ABSCISIN,AUXIN, AND GIBBERELLIN EFFECTS ON THE DEVELOPMENTAL ASPECTS OF ABSCISSION IN COTTON (GOSSYPIUM HIRSUTUM)

The effects of accelerating and retarding amounts of abscisin (Ab II), auxin (IAA), and gibberellin (GA₃) on abscission in explants of 14-day-old cotton (Gossypium hirsutum L.) seedlings were studied. Applications of Ab II, a potent accelerant (0.025 μg/abscission zone), resulted in a lysigenous breakdown of cells in a weakly defined separation layer in contrast to GA₃, an accelerant (0.01 μg/abscission zone), and IAA, a retardant (0.125 μg/abscission zone), which resulted in a schizogenous type of breakdown of cells in a well-defined separation layer, three or more rows of cells wide. Separation usually commenced adaxially with GA₃, abaxially with IAA and in the controls, and either ad- or abaxially with Ab II. Cell division preceded abscission, the number of cells increasing greatly within 24 hr after GA₃ treatment. Tyloses formed in vessel elements throughout the explant, both distal and proximal to the plane of separation in all treatments and in the controls. The retardant, IAA, appeared to stimulate tyloses formation. Tylosis development was not causal but was secondarily related to abscission.