Hormone-directed Transport of Metabolites and its possible Role in Plant Senescence

Abstract

The movement of metabolites and nutrients towards developing seeds, and their accumulation there, appears to play an important role in the regulation of senescence of the shoot in annual plants. The possibility that the directed-transport of nutrients towards developing fruits is regulated by growth hormones has been studied in French bean (Phaseolus vulgaris). Application of 3-indolyl acetic acid (IAA), in lanolin, to peduncles from which the fruits had been removed, resulted in significantly greater accumulation of ³²P (applied to the lower part of the stem) in the region of hormone application than in peduncles treated with lanolin only. When gibberellic acid (GA) or kinetin were applied alone to defruited peduncles they had no significant effect on the accumulation of ³²P at the point of application of hormone, but when either was applied with IAA they greatly enhanced the effect of the latter on movement of ¹⁴C-labelled photosynthates from the leaves to the peduncles. It is suggested that hormone-directed transport may play an important role in directing the movement of nutrients towards developing seeds, which are rich sources of endogenous hormones.