Effect of methyl jasmonate on senescence of broccoli florets

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