Mechanism of indole-3-acetic acid oxidation by plant peroxidases: anaerobic stopped-flow spectrophotometric studies on horseradish and tobacco peroxidases

Abstract

Indole-3-acetic acid (IAA) is a powerful plant growth regulator. The oxidative decarboxylation of IAA by plant peroxidases is thought to be a major degradation reaction involved in controlling the in vivo level of IAA. Horseradish peroxidase isoenzyme C and an anionic tobacco peroxidase isolated from transgenic Nicotiana sylvestris have been used in experiments in vitro designed to determine the mechanism of IAA oxidation. In particular, the initial reduction of ferric to ferrous enzyme, a key step in previously proposed mechanisms, has been investigated by rapid-scan stopped-flow spectrophotometry under strictly anaerobic conditions and at defined oxygen concentrations. The data provide the first evidence for a ternary complex comprising peroxidase, IAA and oxygen that is kinetically competent both at the initiation stage and during the catalytic cycle of IAA oxidation. A general scheme describing the oxidative cycles of both anionic and cationic peroxidases is proposed that includes native ferric enzyme and compound II as kinetically competent intermediates. For anionic peroxidases, addition of hydrogen peroxide switches on the oxidative cycle thereby promoting IAA oxidation. 2-Methyl-IAA is not a substrate of the oxidase reaction, suggesting a specific interaction between plant peroxidases and IAA.

The Emerging Role of Reactive Oxygen Species Signaling during Lateral Root Development

“…Peroxidase activity is also related to cell stem maintenance and cell division and differentiation in the root meristem (Jiang and Feldman, 2005;Tsukagoshi et al, 2010). It is remarkable that plant peroxidase activities have the ability to catalyze IAA (Gazaryan et al, 1996;Cosio et al, 2009), reducing the active auxin pool. Overexpression of an anionic PER in tobacco (Nicotiana tabacum) plants repressed LR formation, likely by oxidizing the IAA and reducing the active auxin needed for the formation of the lateral primordia (Lagrimini et al, 1997).…”

Hydrogen peroxide-independent generation of superoxide catalyzed by soybean peroxidase in response to ferrous ion

“…25 The series of ferrous-dependently stimulated reactions can be divided into several steps, namely, conversion of native enzyme into ferrous intermediate, O 2 25 IAA is an effective inducer of H 2 O 2 -independent O 2 ¡ generation in POX system, 15,26 but at the same time it is also consumed by conventional POX cycle initiated by IAA-dependently produced O 2 ¡ (and derived H 2 O 2 ). 13,14,16,19 Therefore, longlasting action could not be observed. Obviously, Fe 2C is neither consumed by conventional POX cycle nor involved in removal of O 2 ¡ .…”

“…By analogy to the experimental procedure for HRP, 19 spectroscopic determination of SBP concentration was performed based on the measurement of the concentration of heme (e 403nm D 102 mM ¡1 cm ¡1 ). Changes in absorption spectra of SBP in 20 mM K-phosphate buffer (pH 7.0) were recorded on spectrophotometer (Shimadzu UV-1800, Kyoto, Japan) at room temperature with a spectral bandwidth of 1.0 nm in a cuvette with 1-cm light path.…”

Tansley Review No. 111

“…IAA is extremely sensitive to OHd, and can be oxidized rapidly upon exposure to high concentrations of OHd (Brennan & Frenkel, 1983 ;Cakmak, 1988 ;Dunlop & Robacker, 1988). Besides nonenzymic oxidation, IAA is also oxidized by H # O # -dependent peroxidases (Schneider & Wightman, 1975 ;Gazaryan et al, 1996), and O # d − and "O # are involved in this degradation pathway (Metodiewa et al, 1992 …”