Involvement of ethylene in the induction of cotton defoliation by the isoindoldione cinidon-ethyl

The effect of the isoindoldione herbicide cinidon-ethyl on leaf abscission and the role of ethylene synthesis in the mechanism of action were studied in cotton (Gossypium hirsutum L. cv. Stoneville 825). Cinidon-ethyl is a ne w inhibitor of protoporphyrinogen IX oxidase in tetrapyrrole biosynthesis, which leads to the formation of 1-aminocyclopropane-1-carboxylic acid (ACC) -derived ethylene as aside effect (K. Grossmann and H. Schiffer. Pestic. Sc i. 55, 687 (1999)). Foliar application of cinidon-ethyl to young cotton pla nts at the fourth leaf stage resulted in a concentration-dependent increase in ethylene evolution and leaf abscission. Concomitantly, the fresh weight of abscised leaves was decreased. Within 2 days, cinidon-ethyl, strictly l ocalized to blades of primary leaves of plants, induced maximum levels of e thylene, ACC, and conjugated ACC in the tissue. Ethane evolution as an indi cator for membrane peroxidation remained unchanged within this period. Betw een the 2nd and 3rd days, a transient rise in ethylene and particularly ACC was observed in the petiole and abscission zone. Subsequently, leaf abscis sion was induced 4 days after treatment. Radiotracer studies showed that ci nidon-ethyl is effective through contact action. After leaf blade applicati on of [C-14]cinidon-ethyl, only trace amounts of C-14 were translocated bas ipetally to the abscission zone. Therefore, it appears that ACC is transpor ted as a signal from the leaf blade to the abscission zone, where metabolic conversion releases ethylene, which is implicated in leaf abscission. In a ccordance, cinidon-ethyl-induced defoliation was gradually reduced by incre asing concentrations of aminoethoxyvinylglycine, an inhibitor of ethylene f ormation. The effect was completely restored by the addition of ACC, (C) 20 00 Academic Press.