Blue Light and Phytochrome-Mediated Stomatal Opening in the npq1 and phot1 phot2 Mutants of Arabidopsis

Abstract

Recent studies have shown that blue light-specific stomatal opening is reversed by green light and that far-red light can be used to probe phytochrome-dependent stomatal movements. Here, blue-green reversibility and far-red light were used to probe the stomatal responses of the npq1 mutant and the phot1 phot2 double mutant of Arabidopsis. In plants grown at 50 mol m Ϫ2 s Ϫ1 , red light (photosynthetic)-mediated opening in isolated stomata from wild type (WT) and both mutants saturated at 100 mol m Ϫ2 s Ϫ1 . Higher fluence rates caused stomatal closing, most likely due to photo-inhibition. Blue light-specific opening, probed by adding blue light (10 mol m Ϫ2 s Ϫ1 ) to a 100 mol m Ϫ2 s Ϫ1 red background, was found in WT, but not in npq1 or phot1 phot2 double mutant stomata. Under 50 mol m Ϫ2 s Ϫ1 red light, 10 mol m Ϫ2 s Ϫ1 blue light opened stomata in both WT and npq1 mutant stomata but not in the phot1 phot2 double mutant. In npq1, blue light-stimulated opening was reversed by far-red but not green light, indicating that npq1 has a phytochrome-mediated response and lacks a blue light-specific response. Stomata of the phot1 phot2 double mutant opened in response to 20 to 50 mol m Ϫ2 s Ϫ1 blue light. This opening was green light reversible and far-red light insensitive, indicating that stomata of the phot1 phot2 double mutant have a detectable blue light-specific response.Many steps in the sensory-transducing cascade mediating blue light-specific stomatal movements are well characterized (Assmann, 1993). Guard cells are turgor valves that control the dimensions of the stomatal pore by changes in water content caused by changes in their osmotic potential. Blue light-specific stomatal opening is mediated by potassium and chloride uptake and malate biosynthesis. Ion uptake is driven by an electrochemical gradient generated by a proton-pumping ATPase activated by blue light (Tallman, 1992). The activation of the ATPase is mediated by the phosphorylation of its C terminus by a Ser/Thr kinase, facilitated by the binding of a 14-3-3 protein (Kinoshita and Shimazaki, 1999). Blue lightspecific stomatal opening has an action spectrum, showing a maximum at 450 nm and two minor peaks at 420 and 470 nm (Karlsson, 1986).Genetic, biochemical, and physiological studies have identified the chloroplastic carotenoid, zeaxanthin, as a blue light photoreceptor in guard cells (Frechilla et al., 1999). Two recent studies, however, have reported that stomata from the zeaxanthin-less Arabidopsis mutant, npq1, open in response to blue light (Eckert and Kaldenhoff, 2000;Kinoshita et al., 2001) and questioned the validity of the zeaxanthin hypothesis. One of these studies further reported that stomata from the phot1 phot2 double mutant of Arabidopsis lack a blue light response and hypothesized that phototropin is the main photoreceptor mediating blue light responses in guard cells (Kinoshita et al., 2001).The photobiological properties of guard cells complicate the analysis of stomatal opening in response to blue light (Lasceve et al., 1999)...

Green Light Adjusts the Plastid Transcriptome during Early Photomorphogenic Development

“…Certainly the presence of five phytochromes, two cryptochromes, two phototropins, and three other LOV domain receptors suggest the plant light sensor collection coordinates a complex circuit of integrated responses that are dependent upon plant developmental state, tissue, or cell type. Add to this the noted and potential light-sensing roles for zeaxanthin (Frechilla et al, 2000;Talbott et al, 2003), cry-DASH (Brudler et al, 2003), G proteins (Warpeha et al, 1991), and possibly flavinbinding aquaporins (Lorenz et al, 2003) and it is clear that there are many additional candidates that may be modulating the GL plastid response. It also is of interest to determine how the developmentally contrary GL effects integrate with the inductive photomorphogenic responses associated with blue and red wavebands.…”

“…GL specifically inhibits seedling mass (Went, 1957), plant cell culture growth (Klein, 1964), and elongation during gravitropic stimulation (Klein, 1979) among other responses (Klein, 1992). Contemporary studies have shown that GL can reverse blue and UV-B-induced stomatal opening (Frechilla et al, 2000;Eisinger et al, 2003;Talbott et al, 2003). In all of these cases, the response to GL is in direct opposition to the normal progression of light-mediated processes.…”

Evidence for Involvement of Photosynthetic Processes in the Stomatal Response to CO2

“…This response has been shown to involve the activation of a plasma membrane H 1 -ATPase (Kinoshita and Shimazaki, 1999), although the steps leading up to this activation are not clear. The receptor for this response has yet to be identified unequivocally, and there is evidence supporting both zeaxanthin Talbott et al, 2003) and phototropins Doi et al, 2004) for this role. The RL response is also poorly understood, but many data suggest the involvement of guard cell photosynthetic processes.…”

Stomatal Opening Mechanism of CAM Plants

“…A blue light photoreceptor for the signal transduction chain in guard cells has been suggested to be the carotenoid pigment zeaxanthin (Zeiger et al 2002;Talbott et al 2003). Phototropin has also been postulated as a blue light photoreceptor (Kinoshita et al 2001).…”