PLANT PHYSIOLOGY , Vol 103, Issue 2 493-500, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Transpiration Induces Radial Turgor Pressure Gradients in Wheat and Maize Roots
J. Rygol, J. Pritchard, J. J. Zhu, A. D. Tomos and U. Zimmermann
Lehrstuhl fur Biotechnologie, Universitat Wurzburg, Biozentrum, Am Hubland, D-97074 Wurzburg, Germany (J.R., J.J.Z., U.Z.)
Previous studies have shown both the presence and the absence of radial
turgor and osmotic pressure gradients across the cortex of roots. In this
work, gradients were sought in the roots of wheat (Triticum aestivum) and
maize (Zea mays) under conditions in which transpiration flux across the
root was varied This was done by altering the relative humidity above the
plant, by excising the root, or by using plants in which the leaves were
too young to transpire. Roots of different ages (4-65 d) were studied and
radial profiles at different distances from the tip (5-30 mm) were
measured. In both species, gradients of turgor and osmotic pressure
(increasing inward) were found under transpiring conditions but not when
transpiration was inhibited. The presence of radial turgor and osmotic
pressure gradients, and the behavior of the gradient when transpiration is
interrupted, indicate that active membrane transport or radial solvent drag
may play an important role in the distribution of solutes across the root
cortex in transpiring plants. Contrary to the conventional view, the flow
of water and solutes across the symplastic pathway through the
plasmodesmata cannot be inwardly directed under transpiring conditions.
