Quantitative Changes in Gibberellin and Rna Correlated With Senescence of the Shoot Apex in the ‘Alaska’ Pea

Senescence of shoot apices of Pisum sativum L. ‘Alaska’ as measured by cessation of stem elongation was delayed by removal of flowers and by treatment with gibberellin A 3 and was hastened by treatment with AMO‐1618 (2 isopropyl‐4‐dimethylamino‐5‐methylphenyl‐1‐piperi‐dinecarboxylate methyl chloride). Ontogenetic changes in relative endogenous gibberellin levels and in capability of gibberellin biosynthesis in deflowered and control plants were determined indirectly by studying time‐course changes in the sensitivity, as indicated by the growth response, of these plants to applied gibberellin and AMO‐1618. The results of these experiments suggest that the endogenous gibberellin level varies directly with the growth rate. Analyses of total RNA and protein in shoot tips of deflowered and control plants revealed that the levels of these substances also vary directly with growth rate throughout ontogeny. It is concluded that decreases in endogenous gibberellin, RNA and protein are factors correlated with senescence of the shoot apex.