[Hormonal regulation of petiolar abscission in Coleus rehneltianus explants : I. Interaction of IAA, GA3, and ABA in explants].

The interaction of gibberellic acid, indoleacetic acid, and abscisic acid in petiolar abscission of explants from Coleus rehneltianus of different age was investigated. It could be demonstrated that there is nearly no change in the ABA-caused velocity of petiolar abscission when GA3 is applied in addition to ABA on senescent and adult explants. If GA3 and ABA are applied simultaneously to young tissue, abscission is accelerated remarkably. One is forced to assume that under natural conditions GA3 is not involved in the process of leaf abscission.Further experimental data show that simultaneous application of IAA and ABA to proximal tissue exerts but a minor influence on petiolar abscission. The longevity of leaves obviously depends on the flux of ABA and IAA from the lamina. Furthermore the results suggest that in some cases ABA causes an increase in sensitivity of tissue to IAA.