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PLANT PHYSIOLOGY , Vol 108, Issue 1 303-312, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Rapid Response of the Yield Threshold and Turgor Regulation during Adjustment of Root Growth to Water Stress in Zea mays
J. Frensch and T. C. Hsiao
Hydrologic Science, Department of Land, Air and Water Resources, University of California, Davis, California 95616
Responses of cortical cell turgor (P) following rapid changes in osmotic
pressure ([pi]m) were measured throughout the elongation zone of maize (Zea
mays L.) roots using a cell pressure probe and compared with simultaneously
measured root elongation to evaluate: yield threshold (Y) (minimum P for
growth), wall extensibility, growth-zone radial hydraulic conductivity (K),
and turgor recovery rate. Small increases in [pi]m (0.1 MPa) temporarily
decreased P and growth, which recovered fully in 5 to 10 min. Under
stronger [pi]m (up to 0.6 MPa), elongation stopped for up to 30 min and
then resumed at lower rates. Recoveries in P through solute accumulation
and lowering of Y enabled growth under water stress. P recovery was as much
as 0.3 MPa at [pi]m = 0.6 MPa, but recovery rate declined as water stress
increased, suggesting turgor-sensitive solute transport into the growth
zone. Under strong [pi]m, P did not recover in the basal part of the growth
zone, in conjunction with a 30% shortening of the growth zone. Time courses
showed Y beginning to decrease within several minutes after stress
imposition, from about 0.65 MPa to a minimum of about 0.3 MPa in about 15
min. The data concerning Y were not confounded significantly by elastic
shrinkage. K was high (1.3 x 10-10 m2 s-1 MPa-1), suggesting very small
growth-induced water potential gradients.
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