ISOLATION AND REGULATION OF ACCUMULATION OF A MINOR CHROMOPLAST-SPECIFIC PROTEIN FROM CUCUMBER COROLLAS

The differentiation of chloroplasts to chromoplasts in cucumber (Cucum is sativus L.) corollas parallels flower development. Chromoplast biog enesis involves chlorophyll degradation, carotenoid accumulation, and the appearance of a new set of proteins. To study factors involved in chromoplast biogenesis in floral tissues, a minor (in abundance) prote in of about 14 kD, CHRD (chromoplast protein D), was isolated from cuc umber corolla chromoplasts. Immunological characterization revealed th at the protein is chromoplast-specific and that its steady-state level in corollas increases in parallel to flower development. The protein was not detected in cucumber leaves or fruits. Immunological analysis of corollas and fruits from a variety of other plants also did not rev eal cross-reactivity with the CHRD protein antisera. Using an in vitro bud culture system, we analyzed the effect of phytohormones on CHRD e xpression. Gibberellic acid rapidly enhanced, whereas paclobutrazol do wn-regulated, the steady-state level of CHRD. Ethylene also down-regul ated the protein's steady-state level. It is suggested that hormonal c ontrol of chromoplastogenesis is tightly regulated at the tissue/organ level and that mainly developmental signals control carotenoid accumu lation in nonphotosynthetic tissues.