Biomedical subjects

A J Hiatt

Publications and source records attributed to A J Hiatt.

14 recordsLinked to original sources

PubMed1974

The Influence of Nitrate and Chloride Uptake on Expressed Sap pH, Organic Acid Synthesis, and Potassium Accumulation in Higher Plants.

The influence of NO(3) (-) uptake and reduction on ionic balance in barley seedlings (Hordeum vulgare, cv. Compana) was studied. KNO(3) and KCl treatment solutions were used for comparison of cation and anion uptake. The rate of Cl(-) uptake was more rapid than the rate of NO(3) (-) uptake during the first 2 to 4 hours of treatment. There was an acceleration in rate of NO(3) (-) uptake after 4 hours resulting in a sustained rate of NO(3) (-) uptake which exceeded the rate of Cl(-) uptake. The initial (2 to 4 hours) rate of K(+) uptake appeared to be independent of the rate of anion uptake. After 4 hours the rate of K(+) uptake was greater with the KNO(3) treatment than with the KCl treatment, and the solution pH, cell sap pH, and organic acid levels with KNO(3) increased, relative to those with the KCl treatment. When absorption experiments were conducted in darkness, K(+) uptake from KNO(3) did not exceed K(+) uptake from KCl. We suggest that the greater uptake and accumulation of K(+) in NO(3) (-)-treated plants resulted from (a) a more rapid, sustained uptake and transport of NO(3) (-) providing a mobile counteranion for K(+) transport, and (b) the synthesis of organic acids in response to NO(3) (-) reduction increasing the capacity for K(+) accumulation by providing a source of nondiffusible organic anions.

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PubMed1970

An anomaly in potassium accumulation by barley roots: I. Effect of anions, sodium concentration, and length of absorption period.

Excised barley roots accumulated 40 to 50% more K(+) from 0.04 mm than from 0.06 mm KCl when incubated for 24 hours in KCl solutions containing 0.2 mm CaSO(4). This phenomenon was not markedly influenced by the rate of absorption of the counteranion. The presence of Na(+) in the treatment solutions decreased total K accumulation but did not alter the K(+) concentration at which the accumulation peak occurred. Short interval studies indicated that this phenomenon is easily observable after 4 hours and begins to become apparent within 2 hours. In comparison with barley, accumulation of K(+) by excised wheat roots decreased as KCl concentration was increased from 0.02 to 0.06 mm; but K(+) accumulation curve for corn roots showed no peaks or depressions in the concentration range of 0.01 to 0.1 mm. A normal hyperbolic curve was noted for the accumulation of Na(+) from 0.01 to 1 mm NaCl by barley roots.

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PubMed1970

An Anomaly in Potassium Accumulation by Barley Roots: II. Effect of Calcium Concentration and Rubidium-86 Labeling.

When excised barley roots were incubated in 0.01 to 0.1 mm KCl solutions containing 0.2 mm CaSO(4), there was a peak in the K(+) accumulation against concentration curve at 0.02 to 0.04 mm KCl. The peak in the K(+) accumulation curve was shifted to lower K(+) concentrations when Ca(2+) concentration was decreased and to higher K(+) concentrations when Ca(2+) concentration was increased. Increasing Ca(2+) concentration in the treatment solution was observed to be stimulatory, inhibitory, or neutral depending on the K(+) concentration.When (86)Rb was used as an isotopic tracer for K(+), accumulation of K(+) was grossly overestimated, and the apparent K(+) accumulation curve, as estimated with (86)Rb-labeled K(+), was hyperbolic over the concentration range of 0.01 to 0.1 mm. It was concluded that (86)Rb is a poor tracer for K(+) over the concentration range of 0.01 to 0.1 mm. Accumulation of Rb(+) in the presence of K(+) was accurately measured by (86)Rb.

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PubMed1969

Accumulation of potassium and sodium by barley roots in a k-na replacement series.

Excised roots of barley (Hordeum vulgare, var. Campana) were incubated for 24 hr in solutions containing constant total concentrations of KCl and NaCl but in which the mole fractions of K and Na were varied in replacement series. In solutions containing 1, 10, or 50 mm concentrations of K(+) plus Na(+), total cation accumulation was dependent upon the total salt concentration but was relatively independent of the mole fractions of K(+) and Na(+). These results imply that accumulation of K(+) and Na(+) was limited by a common factor. In solutions containing 0.01 mm K(+) plus Na(+) there was a strong preference for K(+) over Na(+) and the sum of K(+) and Na(+) accumulation increased with increasing K(+) concentration.In the replacement series utilizing 0.1 mm K(+) plus Na(+), K(+) accumulation reached a peak at solution concentrations of 0.04 mm K(+) and 0.06 mm Na(+). Potassium accumulation then decreased as Na(+) was further replaced by K(+) to concentrations of 0.06 mm K(+) and 0.04 mm Na(+). Potassium accumulation again increased with additional replacement of Na(+) by K(+).

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PubMed1968

Electrostatic association and donnan phenomena as mechanisms of ion accumulation.

Excised roots of barley (Hordeum vulgare, var. Campana) were incubated for periods up to 24 hours in salt solutions of various concentrations and ion accumulation was determined at various time intervals. The data were consistent with the existence of 2 components of ion uptake, one accounting for ion uptake from solutions below 1 mm and both components contributing to uptake from solutions of concentrations higher than 1 mm.It is proposed that organic and amino acids play an important role in ion accumulation by providing nondiffusible charges which may bind or retain inorganic ions within the cell. Ions would enter the cell by diffusion or exchange from salt solutions of low concentration and become associated with nondiffusible organic ions, principally organic and amino acids. The electrostatic association between inorganic and organic ions would maintain a gradient and diffusion-exchange would occur until equilibrium between the cell and the external solution was reached. It is proposed that the additional component of ion uptake which becomes important at salt concentrations higher than 1 mm is a result of diffusion of neutral salts according to Donnan phenomena. Ion uptake by this proposed mechanism would not necessarily involve the action of carriers.

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PubMed1967

Loss of organic acids, amino acids, k, and cl from barley roots treated anaerobically and with metabolic inhibitors.

Excised roots of barley (Hordeum vulgare, var. Campana) lost organic acids, amino acids, K(+), and Cl(-) within 15 minutes after initiation of anaerobic treatment or treatment with NaCN and 2,4-dinitrophenol. Initial loss of organic acids when roots were placed under N(2) is attributed to a decarboxylation reaction, possibly catalyzed by phosphoenolpyruvate carboxykinase. Organic and amino acids began to leak from the roots to the bathing medium after 1 to 2 hours under N(2), indicating injury to cell membranes. During the first hour of anaerobic treatment, K(+) loss from low-salt roots was equivalent to organic acid loss. Potassium loss from roots containing high levels of KCl was approximately equal to organic acid plus amino acid loss; and Cl(-) loss was approximately equal to amino acid loss. It is postulated that, within cells, organic acids may electrostatically bind an equivalent quantity of cations and that amino acids may bind an equivalent quantity of both cations and anions.

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PubMed1967

Relationship of Cell Sap pH to Organic Acid Change During Ion Uptake.

Excised roots of barley (Hordeum vulgare, var. Campana) were incubated in KCl, K(2)SO(4), CaCl(2), and NaCl solutions at concentrations of 10(-5) to 10(-2)n. Changes in substrate solution pH, cell sap pH, and organic acid content of the roots were related to differences in cation and anion absorption. The pH of expressed sap of roots increased when cations were absorbed in excess of anions and decreased when anions were absorbed in excess of cations. The pH of the cell sap shifted in response to imbalances in cation and anion uptake in salt solutions as dilute as 10(-5)n. Changes in cell sap pH were detectable within 15 minutes after the roots were placed in 10(-3)n K(2)SO(4). Organic acid changes in the roots were proportional to expressed sap pH changes induced by unbalanced ion uptake. Changes in organic acid content in response to differential cation and anion uptake appear to be associated with the low-salt component of ion uptake.

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PubMed1965