Research indicates that calcium ions and signal-modulated ion channels may play a central role in plant cellular signal transduction. Guard cells provide an ideal system for the study of plant signaling, as these cells respond dynamically to hormone and light stimuli in regulating gas exchange. Recent data suggest that calcium regulation of ion channels in the plasma membrane of guard clls provides a basis for physiologically- observed calcium dependent stomatal movements. Preliminary results show that abscisic acid induces increases in cytosolic calcium, which in turn may trigger stomatal closing, thus protecting plants from desiccation. The goals of the proposed research are to achieve an accurate understanding of the molecular mechanisms by which cytosolic calcium and other ions regulate inward rectifying potassium channels and by which mechanisms abscisic acid exerts control over these processes. Isolated guard cells will be studied by simultaneous patch clamp analysis and photometric measurements of cytosolic calcium, allowing the direct investigation of effects of cytosolic and extracellular modulators on signaling events. The knowledge gained from these studies will contribute substantially to our understanding of the molecular mechanisms controlling gas and water exchange in the leaves of plants and will provide a quantitative description of biophysical and biochemical regulation of ion channels in higher plant cells.
