Synthesis of chloroplast proteins by barley leaf segments: effects of senescence induction and kinetin treatment

Synthesis of chloroplast proteins associated with induced leaf senescence in barley (Hordeum vulgare L., var. Hassan) was studied. Leaf segments were incubated for 18-27 h in the dark, floating on distilled water (senescence induction) or on kinetin (senescence retardation). Radioactivity was readily incorporated into plastid protein (followed after different incubation times of leaf segments with [l4C] labelled amino acids) and increased during the first 3 h of incubation. Radioactive plastid polypeptides were analysed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate and fluorography. Several polypeptides (48, 38, 28, 23 and 20 kDa), were synthesized very actively when leaf segments were incubated in the dark, but synthesis was low or absent in greening leaves or when senescence was retarded by kinetin. The results confirm that synthesis of some senescence-specific chloroplast polypeptides is impaired by kinetin treatment.