Apoplasmic and Protoplasmic Water Transport through the Parenchyma of the Potato Storage Organ

Michael, W.; Schultz, A. J.; Meshcheryakov, A. B.; Ehwald, R.

doi:10.1104/pp.115.3.1089

Cited by 20 publications

(7 citation statements)

References 27 publications

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“…If the volume flux on the proposed apoplastic bypath was significant, the median value M obtained with dextran 8 should be lower than that obtained with sugars and salts which might have a small reflection coefficient on the putative apoplastic bypath through the radial endodermis walls. Equal hydraulic effects of isotonic solutions prepared with polymer osmolytes and mannitol have previously been reported in a study on water transport through the living storage parenchyma of the potato tuber (Michael et al 1997). The results given in Table 3 suggest that the radial reflection coefficient is close to unity for all studied osmolytes.…”

Section: Discussionsupporting

confidence: 50%

Visualisation of xylem sap flow direction in isolated fine lateral roots and estimation of the xylem sap osmotic potential

Fritz¹,

Ehwald²

2012

Biologia plant.

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Xylem sap outflow from fine lateral roots (FLRs) isolated from hydroponically grown young maize (Zea mays L.) plants was visualized by local brightening of test solutions contrasted with purified Indian ink particles. Flow into the vessels was indicated by the adsorption of Evans Blue in their walls. The fraction of the FLRs able to exude xylem sap in a mineral medium with 30 mM mannitol decreased with increasing incubation time. This change was strongly retarded, when the FLRs were incubated in a medium containing glucose instead of mannitol. There was a broad range of variation of the osmotic potential of the test solutions (Ψ so ), wherein the fraction of the FLRs showing an initially reversed flow of the xylem sap varied between zero and unity. A median (M) of the osmotic potential of the xylem sap in FLRs (Ψ sx ) was estimated. It represents the value of Ψ so that was lower than Ψ sx in half of the roots of a sample before their transfer to the test solutions (Ψ sxo ). M was dependent on the osmotic potential of the medium used for growth or pre-incubation of the FLRs. Its value was not dependent on the molecular size of the osmolytes used to adjust Ψ so , including dextran 8, which is excluded from cell walls. In all of the studied plants, M was lower than the osmotic potential of the xylem sap collected from the root before isolation of the FLRs. To explain this finding it is assumed that FLRs with Ψ sxo > M had a higher hydraulic conductivity and a larger volume contributed to the exuded sap than those with Ψ sx < M.

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Section: Discussionsupporting

confidence: 50%

Visualisation of xylem sap flow direction in isolated fine lateral roots and estimation of the xylem sap osmotic potential

Fritz¹,

Ehwald²

2012

Biologia plant.

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“…at the endodermis, even when the Casparian strip is water permeable). Note that this interpretation applies to root regions that developed at least a Casparian strip and, thus, does not deny interpretations on the dominant role of intercellular spaces in water flow across slices of potato (Solanum tuberosum) storage organs (Michael et al, 1997).…”

Section: Hydraulic Properties Are Not Always Transferable Between Celmentioning

confidence: 99%

Going with the Flow: Multiscale Insights into the Composite Nature of Water Transport in Roots

Couvreur¹,

Faget²,

Lobet

et al. 2018

Plant Physiol.

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As water often limits crop production, a more complete understanding of plant water capture and transport is necessary. Here, we developed MECHA, a mathematical model that computes the flow of water across the root at the scale of walls, membranes, and plasmodesmata of individual cells, and used it to test hypotheses related to root water transport in maize (Zea mays). The model uses detailed root anatomical descriptions and a minimal set of experimental cell properties, including the conductivity of plasma membranes, cell walls, and plasmodesmata, which yield quantitative and scale-consistent estimations of water pathways and root radial hydraulic conductivity (k r). MECHA revealed that the mainstream hydraulic theories derived independently at the cell and root segment scales are compatible only if osmotic potentials within the apoplastic domains are uniform. The results suggested that the convection-diffusion of apoplastic solutes explained most of the offset between estimated k r in pressure clamp and osmotic experiments, while the contribution of water-filled intercellular spaces was limited. Furthermore, sensitivity analyses quantified the relative impact of cortex and endodermis cell conductivity of plasma membranes on root k r and suggested that only the latter contributed substantially to k r due to the composite nature of water flow across roots. The explicit root hydraulic anatomy framework brings insights into contradictory interpretations of experiments from the literature and suggests experiments to efficiently address questions pertaining to root water relations. Its scale consistency opens avenues for cross-scale communication in the world of root hydraulics.

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“…Yet for the liquid phase, whether flow through living cells occurs more through the wall space (apoplastic path) versus cell to cell across membranes (symplastic path as measured by the cell pressure probe, with plasmodesmata making an uncertain contribution; Kramer and Boyer, 1995) remains unresolved, meaning we do not know for certain which material properties drive r m . Theoretical models have been employed to argue for the dominance of apoplastic flow (Buckley, 2015), but the scant available experimental evidence indicates similar conductivities for the symplastic and apoplastic paths of potato (Solanum tuberosum) parenchyma, and the symplastic path should then dominate transport based on its greater cross-sectional area (Michael et al, 1997). Estimates of cross-membrane hydraulic conductivities based on cell pressure probe measurements of membrane permeabilities also appear sufficient to explain whole-tissue conductances, without the need to invoke large apoplastic flows (Rockwell et al, 2014b).…”

Section: The Potential Mitigation Of Low Vein Density By Mesophyll Hymentioning

confidence: 99%

Leaf Hydraulic Architecture and Stomatal Conductance: A Functional Perspective

Rockwell

Holbrook

2017

Plant Physiol.

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The structure of leaf vasculature viewed over a broad phylogenetic scale from lycophytes to eudicots correlates with stomatal conductance, providing the basis for the hypothesis that increasing vein density drove the evolution of high fluxes in angiosperms. Yet, the relationship between vascular geometry and gas fluxes breaks down at finer phylogenetic scales. In this Update, we derive a simple one-dimensional model suitable for mapping the effects of three-dimensional vascular architecture and transport capacity onto an effective length for transport through the mesophyll. This approach allows us to explore notions of optimality in the hydraulics of reticulately veined leaves, which differ from the two-dimensional case. We then consider limits to stomatal conductance that may derive from genomic constraints on cell size and the role of mechanical advantage. We conclude that more mechanistic modeling of transpiration could help resolve the sensitivity of stomatal, genome, and vein density relationships to the phylogenetic scale of the study.

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Apoplasmic and Protoplasmic Water Transport through the Parenchyma of the Potato Storage Organ

Cited by 20 publications

References 27 publications

Visualisation of xylem sap flow direction in isolated fine lateral roots and estimation of the xylem sap osmotic potential

Visualisation of xylem sap flow direction in isolated fine lateral roots and estimation of the xylem sap osmotic potential

Going with the Flow: Multiscale Insights into the Composite Nature of Water Transport in Roots

Leaf Hydraulic Architecture and Stomatal Conductance: A Functional Perspective

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