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Protein Body Composition in Cuburbita maxima Cotyledons as Determined by Energy Dispersive X-Ray Analysis ¹

^a Department of Biology, McMaster University, Hamilton, Ontario, Canada, L8S 4K1

Energy dispersive x-ray analysis was used to study the composition of certain protein body components in Cucurbita maxima cotyledons. The globoid crystal was rich in phosphorus, potassium, and magnesium. This elemental composition provides further evidence that the globoid crystal in squash cotyledon protein bodies is composed of phytin, a myoinositol hexaphosphoric acid salt of potassium and magnesium. Calcium, a common component of phytin in many species, was absent or present in only trace amounts in the globoid crystals of squash. Results of analyses of globoid crystals from seeds produced in different parts of North America suggest that there is definite specificity for the cations used in phytin deposition. Variations in soil types and other environmental factors seem not to have influenced the type of cation stored. Energy dispersive x-ray analysis of the proteinaceous regions revealed the presence of phosphorus, sulfur, and a trace of chlorine. Sulfur was expected, due to the presence of some sulfur containing amino acids in the protein.