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Journal articles on the topic 'Phloem flow'

Author: Grafiati

Published: 4 June 2021

Last updated: 9 February 2022

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1

Terada, Yasuhiko, Yusuke Horikawa, Akiyoshi Nagata, Katsumi Kose, and Kenji Fukuda. "Dynamics of xylem and phloem sap flow in an outdoor zelkova tree visualized by magnetic resonance imaging." Tree Physiology 40, no. 3 (December 19, 2019): 290–304. http://dx.doi.org/10.1093/treephys/tpz120.

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Abstract Xylem and phloem sap flows in an intact, young Japanese zelkova tree (Zelkova serrata (Thunb.) Makino) growing outdoors were measured using magnetic resonance imaging (MRI). Two propagator-based sequences were developed for q-space imaging: pulse field gradient (PFG) with spin echo (PFG-SE) and stimulated echo (PFG-STE), which were used for xylem and phloem flow measurements, respectively. The data evaluation methods were improved to image fast xylem flow and slow phloem flow. Measurements were taken every 2–3 h for several consecutive days in August 2016, and diurnal changes in xylem and phloem sap flows in a cross-section of the trunk were quantified at a resolution of 1 mm2. During the day, apparent xylem flow volume exhibited a typical diurnal pattern following a vapor pressure deficit. The velocity mapping of xylem sap flow across the trunk cross section revealed that the greatest flow volume was found in current-year earlywood that had differentiated in April–May. The combined xylem flow in the 1- and 2-year-old annual rings also contributed to one-third of total sap flow. In the phloem, downward sap flow did not exhibit diurnal changes. This novel application of MRI in visualization of xylem and phloem sap flow by MRI is a promising tool for in vivo study of water transport in mature trees.

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2

Gould, Nick, Peter E. H. Minchin, and Michael R. Thorpe. "Direct measurements of sieve element hydrostatic pressure reveal strong regulation after pathway blockage." Functional Plant Biology 31, no. 10 (2004): 987. http://dx.doi.org/10.1071/fp04058.

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According to the Münch hypothesis, solution flow through the phloem is driven by a hydrostatic pressure gradient. At the source, a high hydrostatic pressure is generated in the collection phloem by active loading of solutes, which causes a concomitant passive flow of water, generating a high turgor pressure. At the sink, solute unloading from the phloem keeps the turgor pressure low, generating a source-to-sink hydrostatic pressure gradient. Localised changes in loading and unloading of solutes along the length of the transport phloem can compensate for small, short-term changes in phloem loading at the source, and thus, maintain phloem flow to the sink tissue. We tested directly the hydrostatic pressure regulation of the sieve tube by relating changes in sieve tube hydrostatic pressure to changes in solute flow through the sieve tube. A sudden phloem blockage was induced (by localised chilling of a 1-cm length of stem tissue) while sieve-tube-sap osmotic pressure, sucrose concentration, hydrostatic pressure and flow of recent photosynthate were observed in vivo both upstream and downstream of the block. The results are discussed in relation to the Münch hypothesis of solution flow, sieve tube hydrostatic pressure regulation and the mechanism behind the cold-block phenomenon.

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3

Liesche, Johannes, and John Patrick. "An update on phloem transport: a simple bulk flow under complex regulation." F1000Research 6 (December 6, 2017): 2096. http://dx.doi.org/10.12688/f1000research.12577.1.

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The phloem plays a central role in transporting resources and signalling molecules from fully expanded leaves to provide precursors for, and to direct development of, heterotrophic organs located throughout the plant body. We review recent advances in understanding mechanisms regulating loading and unloading of resources into, and from, the phloem network; highlight unresolved questions regarding the physiological significance of the vast array of proteins and RNAs found in phloem saps; and evaluate proposed structure/function relationships considered to account for bulk flow of sap, sustained at high rates and over long distances, through the transport phloem.

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4

Winkler, Andreas, and Moritz Knoche. "Xylem, phloem and transpiration flows in developing European plums." PLOS ONE 16, no. 5 (May 20, 2021): e0252085. http://dx.doi.org/10.1371/journal.pone.0252085.

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Neck shrivel is a quality disorder of European plum (Prunus × domestica L.). It has been suggested that backflow in the xylem (from fruit to tree) could contribute to the incidence of neck shrivel in plum. The objective was to quantify rates of xylem, phloem and of transpiration flow in developing plum fruit. Using linear variable displacement transducers, changes in fruit volume were recorded 1) in un-treated control fruit, 2) in fruit that had their pedicels steam-girdled (phloem interrupted, xylem still functional) and 3) in detached fruit, left in the canopy (xylem and phloem interrupted). Xylem flow rates were occasionally negative in the early hours after sunrise, indicating xylem sap backflow from fruit to tree. Later in the day, xylem flows were positive and generally higher in daytime and lower at night. Significant phloem flow occurred in daytime, but ceased after sunset. During stage II (but not during stage III), the rates of xylem flow and transpiration were variable and closely related to atmospheric vapor pressure deficit. The relative contribution of xylem inflow to total sap inflow averaged 79% during stage II, decreasing to 25% during stage III. In contrast, phloem sap inflow averaged 21% of total sap inflow during stage II, increasing to 75% in stage III. Our results indicate that xylem backflow occurs early in the day. However, xylem backflow rates are considered too low to significantly contribute to the incidence of neck shrivel.

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5

Minchin, PEH, and MR Thorpe. "Is Phloem Transport Due to a Hydrostatic Pressure Gradient? Supporting Evidence From Pressure Chamber Experiments." Functional Plant Biology 14, no. 4 (1987): 397. http://dx.doi.org/10.1071/pp9870397.

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A pressure chamber was used to increase suddenly the hydrostatic pressure in the upper shoot of a Phaseolus vulgaris plant while observing phloem transport of 11C-labelled photoassimilate. Phloem transport in the stem towards the chamber stopped immediately when pressure was applied and then recovered within about 5 min. If the pressure was then released, flow increased again. The results support the hypothesis that flow of photoassimilate in the stem phloem was driven by a hydrostatic pressure gradient.

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6

Peuke, Andreas D. "ABA flow modelling in Ricinus communis exposed to salt stress and variable nutrition." Journal of Experimental Botany 67, no. 18 (July 20, 2016): 5301–11. http://dx.doi.org/10.1093/jxb/erw291.

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Abstract In a series of experiments with Ricinus communis, abscisic acid (ABA) concentrations in tissues and transport saps, its de novo biosynthesis, long-distance transport, and metabolism (degradation) were affected by nutritional conditions, nitrogen (N) source, and nutrient limitation, or salt stress. In the present study these data were statistically re-evaluated, and new correlations presented that underpin the importance of this universal phytohormone. The biggest differences in ABA concentration were observed in xylem sap. N source had the strongest effect; however, nutrient limitation (particularly phosphorus limitation) and salt also had significant effects. ABA was found in greater concentration in phloem sap compared with xylem sap; however, the effect of treatment on ABA concentration in phloem was lower. In the leaves, ABA concentration was most variable compared with the other tissues. This variation was only affected by the N source. In roots, ABA was significantly decreased by nutrient limitation. Of the compartments in which ABA was quantified, xylem sap ABA concentration was most significantly correlated with leaf stomatal conductance and leaf growth. Additionally, ABA concentration in xylem was significantly correlated to that in phloem, indicating a 6-fold concentration increase from xylem to phloem. The ABA flow model showed that biosynthesis of ABA in roots affected the xylem flow of ABA. Moreover, ABA concentration in xylem affected the degradation of the phytohormone in shoots and also its export from shoots via phloem. The role of phloem transport is discussed since it stimulates ABA metabolism in roots.

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7

Mullendore, Daniel L., Carel W. Windt, Henk Van As, and Michael Knoblauch. "Sieve Tube Geometry in Relation to Phloem Flow." Plant Cell 22, no. 3 (March 2010): 579–93. http://dx.doi.org/10.1105/tpc.109.070094.

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8

Gould, Nick, Michael R. Thorpe, Olga Koroleva, and Peter E. H. Minchin. "Phloem hydrostatic pressure relates to solute loading rate: a direct test of the Münch hypothesis." Functional Plant Biology 32, no. 11 (2005): 1019. http://dx.doi.org/10.1071/fp05036.

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According to the Münch hypothesis, a flow of solution through the sieve tubes is driven by a hydrostatic pressure difference between the source (or collection) phloem and the sink (or release) phloem. A high hydrostatic pressure is maintained in the collection phloem by the active uptake of sugar and other solutes, with a concomitant inflow of water. A lower pressure is maintained in the release phloem through solute unloading. In this work we directly test the role of solute uptake in creating the hydrostatic pressure associated with phloem flow. Solute loading into the phloem of mature leaves of barley and sow thistle was reduced by replacing the air supply with nitrogen gas. Hydrostatic pressure in adjacent sieve elements was measured with a sieve-element pressure probe, a cell pressure probe glued to the exuding stylet of aphids that had been feeding from the phloem. Sieve element sap was sampled by aphid stylectomy; sap osmotic pressure was determined by picolitre osmometry and its sugar concentration by enzyme-linked fluorescence assays. Samples were taken with a time resolution of ~2–3 min. In accordance with Münch’s proposal a drop in osmotic and hydrostatic pressure in the source phloem following treatment of the source leaf with N2 was observed. A decrease in sugar concentration was the major contributor to the change in osmotic pressure. By observing these variables at a time resolution of minutes we have direct observation of the predictions of Münch.

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9

Patrick, John W., Wenhao Zhang, Stephen D. Tyerman, Christina E. Offler, and N. Alan Walker. "Role of membrane transport in phloem translocation of assimilates and water." Functional Plant Biology 28, no. 7 (2001): 697. http://dx.doi.org/10.1071/pp01023.

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Most growth and storage organs (sinks) of higher plants import assimilates in solution by bulk flow through the phloem, driven by differences in hydrostatic pressure. These differences in pressure, located between the ends of the interconnecting phloem path, are generated by osmotic water movement, driven in turn by membrane transport of solutes. Sucrose, amino-nitrogen compounds and potassium represent the osmotically important solutes found in phloem contents of most species. Phloem loading and unloading events of these assimilate species play central roles in determining phloem translocation rates and partitioning of assimilates and water. Depending on plant species, leaf vein order and sink type, phloem loading and unloading may follow apoplasmic or symplasmic routes. Irrespective of the cellular pathway followed, assimilates are transported across plasma and organellar membranes. Aquaporins, amino-nitrogen transporters, sucrose transporters and potassium channels have been detected in key sites along the source–phloem–sink transport pathway. Reverse genetics has demonstrated that sucrose/proton symporters are important in transport events necessary for phloem loading in Solanaceousplant species. Drawing on circumstantial evidence, we review possible functions the remaining membrane transporters and channels may serve in driving phloem translocation of assimilates and water from source to sink.

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10

Jensen, Kaare H., Jessica A. Savage, and N. Michele Holbrook. "Optimal concentration for sugar transport in plants." Journal of The Royal Society Interface 10, no. 83 (June 6, 2013): 20130055. http://dx.doi.org/10.1098/rsif.2013.0055.

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Vascular plants transport energy in the form of sugars from the leaves where they are produced to sites of active growth. The mass flow of sugars through the phloem vascular system is determined by the sap flow rate and the sugar concentration. If the concentration is low, little energy is transferred from source to sink. If it is too high, sap viscosity impedes flow. An interesting question is therefore at which concentration is the sugar flow optimal. Optimization of sugar flow and transport efficiency predicts optimal concentrations of 23.5 per cent (if the pressure differential driving the flow is independent of concentration) and 34.5 per cent (if the pressure is proportional to concentration). Data from more than 50 experiments (41 species) collected from the literature show an average concentration in the range from 18.2 per cent (all species) to 21.1 per cent (active loaders), suggesting that the phloem vasculature is optimized for efficient transport at constant pressure and that active phloem loading may have developed to increase transport efficiency.

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11

Harding, RM, and DS Teakle. "Autofluorescence of necrotic phloem cells and laticifers, and a reduced latex flow: new symptoms for papaw dieback disease in Australia." Australian Journal of Agricultural Research 39, no. 5 (1988): 857. http://dx.doi.org/10.1071/ar9880857.

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When petiole and root sections taken from papaw plants affected by dieback disease were examined under a fluorescence microscope, specific autofluorescence was observed in some phloem cells and/or laticifers. Such autofluorescence was never observed in similarly treated sections taken from healthy plants. Light and electron microscopic examination of areas showing specific autofluorescence revealed the presence of necrotic phloem cells, but close examination of these cells failed to show a parasitic agent. Papaw plants affected by dieback disease and showing necrosis of laticifers also displayed a marked reduction in latex flow. The results indicate that autofluorescence of necrotic phloem cells and laticifiers, and a reduced latex flow, are new symptoms of papaw dieback disease in Australia.

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12

Harding, RM, and DS Teakle. "Corrigendum - Autofluorescence of necrotic phloem cells and laticifers, and a reduced latex flow: new symptoms for papaw dieback disease in Australia." Australian Journal of Agricultural Research 39, no. 5 (1988): 857. http://dx.doi.org/10.1071/ar9880857c.

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When petiole and root sections taken from papaw plants affected by dieback disease were examined under a fluorescence microscope, specific autofluorescence was observed in some phloem cells and/or laticifers. Such autofluorescence was never observed in similarly treated sections taken from healthy plants. Light and electron microscopic examination of areas showing specific autofluorescence revealed the presence of necrotic phloem cells, but close examination of these cells failed to show a parasitic agent. Papaw plants affected by dieback disease and showing necrosis of laticifers also displayed a marked reduction in latex flow. The results indicate that autofluorescence of necrotic phloem cells and laticifiers, and a reduced latex flow, are new symptoms of papaw dieback disease in Australia.

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13

Hölttä, Teemu, Timo Vesala, Martti Perämäki, and Eero Nikinmaa. "Refilling of embolised conduits as a consequence of 'Münch water' circulation." Functional Plant Biology 33, no. 10 (2006): 949. http://dx.doi.org/10.1071/fp06108.

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‘Münch water’ is pushed from the phloem to the xylem at locations of phloem sugar unloading. Consequently, an internal radial water potential imbalance is developed in the plant at these sugar-unloading sites. The phloem is at a higher water potential than the xylem. The magnitude of this radial water potential imbalance is determined by the magnitude of the radial water flux and the hydraulic resistance along the phloem-to-xylem pathway. If, as a result, the water potential in the ray parenchyma cells adjacent to xylem conduits is higher than that in the embolised xylem conduits, then a proportion of the water flow from the phloem would be directed towards embolised xylem conduits, in addition to conduits under tension. In this theoretical paper we demonstrate how recycled ‘Münch water’ passing from the phloem to the xylem can induce xylem embolism refilling. We also calculate the conditions and the structural composition of the phloem-to-xylem pathway that are required for embolism refilling by ‘Münch water’ circulation, and the time that is required for the complete refilling of embolised conduits in varying conditions.

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14

THOMPSON, M. V., and N. M. HOLBROOK. "Scaling phloem transport: water potential equilibrium and osmoregulatory flow." Plant, Cell & Environment 26, no. 9 (August 1, 2003): 1561–77. http://dx.doi.org/10.1046/j.1365-3040.2003.01080.x.

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15

Lo Bianco, R., and A. Scalisi. "Phloem and xylem flow contributions to nectarine fruit development." Acta Horticulturae, no. 1314 (June 2021): 463–70. http://dx.doi.org/10.17660/actahortic.2021.1314.57.

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16

Lee, D. R. "Vasculature of the abscission zone of tomato fruit: implications for transport." Canadian Journal of Botany 67, no. 6 (June 1, 1989): 1898–902. http://dx.doi.org/10.1139/b89-241.

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The structural anatomy of the abscission zone in the "knuckle" of the pedicel supporting the tomato fruit may provide an explanation as to how and why a fruit such as a tomato (Lycopersicon esculentum) can accumulate both water and dry matter. There is a significant reduction in xylem and a major increase in phloem cross-sectional area through the knuckle relative to the rest of the pedicel that persists from flowering through to fruit maturity. This will produce a site of high resistance to water flow in the xylem and transfer the demand for water by the fruit to the phloem, thus linking water and dry matter influx into the fruit. Transpiration from the fruit will play a role in initiating or maintaining the flow of phloem sap to the fruit.

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17

Musetti, Rita, Stefanie V. Buxa, Federica De Marco, Alberto Loschi, Rachele Polizzotto, Karl-Heinz Kogel, and Aart J. E. van Bel. "Phytoplasma-Triggered Ca2+ Influx Is Involved in Sieve-Tube Blockage." Molecular Plant-Microbe Interactions® 26, no. 4 (April 2013): 379–86. http://dx.doi.org/10.1094/mpmi-08-12-0207-r.

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Phytoplasmas are obligate, phloem-restricted phytopathogens that are disseminated by phloem-sap-sucking insects. Phytoplasma infection severely impairs assimilate translocation in host plants and might be responsible for massive changes in phloem physiology. Methods to study phytoplasma- induced changes thus far provoked massive, native occlusion artifacts in sieve tubes. Hence, phytoplasma-phloem relationships were investigated here in intact Vicia faba host plants using a set of vital fluorescent probes and confocal laser-scanning microscopy. We focused on the effects of phytoplasma infection on phloem mass-flow performance and evaluated whether phytoplasmas induce sieve-plate occlusion. Apparently, phytoplasma infection brings about Ca2+ influx into sieve tubes, leading to sieve-plate occlusion by callose deposition or protein plugging. In addition, Ca2+ influx may confer cell wall thickening of conducting elements. In conclusion, phytoplasma effectors may cause gating of sieve-element Ca2+ channels leading to sieve-tube occlusion with presumptive dramatic effects on phytoplasma spread and photoassimilate distribution.

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18

Minchin, Peter E. H., and André Lacointe. "Consequences of phloem pathway unloading/reloading on equilibrium flows between source and sink: a modelling approach." Functional Plant Biology 44, no. 5 (2017): 507. http://dx.doi.org/10.1071/fp16354.

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It is now accepted that the transport phloem, linking major sources and sinks, is leaky, and this leakage can be considerable. Hence for phloem transport to function over the long distances observed, a large fraction of this unloaded photosynthate must be reloaded. A fraction of this unloaded solute is used to maintain tissues surrounding the phloem, as well as being stored. Also, pathway unloading/reloading acts as a short-term buffer to source and sink changes. In this work we present the first attempt to include both pathway unloading and reloading of carbohydrate in the modelling of pressure driven flow to determine if this has any significant effect upon source–sink dynamics. Our results indicated that the flow does not follow Poiseuille dynamics, and that pathway unloading alters the solute concentration and hydrostatic pressure profiles. Hence, measurement of either of these without considerable other detail tells us very little about the flow mechanisms. With adequate reloading along the pathway, the effects of pathway unloading can completely compensate for, making the entire system look like one with no pathway unloading.

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19

Ronellenfitsch, Henrik, Johannes Liesche, Kaare H. Jensen, N. Michele Holbrook, Alexander Schulz, and Eleni Katifori. "Scaling of phloem structure and optimality of photoassimilate transport in conifer needles." Proceedings of the Royal Society B: Biological Sciences 282, no. 1801 (February 22, 2015): 20141863. http://dx.doi.org/10.1098/rspb.2014.1863.

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The phloem vascular system facilitates transport of energy-rich sugar and signalling molecules in plants, thus permitting long-range communication within the organism and growth of non-photosynthesizing organs such as roots and fruits. The flow is driven by osmotic pressure, generated by differences in sugar concentration between distal parts of the plant. The phloem is an intricate distribution system, and many questions about its regulation and structural diversity remain unanswered. Here, we investigate the phloem structure in the simplest possible geometry: a linear leaf, found, for example, in the needles of conifer trees. We measure the phloem structure in four tree species representing a diverse set of habitats and needle sizes, from 1 ( Picea omorika ) to 35 cm ( Pinus palustris ). We show that the phloem shares common traits across these four species and find that the size of its conductive elements obeys a power law. We present a minimal model that accounts for these common traits and takes into account the transport strategy and natural constraints. This minimal model predicts a power law phloem distribution consistent with transport energy minimization, suggesting that energetics are more important than translocation speed at the leaf level.

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20

Warren, J. M., H. L. Allen, and F. L. Booker. "Mineral nutrition, resin flow and phloem phytochemistry in loblolly pine." Tree Physiology 19, no. 10 (August 1, 1999): 655–63. http://dx.doi.org/10.1093/treephys/19.10.655.

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21

Gallinger, Jannicke, Kerstin Zikeli, Matthias R. Zimmermann, Louisa M. Görg, Axel Mithöfer, Michael Reichelt, Erich Seemüller, Jürgen Gross, and Alexandra C. U. Furch. "Specialized 16SrX phytoplasmas induce diverse morphological and physiological changes in their respective fruit crops." PLOS Pathogens 17, no. 3 (March 25, 2021): e1009459. http://dx.doi.org/10.1371/journal.ppat.1009459.

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The host-pathogen combinations—Malus domestica (apple)/`Candidatus Phytoplasma mali´, Prunus persica (peach)/`Ca. P. prunorum´ and Pyrus communis (pear)/`Ca. P. pyri´ show different courses of diseases although the phytoplasma strains belong to the same 16SrX group. While infected apple trees can survive for decades, peach and pear trees die within weeks to few years. To this date, neither morphological nor physiological differences caused by phytoplasmas have been studied in these host plants. In this study, phytoplasma-induced morphological changes of the vascular system as well as physiological changes of the phloem sap and leaf phytohormones were analysed and compared with non-infected plants. Unlike peach and pear, infected apple trees showed substantial reductions in leaf and vascular area, affecting phloem mass flow. In contrast, in infected pear mass flow and physicochemical characteristics of phloem sap increased. Additionally, an increased callose deposition was detected in pear and peach leaves but not in apple trees in response to phytoplasma infection. The phytohormone levels in pear were not affected by an infection, while in apple and peach trees concentrations of defence- and stress-related phytohormones were increased. Compared with peach and pear trees, data from apple suggest that the long-lasting morphological adaptations in the vascular system, which likely cause reduced sap flow, triggers the ability of apple trees to survive phytoplasma infection. Some phytohormone-mediated defences might support the tolerance.

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22

Jiang, Fan, Sveta Veselova, Dima Veselov, Guzel Kudoyarova, W. Dieter Jeschke, and Wolfram Hartung. "Cytokinin flows from Hordeum vulgare to the hemiparasite Rhinanthus minor and the influence of infection on host and parasite cytokinins relations." Functional Plant Biology 32, no. 7 (2005): 619. http://dx.doi.org/10.1071/fp04168.

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Using the facultative root hemiparasite Rhinanthus minor L. and Hordeum vulgare L. as a host, the flows, depositions and metabolism of zeatin-type cytokinins [zeatin (Z), zeatin riboside (ZR), zeatin nucleotide (ZN)] within the host, the parasite and between host and parasite have been studied during the period 41–54 d after planting (i.e. ~30–43 d after successful attachment of the parasite to the host). Parasitism decreased the synthesis of Z in the root (by 57%) and decreased xylem flows (by 56%) and metabolism (by 71%) in leaf laminae. However, phloem flows of Z were increased by 3-fold in the host barley. The deposition of Z in the roots of Rhinanthus and the flows in xylem and phloem were increased by 20, 12, 29-fold, respectively, after successfully attaching to the host barley. However, net biosynthesis of Z in Rhinanthus roots decreased by 35% after attachment. This indicates that a large portion (70%) of xylem flow of Z in attached Rhinanthus was extracted from the host. In singly growing Rhinanthus plants, the balance of Z deposition in the shoot was negative (i.e. Z was metabolised and exported back to root in the phloem). Xylem flows and deposition of ZR and ZN showed comparable quantitative changes after attachment. A significant deposition of Z, ZR and ZN was detected in the haustoria of the Rhinanthus / barley association. The possible physiological functions of the large quantities of Z and ZR and ZN derived from the host barley, for the improved leaf development and the stomatal reactions of the parasitising Rhinanthus are discussed.

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23

Andrianifahanana, Mahefa, Karrie Lovins, Roland Dute, Edward Sikora, and John F. Murphy. "Pathway for Phloem-Dependent Movement of Pepper Mottle Potyvirus in the Stem of Capsicum annuum." Phytopathology® 87, no. 9 (September 1997): 892–98. http://dx.doi.org/10.1094/phyto.1997.87.9.892.

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Phloem-dependent movement of pepper mottle potyvirus (PepMoV) through Capsicum annuum occurs in a defined pattern through the stem and into uninoculated leaves. The route of movement of PepMoV through the stem of C. annuum ‘Early Calwonder’ was tracked using immunotissue blot analysis and immunomicroscopy. Virus was shown to move from the inoculated leaf down the stem toward the roots via the external phloem. At some location between the cotyledonary node and the roots, PepMoV entered the internal phloem through which it rapidly spread upward the length of the stem to the young tissues. Translocation of PepMoV through the stem occurred in an asymmetric fashion, i.e., virus remained on the side of the stem to which the inoculated leaf was attached as it translocated the length of the stem. Spread and accumulation of PepMoV into uninoculated leaves appeared to occur in a source-to-sink pattern similar to that described for the flow of photoassimilates and similar to other virus and viroid-host systems.

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24

Rockwell, Fulton E., Jessica T. Gersony, and N. Michele Holbrook. "Where does Münch flow begin? Sucrose transport in the pre-phloem path." Current Opinion in Plant Biology 43 (June 2018): 101–7. http://dx.doi.org/10.1016/j.pbi.2018.04.007.

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25

Clifford, Paul. "The pressure-flow hypothesisof phloem transport: misconceptions in the A-level textbooks." Journal of Biological Education 36, no. 3 (June 2002): 110–12. http://dx.doi.org/10.1080/00219266.2002.9655814.

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26

Tournier, Barthélémy, Martin Tabler, and Kriton Kalantidis. "Phloem flow strongly influences the systemic spread of silencing in GFPNicotiana benthamianaplants." Plant Journal 47, no. 3 (August 2006): 383–94. http://dx.doi.org/10.1111/j.1365-313x.2006.02796.x.

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27

Orlich, Gabriele, Markus Hofbrückl, and Alexander Schulz. "A symplasmic flow of sucrose contributes to phloem loading in Ricinus cotyledons." Planta 206, no. 1 (July 15, 1998): 108–16. http://dx.doi.org/10.1007/s004250050380.

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28

Schulz, Alexander. "Diffusion or bulk flow: how plasmodesmata facilitate pre-phloem transport of assimilates." Journal of Plant Research 128, no. 1 (December 17, 2014): 49–61. http://dx.doi.org/10.1007/s10265-014-0676-5.

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29

MURPHY, RICARDO. "Water Flow Across the Sieve-Tube Boundary: Estimating Turgor and Some Implications for Phloem Loading and Unloading. II. Phloem in the Stem." Annals of Botany 63, no. 5 (May 1989): 551–59. http://dx.doi.org/10.1093/oxfordjournals.aob.a087780.

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30

MURPHY, RICARDO. "Water Flow Across the Sieve-Tube Boundary: Estimating Turgor and Some Implications for Phloem Loading and Unloading. III. Phloem in the Leaf." Annals of Botany 63, no. 5 (May 1989): 561–70. http://dx.doi.org/10.1093/oxfordjournals.aob.a087781.

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31

Bussières, Philippe. "Water import in the young tomato fruit limited by pedicel resistance and calyx transpiration." Functional Plant Biology 29, no. 5 (2002): 631. http://dx.doi.org/10.1071/pp00144.

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Approximately 3 weeks after pollination, the water import rate per unit tomato fruit area generally decreases linearly with fruit radius. In order to explain why, in the first 3 weeks, the water import rate of the fruit is lower than predicted by this regression, a model of water flow through the pedicel and a model of water import based on the potential of water entering the fruit and calyx transpiration were formulated. Using data sets available in the literature, these models predict a water potential drop along the pedicel that decreases sharply during the first 3 weeks, while the calculated hydraulic conductivity of the pedicel phloem, which is presumed to be the main pathway of the water imported in the tomato fruit, increases sharply in the lower range of values known for plant phloem conductivity. These models also predict an increase in water import into young fruit when calyx transpiration is decreased, which is consistent with data from the literature. In order to explain the increasing pedicel phloem conductivity, a model of water flow in the pedicel sieve tubes was formulated based on the literature data for the fruit stalk of Lupinus albus. It was suggested that the conductivity might increase because of the development of pores in the sieve plates. Using this hypothesis, the increase in pore radius values within an acceptable range was calculated. This study shows that, under a wide range of conditions, water import in young tomato fruit is limited by the low potential of the water entering the fruit due to pedicel resistance and calyx transpiration. It provides a model to predict young tomato fruit expansion and a testable hypothesis, which can be checked by measuring the size of the phloem component in the fruit pedicel.

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32

Li, Yaxin, Huan Liu, Xuehui Yao, Jiang Wang, Sheng Feng, Lulu Sun, Si Ma, Kang Xu, Li-Qing Chen, and Xiaolei Sui. "Hexose transporter CsSWEET7a in cucumber mediates phloem unloading in companion cells for fruit development." Plant Physiology 186, no. 1 (February 5, 2021): 640–54. http://dx.doi.org/10.1093/plphys/kiab046.

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Abstract In the fleshy fruit of cucumbers (Cucumis sativus L.), the phloem flow is unloaded via an apoplasmic pathway, which requires protein carriers to export sugars derived from stachyose and raffinose into the apoplasm. However, transporter(s) involved in this process remain unidentified. Here, we report that a hexose transporter, CsSWEET7a (Sugar Will Eventually be Exported Transporter 7a), was highly expressed in cucumber sink tissues and localized to the plasma membrane in companion cells of the phloem. Its expression level increased gradually during fruit development. Down-regulation of CsSWEET7a by RNA interference (RNAi) resulted in smaller fruit size along with reduced soluble sugar levels and reduced allocation of 14C-labelled carbon to sink tissues. CsSWEET7a overexpression lines showed an opposite phenotype. Interestingly, genes encoding alkaline α-galactosidase (AGA) and sucrose synthase (SUS) were also differentially regulated in CsSWEET7a transgenic lines. Immunohistochemical analysis demonstrated that CsAGA2 co-localized with CsSWEET7a in companion cells, indicating cooperation between AGA and CsSWEET7a in fruit phloem unloading. Our findings indicated that CsSWEET7a is involved in sugar phloem unloading in cucumber fruit by removing hexoses from companion cells to the apoplasmic space to stimulate the raffinose family of oligosaccharides (RFOs) metabolism so that additional sugars can be unloaded to promote fruit growth. This study also provides a possible avenue towards improving fruit production in cucumber.

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33

Fitri, Noor, Björn Thiele, Klaus Günther, and Buchari Buchari. "CAPILLARY ELECTROPHORETIC ANALYSIS OF LOW-MOLECULAR-MASS OF CA SPECIES IN PHLOEM SAP OF Ricinus communis L." Indonesian Journal of Chemistry 6, no. 2 (June 14, 2010): 181–85. http://dx.doi.org/10.22146/ijc.21757.

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A capillary electrophoretic (CE) analysis with ultra-violet (UV) detection was performed for further separation of low-molecular-mass (LMM) calcium species in phloem sap of Ricinus communis L. Two different background electrolytes (BGE) were used for the separation; these are (1) hydrogen phosphate/dihydrogen phosphate buffer containing cetyltrimethylammonium bromide (CTAB) as an electro-osmotic flow (EOF) modifier, and (2) boric acid buffer containing CTAB. Various parameters affecting the analysis, including the composition and pH of the BGE were systematically studied. The sensitivity, resolution, baseline noise, migration time of the species peaks, and reproducibility of the method were evaluated under optimised condition. At least 13 UV-active species were optimally separated within about ten minutes. The optimised measurement condition was also achieved using 10 mM hydrogen phosphate/10 mM dihydrogen phosphate containing 0.5 mM CTAB at pH 8.0 as BGE, and by applying voltage of ‑20 kV and temperature of 14°C. Evidently, the analytical method was successfully used for the separation of LMM calcium species in phloem sap of R. communis L. Keywords: capillary electrophoresis, calcium species, phloem sap, Ricinus communis

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34

Jensen, Kaare H., Kirstine Berg-Sørensen, Søren M. M. Friis, and Tomas Bohr. "Analytic solutions and universal properties of sugar loading models in Münch phloem flow." Journal of Theoretical Biology 304 (July 2012): 286–96. http://dx.doi.org/10.1016/j.jtbi.2012.03.012.

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35

Sellier, Damien, and Youcef Mammeri. "Diurnal dynamics of phloem loading: theoretical consequences for transport efficiency and flow characteristics." Tree Physiology 39, no. 2 (February 1, 2019): 300–311. http://dx.doi.org/10.1093/treephys/tpz001.

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36

Voitsekhovskaja, Olga V., Olga A. Koroleva, Denis R. Batashev, Christian Knop, A. Deri Tomos, Yuri V. Gamalei, Hans-Walter Heldt, and Gertrud Lohaus. "Phloem Loading in Two Scrophulariaceae Species. What Can Drive Symplastic Flow via Plasmodesmata?" Plant Physiology 140, no. 1 (December 23, 2005): 383–95. http://dx.doi.org/10.1104/pp.105.068312.

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37

Furch, A. C. U., M. R. Zimmermann, T. Will, J. B. Hafke, and A. J. E. van Bel. "Remote-controlled stop of phloem mass flow by biphasic occlusion in Cucurbita maxima." Journal of Experimental Botany 61, no. 13 (June 28, 2010): 3697–708. http://dx.doi.org/10.1093/jxb/erq181.

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38

Clifford, P. aul. "Teaching the pressure-flow hypothesis of phloem transport in a problem-solving session." Journal of Biological Education 39, no. 1 (December 2004): 35–39. http://dx.doi.org/10.1080/00219266.2004.9655953.

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39

Walsh, Kerry B., Russell C. Sky, and Sharon M. Brown. "The anatomy of the pathway of sucrose unloading within the sugarcane stalk." Functional Plant Biology 32, no. 4 (2005): 367. http://dx.doi.org/10.1071/fp04102.

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The physical path of sucrose unloading in the sugarcane stalk is described. About 50% of the vascular bundles in the internodes were located within 3 mm of the outside of the stalk. These bundles were inactive in long distance sucrose transport, as assessed by dye tracers of phloem flow. A sheath of fibres isolates the phloem apoplast from that of the storage parenchyma. In bundles associated with long distance transport (i.e. in the central region), the fibre sheath is narrowest to either side of the phloem fibre cap, and consists of living cells with plasmodesmata within pits in the secondary wall. Plasmodesmata were also arranged into pit fields between cells of the storage parenchyma. Since the vascular apoplast is isolated from the apoplast of the storage parenchyma, sucrose must move through the symplast of the fibre sheath. The calculated flux of sucrose through plasmodesmata of this cell layer was at the low end of reported values in the literature. Sucrose unloading within the storage parenchyma may also follow a symplastic route, with unloading into the apoplast of the storage parenchyma occurring as part of a turgor mechanism to increase sink strength.

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40

PEUKE, ANDREAS D., CAREL WINDT, and HENK VAN AS. "Effects of cold-girdling on flows in the transport phloem in Ricinus communis: is mass flow inhibited?" Plant, Cell and Environment 29, no. 1 (January 2006): 15–25. http://dx.doi.org/10.1111/j.1365-3040.2005.01396.x.

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41

Thorpe, Michael R., André Lacointe, and Peter E. H. Minchin. "Modelling phloem transport within a pruned dwarf bean: a 2-source-3-sink system." Functional Plant Biology 38, no. 2 (2011): 127. http://dx.doi.org/10.1071/fp10156.

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A mechanistic model of carbon partitioning, based on the Münch hypothesis of phloem transport and implemented with PIAF-Münch modelling platform (Lacointe and Minchin 2008), was tested for an architecture more complex than any tested previously. Using 11C to label photosynthate, responses in transport of photosynthate within a heavily pruned dwarf bean plant (Phaseolus vulgaris L.) to changes in source and sink activities were compared with model predictions. The observed treatment responses were successfully predicted. However, the observations could not be completely explained if the modelled stem contained only one phloem pathway: tracer from a labelled leaf was always detected in both shoot apex and root, whichever of the two leaves was labelled. This shows that bidirectional flow occurred within the stem, with solute moving simultaneously in both directions. Nevertheless, a model architecture with very little more complexity could incorporate such bidirectional flow. We concluded that the model could explain the observations, and that the PIAF-Münch model platform can be expected to describe partitioning in even more complex architectures.

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42

Lacointe, André, and Peter E. H. Minchin. "Modelling phloem and xylem transport within a complex architecture." Functional Plant Biology 35, no. 10 (2008): 772. http://dx.doi.org/10.1071/fp08085.

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The function of the plant’s vasculature, incorporating both phloem and xylem, is of fundamental importance to the survival of all higher plants. Although the physiological mechanism involved in these two transport pathways has been known for some time, quantitative modelling of this has been slow to develop. 1-D continuous models have shown that the proposed mechanisms are quantitatively plausible (Thompson and Holbrook 2003) but more complex geometries (architectures) have remained out of reach because of mathematical difficulties. In this work, we extend the alternative modular approach by Daudet et al. (2002) using recently developed numerical tools which allow us to model complex architectures. After a full description of the extended model, we first show that it efficiently reproduces the results of the continuous approach when applied to the same simple configurations. The model is then applied to a more complex configuration with two sinks, confirming that sink priority is an emergent property of the Münch flow as earlier found with a minimalist model (Minchin et al. 1993). It is further shown how source leaf transpiration can change the relative carbon allocation rates among sinks.

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43

Boyer, John S., and Wendy K. Silk. "Hydraulics of plant growth." Functional Plant Biology 31, no. 8 (2004): 761. http://dx.doi.org/10.1071/fp04062.

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Multicellular plants rely on growth in localised regions that contain small, undifferentiated cells and may be many millimetres from the nearest differentiated xylem and phloem. Water and solutes must move to these small cells for their growth. Increasing evidence indicates that after exiting the xylem and phloem, water and solutes are driven to the growing cells by gradients in water potential and solute potential or concentration. The gradients are much steeper than in the vascular transport system and can change in magnitude or suffer local disruption with immediate consequences for growth. Their dynamics often obscure how turgor drives wall extension for growth, and different flow paths for roots and shoots have different dynamics. In this review, the origins of the gradients, their mode of action and their consequences are discussed, with emphasis on how their dynamics affect growth processes.

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44

Stanfield, Ryan, and Joan Laur. "Aquaporins Respond to Chilling in the Phloem by Altering Protein and mRNA Expression." Cells 8, no. 3 (February 27, 2019): 202. http://dx.doi.org/10.3390/cells8030202.

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Previous experiments using heat exchangers (liquid cooled blocks) to chill a portion of plant stem have shown a transient stoppage in phloem translocation and an increase in measured phloem pressure. Although a chilled-induced stoppage of phloem transport has been known for over 100 years, the mechanism of this phenomenon is still poorly understood. Recently, work has highlighted that aquaporins occur within the plasma membrane of the sieve tubes along the entire source-to-sink pathway, and that isoforms of these water channel proteins may change dynamically. Aquaporins show regulatory roles in controlling tissue and cellular water status in response to environmental hardships. Thus, we tested if protein localization and mRNA transcript abundance changes occur in response to chilling in balsam poplar (Populus balsamifera) using immunohistochemistry and qrtPCR. The results of the immunolocalization experiments show that the labeling intensity of the sieve elements treated for only 2 min of chill time significantly increased for PIP2. After 10 min of chilling, this signal declined significantly to lower than that of the pre-chilled sieve elements. Overall, the abundance of mRNA transcript increased for the tested PIP2s following cold application. We discuss the implication that aquaporins are responsible for the alleviation of sieve tube pressure and the resumption of flow following a cold-induced blockage event.

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45

Froelich, Daniel R., Daniel L. Mullendore, Kåre H. Jensen, Tim J. Ross-Elliott, James A. Anstead, Gary A. Thompson, Hélène C. Pélissier, and Michael Knoblauch. "Phloem Ultrastructure and Pressure Flow: Sieve-Element-Occlusion-Related Agglomerations Do Not Affect Translocation." Plant Cell 23, no. 12 (December 2011): 4428–45. http://dx.doi.org/10.1105/tpc.111.093179.

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46

Raven, John A. "Evolution and palaeophysiology of the vascular system and other means of long-distance transport." Philosophical Transactions of the Royal Society B: Biological Sciences 373, no. 1739 (December 18, 2017): 20160497. http://dx.doi.org/10.1098/rstb.2016.0497.

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Photolithotrophic growth on land using atmospheric CO 2 inevitably involves H 2 O vapour loss. Embryophytes greater than or equal to 100 mm tall are homoiohydric and endohydric with mass flow of aqueous solution through the xylem in tracheophytes. Structural details in Rhynie sporophytes enable modelling of the hydraulics of H 2 O supply to the transpiring surface, and the potential for gas exchange with the Devonian atmosphere. Xylem carrying H 2 O under tension involves programmed cell death, rigid cell walls and embolism repair; fossils provide little evidence on these functions other than the presence of lignin. The phenylalanine ammonia lyase essential for lignin synthesis came from horizontal gene transfer. Rhynie plants lack endodermes, limiting regulation of the supply of soil nutrients to shoots. The transfer of organic solutes from photosynthetic sites to growing and storage tissues involves mass flow through phloem in extant tracheophytes. Rhynie plants show little evidence of phloem; possible alternatives for transport of organic solutes are discussed. Extant examples of the arbuscular mycorrhizas found in Rhynie plants exchange soil-derived nutrients (especially P) for plant-derived organic matter, involving bidirectional mass flow along the hyphae. The aquatic cyanobacteria and the charalean Palaeonitella at Rhynie also have long-distance (relative to the size of the organism) transport. This article is part of a discussion meeting issue ‘The Rhynie cherts: our earliest terrestrial ecosystem revisited’.

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47

Garcia, José Francisco, Eliane Grisoto, Paulo Sérgio Machado Botelho, José Roberto Postali Parra, and Beatriz Appezzato-da-Glória. "Feeding site of the spittlebug Mahanarva fimbriolata (Stål) (Hemiptera: Cercopidae) on sugarcane." Scientia Agricola 64, no. 5 (October 2007): 555–57. http://dx.doi.org/10.1590/s0103-90162007000500014.

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The sugarcane spittlebug Mahanarva fimbriolata (Stål) (Hemiptera: Cercopidae) is a pest of mechanically-harvested sugarcane in Brazil, when trash burning is not performed. To better understand the differences in feeding behavior of adults and nymphs of this pest and the subsequent disorders that arise, stylet penetration through fixation, staining and sectioning was investigated. Nymphs cause a "physiological disorder" damaging the tracheary system of the roots, slowing or preventing water and nutrient flow, with phloem and xylem dehydration. Nymphs insert their stylets through the epidermis, crossing the cortex, endodermis and pericycle before reaching the vascular cylinder, where they feed in the sieve-tube elements of the primary phloem. In contrast, adults feed on leaves, causing "sugarcane burn", and reducing plant photosynthesis. Adults introduce the stylets into the leaf blade through the stomata, passing the chlorophyll-bearing parenchyma cells before reaching the metaxylem in the vascular bundles.

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48

Dewar, R. C. "A Root-Shoot Partitioning Model Based on Carbon-Nitrogen-Water Interactions and Munch Phloem Flow." Functional Ecology 7, no. 3 (June 1993): 356. http://dx.doi.org/10.2307/2390216.

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49

Pagliari, Laura, Sara Buoso, Simonetta Santi, Alexandra C. U. Furch, Marta Martini, Francesca Degola, Alberto Loschi, Aart J. E. van Bel, and Rita Musetti. "Filamentous sieve element proteins are able to limit phloem mass flow, but not phytoplasma spread." Journal of Experimental Botany 68, no. 13 (June 15, 2017): 3673–88. http://dx.doi.org/10.1093/jxb/erx199.

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50

van Bel, Aart J. E., Alexandra C. U. Furch, Jens B. Hafke, Michael Knoblauch, and John W. Patrick. "(Questions)n on phloem biology. 2. Mass flow, molecular hopping, distribution patterns and macromolecular signalling." Plant Science 181, no. 4 (October 2011): 325–30. http://dx.doi.org/10.1016/j.plantsci.2011.05.008.

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