This research investigates the mechanisms of calcium action in plant cells. Calcium is a very important regulatory molecule in all eukaryotes. It is thought to play a role as an intracellular messenger that couples physiological responses to external stimuli. The calcium binding proteins have been extensively studied in animals. In this project, the potential targets of calcium action will be investigated in plants. The goal of the research is to advance our understanding of how calcium mediates the effects of environmental stumuli on plant cells. The green alga Mougeotia has been selected as the experimental organism because it is an attractive biological model of calcium- dependent regulation in plants. The approach will involve purification and characterization of the molecular targets of calcium in Mougeotia: calcium-stimulated proteins and enzymes. The focus will be on a recently discovered calcium stimulated protein kinase of Mougeotia. The purification and characterization of the protein kinase will be carried out. Particular emphasis will be on the elucidation of the molecular basis of calcium regulation by identifying the calcium-binding effector molecules that regulate the activity. Also, in order to determine the role of this kinase in Mougeotia, in vitro and in vivo phosphorylation assays will be used to identify the substrates of the protein kinase. The effects of phosphorylation on the in vitro activities of these substrates will be assessed. The changes in in vivo substrate phosphorylation levels under conditions that trigger or suppress calcium-dependent responses also will be determined.//
