The Experts below are selected from a list of 46362 Experts worldwide ranked by ideXlab platform
Teemu Holtta - One of the best experts on this subject based on the ideXlab platform.
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drought impacts on tree Phloem from cell level responses to ecological significance
Tree Physiology, 2019Co-Authors: Yann Salmon, Teemu Holtta, Sanna Sevanto, Lars Dietrich, Masako Dannoura, Daniel EpronAbstract:: On-going climate change is increasing the risk of drought stress across large areas worldwide. Such drought events decrease ecosystem productivity and have been increasingly linked to tree mortality. Understanding how trees respond to water shortage is key to predicting the future of ecosystem functions. Phloem is at the core of the tree functions, moving resources such as non-structural carbohydrates, nutrients, and defence and information molecules across the whole plant. Phloem function and ability to transport resources is tightly controlled by the balance of carbon and water fluxes within the tree. As such, drought is expected to impact Phloem function by decreasing the amount of available water and new photoassimilates. Yet, the effect of drought on the Phloem has received surprisingly little attention in the last decades. Here we review existing knowledge on drought impacts on Phloem transport from loading and unloading processes at cellular level to possible effects on long-distance transport and consequences to ecosystems via ecophysiological feedbacks. We also point to new research frontiers that need to be explored to improve our understanding of Phloem function under drought. In particular, we show how Phloem transport is affected differently by increasing drought intensity, from no response to a slowdown, and explore how severe drought might actually disrupt the Phloem transport enough to threaten tree survival. Because transport of resources affects other organisms interacting with the tree, we also review the ecological consequences of Phloem response to drought and especially predatory, mutualistic and competitive relations. Finally, as Phloem is the main path for carbon from sources to sink, we show how drought can affect biogeochemical cycles through changes in Phloem transport. Overall, existing knowledge is consistent with the hypotheses that Phloem response to drought matters for understanding tree and ecosystem function. However, future research on a large range of species and ecosystems is urgently needed to gain a comprehensive understanding of the question.
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Drought impacts on tree Phloem
Tree Physiology, 2019Co-Authors: Yann Salmon, Teemu Holtta, Sanna Sevanto, Lars Dietrich, Masako Dannoura, Daniel EpronAbstract:On-going climate change is increasing the risk of drought stress across large areas worldwide. Such drought events decrease ecosystem productivity and have been increasingly linked to tree mortality. Understanding how trees respond to water shortage is key to predicting the future of ecosystem functions. Phloem is at the core of the tree functions, moving resources such as non-structural carbohydrates, nutrients, and defence and information molecules across the whole plant. Phloem function and ability to transport resources is tightly controlled by the balance of carbon and water fluxes within the tree. As such, drought is expected to impact Phloem function by decreasing the amount of available water and new photoassimilates. Yet, the effect of drought on the Phloem has received surprisingly little attention in the last decades. Here we review existing knowledge on drought impacts on Phloem transport from loading and unloading processes at cellular level to possible effects on long-distance transport and consequences to ecosystems via ecophysiological feedbacks. We also point to new research frontiers that need to be explored to improve our understanding of Phloem function under drought. In particular, we show how Phloem transport is affected differently by increasing drought intensity, from no response to a slowdown, and explore how severe drought might actually disrupt the Phloem transport enough to threaten tree survival. Because transport of resources affects other organisms interacting with the tree, we also review the ecological consequences of Phloem response to drought and especially predatory, mutualistic and competitive relations. Finally, as Phloem is the main path for carbon from sources to sink, we show how drought can affect biogeochemical cycles through changes in Phloem transport. Overall, existing knowledge is consistent with the hypotheses that Phloem response to drought matters for understanding tree and ecosystem function. However, future research on a large range of species and ecosystems is urgently needed to gain a comprehensive understanding of the question.
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Effects of the hydraulic coupling between xylem and Phloem on diurnal Phloem diameter variation
Plant cell & environment, 2011Co-Authors: Sanna Sevanto, Teemu Holtta, N. Michele HolbrookAbstract:Measurements of diurnal diameter variations of the xylem and Phloem are a promising tool for studying plant hydraulics and xylem-Phloem interactions in field conditions. However, both the theoretical framework and the experimental verification needed to interpret Phloem diameter data are incomplete. In this study, we analytically evaluate the effects of changing the radial conductance between the xylem and the Phloem on Phloem diameter variations and test the theory using simple manipulation experiments. Our results show that Phloem diameter variations are mainly caused by changes in the radial flow rate of water between the xylem and the Phloem. Reducing the hydraulic conductance between these tissues decreases the amplitude of Phloem diameter variation and increases the time lag between xylem and Phloem diameter variation in a predictable manner. Variation in the amplitude and timing of diameter variations that cannot be explained by changes in the hydraulic conductance, could be related to changes in the osmotic concentration in the Phloem.
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linking Phloem function to structure analysis with a coupled xylem Phloem transport model
Journal of Theoretical Biology, 2009Co-Authors: Teemu Holtta, Maurizio Mencuccini, Eero NikinmaaAbstract:We carried out a theoretical analysis of Phloem transport based on Munch hypothesis by developing a coupled xylem-Phloem transport model. Results showed that the maximum sugar transport rate of the Phloem was limited by solution viscosity and that transport requirements were strongly affected by prevailing xylem water potential. The minimum number of xylem and Phloem conduits required to sustain transpiration and assimilation, respectively, were calculated. At its maximum sugar transport rate, the Phloem functioned with a high turgor pressure difference between the sugar sources and sinks but the turgor pressure difference was reduced if additional parallel conduits were added or solute relays were introduced. Solute relays were shown to decrease the number of parallel sieve tubes needed for Phloem transport, leading to a more uniform turgor pressure and allowing faster information transmission within the Phloem. Because xylem water potential affected both xylem and Phloem transport, the conductance of the two systems was found to be coupled such that large structural investments in the xylem reduced the need for investment in the Phloem and vice versa.
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Linking Phloem function to structure: Analysis with a coupled xylem-Phloem transport model
Journal of Theoretical Biology, 2009Co-Authors: Teemu Holtta, Maurizio Mencuccini, Eero NikinmaaAbstract:We carried out a theoretical analysis of Phloem transport based on Münch hypothesis by developing a coupled xylem-Phloem transport model. Results showed that the maximum sugar transport rate of the Phloem was limited by solution viscosity and that transport requirements were strongly affected by prevailing xylem water potential. The minimum number of xylem and Phloem conduits required to sustain transpiration and assimilation, respectively, were calculated. At its maximum sugar transport rate, the Phloem functioned with a high turgor pressure difference between the sugar sources and sinks but the turgor pressure difference was reduced if additional parallel conduits were added or solute relays were introduced. Solute relays were shown to decrease the number of parallel sieve tubes needed for Phloem transport, leading to a more uniform turgor pressure and allowing faster information transmission within the Phloem. Because xylem water potential affected both xylem and Phloem transport, the conductance of the two systems was found to be coupled such that large structural investments in the xylem reduced the need for investment in the Phloem and .
Eero Nikinmaa - One of the best experts on this subject based on the ideXlab platform.
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linking Phloem function to structure analysis with a coupled xylem Phloem transport model
Journal of Theoretical Biology, 2009Co-Authors: Teemu Holtta, Maurizio Mencuccini, Eero NikinmaaAbstract:We carried out a theoretical analysis of Phloem transport based on Munch hypothesis by developing a coupled xylem-Phloem transport model. Results showed that the maximum sugar transport rate of the Phloem was limited by solution viscosity and that transport requirements were strongly affected by prevailing xylem water potential. The minimum number of xylem and Phloem conduits required to sustain transpiration and assimilation, respectively, were calculated. At its maximum sugar transport rate, the Phloem functioned with a high turgor pressure difference between the sugar sources and sinks but the turgor pressure difference was reduced if additional parallel conduits were added or solute relays were introduced. Solute relays were shown to decrease the number of parallel sieve tubes needed for Phloem transport, leading to a more uniform turgor pressure and allowing faster information transmission within the Phloem. Because xylem water potential affected both xylem and Phloem transport, the conductance of the two systems was found to be coupled such that large structural investments in the xylem reduced the need for investment in the Phloem and vice versa.
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Linking Phloem function to structure: Analysis with a coupled xylem-Phloem transport model
Journal of Theoretical Biology, 2009Co-Authors: Teemu Holtta, Maurizio Mencuccini, Eero NikinmaaAbstract:We carried out a theoretical analysis of Phloem transport based on Münch hypothesis by developing a coupled xylem-Phloem transport model. Results showed that the maximum sugar transport rate of the Phloem was limited by solution viscosity and that transport requirements were strongly affected by prevailing xylem water potential. The minimum number of xylem and Phloem conduits required to sustain transpiration and assimilation, respectively, were calculated. At its maximum sugar transport rate, the Phloem functioned with a high turgor pressure difference between the sugar sources and sinks but the turgor pressure difference was reduced if additional parallel conduits were added or solute relays were introduced. Solute relays were shown to decrease the number of parallel sieve tubes needed for Phloem transport, leading to a more uniform turgor pressure and allowing faster information transmission within the Phloem. Because xylem water potential affected both xylem and Phloem transport, the conductance of the two systems was found to be coupled such that large structural investments in the xylem reduced the need for investment in the Phloem and .
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Linking Phloem function to structure: Analysis with a coupled xylem–Phloem transport model
Journal of theoretical biology, 2009Co-Authors: Teemu Holtta, Maurizio Mencuccini, Eero NikinmaaAbstract:We carried out a theoretical analysis of Phloem transport based on Munch hypothesis by developing a coupled xylem-Phloem transport model. Results showed that the maximum sugar transport rate of the Phloem was limited by solution viscosity and that transport requirements were strongly affected by prevailing xylem water potential. The minimum number of xylem and Phloem conduits required to sustain transpiration and assimilation, respectively, were calculated. At its maximum sugar transport rate, the Phloem functioned with a high turgor pressure difference between the sugar sources and sinks but the turgor pressure difference was reduced if additional parallel conduits were added or solute relays were introduced. Solute relays were shown to decrease the number of parallel sieve tubes needed for Phloem transport, leading to a more uniform turgor pressure and allowing faster information transmission within the Phloem. Because xylem water potential affected both xylem and Phloem transport, the conductance of the two systems was found to be coupled such that large structural investments in the xylem reduced the need for investment in the Phloem and vice versa.
Maurizio Mencuccini - One of the best experts on this subject based on the ideXlab platform.
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allocation stress tolerance and carbon transport in plants how does Phloem physiology affect plant ecology
Plant Cell and Environment, 2016Co-Authors: Jessica A Savage, Maurizio Mencuccini, Sanna Sevanto, Robert Turgeon, Michael J Clearwater, Dustin F Haines, Tamir Klein, Cankui ZhangAbstract:Despite the crucial role of carbon transport in whole plant physiology and its impact on plant–environment interactions and ecosystem function, relatively little research has tried to examine how Phloem physiology impacts plant ecology. In this review, we highlight several areas of active research where inquiry into Phloem physiology has increased our understanding of whole plant function and ecological processes. We consider how xylem–Phloem interactions impact plant drought tolerance and reproduction, how Phloem transport influences carbon allocation in trees and carbon cycling in ecosystems and how Phloem function mediates plant relations with insects, pests, microbes and symbiotes. We argue that in spite of challenges that exist in studying Phloem physiology, it is critical that we consider the role of this dynamic vascular system when examining the relationship between plants and their biotic and abiotic environment.
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linking Phloem function to structure analysis with a coupled xylem Phloem transport model
Journal of Theoretical Biology, 2009Co-Authors: Teemu Holtta, Maurizio Mencuccini, Eero NikinmaaAbstract:We carried out a theoretical analysis of Phloem transport based on Munch hypothesis by developing a coupled xylem-Phloem transport model. Results showed that the maximum sugar transport rate of the Phloem was limited by solution viscosity and that transport requirements were strongly affected by prevailing xylem water potential. The minimum number of xylem and Phloem conduits required to sustain transpiration and assimilation, respectively, were calculated. At its maximum sugar transport rate, the Phloem functioned with a high turgor pressure difference between the sugar sources and sinks but the turgor pressure difference was reduced if additional parallel conduits were added or solute relays were introduced. Solute relays were shown to decrease the number of parallel sieve tubes needed for Phloem transport, leading to a more uniform turgor pressure and allowing faster information transmission within the Phloem. Because xylem water potential affected both xylem and Phloem transport, the conductance of the two systems was found to be coupled such that large structural investments in the xylem reduced the need for investment in the Phloem and vice versa.
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Linking Phloem function to structure: Analysis with a coupled xylem-Phloem transport model
Journal of Theoretical Biology, 2009Co-Authors: Teemu Holtta, Maurizio Mencuccini, Eero NikinmaaAbstract:We carried out a theoretical analysis of Phloem transport based on Münch hypothesis by developing a coupled xylem-Phloem transport model. Results showed that the maximum sugar transport rate of the Phloem was limited by solution viscosity and that transport requirements were strongly affected by prevailing xylem water potential. The minimum number of xylem and Phloem conduits required to sustain transpiration and assimilation, respectively, were calculated. At its maximum sugar transport rate, the Phloem functioned with a high turgor pressure difference between the sugar sources and sinks but the turgor pressure difference was reduced if additional parallel conduits were added or solute relays were introduced. Solute relays were shown to decrease the number of parallel sieve tubes needed for Phloem transport, leading to a more uniform turgor pressure and allowing faster information transmission within the Phloem. Because xylem water potential affected both xylem and Phloem transport, the conductance of the two systems was found to be coupled such that large structural investments in the xylem reduced the need for investment in the Phloem and .
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Linking Phloem function to structure: Analysis with a coupled xylem–Phloem transport model
Journal of theoretical biology, 2009Co-Authors: Teemu Holtta, Maurizio Mencuccini, Eero NikinmaaAbstract:We carried out a theoretical analysis of Phloem transport based on Munch hypothesis by developing a coupled xylem-Phloem transport model. Results showed that the maximum sugar transport rate of the Phloem was limited by solution viscosity and that transport requirements were strongly affected by prevailing xylem water potential. The minimum number of xylem and Phloem conduits required to sustain transpiration and assimilation, respectively, were calculated. At its maximum sugar transport rate, the Phloem functioned with a high turgor pressure difference between the sugar sources and sinks but the turgor pressure difference was reduced if additional parallel conduits were added or solute relays were introduced. Solute relays were shown to decrease the number of parallel sieve tubes needed for Phloem transport, leading to a more uniform turgor pressure and allowing faster information transmission within the Phloem. Because xylem water potential affected both xylem and Phloem transport, the conductance of the two systems was found to be coupled such that large structural investments in the xylem reduced the need for investment in the Phloem and vice versa.
Sylvie Dinant - One of the best experts on this subject based on the ideXlab platform.
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Live-cell imaging of fluorescently tagged Phloem proteins with confocal microscopy
2019Co-Authors: Thibaud Cayla, Rozenn Le Hir, Sylvie DinantAbstract:Confocal laser scanning microscopy can enable observation of Phloem cells in living tissues. Here we describe live imaging of Phloem cells in the leaves and roots of Arabidopsis thaliana using fluorescently tagged proteins, either expressed in the vasculature using Phloem specific promoters or constitutively expressed reference marker lines. Now, the majority of Phloem cell types can be identified, allowing a precise cellular and subcellular localization of Phloem proteins.
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Interactions between the stolbur phytoplasma infection and the Phloem functions in tomato
2015Co-Authors: Federica De Marco, Rozenn Le Hir, Françoise Vilaine, Sandrine Eveillard, Brigitte Batailler, Frédérique Razan, Françoise Gilard, Sylvie DinantAbstract:In higher plants, the allocation of photoassimilates is controlled by the Phloem. Hormones, ions and macromolecules are also transported by Phloem making it a superhighway for long distance signaling. The driving force for Phloem mass flow results from the loading of carbohydrates in source organs. Key factors involved in the metabolism, loading and transport of sugars have been identified, and play a fundamental role in plant development. Such Phloem functions can be hijacked by plant pathogens for their own benefit during infection and systemic colonization. Tomato is a model plant to investigate Phloem activity and the relationships between source and sink organs. Transgenic lines altered in the expression of sucrose transporter genes (SUT1 and SUT2) are available (Hackel et al., 2006). Such plants showed abnormal development and modulation of genes involved in sucrose metabolism and transport. Phytoplasmas, which are Phloem-restricted pathogens, are known to impair Phloem transport causing severe consequences to the entire plant (Christensen, 2005). We have investigated the effect of ‘Candidatus phytoplasma solani’ infection on wild type and transgenic antisense SUT1 and SUT2 tomato lines. We have set up complementary approaches, including observations of plant anatomy and Phloem organization, analyses of Phloem sap metabolite profiles and studies on gene expression. The analyses revealed Phloem hyperproliferation in infected plants and modulation of genes coding for proteins involved in sugars metabolism and callose synthesis. Moreover, one of the antisense lines showed a delay in symptoms appearance. The implications for plant phytoplasma interactions will thus be presented.
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Comparative metabolite profiling of the Phloem saps of maize, tomato and Arabidopsis plants
2015Co-Authors: Federica De Marco, Rozenn Le Hir, Zhazira Yesbergenova-cuny, Marie-laure Magniette, F. Girard, Priscilla Monfalet, Françoise Vilaine, Bertrand Hirel, Sylvie DinantAbstract:In higher plants, two vascular tissues, Phloem and xylem, are responsible for the transport of water, minerals and nutrients between organs. The xylem transports water and minerals absorbed by the roots and the Phloem transports from source to sink organs photoassimilates synthesized in the photosynthetic leaves. The Phloem is essential for higher plants in many developmental and physiological processes. It not only provides the route for the distribution of assimilates but also redistribute mineral nutrients. Additionally, the Phloem is essential for sending information between distant plant organs and steering developmental and defence processes. For example, flowering and tuberization time are controlled by Phloem-mobile signals and important defence reactions on the whole plant level, like systemic acquired resistance or systemic gene silencing, are spread through the Phloem. In addition, recent results demonstrate that also the allocation of mineral nutrients is coordinated by Phloem mobile signaling molecules. However, in many studies the important analysis of Phloem sap is neglected, probably because the content of sieve tubes is not easy to access. We used the EDTA-facilitated exudation method to collect the Phloem sap from three plant species, Maize, Tomato and Arabidopsis. The metabolites present in the samples were analysed by GC-MS or GC-TOF to determine the range of metabolites present in the Phloem sap. We detected more than 50 metabolites, including sugars, amino acids and organic acids. Because of an intrinsic biological variability in the efficiency of exudation depending on the plant samples, we developed a method for the normalisation and the statistical analysis of the Phloem sap metabolite profiles. This study showed that for each species, there is a significant conservation of the Phloem sap content, revealing the strong physical and physiological constraints on Phloem transport. However we observed important differences in the Phloem sap metabolic profiles between plant species, showing different strategies for the allocation of sugars and amino acids between organs.
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Sampling and analysis of Phloem sap
Methods in Molecular Biology, 2013Co-Authors: Sylvie Dinant, Julia KehrAbstract:The transport tubes of the Phloem are essential for higher plants. They not only provide the route for the distribution of assimilates produced during photosynthesis from source to sink organs but also (re-) distribute mineral nutrients. Additionally, the Phloem is essential for sending information between distant plant organs and steering developmental and defense processes. For example, flowering and tuberization time are controlled by Phloem-mobile signals and important defense reactions on the whole plant level, like systemic acquired resistance or systemic gene silencing, are spread through the Phloem. In addition, recent results demonstrate that also the allocation of mineral nutrients is coordinated by Phloem mobile signaling molecules. However, in many studies the important analysis of Phloem sap is neglected, probably because the content of sieve tubes is not easy to access. This chapter will describe the current methods for sampling and analysis of Phloem sap in order to encourage researchers to include the analysis of this crucial compartment in their relevant studies.
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Carbon partitioning: more and more players acting on Phloem loading
2013Co-Authors: Françoise Vilaine, Rozenn Le Hir, Federica De Marco, Catherine Bellini, Sylvie DinantAbstract:Phloem transport between source and sink organs is coupled to the translocation of carbohydrates and other metabolites over long distance. Sucrose is the main photoassimilate used for carbon distribution. In apoplasmic Phloem loader species such as Arabidopsis, energized-sucrose transporters mainly orchestrate sucrose loading in the Phloem. In Arabidopsis, one of them, SUC2, has been shown to be central. It acts both on sugar uptake in minor veins and sucrose retrieval along the transport Phloem pathway. Other actors, such as SWEET proteins, were recently shown to participate to the loading process, potentially acting on efflux from mesophyll cells into Phloem cells. Another potential pathway for sugar loading is the cell-to-cell transfer via plasmodesmata, a mechanism driven by hydrostatic pressure gradients initiated in mesophyll cells. Depending on plant species, symplasmic and/or apoplasmic mechanisms can operate, although there is probably an intimate interplay between both pathways. Our main goal is the identification in Arabidopsis of novel actors acting on Phloem loading. Our approach has been based on the analysis of candidate genes identified on transcriptome profiling of the Phloem tissues, which allowed the identification of several new factors. We also recently developed approaches to analyze the composition of the Phloem sap exudate in order to propose of an integrated view of carbon partitioning.
Sanna Sevanto - One of the best experts on this subject based on the ideXlab platform.
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drought impacts on tree Phloem from cell level responses to ecological significance
Tree Physiology, 2019Co-Authors: Yann Salmon, Teemu Holtta, Sanna Sevanto, Lars Dietrich, Masako Dannoura, Daniel EpronAbstract:: On-going climate change is increasing the risk of drought stress across large areas worldwide. Such drought events decrease ecosystem productivity and have been increasingly linked to tree mortality. Understanding how trees respond to water shortage is key to predicting the future of ecosystem functions. Phloem is at the core of the tree functions, moving resources such as non-structural carbohydrates, nutrients, and defence and information molecules across the whole plant. Phloem function and ability to transport resources is tightly controlled by the balance of carbon and water fluxes within the tree. As such, drought is expected to impact Phloem function by decreasing the amount of available water and new photoassimilates. Yet, the effect of drought on the Phloem has received surprisingly little attention in the last decades. Here we review existing knowledge on drought impacts on Phloem transport from loading and unloading processes at cellular level to possible effects on long-distance transport and consequences to ecosystems via ecophysiological feedbacks. We also point to new research frontiers that need to be explored to improve our understanding of Phloem function under drought. In particular, we show how Phloem transport is affected differently by increasing drought intensity, from no response to a slowdown, and explore how severe drought might actually disrupt the Phloem transport enough to threaten tree survival. Because transport of resources affects other organisms interacting with the tree, we also review the ecological consequences of Phloem response to drought and especially predatory, mutualistic and competitive relations. Finally, as Phloem is the main path for carbon from sources to sink, we show how drought can affect biogeochemical cycles through changes in Phloem transport. Overall, existing knowledge is consistent with the hypotheses that Phloem response to drought matters for understanding tree and ecosystem function. However, future research on a large range of species and ecosystems is urgently needed to gain a comprehensive understanding of the question.
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Drought impacts on tree Phloem
Tree Physiology, 2019Co-Authors: Yann Salmon, Teemu Holtta, Sanna Sevanto, Lars Dietrich, Masako Dannoura, Daniel EpronAbstract:On-going climate change is increasing the risk of drought stress across large areas worldwide. Such drought events decrease ecosystem productivity and have been increasingly linked to tree mortality. Understanding how trees respond to water shortage is key to predicting the future of ecosystem functions. Phloem is at the core of the tree functions, moving resources such as non-structural carbohydrates, nutrients, and defence and information molecules across the whole plant. Phloem function and ability to transport resources is tightly controlled by the balance of carbon and water fluxes within the tree. As such, drought is expected to impact Phloem function by decreasing the amount of available water and new photoassimilates. Yet, the effect of drought on the Phloem has received surprisingly little attention in the last decades. Here we review existing knowledge on drought impacts on Phloem transport from loading and unloading processes at cellular level to possible effects on long-distance transport and consequences to ecosystems via ecophysiological feedbacks. We also point to new research frontiers that need to be explored to improve our understanding of Phloem function under drought. In particular, we show how Phloem transport is affected differently by increasing drought intensity, from no response to a slowdown, and explore how severe drought might actually disrupt the Phloem transport enough to threaten tree survival. Because transport of resources affects other organisms interacting with the tree, we also review the ecological consequences of Phloem response to drought and especially predatory, mutualistic and competitive relations. Finally, as Phloem is the main path for carbon from sources to sink, we show how drought can affect biogeochemical cycles through changes in Phloem transport. Overall, existing knowledge is consistent with the hypotheses that Phloem response to drought matters for understanding tree and ecosystem function. However, future research on a large range of species and ecosystems is urgently needed to gain a comprehensive understanding of the question.
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allocation stress tolerance and carbon transport in plants how does Phloem physiology affect plant ecology
Plant Cell and Environment, 2016Co-Authors: Jessica A Savage, Maurizio Mencuccini, Sanna Sevanto, Robert Turgeon, Michael J Clearwater, Dustin F Haines, Tamir Klein, Cankui ZhangAbstract:Despite the crucial role of carbon transport in whole plant physiology and its impact on plant–environment interactions and ecosystem function, relatively little research has tried to examine how Phloem physiology impacts plant ecology. In this review, we highlight several areas of active research where inquiry into Phloem physiology has increased our understanding of whole plant function and ecological processes. We consider how xylem–Phloem interactions impact plant drought tolerance and reproduction, how Phloem transport influences carbon allocation in trees and carbon cycling in ecosystems and how Phloem function mediates plant relations with insects, pests, microbes and symbiotes. We argue that in spite of challenges that exist in studying Phloem physiology, it is critical that we consider the role of this dynamic vascular system when examining the relationship between plants and their biotic and abiotic environment.
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Phloem transport and drought.
Journal of experimental botany, 2014Co-Authors: Sanna SevantoAbstract:Drought challenges plant water uptake and the vascular system. In the xylem it causes embolism that impairs water transport from the soil to the leaves and, if uncontrolled, may even lead to plant mortality via hydraulic failure. What happens in the Phloem, however, is less clear because measuring Phloem transport is still a significant challenge to plant science. In all vascular plants, Phloem and xylem tissues are located next to each other, and there is clear evidence that these tissues exchange water. Therefore, drought should also lead to water shortage in the Phloem. In this review, theories used in Phloem transport models have been applied to drought conditions, with the goal of shedding light on how Phloem transport failure might occur. The review revealed that Phloem failure could occur either because of viscosity build-up at the source sites or by a failure to maintain Phloem water status and cell turgor. Which one of these dominates depends on the hydraulic permeability of Phloem conduit walls. Impermeable walls will lead to viscosity build-up affecting flow rates, while permeable walls make the plant more susceptible to Phloem turgor failure. Current empirical evidence suggests that Phloem failure resulting from Phloem turgor collapse is the more likely mechanism at least in relatively isohydric plants.
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Effects of the hydraulic coupling between xylem and Phloem on diurnal Phloem diameter variation
Plant cell & environment, 2011Co-Authors: Sanna Sevanto, Teemu Holtta, N. Michele HolbrookAbstract:Measurements of diurnal diameter variations of the xylem and Phloem are a promising tool for studying plant hydraulics and xylem-Phloem interactions in field conditions. However, both the theoretical framework and the experimental verification needed to interpret Phloem diameter data are incomplete. In this study, we analytically evaluate the effects of changing the radial conductance between the xylem and the Phloem on Phloem diameter variations and test the theory using simple manipulation experiments. Our results show that Phloem diameter variations are mainly caused by changes in the radial flow rate of water between the xylem and the Phloem. Reducing the hydraulic conductance between these tissues decreases the amplitude of Phloem diameter variation and increases the time lag between xylem and Phloem diameter variation in a predictable manner. Variation in the amplitude and timing of diameter variations that cannot be explained by changes in the hydraulic conductance, could be related to changes in the osmotic concentration in the Phloem.