RECOVERY OF ETHYLENE BIOSYNTHESIS IN DIAZOCYCLOPENTADIENE (DACP)-TREATED TOMATO FRUIT

Diazocyclopentadiene (DACP), a competitive ethylene action inhibitor b inds irreversibly to the ethylene receptor to reduce tissue responses to ethylene. Tomato fruit (Lycopersicon esculentum Mill cv 'Rondello') were treated with DACP at the mature green stage. Ethylene biosynthes is and respiration rate were depressed. Color changes from green to re d were delayed. Compared to the control, ACC content increased and ACC oxidase activity in vivo decreased in DACP-treated fruit. Thus, decre ase of ethylene production caused by DACP treatment was due to the red uction of ACC oxidase activity. The decline in ripening subsequently r ecovered after DACP treatment. Results from the Northern analysis for gene expression of ACC synthase and ACC oxidase, showed that expressio n of both genes declined in DACP-treated fruit, and then recovered. Th erefore the recovery of ethylene production was due to the recovery in gene expression and activity of ACC oxidase. We conclude that the eff ects of DACP on ethylene biosynthesis are on expression of ACC synthas e and ACC oxidase genes, and/or regulation of ACC oxidase activity.