Applied auxin gradients and abscission in explants.

The influence of applied auxin on abscission in explants (excised cotyledonary nodes) of cotton was investigated.Proximal applications to the stem stump accelerated abscission with all concentrations applied. Distal applications to the petiole stumps retarded abscission with all concentrations applied.Simultaneous applications to petiole and stem stumps accelerated, retarded, or were without effect on abscission depending on the relative amounts applied. Relatively high concentrations proximal on stem stumps accelerated abscission whereas relatively high concentrations distal on petiole stumps retarded abscission. The abscission rates from various combinations resulted in a multiphasic abscission response curve as the amounts applied were increased.Consideration of these and related data in the literature indicates that many factors can have profound effects on the nature of abscission responses to auxin.