REGULATION OF SENESCENCE BY BENZYLAMINOPURINE AND UNICONAZOLE IN INTACT AND EXCISED SOYBEAN COTYLEDONS

The influence of benzylaminopurine (BA) and uniconazole (UCZ) on the s enescence of 14-day-old soybean (Glycine max) was examined by treating cotyledons on intact plants or excised cotyledon discs. Senescence of the cotyledons, measured as the loss of chlorophylls (Chi) a and b, c arotenoids, protein and increased membrane leakiness, was more rapid i n the excised system. In both systems there were high positive correla tions among the conversion of exogenous ACC (1-aminocyclopropane-1-car boxylic acid) to ethylene, lipoxygenase (EC 1.13.11.12) (LOX) activity and Chl a levels which declined as the cotyledons senesced. However, these correlations were not evident in the BA-treated cotyledons which had relatively high Chi levels. Therefore the results of this study d o not support the contention that LOX activity, ACC conversion and sen escence are interrelated. In both systems BA was more effective in del aying senescence compared to the control and UCZ-treated cotyledons. I n the excised system UCZ tended to hasten while in the intact system U CZ delayed senescence. This study demonstrates that UCZ acts as an ant i-senescence agent-when applied to intact plants and the implications of this in post-harvest physiology warrants further investigation.