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-fluencerate 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-state 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 (t l2 =9 sec with 250 smol-m-2.sec' 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 t 1/2 of W9 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 250Lmo'm-2-sec-1, k, = 0.075 sec'1; thermal rate constant kd = 0.0014 sec'1), allowing the calculation of steady-state concentration of B under continuous irradiation. (9). These properties provide a basis for the quantitative analyses of the early sensory reactions by measuring stomatal movement.Many of the BL responses can be induced by a short pulse of BL (10-13). In previous work with stomata, a rapid transient increase in transpiration in Avena leaves caused by a BL pulse as short as 3 sec has been reported (14). In the present study, we have characterized kinetic properties ofthe stomatal response to BL by using pulse stimulation. The responses were quantified in attached leaves of Commelina communis by using gas-exchange techniques. Background irradiation with high-fluence-rate red light (RL) was used to saturate and thereby minimized the component of the stomatal response to BL depending on photosynthesis in guard cells and the underlying mesophyll cells. The obtained results allowed us to test a kinetic model, which predicted the steady-state values of stomatal conductance under continuous BL. MATERIALS AND METHODSPlants of C. communis were grown from seed in pots of soil (Goldstrike potting soil, Master Nurserymen's Assoc., Concord, CA) in a greenhouse. Plants were watered daily, fertilized weekly with a solution of Spoonit (Plantsmith, Mountain View, CA) at ==3 g/liter, and used for experimentation when 4-6 weeks old.Stomatal conductance to water vapor and rates of C...

Blue light activates the plasma membrane H+-ATPase by phosphorylation of the C-terminus in stomatal guard cells

“…Fluence dependency of BL-dependent ATP hydrolysis and phosphorylation of H ⍣ -ATPase Stomatal response in intact leaves and H ϩ pumping in GCPs by BL are both fluence dependent (Iino et al, 1985;Shimazaki et al, 1986). In accord with the physiological responses, ATP hydrolysis by the plasma membrane H ϩ -ATPase was also fluence dependent.…”

“…It began 30 s after the start of stimulation and was sustained for 15 min with the maximum rate at 2.5 min. The GCPs, once stimulated by a single pulse, responded to the second pulse, but the magnitude decreased to 60% when the interval between the first and the second pulse was 20 min, consistent with the response in an intact leaf (Iino et al, 1985). To show that this BL-activated H ϩ pump is the plasma membrane H ϩ -ATPase, ATP hydrolysis in response to BL was determined after immediate disruption of GCPs ( Figure 1B).…”

Enhancement of the Stomatal Response to Blue Light by Red Light, Reduced Intercellular Concentrations of CO2, and Low Vapor Pressure Differences

“…The gas exchange system was located in a darkened room. The illumination protocol was a modification of the dual beam technique (8,13 Responses are summarized in Figure la, and typical results are illustrated in Figure 2. At all background fluence rates of red light, stomata responded to a blue light pulse, resulting in a transient increase in conductance (Figs.…”

“…Plants of Paphiopedilum harrisianum G.S. Ball and Commelina communis L. were raised as described previously (1,8) except for a different watering regime. Plants were either misted (P. harrisianum) or drip irrigated (C. communis) 6 d/ week with an automatic irrigation system (Rain Master Irrigation Systems, Simi Valley, CA).…”

“…The experiments were performed using Paphiopedilum harrisianum, an orchid species which lacks guard cell chloroplasts (5, 12), and Commelina communis. As with other nongrasses (9), these species lack the rapid blue-light-induced transpiration increase, but exhibit a less rapid stomatal opening response which has been clearly attributed to the specific blue light system (8,17,26). …”