Auxin-induced Ethylene Production Research Articles

Auxin-activated MdARF5 induces the expression of ethylene biosynthetic genes to initiate apple fruit ripening.

Summary The gaseous plant hormone ethylene induces the ripening of climacteric fruit, including apple (Malus domestica). Another phytohormone, auxin, is known to promote ethylene production in many horticultural crops, but the regulatory mechanism remains unclear.Here, we found that auxin application induces ethylene production in apple fruit before the stage of commercial harvest, when they are not otherwise capable of ripening naturally.The expression of MdARF5, a member of the auxin response factor transcription factor (TF) family involved in the auxin signaling pathway, was enhanced by treatment with the synthetic auxin naphthaleneacetic acid (NAA). Further studies revealed that MdARF5 binds to the promoter of MdERF2, encoding a TF in the ethylene signaling pathway, as well as the promoters of two 1‐aminocyclopropane‐1‐carboxylic acid synthase (ACS) genes (MdACS3a and MdACS1) and an ACC oxidase (ACO) gene, MdACO1, all of which encode key steps in ethylene biosynthesis, thereby inducing their expression. We also observed that auxin‐induced ethylene production was dependent on the methylation of the MdACS3a promoter.Our findings reveal that auxin induces ethylene biosynthesis in apple fruit through activation of MdARF5 expression.

Effect of benzyladenine (BA) on auxin-induced stem elongation and thickening in tulip (Tulipa gesneriana L.)

It is well known that stem elongation in tulip is induced by the auxin produced in the leaves and gynoecium. Excision of the flower bud and all the leaves in an early stage of tulip growth resulted in almost total inhibition of stem growth, but the inhibition was completely recovered by the exogenous application of auxin to the place from which the flower bud had been removed. Hormonal control of stem thickening in tulip is much less known. Additional application of benzyladenine (BA) to the tulip stem by soaking a cotton wick wrapped around all the internodes only slightly inhibited stem growth induced by IAA at a concentration of 0.1 and 2.0%, but substantially stimulated the thickening of all the internodes. The treatment of the tulip stem with benzyladenine enabled direct contact of the cytokinin with the epidermis, which is an important factor in stem elongation. The experiment conducted in field conditions also showed that BA only slightly inhibited the elongation of the fourth internode induced by IAA, but stimulated the thickening of that internode. IAA applied at a concentration of 2.0% stimulated ethylene production to a much higher extent than IAA at a concentration of 0.1%, and BA affected the auxin-induced ethylene production only to a small extent. Metabolic significance of these findings is discussed.

Reactive oxygen species mediate IAA-lnduced ethylene production in mungbean (Vigna radiata L.) hypocotyls

We reported previously that ROS may function as a downstream component for signaling auxin, a hormone that induces the ethylene production. Here we demonstrated that ROS can act upstream to promote auxin-induced ethylene production in mungbean hypocotyls. When plants were treated with AVG, ethyiene biosynthetic inhibitor, or ACC, ethylene precursor, we found that little effect on the ROS generation. Hypocotyls exposed to H2O2 showed higher ethylene accumulations compared with untreated samples. Furthermore, auxin-induced ethylene production was reduced when tissues were pre-treated with a ROS scavenger, N-acetyl-L-cystein (NAC). We attributed this stimulatory effect to the activation of ethylene biosynthetic enzymes that results from transcriptional up-regulation ofVR- ACS1 andVR- ACS7 to encode ACC synthase, as well as ofVR- ACO1 andVR- ACO2, which encode ACC oxidase.

Inhibitors of ethylene synthesis inhibit auxin-induced stomatal opening in epidermis detached from leaves of Vicia faba L.

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.

Inhibition of auxin-induced ethylene production by salicylic acid in mung bean hypocotyls

Salicylic acid (SA), a common plant phenolic compound, influences diverse physiological and biochemical processes in plants. To gain insight into the mode of interaction between auxin, ethylene, and SA, the effect of SA on auxininduced ethylene production in mung bean hypocotyls was investigated. Auxin markedly induced ethylene production, while SA inhibited the auxin-induced ethylene synthesis in a dose-dependent manner. At 1 mM of SA, auxininduced ethylene production decreased more than 60% in hypocotyls. Results showed that the accumulation of ACC was not affected by SA during the entire period of auxin treatment, indicating that the inhibition of auxin-induced ethylene production by SA was not due to the decrease in ACC synthase activity, the rate-limiting step for ethylene biosynthesis. By contrast, SA effectively reduced not only the basal level of ACC oxidase activity but also the wound-and ethylene-induced ACC oxidase activity, the last step of ethylene production, in a dose-dependent manner. Northern and immuno blot analyses indicate that SA does not exert any inhibitory effect on the ACC oxidase gene expression, whereas it effectively inhibits both the in vivo and in vitro ACC oxidase enzyme activity, thereby abolishing auxin-induced ethylene production in mung bean hypocotyl tissue. It appears that SA inhibits ACC oxidase enzyme activity through the reversible interaction with Fe2+, an essential cofactor of this enzyme. These results are consistent with the notion that ethylene production is controlled by an intimate regulatory interaction between auxin and SA in mung bean hypocotyl tissue.

Effect of ethylene antagonists on auxin-induced inhibition of intact primary root elongation in maize (Zeamays L.)

Root elongation was measured in intact primary roots of maize(Zea mays L.) using a computerized root auxanometer. We examined the fact that root elongation was inhibited by auxin-induced ethylene production. Inhibition of root elongation was closely correlated with the concentrations of the exogenously applied auxin. Auxin-induced inhibition of root elongation was reversed by pretreatment or posttreatment of ethylene biosynthesis antagonists such as aminoethoxyvinylglycine (AVG) and silver ions (Ag2+). The magnitude of recovery effect was dependent on auxin concentrations. Root elongation was inhibited by adding ethylene producing agents such as 1-aminocyclopropane-l-carboxylic acid (ACC) and Ethephon. ACC- and Ethephon-induced inhibition of root elongation was reversed by blocking ethylene biosynthesis or activity. These data suggested that ethylene was involved in auxin-induced inhibition of root elongation and inhibition of root elongation by applied auxin, at least in part, was a reversible process.

Auxin-Induced Epinasty of Tobacco Leaf Tissues (A Nonethylene-Mediated Response).

Interveinal strips (10 x 1.5 mm) excised from growing tobacco (Nicotiana tabacum L. cv Xanthi) leaves curled >300[deg] when incubated for 20 h in 5 to 500 [mu]M [alpha]-naphthalene acetic acid or 50 to 500 [mu]M indole-3-acetic acid. Epinasty was not induced without auxin or by the auxin analog [beta]-naphthalene acetic acid, and less substantial epinasty was induced in midrib and vein segments. Auxin treatment increased the length of both surfaces of strips. Curvature resulted from greater growth on the adaxial side. Epinastic sensitivity of strips to auxin appeared first in the distal third of young leaves (blade 4.5-6.0 cm). In older leaves (8-10 and 12-14 cm), the interveinal tissues throughout were sensitive, whereas in leaves 16- to 18-cm long, sensitivity was reduced in the distal two-thirds. Amino-oxyacetic acid (AOA), an ethylene biosynthesis inhibitor, partially inhibited epinasty at 100 [mu]M. However, a poor correlation between inhibition of ethylene biosynthesis by AOA and its inhibition of curvature and the inability of ethylene to produce epinasty or to reverse the effects of AOA suggests that auxin-induced epinasty is not caused by auxin-induced ethylene production.

VR-ACS6 is an Auxin-Inducible l-Aminocyclopropane-l-carboxylate Synthase Gene in Mungbean (Vigna radiata)

We have isolated four cDNA clones of ACC synthase from etiolated mungbean seedlings treated with auxin. pVR-ACS2, pVR-ACS3 and pVR-ACS6 contained the same sequences as the previously reported DNA fragments, pMAC2, pMAC3 (Botella et al. 1992b) and pMBA1 (Kim et al. 1992), respectively. pVR-ACS1 was identical with pAIM-1 (Botella et al. 1992a). VR-ACS6 was specifically induced in response to the auxin signal. The IAA-induction of VR-ACS6 was very rapid (within 30 min) and insensitive to cycloheximide treatment at concentrations up to 100 microM. Significant accumulation of VR-ACS6 mRNA was detected at 1 microM IAA. The IAA-induced expression of VR-ACS6 was suppressed by ABA and ethylene, but enhanced by BA. These characteristics of VR-ACS6 expression were well correlated with the physiological data of auxin-induced ethylene production in mungbean hypocotyls. VR-ACS1 was strongly induced by cycloheximide, but was found to be not auxin-specific. Inhibitors of either ethylene biosynthesis (AOA) or action (NBD) increased the basal level of VR-ACS1 mRNA.

Inhibition of auxin-induced ethylene production in cucumber fruit discs by carbon dioxide

The induction of ethylene biosynthesis by indole-3-acetic acid (IAA) and its regulation by CO 2 was examined in cucumber ( Cucumis sativus L., var. Sharp-1) fruit discs. Treatment of discs with IAA significantly stimulated ethylene production and the extent depended on IAA concentration upto 1 mM. The increase in IAA-induced ethylene production was accompanied by increase in the activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase (also known as ethylene-forming enzyme) and a massive accumulation of ACC and 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC). The induction of ethylene production by IAA was inhibited by treatment with CO 2 . The extent of inhibition was dependent upon the concentration of CO 2 . Carbon dioxide inhibited IAA-induced ethylene biosynthesis by suppressing ACC synthase and ACC oxidase activities. Additionally, CO 2 inhibited ACC conjugation into MACC. The results indicate that inhibition of ethylene production by CO 2 in cucumber fruit discs following IAA treatment is due to inhibition of both ACC synthesis and ACC oxidation.

Effect of Surfactants on Foliar Penetration of NAA and NAA-induced Ethylene Evolution in Cowpea

Abstract Effects of the surfactants Pace, Regulaid and Tween 20 were determined on foliar penetration of NAA and on NAA-induced ethylene production by cowpea [Vigna unguiculata (L.) Walp. subsp. unguiculata cv. Dixielee]. All three surfactants decreased surface tension of NAA solutions, causing a marked increase in wetting and in droplet : leaf interface area. The greatest increase in NAA penetration was obtained with Regulaid followed by Pace and Tween 20. The surfactant effect was most pronounced during the droplet drying phase, but penetration continued to take place from the deposit after drying. The mode of action of surfactants in enhancing NAA penetration is complex. Regulaid-enhanced penetration closely paralleled the increase in interface area, but similar relationships were not found for Pace or Tween 20, particularly at concentrations above the critical micelle concentration. Surfactant-enhanced NAA penetration caused an increase in NAA-induced ethylene production. There was a strong correlation (r = 0.82) between NAA penetration and ethylene production for doses of 0.5 to 2.5 μg/disk. Above 2.5 μg/disk, ethylene production increased at a decreasing rate. The potential for using auxin-induced ethylene production as an index for quantifying auxin penetration is discussed. Chemical names used: l-naphthaleneacetic acid (NAA), polyoxyethylene polypropoxypropanol dihydroxypropane (Regulaid), polyoxyethylene (20) sorbitan monolaurate (Tween 20), surfactant blend in paraffin base petroleum oil (Pace).

NAA-induced Leaf Epinasty in Chrysanthemum

Abstract Leaves of ‘Mountain Snow’ chrysanthemums (Chrysanthemum morifolium Ramat.), sprayed with 10 mm NAA or 10 mm NAAEE, exhibited severe epinasty after 24 hr, while leaves sprayed with 5 mm ethephon did not. Treatment with 100 μm AOA 24 hr before application reduced ethylene production rate of leaves, but not epinasty. Localized application of NAA to adaxial, abaxial, or both leaf surfaces resulted in similar amounts of leaf epinasty. Epinastic leaves had enlarged adaxial epidermal cells. Size of abaxial epidermal cells was unchanged. This study provides evidence that leaf epinasty of chrysanthemum following NAA application is not the result of auxin-induced ethylene production. Chemical names used: (aminooxy)acetic acid (AOA); 1-naphthaleneacetic acid (NAA); 1-naphthaleneacetic acid ethyl ester (NAAEE); and (2-chloroethyl)phosphonic acid (ethephon).

High Temperature Sensitivity of Auxin-induced Ethylene Production in Mung Bean Hypocotyl Sections

High Temperature Sensitivity of Auxin-induced Ethylene Production in Mung Bean Hypocotyl Sections

Epidermal Cells Do Not Contribute to Auxin-Induced Ethylene Production in Mung Bean Stem Sections

Epidermal Cells Do Not Contribute to Auxin-Induced Ethylene Production in Mung Bean Stem Sections

Effect of silver ions and ethylene on auxin metabolism and auxininduced ethylene production in tobacco leaf discs

The antagonistic effects of ethylene and Ag+ on the metabolism of [1‐14C]indole‐3‐acetic acid (IAA) and on the rates of ethylene production were studied in tobacco leaf discs (Nicotiana rustica var. Brasilia). During the first 10 h of incubation, Ag+‐pretreated leaf discs contained more free [14C]IAA than untreated ones due to decreased oxidative decarboxylation, and the discs also produced more ethylene. Exogenously supplied ethylene nullified these effects of Ag+. However, the most pronounced effect of Ag+ in increasing ethylene production, as well as the strongest antagonistic effect of exogenous ethylene, were found between 24 and 48 h of incubation. During this time span no effect on the level of free IAA and on its decarboxylation could be observed. It is suggested that ethylene exerted its autoinhibitory effect by a feedback control on the IAA‐induced ethylene biosynthesis. Possible mechanisms for the autoinhibitory effect of ethylene are discussed.

Ethylene Biosynthesis and its Regulation in Higher Plants

PATHWAY OF ETHYLENE BIOSyNTHESIS 156 Methionine as an Intermediate ....... 157 S-Adenosylmethionine as an Intermediate 158 I-Aminocyclopropanecarboxylic Acid as an Intermediate . ......... 158 Methionine Cycle ........ 161 Conversion of l-Aminocyclopropanecarboxylic Acid to Ethylene 164 REGULATION OF ETHYLENE BIOSYNTHESIS 167 Regulation in Ripening Fruits and Senescing Flowers ...... 167 Auxin-Induced Ethylene Production 169 Regulation of Ethylene Biosynthesis by Ethylene 169 Stress-Induced Ethylene Production . . . . . . . . 171 Regulation by Light and Carbon Dioxide 173 Inhibitors of Ethylene Biosynthesis : 174 Conjugation of l-Aminocyclopropanecarboxylic Acid to l-(Malonylamino) cyclopropanecarboxylic Acid 178 CONCLUDING REMARKS 180

Inhibition of Auxin-Induced Ethylene Production by Lycoricidinol

Etude du mecanisme par lequel le lycoricidinol isole des bulbes de lycoris radiata supprime l'induction de la production d'ethylene par l'auxine chez Vigna radiata

Auxin-Induced Ethylene Production as Related to Auxin Metabolism in Leaf Discs of Tobacco and Sugar Beet

Exogenously supplied indole-3-acetic acid (IAA) stimulated ethylene production in tobacco (Nicotiana glauca) leaf discs but not in those of sugar beet (Beta vulgaris L.). The stimulatory effect of IAA in tobacco was relatively small during the first 24 hours of incubation but became greater during the next 24 hours. It was found that leaf discs of these two species metabolized [1-(14)C]IAA quite differently. The rate of decarboxylation in sugar beet discs was much higher than in tobacco. The latter contained much less free IAA but a markedly higher level of IAA conjugates. The major conjugate in the sugar beet extracts was indole-3-acetylaspartic acid, whereas tobacco extracts contained mainly three polar IAA conjugates which were not found in the sugar beet extracts. The accumulation of the unidentified conjugates corresponded with the rise of ethylene production in the tobacco leaf discs. Reapplication of all the extracted IAA conjugates resulted in a great stimulation of ethylene production by tobacco leaf discs which was accompanied by decarboxylation of the IAA conjugates. The results suggest that in tobacco IAA-treated leaf discs the IAA conjugates could stimulate ethylene production by a slow release of free IAA. The inability of the exogenously supplied IAA to stimulate ethylene production in the sugar beet leaf discs was not due to a deficiency of free IAA within the tissue but rather to the lack of responsiveness of this tissue to IAA, probably because of an autoinhibitory mechanism existing in the sugar beet leaf discs.

Stimulation of in vitro RNA Synthesis by Pretreating Plants with Auxins is Due to Auxin-Induced Ethylene Production

Summary Nucleoli isolated from mung bean ( Phaseolus aureus ROXB.) hypocotyls were much more active in carrying out in vitro RNA synthesis when prepared from seedlings previously sprayed with solutions of IAA or 2,4-D. No difference was found between the molecular weight of the RNA synthesised by nucleoli from control plants and those sprayed with auxins. The response to auxins developed a few hours after spraying and in vitro nucleolar activity continued to increase for at least 18 h. A large increase in ethylene evolution by auxin-sprayed plants was detected before the stimulation of nucleolar RNA synthesis. A similar stimulation of nucleolar RNA synthesis was found after plants were sprayed with a solution of the ethylene-generating compound ethephon and increased RNA synthesis was observed after exposing plants to ethylene alone. It is suggested that the increase in nucleolar RNA synthesis brought about by spraying plants with auxin is caused by auxin-induced ethylene production. It is further suggested that the enhanced activity is due to an increase in the number of RNA polymerase I molecules bound to the rRNA genes in the nucleoli.

Polyamines Inhibit Biosynthesis of Ethylene in Higher Plant Tissue and Fruit Protoplasts

Ethylene production in apple fruit and protoplasts and in leaf tissue was inhibited by spermidine or spermine. These polyamines, as well as putrescine, inhibited auxin-induced ethylene production and the conversion of methionine and 1-aminocyclopropane-1-carboxylic acid to ethylene. Polyamines were more effective as inhibitors of ethylene synthesis at the early, rather than at the late, stages of fruit ripening. Ca(2+) in the incubation medium reduced the inhibitory effect caused by the amines. A possible mode of action by which polyamines inhibit ethylene production is discussed.

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

Auxin is known to stimulate greatly both C(2)H(4) production and the conversion of methionine to ethylene in vegetative tissues, while amino-ethoxyvinylglycine (AVG) or Co(2+) ion effectively block these processes. To identify the step in the ethylene biosynthetic pathway at which indoleacetic acid (IAA) and AVG exert their effects, [3-(14)C]methionine was administered to IAA or IAA-plus-AVG-treated mung bean hypocotyls, and the conversion of methionine to S-adenosylmethionine (SAM), 1-amino-cyclopropane-1-carboxylic acid (ACC), and C(2)H(4) 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 --> C(2)H(4)) IAA stimulates C(2)H(4) 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 Co(2+) inhibition of IAA-dependent and ACC-dependent ethylene production were similar. The data indicate that Co(2+) exerts its effect by inhibiting the conversion of ACC to ethylene. This conclusion was further supported by the observation that when Co(2+) was administered to IAA-treated tissues, endogenous ACC accumulated while ethylene production declined.