Auxin-induced Ethylene Production and Its Inhibition by Aminoethyoxyvinylglycine and Cobalt Ion

Abstract

Auxin is known to stimulate greatly both C2H4 production and the conversion of methionine to ethylene in vegetative tissues, while aminoethoxyvinylglycine (AVG) or Co2 ion effectively block these processes. To identify the step in the ethylene biosynthetic pathway at which indoleacetic acid (IAA) and AVG exert their effects, 13-14Clmethionine was administered to IAA or IAA-plus-AVG-treated mung bean hypocotyls, and the conversion of methionine to S-adenosylmethionine (SAM), 1-aminocyclopropane-1-carboxylic acid (ACC), and C211 was studied. The conversion of methionine to SAM was unaffected by treatment with IAA or IAA plus AVG, but active conversion of methionine to ACC was found only in tissues which were treated with IAA and which were actively producing ethylene. AVG treatment abolished both the conversion of methionine to ACC and ethylene production. These results suggest that in the ethylene biosynthetic pathway (methionine -* SAM --ACC --C2H) IAA stimulates C2H4 production by inducing the synthesis or activation of ACC synthase, which catalyzes the conversion of SAM to ACC. Indeed, ACC synthase activity was detected only in IAA-treated tissues and its activity was completely inhibited by AVG. This conclusion was supported by the observation that endogenous ACC accumulated after IAA treatment, and that this accumulation was completely eliminated by AVG treatment. The characteristics of Co2' inhibition of IAA-dependent and ACC-dependent ethylene production were similar. The data indicate that Co2+ exerts its effect by inhibiting the conversion of ACC to ethylene. This conclusion was further supported by the observation that when Co2+ was administered to IAA-treated tissues, endogenous ACC accumulated while ethylene production declined.Auxins are known to stimulate ethylene production in a wide variety of plant tissues (1,4,7,8,13,18,25). Many of the effects of auxin on growth and on other processes, such as epinasty, hook opening, inhibition of growth, root induction, and geotropism, are now attributed to its ability to induce ethylene production (1,4,7). In vegetative tissues the rate of ethylene production is thought to be regulated by the internal level of free auxin (1). Cytokinins stimulate ethylene production only slightly, but a remarkable synergistic effect of cytokinins on IAA-induced ethylene production has been observed in etiolated seedlings of several species (4,8,12,13). Auxin-induced ethylene production, as well as other ethylene production systems, are known to be inhibited by AVG2 (2,10,15) and by Co2+ (9,11,14 were germinated and grown in Vermiculite for 3.5 days in darkness at 25 C. Twenty 2-cm-long hypocotyl segments, 1 to 3 cm below the hook, were incubated in 5 ml of a medium consisting of 2% sucrose, 50 ,ug/ml chloramphenicol, and 50 mm Mes buffer (pH 6.1) in a 50-ml Erlenmeyer flask. Where indicated, addenda were 50 ,UM IAA plus 20 ,UM TZ (Tables I, II, and III), 50 ,LM IAA plus 25 ,UM IPA (Table IV, Figs. 1 and 2), 10 ,UM AVG, and 0.2 mm ACC. The flasks were flushed with air...

Functional implications of root cortical senescence for soil resource capture

“…Ethylene has pronounced effects on the rate of RCS. Cobalt(II), a known inhibitor of ethylene synthesis (Yu and Yang 1979), reduced the rate of RCS in root segments on agar media (Lascaris and Deacon 1991b). Seminal and nodal roots treated with exogenous ethylene had 35% and 46% more RCS, respectively compared to the control (aeration) treatment.…”

Ovary and Gametophyte Development Are Coordinately Regulated by Auxin and Ethylene following Pollination.

“…We conducted a series of experiments to determine the effect of various pollination-associated factors and events on ovary development in comparison with senescence-related changes affecting the perianth and whole flower. Figure 7 shows the effect of various pollination-associated factors and events on ethylene production by flowers ( Figures 7A and 78) and the effect of an ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG) (Yu and Yang, 1979). Control flowers left untreated and emasculated flowers did not produce significant amounts of ethylene ( Figure 7A).…”

Inhibition of Ethylene Biosynthesis by Salicylic Acid

“…Kinetics. Measurements of ethylene production from SA inhibited cells in self-buffered growth medium at pH 3.8 were (29). When SA and cobalt were compared, the pattern of slow expression and absence of reversal exhibited by cobalt contrasted sharply with the rapid and reversible inhibition demonstrated by SA (Fig.…”