Calcium oxalate formation is pervasive in plants and can account for the preponderance of calcium in plant organs. Little is known about the physiology and biochemistry of this form of calcium compartmentation. A procedure has been developed to isolate calcium oxalate-forming cells (crystal idioblasts) as protoplasts from Pistia stratiotes. Using this system soluble and insoluble proteins of crystal idioblast and mesophyll protoplasts will be compared by gel electrophoresis to identify idioblast-specific proteins. Protein components of the specialized crystal chamber membranes and possible existence of crystal matrix proteins will also be explored. Biosynthetic pathways for oxalate synthesis in idioblasts and mesophyll cells will be determined. Calcium binding proteins will be identified on gels and blots by standard techniques. Characteristics of calcium uptake by crystal idioblast and mesophyll protoplasts will be determined by exposure to 45Ca (with and without inhibitors of calcium channels, calmodulin, and ATPases) followed by silicone oil centrifugation. These studies will provide valuable information, unobtainable by other means, about mechanisms and regulation of calcium oxalate formation in plants and will further our understanding of the importance of this phenomenon to calcium metabolism of plant tissues.
