The effects of 3,5-diiodo-4-hydroxybenzoic acid on the oxidation of IAA and auxin-induced ethylene production by cress root segments.

In previous research here, 3,5-diiodo-4-hydroxybenzoic acid (DIHB) was shown to promote the elongation of roots of cress (Lepidium sativum) seedlings growing in light, and to inhibit the auxin-induced production of ethylene in this tissue. Although DIHB is a cofactor for the oxidation of indole-3-acetic acid (IAA) by horse-radish peroxidase, it inhibits the decarboxylation of [1-(14)C]IAA by segments excised from cress roots. The inhibition by DIHB of ethylene production by this tissue does not, therefore, arise from a reduction of IAA levels. These findings are discussed in relation to the effects of DIHB on cress root growth.