Effects of Free Radical Scavengers on Stress Ethylene in Soybean Leaves Hypersensitively Reacting to Tobacco Necrosis Virus

The hypersensitive reaction of soybean cuttings to tobacco necrosisvirus is characterized by a large stimulation of stress ethyleneinvolving a marked accumulation of free 1-aminocyclopropane-1-carboxylicacid (ACC) and a moderate increase in ethylene-forming enzyme(EFE) activity. The scavengers of hydroxyl radicals (OH^{dot})sodium benzoate, sodium formate, mannitol and dimethylsulphoxide,did not affect stress ethylene biosynthesis. Propyl gallate,an inhibitor of lipoxygenase enzymes, substantially reducedthe release of stress ethylene from hypersensitive leaves. Thisreduction was not attributable to an inhibitory effect on EFEactivity, but to a strong reduction of free ACC accumulationin leaf tissues. The results suggest that OH^{dot} and the lipoxygenasesystem are not involved in stress ethylene produced during thehypersensitive reaction of soybean to this virus. Glycine max Merr, soybean, ethylene, free radicals, hypersensitivity, tobacco necrosis virus     

Ethylene Production by the Lichen Ramalina duriaei

The lichen Ramalina duriaei evolved ethylene when in a wettedstate, the rate of ethylene evolution being constant for atleast the first 20 h. Inhibitors of the ACC (I-aminocyclopropane-I-carboxylicacid) pathway did not inhibit ethylene production. Metal ionsstimulated the production, with Fe²⁺ being the most effective.This stimulation was not affected by inhibitors of the ACC pathwaybut was inhibited by free radical scavengers such as propylgallateand quercitin. Endogenous ACC content was similar whether thelichens were producing ethylene at a basal rate or during Fe²⁺-stimulatedethylene formation. Malondialdehyde and aldehyde contents werehigher in the presence of Fe²⁺. The results are discussed interms of known pathways of ethylene production by micro-organisms. ACC, ethylene, metal ions, methionine, 2-oxo-methylthiobutyric acid, Ramalina duriaei (De Not.) Bagl     

Characterization and Induction of the Activity of 1-Aminocyclopropane-1-Carboxylate Oxidase in the Wounded Mesocarp Tissue of Cucurbita maxima

1-Aminocyclopropane-1-carboxylate (ACC) oxidase (ethylene-formingenzyme) was isolated from wounded mesocarp tissue of Cucurbitamaxima (winter squash) fruit, and its enzymatic properties wereinvestigated. The enzyme required Fe²⁺ and ascorbate for itsactivity as well as ACC and O₂ as substrates. The in vitro enzymeactivity was enhanced by CO₂. The apparent K_m value for ACCwas 175 µM under atmospheric conditions. The enzyme activitywas inhibited by sulfhydryl inhibitors and divalent cationssuch as Co²⁺, Cu²⁺, and Zn²⁺. ACC oxidase activity was induced at a rapid rate by woundingin parallel with an increase in the rate of ethylene production.The exposure of excised discs of mesocarp to 2,5-norbornadiene(NBD),an inhibitor of ethylene action, strongly suppressed inductionof the enzyme, and the application of ethylene significantlyaccelerated the induction of the activity of ACC oxidase inthe wounded mesocarp tissue. These results suggests that endogenousethylene produced in response to wounding may function in promotingthe induction of ACC oxidase. (Received January 13, 1993; Accepted April 15, 1993)     

The involvement of ethylene in in vitro maturation of mid-binucleate pollen of Nicotiana tabacum

The role of ethylene during in vitro maturation of Nicotianatabacum pollen from the mld-binucleate (MB) stage was analysedby the addition of aminooxyacetic acid (AOA), aminoethoxyvinylglycine(AVG), CoCl₂ and AgNO₃ to the maturation medium (AMGLu). Anincrease in ethylene production was obtained in both isolatedpollen and pollen surrounded by sporophytic tissue during insitu maturation. in vitro maturation of pollen was inhibitedby AOA and AVG; ACC and ethrel were able to overcome this inhibitoryeffect. Cyclohexylamine (CHA) reverted the inhibition provokedby both Ag⁺ and Co²⁺ The results reported in this paper indicatethat ethylene is one of the factors implicated in in vitro maturationof MB pollen of Nicotiana tabacum. Key words: Nicotiana tabacum, maturation, germination, pollen, ethylene     

Effect of Ethylene and Culture Environment on Rice Callus Proliferation

Modifications to the gaseous envelope by callus during culturein Petri dishes were shown to reduce growth and promote necrosisof several rice (Oryza sativa L.) cultivars. Incubatingcallusunder a continuous flow of gas mixtures of known compositionsuggested that the inhibition of growth was caused by the accumulationof ethylene, the depletion of oxygen and, to a lesser extent,the accumulation of carbon dioxide. In order to evaluate theimportance of ethylene accumulation aminoethoxyvinylglycine(AVG), 1-aminocyclopropane-l-carboxylic acid (ACC and silvernitrate (AgNO₃), were added to the nutrient medium and ethylenemeasurements performed during callus culture. Ethylene restrictedcallus growth particularly under high (35 °C) as comparedto moderate (25 °C) temperatures and under illuminated ascompared to darkened incubation. Under illuminated incubationat 25 °C AVG (5 mmol m^–3) and AgNO°(50 mmol m^–3)significantly improvedcallus growth (100 and 60% respectively)while ACC (200 mmol m^–3) significantly decreased growth(40%). AVG and AgNO₃ were less effective under dark incubationat 25 °C where ethylene production was lower. Furthermore,callus growth was significantly better in large as comparedto small culture vessels since the ethylene concentration wasdiluted and more oxygen was available for respiration. Bettercontrol of ethylene and increased oxygen availability couldbe a way ofproducing healthy callus for the formation of embryogenictissues of otherwise recalcitrant cultivars of rice (e.g. IndicaIR42) and may be a way of improving manipulation of other cerealspecies. Key words: 1-Aminocyclopropane-1-carboxylic acid, aminoethoxyvinylglycine, callus, ethylene, Oryza sativa, silver nitrate     

Biosynthesis of auxin-induced ethylene in mung bean hypocotyls

The pathway of ethylene biosynthesis in auxin-treated mung beanhypocotyls was investigated by comparing the specific radioactivitiesof ethylene produced and S-adenosylmethionine (SAM) in the tissuefollowing the administration of 3,4-¹⁴C-methionine, and by analyzingthe methionine metabolites. When the rate of auxin-induced ethyleneproduction was low due to a low concentration of auxin, thespecific radioactivity of ethylene released was always higherthan that of SAM in the tissue. When the tissue was treatedwith auxin, the tissue produced and accumulated a methioninemetabolite which was converted into ethylene more efficientlythan methionine. The metabolite was identified as 1-aminocyclopropane-l-carboxylicacid (ACC) by means of paper and thin-layer chromatography,high voltage paper electrophoresis and co-crystallization. ACCformation was neither inhibited by low oxygen nor by the inhibitoryprotein of ethylene synthesis, but inhibited by aminoethoxyvinylglycine(AVG). ACC application to the tissue greatly reduced incorporationof 3,4-¹⁴C-methionine into ethylene. The control tissue thatwas not treated with auxin also converted ACC into ethyleneindicating that the enzyme which converts ACC into ethyleneis already present in the tissue and that auxin induced productionof the enzymatic system responsible for the conversion of methionineinto ACC. Ethylene synthesis from ACC was not inhibited by AVG,abscisic acid, cycloheximide or actinomycin D, but inhibitedby low oxygen and the inhibitory protein. (Received November 21, 1979; )     

Induction of chitinase and {beta}-1,3-glucanase activity in sunflower suspension cells in response to an elicitor from Phytophthora megasperma f. sp. glycinea (Pmg). Evidence for regulation by ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC)

In heterotrophic cell suspensions of sunflower (Helianthus annuusL. cv. Spanners Allzweck) the effect of Pmg elicitor, a fungalelicitor preparation from Phytophthora megasperma f. sp. glycinea,on the induction of chitinase and ß-1,3-glucanaseactivity was studied in relation to changes in ethylene biosynthesis.Dose-response experiments with Pmg elicitor showed that theonset of the induction of intracellular chitinase and ß-1,3-glucanaseactivity coincided or followed a transient rise in ethyleneand particularly endogenous 1-aminocyclopropane-1-carboxylicacid (ACC) levels within 5 h of application. Treatment with5 µg ml^–1 elicitor stimulated ethylene and ACC levels1.6-fold and 4-fold, relative to control, respectively. Themolar ratio of ACC to ethylene changed from approximately 3:1in controls to 9:1 in treated cells. During further incubation,ethylene formation and, to a lesser degree, ACC levels declinedand the ACC/ethylene ratio increased to 56:1 in elicitor-treatedcells. On a protein basis, the activities of ß-1,3-glucanaseand chitinase increased approximately 5-fold and 8-fold, respectively,48 h after elicitor application. Additional treatment with theACC synthesis inhibitor aminoethoxyvinyiglycine (AVG) decreasedelicitor-induced enzyme activities and the levels of both ethyleneand ACC. Elicitor effects on chitinase and ß-1,3-glucanaseactivities could be fully restored when ACC was additionallyapplied. Concomitantly, the ACC/ ethylene ratio increased. Neithertreatments with ACC alone, which simultaneously increased internalACC and ethylene levels, nor treatments with AVG alone, whichsimultaneously reduced ACC and ethylene levels, could generallystimulate chitinase or ß-1,3-glucanase activitiesin the cells. It is suggested that ACC functions as a promotingfactor in the induction of chitinase and ß-1,3-glucanaseactivity triggered by Pmg elicitor and appears to reverse aninhibiting influence of ethylene. Key words: 1-Aminocyclopropane-1-carboxylic acid, chitinase, ß-1,3-glucanase, ethylene, Helianthus cellsuspension cultures, Phytophthora megasperma-elicitor     

Rapidly induced ethylene formation after wounding is controlled by the regulation of 1-aminocyclopropane-1-carboxylic acid synthesis

Bean leaves from Phaseolus vulgaris L. var. Pinto 111 react to mechanical wounding with the formation of ethylene. The substrate for wound ethylene is 1-aminocyclopropane-1-carboxylic acid (ACC). It is not set free by decompartmentation but is newly synthesized. ACC synthesis starts 8 to 10 min after wounding at 28°C, and 15 to 20 min after wounding at 20°C. Aminoethoxyvinylglycine (AVG), a potent inhibitor of ethylene formation from methionine via ACC, inhibits wound ethylene synthesis by about 95% when applied directly after wounding (incubations at 20°C). AVG also inhibits the accumulation of ACC in wounded tissue. AVG does not inhibit conversion of ACC to ethylene. Wound ethylene production is also inhibited by cycloheximide, n-propyl gallate, and ethylenediaminetetraacetic acid.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG ammoethoxyvinylglycine - EDTA ethylenediaminetetraacetic acid     

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

Auxin is known to stimulate greatly both C₂H₄ production and the conversion of methionine to ethylene in vegetative tissues, while amino-ethoxyvinylglycine (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, [3-¹⁴C]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 C₂H₄ 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 → C₂H₄) 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.     

Development of Ethylene Biosynthesis in Pear Fruits at --1 {degrees}C

Knee, M. 1987. Development of ethylene biosynthesis in pearfruits at — 1 °C.—J. exp. Bot. 38: 1724–1733. The regulation of ethylene synthesis in pear fruits was investigated.During storage for 60 d at — 1 °C the rate of ethylenesynthesis increased 100-fold but the concentration of 1-aminocyclopropane-l-carboxylicacid (ACC) increased only 2-fold and ACC synthase activity waslow. On transfer to 15 °C after storage at — 1 °Cethylene synthesis increased 10-fold within 10 h but ACC synthaseactivity only increased rapidly after 24 h; the decline in ACClevels during the first 16 h at 15 °C was insufficient tosustain ethylene synthesis. Ethylene synthesis was further investigatedusing discs cut from the mid cortex of pear fruits. Synthesiswas inhibited by aminoethoxyvinylglycine (AVG) and amino-oxyaceticacid at all stages of ripening. The rate of synthesis and ACCsynthase activity increased rapidly after slicing of pears heldat — 1 °C but more slowly in discs cut from pearsimmediately after harvest. Cycloheximide (CHI) inhibited theseincreases and reversed increases resulting from pre-incubationof discs. A combination of CHI and AVG abolished the capacityof discs to synthesize ACC and ethylene production was curtailed.Cordycepin and actinomycin-D were less effective as inhibitorsof the development of ethylene synthesis and ACC synthase activitythan as inhibitors of incorporation of 5-[³H] uridine into totalRNA or poly A rich RNA. The ability of discs to develop ethylenesynthesis and ACC synthase activity in the presence and absenceof cordycepin increased concurrently during storage of wholefruits at — 1 °C. This suggested that mRNA for ACCsynthase was formed at — 1 °C. Key words: 1-Aminocyclopropane-l-carboxylic acid, ethylene, fruit ripening, Pyrus communis L. (fruit ripening)     

Preliminary characterization of 1-aminocyclopropane-1-carboxylate oxidase properties from embryonic axes of chick-pea (Cicer arietinum L.) seeds

For a deeper understanding of the germination of chick–pea(Cicer arietinum) seeds, which is dependent upon ethylene synthesis,a crude extract containing authentic ACC oxidase (ACCO) activitywas isolated in soluble form from the embryonic axes of seedsgerminated for 24 h. Under our optimal assay conditions (200mM HEPES at pH 7.0, 4µM FeS0₄, 6 mM Na–ascorbate,1 mM ACC, 20% 0₂, 3% CO₂ , and 10%glycerol) this enzyme was5–fold more active than under the conditions we used initiallyin the present work. The enzyme has the following K_m: 28 µMfor ACC (approximately 4–fold less than in vivo), 1.2%for O₂ (in the presence of an optimal CO₂ concentration of 3%),and 1% for CO₂ in the presence of O₂ (20%). The enzyme is inhibitedby phenanthroline (PNT) (specific chelating agent of ferrousion), and competitively inhibited (K₁, =0.5 mM) by 2–aminoisobutyricacid (AIB), and the enzymatic activity was not detectable inthe absence of CO₂. Under optimal assay conditions, the enzymehas two optimum temperatures (28 C and 35 C) and is inhibitedby divalent metal cations (Zn²⁺> CO²⁺>Ni²⁺>Cu²⁺>Mn²⁺>Mg²⁺) and by salicylic acid, propylgallate, carbonyl cyanidem–chlorophenyl hydrazone (CCCP), dinitrophenol (DNP),and Na–benzoate. The in vitro ACCO activity which we recoveredin soluble form is equivalent to approximately 80–85%of the apparent activity evaluated in vivo. Key words: ACC oxidase, Cicer arietinum, ethylene, germination, seeds     

Biochemical properties of 1-aminocyclopropane-1-carboxylate N-malonyltransferase activity from early growing embryonic axes of chick-pea (Cicer arietinum L.) seeds

In the present work, certain biochemical characteristics ofthe enzyme 1-aminocyclopropane-1-carboxylate N-malonyltransferase(ACC N-MTase) which is responsible for the malonylation of 1-aminocyclopropane-1-carboxylate(ACC) in chickpea (Cicer arietinum) are described. Phosphatebuffer was the most appropriate buffer with regard to enzymestability and, therefore, ACC N-MTase was extracted, assayedand purified in the presence of this buffer. ACC N-MTase waspartially purified approximately 900-fold from embryonic axesof chick-pea seeds using ammonium sulphate precipitation, hydrophobicinteraction and molecular filtration chromatography. By gelfiltration chromatography on Superose-12, the molecular massof the enzyme was estimated to be 54 4 kDa. ACC N-MTase hadan optimal pH and temperature of 7.5 and 40C, respectively,as well as a K_m for ACC and malonyl-CoA of 400 M and 90 M,respectively. D-Phenylalanine was a competitive inhibitor ofACC N-MTase with respect to ACC (K_i of 720 M), whereas co-enzymeA was a competitive product inhibitor with respect to malonyl-CoA(K_i of 300 M) and a non-competitive inhibitor with respectto ACC (K_i of 600 M). Under optimal assay conditions, ACC N-MTasewas strongly inhibited by (a)divalent [Zn²⁺>Mg²⁺>>Co²⁺>Co²⁺>(NH₄)²⁺>Fe²⁺]and monovalent metal cations (Li⁺>Na⁺>K⁺), without activitybeing detected in the presence of Hg²⁺, and (b) PCMB or mersalicacid, suggesting that sulphydryl group(s) are involved at theactive site of the enzyme. Key words: ACC-N-malonyltransferase, Cicer arietinum, embryonic axes, ethylene, germination, seeds     

Biosynthesis of stress ethylene in soybean seedlings: Similarities to endogenous ethylene biosynthesis

The similarity of stress ethylene biosynthesis in whole plants to endogenous ethylene biosynthesis was investigated using two inhibitors of ethylene biosynthesis, aminoethoxyvinylglycine (AVG) and cobalt chloride (Co²⁺); and the intermediates, methionine, S -adenosylmethionine (SAM), and 1-aminocyclopropane-1-carboxylic acid (ACC), of basal ethylene biosynthesis. Stress ethylene production induced by ozone, cadmium, or 2,4-dichlorophenoxyacetic acid was inhibited in hydroponically-grown soybean seedlings in a concentration-dependent manner by both AVG and CO²⁺. The ethylene intermediates evoked responses in intact seedlings similar to that described for endogenous ethylene production in isolated vegetative tissue. The addition of SAM to the hydroponic system relieved AVG inhibition of stress ethylene production. Feeding ACC to the seedlings resulted in increased ethylene production independent of stress application or prior AVG inhibition. Cobalt inhibition of stress ethylene production was relieved by increasing concentrations of ACC. A short lag period of 12–18 min was observed in stress ethylene production following a 30-min ozone exposure. Addition of cycloheximide partially inhibited ozone-induced ethylene production.
These results suggest a common pathway in whole plants for stress ethylene production and endogenous ethylene biosynthesis.     

Ethylene and 1 -Aminocyclopropane-1-Carboxylic Acid Production in flacca, a Wilty Mutant of Tomato, Subjected to Water Deficiency and Pre-treatment with Abscisic Acid

Neill, S. J., McGaw, B. A. and Horgan, R. 1986. Ethylene and1-aminocyclopropane-l-carboxylic acid production in flacca,a wilty mutant of tomato, subjected to water deficiency andpretreatment with abscisic acid —J. exp. Bot. 37: 535–541. Plants of Lycoperstcon esculentum Mill. cv. Ailsa Craig wildtype and flacca (flc) were sprayed daily with H²O or 2?10^–2mol m^–3 abscisic acid (ABA). ABA treatment effected apartial phenotypic reversion of flc shoots; leaf areas wereincreased and transpiration rates decreased. Leaf expansionof wild type shoots was inhibited by ABA. Indoleacetic acid (IAA), ABA and l-aminocyclopropane-l-carboxylicacid (ACC) concentrations were determined by combined gas chromatography-massspectrometry using deuterium-labelled internal standards ABAtreatment for 30 d resulted in greatly elevated internal ABAlevels, increasing from 1?0 to 4?3 and from 0?45 to 4?9 nmolg^–1 fr. wt. in wild type and flc leaves respectively.Endogenous IAA and ACC concentrations were much lower than thoseof ABA. IAA content ranged from 0?05 to 0?1 nmol g^–1 andACC content from 0?07 to 0?24 nmol g^–1 Ethylene emanationrates were similar for wild type and flc shoots. Wilting of detached leaves induced a substantial increase inethylene and ACC accumulation in all plants, regardless of treatmentor type. Ethylene and ACC levels were no greater in flc leavescompared to the wild type. ABA pretreatment did not preventthe wilting-induced increase in ACC and ethylene synthesis. Key words: ABA, ACC, ethylene, wilting, wilty mutants     

Regulation of Auxin-induced Ethylene Biosynthesis. Repression of Inductive Formation of 1-Aminocyclopropane-1-carboxylate Synthase by Ethylene

Changes in the 1-aminocyclopropane-1-carboxylate (ACC) synthaseactivity which regulates auxin-induced ethylene production werestudied in etiolated mung bean hypocotyl segments. Increasesboth in ethylene production and ACC synthase activity in tissuetreated with IAA and BA were severely inhibited by cycloheximide(CHI), 2-(4-methyl-2,6-dinitroanilino)-N-methylpropionamide,actinomycin D and -amanitin. Aminoethoxyvinylglycine (AVG),a potent inhibitor of the ACC synthase reaction, increased theactivity of the enzyme in the tissue 3- to 4-fold. This stimulationalso was severely inhibited by the above inhibitors. Stimulationof the increase in the enzyme content by AVG was partially suppressedby an exogenous supply of ACC or ethylene. Suppression of theincrease in the enzyme took place with 0.3 µl/liter ethylene,and inhibition was increased to 10 µl/liter, which caused65% suppression. Air-flow incubation of the AVG-treated tissue,which greatly decreased the ethylene concentration surroundingthe tissue, further increased the amount of enzyme. Thus, oneeffect of AVG is to decrease the ethylene concentration insidethe tissue. The apparent half life of ACC synthase activity,measured by the administration of CHI, was estimated as about25 min. AVG lengthened the half life of the activity about 2-fold.Feedback repression by ethylene in the biosynthetic pathwayof auxin-induced ethylene is discussed in relation to the effectof AVG. (Received January 22, 1982; Accepted March 26, 1982)     

Role of Ethylene on de Novo Shoot Regeneration from Cotyledonary Explants of Brassica campestris ssp. pekinensis (Lour) Olsson in Vitro

The promotive effect of AgNO₃ and aminoethoxyvinylglycine (AVG) on in vitro shoot regeneration from cotyledons of Brassica campestris ssp. pekinensis in relation to endogenous 1-amino-cyclopropane-1-carboxylic acid (ACC) synthase, ACC, and ethylene production was investigated. AgNO₃ enhanced ACC synthase activity and ACC accumulation, which reached a maximum after 3 to 7 days of culture. ACC accumulation was concomitant with increased emanation of ethylene which peaked after 14 days. In contrast, AVG was inhibitory to endogenous ACC synthase activity and reduced ACC and ethylene production. The promotive effect of AVG on shoot regeneration was reversed by 2-chloroethylphosphonic acid at 50 micromolar or higher concentrations, whereas explants grown on AgNO₃ medium were less affected by 2-chloroethylphosphonic acid. The distinctive effect of AgNO₃ and AVG on endogenous ACC synthase, ACC, and ethylene production and its possible mechanisms are discussed.     

1-Methylcyclopropene and ethylene as regulators of in vitro organogenesis in kiwi explants

In this paper, we study the influence of ACC, AVG and 1-MCP on in vitro organogenesis of kiwi (Actinidia deliciosa) explants and on ethylene metabolism. Results indicated that increasing ethylene production and accumulation in the head space of the culture vessel by adding ACC to the culture medium inhibited organogenesis, except for rooting, which increased and stimulated ACC oxidase activity threefold, whereas AVG increased the length and number of shoots and leaves and inhibited about 80% ACC synthase activity compared with the reference explants. 1-MCP exerts a stimulatory effect analogous to AVG, increasing ACC synthase activity and organogenesis of kiwi explants. This effect is not reverted by the addition of ACC to the culture medium. Therefore, ethylene production and its accumulation in the headspace of the culture vessels seems to be responsible for the inhibition of shoot development as well as increasing rooting in in vitro cultured kiwi explants.     

Ethylene Production by the Kudzu Strains of Pseudomonas syringae pv. phaseolicola Causing Halo Blight in Pueraria lobata (Willd) Ohwi

Significant amounts of ethylene was produced by Pseudomonassolanacearum (all strains), P. syringae pv. phaseolicola (Kudzustrains isolated from Pueraria lobata) and Erwinia rhapontici(2 strains out of 22) out of 24 species, 3 subspecies and 38pathovars of plant pathogenic bacteria tested in yeast extract-peptonebroth. The bean strains of P. syringae pv. phaseolicola causinghalo blight in kindney bean plants did not produce ethylene.The Kudzu strains produced ethylene at a rate of 7 to 100?10^–9nl cell^–1 h^–1, which was 500 to 1,000 times higherthan that of P. solanacearum and several times higher than thatof Penicillium digitatum, the most potent ethylene producerknown among microorganisms. The presence of living cells was essential for ethylene productionby the Kudzu strains. The bacterium effectively produced ethylenefrom amino acids such as glutamate, aspartate and their amides.Although glucose and succinate were also good substrates forethylene biosynthesis, the rate of ethylene production was significantlysmaller than that with glutamate. Methionine, which is knownas the precursor of ethylene in plants, had no effect on ethyleneproduction by the bacterium. 1-Aminocyclopropane-1-carboxylicacid (ACC) also had no effect on ethylene production, and therewas not enough ACC in the bacterial cells to account for thehigh rate of ethylene production. Ethylene production from glutamatewas inhibited by n-propylgallate and EDTA, but not by aminoethoxyvinylglycine.These results indicate that ACC is not involved as an intermediatein the process of ethylene biosynthesis by the bacterium, suggestingthe presence of a pathway different from that of plant tissues. (Received September 4, 1984; Accepted October 27, 1984)     

活性氧在UV-B诱导的玉米幼苗叶片乙烯产生中的作用

 研究了活性氧在UV-B(280～320 nm)诱导的玉米(Zea mays)幼苗叶片乙烯合成中的作用。结果表明,UV-B促进了玉米幼苗活性氧和乙烯的产生;乙 烯合成抑制剂氨氧乙烯基甘氨酸 (AVG)和氨氧乙酸(AOA)能明显减弱UV-B对玉米幼苗乙烯产生的诱导作用,但对活性氧(ROS)的 产生没有明显影 响;ROS的清除剂不但能抑制UV-B诱导的 ROS的产生,而且还可以抑制UV_B诱导的乙烯的产生,但这种抑制作用可以被外源O₂^.-的供体所逆转。这 说明,乙烯的积累不能作为UV-B胁迫下ROS的诱导的因素,相反,ROS的积累则导致了乙烯的积累;因此,ROS可能参与了UV-B胁迫诱导的乙烯的产生 。质膜NADPH氧化酶的抑制剂二苯碘鎓(DPI)和H₂O₂的特异性清除剂过氧化氢酶（CAT）对UV-B胁迫诱导的乙烯积累 几乎没有影响, 这说明H₂O₂ 可能与UV-B诱导的玉米幼苗叶片乙烯的产生无关, 在UV-B诱导的玉米幼苗叶片乙烯的生物合成过程中O₂^.-起着很重要的作用,相关的O₂^.-不是由 NADPH氧化酶催化产生的。