Biomedical subjects

A D Glass

Publications and source records attributed to A D Glass.

34 records · Page 2Linked to original sources

PubMed1990

Studies of the Uptake of Nitrate in Barley : II. Energetics.

Q(10) values for (13)NO(3) (-) influx were determined in ;uninduced' (NO(3) (-)-starved) and ;induced' (NO(3) (-)-pretreated) roots of barley (Hordeum vulgare L.) plants at various concentrations of external NO(3) (-) ([NO(3) (-)](0)). At 0.02 mole per cubic meter [NO(3) (-)](0), Q(10) values for influx were from 3 to 4 between 5 and 10 degrees C. As [NO(3) (-)](0) increased Q(10) values decreased, reaching values of 1.2 and 2.0, respectively, at 20 moles per cubic meter in uninduced and induced plants. The metabolic dependence of (13)NO(3) (-) influx at low and high [NO(3) (-)](0) (0.1 and 20.0 moles per cubic meter, respectively) in uninduced and induced plants was probed by the use of various inhibitors. These experiments confirmed the findings of the Q(10) studies, demonstrating that at low [NO(3) (-)](0) (13)NO(3) (-) influx was extremely sensitive to metabolic inhibition. By contrast, at high [NO(3) (-)](0), influx was relatively insensitive to the presence of inhibitors.

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PubMed1989

Studies of the Regulation of Nitrate Influx by Barley Seedlings Using NO(3).

Using (13)NO(3) (-), effects of various NO(3) (-) pretreatments upon NO(3) (-) influx were studied in intact roots of barley (Hordeum vulgare L. cv Klondike). Prior exposure of roots to NO(3) (-) increased NO(3) (-) influx and net NO(3) (-) uptake. This ;induction' of NO(3) (-) uptake was dependent both on time and external NO(3) (-) concentration ([NO(3) (-)]). During induction influx was positively correlated with root [NO(3) (-)]. In the postinduction period, however, NO(3) (-) influx declined as root [NO(3) (-)] increased. It is suggested that induction and negative feedback regulation are independent processes: Induction appears to depend upon some critical cytoplasmic [NO(3) (-)]; removal of external NO(3) (-) caused a reduction of (13)NO(3) (-) influx even though mean root [NO(3) (-)] remained high. It is proposed that cytoplasmic [NO(3) (-)] is depleted rapidly under these conditions resulting in ;deinduction' of the NO(3) (-) transport system. Beyond 50 micromoles per gram [NO(3) (-)], (13)NO(3) (-) influx was negatively correlated with root [NO(3) (-)]. However, it is unclear whether root [NO(3) (-)] per se or some product(s) of NO(3) (-) assimilation are responsible for the negative feedback effects.

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PubMed1986

A Model for the Regulation of K Influx, and Tissue Potassium Concentrations by Negative Feedback Effects upon Plasmalemma Influx.

By means of a modified Michaelis-Menten equation for K(+) influx, which includes terms for root and external K(+) concentrations (root [K(+)] and [K(+)](0), respectively) it is possible to predict the manner in which short-term (perturbation) fluxes of K(+) into roots of barley plants (Hordeum vulgare cv Fergus) vary with root [K(+)] and [K(+)](0). Influx values derived from this equation were used to predict changes of root and shoot [K(+)] and K(+) absorption rates (as functions of time and [K(+)](0)) from a knowledge of K(+) efflux, relative growth rates of roots and shoots, and the partitioning of absorbed K(+) between these organs. A microcomputer program was employed to model these changes in low-salt plants following transfer to solutions in which [K(+)](0) was maintained at values ranging from 5 to 1000 millimoles per cubic meter. The model was operated on the basis of 10 minute absorption periods which provided data for continuous ;updating' of tissue [K(+)]. The simulations were undertaken for periods corresponding to 30 days. During this time the model accurately predicted the manner in which K(+) influx and root and shoot [K(+)] gradually approach values which are essentially independent of [K(+)](0). The computer program was also used to predict the outcome of changing various external and internal parameters of the proposed regulatory system. The results of these simulations are discussed in the context of current models for negative feedback control of ion fluxes.

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PubMed1985

Regulation of NO(3) Influx in Barley : Studies Using NO(3).

Short-term (10 minutes) measurements of plasmalemma NO(3) (-) influx (phi(oc)) into roots of intact barley plants were obtained using (13)NO(3) (-). In plants grown for 4 days at various NO(3) (-) levels (0.1, 0.2, 0.5 millimolar), phi(oc) was found to be independent of the level of NO(3) (-) pretreatment. Similarly, pretreatment with Cl(-) had no effect upon plasmalemma (13)NO(3) (-) influx. Plants grown in the complete absence of (13)NO(3) (-) (in CaSO(4) solutions) subsequently revealed influx values which were more than 50% lower than for plants grown in NO(3) (-). Based upon the documented effects of NO(3) (-) or Cl(-) pretreatments on net uptake of NO(3) (-), these observations suggest that negative feedback from vacuolar NO(3) (-) and/or Cl(-) acts at the tonoplast but not at the plasmalemma. When included in the influx medium, 0.5 millimolar Cl(-) was without effect upon (13)NO(3) (-) influx, but NH(4) (+) caused approximately 50% reduction of influx at this concentration.

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PubMed1984

Regulation of k influx in barley : effects of low temperature.

Influx and accumulation of K(+) in barley (Hordeum vulgare L. cv Fergus) roots were measured at two temperatures (10 degrees C and 20 degrees C) in plants which had been grown with roots and shoots at 20 degrees C (HT plants), with roots and shoots at 10 degrees C (LT plants), and with roots at 10 degrees C and shoots at 20 degrees C (DT plants). Under conditions where K(+) was in limited supply during the prior growth period, K(+) influx and accumulation were consistently higher in roots of DT and LT plants than in those of HT plants. Thus, it would appear that this low temperature response is not limited specifically to conditions in which temperature differentials are maintained between roots and shoots. Nevertheless, it was generally the case that increases of influx were larger in DT and LT plants so that the temperature differentials may intensify the low temperature response. When K(+) influx was examined over a wide range of root [K(+)], it was seen that the characteristic reduction of influx associated with increased internal [K(+)] was substantially greater in HT than DT or LT plants. Transfer of plants grown under HT conditions to DT or LT regimes led to both short-term and long-term adjustments of influx. The former became apparent within 6 hours of exposure to the new conditions and decayed within minutes of transfer back to 20 degrees C. The long-term adjustments were only apparent after prolonged exposure (days) to the lower root temperature and these did not decay as rapidly. Regardless of shoot temperature, the transfer of roots from 20 degrees C to 10 degrees C caused a gradual increase of root [K(+)] so that 4 days later LT and DT roots contained, respectively, 53.3 and 49.83 micromoles per gram compared to 17.82 micromoles per gram for roots maintained at 20 degrees C.

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PubMed1984

A comparison of methods for determining compartmental analysis parameters.

The traditional method for determining compartmental analysis parameters relies on a visual selection of data points to be used for regression of data from each cellular compartment. This method is appropriate when the compartments are kinetically discrete and are easily discernible. However, where treatment effects on compartment parameters are being evaluated, a more objective method for determining initial parameters is desirable.Three methods were examined for determining initial isotopic contents and half-times of (86)Rb elution from cellular compartments using theoretical data with known parameters. Experimental data from roots of Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) and barley (Hordeum vulgare L.) intact seedlings were also used. The three methods were a visually assisted, linear regression on data of semilog plot of isotope elution versus time, a microcomputer-assisted, linear regression on semilog plot where maximization of the square of the correlation coefficient (r(2)) was the criterion to determine data points needed for each regression and a mainframe computer-assisted, direct nonlinear regression on elution data using a model of the sum of three exponential decay functions. The visual method resulted in the least accurate estimates of compartmental analysis parameters. The microcomputer-assisted and nonlinear regression methods calculated the parameters equally well.

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PubMed1983

Short Term Studies of Nitrate Uptake into Barley Plants Using Ion-Specific Electrodes and ClO(3): I. Control of Net Uptake by NO(3) Efflux.

A computer-controlled multichannel data acquisition system was employed to obtain continuous measurements of net nitrate or chlorate uptake by roots of intact barley plants (Hordeum vulgare cv Betzes) using nitrate-specific electrodes. Plants, previously grown in solutions maintained at 10 or 200 micromolar NO(3) (-) (low N or high N conditions, respectively), were provided with 200 micromolar NO(3) (-) or ClO(3) (-) during the uptake period. Initial rates of NO(3) (-) uptake were several times higher in low N plants than in high N plants. Within 10 min, uptake in the former plants declined to a new steady rate which was sustained for the remainder of the experiment. No such time-dependent changes were evident in the high N plants. Rates and patterns of net chlorate uptake exhibited almost identical dependence upon previous nitrate provision. NO(3) (-) ((36)ClO(3) (-)) influx, by contrast, appeared to be independent of NO(3) (-) pretreatment prior to influx determination. Nitrate efflux, estimated by several different methods, was strongly correlated with internal nitrate concentration of the roots.

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PubMed1983

Short Term Studies of Nitrate Uptake into Barley Plants Using Ion-Specific Electrodes and ClO(3): II. Regulation of NO(3) Efflux by NH(4).

The influence of NH(4) (+), in the external medium, on fluxes of NO(3) (-) and K(+) were investigated using barley (Hordeum vulgare cv Betzes) plants. NH(4) (+) was without effect on NO(3) (-) ((36)ClO(3) (-)) influx whereas inhibition of net uptake appeared to be a function of previous NO(3) (-) provision. Plants grown at 10 micromolar NO(3) (-) were sensitive to external NH(4) (+) when uptake was measured in 100 micromolar NO(3) (-). By contrast, NO(3) (-) uptake (from 100 micromolar NO(3) (-)) by plants previously grown at this concentration was not reduced by NH(4) (+) treatment. Plants pretreated for 2 days with 5 millimolar NO(3) (-) showed net efflux of NO(3) (-) when roots were transferred to 100 micromolar NO(3) (-). This efflux was stimulated in the presence of NH(4) (+). NH(4) (+) also stimulated NO(3) (-) efflux from plants pretreated with relatively low nitrate concentrations. It is proposed that short term effects on net uptake of NO(3) (-) occur via effects upon efflux. By contrast to the situation for NO(3) (-), net K(+) uptake and influx of (36)Rb(+)-labeled K(+) was inhibited by NH(4) (+) regardless of the nutrient history of the plants. Inhibition of net K(+) uptake reached its maximum value within 2 minutes of NH(4) (+) addition. It is concluded that the latter ion exerts a direct effect upon K(+) influx.

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PubMed1982

Simultaneous consideration of tissue and substrate potassium concentration in k uptake kinetics: a model.

The importance of the simultaneous consideration of tissue and substrate concentration in the estimation of ion uptake is discussed. An elaboration of the model of ion uptake, originally proposed by E. Epstein, is developed. The modified model takes both tissue and substrate ion concentration into account and uses true constants in the estimation of uptake. A test case-K(+) uptake by a barley cultivar-has been presented to show the working of the model. The relevance of the modified model is also pointed out.

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PubMed1982

Nitrate Uptake into Barley (Hordeum vulgare) Plants : A New Approach Using ClO(3) as an Analog for NO(3).

Evidence is presented that chlorate is an extremely good analog for nitrate during nitrate uptake by intact barley (Hordeum vulgare cv. Fergus) roots. The depletion of ClO(3) (-) or NO(3) (-) from uptake media over 2 to 6 hours by seedlings was found to be dependent on combined NO(3) (-) plus ClO(3) (-) concentrations, and total anion uptake was equivalent at different NO(3) (-)/ClO(3) (-) ratios. After loading barley seedlings with (36)ClO(3) (-) for 6 hours, kinetic parameters were derived from the analysis of efflux of [(36)Cl] chlorate into unlabeled solution. On the basis of this analysis, the half times for exchange for the cytoplasmic and vacuolar phases were 17 minutes and 20 hours, respectively.Data pooled from a number of different experiments were used to calculate kinetic constants (K(m) and V(max)) for (36)ClO(3) (-) influx into barley roots at different external ClO(3) (-)/NO(3) (-) ratios, using short (10 minutes) influx times. There appeared to be no discrimination by the root cells between ClO(3) (-) and NO(3) (-). Lineweaver-Burk analysis of the interaction between nitrate and chlorate were characteristic of competitive inhibition at low nitrate concentrations (0-0.5 mm). At higher concentrations, in the range of >1 mm, similar interactions between these ions were evident.

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PubMed1981

Correlations between Potassium Uptake and Hydrogen Efflux in Barley Varieties : A POTENTIAL SCREENING METHOD FOR THE ISOLATION OF NUTRIENT EFFICIENT LINES.

Rates of hydrogen ion secretion and potassium ((86)Rb) absorption by intact roots of twenty-four barley varieties were measured in solutions containing K(2)SO(4) (1 x 10(-4) to 1 x 10(-3) molar) plus 5 x 10(-4) molar CaSO(4), at initial pH values in the range 5.3 to 5.5. Fluxes of H(+) and K(+) were strongly correlated in short-term experiments (up to 15 minutes) as well as in long-term experiments (lasting 24 hours). The observed correlations provide the basis for a preliminary screening method, designed to segregate varieties with high rates of potassium uptake by the use of an acid-base indicator (methyl red).

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PubMed1980

Varietal differences in potassium uptake by barley.

Potassium influx isotherms were obtained for 10 cultivars of barley using plants which had been grown with or without potassium (high K(+) and low K(+) plants, respectively), and the cultivars ranked with respect to K(m) or V(max) values for influx with a view to using these rankings as a predictive measure of long term performance under conditions of potassium-limited growth. Analyses of these rankings revealed significant differences between cultivars. Net uptake rates for low K(+) plants, determined over a 24-hour period, confirmed the differences between upper (Herta) and lower (Conquest) ranked cultivars, and established similar differences in the rates of translocation to the shoot. Efflux analyses showed no differences in potassium efflux from the cytoplasm or from the vacuole for these cultivars. Growth rate studies under different conditions of potassium limitation indicated, with some exceptions, strong positive correlations between ranks accorded cultivars on the basis of influx kinetics and those based upon growth rates.

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PubMed1978

Influence of Excision and Aging upon K Influx into Barley Roots: Recovery or Enhancement?

The influx of K(+) from (86)Rb-labeled solutions in the concentration range 0.008 to 0.2 mm into roots of intact plants and excised roots of barley plants (Hordeum vulgare [L.]) previously grown in 5 mm CaSO(4) (low K(+) roots) or 0.5 mm CaSO(4) plus 5 mm KCl (high K(+) roots) was measured. A consistent observation of these experiments was a substantial reduction of influx (usually by about 50%) following excision. The possible leakage of K(+) into the medium and subsequent dilution of specific activity of labeled solutions was eliminated as an explanation for influx reduction in excised low K(+) roots. Reduction of transpirational rates was also without effect upon influx into low K(+) roots. Excision followed by 2 hours aging in 0.5 mm CaSO(4) solution revealed that influx values recovered within the 2 hours to the values obtained in intact roots. It is concluded that much of the literature which describes the enhancement of ion uptake following excision actually describes excision damage followed by recovery.

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PubMed1976

Regulation of potassium absorption in barley roots: an allosteric model.

Plasmalemma influx isotherms for K(+) were measured in the system I concentration range (0.01-0.32 mm), for barley (Hordeum vulgare L.) roots of varying internal K(+) concentration, and Km values for influx calculated. In plants grown for several days in CaSO(4) or in CaSO(4) plus KCl solutions, as well as in plants grown in CaSO(4) for several days and then rapidly loaded with KCl during a pretreatment period, Michaelis constant values were positively correlated with internal K(+) concentrations. Influx of K(+) is shown to be sigmoidally related to internal K(+) concentration and Hill plots of influx data give linear transformations with n = 4. This information is taken as support for an allosteric model for the regulation of K(+) influx in which the "carrier" is envisaged as possessing a single external binding site for K(+) as well as four internal sites for allosteric control of influx.

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PubMed1974

Influence of Phenolic Acids on Ion Uptake: IV. Depolarization of Membrane Potentials.

The membrane potentials of aged, excised barley (Hordeum vulgare L.) root cells were rapidly depolarized by the addition of salicylic acid (o-hydroxybenzoic acid) to the buffered medium bathing root segments. Initial values for membrane potentials were restored very slowly (within 100 minutes) by replacing the phenolic solution by phenolic-free buffer. Several other naturally occurring benzoic and cinnamic acids depolarized cell membrane potentials. The cinnamic acids consistently caused a greater depolarization than the correspondingly substituted benzoic acids. A strong positive correlation was found between the depolarization values (DeltaE) for the benzoic acids and their lipid solubilities. This study supports the hypothesis that the inhibition of ion uptake brought about by naturally occurring phenolic acids is caused by a generalized increase in membrane permeability to inorganic ions.

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PubMed1973

Influence of phenolic acids on ion uptake: I. Inhibition of phosphate uptake.

The influence of naturally occurring phenolic acids on phosphate uptake by barley (Hordeum vulgare L. cv. Karlsberg) roots was examined using (32)P-labeled phosphate. Without exception, all compounds tested, namely, benzoic, 2-hydroxybenzoic, 4-hydroxybenzoic, 3,4-dihydroxybenzoic, 3,4,5-trihydroxybenzoic, 4-hydroxy-3-methoxybenzoic, 4-hydroxy-3,5-dimethoxybenzoic, cinnamic, 2-hydroxycinnamic, 4-hydroxycinnamic, 3,4-dihydroxycinnamic, 4-hydroxy-3-methoxycinnamic, and 4-hydroxy-3,5-dimethoxycinnamic acids, inhibited uptake.The degree of inhibition correlated well with the lipid solubility of these phenolic compounds. This as well as kinetic data support the hypothesis of inhibition through altered membrane properties.

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