RNA AND PROTEIN METABOLISM IN SENESCENT SHOOT APICES OF ‘ALASKA’ PEAS

Abstract

Senescence of shoot apices of Pisum sativum L. ‘Alaska’ as measured by cessation of stem elongation was delayed by removal of flowers. Analyses of total RNA, nitrogen, protein and inorganic phosphorus in shoot tips of deflowered and control (flower‐ and fruit‐bearing) plants throughout ontogeny revealed that the levels of all these metabolites declined during senescence. Also throughout ontogeny shoot tips of control and deflowered plants were compared with respect to their ability to enzymically degrade RNA and to take up and incorporate P32‐orthophosphate into RNA. The specific activity of ribonuclease increased as senescence progressed while the absolute activity appeared to decrease in correlation with a decrease in total nitrogen content. Compared with nonsenescing shoot tips, senescing shoot tips accumulated less P32 but exhibited an apparent enhancement of P32 incorporation into RNA, which was attributed to a reduction in the endogenous phosphorus pool causing a smaller dilution of the accumulated P32. It is concluded that decreases in the levels of RNA, protein and inorganic phosphorus and in the tran‐spirational uptake of nutrients are factors correlated with senescence of the shoot apex.