ISOLATION AND CHARACTERIZATION OF A CHROMOPLAST-SPECIFIC CAROTENOID-ASSOCIATED PROTEIN FROM CUCUMIS-SATIVUS COROLLAS

The differentiation of chloroplasts to chromoplasts in corollas of cuc umber (Cucumis sativus) is subject to developmental control. To study factors involved in the chloroplast-chromoplast conversion, a chromopl ast-specific protein of 35 kD was isolated, and polyclonal antibodies were prepared against it. This protein was found to be a principal com ponent of the carotenoid-protein complex resolved from chromoplast mem branes by nondenaturing gel electrophoresis. Immunological studies rev ealed that expression of this protein is regulated in a temporal and t issue-specific manner. Its steady-state level increased in parallel wi th flower development and carotenoid accumulation, peaking in mature f lowers and then rapidly decreasing to very low levels. The protein was not detectable in cucumber leaves or fruits. To ascertain whether an organ-specific system regulates the chloroplast-chromoplast conversion and to enable future molecular studies of factors involved in this re gulation, an in vitro bud culture system was established. Patterns of expression of the 35-kD protein and carotenoids in corollas of detache d buds were similar to those in intact buds.