Relation of gibberellic acid-induced growth of wheat coleoptiles with indole acetic acid

Abstract

Summary Gibberellic acid (GA3) induced elongation of wheat coleoptile sections and its relation with endogenous indole acetic acid was studied. Growth promotion by GA was reduced to half when oxidation of endogenous IAA was prevented by pretreatment of the coleoptiles with EDTA or a mixture of chlorogenic acid and 2,2′-dipyridyl. The effect of GA was reduced to ¼ when the endogenous methyleneoxindole (MeOx), an oxidation product of IAA, was made unavailable to GA3 during its action. External application of hydroxymethyloxindole (HMO), earliest oxidation product of IAA, helped GA to regain its full activity even when oxidation of endogenous IAA was inhibited. It is concluded that endogenous IAA, more precisely, its oxidation products, were necessary for GA in exhibiting its growth promoting activity on wheat coleoptile sections.