Kinetic properties of the blue-light response of stomata

Abstract

The stomatal response to blue light was analyzed with gas-exchange techniques in Commelina communis L. leaves by using high-fluence-rate short pulses. Pulses of blue light were given under a background of high-fluence-rate red light, which maintained photosynthesis at near saturation and stomatal conductance at a steady state. A single blue light pulse of 1-100 sec induced an increase in stomatal conductance, which peaked after 15 min and then returned to the initial steady-stte level within 50-60 min after the pulse. The response could be repeatedly induced in the same leaf. Red light pulses on a red background did not induce any comparable response. The stomatal response quantified by integrating the conductance increases after pulse application approached saturation with increasing pulse duration (t1/2 .apprxeq. 9 sec with 250 .mu.mol .cntdot. m-2 .cntdot. sec-1 of blue light). After a saturating pulse, sensitivity to a second pulse was restored slowly. This recovery response, quantified from the conductance increases caused by the two pulses, approached saturation with a t1/2 of .apprxeq. 9 min. These results were used to test a model in which a molecular component in the sensory transduction process is considered to exist in two interconvertible forms, A and B. If B is the physiologically active form inducing stomatal opening, then A is the inactive form. The A to B conversion is a light-induced reaction and the B to A conversion is a thermal reaction. Rate constants for these reactions were estimated from single- and double-pulse experiments (at a fluence rate of 250 .mu.mol .cntdot. m-2 .cntdot. sec-1, k1 = 0.075 sec-1; thermal rate constant kd = 0.0014 sec-1), allowing the calculation of steady-state concentration of B under continuous irradiation. The calculated values accurately predicted the steady-state stomatal conductances under continuous blue light.