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D G Edwards

Publications and source records attributed to D G Edwards.

25 records · Page 2Linked to original sources
PubMed1970

Potassium Fluxes during Potassium Absorption by Intact Barley Plants of Increasing Potassium Content.

The presence of previously absorbed K in plants caused a marked reduction in the short term influx of (86)Rb-labeled K into roots of barley seedlings. The influx values agreed with net K absorption rates into intact plants, thus suggesting that K efflux was negligible in comparison with influx.Earlier interpretations of a large K efflux component from excised roots approaching equilibrium K concentrations are considered to be due to an underestimation of net K absorption rates resulting from xylem exudation as the K status of the roots increased.

Journal Article↗
PubMed1968

Interactions between potassium and calcium in their absorption by intact barley plants. I. Effects of potassium on calcium absorption.

Increasing concentrations of K (20, 200, 2000 mum) in the nutrient solution depressed Ca content and concentration in barley plants growing in nutrient solutions of low Ca concentrations (250 and 2500 mum). Increasing K from 20 to 200 mum depressed Ca absorption more than increasing K from 200 to 2000 mum K.The strong depression of Ca absorption by low concentrations of K must involve a different process from that studied by other workers at high concentrations of K. Since the depression in net absorption of Ca was as great at 250 as at 2500 mum Ca the results fail to support previous suggestions that a specific mechanism for Ca absorption operates at low Ca concentrations. It is suggested that, at the low concentrations of K and Ca likely to be found at the root surface in many soil solutions, the above mentioned effect of K in inhibiting Ca absorption may be important in the Ca nutrition of plants.

Journal Article↗
PubMed1968

Interaction Between Potassium and Calcium in Their Absorption by Intact Barley Plants. II. Effects of Calcium and Potassium Concentration on Potassium Absorption.

Rates of K absorption by young barley plants grown for 20 days in flowing nutrient solutions have been studied at 3 solution K concentrations (20, 200, and 2000 mum) and at 2 Ca concentrations (250 and 2500 mum). Increasing solution K increased plant K content, concentration, and rate of absorption: solution Ca concentrations had no effect at any K level.Rates of K absorption were only one-half to one-fifth of those reported for excised barley roots at similar K concentrations in solution. If the reported rates of K absorption by the high-affinity mechanism in excised barley roots were maintained in growing plants they would have given, within 3 days, the equilibrium concentrations of K in plants of the present experiment. Thereafter the rates of K absorption by the high-affinity mechanism would have been more than adequate to maintain plant K and would need to have been compensated by K efflux.It is suggested that, for all concentrations of K in solution, the high-affinity mechanism dominates the absorption of K by barley plants grown for more than a few days.

Journal Article↗
PubMed1966

Cation effects on chloride fluxes and accumulation levels in barley roots.

Accumulation of Cl(-) by excised barley roots, as of K(+), approaches a maximum level at which the ion influx and efflux rates become equal. The rate of Cl(-) influx at this equilibrium is close to the initial rate while the efflux rate increases with time from zero to equality with influx. The Cl(-) fluxes are independent of simultaneous exchange flux of the cations, but depend on the nature and concentration of the salt solutions from which they originate. The Cl(-) content at equilibrium, however, is largely independent of the external concentrations. The approach to equilibrium reflects the presence of the cation. Cl(-) flux equilibrium is attained more rapidly in KCl than in CsCl or CaCl(2). This is presumably an effect of much slower distribution of Cs(+) and Ca(++) than of K(+) within the roots. Accumulated Cs(+) appears to form a barrier to ion movement primarily within the outermost cells, thereby reducing influx and ultimately efflux rates of both Cl(-) and cations. Slow internal mixing and considerable self-exchange of the incoming ions suggest internal transport over a series of steps which can become rate-limiting to the accumulation of ions in roots.

Biological Transport↗
PubMedDate not supplied

Potassium-sparing effect of amiloride in a diuretic factorial study in man.

1. The effects of amiloride (M, 20 mg/day), chlorothiazide (C, 1000 mg/day), ethacrynic acid (E, 100 MG/day) and frusemide (F, furosemide 80 mg/day, given alone and in combination, were investigated in eight patients in a 2(4) factorial study. Effects between blocks of four treatments in each sixteen-treatment replicate were confounded with higher interactions to allow for differences between early and late diuresis. 2. All patients exhibited marked diuresis, with significant mean increases in daily urinary sodium excretion (P smaller than 0.05) and urinary volume (P smaller than 0.01) induced by chlorothiazide, frusemide and ethacrynic acid (68, 69 and 38%; and 35, 40 and 34%, respectively). Amiloride appeared to be half to one-third as potent as the other diuretics. 3. Amiloride produced a significant potassium-sparing effect (P smaller than 0.01), reducing urinary potassium excretion by 30%, compared to significant urinary potassium wasting with frusemide (increase of 33%, P smaller than 0.01) and chlorothiazide (increase of 31%, P smaller than 0.05). 4. No adverse reactions occurred, but serum potassium levels twice rose to 6 mmol/l and subsided without additional therapy, and on one occasion fell to 2.5 mmol/l, requiring a potassium supplement for 4 days. 5. It was concluded from these factorial studies that amiloride is a mild diuretic and potent potassium-sparing agent acting independently and additively in combination with chlorothiazide, ethacrynic acid or frusemide. For the three latter diuretics, all two-drug interactions were simply additive also, without evidence of synergism or antagonism between drugs.

Amiloride↗