9305154 Crain Perception of environmental conditions and initiation of appropriate responses to these conditions is crucial for survival of all organisms. Additionally, individual cells of multicellular organisms must perceive and respond to internal signals, such as hormones, which coordinate the behavior and physiology of the whole organism. In contrast to the case for animal systems, little is known about transduction pathways coupling signals to cellular responses in plants. The coupling of light reception to leaflet movement in the tropical legume Samanea saman and of environmental stress to deflagellation in the unicellular alga Chlamydomonas reinhardtii are signal response systems that appear to involve calcium. Phosphoinositide turnover, which produces inositol phosphates and diacylglycerol, is hypothesized to mediate these responses by mobilizing intracellular calcium and stimulating protein phosphorylation. To elucidate the role of phosphoinositide turnover in these systems: (1) the kinetics and properties of the coupling between signal and cellular response(s) will be investigated, (2) temporal changes in phosphoinositide metabolism and intracellular calcium levels will be correlated with signal reception and cellular response(s), and (3) the effects of metabolites of phosphoinositide turnover and of agents that perturb the functioning of phosphoinositide metabolism and calcium homeostasis on cellular responses to signals will be examined. %%% The detailed mechanisms by which plants respond to signals, such as light, that they receive from their environment are not known. Dr. Crain will study this in two systems: the light-responsive pulvinar cells of a tropical legume and a green alga which responds to stress by shedding its flagellae. The legume, S. saman, has compound leaves, the leaflets of which open in the light and close in the dark. The movements of these leaflets are effected by changes in turgor of the pulvinar cells. Turgor chan ges are caused by ion fluxes regulated by light. Recent studies have indicated that calcium ions are important in this response, and since inositol triphosphate has been shown to regulate calcium in a number of systems, Dr. Crain will study the formation and breakdown of this metabolite in cells and subcellular fractions of the pulvinus, the part of the leaf that moves in response to light. He will carry out similar studies of the role of calcium and phosphoinositides in the flagellar shedding by the green alga in response to environmental stresses. These studies will provide important new information on the biochemical mechanisms by which plants respond to changes in their environment. ***
