GIBBERELLIN-INDUCED DELAY OF LEAF SENESCENCE OF ALSTROEMERIA CUT FLOWERING STEMS IS NOT CAUSED BY AN INCREASE IN THE ENDOGENOUS CYTOKININ CONTENT

The effects of various chemically pure gibberellins and cytokinins on leaf yellowing of Alstroemeria were described. The loss of chlorophyll was measured both in leaves of cut flowering stems and in a model sys tem consisting of detached leaf tips. It was demonstrated that plant g rowth substances affected chlorophyll loss in both systems to the same extent. Leaf senescence was delayed by various gibberellins and cytok inins. The results demonstrated that some of the gibberellins (GA, and GA,) are far more effective in delaying chlorophyll loss than GA,, wh ich is commonly used as a postharvest treatment for Alstroemeria cut f lowering stems. Immunoassays were used to demonstrate that the effect of gibberellins on leaf yellowing does not involve an increase in the endogenous cytokinin concentrations in the leaves as an intermediate s tep.