Effect of Photoperiod on Polyamine Metabolism in Apical Buds of G2 Peas in Relation to the Induction of Apical Senescence

Polyamine content and arginine decarboxylase activity of apical buds were measured to determine whether polyamines are required to prevent apical senescence in pea. Polyamines were assayed as dansyl derivatives which were separated by reverse phase high performance liquid chromatography and detected by fluorescence spectrophotometry. High polyamine concentrations were found in the vigorous apices of plants grown under a short day photoperiod during which senescence is delayed. As the apex senesced in long days, the amounts of polyamines per organ declined in parallel with decreases in the size of the apical bud. However, a decrease in polyamine concentration, due mainly to a change in spermidine, occurred at the time of marked reduction in bud size and growth rate, but not before the onset of the early symptoms of senescence. No correlation was found with arginine decarboxylase. The results suggest polyamines may be required to support bud growth, but the photoperiodic mechanism which governs apical senescence of G2 peas does not exert control through polyamine metabolism.