Light Sensing by Guard Cell Chloroplasts: Large Antenna Size and High Electron Transport Rates

Abstract

Stomata constitute a critical interface between the plant and environment. Light is a major environmental signal for stomata! movements under natural light conditions (1). Guard cells transduce light intensity into modulated stomatal conductances in a sensory transducing cascade that involves light sensing at the guard cell chloroplast, activation of a proton pumping ATPase at the guard cell plasma membrane, ion uptake, synthesis of organic solutes, guard cell osmoregulation and stomatal opening (1–4). The stomatal response to light has two distinct components, one mediated by photosynthesis in the guard cell chloroplast, and the other depending on a specific guard cell response to blue light (5,6). The regulation of the stomatal response to light has been extensively studied in isolated guard cells, but the precise mechanisms regulating light-dependent stomatal movements over daily time courses are poorly understood. In the present study we used fast and slow chlorophyll a fluorescence induction kinetics over a daily time course to probe light sensing by the guard cell chloroplast (GCC) and compared it with their mesophyll (MCC) counterparts.