CHANGES IN PLASTID ULTRASTRUCTURE AND PROTEINS DURING THE DEVELOPMENT OF SQUASH FRUITS
We first investigated the ultrastructural changes of plastids of two fruit pigment genotypes of squash with isogenic backgrounds (YY and BB). In YY ovaries at anthesis chloroplasts contained granular osmiophilic bodies and a few thylakoids, having two features of chromoplasts and chloroplasts in the same organs. After anthesis grana structure gradually disappeared and the typical membranous chromoplasts formed at fruit maturity. On the other hand, proplastids observed in BB ovaries transformed directly into chromoplasts as fruits matured. The same fruits at different developmental stages were also used for protein analysis to provide the relationship between changes in ultrastructure and in protein profiles during plastid differentiation. SDS-PAGE showed that qualitatively similar total plasstid polypeptides for two lines at all stages of growth even though there were quantitative decreases or increases in the contents of a few polypeptides. Soluble and membrane associated proteins were extracted from total tissue of subepidermis of squash and showed remarkable differences regarding the relative amounts of many protein species from ovaries and mature fruits. Reduced amounts of the large and small subunits of RuBPCO were obvious especially in immature fruits compared with LS and SS of RuBPCO of squash leaves.