Using electrophysiological (patch clamping) techniques, this investigator has shown that blue light activates a hyperpolarizing proton pump at the guard cell membrane. Hyperpolarization creates a gradient for potassium influx, presumed to occur through potassium-specific ion channels, resulting in water uptake, cell swelling, and stomatal opening. The goals of the proposed research are to investigate the possibility that blue-light-activation of the proton pump and/or regulation of potassium channel opening is mediated by the phosphatidylinositol (PI) pathway. Preliminary experiments indicate that analogs of diacylglycerol, a component of the PI pathway, can enhance light-stimulated opening of stomata in epidermal peels. Patch clamping will be used to determine the effects of these and other biochemical regulators of the PI pathway on blue-light-stimulated ion pumping and potassium channel kinetics of guard cell protoplasts. The electrophysiological response to blue light of guard cells from an Arabidopsis thaliana mutant (phi 3-4) will also be characterized. This mutant lacks a phototropic response, and also exhibits reduced stomatal opening under blue illumination. Blue light mediates a variety of responses in plants, such as opening of stomatal pores to allow gas and water exchange, bending toward light, and chloroplast development. The proposed research will focus on the stomatal response and will contribute to a clearer understanding of the cellular mechanisms by which plants detect and respond to blue light.
