Light, Stomatal Function and Energy Transduction in Guard Cells

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Stomata regulate gas exchange in leaves, thus affecting productivity and the water balance of the plant. Stomatal control depends on sensory transduction by guard cells of internal and external stimuli, translating information about prevailing conditions in the leaf environment to modulation of the size of stomatal apertures. The overall objective of this research program is to understand the signal perception, metabolic transduction, and aperture regulation during the movements of stomata in response to light. Recent studies have shown that light activates proton pumping at the guard cell plasmalemma via two different transduction pathways, one activated by a blue light photoreceptor and the other by the guard cell chloroplast. The aim of this proposal is the detailed characterization of the sensory transduction steps involved in pump activation. Using the electrophysiological technique of patch clamping, metabolic and photobiological features of the two pathways will be investigated, including critical concentrations of ATP and other cofactors, fluence-rate dependence, specific pharmacological properties, and interactive features between the two pathways in connection with the guard cell response to solar radiation. The identity of the blue light photoreceptor will be investigated by spectroscopic analysis at low and room temperature. Gas exchange techniques with intact leaves will be used to correlate resolved features at the subcellular and cellular level with stomatal performance under physiological conditions. Stomata are pores in the surface of a leaf which regulate the passage of water and gasses into and out of the leaf's tissue. Proper traffic through the stomata is vital for the plant's ability to conduct photosynthesis and maintain its water balance. The stomata open and close in response to environmental stimuli. The results of this research will enhance our understanding of the cellular mechanisms which regulate the movements of stomata, and more generally, will increase basic knowledge of the mechanisms of sensory transduction and ion transport in plant cells.