Biomedical subjects

P M Ray

Publications and source records attributed to P M Ray.

At least 37 records · Page 2Linked to original sources

PubMed1981

pH-Dependent Interactions between Pea Cell Wall Polymers Possibly Involved in Wall Deposition and Growth.

In an effort to detect a pH-dependent release of polymers such as xyloglucans, thought to be involved in auxin-induced cell wall expansion during growth, radioactively labeled cell walls from pea stem tissue were incubated at different pH values, and changes in water-soluble, ethanol- or trichloroacetic acid-insoluble components were determined. This revealed the occurrence, at neutral pH, of a time- and pH-dependent binding of soluble pectin, in the walls, to a heat-labile, presumably protein, wall component, yielding a trichloroacetic acid-insoluble pectin-protein complex. This reaction, which can also be observed between polymers in water extracts of cell walls, is inhibited at low pH and by Ca(2+), and appears to be of a physical, possibly lectin-like, nature. Progressive binding of pectin or of the pectin-protein complex to the insoluble wall structure is also observed. These reactions may be involved in wall assembly during its deposition, and may participate in, or be analogous to pH-dependent physical interactions that participate in, wall extension during cell growth.

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PubMed1981

Evidence for Receptor Function of Auxin Binding Sites in Maize : RED LIGHT INHIBITION OF MESOCOTYL ELONGATION AND AUXIN BINDING.

When 3- to 4-day-old dark-grown maize (Zea mays L. WF9 x Bear 38) seedlings are given red light, auxin-binding activity localized on endoplasmic reticulum membranes of the mesocotyl begins to decrease after 4 hours; by 9 hours, it falls to 50 to 60% of that in dark controls, on either a fresh weight or total particulate protein basis. Endoplasmic reticulum-localized NADH:cytochrome c reductase activity decreases in parallel. Loss of binding is due to decrease in number of sites, with no change in their affinity for auxin (K(d) 0.2 micromolar for naphthalene-1-acetic acid). Elongation of mesocotyl segments in response to auxin decreases with a similar time course. Elongation of segments from irradiated plants shows the same apparent affinity for auxin as that of the dark controls. Auxin-binding activity and elongation response also decrease in parallel down the length of the mesocotyl. These observations are consistent with a role of endoplasmic reticulum-localized auxin binding sites as receptors for auxin action in cell elongation.

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PubMed1980

Cooperative action of beta-glucan synthetase and UDP-xylose xylosyl transferase of Golgi membranes in the synthesis of xyloglucan-like polysaccharide.

Golgi membranes of pea seedling tissue contain a UDP xylose:polysaccharide xylosyl transferase, the action of which is stimulated by UDP glucose. In the presence of both nucleotide-sugars a heteropolysaccharide containing both xylose and glucose (xyloglucan) is produced. Transfer of xylose and glucose units is presumed to be due to separate enzymes, because their properties differ in a number of respects. Xylosyl units appear to be transferred to a glucan core polysaccharide that is produced from UDP glucose by beta-1,4-glucan synthetase. This, rather than cellulose biosynthesis, is inferred to be the in vivo role of Golgi membrane beta-1,4-glucan synthetase.

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PubMed1978

Labeling of the Plasma Membrane of Pea Cells by a Surface-localized Glucan Synthetase.

When radioactive UDP-glucose is supplied to 1-millimeter-thick slices of pea (Pisum sativum) stem tissue, radioactive glucose becomes incorporated into membrane-bound polysaccharides. Evidence is given that this incorporation does not result from breakdown of UDP-glucose and utilization of the resultant free glucose, and that the incorporation most likely takes place at the cell surface, leading to a specific labeling of the plasma membrane. The properties of the plasma membrane that are indicated by this method of recognition, including the association of K(+)-stimulated ATPase activity with the plasma membrane, resemble properties inferred using other approaches. The membrane-associated polysaccharide product formed from UDP-glucose is largely 1,3-linked glucan, presumably callose, and does not behave as a precursor of cell wall polymers. No substantial amount of cellulose is formed from UDP-glucose in this procedure, even though these cells incorporate free glucose rapidly into cellulose. This synthetase system that uses external UDP-glucose may serve for formation of wound callose.

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PubMed1977

Phospholipid-synthesizing Enzymes Associated with Golgi Dictyosomes from Pea Tissue.

Golgi dictyosomal membranes isolated from pea (Pisum sativum) stem tissue, using a combination of rate zonal and isopycnic sucrose density centrifugation, were shown to bear cytidine diphosphate-choline:diglyceride phosphorylcholinetransferase, CDP-ethanolamine:diglyceride phosphorylethanolaminetransferase, and CTP:phosphorylcholine cytidyltransferase activities. Although the majority of the activity of the phospholipid-synthesizing enzymes was associated with the endoplasmic reticulum, the activity found in the Golgi system was about 25% of the total activity. These results suggest that Golgi dictyosomes probably synthesize at least part of the membrane phospholipids that they may need for their secretory function and for dictyosomal proliferation during cell growth, rather than importing this material entirely from the endoplasmic reticulum.

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PubMed1977

Characterization of naphthaleneacetic Acid binding to receptor sites on cellular membranes of maize coleoptile tissue.

Characteristics of and optimum conditions for saturable ("specific") binding of [(14)C]naphthaleneacetic acid to sites located on membranous particles from maize (Zea mays L.) coleoptiles are described. Most, if not all, of the specific binding appears to be due to a single kinetic class of binding sites having a K(D) of 5 to 7 x 10(-7)m for naphthalene-1-acetic acid (NAA). Binding of NAA is insensitive to high monovalent salt concentrations, indicating that binding is not primarily ionic. However, specific binding is inhibited by Mg(2+) or Ca(2+) above 5 mm. Specific binding is improved by organic acids, especially citrate. Binding is heat-labile and is sensitive to agents that act either on proteins or on lipids. Specific binding is reversibly inactivated by reducing agents such as dithioerythritol; a reducible group, possibly a disulfide group, may be located at the binding site and required for its function. The affinity of the specific binding sites for auxins is modified by an unidentified dialyzable, heat-stable, apparently amphoteric, organic factor ("supernatant factor") found in maize tissue.

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PubMed1977

Auxin-binding Sites of Maize Coleoptiles Are Localized on Membranes of the Endoplasmic Reticulum.

Sites in maize (Zea mays L.) coleoptile homogenates that reversibly bind naphthalene-1-acetic acid with high affinity and may represent receptor sites for auxins are located primarily on cellular membranes that show the enzymic and buoyant density characteristics of membranes of the rough endoplasmic reticulum. The sites remain attached to the endoplasmic reticulum (ER) membranes after the ribosomes have been stripped off them. Binding sites for naphthylphthalamic acid, an inhibitor of auxin transport, are located on membranes different from those that carry the naphthalene-1-acetic-acid (NAA)-binding sites, and which are probably plasma membrane. The two kinds of binding sites can be largely separated by appropriate density gradient centrifugation. The results raise the possibility that primary auxin action occurs at ER membranes and could represent facilitation of the transfer of hydrogen ions and nascent secretory protein into the ER lumen followed by secretory transport of these products to the cell exterior via the Golgi system.

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PubMed1977

Specificity of Auxin-binding Sites on Maize Coleoptile Membranes as Possible Receptor Sites for Auxin Action.

Dissociation coefficients of auxin-binding sites on maize (Zea mays L.) coleoptile membranes were measured, for 48 auxins and related ring compounds, by competitive displacement of (14)C-naphthaleneacetic acid from the binding sites. The sites bind with high affinity several ring compounds with acidic side chains 2 to 4 carbons long, and much more weakly bind neutral ring compounds and phenols related to these active acids, most phenoxyalkylcarboxylic acids, and arylcarboxylic acids except benzoic acid, which scarcely binds, and triiodobenzoic acids, which bind strongly. Specificity of the binding is narrowed in the presence of a low molecular weight "supernatant factor" that occurs in maize and other tissues. Activity of many of the analogs as auxin agonists or antagonists in the cell elongation response was determined with maize coleoptiles. These activities on the whole roughly parallel the affinities of the binding sites for the same compounds, especially affinities measured in the presence of supernatant factor, but there are some quantitative discrepancies, especially among phenoxyalkylcarboxylic acids. In view of several factors that can cause receptor affinity and biological activity values to diverge quantitatively among analogs, the findings appear to support the presumption that the auxin-binding sites may be receptors for auxin action.

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PubMed1976

Rapid Auxin-induced Decrease in Free Space pH and Its Relationship to Auxin-induced Growth in Maize and Pea.

A pH microelectrode has been used to investigate the auxin effect on free space pH and its correlation with auxin-stimulated elongation in segments of pea (Pisum sativum) stem and maize (Zea mays var. Bear Hybrid) coleoptile tissue. Auxin induces a decrease in free space pH in both tissues. In maize coleoptiles, free space pH begins to fall within about 12 minutes of exposure to auxin and decreases by about 1 pH unit by approximately 30 minutes. In pea, pH begins to decrease within an average of 15 to 18 minutes of exposure to auxin and falls by about 0.9 pH unit by approximately 40 minutes. Auxin-stimulated elongation, measured in the same two tissues similarly prepared, appears in maize at the earliest 18 minutes after auxin application, while in pea it appears at the earliest 21 to 24 minutes after auxin application. The auxin analogs p-chlorophenoxyisobutyric acid and phenylacetic acid do not stimulate elongation above control levels in maize or pea tissue segments and do not cause a decrease in free space pH in either tissue. These findings are consistent with the acid secretion theory of auxin action.

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PubMed1975

Promotion of Xyloglucan Metabolism by Acid pH.

Like indoleacetic acid, buffers of acidic pH, which stimulate elongation of pea (Pisum sativum var. Alaska) stem tissue, induce the appearance within the tissue of a watersoluble xyloglucan polymer that probably arises from previously deposited wall material. Neutral pH buffers, which inhibit the elongation response to indoleacetic acid in this tissue, inhibit indoleacetic acid-induced increase in soluble xyloglucan. The findings provide further evidence that release of soluble xyloglucan from the cell walls of pea results from the biochemical action on the cell wall that is responsible for wall extension. The data also indicate that treatment of tissue with either auxin or acidic pH has a similar biochemical effect on the cell wall. This is consistent with the H(+) secretion theory of auxin action.

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PubMed1974

Turnover of cell wall polysaccharides in elongating pea stem segments.

Turnover of cell wall polysaccharides and effects of auxin thereon were examined after prelabeling polysaccharides by feeding pea (Pisum sativum var. Alaska) stem segments (14)C-glucose, then keeping the tissue 7 hours in unlabeled glucose with or without indoleacetic acid. There followed an extraction, hydrolysis, and chromatography procedure by which labeled monosaccharides and uronic acids were released and separated with consistently high recovery. Most wall polymers, including galacturonan and cellulose, did not undergo appreciable turnover. About 20% turnover of starch, which normally contaminates cell wall preparations but which was removed by a preliminary step in this procedure, occurred in 7 hours. Quantitatively, the principal wall polymer turnover process observed was a 50% decrease in galactose in the pectinase-extractable fraction, including galactose attached to a pectinase-resistant rhamnogalacturonan. Other pectinase-resistant galactan(s) did not undergo turnover. No turnover was observed in arabinans, but a doubling of radioactivity in arabinose of the pectinase-resistant, hot-acid-degradable fraction occurred in 7 hours, possibly indicating conversion of galactan into arabinan. None of the above changes was affected by indoleacetic acid, but a quantitatively minor turnover of a pectinase-degradable xyloglucan was found to be consistently promoted by indole-acetic acid. This was accompanied by a reciprocal increase in water-soluble xyloglucan, suggesting that indoleacetic acid induces conversion of wall xyloglucan from insoluble to water-soluble form. The results indicate a highly selective pattern of wall turnover processes with an even more specific influence of auxin.

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PubMed1974

Relationship between Promotion of Xyloglucan Metabolism and Induction of Elongation by Indoleacetic Acid.

Auxin promotes the liberation of a xlyoglucan polymer from the cell walls of elongating pea (Pisum sativum) stem segments. The released polymer can be isolated from the polysaccharide fraction of the water-soluble portion of tissue homogenates, thus providing as assay for this kind of metabolism. Promotion of xyloglucan metabolism by auxin begins within 15 minutes of hormone presentation. The effect increases with auxin concentration in a manner similar to the hormone effect on elongation. However, the xyloglucan effect of auxin occurs perfectly normally when elongation is completely blocked by mannitol. Metabolic inhibitors and Ca(2+), on the other hand, inhibit auxin promotion of elongation and of xyloglucan metabolism in parallel. The results suggest that the changes in xyloglucan reflect the means by which auxin modifies the cell wall to cause elongation.

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PubMed1973

Regulation of beta-Glucan Synthetase Activity by Auxin in Pea Stem Tissue: I. Kinetic Aspects.

Treatment of pea stem segments with indoleacetic acid (IAA) causes within 1 hour a 2- to 4-fold increase in activity of particulate uridine diphosphoglucose-dependent beta-glucan synthetase obtainable from the tissue. The IAA effect is observable in tissue from all parts of the elongation zone of the pea stem, and also in older tissue that is not capable of a cell enlargement response to IAA. A large increase in activity is caused by IAA only if synthetase activity in the isolated tissue has first been allowed to fall substantially below the intact plant level, and only if sucrose is supplied along with IAA. Treatment of tissue with sucrose alone after a period of sugar starvation causes a transient rise of synthetase activity. The decline in synthetase activity in absence of IAA, the rise caused by IAA, and the transient rise caused by sucrose are all strongly temperature-dependent. IAA and sucrose do not affect the activity of isolated synthetase particles. Synthetase activity in vivo is sensitive to as low as 0.1 mum IAA and is increased by IAA analogues that are active as auxins on elongation but not by nonauxin analogues. Activity begins to rise 10 to 15 minutes after exposure to IAA, which places this among the most rapid enzyme effects of a plant growth regulator heretofore demonstrated, and among the most rapid known metabolic effects of auxins. The effect is seen also with polysaccharide synthetase activity using uridine diphosphate-galactose or uridine diphosphate-xylose as substrates, and to a lesser extent with guanosine diphosphoglucose-dependent glucan synthetase activity. Glucan synthetase from IAA-treated tissue appears to have a higher affinity for uridine diphosphate-glucose than the control.

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PubMed1973

Regulation of beta-Glucan Synthetase Activity by Auxin in Pea Stem Tissue: II. Metabolic Requirements.

The 2- to 4-fold rise in particle-bound beta-glucan synthetase (uridine diphosphate-glucose: beta-1, 4-glucan glucosyltransferase) activity that can be induced by indoleacetic acid in pea stem tissue is not prevented by concentrations of actinomycin D or cycloheximide that inhibit growth and macromolecule synthesis. The rise is concluded to be a hormonally induced activation of previously existing, reversibly deactivated enzyme. The activation is not a direct allosteric effect of indoleacetic acid or sugars. It is blocked by inhibitors of energy metabolism, by 2-deoxyglucose, and by high osmolarity, but not by Ca(2+) at concentrations that inhibit auxin-induced elongation and prevent promotion of sugar uptake by indoleacetic acid, and not by alpha, alpha'-dipyridyl at concentrations that inhibit formation of hydroxyproline. Regulation of the system could be due either to an ATP-dependent activating reaction affecting this enzyme, or to changes in levels of a primer or a lipid cofactor.

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PubMed1973

Inactivity of 3-methyleneoxindole as mediator of auxin action on cell elongation.

The recently reported growth-promoting ability of 3-methyl-eneoxindole was examined in order to test the hypothesis that indole-3-acetic acid acts as a growth promoter only after oxidative conversion to 3-methyleneoxindole. Methyleneoxindole was synthesized from indole-3-acetic acid and N-bromosuccinimide, and its identity was confirmed by ultraviolet absorption, infrared absorption, mass spectrometry, and melting point. Methyleneoxindole was found to lack growth-promoting activity in coleoptile and pea (Pisum sativum) stem segments. Chlorogenic acid, an inhibitor of the oxidation of indole-3-acetic acid, was found to have no inhibitory effect on growth promotion by indole-3-acetic acid. It is concluded that 3-methyleneoxindole is inactive as a growth promoter and therefore does not mediate the action of auxin on cell elongation.

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PubMed1971

Induction of coleoptile elongation by carbon dioxide.

The ability of CO(2) to induce elongation of Avena sativa coleoptile segments was examined with the use of a high resolution growth-recording device. CO(2)-saturated water causes an 8- to 16-fold promotion in the rate of elongation within 1 minute. This elongation is insensitive to a variety of metabolic inhibitors that suppress auxin-induced elongation, and the CO(2) effect cannot be prevented by pretreatment with these inhibitors. Buffers of pH 3 to 4 also stimulate elongation quickly, and it seems that at least a major part of the action of CO(2) depends upon its ability to reduce pH. The rate of elongation of auxin-promoted segments can be further enhanced by treatment with CO(2) but not vice versa.The response to CO(2) can be inhibited by mannitol at osmotic concentrations that inhibit normal growth, by calcium, and by brief pretreatment with heavy water (D(2)O). The elongation rate that results from CO(2) treatment is sensitive to temperature, but the induction by CO(2) itself appears to be almost temperature-independent.Elongation following treatment with CO(2) may be a physical flow phenomenon, essentially independent of immediate biochemical participation, which occurs when wall polymer interactions that normally restrict strain in the cell wall are weakened or broken by CO(2) in a manner that in effect substitutes for the role of metabolism in normal auxin-inducible cell enlargement.

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PubMed1971

Regulation by auxin of carbohydrate metabolism involved in cell wall synthesis by pea stem tissue.

Promotion of cell wall synthesis (from glucose) in pea (Pisum sativum) stem segments by indoleacetic acid (IAA) develops over a period of 1 to 2 hours and is comprised of a promotion of glucose uptake plus a promotion of the utilization of absorbed glucose. The effect of IAA resembles, in these and other respects, its effect on cell wall synthesis in oat coleoptile segments, but the pea system differs in not being inhibited by galactose or mannose, in involving considerably more isotope dilution by endogenous substrates, and in certain other respects.EFFECTOR INFLUENCES UPON AND TOTAL ACTIVITIES OF THE FOLLOWING ENZYMES OBTAINED FROM ETIOLATED PEA STEM SEGMENTS PRETREATED WITH OR WITHOUT IAA WERE EXAMINED: phosphoglucomutase, uridine diphosphate glucose (UDP-glucose) pyrophosphorylase, nucleoside diphosphokinase, UDP-glucose dehydrogenase, inorganic pyrophosphatase, hexokinase (particulate and soluble), and UDP-glucose-beta-1,4-glucan-glucosyl transferase (beta-glucan synthetase). The first three enzymes mentioned exhibit high activity relative to the flux in vivo, do not appear to show physiologically significant effector responses, and are concluded not to be control points. UDP-glucose dehydrogenase activity is regulated by UDP-xylose. Hexokinase is a potential control point but does not exhibit regulatory effects related to the IAA response. beta-Glucan synthetase is the only one of these enzymes with activity which is increased by treatment of tissue with IAA, and this may be responsible for the effect of IAA on wall synthesis.Assays of metabolite pools support the conclusion that stimulation of polysaccharide synthesis by IAA is due partly to changes in hexokinase reaction rate resulting from an increase in metabolic glucose pool size caused by increased glucose uptake, and partly to increased activity at the polysaccharide synthetase level.

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PubMed1969

ISOLATION OF beta-GLUCAN SYNTHETASE PARTICLES FROM PLANT CELLS AND IDENTIFICATION WITH GOLGI MEMBRANES.

A variety of particle-bound synthetases that use sugar nucleotides as glycosyl donors for the formation of polysaccharides similar to those of the cell wall have been demonstrated in mung beans and other plant tissues,(1) but the particles in question have not been previously identified.(2, 3) The polysaccharide synthetase particles from peas that form mainly beta-1,4-glucan from UDPG and GDPG have now been separated from other cell particles by combinations of velocity and isopycnic density gradient centrifugation. The particles have an effective density of about 1.15 gm cm(-3), exhibit latent nucleoside diphosphatase activity upon IDP, UDP, GDP, and to a lesser extent upon ADP, and also possess acid phosphatase and weak ATPase activity. The isolated synthetase particles consist of somewhat condensed Golgi dictyosomes and free dictyosomal membranes bearing vesicles. It is concluded that the synthetase particles are Golgi membranes. The nucleoside diphosphatase activity of these particles may represent inactivated polysaccharide synthetase.

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