Grapevine fruit set: Physiology of the abscission zone

Effects of ethylene and of 'anti-ethylene' compounds on the floral pedicel abscission zone in grapevines were analysed via a laboratory model consisting of isolated flowers held in Petri dishes. Our model permitted precise determination of abscission and enabled us to test a range of physiologically-active compounds including ethylene precursors, and antagonists of ethylene action. For example, a precursor of ethylene, 1-aminocyclopropane-l-carboxylic acid, had the same effect as ethylene in promoting abscission. Conversely, an inhibition of ethylene action by silver thiosulfate or an inhibition of ethylene synthesis by amino-oxyacetic acid both strongly inhibited abscission zone function. The same type of effect can be obtained by increasing the proportion of auxin with regard to ethylene. The abscission zone of the isolated flower pedicel of grapevine conforms to the classic model of hormone-mediated operation of a pre-existing abscission zone. Our definition of hormone regulation holds practical implications for viticulture and offers new possibilities for controlling berry drop.