Littérature scientifique sur le sujet « Stem photosynthesi »
Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres
Consultez les listes thématiques d’articles de revues, de livres, de thèses, de rapports de conférences et d’autres sources académiques sur le sujet « Stem photosynthesi ».
À côté de chaque source dans la liste de références il y a un bouton « Ajouter à la bibliographie ». Cliquez sur ce bouton, et nous générerons automatiquement la référence bibliographique pour la source choisie selon votre style de citation préféré : APA, MLA, Harvard, Vancouver, Chicago, etc.
Vous pouvez aussi télécharger le texte intégral de la publication scolaire au format pdf et consulter son résumé en ligne lorsque ces informations sont inclues dans les métadonnées.
Articles de revues sur le sujet "Stem photosynthesi"
1
Zagorchev, Lyuben, Alexandra Atanasova, Ivanela Albanova, Anelia Traianova, Petko Mladenov, Margarita Kouzmanova, Vasilij Goltsev, Hazem M. Kalaji et Denitsa Teofanova. « Functional Characterization of the Photosynthetic Machinery in Smicronix Galls on the Parasitic Plant Cuscuta campestris by JIP-Test ». Cells 10, no 6 (5 juin 2021) : 1399. http://dx.doi.org/10.3390/cells10061399.
Texte intégralRésumé :
Members of the genus Cuscuta are generally considered to be non-photosynthetic, stem-holoparasitic flowering plants. Under certain circumstances, at least some members of the genus are capable of limited photosynthesis. The galls of the Smicronyx weevils formed on Cuscuta campestris are particularly rich in chlorophylls compared to the stem of the parasitic plant. In the present study, we aimed to characterize the photosynthetic activity in the inner and outer gall cortices in comparison to the non-photosynthetic stems and a reference plant (Arabidopsis thaliana). The recorded prompt chlorophyll fluorescence transients were analyzed using JIP test. Detailed analysis of the chlorophyll fluorescence confirmed the presence of actively functioning photosynthetic machinery, especially in the inner cortex of the galls. This photosynthesis, induced by the insect larvae, did not reach the levels of the photosynthetic activity in Arabidopsis thaliana plants. Thylakoid protein complexes were identified by separation with two-dimensional Blue Native/SDS PAGE. It appeared that some of the complexes presented in A. thaliana are missing in C. campestris. We hypothesize that the insect-triggered transition from non-photosynthetic to photosynthetic tissue in the gall is driven by the increased requirements for nutrients related to the larval nutrition.
2
Alessio, Giorgio A., Fabrizio Pietrini, Federico Brilli et Francesco Loreto. « Characteristics of CO2 exchange between peach stems and the atmosphere ». Functional Plant Biology 32, no 9 (2005) : 787. http://dx.doi.org/10.1071/fp05070.
Texte intégralRésumé :
Gas exchange by stems is dominated by respiratory CO2 emission, but photosynthetic CO2 uptake might also occur in stem bark. We show that light-dependent CO2 uptake was present and often exceeded CO2 release by respiration in illuminated current-year peach (Prunus persica L.) stems. Respiration of peach stems, as detected by 12CO2 release into air in which the natural concentration of 12CO2 was replaced with 13CO2, was lower in the light than in the dark, but this accounted for only a fraction of the observed total CO2 uptake by illuminated stems. Stem photosynthesis was saturated at low light and was negatively affected by elevated assay temperatures (30°C), especially when combined with light intensities above saturation. An inefficient mechanism of heat dissipation by transpiration in stomata-free stems might help explain this effect. Photosynthesis was rapidly stimulated and the electron transport rate was reduced when photorespiration was suppressed by exposure to low (2 kPa) oxygen. The time-course of these changes was closely associated with a transient burst of CO2 uptake concurrent with a reduced inhibition of fluorescence yield. Photosynthesis was also stimulated by exposure to elevated (twice ambient) CO2 concentration. These combined measurements of gas exchange and fluorescence suggested that (a) photorespiration may also be active in the bark of peach stems, (b) O2 and CO2 concentrations in the bark of peach stems may be similar to ambient concentrations, (c) a large amount of electron transport unrelated to photosynthesis and photorespiration may also be present in peach stems, and (d) stem photosynthesis may be enhanced under future atmospheric conditions.
3
Míguez, Fátima, Beatriz Fernández-Marín, Antonio Hernández, José Maria Becerril et José Ignacio García-Plazaola. « Does age matter under winter photoinhibitory conditions ? A case study in stems and leaves of European mistletoe (Viscum album) ». Functional Plant Biology 42, no 2 (2015) : 175. http://dx.doi.org/10.1071/fp14083.
Texte intégralRésumé :
European mistletoe (Viscum album L.) is a hemiparasitic plant with perennial leaves and photosynthetic stems easily discernible according to their age. These properties make V. album the perfect species to (i) compare the mechanisms of seasonal acclimation of photosynthetic stems with those of leaves, and (ii) evaluate the influence of ageing in the efficiency of photosynthetic tissues. To achieve these general objectives, photosynthetic pigments, maximal photochemical efficiency of PSII (Fv/Fm), recovery kinetics and key thylakoidal proteins were analysed during winter and spring in leaves and at different age stems. During winter, some woody species are able to maintain photosynthetic activity, but at lower rates than during spring. In the case of V. album, photosynthetic relevance of green stems appears equal to leaves in terms of total area. Besides, mistletoe stems are able to maintain higher Fv/Fm and lower level of antioxidants than leaves, especially during winter season. The recovery from winter photoinhibition is also faster in stems than in leaves. Thylakoidal protein composition (mainly high levels of D1) also supports the idea of stems as main photosynthetic organs in V. album during winter. Further, in winter, the level of photoinhibition of V. album stems decreased concomitantly with ageing. This work highlights the importance of stem photosynthesis in plant carbon balance and demonstrates that ageing does not necessarily imply a loss of vitality in stems.
4
Rey-Sanchez, Camilo, et Juan M. Posada. « Effect of temporally heterogeneous light on photosynthetic light use efficiency, plant acclimation and growth in Abatia parviflora ». Functional Plant Biology 46, no 7 (2019) : 684. http://dx.doi.org/10.1071/fp18279.
Texte intégralRésumé :
Individual leaves have a unique instantaneous photosynthetic photon flux density (PPFD) at which net photosynthetic light use efficiency (ϵL, the ratio between net photosynthesis and PPFD) is maximised (PPFDϵmax). When PPFD is above or below PPFDϵmax, efficiency declines. Thus, we hypothesised that heterogeneous PPFD conditions should increase the amount of time leaves photosynthesise at a PPFD different than PPFDϵmax and result in reduced growth. To date, this prediction has not been rigorously tested. Here, we exposed seedlings of Abatia parviflora Ruiz & Pav to light regimes of equal total daily irradiance but with three different daily time courses of PPFD: constant PPFD (No_H), low heterogeneity (Low_H) and high heterogeneity (High_H). Mean ϵL, leaf daily photosynthesis and plant growth were all significantly higher in No_H and Low_H plants than in High_H plants, supporting our hypothesis. In addition, mean ϵL was positively related to final plant biomass. Unexpectedly, High_H plants had more etiolated stems and more horizontal leaves than No_H and Low_H plants, possibly due to exposure to low PPFD in the morning and afternoon. In conclusion, PPFD heterogeneity had an important effect on average ϵL, photosynthesis and growth, but also on allocation and plant morphology.
5
Armitage, A. M., N. G. Seager, I. J. Warrington et D. H. Greer. « LIGHT, TEMPERATURE AND PHOTOPERIOD AFFECT THE USEFULNESS OF OXYPETALUM CAERULEUM, TWEEDIA, AS A CUT FLOWER CROP. » HortScience 25, no 9 (septembre 1990) : 1160d—1160. http://dx.doi.org/10.21273/hortsci.25.9.1160d.
Texte intégralRésumé :
A progressive increase in temperature from 14 to 30C resulted in linear increases in stem length and node number and decreases in stem diameter and stem strength. Higher temperatures also resulted in additional flower abortion, reduced time to flowering and fewer flowering stems per inflorescence. Reduction in the photosynthetic photon flux (PPF) from 695 to 315 μmole m-2s-1 had similar effects as increasing the temperature on vegetative parameters but had little effect on reproductive parameters. The rate of stem elongation was greatest at low PPF for all temperatures and at high temperature for all PPF treatments. Net photosynthesis rose between 14 and 22C and declined at 30C for all PPF treatments. Long photoperiods (12, 14 hr.) resulted in longer internodes, longer stems and more flowers per cyme than short photoperiods (8, 10 hr) but photoperiod had little effect on flowering time.
6
Wittmann, Christiane, et Hardy Pfanz. « Bark and woody tissue photosynthesis : a means to avoid hypoxia or anoxia in developing stem tissues ». Functional Plant Biology 41, no 9 (2014) : 940. http://dx.doi.org/10.1071/fp14046.
Texte intégralRésumé :
In woody plants, oxygen transport and delivery via the xylem sap are well described, but the contribution of bark and woody tissue photosynthesis to oxygen delivery in stems is poorly understood. Here, we combined stem chlorophyll fluorescence measurements with microsensor quantifications of bark O2 levels and oxygen gas exchange measurements of isolated current-year stem tissues of beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) to investigate how bark and woody tissue photosynthesis impairs the oxygen status of stems. Measurements were made before bud break, when the axial path of oxygen supply via the xylem sap is impeded. At that time, bark O2 levels showed O2 concentrations below the atmospheric concentration, indicating hypoxic conditions or O2 deficiency within the inner bark, but the values were always far away from anoxic. Under illumination bark and woody tissue photosynthesis rapidly increased internal oxygen concentrations compared with plants in the dark, and thereby counteracted against localised hypoxia. The highest photosynthetic activity and oxygen release rates were found in the outermost cortex tissues. By contrast, rates of woody tissue photosynthesis were considerably lower, due to the high light attenuation of the bark and cortex tissues, as well as resistances in radial oxygen diffusion. Therefore, our results confirm that bark and woody tissue photosynthesis not only play a role in plant carbon economy, but may also be important for preventing low oxygen-limitations of respiration in these dense and metabolically active tissues.
7
Kumar, Sunjeet, Xinfang Huang, Gaojie Li, Qun Ji, Kai Zhou, Guopeng Zhu, Weidong Ke, Hongwei Hou, Honglian Zhu et Jingjing Yang. « Comparative Transcriptomic Analysis Provides Novel Insights into the Blanched Stem of Oenanthe javanica ». Plants 10, no 11 (17 novembre 2021) : 2484. http://dx.doi.org/10.3390/plants10112484.
Texte intégralRésumé :
In the agricultural field, blanching is a technique used to obtain tender, sweet, and delicious water dropwort stems by blocking sunlight. The physiological and nutritional parameters of blanched water dropwort have been previously investigated. However, the molecular mechanism of blanching remains unclear. In the present study, we investigated transcriptomic variations for different blanching periods in the stem of water dropwort (pre, mid, post-blanching, and control). The results showed that many genes in pathways, such as photosynthesis, carbon fixation, and phytohormone signal transduction as well as transcription factors (TFs) were significantly dysregulated. Blanched stems of water dropwort showed the higher number of downregulated genes in pathways, such as photosynthesis, antenna protein, carbon fixation in photosynthetic organisms, and porphyrin and chlorophyll metabolism, which ultimately affect the photosynthesis in water dropwort. The genes of hormone signal transduction pathways (ethylene, jasmonic acid, brassinosteroid, and indole-3-acetic acid) showed upregulation in the post-blanched water dropwort plants. Overall, a higher number of genes coding for TFs, such as ERF, BHLH, MYB, zinc-finger, bZIP, and WRKY were overexpressed in blanched samples in comparison with the control. These genes and pathways participate in inducing the length, developmental processes, pale color, and stress tolerance of the blanched stem. Overall, the genes responsive to blanching, which were identified in this study, provide an effective foundation for further studies on the molecular mechanisms of blanching and photosynthesis regulations in water dropwort and other species.
8
Hill, Judson P., et Matthew J. Germino. « Coordinated variation in ecophysiological properties among life stages and tissue types in an invasive perennial forb of semiarid shrub steppe ». Canadian Journal of Botany 83, no 11 (novembre 2005) : 1488–95. http://dx.doi.org/10.1139/b05-116.
Texte intégralRésumé :
Semiarid lands of North America are vulnerable to invasion by exotic forbs that frequently have an extended phenology compared with native herbaceous species. We hypothesized that photosynthetic stems, rosette leaves, and cauline leaves of Centaurea maculosa Lam. (knapweed) would differ in ecophysiological specialization and that these differences would enhance plant carbon uptake across seasonal variations in microclimate. Photosynthesis, water relations, and morphological features of C. maculosa were measured under natural variations in temperature and soil water, and under manipulated light environments, in adults compared with seedlings having only rosette leaves. Carbon gain was greater in adults than in seedlings owing to high photosynthesis in cauline and rosette leaves when water was abundant. Otherwise, photosynthesis was relatively lower but persistent through drought in all tissues and ages until senescence. Photosynthesis decreased with water stress in all tissues except stems. Stems comprised up to 36% of photosynthetic area following senescence of rosette leaves during seasonal drought. Seedlings expressed shade acclimation compared with rosette and especially cauline leaves of adults, although adult rosette leaves had flexible photosynthetic light responses. Contrasting ecophysiological specializations of photosynthetic tissues enhance carbon gain of adult C. maculosa as light, water, and temperature vary during its relatively long growth season.
9
Guralnick, Lonnie J., Gerald Edwards, Maurice S. B. Ku, Brandon Hockema et Vince Franceschi. « Photosynthetic and anatomical characteristics in the C4crassulacean acid metabolism-cycling plant Portulaca grandiflora ». Functional Plant Biology 29, no 6 (2002) : 763. http://dx.doi.org/10.1071/pp01176.
Texte intégralRésumé :
This paper originates from a presentation at the IIIrd International Congress on Crassulacean Acid Metabolism, Cape Tribulation, Queensland, Australia, August 2001. Portulaca grandiflora (Lind.) is a succulent species with C4 photosynthesis and crassulacean acid metabolism (CAM) cycling in leaves, and CAM-idling type photosynthesis in stems. We investigated the level and localization of carbon fixation enzymes and photosynthetic activity of leaves and stems of P. grandiflora under well-watered and drought conditions. As CAM activity increased during water stress, the leaf water-storage tissue collapsed, presumably transferring water to the bundle sheath and mesophyll cells, and so maintaining the C4 photosynthetic pathway. Tissue prints indicated an increase in phosphoenolpyruvate carboxylase (PEPC) in the water-storage tissue of leaves and the cortex of stems. Immunoblot analyses after 10 d of water stress showed that leaves had a slight decrease in the proteins of the C4-CAM pathway, while at the same time a new isoform of NADP-malic enzyme (NADP-ME) appeared. In contrast, the stem showed increases in proteins of the CAM pathway when water stressed. Under water stress, diurnal fluctuation in acidity in leaves was not accompanied by a net gain or loss of CO2 at night, and there was sustained, but decreased, fixation of CO2 during the day, characteristic of CAM cycling. High gross rates of O2 evolution were maintained during the day under water stress, suggesting induction of alternative electron sinks. With induced diurnal fluctuations in acidity in stems, there was no net carbon gain during the day or night. These results demonstrate, for the first time, that the stem of P. grandiflora is an inducible CAM-idling tissue. Our results also indicate that the C4 and CAM pathways operate independently of one another in P. grandiflora.
10
Voznesenskaya, Elena V., Nuria K. Koteyeva, Asaph Cousins et Gerald E. Edwards. « Diversity in structure and forms of carbon assimilation in photosynthetic organs in Cleome (Cleomaceae) ». Functional Plant Biology 45, no 10 (2018) : 983. http://dx.doi.org/10.1071/fp17323.
Texte intégralRésumé :
Photosynthesis in different organs of Cleome was analysed in four species known to have differences in leaf photosynthesis: Cleome africana Botsch. (C3), Cleome paradoxa R.Br. (C3-C4 intermediate), Cleome angustifolia Forssk. and Cleome gynandra L. (C4). The chlorophyll content, carbon isotope composition, stomatal densities, anatomy, levels and compartmentation of some key photosynthetic enzymes, and the form and function of photosynthesis were determined in different organs of these species. In the three xerophytes, C. africana, C. paradoxa, and C. angustifolia, multiple organs contribute to photosynthesis (cotyledons, leaves, petioles, stems and pods) which is considered important for their survival under arid conditions. In C. africana, all photosynthetic organs have C3 photosynthesis. In C. paradoxa, cotyledons, leaves, stems and petioles have C3-C4 type features. In C. angustifolia, the pods have C3 photosynthesis, whereas all other organs have C4 photosynthesis with Kranz anatomy formed by a continuous, dual layer of chlorenchyma cells. In the subtropical C4 species C. gynandra, cotyledons, leaves, and pods develop C4 photosynthesis, with Kranz anatomy around individual veins; but not in stems and petioles which have limited function of photosynthesis. The diversity in forms and the capacity of photosynthesis in organs of these species to contribute to their carbon economy is discussed.
Thèses sur le sujet "Stem photosynthesi"
1
Phraprasert, Phakpoom. « C4-like photosynthesis within the stem of C3-rice ». Thesis, University of Sheffield, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616987.
Texte intégral
2
Süss, Björn [Verfasser]. « Entwicklung eines Step-Scan FTIR-Experiments zur Untersuchung der lichtinduzierten Wasserspaltung der oxygenen Photosynthese / Björn Süss ». Berlin : Freie Universität Berlin, 2011. http://d-nb.info/1026358337/34.
Texte intégral
3
Orfei, Elisabetta. « A step further toward the application of layered double hydroxides in Sustainable Catalysis : from artificial photosynthesis to wastewater treatment ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24403/.
Texte intégralRésumé :
Layered-Double Hydroxides (LDHs) are known to be versatile materials that can be potentially applied in different fields. This work is focused on their specific application in artificial photosynthesis and wastewater treatment. Indeed, their catalytic properties make them possible candidates for photoelectrodes in photo-electrochemical cells (PEC), a recent technology exploited for solar fuel production, and Dye-Sensitised Solar Cells (DSSC), also known as third generation photovoltaics. Furthermore, the possibility to directly intercalate a dye in the LDH interlayer makes these materials able to absorb even more solar light and, potentially, less sensitive to dye degradation, if the latter is adsorbed on the LDH surface. In this work, LDHs were prepared by coprecipitation method, and subsequently applied onto a conductive transparent substrate by screen-printing with suitable inks. Finally, complete PEC and DSSC prototypes were assembled and tested for solar fuels production or electricity generation. Furthermore, a first trial was made to use LDHs as catalysts for the degradation of 4-nitrophenol, a well-known organic pollutant mostly found in wastewaters. The results obtained confirmed that LDH are versatile materials that can be potentially applied in all the explored fields.
4
Green, Jayne. « The characterisation of the magnesium chelatase step of chlorophyll biosynthesis within Chlamydomonas reinhardtii, Arabidopsis thaliana and a range of photosynthetic organisms ». Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286884.
Texte intégral
5
Liang, Zhiyong [Verfasser]. « Photosynthetic Water Oxidation in Plants and Cyanobacteria - Activation Energy of the O-O Bond Formation Step and Substrate Analogue NH3 / Zhiyong Liang ». Berlin : Freie Universität Berlin, 2018. http://d-nb.info/1160235724/34.
Texte intégral
6
Hancock, Harmony Alise. « One Step Closer to Non-Invasive : Quantifying Coral Zooxanthellae Pigment Concentrations Using Bio-Optics ». NSUWorks, 2012. http://nsuworks.nova.edu/occ_stuetd/189.
Texte intégralRésumé :
Due to the invasive nature of quantification techniques, baseline pigment data for coral-dwelling zooxanthellae are not known. In an attempt to develop a model for non-invasive estimation of zooxanthellae pigment concentrations from corals, field samples were taken from Porites rus and P. lutea in Apra Harbor, Guam. In-situ reflectance spectra (R400-R800) from 22 coral colonies were collected. “Coral truthing” was accomplished by extracting corresponding tissue core samples. Subsequent analysis to quantify the concentrations of 6 zooxanthellae pigments (µg cm-2) was performed using HPLC. Trials of multiple linear regressions were attempted (EJ Hochberg) and found inappropriate, despite previous success. The multivariate calibration technique partial least squares regression (PLS-R) is an excellent tool in the case of co-linear variables. Thus, PLS-R was attempted for chlorophyll c2 and peridinin after demonstration of co-linearity. This may be an appropriate approach for development of bio-optical models to estimate zooxanthellae pigment concentrations. Further, the dinoflagellate diagnostic pigment peridinin may be of great value for reef-scale remote sensing of changes in coral status in the future.
7
Hickey, Cain Charles. « Vines of different capacity and water status alter the sensory perception of Cabernet Sauvignon wines ». Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/42667.
Texte intégralRésumé :
Reducing disease and increasing fruit quality in vigorous vineyards with dense canopies is demanding of time and resources; unfortunately, vineyards of this nature are common in humid environments. This study investigated the effectiveness with which vine capacity and water status could be regulated as well as if they related to fruit quality and wine sensory perception. The treatments regulating vine size and water status were under-trellis groundcover, root manipulation, rootstocks, and irrigation. Treatments were arranged in a strip-split-split plot design before the introduction of the irrigation treatment resulted in incomplete replication in each block. Treatment levels were under-trellis cover crop (CC) compared to under-trellis herbicide (Herb); root restriction bags (RBG) compared to no root manipulation (NRM); three compared rootstocks (101-14, 420-A, riparia Gloire); low water stress (LOW) compared to high water stress (HIGH). Vines grown with RBG and CC regulated vegetative growth more so than conventional treatments, resulting in 56% and 23% greater cluster exposure flux availability (CEFA). High water stress (HIGH) and RBG reduced stem water potential and discriminated less against 13C. Vines grown with RBG and CC consistently reduced harvest berry weight by 17 and 6% compared to conventional treatments. Estimated phenolics were consistently increased by RBG and were correlated with berry weight, vine capacity and CEFA. Sensory attributes were significantly distinguishable between wines produced from vines that differed in both vine capacity and water status, amongst other responses. Treatments have been identified that can alter the sensory perception of wines, with the potential to improve wine quality.Master of Science
8
LU, HSIAO-CHI, et 呂曉騏. « Contribution of Carbon Dioxide in Bamboo Stem to Photosynthesis ». Thesis, 2018. http://ndltd.ncl.edu.tw/handle/gxy2eb.
Texte intégralRésumé :
碩士東海大學
生命科學系
106
Bamboo (Bambusoideae) is a large common grass in Asia-Pacific region and North America, the internodes of most bamboo stems are hollow and separated by diaphragms, and the stems of many bamboo species are green. According to previous studies, their highest growth rate can achieve more than one meter per day. Previous studies showed that the concentration of carbon dioxide inside stem cavity was 10s of thousands ppm. The objective of this study was to examine whether bamboo can re-fix the respiratory CO2 accumulated in stem cavity. If bamboos are capable of utilizing the high concentration of respiratory CO2 inside the stem (CO2 refixation), they can reduce the frequency and duration of stomata openings and improve the water use efficiency of photosynthesis. I Selected 40 Phyllostachys makinoi Hayata for daytime shading experiment (DSE), 30 Dendrocalamus latiflorus Munro for night lighting experiments (NLE) at Lianhuachi Forest Research Center (Nantou County, Central Taiwan), For DSE experiment, samples were randomly assigned to light group and shading group. CO2 concentration inside the bamboo stems were extracted and analyzed for each individual after 8 hours and ten days of treatments. In NLE experiment, bamboo shoots were randomly assigned to light treatment, heat treatment, and control and the treatments were carried out for 3 hours. For DSE, the average concentration of CO2 inside DSE bamboo stem was 108,253ppm, and the treatment effect were not significant after 8 hours. After ten days of shading, CO2 concentration under shading treatment was significantly lower than light group (control). In NLE, the mean CO2 concentration inside bamboo stems was 32625 ppm, CO2 concentration under light treatment was significantly lower than in the heating group, despite the fact that both treatments had the same surface temperature. This suggested that the CO2 stored in bamboo stem was re-absorbed under light treatment. My results demonstrated that bamboos were capable of utilizing ample amount of carbon inside their stems. Future studies on the roles of carbon refixation in such fast growing species and their drought resistance are encouraged.
9
Zhao, Nan. « Vibrational Properties of Quinones in Photosynthetic Reaction Centers ». 2014. http://scholarworks.gsu.edu/phy_astr_diss/68.
Texte intégralRésumé :
Fourier transform infrared difference spectroscopy (FTIR DS) is widely used to study the structural details of electron transfer cofactors in photosynthetic protein complexes. In photosynthetic proteins quinones play an important role, functioning as a cofactor in light-driven electron transfer.
In photosystem I (PS I) phylloquinone (PhQ) functions as an intermediary in electron transfer. To investigate the properties of PhQ that occupies the, so called, A1 binding site in PS I, time-resolved step-scan FTIR DS, with 5µs time resolution at 77K has been used. By replacing PhQ in the A1 binding site with specifically isotope labeled version, information on the vibrational frequencies associated specifically with the quinone in the binding site were obtained, which could be compared to the vibrational properties of quinone in solution or quinones in other protein binding sites. To further aid in assessing the origin of bands in the spectra, quantum mechanics /molecular mechanics (QM/MM) ONIOM type calculations were undertaken. ONIOM is an acronym for Our own N-layered Integrated molecular Orbital and molecular Mechanics. We find that the phytyl tail of PhQ does not play an important role in the orientation of PhQ in the A1 binding site. We also find that PhQ, in both neutral and reduced states, is strongly hydrogen bonded.
To test and verify the applicability of our QM/MM approach, ONIOM calculations were also undertaken for ubiquinone and a variety of other quinones incorporated into the, so called, QA binding site in purple bacteria photosynthetic reaction centers. The calculated and experimental spectra agree well, demonstrating the utility and applicability of our ONIOM approach. Hydrogen bonding to the carbonyl groups of quinones in the QA binding site was shown to be relatively weak, and it was found that hydrogen bonding to neutral ubiquinone in purple bacterial reaction centers can be considered in purely electrostatic terms, contrary to the widely held belief that the hydrogen bonding amino acids should be treated quantum mechanically.
10
Tyo, Keith E., et Gregory Stephanopoulos. « Inverse Metabolic Engineering of Synechocystis PCC 6803 for Improved Growth Rate and Poly-3-hydroxybutyrate Production ». 2004. http://hdl.handle.net/1721.1/7482.
Texte intégralRésumé :
Synechocystis PCC 6803 is a photosynthetic bacterium that has the potential to make bioproducts from carbon dioxide and light. Biochemical production from photosynthetic organisms is attractive because it replaces the typical bioprocessing steps of crop growth, milling, and fermentation, with a one-step photosynthetic process. However, low yields and slow growth rates limit the economic potential of such endeavors. Rational metabolic engineering methods are hindered by limited cellular knowledge and inadequate models of Synechocystis. Instead, inverse metabolic engineering, a scheme based on combinatorial gene searches which does not require detailed cellular models, but can exploit sequence data and existing molecular biological techniques, was used to find genes that (1) improve the production of the biopolymer poly-3-hydroxybutyrate (PHB) and (2) increase the growth rate. A fluorescence activated cell sorting assay was developed to screen for high PHB producing clones. Separately, serial sub-culturing was used to select clones that improve growth rate. Novel gene knock-outs were identified that increase PHB production and others that increase the specific growth rate. These improvements make this system more attractive for industrial use and demonstrate the power of inverse metabolic engineering to identify novel phenotype-associated genes in poorly understood systems.Singapore-MIT Alliance (SMA)
Livres sur le sujet "Stem photosynthesi"
1
Evert. Topics in Botany Lab Separates : Primary Structure of the Stem. W H Freeman & Co (Sd), 1998.
Trouver le texte intégral
2
Evert. Topics in Botany Lab Separates : Woody Stems. W H Freeman & Co (Sd), 1998.
Trouver le texte intégralChapitres de livres sur le sujet "Stem photosynthesi"
1
Gessler, Arthur, et Juan Pedro Ferrio. « Postphotosynthetic Fractionation in Leaves, Phloem and Stem ». Dans Stable Isotopes in Tree Rings, 381–96. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-92698-4_13.
Texte intégralRésumé :
AbstractStable carbon isotope ratios (δ13C) in organic matter convey important integrated and (if assessed in the tree ring archive) dateable information on plant physiology and related environmental drivers. While the generation of the δ13C signal in the primary assimilates in the leaves via photosynthetic carbon isotope fractionation is well understood, we still lack detailed knowledge of the processes that determine the isotopic fractionation in downstream processes in the leaves and during the transport in the stem, which in turn affect δ13C in the tree-ring archive. We here provide an update on processes that drive post-carboxylationcarbon isotope fractionation in the leaves, on potential changes in δ13C related to phloem loading and transport and we also discuss the role of stem CO2 fluxes (bark photosynthesis, stem respiration and CO2 fixation by phosphoenol pyruvate carboxylase). Moreover, we address the impact of carbon storage and remobilization on the intra-annual variation of δ13C in tree rings. Finally, we point to the potential importance of the intra-molecularcarbon isotope distribution in carbohydrates for tree ring δ13C and its relation to shifts in metabolic pathways.
2
Cernusak, Lucas A., et Nerea Ubierna. « Carbon Isotope Effects in Relation to CO2 Assimilation by Tree Canopies ». Dans Stable Isotopes in Tree Rings, 291–310. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-92698-4_9.
Texte intégralRésumé :
AbstractThe carbon atoms deposited in tree rings originate from the CO2 in the atmosphere to which the tree’s canopy is exposed. Thus, the first control on the stable carbon-isotope composition of tree rings is by δ13C of atmospheric CO2. There has been an inter-annual trend of decreasing δ13C of atmospheric CO2 over the past two centuries as a result of combustion of fossil fuels and land-use change. Atmospheric CO2 is, for the most part, well mixed, but the sub-canopy air space can become depleted in 13C due to inputs from soil and plant respiration when turbulent exchange with the troposphere is hindered, for example by a high leaf area index at night. This is less likely to occur during daytime when turbulence is higher and photosynthesis takes place. Discrimination against 13C (∆13C) occurs upon assimilation of atmospheric CO2 by C3 photosynthesis. Trees using the C3 photosynthetic pathway comprise the overwhelming majority of all trees. The primary control on the extent of discrimination during C3 photosynthesis is the drawdown in CO2 concentration from the air outside the leaf to the site of carboxylation in the chloroplast. Part of this drawdown is captured by ci/ca, that is, the ratio of intercellular to ambient CO2 concentrations. The ci/ca represents the balance between the CO2 supply by stomata and its demand by photosynthesis. It can be related to water-use efficiency, the amount of CO2 taken up by photosynthesis for a given amount of water loss to the atmosphere, assuming a given evaporative demand. To predict time-averaged ci/ca from wood ∆13C, a simplified, linear model can be employed. In this linear model, the slope is determined by $$\overline{b }$$ b ¯ , the effective enzymatic discrimination. The value of $$\overline{b }$$ b ¯ can be estimated by comparing wood ∆13C to representative measurements of ci/ca. The $$\overline{b }$$ b ¯ was originally estimated from observations of leaf tissue to have a value of 27‰. We compiled data for woody stem tissue here, and our analysis suggests that a lower $$\overline{b }$$ b ¯ should be used in the simplified model for wood ($$\overline{b }$$ b ¯ = 25.5‰) than for leaves ($$\overline{b }$$ b ¯ = 27‰). This is also consistent with widespread observations that woody tissues are enriched in 13C compared to leaves.
3
Gibson, Arthur Charles. « Photosynthetic Stems of Nonsucculent Plants ». Dans Structure-Function Relations of Warm Desert Plants, 91–116. Berlin, Heidelberg : Springer Berlin Heidelberg, 1996. http://dx.doi.org/10.1007/978-3-642-60979-4_4.
Texte intégral
4
Schmittmann, G., B. Moerschbacher et H. J. Reisener. « Changes in Photosynthesis of Wheat Plants Infected by Stem Rust ». Dans Current Research in Photosynthesis, 3591–94. Dordrecht : Springer Netherlands, 1990. http://dx.doi.org/10.1007/978-94-009-0511-5_811.
Texte intégral
5
James, E. K., F. R. Minchin, K. Oxborough, A. Cookson, N. R. Baker, J. F. Witty, R. M. M. Crawford et J. I. Sprent. « Photosynthetic Oxygen Evolution within Sesbania rostrata Stem Nodules ». Dans Biological Nitrogen Fixation for the 21st Century, 502. Dordrecht : Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-5159-7_312.
Texte intégral
6
Inoue, N., Y. Kashino, H. Koike et K. Satoh. « One Step Separation of Membranes of Cyanobacterium by Linear Gradient Floatation Centrifugation ». Dans Photosynthesis : Mechanisms and Effects, 1839–42. Dordrecht : Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-3953-3_430.
Texte intégral
7
Gourion, Benjamin, Katia Bonaldi et Eric Giraud. « Metabolism of Photosynthetic Bradyrhizobia during Root and Stem Symbiosis withAeschynomeneLegumes ». Dans Biological Nitrogen Fixation, 281–92. Hoboken, NJ, USA : John Wiley & Sons, Inc, 2015. http://dx.doi.org/10.1002/9781119053095.ch28.
Texte intégral
8
Mitome, Yuta, Satoshi Iriyama, Keiko Sato et Igor V. Volivich. « Efficient Energy Transfer in Network Model of Photosynthesis ». Dans STEAM-H : Science, Technology, Engineering, Agriculture, Mathematics & ; Health, 59–69. Cham : Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-74971-6_7.
Texte intégral
9
Johnson, Giles, Peter Horton, Julie Scholes et Philip Grime. « Fluorescence Responses on Step Changes in Irradiance by Plants from Different Light Habitats ». Dans Current Research in Photosynthesis, 3155–58. Dordrecht : Springer Netherlands, 1990. http://dx.doi.org/10.1007/978-94-009-0511-5_711.
Texte intégral
10
Vecchia, F. Dalla, A. Zuppini, B. Baldan, P. Mariani et N. Rascio. « Photosynthetic Behaviour of Leaves and Stems of Some Aquatic Plants ». Dans Photosynthesis : from Light to Biosphere, 4467–70. Dordrecht : Springer Netherlands, 1995. http://dx.doi.org/10.1007/978-94-009-0173-5_1049.
Texte intégralActes de conférences sur le sujet "Stem photosynthesi"
1
Stupko, V. Yu, M. A. Timina et N. A. Neshumaeva. « Preliminary assessment of photosynthetic features of winter rye cultivars selected by the Krasnoyarsk Research Institute of Agriculture ». Dans II All-Russian scientific conference with international participation "Achievements of science and technology". Krasnoyarsk Science and Technology City Hall, 2023. http://dx.doi.org/10.47813/dnit-ii.2023.7.556-563.
Texte intégralRésumé :
When comparing ancient and modern rye cultivars, in addition to the difference in height, differences in the content of photosynthetic pigments in tissues are also noted. However, it remains unclear whether the change in pigment content is related to the change in plant architectonics. Plants of winter rye cultivars which differ in plant height were collected under the conditions of crop rotation of the Krasnoyarsk Research Institute of Agriculture. The concentrations of chlorophylls a and b and carotenoids were determined in the flag leaves and stems of winter rye at the “booting-earing” stage. The weight of the above-ground biomass was determined with the hay-harvest method. The stem length increases from the Arga cultivar to the cv. Krasnoyarskaya universalnaya and further to the cv. Yeniseyka. The relationship between the level of photosynthetic pigments and the height of plants as well as their wet biomass was assessed. A trend line toward an increase in the content of chlorophylls and carotenoids, assessed per leaf area, and biomass was revealed against the background of a decrease in stem height. When assessing the pigment content per mass of organs, the trend is less pronounced and is observed only when comparing the varieties Arga and Krasnoyarskaya universalnaya with the highest cultivar Yeniseyka.
2
Meech, S. R., A. J. Hoff et D. A. Wiersma. « Ultrafast electron-transfer processes in photosynthetic reaction centers. Photon-echo and holeburning studies of optical excitations in Rhodopseudomonas viridis and sphaeroides ». Dans International Conference on Ultrafast Phenomena. Washington, D.C. : Optica Publishing Group, 1986. http://dx.doi.org/10.1364/up.1986.wb1.
Texte intégralRésumé :
One of the most intriguing and fundamental processes on our planet is photosynthesis, whereby light is converted into chemical energy. The first step in the chain of events is known to involve a charge-separation reaction in which a specialized chlorophyll (Chl) or bacteriochlorophyll (BChl) pigment-complex reduces a nearby pheophytin (Ph) molecule. In subsequent reactions the electron moves along a chain of acceptors and finally becomes stabilized such that the remaining potential energy can be used in metabolic reactions. It is obvious that these fundamental electron-transfer reactions have been an ongoing challenge to spectroscopists. Since the functioning pigment-protein complex was isolated in pure form (1) much progress has been made towards elucidating the architecture of the pigment complex and the optical dynamics of the system. Very recently these investigations were greatly stimulated by an X-ray structural determination of the reaction center of the photosynthetic bacterium Rhodopseudomonas viridis (2). One of the most interesting findings was that the pigments spatial arrangement was such that it contained a quasi C2-axis with a dimer at one end. It was known from previous time-resolved experiments that this dimer played a crucial role in the initial events of the charge separation. It is apparent that with the structure at hand one can ask very specific questions about the functioning of the reaction centre, such as: why is there a dimer; what is the role of the intermediate chlorophyll and why does the reaction only proceed along one branch of the pseudo-symmetric pigment complex?
3
Chachisvilis, M., T. Pullerits, W. Westerhuis, C. N. Hunter et V. Sundström. « Exciton Coherence in Photosynthetic Light-Harvesting ». Dans International Conference on Ultrafast Phenomena. Washington, D.C. : Optica Publishing Group, 1996. http://dx.doi.org/10.1364/up.1996.fc.2.
Texte intégralRésumé :
Excitation transfer in photosynthetic pigments is generally described as incoherent Förster hopping, but the exciton concept has also been applied for photosynthetic antenna systems (1,2). In that case excitation energy is delocalized over a number of pigment molecules and the dynamics occurs through the relaxation between different exciton states. However, often it is not so straightforward to unambiguously distinguish in experiment the two qualitatively different kinetic processes, incoherent hopping and exciton relaxation. The actual dynamics can be a combination of these limiting cases. For example, smaller sections of the full system might behave as a small exciton whereas the dynamics on a larger scale may correspond to the hopping-like transfer of this small exciton. An argument against the pure incoherent Förster mechanism is the recent observation of coherent nuclear motions in the antenna complexes of photosynthetic bacteria (3). The vibrational coherence is preserved for at least the same time as the estimated single step transfer time in these systems. This implies that one of the main assumptions of the Förster theory that the vibronic relaxation occurs much faster than the excitation transfer is not fulfilled. Furthermore, the structural data of several light-harvesting proteins (4,5) show densely packed pigment systems, where exciton interactions are quite strong.
4
van Noort, P. I., T. J. Aartsma et J. Amesz. « Energy transfer and primary charge separation in heliobacteria by picosecond transient absorption spectroscopy. » Dans International Conference on Ultrafast Phenomena. Washington, D.C. : Optica Publishing Group, 1992. http://dx.doi.org/10.1364/up.1992.mc29.
Texte intégralRésumé :
In photosynthetic bacteria the excitation energy of excited antenna pigments is transferred to the reaction center within tens of picoseconds. After trapping of the excitation energy by the reaction center, charge separation is induced as the first step in a series of electron transfer reactions.
5
Xie, X., M. Du, S. J. Rosenthal, T. J. DiMagno, M. E. Schmidt, J. R. Norris et G. R. Fleming. « Femtosecond Spontaneous Fluorescence Studies of Photosynthetic Bacterial Reaction Centers. » Dans International Conference on Ultrafast Phenomena. Washington, D.C. : Optica Publishing Group, 1992. http://dx.doi.org/10.1364/up.1992.mc9.
Texte intégralRésumé :
The mechanism of the initial electron transfer step in the reaction center of photosynthetic bacteria has been the subject of intense study over the past 10 years. This initial step is ultrafast, occurring in about 3 ps at room temperature [1]. As the understanding of the reaction center improves the need arises for more precise kinetic data. In particular, questions arise to the exponentiality of the observed kinetic signals [2], the possibility of differing behavior at different wavelengths [3], the existence of oscillatory components [2], and of spectral shifts accompanying the excitation and subsequent electron transfer processes. We measured the spontaneous fluorescence decay of P* in Rb. Sphaeroidis R26, Rb. Capsulatus, and mutantsof Rb. Capsulatus using the upconversion technique. For all samples QA was chemically reduced with the exception of the Rb. Sphaeroidis R26 sample for which the quinone was removed. The Rb. Spaeroidis R26 quinone removed measurements with both direct excitation of P at 850 nm and indirect excitation through internal conversion from PQX and energy transfer from BChl excited at 608 nm. All other samples were excited @ 850 nm. Excitation at 608 nm was provided by an antiresonant ring dye laser amplified at 100 Khz by a YAG regen yielding 60 fs pulses [4]. Experiments using 850 nm excitation were performed with a Coherent Mira 900 F Ti sapphire laser operating at 76 MHz with 95 fs pulses [5]. The instrument response functions at 940 nm emission for the two apparatus is ~180 fs. A typical data set is shown in Figure 1. All the samples showed nonexponential decay (see Figure 1) which could be adequately fit by a sum of two exponentials. The shorter component compares very well with the single components determined by stimulated emission [6]. However, the improved dynamic range and absence of other components (excited state absorption and ground state bleaching) make the nonexponentiality very clear. With 850 nm excitation we were unable to detect a risetime for fluorescence at 940 nm. With 610 nm excitation a risetime of 200 fs is apparent (Figure 2). This risetime results from a combination of energy transfer from the accessory pigments and electronic relaxation with the special pair manifold.
6
Wachtveitl, J., T. Arlt, H. Huber, H. Penzkofer et W. Zinth. « The Primary Electron Transfer in Bacterial Reaction Centers with Altered Energetics of the Primary Acceptor ». Dans International Conference on Ultrafast Phenomena. Washington, D.C. : Optica Publishing Group, 1996. http://dx.doi.org/10.1364/up.1996.tud.2.
Texte intégralRésumé :
Recent femtosecond experiments on bacterial reaction centers (RCs) could show that a bacteriochlorophyll anion is formed in the first step of the photosynthetic charge separation process [1]. This reaction was interpreted as the reduction of the monomeric bacteriochlorophyll molecule BA, located on one of the two pigment branches, between the primary donor (P, a bacteriochlorophyll dimer) and the secondary acceptor (HA, a bacteriopheophytin molecule).
7
De Caro, C., T. H. M. Creemers, R. W. Visschers, R. van Grondelle et S. Völker. « Spectral Hole-Burning in Photosynthetic Pigment-Protein Complexes : Size-Dependent Dynamics ». Dans Spectral Hole-Burning and Related Spectroscopies : Science and Applications. Washington, D.C. : Optica Publishing Group, 1994. http://dx.doi.org/10.1364/shbs.1994.wd19.
Texte intégralRésumé :
The initial step in the photosynthetic process is the absorption of light by chlorophyll-type molecules bound to proteins in so-called light-harvesting (LH) complexes, and the subsequent transfer of the excitation energy among these antennae until it is trapped by the reaction center (RC). This entire process occurs in less than 100 ps. In the RC an electron is then transferred across the biological membrane, by which an electrochemical potential gradient is generated and the energy stored for subsequent processes.
8
Bandaruk, R. S., I. E. Butchenkov et E. R. Gritskevitch. « VARIETY OF LIFE FORMS OF JUNIPERUS COMMUNIS L. AS AN INDICATOR OF ECOLOGICAL PLASTICITY IN THE URBAN ENVIRONMENT ». Dans SAKHAROV READINGS 2021 : ENVIRONMENTAL PROBLEMS OF THE XXI CENTURY. International Sakharov Environmental Institute of Belarusian State University, 2021. http://dx.doi.org/10.46646/sakh-2021-2-338-341.
Texte intégralRésumé :
The urban environment is distinguished by the originality of environmental factors, the specificity of manmade impacts, leading to a significant transformation of the environment. Plants are the main factor in the ecological stabilization of the urban environment due to their vital activity, and, above all, photosynthesis and the ability to accumulate pollutants. The aim of the work is to study the bioecological characteristics of the common juniper in the urban environment. In the course of the research, it was found that in urbanized areas, J. communis has a more diverse range of life forms than in natural conditions. Along with single-stemmed trees prevailing in the natural environment, new geoxyl small- and multi-stem trees and aeroxil tree-bush are formed.
9
Gupta, Ankita, Lakhwinder Kaur et Gurmeet Kaur. « Comparitive Analysis of Segmentation Methods for Wheat Canopy Extraction ». Dans International Conference on Women Researchers in Electronics and Computing. AIJR Publisher, 2021. http://dx.doi.org/10.21467/proceedings.114.7.
Texte intégralRésumé :
Global food demand is expected to be doubled by 2050, while natural resources are continuously under threat due to unpredictable climatic changes. This challenge can be tackled by increasing the yield of the crops and by reducing abiotic stresses such as water stress. Research shows that due to water stress the morphology and the structure of plant’s canopy changes. The first step in building early water stress detection system is to extract accurate area where photosynthetic activities of the plant are occurring. In this research work, comparative analysis of seven different segmentation algorithms viz., convolution gradient-based, watershed, mean-shift, k-means, Global static thresholding, Otsu thresholding and hybrid approach (combination of Global Static thresholding with k-means) has been analyzed in order to identify the most probable area of canopy where maximum photosynthetic signals can be captured. The comparison is done in terms of IoU metric. The comparative results indicate that the most appropriate method for wheat canopy segmentation is a hybrid approach, which achieves IoU score of 59.8 and its runner up algorithm is Global Static Thresholding with an IoU score 53.8.
10
Arakawa, Hironori, Zhigang Zou, Kazuhiro Sayama et Ryu Abe. « Solar Hydrogen Production : Direct Water Splitting Into Hydrogen and Oxygen by New Photocatalysts Under Visible Light Irradiation ». Dans ASME 2003 International Solar Energy Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/isec2003-44301.
Texte intégralRésumé :
The photocatalytic splitting of water into hydrogen and oxygen using solar energy is one of the most attractive renewable sources of hydrogen fuel. Therefore, considerable efforts have been paid in developing photocatalysts capable of using visible light, which accounts for about 43% of the solar energy. However such a photocatalyst has not been developed so far. We have developed a new Ni-doped indium-tantalum oxide photocatalyst, In1-xNixTaO4 (x = 0.0∼0.2), which induced direct splitting of water into stoichiometric amount of oxygen and hydrogen under visible light irradiation with a quantum yield of about 0.66% at 420.7 nm. We have also developed a new two-step water splitting system using two different semiconductor photocatalysts, Pt/WO3 photocatalyst for oxygen evolution and Pt/SrTiO3(Cr-Ta-doped) photocatalyst for hydrogen evolution, and a redox mediator, I−/IO3−, mimicking the Z-scheme mechanism of the natural photosynthesis. The quantum yield of this system was about 0.1% at 420.7nm. Both photocatalytic methods are the first examples for visible light water splitting system in the world.
Rapports d'organisations sur le sujet "Stem photosynthesi"
1
Christopher, David A., et Avihai Danon. Plant Adaptation to Light Stress : Genetic Regulatory Mechanisms. United States Department of Agriculture, mai 2004. http://dx.doi.org/10.32747/2004.7586534.bard.
Texte intégralRésumé :
Original Objectives: 1. Purify and biochemically characterize RB60 orthologs in higher plant chloroplasts; 2. Clone the gene(s) encoding plant RB60 orthologs and determine their structure and expression; 3. Manipulate the expression of RB60; 4. Assay the effects of altered RB60 expression on thylakoid biogenesis and photosynthetic function in plants exposed to different light conditions. In addition, we also examined the gene structure and expression of RB60 orthologs in the non-vascular plant, Physcomitrella patens and cloned the poly(A)-binding protein orthologue (43 kDa RB47-like protein). This protein is believed to a partner that interacts with RB60 to bind to the psbA5' UTR. Thus, to obtain a comprehensive view of RB60 function requires analysis of its biochemical partners such as RB43. Background & Achievements: High levels of sunlight reduce photosynthesis in plants by damaging the photo system II reaction center (PSII) subunits, such as D1 (encoded by the chloroplast tpsbAgene). When the rate of D1 synthesis is less than the rate of photo damage, photo inhibition occurs and plant growth is decreased. Plants use light-activated translation and enhanced psbAmRNA stability to maintain D1 synthesis and replace the photo damaged 01. Despite the importance to photosynthetic capacity, these mechanisms are poorly understood in plants. One intriguing model derived from the algal chloroplast system, Chlamydomonas, implicates the role of three proteins (RB60, RB47, RB38) that bind to the psbAmRNA 5' untranslated leader (5' UTR) in the light to activate translation or enhance mRNA stability. RB60 is the key enzyme, protein D1sulfide isomerase (Pill), that regulates the psbA-RN :Binding proteins (RB's) by way of light-mediated redox potentials generated by the photosystems. However, proteins with these functions have not been described from higher plants. We provided compelling evidence for the existence of RB60, RB47 and RB38 orthologs in the vascular plant, Arabidopsis. Using gel mobility shift, Rnase protection and UV-crosslinking assays, we have shown that a dithiol redox mechanism which resembles a Pill (RB60) activity regulates the interaction of 43- and 30-kDa proteins with a thermolabile stem-loop in the 5' UTR of the psbAmRNA from Arabidopsis. We discovered, in Arabidopsis, the PD1 gene family consists of II members that differ in polypeptide length from 361 to 566 amino acids, presence of signal peptides, KDEL motifs, and the number and positions of thioredoxin domains. PD1's catalyze the reversible formation an disomerization of disulfide bonds necessary for the proper folding, assembly, activity, and secretion of numerous enzymes and structural proteins. PD1's have also evolved novel cellular redox functions, as single enzymes and as subunits of protein complexes in organelles. We provide evidence that at least one Pill is localized to the chloroplast. We have used PDI-specific polyclonal and monoclonal antisera to characterize the PD1 (55 kDa) in the chloroplast that is unevenly distributed between the stroma and pellet (containing membranes, DNA, polysomes, starch), being three-fold more abundant in the pellet phase. PD1-55 levels increase with light intensity and it assembles into a high molecular weight complex of ~230 kDa as determined on native blue gels. In vitro translation of all 11 different Pill's followed by microsomal membrane processing reactions were used to differentiate among PD1's localized in the endoplasmic reticulum or other organelles. These results will provide.1e insights into redox regulatory mechanisms involved in adaptation of the photosynthetic apparatus to light stress. Elucidating the genetic mechanisms and factors regulating chloroplast photosynthetic genes is important for developing strategies to improve photosynthetic efficiency, crop productivity and adaptation to high light environments.
2
Granot, David, et Noel Michelle Holbrook. Role of Fructokinases in the Development and Function of the Vascular System. United States Department of Agriculture, janvier 2011. http://dx.doi.org/10.32747/2011.7592125.bard.
Texte intégralRésumé :
Plant vascular tissues are superhighways whose development and function have profound implications for productivity, yield and stress response. Preliminary studies by the PI indicated that sugar metabolism mediated by fructokinases (FRKs) has a pronounced effect on the transport properties of the xylem. The goal of this research was to determine how the main fructokinase gene, FRK2, and the only plastidic fructokinase, FRK3, influence vascular development and physiology, emphasizing processes that occur at both the cellular and organismic level. We found that both genes are expressed in vascular tissues, but FRK3 is expressed primarily in vascular tissues of mature petioles. Vascular anatomy of plants with antisense suppression of FRK2 uncovered that FRK2 is necessary for xylem and phloem development, most likely due to its role in vascular cell-wall synthesis, and affects vascular development all over the plant. As a result, suppression of FRK2 reduced hydraulic conductivity of roots, stem and leaves and restricted sugar phloem transport. Vascular anatomy of plants with RNAi suppression of FRK3 uncovered that FRK3 is required for vascular development in mature petiole but its role is partially complemented by FRK2. Suppression of FRK3 combined with partial suppression of FRK2 had effects completely different from that of FRK2 suppression, resulting in wilting of mature leaves rather than young leaves of FRK2 suppressed plants, and decreased export of photoassimilates. This primary effect of FRK2 suppression on mature petioles had a secondary effect, reducing the hydraulic conductivity in roots and stem. The very fact that a plastidic fructokinase plays a role in vascular development is quite surprising and we are still seeking to uncover its metabolic mode-of-action. Yet, it is clear that these two fructokinases have different roles in the coordination between photosynthetic capacity and vascular development. We have started analyzing the role of the last third FRK, FRK1, and discovered that it is also expressed exclusively in vascular tissues. It appears therefore, that all FRKs studied here are involved in vascular development. An interesting unexpected outcome of this study was the connection of FRK2 with hormonal regulation of vascular development, most likely auxin. This observation together with the yet to be solved questions on the exact roles of FRK3 are the subjects of our current efforts.
3
Wolf, Shmuel, et William J. Lucas. Involvement of the TMV-MP in the Control of Carbon Metabolism and Partitioning in Transgenic Plants. United States Department of Agriculture, octobre 1999. http://dx.doi.org/10.32747/1999.7570560.bard.
Texte intégralRésumé :
The function of the 30-kilodalton movement protein (MP) of tobacco mosaic virus (TMV) is to facilitate cell-to-cell movement of viral progeny in infected plants. Our earlier findings have indicated that this protein has a direct effect on plasmodesmal function. In addition, these studies demonstrated that constitutive expression of the TMV MP gene (under the control of the CaMV 35S promoter) in transgenic tobacco plants significantly affects carbon metabolism in source leaves and alters the biomass distribution between the various plant organs. The long-term goal of the proposed research was to better understand the factors controlling carbon translocation in plants. The specific objectives were: A) To introduce into tobacco and potato plants a virally-encoded (TMV-MP) gene that affects plasmodesmal functioning and photosynthate partitioning under tissue-specific promoters. B) To introduce into tobacco and potato plants the TMV-MP gene under the control of promoters which are tightly repressed by the Tn10-encoded Tet repressor, to enable the expression of the protein by external application of tetracycline. C) To explore the mechanism by which the TMV-MP interacts with the endogenous control o~ carbon allocation. Data obtained in our previous project together with the results of this current study established that the TMV-MP has pleiotropic effects when expressed in transgenic tobacco plants. In addition to its ability to increase the plasmodesmal size exclusion limit, it alters carbohydrate metabolism in source leaves and dry matter partitioning between the various plant organs, Expression of the TMV-MP in various tissues of transgenic potato plants indicated that sugars and starch levels in source leaves are reduced below those of control plants when the TMV-MP is expressed in green tissue only. However, when the TMV-MP was expressed predominantly in PP and CC, sugar and starch levels were raised above those of control plants. Perhaps the most significant result obtained from experiments performed on transgenic potato plants was the discovery that the influence of the TMV-MP on carbohydrate allocation within source leaves was under developmental control and was exerted only during tuber development. The complexity of the mode by which the TMV-MP exerts its effect on the process of carbohydrate allocation was further demonstrated when transgenic tobacco plants were subjected to environmental stresses such as drought stress and nutrients deficiencies, Collectively, these studies indicated that the influence of the TMV-MP on carbon allocation L the result of protein-protein interaction within the source tissue. Based on these results, together with the findings that plasmodesmata potentiate the cell-to-cell trafficking of viral and endogenous proteins and nucleoproteins complexes, we developed the theme that at the whole plant level, the phloem serves as an information superhighway. Such a long-distance communication system may utilize a new class of signaling molecules (proteins and/or RNA) to co-ordinate photosynthesis and carbon/nitrogen metabolism in source leaves with the complex growth requirements of the plant under the prevailing environmental conditions. The discovery that expression of viral MP in plants can induce precise changes in carbon metabolism and photoassimilate allocation, now provide a conceptual foundation for future studies aimed at elucidating the communication network responsible for integrating photosynthetic productivity with resource allocation at the whole-plant level. Such information will surely provide an understanding of how plants coordinate the essential physiological functions performed by distantly-separated organs. Identification of the proteins involved in mediating and controlling cell-to-cell transport, especially at the companion cell-sieve element boundary, will provide an important first step towards achieving this goal.