Chloroplast Protein Synthesis During Barley Leaf Growth and Senescence: Effect of Leaf Excision

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Abstract
Chloroplast protein synthesis was measured during the expansion, maturity and senescence of the oldest leaf of barley, Hordeum vulgare L., var. Hassan. A maximum rate of protein synthesis occurred near the end of the expansion stage 9 d after sowing. Protein synthesis increased again at the beginning of senescence and reached a new maximum at day 14 after sowing. Detachment and incubation of leaves in the dark stimulated chioroplast protein synthesis by fully expanded or by senescent leaves but not by expanding leaves. If the detached leaves were kept in the light, chloroplast protein synthesis was stimulated in fully expanded but not in senescent leaves. Short treatments (18 h) of leaf segments with growth substances in either light or in darkness, significantly changed the rate of protein synthesis shown by chloroplasts. The relationship between chloroplast protein synthesis and leaf senescence is discussed.