REGULATION OF THE RIPENING OF TOMATO PERICARP DISKS BY GA(3) AND DIVALENT-CATIONS

We have used a tomato (Lycopersicon esculentum Mill.) pericarp disc system to study the inhibition of ripening caused by diazocyclopentadiene (DACP), gibberellic acid (GA(3)) and calcium (CaCl2), and to compare their modes of action. Treatment of discs with 1-aminocyclopropane carboxylic acid (ACC) accelerated their ripening while DACP treatment eliminated ripening in the absence or presence of a treatment with the ethylene precursor. Both GA(3) and calcium retarded color development and tissue softening. Calcium delayed the onset of the climacteric rise in respiration and ethylene evolution, but GA(3) had no consistent effect in this respect. The different modes of action of the two inhibitors were emphasized by the synergistic effect on inhibition of ripening obtained when both were simultaneously applied. Inhibition of color development and softening was also achieved by applying other divalent cations such as strontium and barium. However, no such effect was observed with manganese or with the monovalent cations potassium and sodium. We concluded that calcium inhibition of ripening is not specific and is not necessarily mediated by the calcium calmodulin complex.