Abscission responses to moisture stress, auxin transport inhibitors, and ethephon.

The three abscission-inducing agents - water stress, Ethephon, and auxin transport inhibitors-acted synergistically to promote leaf fall in cotton (Gossypium hirsutum L.). However, the synergism was primarily between stress and Ethephon. Auxin transport inhibitors did not promote the effect of stress alone, only promoted the effect of Ethephon in well watered plants and gave a very small promotion with stress and Ethephon together. Abscission was rapid in stressed plants treated with Ethephon and an auxin transport inhibitor, while leaves fell more slowly from well watered plants treated with Ethephon alone. This suggests that water stress or auxin transport inhibitors influence initial events in abscission; since an auxin transport inhibitor will replace the effect of stress but not Ethephon, an initial event in stress-induced abscission appears to be inhibition of auxin transport. Ethephon promoted lateral bud release, and auxin transport inhibitors did not duplicate that effect alone or promote it in combination with Ethephon.