Abscisic acid (ABA) inhibits the production of
ethylene induced by
water stress in excised wheat leaves and counteracts the stimulatory effect of
6-benzyladenine (BA) on this process. The stimulatory effect of BA and the inhibitory effect of ABA were equally pronounced whether external or endogenous
ethylene levels were determined. When leaves were sprayed or floated on solutions of BA,
indole-3-acetic acid (IAA),
gibberellic acid (GA3), or ABA, the relative activities of these growth regulators on stress-induced
ethylene at 10(-4) mol l(-1) were BA>IAA >GA3>controls>ABA. In non-stressed leaves, however, where the levels of
ethylene produced were 2-20 times smaller, the relative activities were IAA >BA>GA3>controls>ABA. The effects of BA and ABA spray treatment on
water stress induced
ethylene were closely similar whether the solutions were applied 2 or 18 h prior to the initiation of
water stress. The relationships between the levels of endogenous growth regulators in the plant and
ethylene release induced by
water stress are discussed.