The effects of syntheticdl-dormin (Abscisin II) on the growth of the oat mesocotyl.

The growth-inhibitory properties of syntheticdl-dormin (Abscisin II) and itstrans, trans isomer were assayed using the oat mesocotyl section. Growth of this tissue was promoted by IAA and GA; dormin inhibited the elongation caused by both compounds and also the small amount of growth that occurred in blank buffer. A given concentration of dormin inhibited growth to about the same proportion in all these cases. IAA and GA mixtures stimulated growth in the presence of 2.0 mg/l dormin slightly more than the sum of growth with IAA+2.0 mg/l and GA+2.0 mg/l dormin. At lower concentrations of dormin (0.02 mg/l and below) the relationship was reversed. Dormin inhibited growth slightly at 0.02 mg/l but below that concentration it had no observable effect.Kinetin did not affect mesocotyl elongation, nor did it interact with the inhibition of IAA- or GA-stimulated growth.Thetrans, trans isomer had 1/30th the activity of the natural 2-cis-4-trans compount; when they were assayed together in mixtures of different proportions the inhibitions were additive.Most experiments were carried out with GA3 but dormin also inhibited the action of gibberellins 1, 4, 5, 6, 7 and 9. The action of dormin was not competitive with that of IAA or GA.The effect of dormin as an inhibitor of plant growth is discussed.