Phytochrome and hormone control of polypeptides synthesized by chloroplasts of senescent barley leaves

To identify the polypeptides involved in the mechanism of leaf senescence, light-driven protein synthesis was assayed with chloroplasts isolated from barley leaf segments incubated during 20 h under different light and hormone treatments affecting senescence. The radioactive products were analyzed by SDS-PAGE and fluorography. The synthesis of some polypeptides was stimulated by ABA (66, 44, 30, 22, 20, kDa) and ethylene (66, 50, 48, 44, kDa) which accelerate senescence. Kinetin and red light (in an effect mediated by phytochrome), which retard senescence, inhibited the synthesis of some polypeptides (50, 48, 37, kDa) and stimulated the synthesis of others (54, 32, kDa). Probably phytochrome and hormones control senescence by affecting the synthesis of specific polypeptides.