Indole-3-acetic acid control on acidic oat cell wall peroxidases

Incubation of oat coleoptile segments with 40 mu M indoleacetic acid (IAA) induced a decrease of 35-60% in peroxidase activity at the cell wall compar tment. Treatment with IAA also produced a similar decrease in the oxidation of NADH and IAA at the cell wall. Isoelectric focusing of ionic, covalent, and intercellular wall peroxidase fractions showed that acidic isoforms (p I 4.0-5.5) were reduced preferentially by IAA treatment. Marked differences were found between acidic and basic wall isoperoxidases in relation to the ir efficacy in the oxidation of IAA. A peroxidase fraction containing acidi c isoforms oxidized IAA with a V-max/s(0.5) value of 2.4 x 10(-2) min(-1) g fw(-1), 4.0 times higher than that obtained for basic peroxidase isoforms (0.6 x 10-2 min(-1) g fw(-1)). In contrast, basic isoforms were more effici ent than acidic isoperoxidases in the oxidation of coniferyl alcohol or fer ulic acid with H2O2 (5.6 and 2.1 times, respectively). The levels of diferu late and lignin in the walls of oat coleoptile segments were not altered by treatment with lAA. The decrease in cell wall peroxidase activity by IAA w as related more to reduced oxidative degradation of the hormone than to cov alent cell wall cross-linking.