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.