Role of IAA-Oxidase in Abscission Control in Cotton.

The potential role of indoleactic acid (IAA)-oxidase as an in vivo abscission regulating system in the cotton (Gossypium hirsutum L.) cotyledonary explant was investigated. Phenols (usually monophenols), which are cofactors of cotton IAA-oxidase in vitro, accelerated abscission. Phenols (usually orthodihydroxyphenols), which inhibit cotton IAA-oxidase in vitro, inhibited abscission. Inhibition or stimulation of abscission was accomplished by phenols both with and without IAA. Results were similar when treatments were applied as lanolin pastes to the cut petiole ends or as solutions in which explants were submerged. An abscission accelerating phenol stimulated the decarboxylation of IAA-1-(14)C by explants and an abscission inhibiting phenol inhibited the decarboxylation of IAA-1-(14)C.The mechanism of abscission regulation by the phenolic compounds was concluded to involve auxin destruction via IAA-oxidase.In addition to the direct relationship of this study to abscission, the results support the more general hypothesis that IAA-oxidase acts in vivo to regulate auxin levels.