aminoethoxyvinylglycine and indoleacetic-acid

Silver nitrate and aminoethoxyvinylglycine (AVG) are often used to inhibit perception and biosynthesis, respectively, of the phytohormone ethylene. In the course of exploring the genetic basis of the extensive interactions between ethylene and auxin, we compared the effects of silver nitrate (AgNO(3)) and AVG on auxin responsiveness. We found that although AgNO(3) dramatically decreased root indole-3-acetic acid (IAA) responsiveness in inhibition of root elongation, promotion of DR5-beta-glucuronidase activity, and reduction of Aux/IAA protein levels, AVG had more mild effects. Moreover, we found that that silver ions, but not AVG, enhanced IAA efflux similarly in root tips of both the wild type and mutants with blocked ethylene responses, indicating that this enhancement was independent of ethylene signaling. Our results suggest that the promotion of IAA efflux by silver ions is independent of the effects of silver ions on ethylene perception. Although the molecular details of this enhancement remain unknown, our finding that silver ions can promote IAA efflux in addition to blocking ethylene signaling suggest that caution is warranted in interpreting studies using AgNO(3) to block ethylene signaling in roots.

Topics: Arabidopsis; Drug Interactions; Ethylenes; Glucuronidase; Glycine; Growth Inhibitors; Indoleacetic Acids; Plant Roots; Signal Transduction; Silver Nitrate

Using leaf epidermis from Vicia faba, we tested whether auxin-induced stomatal opening was initiated by auxin-induced ethylene synthesis. Epidermis was dark-incubated in buffered KNO3 containing 0.1 mM alpha-napthalene acetic acid or 1 mM indole-3-acetic acid. Maximum net opening was ca. 4 micron after 6 h. Opening was reversed by 20 microM ABA, 0.1 mM CaCl2. 1-Aminocyclopropane carboxylic acid (ACC) synthase catalyzes synthesis of ACC, the immediate precursor to ethylene. Auxin-induced stomatal opening was fully inhibited by 10 microM 1-aminoethoxyvinylglycine (AVG), an ACC synthase inhibitor. In solutions containing AVG, auxin-induced opening was restored in a concentration-dependent manner by exogenous ACC, but not in control solutions lacking an auxin. ACC-mediated reversal of AVG-inhibition of stomatal opening was inhibited by alpha-aminoisobutyric acid (AIB), an inhibitor of ACC oxidase, the last enzyme in the ethylene biosynthetic pathway, by 10 microM silver thiosulfate (STS), an inhibitor of ethylene action, and by 20 microM ABA, 0.1 mM CaCl2. CoCl2, an inhibitor of ethylene synthesis, also inhibited auxin-induced opening. Both STS and CoCl2 inhibited opening induced by light or by fusicoccin, but neither light- nor fusicoccin-induced opening was inhibited by AVG. These results support the hypothesis that auxin-induced stomatal opening is mediated through auxin-induced ethylene production by guard cells.

Topics: Amino Acid Oxidoreductases; Amino Acids, Cyclic; Aminoisobutyric Acids; Cobalt; Ethylenes; Glycine; Indoleacetic Acids; Lyases; Plant Leaves; Rosales; Thiosulfates

We tested the involvement of ethylene in maize (Zea mays L.) root gravitropism by measuring the kinetics of curvature and lateral auxin movement in roots treated with ethylene, inhibitors of ethylene synthesis, or inhibitors of ethylene action. In the presence of ethylene the latent period of gravitropic curvature appeared to be increased somewhat. However, ethylene-treated roots continued to curve after control roots had reached their final angle of curvature. Consequently, maximum curvature in the presence of ethylene was much greater in ethylene-treated roots than in controls. Inhibitors of ethylene biosynthesis or action had effects on the kinetics of curvature opposite to that of ethylene, i.e. the latent period appeared to be shortened somewhat while total curvature was reduced relative to that of controls. Label from applied 3H-indole-3-acetic acid was preferentially transported toward the lower side of stimulated roots. In parallel with effects on curvature, ethylene treatment delayed the development of gravity-induced asymmetric auxin movement across the root but extended its duration once initiated. The auxin transport inhibitor, 1-N-naphthylphthalamic acid reduced both gravitropic curvature and the effect of ethylene on curvature. Since neither ethylene nor inhibitors of ethylene biosynthesis or action prevented curvature, we conclude that ethylene does not mediate the primary differential growth response causing curvature. Because ethylene affects curvature and auxin transport in parallel, we suggest that ethylene modifies curvature by affecting gravity-induced lateral transport of auxin, perhaps by interfering with adaptation of the auxin transport system to the gravistimulus.

Topics: Aminooxyacetic Acid; Biological Transport; Centrifugation; Cobalt; Ethylenes; Glycine; Gravitropism; Herbicides; Indoleacetic Acids; Phthalimides; Plant Growth Regulators; Plant Roots; Silver Nitrate; Time Factors; Zea mays

The present study was designed to establish the role of an essential hormone controlling sex expression in cucumber. A potent anti-ethylene agent, AgNO3, completely inhibited pistillate flower formation caused by IAA, ACC or ethephon. Inhibitors of ethylene biosynthesis, AVG and CoCl2 also suppressed feminization due to exogenous IAA or ACC. Though AVG also suppressed ethephon-induced feminization, this may be due to the second effect of AVG rather than the effect on ACC biosynthesis. These results confirm that ethylene is a major factor regulating feminization and that exogenous auxin induces pistillate flower formation through its stimulation of ethylene production, rather than ACC production.

Topics: Amino Acids; Amino Acids, Cyclic; Antimutagenic Agents; Cobalt; Cucumis sativus; Ethylenes; Glycine; Indoleacetic Acids; Organophosphorus Compounds; Plant Growth Regulators; Silver Nitrate