Studies on Auxin Protectors. V. On the Mechanism of IAA Protection by Protector-I of the Japanese Morning Glory

Abstract

Abstract. The mechanism of auxin protection by auxin protector-I (Pr-I) of

Studies on Auxin Protectors. VII. Association of Auxin Protectors With Crown Gall Development in Sunflower Stems

“…Thus auxin protection is greatest in leaves and interriodes elongating most rapidly, and diminishes as the tissue matures (29,30). Similar substances have been identified in other plants such as tobacco (15,16), cocklebur, Kalanchoe, Nicotiana affinis, N. glauca, N. ri'stica, sunflower, and tomato (24, and (25).…”

“…The association of high levels of auxin protectors with the juvenile state will be reported elsewhere, as will a more detailed discussion of why these substances are probably causally related to the juvenile state. Suffice it to point out here that protector-I of the Japanese morning glory exerts its protecting activity by acting as an antioxidant which interferes with the peroxidase-catalyzed oxidation of IAA (22,25). Preliminary experiments have indicated that this is also true of protectors A anid II, and that all 3 protectors may act as poisers, stabilizing the redox state of chemical systems, not merely the oxidation of IAA.…”

“…The "high molecular weight" auxin protectors are labile substances that are readily oxidized upon exposure to air, especially in the presence of Mn2' and a phenolic cofactor (22,25), as used by Lipetz and Galston. Thus it is possible for crown gall tissue to both contain more enzvme and yet destroy less auxin.…”

Proposed Model for the Peroxidase-Catalyzed Oxidation of Indole-3-acetic Acid in the Presence of the Inhibitor Ferulic Acid

“…Both indole-3-acetic acid and ferulic acid are substrates of horseradish peroxidase in the presence of H202, and indole-3-acetic acid competitively inhibits the oxidation of ferulic acid. A model for the enzymatic oxidation of indole-3-acetic acid catalyzed by peroxidase is proposed.It is well established that plants contain enzymes (5,11,15,(18)(19)(20)21). Most inhibitors are of low molecular weight, although Stonier et al (18,20) reported phenolic inhibitors from Pharbitis with molecular weights of 5,000 to 10,000, based upon behavior on sephadex gels.…”

“…Most inhibitors are of low molecular weight, although Stonier et al (18,20) reported phenolic inhibitors from Pharbitis with molecular weights of 5,000 to 10,000, based upon behavior on sephadex gels. The association of high inhibitor concentrations with actively growing tissues suggests that inhibitors promote growth by preventing IAA destruction by endogenous IAA oxidase-the "auxin protector" concept of Stonier and Yoneda (20).Several workers have sought to clarify the mechanism(s) by which phenolic inhibitors delay the peroxidase-catalyzed oxidation of IAA (15,(18)(19)(20)21 Gordon and Weber (6). Two ml of test solution were mixed with 4 ml of reagent, and absorbance was measured at 525 nm on a Coleman 46 spectrophotometer equipped with a Gilson transferator.…”