The Role of 1-Aminocyclopropane-1-carboxylic acid in the Control of Low Temperature Induced Ethylene Production in Leaf Tissue of Phaseolus vulgaris L .

Ethylene production from leaf discs of dwarf bean (Phaseolausvulgaris L.) was less than 02 nl g^–1 h^–1 at 5 Cbut rapidly increased tenfold on transfer to 25 C. The lowethylene production at 5 C and the potential for overshootproduction on transfer to 25C were not associated with accumulationof the ethylene synthesis intermediate 1-aminocyclopropane-1-carboxylicacid (ACC). Addition of exogenous ACC to leaf discs incubatedat 5C increased ethylene production, while similarly incubatedleaf discs did not synthesize increasing amounts of endogenousACC until they were transferred to 25 C. The basis for theovershoot in ethylene production when leafdiscs were transferredfrom 5 to 25 C appears to reside in changes to the pathwayleading to the synthesis of ACC or an earlier intermediate inthe pathway of ethylene biosynthesis. Ethylene, 1-aminocyclopropane-l-carboxylic acid, Phuseolru vulgaris L., dwarf bean, temperature     

Induction of 1-Aminocyclopropane-1-carboxylic Acid Synthase in Wounded Mesocarp Tissue of Winter Squash Fruit and the Effects of Ethylene

1-Aminocyclopropane-1-carboxylic acid (ACC) synthase activityincreased rapidly after wounding of mesocarp tissue of wintersquash fruit (Cucurbita maxima Duch.) and reached a peak at16 h after excision and then declined sharply. The rise in ACCsynthase activity was followed by increases in the endogenousACC content and the rate of ethylene production. The activityof ethylene forming enzyme (EFE) also increased rapidly in theexcised discs of mesocarp of winter squash fruit. ACC synthase activity was strongly inhibited by aminoethoxyvinylglycinewith a Ki value of 2.1 µM. Michaelis-Menten constant ofACC synthase for S-adenosylmethionine was 13.3 µM. Ethylene suppressed the induction of ACC synthase in the woundedmesocarp tissue. The suppression by ethylene increased withthe increasing concentrations of applied ethylene and the maximumeffect was obtained at about 100 µl 1^–1 ethylene,at which point the induction was suppressed by 54%. Ethylenedid not inhibit ACC synthase activity, nor did it suppress theinduction of EFE, but rather it slightly enhanced the latter. (Received August 24, 1984; Accepted October 29, 1984)     

Regulation of Tracheary Element Differentiation by Exogenous L-Methionine in Callus of Soya Bean Cultivars

The relationship between the induction of tracheary elementdifferentiation and exogenous L-methionine was examined in agar-growncultures of soya bean callus initiated from Glycine max L. ‘Wayne’and ‘Clark 63’. Although Wayne is a normal cultivarsoya bean, seedlings of Clark 63 exhibit abnormal growth at25 °C due to exessive ethylene biosynthesis at this temperature.Wayne callus showed increased xylogenesis in the presence ofexogenous L-methionine (3.7 µg 1^–1) in comparisonto IAA–KN controls at both 20 and 25 °C. Clark 63callus produced greater numbers of tracheary elements in responseto exogenous L-methionine only at 25 °C. The induction ofxylem differentiation was independent of the maintenance temperatureof the stock cultures of both cultivars. Xylogenesis initiatedbyan IAA–KN medium was inhibited by the addition of AgNO₃(20 mg 1^–1) to the extent of 76.5 per cent in cv. Wayneand 6 per cent in cv. Clark 63. The inhibitory effect was partiallyreversed by the addition of L-methionine (3.7 µg 1^–1)to the IAA–KN–AgNO₂ medium. These data support thehypothesis that xylogenesis in vitro involves auxin, cytokininand ethylene. differentiation, xylogenesis, L-methionine, ethylene, Glycine max L., soya bean, callus culture, auxin, kinetin     

Ethylene Production by Cell-Free Extract of the Kudzu Strain of Pseudomonas syringae pv.phaseolicola

A cell-free ethylene-forming system of Pseudomonas syringaepv.phaseolicola (Kudzu strain) was characterized by its psychrophilictrait. Ethylene was most effectively produced from -ketoglutaricacid (-KG) at 0.5 mM followed by glutamate and then istidineat 5 to 10 mM. The presence of FeSO₄ was essential to the cell-freesystem. DTT and histidine greatly stimulated ethylene production;the latter could be substituted to some extent by its analogues.The optimum pH value and temperature for the ethylene-formingreactions were pH 7.0 and 25?C, respectively. Ethylene formationfrom -KG was inhibited in the presence of carbonates or organicacids of the TCA cycle, whereas that from glutamate was inhibitedin the presence of ammonium salts. Ethylene production from-keto--methylthiobutyric acid in the cell-free system was largelydependent on non-enzymical processes in the presence of DTTand FeSO₄. The ethylene-forming reactions were inhibited completelyby 1 mM n-propyl gallate and 1 mM p-chloromercuribenzoic acidand partly by coenzymes such as pyridoxal-1-phosphate, folicacid, and flavin mononucleotide at 5mM. The complete systemfor the highest ethylene production consisted of: 0.5 mM -KG,50 mM HEPES (pH 7.0), 5 mM DTT, 0.5 mM FeSO₄, and 10 mM histidine.The amount of ethylene produced in this system was equivalentto 40 to 50% of that produced by the living cells. (Received October 22, 1986; Accepted January 19, 1987)     

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     

Evidence for Involvement of the Superoxide Radical in the Conversion of 1-Aminocyclopropane-1-Carboxylic Acid to Ethylene by Pea Microsomal Membranes

Electron spin resonance (ESR) spectroscopy has provided evidencefor involvement of the superoxide anion (O₂^–) radicalin the conversion of l-aminocyclopropane-l carboxylic acid (ACC)to ethylene by microsomal membranes from etiolated pea seedlings.Formation of ethylene from ACC by the membrane system is oxygen-dependent,heat denaturable, inhibited by the radical scavenger n-propylgallate and sensitive to superoxide dismutase (SOD) and catalase.Addition of 1,2-dihydroxybenzene-3,5-disulfonic acid (Tiron)to the reaction mixture results in formation of the Tiron semiquinone(Tiron radical) ESR signal derived from O₂^–, and alsoinhibits ethylene production. The radical signal is oxygen-dependentand inhibited by SOD and catalase, but is formed both in thepresence and absence of ACC. Heat denaturation of the microsomalenzyme system completely blocks formation of the radical signal.The data collectively suggest that O₂^– generated by amembrane-bound enzyme facilitates the conversion of ACC to ethylene. (Received September 8, 1981; Accepted January 19, 1982)     

Regulation of ACC-Dependent Ethylene Production by Excised Leaves from Normal and Albino Zea mays L. Seedlings

Dunlap, J. R. 1988. Regulation of ACC-dependent ethylene productionby excised leaves from normal and albino Zea mays L. seedlings.—J.exp. Bot. 39: 1079–1089. Albino corn (Zea mays L.) seedlings lacking natural leaf pigmentswere obtained by germinating seeds treated with fluridone, aninhibitor of carotenoid biosynthesis. Basal rates of ethyleneproduction were less than 2.0 nl g^–1 fr. wt h^–1in both treated (albino) and untreated (normal) leaves but increasedby 10- to 20-fold in the presence of added ACC. ACC-dependentethylene production (ADEP) was inhibited by cobalt or cyanideions and stimulated by NaHCO₃, CO₂ and light. ADEP in both tissueswas stimulated by glucose, fructose, galactose and sucrose.The accumulation of respiratory CO₂ did not account for thecarbohydrate response. The decline in the ADEP characteristicof albino leaf tissue was slowed by incubation in the presenceof sucrose. IAA and ABA stimulated ADEP in normal leaves butinhibited ADEP in albino leaves. Sucrose-stimulated ADEP wasinhibited in albino leaf tissue treated with IAA or ABA indicatinga possible role for the chloroplast in carbohydrate-facilitatedADEP. However, results from this study suggest that chloroplastsperform a function in the regulation of ethylene productionby leaf tissue that extends beyond merely influencing internallevels of CO₂. In the absence of detectable ACC, EFE was responsiblefor the entire series of responses expressed in regulation ofethylene biosynthesis by corn seedling leaf tissue. Key words: Corn, ethylene, sugars, phytohormones     

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     

A Possible Regulation of Ethylene Production by the Epidermis in Mung Bean Hypocotyl Sections

IAA-induced and l-aminocyclopropane-l-carboxylic acid (ACC)-dependentethylene production in etiolated mung bean (Vigna radiata [L]Wilczek) hypocotyl sections does not occur in epidermal cells(Todaka and Imaseki 1985). Mung bean hypocotyls contain a proteinwhich inhibits auxin-induced ethylene biosynthesis in hypocotylsections (Sakai and Imaseki 1975a, b). This inhibitory proteinwas also found to inhibit ACC-dependent ethylene productionin hypocotyl sections, but not in hypocotyl sections from whichthe epidermis had been removed. Uptake of ACC by both unpeeledand peeled sections was not inhibited by the protein. Similarly,IAA-induced ethylene production was inhibited by the proteinin unpeeled hypocotyl sections, but not in peeled sections.The protein was not inactivated in peeled sections, as proteinsynthesis by peeled sections was inhibited to the same extentas in unpeeled sections. The protein inhibited incorporationof 3,4-[¹⁴C]-methionine into ACC and ethylene in unpeeled sections,but not in peeled sections, whereas oxidation of the labeledmethionine into CO₂ was inhibited by the protein to a similarextent in both types of hypocotyl sections. KCN, a potent inhibitorof ethylene production, inhibited both IAA-induced and ACC-dependentethylene production in both peeled and unpeeled hypocotyl sections.It is likely that the epidermis plays some role in controllingethylene production which occurs in stem cells other than epidermalcells. (Received July 16, 1985; Accepted October 21, 1985)     

The Stimulation of Ethylene Synthesis in Nicotiana tabacum Leaves by the Phytotoxin Coronatine

Coronatine is a chlorosis-inducing toxin produced by the plant pathogen Pseudomonas syringae pv atropurpurea. This bacterium is the causal agent of chocolate spot disease, in which brown lesions with chlorotic margins develop on the leaves of Lolium multiflorum Lam. Among the many physiological changes to plants caused by coronatine is the stimulation of ethylene production from bean leaves. The ethyl-substituted side chain of coronatine is an analog of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC). We have examined the question of whether part or all of the released ethylene comes from the breakdown of coronatine itself. The rate of ethylene release from leaves of Nicotiana tabacum was proportional to the concentration of coronatine applied to the leaf surface. The lowest effective concentration of coronatine, applied to leaves at 15 pmol cm⁻² of leaf area, resulted in the production of 44 pmol of ethylene cm⁻² over a period of 4 h. The maximum rate of ethylene production occurred 28 to 32 h after application of coronatine. The specific activity of ethylene produced by discs cut from coronatine-treated Nicotiana tabacum leaves floating on a solution containing 10 mm [U-¹⁴C]methionine was consistent with its exclusive origin from methionine. ACC accumulated in the coronatine-treated tissue. ACC synthase activity increased in Phaseolus aureus hypocotyls during a 6-h treatment with coronatine. Thus, coronatine induces the synthesis of ethylene from methionine.     

Early detection of bean infection by Pseudomonas syringae in asymptomatic leaf areas using chlorophyll fluorescence imaging

Chlorophyll fluorescence imaging has been used to analyse the response elicited in Phaseolus vulgaris after inoculation with Pseudomonas syringae pv. phaseolicola 1448A (compatible interaction) and P. syringae pv. tomato DC3000 (incompatible interaction). With the aim of modulating timing of symptom development, different cell densities were used to inoculate bean plants and the population dynamics of both bacterial strains was followed within the leaf tissue. Fluorescence quenching analysis was carried out and images of the different chlorophyll fluorescence parameters were obtained for infected as well as control plants at different timepoints post-infection. Among the different parameters analysed, we observed that non-photochemical quenching maximised the differences between the compatible and the incompatible interaction before the appearance of visual symptom. A decrease in non-photochemical quenching, evident in both infiltrated and non-infiltrated leaf areas, was observed in P. syringae pv. phaseolicola-infected plants as compared with corresponding values from controls and P. syringae pv. tomato-infected plants. No photoinhibitory damage was detected, as the maximum photosystem II quantum yield remained stable during the infection period analysed.     

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

Auxin-induced and 1-aminocyclopropane-1-carboxylic acid (ACC)-dependentethylene production in mung bean (Vigna radiata [L] Wilczek)hypocotyl sections, from which epidermis had been removed, wasinvestigated. Ethylene production in hypocotyl sections withoutepidermis was induced by treatment with IAA, and also occurredfrom exogenously supplied ACC in the presence of 0.2 M mannitol.Isolated epidermal strips alone failed to produce substantialamounts of ethylene in response to IAA or from exogenous ACC.3,4-[¹⁴C]-Methionone was incorporated into both ACC and ethylenein peeled sections treated with IAA, but not in the isolatedepidermal strips. Radioactive ACC, however, was detected inthe epidermal strips separated from the unpeeled sections previouslyfed with 3,4-[¹⁴C]-methionine in the presence of IAA. We concludethat the Site of auxin-induced ethylene production is not inthe epidermis, but in other hypocotyl cells, and that epidermalcells lack the activity which converts ACC to ethylene. (Received January 28, 1985; Accepted May 4, 1985)     

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     

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)     

Chilling-Induced Ethylene Production in Relation to Chill-Sensitivity in Phaseolus spp.

Guye, M. G, Vigh, L. and Wilson, J. M. 1987. Chilling-inducedethylene production in relation to chill-sensitivity in Phaseolusspp.—J. exp. Bot. 38: 680–690. Ethylene production from the primary leaves of six bean (Phaseolusspp.) cultivars known to differ in chill-sensitivity, was monitoredat 23 ?C following chilling of whole plants at 5 ?C for 24 h.The more chill-tolerant cultivars produced greater amounts ofchilling-induced ethylene than the chill-sensitive cultivars.The onset of maximum ethylene production rates and the followingdecline in rates was more rapid in chill-tolerant cultivars.This pattern of ethylene production was also similar when chill-tolerancewas chemically enhanced by choline treatment. The low levelsof ethylene production in chill-sensitive genotypes was alsoreflected by their poor ability to convert the exogenously appliedethylene precursor, 1-aminocyclopropane-l-carboxylic acid (ACC),to ethylene. Moderate levels of leaf water deficit induced by chilling chill-tolerantcultivars and choline treated plants appeared to stimulate chilling-inducedethylene production. High levels of leaf wilt, shown by morechill-sensitive cultivars, reduced this stimulatory effect.Ethylene production was slightly greater when warming was carriedout in the light rather than in the dark. Key words: Ethylene, ACC, choline, chill-sensitivity, Phaseolus     

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     

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     

Stimulation of ethylene production in bean leaf discs by the pseudomonad phytotoxin coronatine

Coronatine is a toxin produced by Pseudomonas syringae pv. glycinea which induces the same chlorotic response in bean leaves as does infection by the bacterial pathogen. Although the structure of coronatine is known, the biological mode of action is not. One possible clue to its activity is the ethyl-substituted cyclopropane side chain of the molecule. This part structure (1-amino-2-ethycyclopropane-1-carboxylic acid or AEC) is an analog of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC).     

Cell Surface Properties of Pseudomonas syringae pv. phaseolicola Wild-type and hrp Mutants

The cell surface hydrophobicity and charge as well as surface polysaccharides of eight independent prototrophic hrp::-Tn5 mutants (Lindgren et al., J. Bacteriol. 168 , 512–522, 1986) were compared to the wild-type parent strain NPS3121 of Pseudomonas syringae pv. phaseolicola. No significant differences were found in cell surface charge, but mutant strain NPS4005 exhibited significantly lower cell surface hydrophobicity than the wild-type and the other mutant strains. The mutant strains all retained the ability to produce the exopolysaccharides (EPS) levan, a neutral fructan, and alginate, an acidic polymer. Relative amounts of EPS produced in vitro was dependent on culture conditions. Lipopolysaccharide (LPS) chemotypes were similar for all nine strains. Chemical as well as ¹³C-NMR analyses of the O-antigens from four wild-type strains of P. s. pv. phaseolicola representing two physiological races as well as the O-antigens of two strains of P. s. pv. syringae which belong to the same serogroup as P. s. pv. phaseolicola indicated that all of the O-antigens were very similar if not identical. LPS of three strains of P. s. pv. phaseolicola produced in vitro or in planta were also compared and no significant differences were detected. The altered phenotype of the Tn5 mutants of P. s. pv. phaseolicola does not appear to be due to changes in the ability to produce exopolysaccharides or to an altered composition of cell surface polysaccharides (LPS and EPS). However, a change in an unidentified cell surface component(s) leading to lowered cell surface hydrophobicity of mutant strain NPS4005 may be important.     

Ethylene and Ethane Production in 2,4-D Treated and Salt Treated Tobacco Tissue Cultures

Gas chromatography was used to measure ethylene (ethene) andethane production by tobacco (Nicotiana tabacum cv. Wisconsinno. 38) callus tissues grown on media containing inorganic saltsaccording to Murashige and Skoog (1962), sucrose, myo-inositol,thiamine-HCl kinetic according to Linsmaier and Skoog (1965),and either 2,4-dichiorophenoxyacetic acid (2,4-D) in the range0–100 mgl^–1 or 2 mgl^–1 indoi-3-ylacetic acidplus NaCl in the range 0–200 Meq l^–1. Ethylene productionrates were high (> 500 nl h^–1 g^1– fresh weight)initially in all treatments. Subsequently, ethylene productiondeclined in rapidly growing cultures but remained high in moderatelyand severely 2,4-D (> 0·5 mgl^–1) stressed andin severely NaCl (150 Meql^–1) stressed cultures. Highinitial rates of ethane production (> 200 nl h^–1 g^–1fresh weight) were obtained under conditions of severe stresscaused by 2,4-D or NaCl but not in control or moderately inhibitedcultures. With further incubation ethane production declinedin the severely stressed cultures. It is concluded that ethyleneproduction can be used as an index of moderate 2,4-D stressand severe NaCl stress by virtue of the high persisting ratesof ethylene production in stressed cultures. Ethane productioncan be used as an early index of severe stress caused by either2,4-D or NaCl in vitro. Nicotiana tabacum L., tobacco, ethylene, ethenen, ethane, 2,4-dichlorophenoxyacetic acid, auxin, stress, callus tissue