Co-Transport Systems (Current Topics in Membranes)

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In 1-week-old barley seedlings, for example, the rate of guttation of the primary leaf ranges from 1.

Based on these figures it cannot be excluded that a water co-transport loading of xylem vessels contributes significantly to water flow associated with guttation. A more thorough quantitative assessment requires studies in which the rates of night- and daytime transpirational water loss are analysed together with the rates of guttation and the net rate of photosynthetic carbon assimilation.

An alternative approach is to take exudation rates of isolated root systems as being representative of the ability of plants to establish a root pressure that can drive water flow associated with guttation. If such rates were sustained in intact plants during the entire night period, between 0.

On the basis of the energy involved, this does not rule out the possibility that a water cotransport mechanism of xylem loading contributes significantly to exudation and possibly guttation rates in barley plants. The main aim of the above calculations was to assess the energetic sustainability of a water co-transport mechanism in relation to the overall energy and water flow budget of the plant.

Membrane Transport

The question was whether the movement of substances other than water can energize the co-transport of water across the plasma membrane of xylem parenchyma cells. This energy could be used to drive the movement, or synthesis, of other substances rather than being lost as heat. Given the daytime transpiration rate of a 2- to 3-week-old barley plant 5.

While these figures are small in comparison with the energy that can be assimilated through photosynthesis, they may provide a significant additional source of energy at times when photosynthesis is impaired or in those parts of the plant xylem filling in roots that do not photosynthesize themselves. The amount of energy E which is potentially released in association with water movement from xylem parenchyma cells into xylem vessels during daytime transpiration in a 2- to 3-week-old barley plant.

Co-Transport Systems, Volume 70 - 1st Edition

Water spontaneously enters the xylem vessel. Currently no mechanistic model that can link the energy released through the movement of water through the phospholipid bilayer or through aquaporins to the movement or catalytic modification of other substances exists. Is it possible that there exists something like an H 2 O-driven ATP-synthase in the plasma membrane of plant cells? Finally, a comment as to how aquaporins fit into any putative mechanism of co-transport of water see also Wegner, or H 2 O-driven ATP-synthase. Aquaporins occur ubiquitously in plant cell membranes, and many aquaporins facilitate the movement of water across membranes for reviews, see Tyerman et al.

While this raises questions regarding the existence and significance of such mechanisms, and also regarding the biological role of a water-transporting function of aquaporins e.


Hill et al. The question is rather why these xylem tensions and reverse osmotic gradients can be measured despite the existence of aquaporins. These conditions have repeatedly been shown to turn off the aquaporin pathway Tournaire-Roux et al. I would like to thank Tim J. Flowers, John S. Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account. Sign In. Advanced Search. Article Navigation.

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Close mobile search navigation Article Navigation. Volume Article Contents. Energetic feasibility of the water co-transport mechanism. Transpirational water flow as a potential source of energy. The significance of water co-transport for sustaining transpirational water flow in plants: a quantitative approach Wieland Fricke. E-mail: wieland02fricke yahoo. Oxford Academic. Google Scholar.

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Cite Citation. Permissions Icon Permissions. Barley , chemical energy , transpiration , water co-transport , water-driven ATP-synthase , water potential , xylem. View large Download slide. Table 1.

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View Large. Search ADS. The contrasting influence of short-term hypoxia on the hydraulic properties of cells and roots of wheat and lupin. Cellular and whole-plant chloride dynamics in barley: insights into chloride—nitrogen interactions and salinity responses. Nighttime stomatal conductance and transpiration in C 3 and C 4 plants.

Environmental stress and genetics influence night-time leaf conductance in the C-4 grass Distichlis spicata. The effects of abscisic acid and cytokinins. The intercellular distribution of vacuolar solutes in the epidermis and mesophyll of barley leaves changes in response to NaCl. Molecular physiology and pathophysiology of electroneutral cation—chloride cotransporters. Water uptake of seminal and adventitious roots in relation to whole-plant water flow in barley Hordeum vulgare L.

Google Preview. Water use efficiency of short-rotation Salix viminalis at leaf, tree and stand scales. Comparative measurements of xylem pressure in transpiring and non-transpiring leaves by means of the pressure chamber and the xylem pressure probe.


Xylem and cell turgor pressure probe measurements in intact roots of glycophytes: transpiration induces a change in the radial and cellular reflection coefficients. Do root hydraulic properties change during the early vegetative stage of plant development in barley Hordeum vulgare? Cytosolic pH regulates root water transport during anoxic stress through gating of aquaporins. Plant aquaporins: their molecular biology, biophysics and significance for plant water relations. Root pressure and beyond: energetically uphill water transport into xylem vessels? Direct measurement of xylem pressure in leaves of intact maize plants.

A test of the cohesion—tension theory taking hydraulic architecture into consideration. All rights reserved. For permissions, please email: journals. Issue Section:. Download all figures. Supplementary data. Supplementary Data. Comments 0. Add comment Close comment form modal.

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