Role of protein synthesis and light in the regulation of senescence in detached barley leaves

The role of protein synthesis in senescence and in the inhibition of senescence by light and kinetin was studied in barley (Hordeum vulgare L. cv. Hassan) leaves with different inhibitors of protein synthesis. A comparison of the actions of D‐ and L‐chloramphenicol was made to compensate for the effects of D‐chloramphenicol not mediated by inhibition of protein synthesis. The involvement of phytochrome was also studied. The results suggest that: 1) cytoplasmic protein synthesis is required for senescence in the light and in the dark; 2) chloroplasts, in the dark, synthesize protein which accelerates senescence; 3) kinetin inhibits the synthesis by chloroplasts of senescence‐accelerating protein; 4) light changes the type of protein synthesized by chloroplasts from those accelerating to those retarding senescence; and 5) lightretar‐dation of senescence is mediated by phytochrome and, probably, by photophos‐phorylation.