THE INTRAVACUOLAR ORGANIC MATRIX ASSOCIATED WITH CALCIUM-OXALATE CRYSTALS IN LEAVES OF VITIS

In Vitis (grape) calcium oxalate crystals form in a needlelike morphol ogy unique to plants, presenting an intriguing system of biological co ntrol over mineral formation. Crystals develop within an organic matri x which appears to provide control over the sites and forms of crystal deposition; however, little is known about the chemical nature of the matrix. A procedure has been developed to isolate crystals along with their associated intravacuolar matrix from leaves of grape, and studi es have been initiated into the chemical composition of the matrix by characterizing elemental content, carbohydrates, and protein. The isol ated matrix consisted of two structural phases, membrane chambers encl osing developing crystals, and a water-soluble phase surrounding the c rystal chambers. Elemental analysis detected substantial calcium and p otassium, as well as some iron in the water-soluble phase. Analysis of the water-soluble matrix by GC-MS showed that it contained an unusual polymer with novel glucuronic acid linkages. In addition, linkage ana lysis indicated 5-linked arabinans, arabinogalactan, and various manno syl units typical of complex carbohydrates of N-linked glycoproteins. SDS-PAGE analysis of the water-soluble matrix and crystal chambers sho wed that each had distinct banding profiles in silver-stained gels, wi th prominent 60 and 70 kDa polypeptides in crystal chamber extracts. D emineralization studies provided direct evidence that the isolated mat rix promotes crystal nucleation. The findings about the organic matrix associated with calcium oxalate crystals in grape are discussed in re lation to crystal nucleation and growth and features shared with anima l and microbial biomineralization systems.