PLANT PHYSIOLOGY , Vol 103, Issue 4 1107-1114, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Kinematics and Dynamics of Sorghum (Sorghum bicolor L.) Leaf Development at Various Na/Ca Salinities (I. Elongation Growth)
N. Bernstein, A. Lauchli and W. K. Silk
Department of Land, Air and Water Resources, University of California, Davis, California 95616
In many salt-sensitive species, elevated concentrations of Ca in the root
growth media ameliorate part of the shoot growth reduction caused by NaCl
stress. The physiological mechanisms by which Ca exerts protective effects
on leaf growth are still not understood. Understanding growth inhibition
caused by a stress necessitates locating the leaf expansion region and
quantifying the profile of the growth reduction. This will enable
comparisons and correlations with spatial gradients of probable
physiologically inhibiting factors. In this work we applied the methods of
growth kinematics to analyze the effects of elevated Ca concentrations on
the spatial and temporal distributions of growth within the intercalary
expanding region of salinized sorghum (Sorghum bicolor [L.] Moench, cv NK
265) leaves. NaCl (100 mM) caused a decrease in leaf elongation rate by
shortening the leaf growing zone by 20%, as well as reducing the peak value
of the longitudinal relative elemental growth rate (REG rate). Increasing
the Ca concentrations from 1 to 10 mM restored the length of the growing
zone of both emerged and unemerged salinized leaves and increased the peak
value of the REG rate. The beneficial effects of supplemental Ca were,
however, more pronounced in leaves after their appearance above the whorl
of encircling older leaf sheaths. Elevated Ca then resulted in a peak value
of REG rate higher than in the salinized leaves. The peak value of
unemerged leaves was not increased, although it was maintained over a
longer distance. The duration of elongation growth associated with a cell
during its displacement from the leaf base was longer in salinized than
control leaves, despite the fact that the elongation zone was shorter in
salinity. Although partially restoring the length of the elongation region,
supplemental Ca had no effect on the age of cessation of growth. Elongation
of a tissue element, therefore, ceased when a cellular element reached a
certain age and not a specific distance from the leaf base.
