ABSCISSION IN CITRUS LEAF EXPLANTS: ROLE OF ABA-INDUCED ETHYLENE

Abscisic acid (ABA) stimulates ethylene production and abscission in Shamouti (Citrus sinensis L. Osbeck). The question whether ABA induces abscission directly or whether its action is mediated by ethylene was studied using aminoethoxyvinylglycine (AVG). AVG inhibited ethylene formation, activity of cellulase and polygalacturonase, and abscission in ABA-treated explants.
AVG did not inhibit the increase in the activity of the cell-wall degrading enzymes or abscission in saturating level of externally supplied ethylene.
The data suggest that in citrus leaf explants the induction of abscission by ABA is mediated by ethylene.
The simulatory effect of ABA in ethylene production resulted from enhancement of 1-aminocyclopropane-1-carboxylic acid (ACC) formation.
ABA had little effect on the conversion of ACC to ethylene.

The effect of ABA on ethylene formation was already detected 2 h after the initiation of treatment, suggesting that the effect of ABA is direct and not via enhancement of senescence.
Mature leaves were the most sensitive to ABA while young and senescing leaves were much less responsive.
Mature leaves responded even better after 24 h of aging.
The promotive effect of ABA on ethylene production in intact organs was small but could be increased by various forms of wounding.
This fact raises the question whether ABA is a natural regulator of ethylene production and hence of ethylene mediated processes such as abscission.

VII International Symposium on Plant Growth Regulators in Fruit Production

R. Goren, E. Dagan, O. Sagee, J. Riov, S.F. Yang

aminoethoxyvinylglycine (AVG), 1-aminocyclopropane-1-carboxylic acid (ACC), cellulase, ethylene forming enzymes (EFE), polygalacturonase

https://doi.org/10.17660/ActaHortic.1993.329.5