosynthesis and reduced responses. In addition, a genetic analysis indicated that AtSdr4L is epistatic to DELAY OF GERMINATION1 (DOG1) for dormancy and acts upstream of RGA-LIKE 2 (RGL2) in the GA pathway. We propose that AtSdr4L regulates seed dormancy and germination by mediating both the DOG1 and GA pathways.
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Barrero, Jose M., Marie M. Dorr, Mark J. Talbot, Shinnosuke Ishikawa, Taishi Umezawa, Rosemary G. White, and Frank Gubler. "A role for PM19-Like 1 in seed dormancy in Arabidopsis." Seed Science Research 29, no. 3 (July 26, 2019): 184–96. http://dx.doi.org/10.1017/s0960258519000151.
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AbstractThe understanding of the genetic basis of grain dormancy in wheat has rapidly improved in the last few years, and a number of genes have been identified related to that trait. We recently identified the wheat genes TaPM19-A1 and -A2 and we have now taken the first step towards understanding the role of this class of genes in seeds. By investigating the Arabidopsis homologous PM19-Like 1 (PM19L1) we have found that it has a seed-specific expression pattern and, while its expression is higher in dormant than in non-dormant seeds, knock-out mutations produced seeds with increased dormancy. Not only primary dormancy, but also secondary dormancy in response to high temperature was increased by the loss-of-function. We have also examined the function of PM19L1 by localizing the PM19 protein primarily to the cotyledon cells in seeds, possibly in membranes. By investigating the co-expression network of this gene we have found that it is connected to a small group of abscisic acid (ABA)-induced seed maturation and storage-related genes. The function of PM19L1 represents a good opportunity to explore the interactions of key factors that can influence seed dormancy such as ABA, temperature and membrane properties.
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Cheam, AH. "Patterns of change in seed dormancy and persistence of Bromus diandrus Roth. (great brome) in the field." Australian Journal of Agricultural Research 37, no. 5 (1986): 471. http://dx.doi.org/10.1071/ar9860471.
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Mature seeds of great brome (Bromus diandrus Roth;.) from Western Australia were dormant when freshly harvested. This dormancy was lost progressively over summer. The rate of loss of dormancy was more rapid in the northern than in the southern accessions. Compared with bare soil, a wheat stubble microenvironment favoured the relief of dormancy during the initial period of dormancy breakdown. Shallow burial of newly shed dormant seeds also accelerated the after-ripening process. Germination of non-dormant seeds during summer was minimised by high temperatures and low soil moisture content. By autumn/winter, almost all the seeds became germinable. At 20/10�C, the temperature regime corresponding to late autumn, 95-99% germination occurred under constant darkness, but in the light germination varied from 55 to 95%. In the field, complete mass germination did not occur but germination was a well-defined event. There was little germination following this pulse until the succeeding autumn/winter. The seed bank of great brome appears to be essentially a transient one, but this is the subject of further work. The concentration of germination at a single time of year, and the very small carryover of seeds to successive years, suggest that good control should be achieved by a single, timely cultivation or spraying.
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Baldos, Orville C., Joseph DeFrank, Matthew Kramer, and Glenn S. Sakamoto. "Storage Humidity and Temperature Affect Dormancy Loss and Viability of Tanglehead (Heteropogon contortus) Seeds." HortScience 49, no. 10 (October 2014): 1328–34. http://dx.doi.org/10.21273/hortsci.49.10.1328.
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Tanglehead (Heteropogon contortus) is a drought- and fire-tolerant native Hawaiian grass that possesses seed dormancy on shedding. Although a dry after-ripening period is known to break dormancy, specific storage conditions to optimize this are not known. This study examined the effects of storage temperature and equilibrium relative humidity (eRH) on tanglehead seed dormancy loss and viability. Fresh seeds harvested in Mar. and Oct. 2011 were stored for 30 days in three eRH levels (12%, 50%, and 75%) and then incubated for 0, 1, 3, 6, 9, and 12 months at three temperatures [10, 20 (ambient in laboratory), and 30 °C]. The eRHs were maintained during incubation by sealing seeds in airtight packages. Seed germination and tetrazolium tests were conducted after each incubation period to determine dormancy loss and seed viability. Analysis of germination and seed viability data indicated a significant interaction among eRH, storage temperature, incubation period, and seed harvest month. Storage at 12% eRH and 30 °C for 12 months optimized dormancy loss of tanglehead seeds. Seeds remained viable in all eRH and temperature combinations except those stored at either 75% eRH and 20 °C or 75% eRH and 30 °C. In these treatment combinations, significant seed deterioration and loss of viability were recorded. Harvest time (i.e., harvest month) within the year also affected the rate of dormancy loss of seeds. March-harvested seeds achieved maximum dormancy loss 3 months earlier than seeds harvested in October.
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Jones, Steve K., Peter G. Gosling, and Richard H. Ellis. "Reimposition of conditional dormancy during air-dry storage of prechilled Sitka spruce seeds." Seed Science Research 8, no. 2 (June 1998): 113–22. http://dx.doi.org/10.1017/s0960258500004001.
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AbstractPrechilling seeds of Sitka spruce (Picea sitchensis[Bong.] Carr.) at 4°C with 30% moisture content for 12–14 weeks (84–98 d) removed conditional dormancy (i.e. they were then able to germinate at 10°C). The non-dormant status was preserved after redrying to 6% moisture content. However, conditional dormancy was gradually reimposed during subsequent air-dry storage at 4°C and 6% seed moisture content in all five seed lots tested. Further investigations with one seed lot showed that reimposition was reversed by a second prechill treatment, but was reimposed again during subsequent air-dry storage. The trend of dormancy reimposition within seed lots over time was quantified by negative exponential relations between ability to germinate at 10°C and duration of air-dry storage. The progress of dormancy reimposition was influenced by seed storage moisture content and was most rapid at 4–10%. At higher moisture contents (15 and 20%) the rate of the reimposition of conditional dormancy was much reduced, while at moisture contents of 25 and 30% further loss in dormancy occurred. Thus it is clear that dormancy reimposition occurred during storage at low water potential rather than solely during desiccation from high to low water potential.
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Gallagher, Robert S., Kathryn J. Steadman, and Andrew D. Crawford. "Alleviation of dormancy in annual ryegrass (Lolium rigidum) seeds by hydration and after-ripening." Weed Science 52, no. 6 (December 2004): 968–75. http://dx.doi.org/10.1614/ws-04-075r.
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The effect of hydration (priming) treatment on dormancy release in annual ryegrass seeds from two populations was investigated. Hydration duration, number, and timing with respect to after-ripening were compared in an experiment involving 15 treatment regimens for 12 wk. Seeds were hydrated at 100% relative humidity for 0, 2, or 10 d at Weeks 1, 6, or 12 of after-ripening. Dormancy status was assessed after each hydration treatment by measuring seed germination at 12-hourly alternating 25/15 C (light/dark) periods using seeds directly from the hydration treatment and seeds subjected to 4 d postpriming desiccation. Seeds exposed to one or more hydration events during the 12 wk were less dormant than seeds that remained dry throughout after-ripening. The longer hydration of 10 d promoted greater dormancy loss than either a 2-d hydration or no hydration. For the seed lot that was most dormant at the start of the experiment, two or three rather than one hydration event or a hydration event earlier rather than later during after-ripening promoted greater dormancy release. These effects were not significant for the less-dormant seed lot. For both seed lots, the effect of a single hydration for 2 d at Week 1 or 6 of after-ripening was not manifested until the test at Week 12 of the experiment, suggesting that the hydration events alter the rate of dormancy release during subsequent after-ripening. A hydrothermal priming time model, usually used for modeling the effect of priming on germination rate of nondormant seeds, was successfully applied to dormancy release resulting from the hydration treatments.
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Cardina, John, and Denise H. Sparrow. "Temporal changes in velvetleaf (Abutilon theophrasti) seed dormancy." Weed Science 45, no. 1 (February 1997): 61–66. http://dx.doi.org/10.1017/s0043174500092481.
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Primary physical dormancy caused by seed coat impermeability to water is a major reason for the persistence of velvetleaf in soil seedbanks. Understanding temporal trends in seed dormancy status will help predict potential emergence in the spring. Experiments were begun in 1992 and 1993 to determine the effects of velvetleaf seed maturation time, storage environment, and storage duration on changes in seed dormancy and germination over 20 mo. Seeds buried 1 and 10 cm deep exhibited a 30 to 70% decline in physical dormancy from maturity until winter, little change in dormancy from winter through the following summer, and a further decline the next autumn. The loss of physical dormancy was more rapid for early than for late maturing seeds and more rapid in 1992 than in 1993. Physical dormancy of seeds held at 4 C declined steadily, at a rate of approximately 0.8% per day, over the course of the study. Germination of seeds buried 1 cm averaged 23 to 37% in the first spring after harvest, which was equivalent to 68 to 100% of seeds that had lost physical dormancy over autumn and winter. The percentage of seeds with enforced dormancy reflected the loss of physical dormancy during autumn and the loss of seeds to germination during spring and summer. Additional information on how autumn temperature and moisture conditions influence the pattern of dormancy decline could aid in explaining the variation in velvetleaf infestations over time.
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Mira, Sara, Luciana Veiga-Barbosa, and Félix Pérez-García. "Seed dormancy and longevity variability of Hirschfeldia incana L. during storage." Seed Science Research 29, no. 2 (May 9, 2019): 97–103. http://dx.doi.org/10.1017/s0960258519000072.
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AbstractWe studied the variability of germination, dormancy and viability loss of Hirschfeldia incana seeds in relation to seed size. Seeds were stored at 35°C under humid [75% relative humidity (RH)] or dry (33% RH) conditions. Seed germination and electrolyte leakage were evaluated periodically. Small seeds had lower longevity at humid or dry storage conditions (5 or 407 days, respectively) than large or intermediate seeds (7–9 or 536–727 days, respectively). Moreover, H. incana shows variability in seed dormancy related to seed size within a population, with small seeds having lower dormancy (13%) than intermediate (50%) or large seeds (72%). Dormancy was partially released after a short storage at 35°C and humid conditions. Under dry storage conditions, endogenous dormancy cycles were observed for over a year, and longer times of storage had a dormancy-breaking effect through dry after-ripening. Results suggest a dual strategy producing non-dormant seeds with low longevity that will germinate immediately after dispersal, and seeds with greater longevity that will delay germination. Membrane permeability increased linearly with ageing at both humid and dry storage (R2 = 0.60). Small seeds showed greater conductivity than intermediate or large seeds (0.7, 0.4 or 0.3 mS g–1 dry weight, respectively, at the 80% germination). The conductivity test could be used to evaluate the quality of H. incana seeds and would allow us to identify dormant (non-germinating) seed lots as viable. However, the influence of storage conditions and variability within a seed population on seed longevity should be taken into account when evaluating seed quality.
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Showler, Allan T., Weste L. A. Osbrink, and Kimberly H. Lohmeyer. "Horn Fly, Haematobia irritans irritans (L.), Overwintering." International Journal of Insect Science 6 (January 2014): IJIS.S15246. http://dx.doi.org/10.4137/ijis.s15246.
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The horn fly, Haematobia irritans irritans (L.), is an ectoparasitic blood feeder mainly on cattle. Its cosmopolitan distribution extends from boreal and grassland regions in northern and southern latitudes to the tropics. Stress and blood loss from horn flies can reduce cattle weight gain and milk production. Horn flies show substantial plasticity in their response to winter. Populations in warmer, lower latitudes have been reported to overwinter in a state of dormancy, but most overwinter as active adults in normal or reduced numbers. As latitudes increase, winters are generally colder, and correspondingly, larger percentages of horn fly populations become dormant as pharate adults (a post-pupal, pre-emergent stage) or die. Reports on the effect of elevation on horn fly dormancy at high elevations were contradictory. When it occurs, dormancy takes place beneath cattle dung pats and in the underlying soil. The horn fly's mode of dormancy is commonly called diapause, but the collective research on horn fly diapause (behavioral and biochemical) is not conclusive. Understanding the horn fly's overwintering behaviors can lead to development of pre-dormancy insecticide spray strategies in colder latitudes while other strategies must be determined for warmer regions.
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Batlla, Diego, and Andrés Mateo Agostinelli. "Thermal regulation of secondary dormancy induction inPolygonum aviculareseeds: a quantitative analysis using the hydrotime model." Seed Science Research 27, no. 3 (June 19, 2017): 231–42. http://dx.doi.org/10.1017/s0960258517000198.
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AbstractFor seed banks showing seasonal changes in their dormancy level, the possibility of predicting temporal patterns of emergence depends on establishing a robust relationship between temperature and the rate of dormancy loss and induction. However, although the effect of temperature on dormancy loss has been extensively studied, less work has been advocated to the quantification of temperature effects on dormancy induction. In the present work, we quantified temperature regulation of dormancy induction inPolygonum aviculareseeds using the hydrotime model. To study induction into secondary dormancy, seeds previously released from primary dormancy through stratification at 5°C were stored at dormancy-inductive temperatures of 10, 15, 20 and 25°C for different periods. During storage, seeds were germinated at different temperatures and water potentials, and hydrotime model parameters were derived. Changes in hydrotime model parameters (mean base water potential for germination and its standard deviation, and the hydrotime required for germination) during dormancy induction were described by adjusting exponential equations. Obtained results indicated a minimum temperature for dormancy induction of 8.7°C and the existence of a bi-linear relationship between rate of induction into secondary dormancy and storage temperature, in which storage temperatures around 25°C showed a higher dormancy induction rate than those below 20°C. Developed model equations were then used to predict changes in germination behaviour during dormancy induction at different temperatures, showing a good agreement between simulated and observed values.
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Sønsteby, Anita, Tomasz L. Woznicki, and Ola M. Heide. "A simple and convenient method for determination of entrance into dormancy in woody plants." Journal of Berry Research 10, no. 4 (December 15, 2020): 559–71. http://dx.doi.org/10.3233/jbr-200534.
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BACKGROUND: Bud dormancy is a quantitative condition that is gradually acquired and lost. Better and more convenient methods for assessment of the time of dormancy entrance of woody plants are highly needed. OBJECTIVE: To demonstrate a simple and convenient method for determination of dormancy in woody plants. METHODS: We employed a seasonal series of soft tipping of vigorously growing annual shoots and used the loss of ability of subtending lateral buds to break and grow as a measure of entrance into dormancy. RESULTS: There was a gradual decline in the ability of the buds to burst and grow during the month of July and early August, culminating with a complete loss of this ability. This coincided with the known time of growth cessation and dormancy induction in shoots of intact plants and occurred in the berry shrubs raspberry and black currant and the forest tree silver birch. CONCLUSIONS: The decline and loss of ability of the buds to grow during late summer is a direct expression of the entrance of buds into the state of endodormancy, rendering the tipping method a simple and convenient method for precise determination of the time of entrance into dormancy in woody plants.
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Schneider, Wendy L., and David J. Gifford. "Loblolly pine seed dormancy. I. The relationship between protein synthesis and the loss of dormancy." Physiologia Plantarum 90, no. 2 (February 1994): 246–52. http://dx.doi.org/10.1034/j.1399-3054.1994.900202.x.
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Schneider, Wendy L., and David J. Gifford. "Loblolly pine seed dormancy. I. The relationship between protein synthesis and the loss of dormancy." Physiologia Plantarum 90, no. 2 (February 1994): 246–52. http://dx.doi.org/10.1111/j.1399-3054.1994.tb00384.x.
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Johnson, Russell R., and William E. Dyer. "Degradation of endosperm mRNAs during dry afterripening of cereal grains." Seed Science Research 10, no. 3 (September 2000): 233–41. http://dx.doi.org/10.1017/s096025850000026x.
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AbstractThe endosperm of dormant wild oat (Avena fatuaL.) grains contains a number of mRNAs, including low levels of transcripts encoding avenin (AV10), puroindoline-like (AV1) and serine proteinase inhibitor-like (Z1) proteins. During dry afterripening, a period of warm dry storage that relieves dormancy, the abundance of these intact transcripts gradually declined to undetectable levels in pooled grain samples. In contrast, the three mRNAs did not decline in grains stored for the same period at −20°C, and levels of mRNA decay products derived from these transcripts did not change during afterripening. Disappearance of the three intact mRNAs was not a general phenomenon, since abundance of more than 5000 other seed mRNAs did not change during this period. Additional experiments were conducted to test the idea that the presence of these transcripts was positively correlated with seed dormancy status. First, the rate of intactZ1mRNA decline was similar to the rate of dormancy relief during 9 months of afterripening. Second, cultivated oat (A. sativa) grains (which are not dormant at maturity) contained much lower levels of these mRNAs than did highly dormant wild oat grains. Third, levels of full-lengthAV1andZ1mRNAs remained constant in dormant grains during 6 d of imbibition. However, Northern analyses of individual grains from a partially afterripened seed lot showed that amounts of intactAV1orZ1mRNAs were highly variable in germinating and dormant grains and were not correlated with dormancy status. Even though loss of these transcripts occurred under the same environmental conditions that promote afterripening, a causal relationship between the two processes seems unlikely. The apparently specific mechanism(s) by which these mRNAs are degraded in endosperm tissue may represent a novel post-transcriptional process for regulating levels of certain transcripts in dry grains.
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Dekkers, Bas J. W., and Leónie Bentsink. "Regulation of seed dormancy by abscisic acid and DELAY OF GERMINATION 1." Seed Science Research 25, no. 2 (January 16, 2015): 82–98. http://dx.doi.org/10.1017/s0960258514000415.
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AbstractPhysiological dormancy has been described as a physiological inhibiting mechanism that prevents radicle emergence. It can be caused by the embryo (embryo dormancy) as well as by the structures that cover the embryo. One of its functions is to time plant growth and reproduction to the most optimal season and therefore, in nature, dormancy is an important adaptive trait that is under selective pressure. Dormancy is a complex trait that is affected by many loci, as well as by an intricate web of plant hormone interactions. Moreover, it is strongly affected by a multitude of environmental factors. Its induction, maintenance, cycling and loss come down to the central paradigm, which is the balance between two key hormonal regulators, i.e. the plant hormone abscisic acid (ABA), which is required for dormancy induction, and gibberellins (GA), which are required for germination. In this review we will summarize recent developments in dormancy research (mainly) in the model plant Arabidopsis thaliana, focusing on two key players for dormancy induction, i.e. the plant hormone ABA and the DELAY OF GERMINATION 1 (DOG1) gene. We will address the role of ABA and DOG1 in relation to various aspects of seed dormancy, i.e. induction during seed maturation, loss during dry seed afterripening, the rehydrated state (including dormancy cycling) and the switch to germination.
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Chen, Xiaoyu, Yun Tian, and Xiangyang Lu. "Breeding of the Dormant Thermosensitive Genic Male-Sterile Lines of Early Rice to Overcome Pre-Harvest Sprouting of the Hybrid Seeds." Agronomy 8, no. 9 (September 16, 2018): 191. http://dx.doi.org/10.3390/agronomy8090191.
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The pollen development of male-sterile lines should be conducted during the high temperature season to ensure the sterility of male-sterile line pollen and the safety of hybrid seed production in the breeding of thermosensitive genic male-sterile (TGMS) lines of early rice. However, the mature hybrid rice seeds are prone to pre-harvest sprouting (PHS) during hot, rainy days, which leads to the decrease of hybrid rice seed quality or a loss of utilization value. In this study, with an aim to bring a dormancy trait from the dormant genotype to the current low-dormant TGMS lines, a common wild rice “Chaling” (Oryza rufipogon), which has strong seed dormancy, a large black stigma, and a high exsertion rate, was hybridized with the early rice TGMS line “Zhu 1S,” which often exhibits PHS. After screening for early maturing and seed dormancy, the early rice “Yezao S” and “Yezhuzao S,” with the characteristic of seed dormancy, were selected. The critical temperature of high temperature sterility for these two male-sterile lines was below 23.5 °C. The stigma of “Yezao S” was black and its exsertion rate was 79.9%, while “Yezhuzao S” had a colorless stigma with an exsertion rate of 76.8%. The expression of the genes OsNCEDs in “Yezao S” and “Yezhuzao S” were significantly higher than that in “Zhu 1S” the 15th day after heading, and the abscisic acid (ABA) content was also higher than that of “Zhu 1S” the 20th day after heading. The results indicated that introducing the dormancy characteristics from wild rice “Chaling” into the early rice TGMS lines was an effective way to prevent PHS.
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Batlla, Diego, and Roberto Luis Benech-Arnold. "A predictive model for dormancy loss in Polygonum aviculare L. seeds based on changes in population hydrotime parameters." Seed Science Research 14, no. 3 (September 2004): 277–86. http://dx.doi.org/10.1079/ssr2004177.
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Changes in population hydrotime parameters were determined during stratification inPolygonum aviculareL. seeds in order to model dormancy loss. Seeds buried in pots were stored at three temperatures (1.6, 7 and 12°C) for 110 d and were exhumed at regular intervals during the storage period. Exhumed seeds were incubated at different water potentials at 15°C and germination time courses were analysed to determine hydrotime parameters. The population mean base water potential (Ψb(50)) decreased concomitantly with seed dormancy, while the hydrotime constant (θH) and the standard deviation of base water potential (θΨb) displayed only minor changes. Based on these results, a model for simulatingP. aviculareseed dormancy loss in relation to low temperature was developed. The model employs Ψb(50) as an index of mean seed population dormancy status. While Ψb(50) was allowed to vary as seeds were released from dormancy, θHand θΨbwere held constant. Changes in Ψb(50) were related to the time and temperature, using a previously developed thermal stratification time index (Stt), which quantifies the accumulation of thermal time units below a threshold temperature required for dormancy loss to occur. Therefore, Ψb(50) varied in relation to the accumulation ofSttaccording to time and temperature. Model performance showed acceptable prediction of timing and percentage of germination of seeds buried in irrigated plots, but did not accurately predict germination of seeds exhumed from rain-fed plots. Thus, environmental factors other than temperature could also be involved in the regulation of dormancy status of buried seeds under field conditions.
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Batlla, Diego, Virginia Verges, and Roberto Luis Benech-Arnold. "A quantitative analysis of seed responses to cycle-doses of fluctuating temperatures in relation to dormancy: Development of a thermal time model forPolygonum aviculareL. seeds." Seed Science Research 13, no. 3 (September 2003): 197–207. http://dx.doi.org/10.1079/ssr2003137.
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AbstractThe sensitivity ofPolygonum aviculareL. seeds to the dormancy-breaking effect of cycle-doses of fluctuating temperature changes as seeds lose dormancy due to storage under stratification temperatures. Sensitivity changes during seed stratification were characterized by a decrease in the number of cycles required to saturate the germination response, and by a progressive loss of the requirement for temperature fluctuations for dormancy breakage in increasing fractions of the seed population. The rate of these changes was dependent on the temperature at which seeds were stored for stratification; lower storage temperatures produced higher rates of change than higher storage temperatures. Germination curves, obtained in response to the effect of fluctuating temperature cycle-doses for seeds stratified at variable temperatures and times of storage, were brought to a common stratification thermal time (Stt) scale by accumulating thermal time units under a threshold temperature for dormancy loss to occur. Results showed that those seeds that had accumulated similarSttunits during stratification under different storage temperatures presented a similar germination response. Therefore, response-curve functions were adjusted to germination data of exhumed seeds that had accumulated similarStt, obtaining a family of germination response curves in relation toSttaccumulation during storage. Based on these results, a simulation model was constructed relating dynamic changes in the parameters that determine germination response curves in relation toSttaccumulation. The model was tested against independent data, showing a good description of the dynamics of changes in the fraction of the seed population requiring temperature fluctuation for dormancy breakage as dormancy release progressed.
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Norton, M. R., F. Lelièvre, and F. Volaire. "Summer dormancy in Dactylis glomerata L.: the influence of season of sowing and a simulated mid-summer storm on two contrasting cultivars." Australian Journal of Agricultural Research 57, no. 5 (2006): 565. http://dx.doi.org/10.1071/ar05237.
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A series of trials to increase understanding of the summer dormancy trait in Dactylis glomerata was conducted. Autumn-sown reproductive and younger, spring-sown plants of 2 drought-resistant cultivars, contrasting for summer dormancy, were established and then tested in summer 2002 under long drought, drought + mid-summer storm, or full irrigation. The autumn-sown reproductive plants of cv. Kasbah were summer dormant under all moisture regimes and exhibited the characteristic traits including growth cessation, rapid herbage senescence, and dehydration of surviving organs (–6.7 MPa). Cultivar Kasbah used 8% less soil water over the summer and also began to rehydrate its leaf bases from conserved soil water before the drought broke. The non-dormant cv. Medly grew for 10 days longer under drought and whenever moisture was applied; Medly also responded to the storm with a decline in dehydrin expression in leaf bases, whereas no decline occurred in Kasbah, presumably because it remained dormant and therefore much drier. The irrigated, younger, spring-sown swards of cv. Kasbah had restrained growth and produced only about 25% of the herbage of cv. Medly. Drought reduced activity and growth of young plants of both cultivars, but whereas Medly regrew in response to the storm, cv. Kasbah did not, indicating that dormancy, although only partially expressed after spring sowing, was reinforced by summer drought. A longer drought in 2003 caused a 22% loss of the basal cover in cv. Medly, whereas Kasbah fully maintained its sward and therefore produced a higher post-drought autumn yield. This work confirms summer dormancy as a powerful trait for improving persistence over long, dry summers.
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Bair, Necia B., Susan E. Meyer, and Phil S. Allen. "A hydrothermal after-ripening time model for seed dormancy loss in Bromus tectorum L." Seed Science Research 16, no. 1 (March 2006): 17–28. http://dx.doi.org/10.1079/ssr2005237.
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After-ripening, the loss of dormancy under dry conditions, is associated with a decrease in mean base water potential for germination ofBromus tectorumL. seeds. After-ripening rate is a linear function of temperature above a base temperature, so that dormancy loss can be quantified using a thermal after-ripening time (TAR) model. To incorporate storage water potential into TAR, we created a hydrothermal after-ripening time (HTAR) model. Seeds from twoB. tectorumpopulations were stored under controlled temperatures (20 or 30 °C) and water potentials (−400 to −40 MPa). Subsamples were periodically removed from each storage treatment and incubated at 15 or 25 °C to determine germination time courses. Dormancy status (mean base water potential) was calculated from each time course using hydrothermal time equations developed for each seed collection. Seeds stored at −400 MPa did not after-ripen. At water potentials from −400 to −150 MPa, the rate of after-ripening increased approximately linearly with increasing water potential. Between −150 and −80 MPa, there was no further increase in after-ripening rate, while at −40 MPa seeds did not after-ripen and showed loss of vigour. These results suggest that the concept of critical water potential thresholds, previously shown to be associated with metabolic activity and desiccation damage in partially hydrated seeds, is also relevant to the process of after-ripening. The HTAR model generally improved field predictions of dormancy loss when the soil was very dry. Reduced after-ripening rate under such conditions provides an ecologically relevant explanation of how seeds prolong dormancy at high summer soil temperatures.
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Sharif-Zadeh, Farzad, and Alistair J. Murdoch. "The effects of different maturation conditions on seed dormancy and germination ofCenchrus ciliaris." Seed Science Research 10, no. 4 (December 2000): 447–57. http://dx.doi.org/10.1017/s0960258500000490.
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AbstractSeeds ofCenchrus ciliarisL. were produced under different hydro–photo–thermal environments with and without fertilizer. Dormancy loss of spikelets and extracted caryopses was tested during dry after-ripening at 40°C and 43% equilibrium relative humidity. Caryopses had higher initial germination and lost their dormancy faster than spikelets. Dormancy of both caryopses and spikelets generally decreased with an increase of maturation temperature and fertility, whereas dormancy increased if water stress was imposed during maturation. The latter effect was smaller when the mother plants were exposed to water stress after caryopses were fully formed than when water stress cycles were applied throughout maturation. Daylength extension (to 14 or 18 h d-1) by artificial light increased dormancy of both caryopses and spikelets. The effect of long days declined when plants were exposed to natural daylight for more than 10 h d-1. The after-ripening curves were consistent with the hypothesis that dormancy periods of individual seeds are normally distributed within each seed lot. Rates of loss of dormancy were quantified by the slopes of these curves. In a given experiment, these rates were identical for caryopses but not always for spikelets that matured in diverse environments. Even for caryopses, however, the slopes varied between experiments. Therefore, the results do not support the hypothesis that a dormancy model can be applied universally to all seed lots ofCenchrus ciliaris. Methods of predicting the period of after-ripening required to achieve desired levels of dormancy for reseeding degraded rangelands are discussed.
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Tesio, Melania, Yilang Tang, Katja Müdder, Massimo Saini, Lisa von Paleske, Elizabeth Macintyre, Manolis Pasparakis, Ari Waisman, and Andreas Trumpp. "Hematopoietic stem cell quiescence and function are controlled by the CYLD–TRAF2–p38MAPK pathway." Journal of Experimental Medicine 212, no. 4 (March 30, 2015): 525–38. http://dx.doi.org/10.1084/jem.20141438.
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The status of long-term quiescence and dormancy guarantees the integrity of hematopoietic stem cells (HSCs) during adult homeostasis. However the molecular mechanisms regulating HSC dormancy remain poorly understood. Here we show that cylindromatosis (CYLD), a tumor suppressor gene and negative regulator of NF-κB signaling with deubiquitinase activity, is highly expressed in label-retaining dormant HSCs (dHSCs). Moreover, Cre-mediated conditional elimination of the catalytic domain of CYLD induced dHSCs to exit quiescence and abrogated their repopulation and self-renewal potential. This phenotype is dependent on the interactions between CYLD and its substrate TRAF2 (tumor necrosis factor–associated factor 2). HSCs expressing a mutant CYLD with an intact catalytic domain, but unable to bind TRAF2, showed the same HSC phenotype. Unexpectedly, the robust cycling of HSCs lacking functional CYLD–TRAF2 interactions was not elicited by increased NF-κB signaling, but instead by increased activation of the p38MAPK pathway. Pharmacological inhibition of p38MAPK rescued the phenotype of CYLD loss, identifying the CYLD–TRAF2–p38MAPK pathway as a novel important regulator of HSC function restricting HSC cycling and promoting dormancy.
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Al-Asadi, Mazin Gh, Marcos Castellanos, Sean T. May, Nigel H. Russell, Claire H. Seedhouse, and Monica Pallis. "Molecular Signature of Dormancy in CD34+CD38- Acute Myeloid Leukaemia Cells." Blood 128, no. 22 (December 2, 2016): 1660. http://dx.doi.org/10.1182/blood.v128.22.1660.1660.
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Abstract Chemotherapy drugs tend to spare cells in a state of dormancy (G0 phase of the cell cycle). Relapse of acute myeloid leukaemia (AML) is likely in part due to dormant cells evading remission-induction chemotherapy. Dormant AML cells have been identified in the bone marrow endosteal region which is characterised by an excess of TGFβ1 and a shortage of nutrients. We developed and characterized an in-vitro model of AML cell dormancy by exploiting these features. Following preliminary investigation of several cell lines, the CD34+CD38- line TF1a was selected for in depth investigation. TF1a cells showed 72% inhibition of proliferation (p<0.001), with features of dormancy, in response to 72 hours TGFβ1+mTOR inhibitor treatment (mTOR pathway inhibition mimics major effects of nutrient scarcity).This treatment caused loss of Ki-67, as well as upregulating ALDH and CD34 and causing nuclear translocation of FOXO3a. In contrast to conventional serum-withdrawal assays for dormancy, the treatment had no impact on cell viability, assessed by Annexin V assay. Nor did the treatment lead to cell differentiation, assessed by CD11b staining and morphology. Using whole human genome expression microarray and by intersecting differentially regulated genes in dormancy-induced TF1a cells in comparison to their proliferating (untreated) counterparts, we identified 240 genes which are significantly up-regulated >2 fold including genes involved in stemness, chemoresistance and tumour suppressor genes in addition to genes involved in canonical cell cycle regulation. There was striking upregulation of genes involved in adhesion and migration: raised expression levels of SPP1 (the gene coding for osteopontin), ITGB3, ITGB4, ITGA3 and CD44 in dormant cells were confirmed by real-time PCR. The most upregulated gene was SPP1/osteopontin (16 fold). Immunocytochemistry of biopsy material from AML patients confirmed high levels of osteopontin in the cytoplasm of blasts near the paratrabecular bone marrow. Osteopontin and other genes identified in this model, including well-characterised genes (e.g. CD44, CD47, CD123, ABBC3 and CDKN2B) as well as little-known ones (e.g. PTPRU, ITGB3 and BTG2), are potential therapeutic targets in dormant AML cells. Disclosures No relevant conflicts of interest to declare.
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Ma, Hongyuan, Todd E. Erickson, Jeffrey L. Walck, and David J. Merritt. "Interpopulation variation in germination response to fire-related cues and after-ripening in seeds of the evergreen perennial Anigozanthos flavidus (Haemodoraceae)." International Journal of Wildland Fire 29, no. 10 (2020): 950. http://dx.doi.org/10.1071/wf19195.
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Variations in the degree of seed dormancy expressed among conspecific populations provide a basis for improving understanding of the mechanisms controlling species persistence, especially in fire-prone ecosystems. We investigated seed germination of 12 Anigozanthos flavidus populations in response to various fire-related cues that included exposure to karrikinolide, glyceronitrile and smoke water at five temperatures, and the effects of heat shock and its interaction with glyceronitrile. Seeds from populations with deep-degree dormancy (DD) and light-degree dormancy (LD) were subjected to 0–8 months of after-ripening, and the viability of the ungerminated seeds was tested. The degree of seed dormancy and responses to fire-related cues were highly variable among populations. Glyceronitrile and smoke water significantly improved germination in 12 and 8 populations respectively. Heat significantly enhanced germination in all populations, but was less effective when combined with glyceronitrile. After-ripening for 3 months increased germination, whereas ≥4 months led to secondary dormancy or loss of viability. Loss of viability was greater for DD than for LD seeds. Interpopulation variations in the degree of seed dormancy, seed germination requirements for fire-related cues and germination viability in response to after-ripening in A. flavidus contribute to persistence in the variable and unpredictable Mediterranean environment.
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Saini, Hargurdeep S., Pawan K. Bassi, and Mary S. Spencer. "Interactions Among Ethephon, Nitrate, and After-Ripening in the Release of Dormancy of Wild Oat (Avena fatua) Seed." Weed Science 34, no. 1 (January 1986): 43–47. http://dx.doi.org/10.1017/s0043174500026424.
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Germination of dormant wild oat (Avena fatuaL. # AVEFA) seed was examined in response to various concentrations of ethephon (2-chloroethylphosphonic acid), KNO3, or both together in the dark at temperatures ranging from 7 to 32 C. Both chemicals significantly (P = 0.05) promoted germination and their effects were additive. Maximum stimulation of germination in response to all treatments occurred at 7 C, with a gradual decrease in reponse as temperature or duration of after-ripening, the seed that retained dormancy during storage remained responsive to ethephon also occurred during storage of mature seed at 3 to 32 C. The rate and extent of this dormancy loss increased with an increase in storage temperature. Regardless of the temperature or duration of after-ripening, the seed that retained dormancy during storage remained responsive to ethephon and KNO3treatments. Suitable combinations of after-ripening, ethephon, and KNO3induced over 90% germination of seed that was dormant at maturity. Experimental evidence has been obtained that suggests that this percentage may represent the total number of viable seed in the population. While ethephon promoted seed germination, it severely stunted root and shoot growth of the resulting seedlings. It appears that strategies could be developed to combine the use of ethephon and nitrate with the natural process of after-ripening to enhance and synchronize wild oat germination.
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Pound, Leanne M., Phillip J. Ainsley, and José M. Facelli. "Dormancy-breaking and germination requirements for seeds of Acacia papyrocarpa, Acacia oswaldii and Senna artemisioides ssp.×coriacea, three Australian arid-zone Fabaceae species." Australian Journal of Botany 62, no. 7 (2014): 546. http://dx.doi.org/10.1071/bt14077.
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Physical dormancy is common in seeds of arid-land legumes. Improved understanding of germination requirements of hard-seeded species will further our understanding of arid lands and aid restoration projects. We studied the germination responses of Acacia papyrocarpa (Benth.), A. oswaldii (F.Muell) and Senna artemisioides (Gaudich. ex DC.) Randell ssp. × coriacea (Benth.) Randell from a chenopod shrubland in South Australia. Imbibition testing indicated that all three species had physical dormancy, but the proportion of dormant seeds was lower in A. oswaldii. This corresponded to a thinner testa in this species. Mechanisms tested to scarify seeds included mechanical scarification and different durations of wet or dry heat. Mechanically scarified seeds germinated readily, reaching maximum numbers in 10–15 days, independently of incubation temperatures, with the exception of S. artemisioides seeds, which germinated at a slower rate in cooler temperatures. Overall, wet heat was more effective than dry heat to alleviate physical dormancy, whereas dry heat in some cases resulted in seed mortality. On the basis of these results, it is recommended that seeds of A. papyrocarpa and S. artemisoides be pretreated with wet heat in future restoration programs. No pre-treatment is required for dormancy loss in A. oswaldii seeds. The different responses of seeds of these species suggest that their populations have varying strategies for persistence in this unpredictable environment.
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Shirazi, A. M., and L. H. Fuchigami. "“NEAR-LETHAL” STRESS EFFECTS ON ENDO DORMANCY, COLD ACCLIMATION, AND RECOVERY OF RED-OSIER DOGWOOD PLANTS." HortScience 27, no. 6 (June 1992): 685f—685. http://dx.doi.org/10.21273/hortsci.27.6.685f.
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“Near-lethal” (NL) stresses from varied sources, e. g. NL-heat (47°C-lhr), NL-freeze (-7°C -lhr), and NL-hydrogen cyanamide (0.5-1 M), overcame endo-dormancy in red-osier dogwood (Cornus sericea L.) plants. Near-lethal heat stress applied at early rest (Oct.) had a slight effect on cold acclimation, whereas at late rest (Dec.), NL-stress resulted in the rapid loss of hardiness at warm or natural environment conditions. Recovery of plants from NL-stresses was dependent on the stage of development and temperature. Less dieback occurred with later stage of endo-dormancy, and at warmer temperatures. Dormant plants in October exposed to other NL-stresses, e. g., freezing temperature and hydrogen cyanamide, also caused plant dieback at 0°C and recovered at 23°C post-environment treatment. Conditions that favored recovery also favored production of glutathione.
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Sohindji, Fernand S., Dêêdi E. O. Sogbohossou, Herbaud P. F. Zohoungbogbo, Carlos A. Houdegbe, and Enoch G. Achigan-Dako. "Understanding Molecular Mechanisms of Seed Dormancy for Improved Germination in Traditional Leafy Vegetables: An Overview." Agronomy 10, no. 1 (January 1, 2020): 57. http://dx.doi.org/10.3390/agronomy10010057.
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Loss of seed viability, poor and delayed germination, and inaccessibility to high-quality seeds are key bottlenecks limiting all-year-round production of African traditional leafy vegetables (TLVs). Poor quality seeds are the result of several factors including harvest time, storage, and conservation conditions, and seed dormancy. While other factors can be easily controlled, breaking seed dormancy requires thorough knowledge of the seed intrinsic nature and physiology. Here, we synthesized the scattered knowledge on seed dormancy constraints in TLVs, highlighted seed dormancy regulation factors, and developed a conceptual approach for molecular genetic analysis of seed dormancy in TLVs. Several hormones, proteins, changes in chromatin structures, ribosomes, and quantitative trait loci (QTL) are involved in seed dormancy regulation. However, the bulk of knowledge was based on cereals and Arabidopsis and there is little awareness about seed dormancy facts and mechanisms in TLVs. To successfully decipher seed dormancy in TLVs, we used Gynandropsis gynandra to illustrate possible research avenues and highlighted the potential of this species as a model plant for seed dormancy analysis. This will serve as a guideline to provide prospective producers with high-quality seeds.
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Leistikow, Rachel L., Russell A. Morton, Iona L. Bartek, Isaac Frimpong, Karleen Wagner, and Martin I. Voskuil. "The Mycobacterium tuberculosis DosR Regulon Assists in Metabolic Homeostasis and Enables Rapid Recovery from Nonrespiring Dormancy." Journal of Bacteriology 192, no. 6 (December 18, 2009): 1662–70. http://dx.doi.org/10.1128/jb.00926-09.
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ABSTRACT Mycobacterium tuberculosis survives in latently infected individuals, likely in a nonreplicating or dormancy-like state. The M. tuberculosis DosR regulon is a genetic program induced by conditions that inhibit aerobic respiration and prevent bacillus replication. In this study, we used a mutant incapable of DosR regulon induction to investigate the contribution of this regulon to bacterial metabolism during anaerobic dormancy. Our results confirm that the DosR regulon is essential for M. tuberculosis survival during anaerobic dormancy and demonstrate that it is required for metabolic processes that occur upon entry into and throughout the dormant state. Specifically, we showed that regulon mechanisms shift metabolism away from aerobic respiration in the face of dwindling oxygen availability and are required for maintaining energy levels and redox balance as the culture becomes anaerobic. We also demonstrated that the DosR regulon is crucial for rapid resumption of growth once M. tuberculosis exits an anaerobic or nitric oxide-induced nonrespiring state. In summary, the DosR regulon encodes novel metabolic mechanisms essential for M. tuberculosis to survive in the absence of respiration and to successfully transition rapidly between respiring and nonrespiring conditions without loss of viability.
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Wilson, Leanne C., Alden Braul, and Martin H. Entz. "Characteristics of Black Medic Seed Dormancy Loss in Western Canada." Agronomy Journal 109, no. 4 (July 2017): 1404–13. http://dx.doi.org/10.2134/agronj2016.10.0604.
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Carta, Angelino, Gianni Bedini, Angela Giannotti, Laura Savio, and Lorenzo Peruzzi. "Mating system modulates degree of seed dormancy in Hypericum elodes L. (Hypericaceae)." Seed Science Research 25, no. 3 (July 22, 2015): 299–305. http://dx.doi.org/10.1017/s0960258515000252.
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AbstractKnowledge of processes responsible for seed dormancy can improve our understanding of the evolutionary dynamics of reproductive systems. We examined the influence of the breeding system on primary seed dormancy in Hypericum elodes, an Atlantic–European softwater pools specialist plant that exhibits a mixed mating strategy (the ability to both self- and cross-pollinate) to set seeds. Seeds were obtained through hand pollination treatments performed in a natural population during three consecutive years. Primary dormancy of seeds recovered from each pollination treatment was measured by analysing the seed germination response at dispersal and after various periods of cold stratification. While all collected seeds exhibited physiological dormancy, the degree of primary dormancy was associated with the pollination treatments. Weak and rapid loss of primary dormancy characterized seeds recovered from self-pollinated flowers, while stronger dormancy was found in seeds obtained from cross-pollination. The association between pollination treatments and primary dormancy indicated that the mating system should be considered as a source of variation for dormancy degree, proportional to self- and cross-pollinations (selfing rate) within populations of this species. These results suggest that by shedding seeds with various degrees of dormancy, plants may distribute their offspring across time by means of polymorphism in germination response. We conclude that seed germination alone is not an appropriate fitness measure for inbreeding depression estimates, unless dormancy is removed.
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Norton, M. R., F. Volaire, and F. Lelièvre. "Summer dormancy in Festuca arundinacea Schreb.; the influence of season of sowing and a simulated mid-summer storm on two contrasting cultivars." Australian Journal of Agricultural Research 57, no. 12 (2006): 1267. http://dx.doi.org/10.1071/ar06082.
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Due to the shortage of information on summer dormancy in tall fescue (Festuca arundinacea, syn. Lolium arundinaceum), we tested the response of 2 cultivars of differing dormancy expression and growth stage to a range of summer moisture conditions, including full irrigation, drought, and a simulated mid-summer storm and analysed whether traits associated with summer dormancy conferred better survival under severe field drought. Autumn-sown reproductive and younger, spring-sown plants of 2 cultivars, claimed to exhibit contrasting summer dormancy, were established and then tested in summer 2002 under either long drought, drought + simulated mid-summer storm, or full irrigation. The autumn-sown reproductive plants of cv. Flecha exhibited traits that can be associated with partial summer dormancy since under summer irrigation they reduced aerial growth significantly and exhibited earlier herbage senescence. Moreover, cv. Flecha used 35% less soil water over the first summer. However, the water status of leaf bases of young vegetative tillers of both cultivars was similar under irrigation and also throughout most of the drought (leaf potential and water content maintained over –4 MPa and at approx. 1 g H2O/g DM, respectively). The summer-active cv. Demeter did not stop leaf elongation even in drought and produced twice as much biomass as Flecha under irrigation. Cultivar Demeter responded to the simulated storm with a decline in dehydrin expression in leaf bases, whereas no decline occurred in Flecha, presumably because it remained partially dormant. The younger, spring-sown swards of both cultivars had similar biomass production under summer irrigation but whereas Demeter regrew in response to the simulated storm, cv. Flecha did not, indicating that dormancy, although only partially expressed, was reinforced by summer drought. In all trials, cv. Flecha out-yielded Demeter in autumn regrowth. In particular, the severe drought in 2003 caused a 25% loss of the basal cover in cv. Demeter, whereas Flecha fully maintained its sward allowing it to produce a higher post-drought autumn yield. This work links summer dormancy with higher persistence over long, dry summers.
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Sadawarti, Murlidhar J., K. K. Pandey, B. P. Singh, and R. K. Samadiya. "A review on potato microtuber storability and dormancy." Journal of Applied and Natural Science 8, no. 4 (December 1, 2016): 2319–24. http://dx.doi.org/10.31018/jans.v8i4.1132.
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Potato microtubers plays important role in seed potato production technology as it has great advantage of storage, transport and mechanization due to their little size and reduced weight. Dormancy in potato microtubers is very important and storage conditions as well as size of microtubers influences the dormancy in microtubers. Increasing size of the micro-tuber resulted in significant increase in the viability and sprouting ability of microtubers with reduced durations of dormancy and weight loss at the end of storage. Small microtubers are more vulnerable to storage damage. The larger microtubers lost moisture content more slowly and retained firmness longer when stored at 40C. Development of dormancy during storage strongly affected by the storage condition especially the temperature regime, the presence of light and the relative humidity. The dormancy duration was linearly and inversely correlated with the length of storage. Storage containers and conditions are also important for microtuber storage. Endogenous hormones ABA, ethylene, cyokinin and gibberllic acid play a significant role in tuber dormancy regulation.Microtubers with thick diameter which have passed more times in dormancy and have better functionality than small microtubers with less time in dormancy. Growth regulators like gibberellic acid, thiourea, gibberllic acid + thiourea, randite and carbon disulphide plays significant role in dormancy breaking of microtubers.
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Pallais, Noël, José Santos-Rojas, and Rosario Falcón. "Storage Temperature Affects Sexual Potato Seed Dormancy." HortScience 31, no. 1 (February 1996): 99–101. http://dx.doi.org/10.21273/hortsci.31.1.99.
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Sexual potato (Solanum tuberosum L.) seeds require many months of afterripening in dry storage to completely lose dormancy and germinate readily at >25C. We examined the relationship between storage temperature and seed dormancy, as assessed by the percentage of germination after 4 days. Two F1 hybrid lots of `Desiree' × 7XY.1 were used; one seed lot was produced by carefully removing half of the developing tubers from the mother plant during seed development, and the control remained undisturbed. Seeds were stored with 3.4% moisture (dry-weight basis) at 10, 20, 30, 40, and 50C and were tested eight times during 29 months for daily germination at 27/40C (21/3 h) for the first 8 days, followed by 6 days at 17C. After 29 months of storage, final germination was <97% only when control seeds were stored at 50C, in which germination was 72%. Germination after 4 days increased curvilinearly with increasing storage temperature, and both seed lots similarly lost dormancy (germination >90%) after 10 months at 40C. Optimum germination levels were maintained after 29 months at 40C. Seeds stored at 50C never completely lost dormancy, and after 7 months of storage, germination at 4 days gradually decreased to zero. Dormancy was eventually lost after 29 months in most seeds stored at <40C, and differences between seed lots suggest that removing tubers from the mother plant increased dormancy. We conclude that dry potato seeds can be safely afterripened at temperatures up to 40C; lower temperatures slow the rate of dormancy loss, and higher ones are detrimental to seed quality.
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Landová, M., K. Hamouzová, J. Soukup, M. Jursík, J. Holec, and G. R. Squire. "Population density and soil seed bank of weed beet as influenced by crop sequence and soil tillage." Plant, Soil and Environment 56, No. 11 (November 16, 2010): 541–49. http://dx.doi.org/10.17221/1457-pse.
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Dynamics of population density and soil seed bank of weed beet was studied in a 5 year crop rotation consisting of spring barley, and sugar beet. Beside the crop rotation experiment, the seeds of weed beet were studied for their dormancy and viability in soil seed bank over the period of four years. The obtained data indicates that weed beet was able to produce seeds only in sugar beet, but not in barley. In sugar beet, its reproductive potential allows weed beet to restore and increase the soil seed bank of glomerules rapidly. Common infestation of sugar beet is able to persist over more than the 2-year period between repeated introductions of sugar beet in crop rotation. The experiment has also proven the negative effect of weed beet presence on sugar beet yield. The sugar beet root yield decreased of 0.4 t/ha with every 1000 weed beet plants per hectare. The yearly loss of viable seeds was about 75%. The number of surviving seeds decreased exponentially in time. Less than 2% of seeds remained viable after three years in the soil. Seasonal fluctuations of seed dormancy were observed. Seeds were dormant in autumn, lost dormancy in winter and recovered it in late summer.
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Schutte, Brian J., Emilie E. Regnier, and S. Kent Harrison. "Seed Dormancy and Adaptive Seedling Emergence Timing in Giant Ragweed (Ambrosia trifida)." Weed Science 60, no. 1 (March 2012): 19–26. http://dx.doi.org/10.1614/ws-d-11-00049.1.
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Giant ragweed germination is delayed by both a physiological dormancy of the embryo (embryo dormancy) and an inhibitory influence of embryo-covering structures (covering structure-enforced [CSE] dormancy). To clarify the roles of embryo and CSE dormancy in giant ragweed seedling emergence timing, we conducted two experiments to address the following objectives: (1) determine changes in germinability for giant ragweed dispersal units (hereafter “involucres”) and their components under natural burial conditions, and (2) compare embryo and CSE dormancy alleviation and emergence periodicity between successional and agricultural populations. In Experiment 1, involucres were buried in crop fields at Columbus, OH, periodically excavated, and brought to the laboratory for dissection. Involucres, achenes, and embryos were then subjected to germination assays at 20 C. In Experiment 2, temporal patterns of seedling emergence were determined at a common burial site. Reductions in embryo and CSE dormancy were compared with controlled-environment stratification followed by germination assays at 12 and 20 C, temperatures representative of soil conditions in spring and summer. Results indicated that overwinter dormancy loss involved sequential reductions in embryo and CSE dormancy. CSE dormancy, which may limit potential for fatal germination during fall, was caused by the pericarp and/or embryo-covering structures within the pericarp. In Experiment 2, successional populations emerged synchronously in early spring, whereas agricultural populations emerged throughout the growing season. Levels of embryo dormancy were greater in the agricultural populations than the successional populations, but CSE dormancy levels were similar among populations. In 12 C germination assays, embryo dormancy levels were positively correlated with time required to reach 95% cumulative emergence (run 1:r= 0.81, P = 0.03; run 2:r= 0.76, P = 0.05). These results suggest that late-season emergence in giant ragweed involves high levels of embryo dormancy that prevent germination at low temperatures in spring.
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Hacisalihoglu, Gokhan, and Anwar A. Khan. "Differential Control of Embryo Growth Potential in Lettuce and Tomato Seeds." HortScience 32, no. 3 (June 1997): 527A—527. http://dx.doi.org/10.21273/hortsci.32.3.527a.
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The effects of chemical or physical factors during pregermination imbibition phase, or on dry seeds, on embryo growth potential (EGP) was studied in lettuce (Grand Rapids and Mesa 659) and tomato (H-9889) seeds in relation to dormancy, invigoration, and vigor loss. Embryos were excised from treated seeds (washed if imbibed in chemical solutions) and their growth rate (a measure of EGP) followed at 25°C at high magnification (X55). Treated seeds were also germinated at 25°C. In lettuce seeds, dormancy inducing treatments, i.e., a 2-day dark soak at 25°C with 50–100 μM tetcyclacis (TCY) or a 2-day dark soak in water at 35°C, reduced the subsequent embryo growth and germination rate at 25°C. The reduction was prevented by 1 mM GA4+7 or irradiation applied during dormancy induction. A -d osmoconditioning (OC) at 15C with -1.2 MPa PEG-8000 solution in light or in dark with added GA4+7 enhanced the EGP; addition of TCY reduced the EGP and the TCY inhibition reversed by GA4+7. A progressive reduction in EGP occurred with increase in vigor loss. In tomato seeds, a soak with 100 μM TCY in light or dark for 2 days at 30°C induced a dormancy, but had little effect on EGP. Application of GA4+7 plus TCY prevented dormancy induction without affecting EGP. A 4-day matriconditioning (MC) at 25°C in light or dark with moist Micro-Cel E enhanced the EGP; TCY and/or GA added during MC, had little effect on EGP. EGP progressively decreased as the aging period increased. Thus, in lettuce, the EGP is coupled with the reversible –GA/+GA or phytochrome-controlled dormancy induction/release process, enabling germination, its inhibition, or its enhancement. In tomato, the EGP is not subject to light or GA control. Reduction in EGP, accompanying vigor loss in both seeds, is independent of light or GA action.
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Iglesias-Fernández, Raquel, María del Carmen Rodríguez-Gacio, and Angel J. Matilla. "Progress in research on dry afterripening." Seed Science Research 21, no. 2 (January 6, 2011): 69–80. http://dx.doi.org/10.1017/s096025851000036x.
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AbstractThe transition from the dormant to the non-dormant state of a viable and mature seed can take place at low hydration by exposure to air-dry storage conditions (dry afterripening; AR). The events occurring during this loss of dormancy are of considerable physiological, ecological and agricultural interest. AR may be attributable to increased sensitivity to germination-stimulating factors and a widening of the temperature window for germination. Genetic, –omics and physiological studies on this mode of dormancy breaking provide support for a key role of the balance between gibberellin (GA) and abscisic acid (ABA) metabolism and sensitivity. Recent evidence also supports a possible role for ethylene (ET) in this complex signalling network that is necessary for AR implementation. However, hormone-independent signals, such as reactive oxygen species (ROS), nitrate (NO _{3}^{ - } ) or nicotinamide adenine dinucleotide (NAD+), also appear to be involved. The way in which hormone- and non-hormone-signalling pathways affects each other (cross-talk) is still under study. This review provides updated information on the programmes that overcome seed dormancy. Thus, we have reviewed: (1) the –omic status in dry seeds; (2) the relationship between temperature and nitrate signalling and AR; (3) alterations in ABA/GA synthesis and signalling; (4) the action of hormone molecules other than ABA and GA (i.e. ET, salicylic and jasmonic acids); and (5) participation of reactive oxygen species (ROS), NAD+ and protein carbonylation. Taken together, the acquisition and implementation of dry AR involve a complex signalling network that is difficult to disentangle.