Methoxylation modifies the activity of 1,2-benzisoxazole-3-acetic acid: 6,7-dimethoxy-1,2-benzisoxazole-3-acetic acid is an auxin antagonist in cytokinin mediated processes

Abstract

The insertion of a methoxy group in different positions of the aromatic ring modifies the activity of 1,2-benzisoxazole-3-acetic acid (BOAA), a specific morphogenetic compound with no activity on cell elongation or root growth. Monomethoxylation in the 4- and 7-position is critical in determining the kind of activity: 4-OMeBOAA induces stem elongation, inhibits root growth and does not improve shoot production; 7-OMeBOAA inhibits stem elongation and shoot production and is unable to induce root growth. 6,7-OMeBOAA, inactive on stem elongation and root growth, is unable to induce the expression of Pg5-GUS gene in the presence of BAP and inhibits the expression of this gene when induced by BAP plus IAA. Furthermore, 6,7-OMeBOAA inhibits completely shoot production and can therefore be regarded as an auxin antagonist in these cytokinin-mediated processes.