Abscission of grapevine fruitlets in relation to ethylene biosynthesis

The ethylene content of grapevine (Vitis vinifera, cv. Chardonnay) flowers and fruitlets was followed during flowering, i.e. from stage 18 to stage 32 (EICHHORN and LORENZ 1977). A strong rise of ethylene was observed at the beginning of abscission, corresponding to stage 23. High levels of ethylene were found in the whole period in which abscission occurred, indicating a possible role of ethylene in grapevine fruitlet abscission. The rise of ethylene was associated with a rise of 1-aminocyclopropane-1-carboxylic acid (ACC) content and ACC oxidase activity. At the end of abscission (stage 28-29), the levels of ethylene, ACC and ACC oxidase activity decreased to a level close to that at pre-bloom. The ethylene evolution in two clones with different sensitivity to berry drop revealed the relationship between ethylene and the intensity of abscission, and confirmed that the abscission promoting effect of ethylene depends on the phenological stage. Results are discussed with regard to possible hormonal interactions between ethylene, ACC, ACC oxidase and abscisic acid.