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Biomedical subjects

S F Yang

Publications and source records attributed to S F Yang.

At least 91 records · Page 5Linked to original sources
PubMed1985

Promotion by Ethylene of the Capability to Convert 1-Aminocyclopropane-1-carboxylic Acid to Ethylene in Preclimacteric Tomato and Cantaloupe Fruits.

The intact fruits of preclimacteric tomato (Lycopersicon esculentum Mill) or cantaloupe (Cucumis melo L.) produced very little ethylene and had low capability of converting 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. When these unripe tomato or cantaloupe fruits were treated with ethylene for 16 hours there was no increase in ACC content or in ethylene production rate, but the tissue's capability to convert ACC to ethylene increased markedly. Such an effect was also observed in fruits of tomato mutants rin and nor, which do not undergo ripening and the climacteric increase in ethylene production during the senescence. The development of this ethylene-forming capability induced by ethylene increased with increasing ethylene concentration (from 0.1 to 100 microliters per liter) and duration (1 to 24 hours); when ethylene was removed this capability remained high for sometime (more than 24 hours). Norbornadiene, a competitive inhibitor of ethylene action, effectively eliminated the promotive effect of ethylene in tomato fruit. These data indicate that the development of the capability to convert ACC to ethylene in preclimacteric tomato and cantaloupe fruits are sensitive to ethylene treatment and that when these fruits are exposed to exogenous ethylene, the increase in ethylene-forming enzyme precedes the increase in ACC synthase.

Journal Article↗
PubMed1985

Ethylene Promotes the Capability To Malonylate 1-Aminocyclopropane-1-carboxylic Acid and d-Amino Acids in Preclimacteric Tomato Fruits.

When whole unripe green tomato fruits (Lycopersicon esculentum Mill, cv T(3)) were treated with ethylene (10 microliters per liter) for 18 hours, the fruit's ability to convert 1-aminocyclopropane-1-carboxylic acid (ACC) to N-malonyl-ACC (MACC) increased markedly and such an effect was also observed in fruits of mutant nor, which cannot ripen normally. The promotion of the capability to malonylate ACC by ethylene increased with the increasing ethylene concentration from 0.1 to 100 microliters per liter and with increasing duration of ethylene treatment up to 8 hours; a longer duration of ethylene treatment did not further increase the malonylation capability. When ethylene was withdrawn, the promotion disappeared within 72 hours. Norbornadiene, a competitive inhibitor of ethylene action, effectively eliminated the promotive effect of ethylene. Ethylene treatment also promoted the fruits' capability to conjugate d-amino acids and alpha-amino-isobutyric acid. Since the increase in the tissue's capability to malonylate ACC was accompanied by an increase in the extractable activity of ACC and d-amino acid malonyltransferase, ethylene is thought to promote the development of ACC/d-amino acid malonyltransferase in unripe tomato fruits.

Journal Article↗
PubMed1984

Stereoselectivity of 1-aminocyclopropanecarboxylate malonyltransferase toward stereoisomers of 1-amino-2-ethylcyclopropanecarboxylic acid.

A malonyltransferase isolated from mungbean (Vigna radiata L.) hypocotyls catalyzed the malonylation of both 1-aminocyclopropane-1-carboxylic acid (ACC) and D-amino acids. The possibility that ACC was recognized by the enzyme as a D-amino acid was investigated by examining the efficiencies of the four stereoisomers of 1-amino-2-ethylcyclopropane-1-carboxylic acid (AEC) serving as substrates of malonyltransferase and as inhibitors of ACC malonyltransferase. Although all four isomers were malonylated by the enzyme and competitively inhibited the malonylation of ACC to N-malonyl-ACC, (1R,2S)-AEC and (1R,2R)-AEC, both of which have an R-configuration as a D-amino acid, had lower Km and Ki values (0.1 to 0.2 mM) than their enantiomers, (1S,2R)-AEC (Km and Ki values were about 1 mM) and (1S,2S)-AEC (Km and Ki values were higher than 10 mM), which have an S-configuration as an L-amino acid. Similarly, (R)-isovaline (2-amino-2-methylbutanoic acid), which has an R-configuration as a D-amino acid, inhibited more effectively the enzymatic conversion of ACC to malonyl-ACC than did (S)-isovaline, which has an S-configuration as an L-amino acid. In mungbean hypocotyls (1R,2S)-AEC and (1R,2R)-AEC were also more efficiently converted into malonyl conjugates and more efficiently inhibited the conversion of radioactive ACC into malonyl-ACC than their enantiomers, although the differences in efficiency among stereoisomers were smaller in hypocotyls than in enzymatic reactions. These results suggest that ACC is recognized by the enzyme as a D-amino acid.

Acyltransferases↗
PubMed1984

Formation of cyanide from carbon 1 of 1-aminocyclopropane-1-carboxylic acid during its conversion to ethylene.

It has been shown that 1-aminocyclopropane-1-carboxylic acid (ACC) is the immediate precursor of ethylene, which is derived from C-2 and C-3 of ACC. When [1-(14)C]ACC was administered to etiolated mungbean (Vigna radiata) hypocotyls, approximately 16% of the ACC was converted to ethylene and about 10% of the radioactivity was converted to [(14)C]asparagine in 7 hr. In etiolated epicotyls of common vetch (Vicia sativa), after 7 hr about 14% of the ACC was converted to ethylene and 16% of the radioactivity was converted to beta-cyanoalanine plus gamma-glutamyl-beta-cyanoalanine. Itis known that in most plants cyanide is metabolized to asparagine via the intermediate beta-cyanoalanine, whereas in a fewplants such as V. sativa, beta-cyanoalanine is converted to the conjugate gamma-glutamyl-beta-cyanoalanine. We confirmed that [(14)C]cyanide was metabolized into [(14)C]asparagine in mungbean and into [(14)C]cyanoalanine plus its conjugate in V. sativa. Moreover, after feeding plant tissue with [1-(14)C]ACC, [(14)C]asparagine isolated from mungbean and beta-[(14)C]cyanoalanine from V. sativa were labeled in the C-4 position, as would be expected if these two compounds were derived from [(14)C]cyanide. When the conversion of ACC to ethylene in V. sativa tissue was inhibited by high temperature (41 degrees C), the conversion of [1-(14)C]ACC to beta-[(14)C]cyanoalanine and gamma-glutamyl-beta-[(14)C]cyanoalanine was similarly inhibited. When [carboxyl-(14)C]ACC was administered to mungbean and V. sativa, (14)CO(2) was recovered in an amount equivalent to the amount of ethylene produced. These data indicate that in the conversion of ACC to ethylene the carboxyl group yields CO(2), and C-1 is released as HCN.

Journal Article↗
PubMed1983

Identification and Metabolism of 1-(Malonylamino)cyclopropane-1-carboxylic Acid in Germinating Peanut Seeds.

Peanut seeds (Arachis hypogea L. Yue-you 551) contain 50 to 100 nanomoles per gram conjugated 1-aminocyclopropanecarboxylic acid (ACC). Based on paper chromatography, paper electrophoresis, and gas chromatography-mass spectrometry, it was verified that the major ACC conjugate was N-malonyl-ACC (MACC). Germinating peanut seeds converted [2-(14)C]ACC to ethylene 70 times more efficiently than N-malonyl-[2-(14)C]ACC; when ACC was administered, most of it was metabolized to MACC. Germinating peanut seeds produced ethylene and converted l-[3,4-(14)C]methionine to ethylene; this ethylene biosynthesis was inhibited by aminoethoxyvinylglycine. These data indicate that MACC occurs in peanut seeds but does not serve as the source of ethylene during germination; ethylene is, however, synthesized from methionine via ACC.

Journal Article↗
PubMed1983

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.

Journal Article↗
PubMed1983

Role of ethylene in the senescence of detached rice leaves.

The role of ethylene in the senescence of detached rice leaves in relation to their changes in 1-aminocyclopropane-1-carboxylic acid (ACC) content and ethylene production was studied. In freshly excised rice leaf segments, ACC level and ethylene production rates were very low. Following incubation, the rates of ethylene production increased and reached a maximum in 12 h, and subsequently declined. The rise of ethylene production was associated with a 20- to 30-fold increase in ACC level.Ethylene seems to be involved in the regulation of the senescence of detached rice leaves. This conclusion was based on the observations that (a) maximum ethylene production preceded chlorophyll degradation, (b) ACC application promoted chlorophyll degradation, (c) inhibitors of ethylene production and ethylene action retarded chlorophyll degradation, and (d) various treatments such as light, cycloheximide, alpha,alpha-dipyridyl, Ni(2+), and cold temperature, which retarded chlorophyll degradation, also inhibited ethylene production.Abscisic acid promoted senescence but significantly decreased ethylene production, whereas benzyladenine retarded senescence but promoted ethylene production. This is interpreted to indicate that abscisic acid treatment increased the tissue sensitivity to ethylene, whereas benzyladenine treatment decreased it.

Journal Article↗
PubMed1982

Enhancement of wound-induced ethylene synthesis by ethylene in preclimacteric cantaloupe.

Although intact fruits of unripe cantaloupe (Cucumis melo L.) produce very little ethylene, a massive increase in ethylene production occurred in response to excision. The evidence indicates that this wound ethylene is produced from methionine via 1-aminocyclopropanecarboxylic acid (ACC) as in ripening fruits. Excision induced an increase in both ACC synthase and the enzyme converting ACC to ethylene. Ethylene further increased the activity of the enzyme system converting ACC to ethylene. The induction by ethylene required a minimum exposure of 1 hour; longer exposure had increasingly larger effect. The response was saturated at approximately 3 microliters per liter ethylene and was inhibited by Ag(+). Neither ethylene nor ACC had a promotive or inhibitory effect on ACC synthase beyond the effect attributable to wounding.

Journal Article↗
PubMed1982

Autoinhibition of Ethylene Production in Citrus Peel Discs : SUPPRESSION OF 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID SYNTHESIS.

Wound ethylene formation induced in flavede tissue of citrus fruit (Citrus paradisi MacFad. cv. Ruby Red) by slicing was almost completely inhibited by exogenous ethylene. The inhibition lasted for at least 6 hours after removal of exogenous ethylene and was then gradually relieved. The extent of inhibition was dependent upon the concentration of ethylene (1 to 10 microliters/liter) and the duration of treatment. The increase in wound ethylene production in control discs was paralleled by an increase in 1-aminocyclopropane-1-carboxylic acid (AAC) content, whereas in ethylene-treated discs there was little increase in ACC content. Application of ACC completely restored ethylene production in ethylene-pretreated discs, indicating that the conversion of ACC to ethylene is not impaired by the presence of ethylene. Thus, autoinhibition of ethylene synthesis was exerted by reducing the availability of ACC. Ethylene treatment resulted in a decrease in extractable ACC synthase activity, but this decrease was too small to account for the marked inhibition of ACC formation. The data indicate that autoinhibition of ethylene production in citrus flavede discs results from suppression of ACC formation through repression of the synthesis of ACC synthase and inhibition of its activity.

Journal Article↗
PubMed1982

Effects of exogenous ethylene on ethylene production in citrus leaf tissue.

Exogenous ethylene stimulated ethylene production in intact citrus (Citrus sinensis L. Osbeck cv. "Washington Navel") leaves and leaf discs following a 24-hour exposure. Studies with leaf discs showed that ethylene production decreased when ethylene was removed by aeration. The extent of stimulation was dependent upon the concentration of exogenous ethylene (1-10 microliters per liter). Silver ion blocked the autocatalytic effect of ethylene at concentrations of 0.5 millimolar and lower, but increased ethylene production at higher concentrations. The stimulating effect of ethylene resulted from the enhancement of both 1-aminocyclopropane-1-carboxylic acid (ACC) formation and the conversion of ACC to ethylene. Whereas autocatalysis was evident following 24 hours incubation, autoinhibition of wound- and mannitol-induced ethylene production was observed during the first 24-hour incubation. Ethylene treatment during this period resulted in a marked decrease in ACC levels and ethylene production rates. Furthermore, in leaf discs treated for 24 hours with ethylene, ethylene production rates increased greatly during the first 2 hours after removal of exogenous ethylene by aeration. This increase was eliminated if the discs were transferred to propylene instead of air, indicating that the autocatalytic effect of ethylene is counteracted by its autoinhibitory effect. It is suggested that autocatalysis involves increased synthesis of ACC synthase and the enzyme responsible for the conversion of ACC to ethylene, whereas autoinhibition involves suppression of the activity of these two enzymes.

Journal Article↗
PubMed1982

Stimulation of ethylene production in citrus leaf discs by mannitol.

Wound ethylene formation induced in leaf tissue of citrus (Citrus sinensis [L.] Osbeck cv. "Washington Navel") by excision was significantly stimulated by mannitol after a lag period of about 6 hours. The extent of stimulation was dependent upon the concentration of mannitol (10 to 100 millimolar). This increased ethylene production was not simply due to osmotic effect or water stress as other osmoticums tested failed to exert such an effect. The stimulatory effect of mannitol resulted from both the enhancement of 1-aminocyclopropane-1-carboxylic acid (ACC) formation and the conversion of ACC to ethylene. The effect on the latter step was particularly pronounced in aged discs. The use of labeled mannitol showed that it was taken up by the leaf discs, utilized for respiration, and metabolized to sucrose, but no radioactivity was detected in the ethylene.

Journal Article↗
PubMed1982

Stereospecific conversion of 1-aminocyclopropanecarboxylic Acid to ethylene by plant tissues : conversion of stereoisomers of 1-amino-2-ethylcyclopropanecarboxylic Acid to 1-butene.

Inasmuch as the molecule of 1-aminocyclopropanecarboxylic acid (ACC) possesses reflective symmetry but lacks rotational symmetry, the two chemically alike methylene groups can be distinguished by a stereospecific enzyme. To determine whether ACC conversion to ethylene by plant tissues proceeds in a stereospecific fashion, the four stereoisomers of 1-amino-2-ethylcyclopropanecarboxylic acid (AEC) were administered to postclimacteric apple (Malus sylvestris Mill., var. Golden Delicious), excised preclimacteric cantaloupe (Cucumis melo L., var. reticulatis Naud cv. PMR-45), and etiolated mung bean (Vigna radiata L., Wilczek, var. Berken) hypocotyls. In each case (1R,2S)-AEC was the preferred substrate yielding 1-butene. In contrast, all AEC isomers were converted equally well to butene by chemical oxidation using NaOCl. Both ACC and AEC appear to be substrates for the same enzyme since both reactions are inhibited in parallel by N(2) or Co(2+), both reactions are induced in parallel by excision, and when both substrates are present simultaneously each will act as an inhibitor with respect to the other. The aforementioned observations indicate that ACC is stereospecifically converted to ethylene. For AEC to be the most active precursor of 1-butene, the ethyl substituent should be trans to the carboxyl group and the pro-(S) methylene group should be unsubstituted. This observation leads to the suggestion that the enzyme interacts with amino, carboxyl, and pro-(S) methylene groups, a configuration corresponding to a l-amino acid. This view is consistent with the observation that the l-forms of alanine and methionine inhibit the conversion of ACC to ethylene more than the corresponding d-amino acids in the mung bean hypocotyl system.

Journal Article↗
PubMed1982

A simple method for the determination of resistance to gas diffusion in plant organs.

A simple method was developed for the determination of resistance coefficients for ethylene diffusion in plant tissues based on the kinetic analysis of the efflux of preloaded ethane gas. Efflux curves were analyzed to obtain first-order rate constants and resistance coefficients. Resistance coefficients determined by the ethane efflux and steady-state methods were found to agree well. Employing the ethane efflux method, it was shown that over 97% of gas exchange of tomato (Lycopersicum esculentum Mill., cv. ;Ace') fruits occurs through the stem scar. The resistances to diffusion of tomato skin and stem scar were found to be 280,000 and 300 seconds per centimeter, respectively; the combined resistance of intact tomato fruits was approximately 7,800 seconds per centimeter. The ethane efflux method was employed to show that plastic shrink-wrapping of English cucumbers (Cucumis sativus L. var anglicus Bailey) increased the resistance to ethane diffusion from 1.1 x 10(3) to 23 x 10(3) seconds per centimeter.

Journal Article↗
PubMed1982

Dark metabolism of carbon monoxide in lettuce leaf discs.

In the dark, leaf tissue of crisphead lettuce (Lactuca sativa L.) metabolized (14)CO to (14)CO(2) and acid-stable products. Tissue incubated at 2.5 degrees C for 3.5 hours and 48 hours converted about 1% and 17%, respectively, of the applied (14)CO to (14)CO(2), and incorporated about 0.04% and 0.6% of the (14)C in acid-stable products. Examination of soluble acid-stable products from (14)CO and (14)CO(2)-treated leaf tissue revealed that the labeling patterns of both treatments were identical during the 3.5-hour and the 48-hour incubation periods. Malate, citrate, and aspartate together comprised 70% or more of the soluble radioactivity from both treatments. Incorporation of radioactivity from CO into soluble acid-stable products during a 3-hour incubation period at 2.5 degrees C was inhibited 90% by adding 3% nonradioactive CO(2). These results indicate that in head lettuce in the dark (14)CO is metabolized primarily to (14)CO(2) which is the precursor of acid-stable products. In leaf discs at 2.5 degrees C, the apparent K(m) for CO oxidation to CO(2) was 5.3 microliters per liter and the V(max) was 9.7 nanoliters per gram per hour. The mitochondrial fraction of the leaf homogenate was the most active fraction to oxidize CO to CO(2), and this activity was heat-labile and cyanide-sensitive.

Journal Article↗
PubMed1982

Sulfite-induced lipid peroxidation in chloroplasts as determined by ethane production.

Ethane formation, as a measure of lipid peroxidation, was studied in spinach (Spinacia oleracea L.) chloroplasts exposed to sulfite. Ethane formation required sulfite and light, and occurred with concomitant oxidation of sulfite to sulfate. In the dark, both ethane formation and sulfite oxidation were inhibited. Ethane formation was stimulated by ferric or ferrous ions and inhibited by ethylenediamine tetraacetate. The photosynthetic electron transport modulators, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and phenazine methosulfate, inhibited both sulfite oxidation and ethane formation. Methyl viologen greatly stimulated ethane formation, but had little effect on sulfite oxidation. Methyl viologen, in the absence of sulfite, caused only a small amount of ethane formation in comparison to that produced with sulfite alone. Sulfite oxidation and ethane formation were effectively inhibited by the radical scavengers, 1,2-dihydroxybenzene-3,5-disulfonic acid and ascorbate. Ethanol, a hydroxyl radical scavenger, inhibited ethane formation only to a small degree; formate, which converts hydroxyl radical to superoxide radical, caused a small stimulation in both sulfite oxidation and ethane formation. Superoxide dismutase inhibited ethane formation by 50% when added at a concentration equivalent to that of the endogenous activity. Singlet oxygen did not appear to play a role in ethane formation, inasmuch as the singlet oxygen scavengers, sodium azide and 1,4-diazobicyclo-[2,2,2]-octane, were not inhibitory. These data are consistent with the view that O(2) is reduced by the photosynthetic electron transport system to superoxide anion, which in turn initiates the free radical oxidation of sulfite, and the free radicals produced during sulfite oxidation were responsible for the peroxidation of membrane lipids, resulting in the formation of ethane.

Journal Article↗
PubMed1982

Inhibition of ethylene synthesis in tomato plants subjected to anaerobic root stress.

Enhanced ethylene production and leaf epinasty are characteristic responses of tomato (Lycopersicon esculentum Mill.) to waterlogging. It has been proposed (Bradford, Yang 1980 Plant Physiol 65: 322-326) that this results from the synthesis of the immediate precursor of ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), in the waterlogged roots, its export in the transpiration stream to the shoot, and its rapid conversion to ethylene. Inhibitors of the ethylene biosynthetic pathway are available for further testing of this ACC transport hypothesis: aminooxyacetic acid (AOA) or aminoethoxyvinylglycine (AVG) block the synthesis of ACC, whereas CO(2+) prevents its conversion to ethylene. AOA and AVG, supplied in the nutrient solution, were found to inhibit the synthesis and export of ACC from anaerobic roots, whereas Co(2+) had no effect, as predicted from their respective sites of action. Transport of the inhibitors to the shoot was demonstrated by their ability to block wound ethylene synthesis in excised petioles. All three inhibitors reduced petiolar ethylene production and epinasty in anaerobically stressed tomato plants. With AOA and AVG, this was due to the prevention of ACC import from the roots as well as inhibition of ACC synthesis in the petioles. With Co(2+), conversion of both root- and petiole-synthesized ACC to ethylene was blocked. Collectively, these data support the hypothesis that the export of ACC from low O(2) roots to the shoot is an important factor in the ethylene physiology of waterlogged tomato plants.

Journal Article↗