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PubMed1988

beta-Glucoside Activators of Mung Bean UDP-Glucose: beta-Glucan Synthase : I. Identification of an Endogenous beta-Linked Glucolipid Activator.

Heat-stable activators of membranous beta-glucan synthase have been isolated from the supernatant fraction of crude mung bean (Vigna radiata) extracts by DEAE-cellulose and silica-gel chromatography. One of the activators has been partially purified and characterized on the basis of susceptibility to various enzymes and by analysis of the products formed upon total acid hydrolysis, alkaline-methanolysis, and beta-glucosidase digestion. This activator has the characteristics of a 1,2-dioleoyl diglyceride containing beta-linked glucose residue(s) at the C-3 position. When expressed per mole of glucosyl residues, the maximal K(a) value of the activator is estimated to be 25 micromolar. Both the intact glucosyl and fatty acid moiety are essential to the stimulatory effect of the activator.

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PubMed1988

Changes in the Level of [C]Indole-3-Acetic Acid and [C]Indoleacetylaspartic Acid during Root Formation in Mung Bean Cuttings.

Changes in the levels of [(14)C]indole-3-acetic acid (IAA) and [(14)C]indole-acetylaspartic acid (IAAsp) were examined during adventitious root formation in mung bean (Vigna radiata [L.] R. Wilcz. ;Berken') stem cuttings. IAAsp was identified by GC-MS as the primary conjugate in IAA-treated cuttings. During root formation in IAA-treated cuttings, the level of [(14)C]IAAsp increased rapidly the first day and then declined; [(14)C]IAA was rapidly metabolized and not detected after 12 hours.

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PubMed1988

Oxidative decarboxylation of branched-chain 2-oxo Fatty acids by higher plant peroxisomes.

Peroxisomes from mung bean (Vigna radiata L.) hypocotyls catalyze, in the presence of branched-chain 2-oxo fatty acid, CoASH and NAD, the release of CO(2), and the formation of NADH and acyl-CoA. The acyl-CoA contains one carbon atom less than the branched-chain 2-oxo fatty acid and serves as substrate for the peroxisomal acyl-CoA oxidase. CO(2) release, NADH and acyl-CoA formation occur in 1:1:1 stoichiometry. For the first time the data demonstrate directly the oxidative decarboxylation of branched-chain 2-oxo fatty acids in higher plants and a location of this activity in the peroxisomes.

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PubMed1988

Cyanide metabolism in relation to ethylene production in plant tissues.

HCN is the putative product of C-1 and amino moieties of 1-aminocyclopropane-1-carboxylic acid (ACC) during its conversion to ethylene. In apple (Malus sylvestrus Mill.) slices or auxin-treated mungbean (Vigna radiata L.) hypocotyls, which produced ethylene at high rates, the steady state concentration of HCN was found to be no higher than 0.2 micromolar, which was too low to inhibit respiration (reported Ki for HCN to inhibit respiration was 10-20 micromolar). However, these tissues became cyanogenic when treated with ACC, the precursor of ethylene, and with 2-aminoxyacetic acid, which inhibits beta-cyanoalanine synthase, the main enzyme to detoxify HCN; the HCN levels in these tissues went up to 1.7 and 8.1 micromolar, respectively. Although ethylene production by avocado (Persea gratissima) and apple fruits increased several hundred-fold during ripening, beta-cyanoalanine synthase activity increased only one- to two-fold. These findings support the notion that HCN is a co-product of ethylene biosynthesis and that the plant tissues possess ample capacity to detoxify HCN formed during ethylene biosynthesis so that the concentration of HCN in plant tissues is kept at a low level.

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PubMed1988

Inhibition of nodule functioning in cowpea by a xanthine oxidoreductase inhibitor, allopurinol.

Allopurinol (1H-pyrazolo-[3,4-d]pyrimidine-4-ol), an inhibitor of xanthine oxidation in ureide-producing nodulated legumes, was taken up from the rooting medium, translocated in xylem, and transferred to nodules of both the ureide-forming cowpea (Vigna unguiculata L. Walp.) and the amide-forming white lupin (Lupinus albus L.). Cowpea suffered severe nitrogen deficiency, extreme chlorosis, and reduced growth, whereas lupin was unaffected by the inhibitor. Similar results were obtained with oxypurinol (1H-pyrazolo-[3,4-d]pyrimidine-4,6-diol). Xylem composition of symbiotic cowpea was markedly changed by allopurinol. Ureides fell to a very low level, but xanthine and, to a lesser extent, hypoxanthine increased markedly. Xylem glutamine was also reduced, but there was little change in other amino acids. Nitrogenase (EC 1.7.99.2) activity of intact nodulated plants or nodulated root segments of plants treated with allopurinol or oxypurinol for 24 hours or more was severely inhibited in cowpea but unaffected in lupin for periods of exposure up to 9 days. Nitrogenase activity of slices of nodules prepared from allopurinol-treated cowpea showed inhibition comparable to that of intact plants. Breis prepared from nodules of treated plants showed no reduction in nitrogenase, nor was there reduction in activity of breis following addition of allopurinol, xanthine, or a range of purine pathway intermediates. Increasing the O(2) concentration in assays above 20% (volume/volume) reversed inhibition of nitrogenase by allopurinol in intact nodulated roots. It was concluded for cowpea that allopurinol not only inhibited ureide synthesis but also caused inhibition of nitrogenase activity, thereby leading to progressive dysfunction and eventual senescence of nodules. The mechanistic relationships between inhibition of ureide biosynthesis, changes in gaseous diffusion resistance, and reduced nitrogenase activity remain obscure.

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PubMed1989

Purification and characterization of tonoplast ATPase from etiolated mung bean seedlings.

The tonoplast ATPase from etiolated seedlings of Vigna radiata L. (mung bean) was isolated using a two-step detergent solubilization modified from Mandala and Taiz (S Mandala, L Taiz [1985] Plant Physiol 78: 327-333). After ultracentrifugation on 10 to 28% sucrose gradient, the ATPase showed a 31.6-fold purification over the initial specific activity of the starting tonoplast-enriched membranes. The purified ATPase used Mg(2+)-ATP as the preferred substrate. The tonoplast ATPase was isolated in a form with characteristics similar to that on its native membrane environment. Analysis by SDS-PAGE revealed two prominent bands with molecular weights of 78,000 (alpha subunit) and 64,000 (beta subunit). The intensity of Coomassie blue staining showed a 1:1 stoichiometry for alpha and beta subunits. The amino acid composition of alpha and beta subunits also confirmed the suggested stoichiometry of the subunit composition of the tonoplast ATPase. Moreover, radiation inactivation analysis yielded a functional size of 414 +/- 24 and 405 +/- 25 kilodaltons for soluble and membrane bound tonoplast ATPases, respectively. It is possible that the functioning tonoplast ATPase may be in a form of alphabeta-heteromultimer.

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PubMed1989

Manipulating membrane Fatty Acid compositions of whole plants with tween-Fatty Acid esters.

This paper describes a method for manipulating plant membrane fatty acid compositions without altering growth temperature or other conditions. Tween-fatty acid esters carrying specific fatty acids were synthesized and applied to various organs of plants growing axenically in glass jars. Treated plants incorporated large amounts of exogenous fatty acids into all acylated membrane lipids detected. Fatty acids were taken up by both roots and leaves. Fatty acids applied to roots were found in leaves, while fatty acids applied to leaves appeared in both leaves higher on the plant and in roots, indicating translocation (probably in the phloem). Foliar application was most effective; up to 20% of membrane fatty acids of leaves above the treated leaf and up to 40% of root membrane fatty acids were exogenously derived. Plants which took up exogenous fatty acids changed their patterns of fatty acid synthesis such that ratios of saturated to unsaturated fatty acids remained essentially unaltered. Fatty acid uptake was most extensively studied in soybean (Glycine max [L.] Merr.), but was also observed in other species, including maize (Zea mays L.), mung beans (Vigna radiata L.), peas (Pisum sativum L.), petunia (Petunia hybrida L.) and tomato (Lycopersicon esculentum Mill.). Potential applications of this system include studying internal transport of fatty acids, regulation of fatty acid and membrane synthesis, and influences of membrane fatty acid composition on plant physiology.

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PubMed1989

Control of alpha-Amylase Development in Cotyledons during and following Germination of Mung Bean Seeds.

Developmental patterns of alpha-amylase in Vigna radiata cotyledons during and following germination were quite different depending on the differences in the treatments of cotyledons during the imbibitional stage. When axis-detached cotyledons were imbibed in water with seed-coats attached, alpha-amylase activity did not increase and remained low. On the other hand, when the cotyledons were imbibed in water after seed-coat removal, the enzyme activity increased markedly. If the axis was attached to the cotyledons, alpha-amylase showed a marked development even under the former imbibition conditions. These changes in the enzyme activity were in parallel with those in the enzyme content, and the content, in turn, was dependent upon the availability of mRNA for alpha-amylase. We propose that the regulation of the development of alpha-amylase in cotyledons may involve some factor(s) inhibitory to accumulation of alpha-amylase mRNA, which is present in dry cotyledons and can be removed from cotyledons by leakage or by the presence of the axis.

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PubMed1989

Salinity effects on photosynthesis in isolated mesophyll cells of cowpea leaves.

Mesophyll cells from leaves of cowpea (Vigna unquiculata [L.] Walp.) plants grown under saline conditions were isolated and used for the determination of photosynthetic CO(2) fixation. Maximal CO(2) fixation rate was obtained when the osmotic potential of both cell isolation and CO(2) fixation assay media were close to leaf osmotic potential, yielding a zero turgor pressure. Hypotonic and hypertonic media decreased the rate of photosynthesis regardless of the salinity level during plant growth. No decrease in photosynthesis was obtained for NaCl concentrations up to 87 moles per cubic meter in the plant growing media and only a 30% decrease was found at 130 moles per cubic meter when the osmotic potential of cell isolation and CO(2) fixation media were optimal. The inhibition was reversible when stress was relieved. At 173 moles per cubic meter NaCl, photosynthesis was severely and irreversibly inhibited. This inhibition was attributed to toxic effects caused by high Cl(-) and Na(+) accumulation in the leaves. Uptake of sorbitol by intact cells was insignificant, and therefore not associated with cell volume changes. The light response curve of cells from low salinity grown plants was similar to the controls. Cells from plants grown at 173 moles per cubic meter NaCl were light saturated at a lower radiant flux density than were cells from lower salinity levels.

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PubMed1989

Peroxisomal degradation of branched-chain 2-oxo acids.

Branched-chain 2-oxo acids which are formed by transamination of leucine, isoleucine, and valine are metabolized by the peroxisomes from mung bean (Vigna radiata L.) hypocotyls. Acylcoenzyme A (CoA) thio ester intermediates of the pathways were separated by reversed-phase high performance liquid chromatography. Retention time and cochromatography of individual acyl-CoA reference standards were used for identification of the acyl-CoA esters separated from the assay mixtures. Based on the results of identification and those of kinetic experiments, pathways of the peroxisomal degradation of 2-oxoisocaproate, 2-oxoisovalerate, and 2-oxo-3-methylvalerate are suggested.

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PubMed1990

Purification and characterization of a cysteine endopeptidase in cotyledons of germinated mung bean seeds.

A cysteine endopeptidase (EC 3.4.22.-) present in cotyledons of mung bean (Vigna radiata) seedlings was purified to homogeneity, as judged by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). This proteinase has an apparent molecular mass of 33 kilodaltons as estimated by SDS-PAGE and belongs to the class of cysteine proteinases as judged by the effects of various proteinase inhibitors on the activity of the enzyme. When proangiotensin is used as a substrate, the enzyme preferentially hydrolyzes the peptide bonds formed by the amino group of Leu or lle in this oligopeptide chain; for the enzyme to cleave those bonds, peptide sequences consisting of at least three amino acid residues on the amino side of Leu or lle must be present. The proteinase readily digests globulin present in mung bean cotyledons to smaller polypeptides.

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PubMed1990

Effects of heat shock on amino Acid metabolism of cowpea cells.

When cowpea (Vigna unguiculata) cells maintained at 26 degrees C are transferred to 42 degrees C, rapid accumulation of gamma-aminobutyrate (>10-fold) is induced. Several other amino acids (including beta-alanine, alanine, and proline) are also accumulated, but less extensively than gamma-aminobutyrate. Total free amino acid levels are increased approximately 1.5-fold after 24 hours at 42 degrees C. Heat shock also leads to release of amino acids into the medium, indicating heat shock damage to the integrity of the plasmalemma. Some of the changes in metabolic rates associated with heat shock were estimated by monitoring the (15)N labeling kinetics of free intracellular, extracellular and protein-bound amino acids of cultures supplied with (15)NH(4) (+), and analyzing the labeling data by computer simulation. Preliminary computer simulation models of nitrogen flux suggest that heat shock induces an increase in the gamma-aminobutyrate synthesis rate from 12.5 nanomoles per hour per gram fresh weight in control cells maintained at 26 degrees C, to as high as 800 nanomoles per hour per gram fresh weight within the first 2 hours of heat shock. This 64-fold increase in the gamma-aminobutyrate synthesis rate greatly exceeds the expected (Q(10)) change of metabolic rate of 2.5- to 3-fold due to a 16 degrees C increase in temperature. We suggest that this metabolic response may in part involve an activation of glutamate decarboxylase in vivo, perhaps mediated by a transient cytoplasmic acidification. Proline appears to be synthesized from glutamate and not from ornithine in cowpea cells. Proline became severalfold more heavily labeled than ornithine, citrulline and arginine in both control and heat-shocked cultures. Proline synthesis rate was increased 2.7-fold by heat shock. Alanine, beta-alanine, valine, leucine, and isoleucine synthesis rates were increased 1.6-, 3.5-, 2.0-, 5.0-, and 6.0-fold, respectively, by heat shock. In contrast, the phenylalanine synthesis rate was decreased by 50% in response to heat shock. The differential effects of heat stress on metabolic rates lead to flux and pool size redistributions throughout the entire network of amino acid metabolism.

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PubMed1990

Isolation of a cDNA Clone for alpha-Amylase in Mung Bean Cotyledons : Analysis of alpha-Amylase mRNA Levels in Cotyledons during and following Germination of Mung Bean Seeds.

A cDNA was isolated that codes for alpha-amylase in mung bean (Vigna radiata) cotyledons, and the nucleotide sequence was determined. The deduced amino acid sequence (421 amino acid residues) is about 65% homologous with those of barley alpha-amylases. By comparing the deduced sequence with the sequence of the purified alpha-amylase, it was inferred that 23 N-terminal amino acids of a nascent polypeptide represent a signal peptide. Northern blot analysis showed that the levels of alpha-amylase mRNA are in parallel with the activities of alpha-amylase synthesis in cotyledons. Under the conditions where the solute leakage from cotyledons is accelerated during imbibition, a rapid increase in the amount of the alpha-amylase mRNA occurs. We postulate that a factor(s) which regulates in an inhibitory manner the alpha-amylase expression at the transcriptional level may be present in dry cotyledons and be removed by leakage.

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PubMed1991

Chilling-Induced Inactivation and Its Recovery of Tonoplast H-ATPase in Mung Bean Cell Suspension Cultures.

The processes involved in adaptation to cold temperature were examined by growing suspension cultured cells of mung bean (Vigna radiata [L.] Wilczek) at 2 degrees C for various periods of time and assaying the activities of various membrane-bound enzymes in vitro. The tonoplast H(+)-ATPase activity and the ATP-proton transport extracted from cells incubated at 2 degrees C declined rapidly and reached a minimum level after 10 hours. The inactivation was reversible within 24 hours of chilling. The recovery of the cold-inactivated H(+)-ATPase was found to proceed in two steps, a faster recovery of ATP hydrolysis activity and a slower recovery of the proton transport. The recovery was markedly inhibited by the presence of azide, but not affected by 0.578 millimolar cycloheximide. This suggested the involvement of an energy process that had no requirement for de novo synthesis of protein. The cold-induced inactivation of the H(+)-ATPase may be due to a structural alteration of the enzyme. The slower recovery of proton transport relative to ATP hydrolysis during warming suggests that the protogenic domains in the enzyme may be affected differently by chilling.

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PubMed1991

Comparison of Temperature Dependency of Tonoplast Proton Translocation between Plants Sensitive and Insensitive to Chilling.

Proton transport activities in isolated tonoplast vesicles were measured as quenching of fluorescence of acridine orange. A marked difference in the temperature dependency of two types of tonoplast proton transports, i.e. ATP- and pyrophosphate-driven, was observed between two leguminous plants sensitive (mung bean, Vigna radiata [L.] Wilczek) and insensitive (pea, Pisum sativum L.) to chilling. In tonoplast vesicles isolated from hypcotyls of mung bean seedlings that were germinated for 3.5 days at 26 degrees C in the dark, the total amount of fluorescence quenching at the steady state in both types of proton pumps, as a measurement of the inside-acidic pH gradient across the membrane vesicles, was markedly suppressed under temperatures below 10 degrees C. In tonoplast vesicles isolated from epicotyls of pea seedlings, which were germinated for 7 days at 18 degrees to 23 degrees C in the dark, no suppression occurred in the formations of the pH gradient in either type of proton pump, even at 0 degrees C. The cause of the low temperature-induced suppression of the proton pumps in mung bean tonoplasts seems to be not an increased permeability of the membrane vesicles to protons or accompanying anions and cations, but instead a marked inhibition in the catalytic activity of both enzymes under low temperatures.

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PubMed1991

Effect of pO(2) on the Formation and Status of Leghemoglobin in Nodules of Cowpea and Soybean.

Nodulated cowpea (Vigna unguiculata [L.] Walp. cv Vita 3: Bradyrhizobium strain CB756) and soybean (Glycine max [L.] Merr. cv White Eye: Bradyrhizobium strain CB1809) were grown with their root systems maintained in a flowing gas stream containing a range of pO(2) (1-80%, v/v) in N(2) for up to 28 days after planting. At the extremes of sub- and supra-ambient pO(2), the levels of leghemoglobin (Lb) in nodules were reduced. However, neither the proportional composition of Lb component proteins (eight in soybean, three in cowpea) nor their oxidation state was affected by pO(2). Short-term changes in pO(2) (transferring plants grown with sub- or supra-ambient pO(2) in the rhizosphere to air or vice versa) caused a significant decline in Lb content and, in cowpea but not soybean, where pO(2) was increased, a higher percentage of oxidation of Lb. Combining data on changes in Lb level of cowpea nodules grown in sub-ambient pO(2) with those for their structural adaptation to an under supply of O(2) indicated that, despite the nodules having a lower level of Lb, the amount per infected cell was increased by up to twofold and per bacteroid up to fivefold (in those from 1% O(2)) compared to those grown in air. Progressive decline in pO(2) resulted in a progressive increase on this basis, indicating a close relationship between Lb content and the adaptation of nodule functioning to external O(2) level.

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PubMed1991

Xyloglucan antibodies inhibit auxin-induced elongation and cell wall loosening of azuki bean epicotyls but not of oat coleoptiles.

Polyclonal antibodies were raised in rabbits against isoprimeverose (Xyl(1)Glc(1)), xyloglucan heptasaccharides (Xyl(3)Glc(4)), and octasaccharides (Gal(1)Xyl(3)Glc(4)). Antibodies specific for hepta- and octasaccharides suppressed auxin-induced elongation of epicotyl segments of azuki bean (Vigna angularis Ohwi and Ohashi cv Takara). These antibodies also inhibited auxin-induced cell wall loosening (decrease in the minimum stress-relaxation time and the relaxation rate of the cell walls) of azuki segments. However, none of the antibodies influenced auxin-induced elongation or cell wall loosening of coleoptile segments of oat (Avena sativa L. cv Victory). Auxin caused a decrease in molecular mass of xyloglucans in the cell walls of azuki epicotyls and oat coleoptiles. The antibodies inhibited such a change in molecular mass of xyloglucans in both species. Preimmune serum exhibited little or no inhibitory effect on auxin-induced elongation, cell wall loosening, or breakdown of xyloglucans. The results support the view that the breakdown of xyloglucans is associated with the cell wall loosening responsible for auxin-induced elongation in dicotyledons. The view does not appear to be applicable to poaceae, because the inhibition of xyloglucan breakdown by the antibodies did not influence auxin-induced elongation or cell wall loosening of oat coleoptiles.

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PubMed1991

Association of phosphoenolpyruvate phosphatase activity with the cytosolic pyruvate kinase of germinating mung beans.

The procedure of Malhotra and Kayastha ([1990] Plant Physiology 93: 194-200) for the purification to homogeneity of a phosphoenolpyruvate-specific alkaline phosphatase (PEP phosphatase) from germinating mung beans (Vigna radiata) was followed. Although a higher specific activity of 1.4 micromoles pyruvate produced per minute per milligram protein was obtained, the final preparation was less than 10% pure as judged by polyacrylamide gel electrophoresis. Attempts to further purify the enzyme resulted in loss of activity. The partially purified enzyme contained significant pyruvate kinase activity (0.13 micromole pyruvate produced per minute per milligram protein) when assayed at pH 7.2, but not at pH 8.5. The PEP phosphatase activity of the final preparation exhibited hysteresis; a lag time of 5 to 6 minutes was required before a steady-state reaction rate was attained. A western blot of the final preparation revealed an immunoreactive 57 kilodalton polypeptide when probed with monospecific rabbit polyclonal antibodies prepared against germinating castor bean cytosolic pyruvate kinase. No antigenic cross-reaction of the final preparation was observed with antibodies against castor bean leucoplast pyruvate kinase, or black mustard PEP-specific acid phosphatase. Nondenaturing polyacrylamide gel electrophoresis of the final preparation resulted in a single PEP phosphatase activity band; when this band was excised and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and western blotting, a 57 kilodalton silver-staining polypeptide was obtained that strongly cross-reacted with the anti-(cytosolic pyruvate kinase) immunoglobulin G. It is suggested that mung bean PEP-specific alkaline phosphatase activity is due to cytosolic pyruvate kinase, in which pyruvate and ortho-phosphate are formed in the absence of ADP.

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