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R L Travis

Publications and source records attributed to R L Travis.

At least 19 recordsLinked to original sources
PubMed2001

Response of Acala cotton to nitrogen rates in the San Joaquin Valley of California.

The responses of Acala cotton (Gossypium hirsutum L.) in California to a range of applied nitrogen (N) treatments were investigated in a 5-year, multisite experiment. The experiment's goals were to identify crop growth and yield responses to applied N and provide information to better assess the utility of soil residual N estimates in improving fertilizer management. Baseline fertilizer application rates for the lowest applied N treatments were based on residual soil nitrate-N (NO3-N) levels determined on soil samples from the upper 0.6 m of the soil collected prior to spring N fertilization and within 1 week postplanting each year. Results have shown positive cotton lint yield responses to increases in applied N across the 56 to 224 kg N/ha range in only 41% (16 out of 39) of test sites. Soil NO3-N monitoring to a depth of 2.4 m in the spring (after planting) and fall (postharvest) indicate most changes in soil NO3- occur within the upper 1.2 m of soil. However, some sites (those most prone to leaching losses of soluble nutrients) also exhibited net increases in soil NO3-N in the 1.2- to 2.4-m depth zone when comparing planting time vs. postharvest data. The lack of yield responses and soil NO3-N accumulations at some sites indicate that more efforts should be put into identifying the amount of plant N requirements that can be met from residual soil N, rather than solely from fertilizer N applications.

California↗
PubMed1996

Effect of root perturbation and excision on nitrate influx and efflux in barley (Hordeum vulgare) seedlings.

The effects of perturbation and excision on net NO3- uptake, influx and efflux in roots of 8-day-old barley (Hordeum vulgare L.) seedlings induced with NO3- or NO2- were determined. Perturbation was simulated by mechanically striking the intact roots with a glass rod. Perturbation or excision of roots and subsequent division into small segments had little effect on NO3- influx, but briefly inhibited net uptake which recovered within a few min. While in perturbed roots net uptake rates recovered to the same level as in control roots, full recovery did not occur in excised roots. Inhibition of net uptake was due to stimulation on NO3- efflux. The recovery time and level of inhibition of net NO3- uptake and/or stimulation of efflux were a function of extent of perturbation, or the number of segments following excision, and root NO3- concentration. NO3- efflux was further stimulated when roots were perturbed after cytoplasmic NO3- had been depleted, indicating that both the plasmalemma and tonoplast may be affected. In excised roots both NO3- influx and efflux decreased with age due to depletion of energy sources. The results indicate that root perturbation and excision had no effect on NO3- influx but inhibited net uptake by stimulating efflux.

Glucose↗
PubMed1995

Effect of pH and calcium on short-term NO3- fluxes in roots of barley seedlings.

The effect of pH and Ca2+ on net NO3- uptake, influx, and efflux by intact roots of barley (Hordeum vulgare L.) seedlings was studied. Seedlings were induced with NO3- or NO2-. Net NO3- uptake and efflux, respectively, were determined by following its depletion from, and accumulation in, the external solution. Since roots of both uninduced and NO2(-)-induced seedlings contain little internal NO3- initial net uptake rates are equivalent to influx (M. Aslam, R.L. Travis, R.C. Huffaker [1994] Plant Physiol 106: 1293-1301). NO3-, uptake (influx) by these roots was little affected at acidic pH. In contrast, in NO3(-)-induced roots, which accumulate NO3-, net uptake rates decreased in response to acidic pH. Under these conditions, NO3- efflux was stimulated and was a function of root NO3- concentration. Conversely, at basic pH, NO3- uptake by NO3- and NO2(-)-induced and uninduced roots decreased, apparently because of the inhibition of influx. Calcium had little effect on NO3- uptake (influx) by NO2(-)-induced roots at either pH 3 or 6. However, in NO3(-)-induced roots, lack of Ca2+ at pH 3 significantly decreased net NO3- uptake and stimulated efflux. The results indicate that at acidic pH the decrease in net NO3- uptake is due to the stimulation of efflux, whereas at basic pH, it is due to the inhibition of influx.

Calcium↗
PubMed1994

Characterization of the association of nitrate reductase with barley (Hordeum vulgare L.) root membranes.

The nature of the association between nitrate reductase (NR) and membranes was examined. Nitrate reductase activity (NRA) associated with the microsomal fraction of barley (Hordeum vulgare L.) roots amounted to 0.6 to 0.8% of soluble NRA following sonication in the presence of 250 mM KI and repeated osmotic shock. This treatment removed all contaminating soluble NRA from microsomes of uninduced barley roots that had been homogenized in a soluble extract from roots of NO3(-)-induced plants. On continuous sucrose gradients, NRA co-migrated specifically with VO4(-)-sensitive ATPase activity, a plasma membrane (PM) marker; activity of glucose-6-phosphate dehydrogenase, assayed as cytosolic marker, co-migrated with NRA. Microsomal NRA was absent in barley deficient in soluble NR. Perturbation and trypsinolysis experiments with PM vesicles isolated by aqueous two-phase partitioning indicated that NR is associated with the periphery of the cytoplasmic face of the bilayer. These results demonstrate that PM and soluble NRs are essentially the same protein but that the membrane-associated form is tightly bound. Although it is possible that PM-associated NR exists in vivo, unequivocal evidence for this has yet to be shown. However, PM NR is definitely present in vitro.

Adenosine Triphosphatases↗
PubMed1993

Health care reform.

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Delivery of Health Care↗
PubMed1992

Comparative kinetics and reciprocal inhibition of nitrate and nitrite uptake in roots of uninduced and induced barley (Hordeum vulgare L.) seedlings.

Nitrate and NO2- transport by roots of 8-day-old uninduced and induced intact barley (Hordeum vulgare L. var CM 72) seedlings were compared to kinetic patterns, reciprocal inhibition of the transport systems, and the effect of the inhibitor, p-hydroxymercuribenzoate. Net uptake of NO3- and NO2- was measured by following the depletion of the ions from the uptake solutions. The roots of uninduced seedlings possessed a low concentration, saturable, low Km, possibly a constitutive uptake system, and a linear system for both NO3- and NO2-. The low Km system followed Michaelis-Menten kinetics and approached saturation between 40 and 100 micromolar, whereas the linear system was detected between 100 and 500 micromolar. In roots of induced seedlings, rates for both NO3- and NO2- uptake followed Michaelis-Menten kinetics and approached saturation at about 200 micromolar. In induced roots, two kinetically identifiable transport systems were resolved for each anion. At the lower substrate concentrations, less than 10 micromolar, the apparent low Kms of NO3- and NO2- uptake were 7 and 9 micromolar, respectively, and were similar to those of the low Km system in uninduced roots. At substrate concentrations between 10 and 200 micromolar, the apparent high Km values of NO3- uptake ranged from 34 to 36 micromolar and of NO2- uptake ranged from 41 to 49 micromolar. A linear system was also found in induced seedlings at concentrations above 500 micromolar. Double reciprocal plots indicated that NO3- and NO2- inhibited the uptake of each other competitively in both uninduced and induced seedlings; however, Ki values showed that NO3- was a more effective inhibitor than NO2-. Nitrate and NO2- transport by both the low and high Km systems were greatly inhibited by p-hydroxymercuribenzoate, whereas the linear system was only slightly inhibited.

Biological Transport↗
PubMed1989

Effect of Inhibition of Glycosylation on the Appearance of a 60 kD Membrane Glycopolypeptide in Endomembrane Fractions of Soybean Root.

Endomembrane (endoplasmic reticulum, Golgi apparatus, plasma membrane) proteins of soybean (Glycine max) root cells are highly glycosylated. We investigated whether N-linked oligosaccharide moieties are essential for the correct intracellular transport of plant endomembrane glycoproteins. Excised roots were incubated with tunicamycin, to block cotranslational glycosylation of proteins, and dual labeled with [(3)H]glucosamine and [(35)S] (methionine, cysteine). In the presence of tunicamycin, the incorporation of glucosamine into membrane proteins was inhibited by 60 to 90% while amino acid incorporation was only slightly affected. Autoradiograms of two-dimensionally separated polypeptides from each endomembrane fraction revealed the presence of at least one new polypeptide in tunicamycin-treated tissue. The new polypeptide was of the same isoelectric point but lower molecular weight than a preexisting polypeptide. The new polypeptide was unreactive to concanavalin A, as opposed to the preexisting polypeptide, suggesting the absence of the glycan portion. Trifluoromethanesulfonic acid and N-glycanase were used to cleave the carbohydrate from the preexisting concanavalin A binding polypeptide. In each case a deglycosylated polypeptide of the same isoelectric point and molecular weight as the new polypeptide from tunicamycin-treated tissue resulted. Since the absence of carbohydrate from the new endomembrane polypeptide did not prevent its appearance on autoradiograms of Golgi and plasma membrane, intracellular transport and intercalation of newly synthesized glycoproteins into plant cell membranes may not require the presence of polysaccharide moieties.

Journal Article↗
PubMed1985

Phospholipid composition of a plasma membrane-enriched fraction from developing soybean roots.

Phospholipid polar head group and fatty acid composition were determined for plasma membrane enriched fractions from developing soybean root (Glycine max [L.] Merr. cult. Wells II). Plasma membrane vesicles were isolated from meristematic and mature sections of four-day-old dark grown soybean roots at pH 7.8 and in the presence of 5 millimolar ethylenediaminetetraacetate, 5 millimolar ethyleneglycol-bis (beta-aminoethyl ether)N,N tetraacetic acid, and 10 millimolar NaF. Lipid extracts analyzed for phospholipid composition revealed two major phospholipid components: phosphatidylcholine and phosphatidylethanolmine. Minor phospholipid components identified were phosphatidylinositol, phosphatidylserine, phosphatidylglycerol, and diphosphatidylglycerol. Lipid degradation by endogenous phospholipase D during membrane isolation at pH 6.5 and in the absence of chelating agents and NaF resulted in the recovery of large amounts of phosphatidic acid. Phosphatidylcholine was the principal substrate for phospholipase D.Fatty acid composition was determined for plasma membrane phosphatidylcholine and phosphatidylethanolamine from meristematic and mature root tissue. The fatty acids identified were 16:0, 18:0, 18:1, 18:2, and 18:3. Fatty acid composition varied with both phospholipid class and the developmental stage of the root. Results suggest that differences in the composition of the major phospholipids of plasma membrane from meristemaic and mature root sections occur in the fatty acids and not in the polar head groups. These differences and those found in the composition of the polar head groups of the minor phospholipid components, e.g. phosphatidylglycerol, may be significant for structure-function relationships within the membrane.

Journal Article↗
PubMed1982

A comparative evaluation of the level of concanavalin a binding by enriched plasma membrane fractions from developing soybean roots.

The Concanavalin A (Con A) binding capacity of plasma membranes isolated from meristematic and mature regions of four-day-old soybean (Glycine max L. Merr. cv. Wells) roots was compared. Con A binding was studied using a radiochemical assay with tritiated ((3)H)-Con A and by an electron microscope technique using Con A-ferritin (Con A-F). In both cases, plasma membranes isolated from meristematic tissue bound significantly more Con A than did corresponding membranes from mature tissue. The relative difference in reactivity, as determined by the two procedures, was approximately 49% ((3)H-Con A) and 46% (Con A-F). In contrast, K(m) values, determined from (3)H-Con A binding curves, were approximately the same, indicating that receptor sites on plasma membranes from both sources were qualitatively similar.Since Con A specifically interacts with saccharide-containing portions of membrane glycoproteins and/or glycolipids, the data suggests that there is a decrease in the concentration of those components in plasma membranes during development or that there are qualitative changes in the structure of their oligosaccharide side chains.

Journal Article↗
PubMed1981

Characterization and quantitation of concanavalin a binding by plasma membrane enriched fractions from soybean root.

The binding of concanavalin A (Con A) to soybean root membranes in plasma membrane enriched fractions (recovered from the 34/45% interface of simplified discontinuous sucrose density gradients) was studied using a radiochemical assay employing tritiated ((3)H)-Con A. The effect of lectin concentration, time, and membrane protein concentration on the specific binding of (3)H-Con A by the membranes was evaluated. Kinetic analyses showed that Con A will react with membranes in that fraction in a characteristic and predictable manner. The parameters for an optimal and standard binding assay were established. Maximal binding occurred with Con A concentrations in the range of 8 to 16% of the total membrane protein with incubation times greater than 40 min at 22 C. Approximately 10(15) molecules of (3)H-Con A were bound per microgram of membrane protein at saturation. Binding was reversible. Greater than 92% of the total Con A bound at saturation was released by addition of alpha-methyl mannoside.A major peak of (3)H-Con A binding was also observed in fractions recovered from the 25/30% interface of a complex discontinuous sucrose density gradient when membranes were isolated in the absence of Mg(2+). When high Mg(2+) was present in the isolation and gradient media, the peak was shifted to a fraction recovered from the 34/38% sucrose interface. These results suggest that Con A binding sites are also present on membranes of the endoplasmic reticulum. The amount of Con A bound by endoplasmic reticulum membranes was at least twice the amount bound by membranes in plasma membrane enriched fractions when binding was compared on a per unit membrane protein basis. In contrast, mitochondrial inner membranes, which equilibrate at the same density as plasma membranes, had little ability to bind the lectin.

Journal Article↗
PubMed1980

Characterization of Soybean Plasma Membrane during Development: FREE STEROL COMPOSITION AND CONCANAVALIN A BINDING STUDIES.

PLASMA MEMBRANE PREPARATIONS FROM SOYBEAN ROOT AND HYPOCOTYL CONTAINED THE FOLLOWING FREE STEROLS: cholesterol, campesterol, stigmasterol, and sitosterol. The cholesterol level was relatively low in root plasma membrane (less than 0.5%) but was 1.4 to 2.4% in hypocotyl membrane. The relative levels of the three other sterols fluctuated with cellular development and tissue source. Campesterol level decreased with the development of both root and hypocotyl membrane. With development, stigmasterol increased greatly in root membrane but remained constant in hypocotyl membrane, and sitosterol, the major free sterol component of all membrane preparations, decreased in root membrane but increased slightly in hypocotyl membrane.Electron microscope studies indicated that all root plasma membrane preparations were equivalent in terms of relative purity. Hypocotyl membrane preparations contained significantly greater levels of contaminating membrane components.Root plasma membrane fractions were between 70 and 80% pure as determined by staining with the phosphotungstic acid-chromic acid procedure (PACP). Staining was most definitive for vesicles present in complete cross-section. Electron micrographs showed that vesicles treated with concanavalin A (Con A)-ferritin were extensively labeled at the outer surface indicating the presence of mannosyl and/or glucosyl residues at the vesicle surface. Densities of ferritin were highest on vesicles present in oblique section. PACP and Con A-ferritin were thus complementary with respect to topological specificity.The percentage of Con A-ferritin-labeled and/or PACP-stained vesicles in plasma membrane root preparations was greater than 80%. Con A did not bind in purified tonoplast preparations, and binding was reduced in regions of low PACP reactivity in a root membrane fraction containing a lowered proportion of plasma membrane. Con A specificity for the plasma membrane in subcellular membrane preparations is discussed.

Journal Article↗
PubMed1980

Electrophoretic comparison of polypeptides from enriched plasma membrane fractions from developing soybean roots.

The polypeptide complement of enriched soybean (Glycine max [L.] Merr. cult. wells) root plasma membrane fractions was studied by two-dimensional gel electrophoresis. Good resolution was obtained when polypeptides were solubilized in sodium dodecyl sulfate and when butylated hydroxytoluene was included in the vesicle isolation and solubilization media. The pattern obtained on the two-dimensional slab gel for root plasma membrane was characteristic for that membrane. The polypeptide complements from mitochondrial membranes and from enriched fractions of three other endomembrane components were solubilized and electrophoresed for comparison. Each membrane preparation was identifiable on the basis of its characteristic electrophoretogram. Electrophoresis of protein solubilized from plasma membrane fractions isolated from meristematic and mature root tissue revealed both qualitative and quantitative differences in the respective protein complements.

Journal Article↗
PubMed1979

Partial Characterization of a Potassium-stimulated Adenosine Triphosphatase from the Plasma Membrane of Meristematic and Mature Soybean Root Tissue.

A K(+)-stimulated adenosine triphosphatase was partially characterized in plasma membrane from meristematic and mature soybean root tissue. The substrate concentrations required for maximum enzyme activity (3 millimolar Mg.ATP) and pH optimum (6.5) were similar for both systems. Enrichment studies, performed to ensure that the membrane vesicle preparations were comparable, indicated similar purity levels at selected steps during purification. Phospholipid and sterol analyses further substantiated their similarity.Enzyme studies revealed significantly greater ATPase activity, per unit membrane protein, in the meristematic region. Mixing experiments indicated that the lower level of activity associated with vesicles from mature tissue was not due to endogenous inhibitor(s).

Journal Article↗
PubMed1979

Analysis of the Distribution of Potassium-stimulated Adenosine Triphosphatase Activity in Soybean Root.

The distribution of activity of a potassium-stimulated ATPase associated with the plasma membrane was determined in 4-day-old soybean roots. Changes in protein-based specific activity of the enzyme coincided with developmental changes in the root. Activity was low in the region of the root cap, increased to a maximum in the meristematic region, decreased to a minimum as cell elongation proceeded, and then increased as lateral root development began. Analysis of the data indicated that fluctuations in enzyme activity can be described by a three-phase system which can be approximated by a linear-linear-linear piece-wise regression curve. The need for constructing a biological model to describe plasma membrane development is suggested.

Journal Article↗