Effect of Methyl Jasmonate on Senescence of Broccoli Florets

Broccoli (Brassica oleracea L. cv Italica) florets senesced rapidly after harvest at ambient temperatures. During senescence at 20°C, the rate of ethylene production of florets significantly increased, concurrent with a rapid yellowing of sepals ascribed to chlorophyll degradation. 1-Aminocyclopropane-1-carboxylic acid (ACC) oxidase activity in florets also rapidly increased to a peak ; the enzyme activity then declined sharply, paralleling the increased pattern of ethylene production. Treatment of florets with 1 mM methyl jasmonate (MJ) significantly promoted ethylene production and ACC oxidase activity during senescence, attaining a higher peak faster than the control. Chlorophyll loss and a concurrent enhancement of ACC synthase activity by exogenous 1 mM MJ were accelerated to a greater extent than those of the control. The rise in ethylene production was reduced and delayed by treatment with 10 mM diethyldithiocarbamate (DIECA) that is thought to be an inhibitor of jasmonate biosynthesis. These results suggest that jasmonates may be associated with promoting senescence by enhancing ethylene production in broccoli florets.