PLANT PHYSIOLOGY , Vol 108, Issue 3 1161-1170, Copyright © 1995 by American Society of Plant Biologists
|
WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
The Role of Potassium Channels in the Temperature Control of Stomatal Aperture
N. Ilan, N. Moran and A. Schwartz
Department of Agricultural Botany, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot 76100, Israel (N.I., A.S.)
We used the patch-clamp technique to examine the effect of temperature
(13-36[deg]C) on the depolarization-activated K channels (KD channels) and
on the hyperpolarization-activated channels (KH channels) in the plasma
membrane of Vicia faba guard-cell protoplasts. The steady-state whole-cell
conductance of both K channel types increased with temperature up to
20[deg]C. However, whereas the whole-cell conductance of the KH channels
increased further and saturated at 28[deg]C, that of KD channels decreased
at higher temperatures. The unitary conductance of both channel types
increased with temperature like the rate of diffusion in water (temperature
quotient of approximately 1.5), constituting the major contribution to the
conductance increase in the whole cells. The mean number of available KH
channels was not affected significantly by temperature, but the mean number
of available KD channels increased significantly between 13 and 20[deg]C
and declined drastically above 20[deg]C. This decrease and the reduced
steady-state voltage-dependent probability of opening of the KD channels
above 28[deg]C (because of a shift of voltage dependence by +21 mV) account
for the depression of the whole-cell KD conductance at the higher
temperatures. This may be a basic mechanism by which leaves of well-watered
plants keep their stomata open during heat stress to promote cooling by
transpiration.
