Oxindole-3-acetic Acid, an Indole-3-acetic Acid Catabolite in Zea mays.

A prior study (13) from this laboratory showed that oxidation of exogenously applied indole-3-acetic acid (IAA) to oxindole-3-acetic acid (OxIAA) is the major catabolic pathway for IAA in Zea mays endosperm. In this work, we demonstrate that OxIAA is a naturally occurring compound in shoot and endosperm tissue of Z. mays and that the amount of OxIAA in both shoot and endosperm tissue is approximately the same as the amount of free IAA. Oxindole-3-acetic acid has been reported to be inactive in growth promotion, and thus the rate of oxidation of IAA to OxIAA could be a determinant of IAA levels in Z. mays seedlings and could play a role in the regulation of IAA-mediated growth.