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John W Patrick - One of the best experts on this subject based on the ideXlab platform.
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the cellular pathway of Photosynthate transfer in the developing wheat grain ii a structural analysis and histochemical studies of the pathway from the crease phloem to the endosperm cavity
Plant Cell and Environment, 1995Co-Authors: H L Wang, Christina E Offler, John W PatrickAbstract:In the developing wheat grain, Photosynthate is transferred longitudinally along the crease phloem and then laterally into the endosperm cavity through the crease vascular parenchyma, pigment strand and nucellar projection. In order to clarify this cellular pathway of Photosynthate unloading, and hence the controlling mechanism of grain filling, the potential for symplastic and apoplastic transfer was examined through structural and histochemical studies on these tissue types. It was found that cells in the crease region from the phloem to the nucellar projection are interconnected by numerous plasmodesmata and have dense cytoplasm with abundant mitochondria. Histochemical studies confirmed that, at the stage of grain development studied, an apoplastic barrier exists in the cell walls of the pigment strand. This barrier is composed of lignin, phenolics and suberin. The potential capacity for symplastic transfer, determined by measuring plasmodesmatal frequencies and computing potential sucrose fluxes through these plasmodesmata, indicated that there is sufficient plasmodesmatal cross-sectional area to support symplastic unloading of Photosynthate at the rate required for normal grain growth. The potential capacity for membrane transport of sucrose to the apoplast was assessed by measuring plasma membrane surface areas of the various cell types and computing potential plasma membrane fluxes of sucrose. These fluxes indicated that the combined plasma membrane surface areas of the sieve element–companion cell (se–cc) complexes, vascular parenchyma and pigment strand are not sufficient to allow sucrose transfer to the apoplast at the observed rates. In contrast, the wall ingrowths of the transfer cells in the nucellar projection amplify the membrane surface area up to 22-fold, supporting the observed rates of sucrose transfer into the endosperm cavity. We conclude that Photosynthate moves via the symplast from the se–cc complexes to the nucellar projection transfer cells, from where it is transferred across the plasma membrane into the endosperm cavity. The apoplastic barrier in the pigment strand is considered to restrict solute movement to the symplast and block apoplastic solute exchange between maternal and embryonic tissues. The implications of this cellular pathway in relation to the control of Photosynthate transfer in the developing grain are discussed.
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Cellular pathway of Photosynthate transport in coats of developing seed of Vicia faba L. and Phaseolus vulgaris L. I. Extent of transport through the coat symplast
Journal of Experimental Botany, 1995Co-Authors: John W Patrick, Christina E Offler, X D WangAbstract:The extent of post-phloem solute transport through the coat symplasts of developing seeds of Vicia faba L. and Phaseolus vulgaris L. was evaluated. For Vicia seed coats, the membrane-impermeant fluorochrome, CF, moved radially from the chalazal vein to reach the chlorenchyma and thin-walled parenchyma transfer cell layers. Thereafter, the fluorochrome moved laterally in these two cell layers around the entire circumference of the seed coat. Transfer of CF from the chalazal vein was inhibited by plasmolysis of attached «empty» seed coats. In contrast, the spread of phloemimported CF was restricted to the ground parenchyma of Phaseolus seed coats. Fluorochrome loaded into the outermost ground parenchyma cell layer was rendered immobile following plasmolysis of excised seed-coat halves. Phloem-imported [ 14 C]sucrose and the slowly membrane permeable sugar, L-[ 14 C]glucose, were partitioned identically between the vascular and non-vascular regions of intact Vicia seed coats. For 14 C-Photosynthates, these partitioning patterns in attached «empty» Vicia seed coats were unaffected by PCMBS, but inhibited by plasmolysis. Tissue autoradiographs of intact Phaseolus seed coats demonstrated that a pulse of 14 C-Photosynthate moved from the veins to the ground tissues. In excised Vicia seed coats, preloaded with 14 C-Photosynthates, the cellular distribution of residual 14 C-label was unaffected by PCMBS. In contrast, PCMBS caused the 14 C-Photosynthate levels to be elevated in the veins and ground parenchyma relative to the branch parenchyma of Phaseolus seed coat halves. Based on the above findings, it is concluded that the phloem of Vicia seed coats is interconnected to two major symplastic domains; one comprises the chlorenchyma, the other the thin-walled parenchyma plus thin-walled parenchyma transfer cells. For Phaseolus seed coats, the phloem forms a major symplastic domain with the ground parenchyma
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the cellular pathway of short distance transfer of Photosynthates and potassium in the elongating stem of phaseolus vulgaris l stem anatomy solute transport and pool sizes
Annals of Botany, 1994Co-Authors: Robyn M Wood, John W Patrick, Christina E OfflerAbstract:Abstract Based on an uniform elongation growth pattern and cellular structure, the apical 0·5-2·5 cm elongation zone of internode 2 of Phaseolus vulgaris L. seedlings was selected as an experimental system to study the radial pathway of Photosynthate and potassium transfer from the phloem. An histological examination of the phloem within the elongation zone of internode 2 showed that both proto- and meta- phloem sieve elements were present. The former were fully differentiated at the commencement of elongation and became crushed as elongation proceeded. In contrast, about 50% of the final number of metaphloem sieve element-companion cell complexes differentiated during the same period. The phloem delivered some 99% of the sucrose and 72-82% of the potassium accumulated by the elongation zone. Solute budgets showed that, of the Photosynthates and potassium entering the elongation zone, approximately 40% were retained and 60% transferred to the shoot apex. Thus, the elongating stem acts not only as a significant sink for Photosynthates and potassium, but also as an axial phloem transport system to supply the shoot apex. Within the elongation zone, the principal tissue sinks were determined by the cellular localisation of [14C] Photosynthates and potassium by microautoradiography and ion electron microprobe analysis respectively. About 80% of the Photosynthates and potassium were located outside the phloem. The cortex and pith exhibited the greatest accumulation for Photosynthates and the pith for potassium.
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pathway of Photosynthate transfer in the developing seed of vicia faba l a structural assessment of the role of transfer cells in unloading from the seed coat
Journal of Experimental Botany, 1993Co-Authors: Christina E Offler, John W PatrickAbstract:Photosynthate movement within the coat of the developing seed of Vicia faba occurs radially inward from the restricted vascular system and laterally through the non-vascularized region of the seed coat prior to exchange to the seed apoplast. Thin-walled parenchyma/transfer cells line the entire inner surface of the seed coat and thus are located at the terminus of the Photosynthate transfer pathway. The principal cellular route of transfer within the seed coat and the role of the thin-walled parenchyma/transfer cells in membrane exchange to the seed apoplast has been investigated. Sucrose fluxes, computed from estimates of the plasma membrane surface areas of the cell types of the pathway, the plasmodesmatal cross-sectional areas interconnecting contiguous cells and the observed rate of sucrose delivery to the embryo indicate that sieve element unloading and subsequent transfer to the thin-walled parenchyma/transfer cells is through the symplast
Christina E Offler - One of the best experts on this subject based on the ideXlab platform.
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the cellular pathway of Photosynthate transfer in the developing wheat grain ii a structural analysis and histochemical studies of the pathway from the crease phloem to the endosperm cavity
Plant Cell and Environment, 1995Co-Authors: H L Wang, Christina E Offler, John W PatrickAbstract:In the developing wheat grain, Photosynthate is transferred longitudinally along the crease phloem and then laterally into the endosperm cavity through the crease vascular parenchyma, pigment strand and nucellar projection. In order to clarify this cellular pathway of Photosynthate unloading, and hence the controlling mechanism of grain filling, the potential for symplastic and apoplastic transfer was examined through structural and histochemical studies on these tissue types. It was found that cells in the crease region from the phloem to the nucellar projection are interconnected by numerous plasmodesmata and have dense cytoplasm with abundant mitochondria. Histochemical studies confirmed that, at the stage of grain development studied, an apoplastic barrier exists in the cell walls of the pigment strand. This barrier is composed of lignin, phenolics and suberin. The potential capacity for symplastic transfer, determined by measuring plasmodesmatal frequencies and computing potential sucrose fluxes through these plasmodesmata, indicated that there is sufficient plasmodesmatal cross-sectional area to support symplastic unloading of Photosynthate at the rate required for normal grain growth. The potential capacity for membrane transport of sucrose to the apoplast was assessed by measuring plasma membrane surface areas of the various cell types and computing potential plasma membrane fluxes of sucrose. These fluxes indicated that the combined plasma membrane surface areas of the sieve element–companion cell (se–cc) complexes, vascular parenchyma and pigment strand are not sufficient to allow sucrose transfer to the apoplast at the observed rates. In contrast, the wall ingrowths of the transfer cells in the nucellar projection amplify the membrane surface area up to 22-fold, supporting the observed rates of sucrose transfer into the endosperm cavity. We conclude that Photosynthate moves via the symplast from the se–cc complexes to the nucellar projection transfer cells, from where it is transferred across the plasma membrane into the endosperm cavity. The apoplastic barrier in the pigment strand is considered to restrict solute movement to the symplast and block apoplastic solute exchange between maternal and embryonic tissues. The implications of this cellular pathway in relation to the control of Photosynthate transfer in the developing grain are discussed.
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Cellular pathway of Photosynthate transport in coats of developing seed of Vicia faba L. and Phaseolus vulgaris L. I. Extent of transport through the coat symplast
Journal of Experimental Botany, 1995Co-Authors: John W Patrick, Christina E Offler, X D WangAbstract:The extent of post-phloem solute transport through the coat symplasts of developing seeds of Vicia faba L. and Phaseolus vulgaris L. was evaluated. For Vicia seed coats, the membrane-impermeant fluorochrome, CF, moved radially from the chalazal vein to reach the chlorenchyma and thin-walled parenchyma transfer cell layers. Thereafter, the fluorochrome moved laterally in these two cell layers around the entire circumference of the seed coat. Transfer of CF from the chalazal vein was inhibited by plasmolysis of attached «empty» seed coats. In contrast, the spread of phloemimported CF was restricted to the ground parenchyma of Phaseolus seed coats. Fluorochrome loaded into the outermost ground parenchyma cell layer was rendered immobile following plasmolysis of excised seed-coat halves. Phloem-imported [ 14 C]sucrose and the slowly membrane permeable sugar, L-[ 14 C]glucose, were partitioned identically between the vascular and non-vascular regions of intact Vicia seed coats. For 14 C-Photosynthates, these partitioning patterns in attached «empty» Vicia seed coats were unaffected by PCMBS, but inhibited by plasmolysis. Tissue autoradiographs of intact Phaseolus seed coats demonstrated that a pulse of 14 C-Photosynthate moved from the veins to the ground tissues. In excised Vicia seed coats, preloaded with 14 C-Photosynthates, the cellular distribution of residual 14 C-label was unaffected by PCMBS. In contrast, PCMBS caused the 14 C-Photosynthate levels to be elevated in the veins and ground parenchyma relative to the branch parenchyma of Phaseolus seed coat halves. Based on the above findings, it is concluded that the phloem of Vicia seed coats is interconnected to two major symplastic domains; one comprises the chlorenchyma, the other the thin-walled parenchyma plus thin-walled parenchyma transfer cells. For Phaseolus seed coats, the phloem forms a major symplastic domain with the ground parenchyma
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the cellular pathway of short distance transfer of Photosynthates and potassium in the elongating stem of phaseolus vulgaris l stem anatomy solute transport and pool sizes
Annals of Botany, 1994Co-Authors: Robyn M Wood, John W Patrick, Christina E OfflerAbstract:Abstract Based on an uniform elongation growth pattern and cellular structure, the apical 0·5-2·5 cm elongation zone of internode 2 of Phaseolus vulgaris L. seedlings was selected as an experimental system to study the radial pathway of Photosynthate and potassium transfer from the phloem. An histological examination of the phloem within the elongation zone of internode 2 showed that both proto- and meta- phloem sieve elements were present. The former were fully differentiated at the commencement of elongation and became crushed as elongation proceeded. In contrast, about 50% of the final number of metaphloem sieve element-companion cell complexes differentiated during the same period. The phloem delivered some 99% of the sucrose and 72-82% of the potassium accumulated by the elongation zone. Solute budgets showed that, of the Photosynthates and potassium entering the elongation zone, approximately 40% were retained and 60% transferred to the shoot apex. Thus, the elongating stem acts not only as a significant sink for Photosynthates and potassium, but also as an axial phloem transport system to supply the shoot apex. Within the elongation zone, the principal tissue sinks were determined by the cellular localisation of [14C] Photosynthates and potassium by microautoradiography and ion electron microprobe analysis respectively. About 80% of the Photosynthates and potassium were located outside the phloem. The cortex and pith exhibited the greatest accumulation for Photosynthates and the pith for potassium.
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pathway of Photosynthate transfer in the developing seed of vicia faba l a structural assessment of the role of transfer cells in unloading from the seed coat
Journal of Experimental Botany, 1993Co-Authors: Christina E Offler, John W PatrickAbstract:Photosynthate movement within the coat of the developing seed of Vicia faba occurs radially inward from the restricted vascular system and laterally through the non-vascularized region of the seed coat prior to exchange to the seed apoplast. Thin-walled parenchyma/transfer cells line the entire inner surface of the seed coat and thus are located at the terminus of the Photosynthate transfer pathway. The principal cellular route of transfer within the seed coat and the role of the thin-walled parenchyma/transfer cells in membrane exchange to the seed apoplast has been investigated. Sucrose fluxes, computed from estimates of the plasma membrane surface areas of the cell types of the pathway, the plasmodesmatal cross-sectional areas interconnecting contiguous cells and the observed rate of sucrose delivery to the embryo indicate that sieve element unloading and subsequent transfer to the thin-walled parenchyma/transfer cells is through the symplast
Peter Hogberg - One of the best experts on this subject based on the ideXlab platform.
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partitioning of soil respiration into its autotrophic and heterotrophic components by means of tree girdling in old boreal spruce forest
Forest Ecology and Management, 2009Co-Authors: Peter Hogberg, Mikaell Ottosson Lofvenius, Anders NordgrenAbstract:Abstract Forests accumulate much less carbon than the amount fixed through photosynthesis because of an almost equally large opposing flux of CO2 from the ecosystem. Most of the return flux to the atmosphere is through soil respiration, which has two major sources, one heterotrophic (organisms decomposing organic matter) and one autotrophic (roots, mycorrhizal fungi and other root-associated microbes dependent on recent Photosynthate). We used tree-girdling to stop the flow of Photosynthate to the belowground system, hence, blocking autotrophic soil activity in a 120-yr-old boreal Picea abies forest. We found that at the end of the summer, two months after girdling, the treatment had reduced soil respiration by up to 53%. This figure adds to a growing body of evidence indicating (t-test, d.f. = 7, p
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high temporal resolution tracing of Photosynthate carbon from the tree canopy to forest soil microorganisms
New Phytologist, 2007Co-Authors: Peter Hogberg, Mona N Hogberg, S G Gottlicher, Nicholas R Betson, S G Keel, Daniel B Metcalfe, Catherine Campbell, A Schindlbacher, Vaughan Hurry, Thomas LundmarkAbstract:• Half of the biological activity in forest soils is supported by recent tree Photosynthate, but no study has traced in detail this flux of carbon from the canopy to soil microorganisms in the fie ...
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large scale forest girdling shows that current photosynthesis drives soil respiration
Nature, 2001Co-Authors: Peter Hogberg, Anders Nordgren, Alf Ekblad, Mona N Hogberg, Mikaell Ottossonlofvenius, Nina Buchmann, Andy F S Taylor, Gert Nyberg, David ReadAbstract:The respiratory activities of plant roots, of their mycorrhizal fungi and of the free-living microbial heterotrophs (decomposers) in soils are significant components of the global carbon balance, but their relative contributions remain uncertain1,2. To separate mycorrhizal root respiration from heterotrophic respiration in a boreal pine forest, we conducted a large-scale tree-girdling experiment, comprising 9 plots each containing about 120 trees. Tree-girdling involves stripping the stem bark to the depth of the current xylem at breast height terminating the supply of current Photosynthates to roots and their mycorrhizal fungi without physically disturbing the delicate root–microbe–soil system. Here we report that girdling reduced soil respiration within 1–2 months by about 54% relative to respiration on ungirdled control plots, and that decreases of up to 37% were detected within 5 days. These values clearly show that the flux of current assimilates to roots is a key driver of soil respiration; they are conservative estimates of root respiration, however, because girdling increased the use of starch reserves in the roots. Our results indicate that models of soil respiration should incorporate measures of photosynthesis and of seasonal patterns of Photosynthate allocation to roots.
Richard D Bardgett - One of the best experts on this subject based on the ideXlab platform.
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Drought decreases incorporation of recent plant Photosynthate into soil food webs regardless of their trophic complexity
Global Change Biology, 2019Co-Authors: Mathilde Chomel, Franciska T De Vries, Jocelyn M. Lavallee, Nil Alvarez-segura, Jennifer M Rhymes, Mark Emmerson, Elizabeth M Baggs, Francisco Castro, Tancredi Caruso, Richard D BardgettAbstract:: Theory suggests that more complex food webs promote stability and can buffer the effects of perturbations, such as drought, on soil organisms and ecosystem functions. Here, we tested experimentally how soil food web trophic complexity modulates the response to drought of soil functions related to carbon cycling and the capture and transfer below-ground of recent Photosynthate by plants. We constructed experimental systems comprising soil communities with one, two or three trophic levels (microorganisms, detritivores and predators) and subjected them to drought. We investigated how food web trophic complexity in interaction with drought influenced litter decomposition, soil CO2 efflux, mycorrhizal colonization, fungal production, microbial communities and soil fauna biomass. Plants were pulse-labelled after the drought with 13 C-CO2 to quantify the capture of recent Photosynthate and its transfer below-ground. Overall, our results show that drought and soil food web trophic complexity do not interact to affect soil functions and microbial community composition, but act independently, with an overall stronger effect of drought. After drought, the net uptake of 13 C by plants was reduced and its retention in plant biomass was greater, leading to a strong decrease in carbon transfer below-ground. Although food web trophic complexity influenced the biomass of Collembola and fungal hyphal length, 13 C enrichment and the net transfer of carbon from plant shoots to microbes and soil CO2 efflux were not affected significantly by varying the number of trophic groups. Our results indicate that drought has a strong effect on above-ground-below-ground linkages by reducing the flow of recent Photosynthate. Our results emphasize the sensitivity of the critical pathway of recent Photosynthate transfer from plants to soil organisms to a drought perturbation, and show that these effects may not be mitigated by the trophic complexity of soil communities, at least at the level manipulated in this experiment.
Hipólito Medrano - One of the best experts on this subject based on the ideXlab platform.
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effect of water stress on partitioning of 14c labelled Photosynthates in vitis vinifera
Functional Plant Biology, 2004Co-Authors: Josefina Bota, Oleg Stasyk, Jaume Flexas, Hipólito MedranoAbstract:The influence of fruits on export and distribution of Photosynthates was studied in Vitis vinifera L. cv. Tempranillo using 14C labelling. Also, the influence of water stress was analysed in fruiting and fruitless plants of Tempranillo and fruiting plants of cv. Alfonso Lavallee. In fruitless plants of Tempranillo, reserve organs (trunk, roots and lower shoot) represented 80% of total plant dry matter (DM), and imported up to 90% of the total 14C exported from the fed leaf. Therefore, the distribution pattern of Photosynthates in these plants reflected mainly the sink size. However, the presence of fruits in Tempranillo strongly stimulated 14C export and changed the distribution pattern of assimilates. Fruits imported up to 70–80% of the total 14C exported, while representing only 25% of the total plant DM. Therefore, the strength of fruits as carbon sinks was independent of sink size, and it is discussed on the basis of a water potential gradient theory. Water stress caused a significant reduction of leaf water potential, photosynthesis and stomatal conductance, but caused only a slight, non-significant, decrease of carbohydrate export from the fed leaves, and did not affect the distribution pattern of 14C except in some minor fractions in Tempranillo. The 14C distribution into different fruit components was also unaffected. In contrast, in Alfonso Lavallee water stress resulted in a highly significant reduction of export, and an altered Photosynthate distribution pattern. These differences could be due to the lower water potential attained in stressed Alfonso Lavallee plants.