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PubMed1973

Effects of Potassium Deficiency on the Photosynthesis and Respiration of Leaves of Sugar Beet under Conditions of Low Sodium Supply.

Sugar beet plants (Beta vulgaris L. cv. F58-554H1) were germinated and cultured under standardized environmental conditions. The effects of K deficiency on photosynthetic and respiratory CO(2) exchange rates of attached leaves were studied under conditions of low Na supply by withholding both Na and K from the culture medium at cut-off (28 days after planting). Potassium and Na concentrations in the leaf blade and petiole decreased rapidly during the 8 days after cut-off, then more slowly.Photosynthetic CO(2) uptake per unit leaf area decreased rapidly with time after cut-off to 23% of the control rate in 17 days. Mesophyll resistance to CO(2) (r(m)) increased sharply after cut-off, r(m) eventually attaining 8.3 sec cm(-1). Leaf (mainly stomatal) diffusion resistance, r(1)', also increased rapidly from 4 days after cut-off, reaching 1.9 sec cm(-1) 13 days later. The photorespiratory evolution of CO(2) into CO(2)-free air decreased progressively after cut-off, but the rate of dark respiratory CO(2) evolution increased. It was concluded that withholding Na as well as K at cut-off increased the deleterious effects of K deficiency on photosynthesis and stomatal opening.

Journal Article↗
PubMed1972

The effect of oxygen concentration on the growth and metabolism of Saccharomyces cerevisiae grown with excess of potassium or in potassium-deficient media.

1. Saccharomyces cerevisiae cells grown in limiting K(+) concentration have their growth inhibited by O(2) concentrations above 40%. With these conditions the cells grow very large and are unable to maintain ionic gradients when washed with water. 2. Cells grown in excess of K(+) showed the same pattern of change in cell size with change in O(2) concentration, but the magnitude of the changes was much less. Cells grown in excess of K(+) were not leaky. 3. Cell death, growth and development of ;leakiness' were not correlated in the cells grown in limiting K(+) concentration. 4. The activities of both alcohol dehydrogenase and cytochrome oxidase were higher in K(+)-deficient cells than in the cells grown with excess of K(+). The differences were much larger when the measurements were made on a cellular basis than when made on a protein basis. 5. In 100% O(2) 3mm-K(+) in the medium was sufficient to produce normal yeast cells.

Aerobiosis↗
PubMed1972

Polyamine metabolism in potassium-deficient bacteria.

The metabolism of polyamines was studied in K(+)-dependent strains of Escherichia coli. When these stringent organisms were in a medium containing Na(+) instead of K(+), protein synthesis was arrested, but synthesis of ribonucleic acid continued as it would in a relaxed organism. The Na(+) medium inhibited synthesis of spermidine and S-adenosylmethionine. However, the synthesis of putrescine was accelerated at least five- to eightfold. Exogenous ornithine doubled even this rate of putrescine synthesis but did not increase the low level of putrescine synthesis in the K(+) medium. In K(+) or Na(+) media, with or without 0.3 mm arginine, putrescine was derived almost entirely from ornithine via ornithine decarboxylase. Addition of spermidine (5 mm) to a Na(+) culture markedly inhibited putrescine synthesis. The ornithine decarboxylase of an extract of a K(-)-dependent strain prepared at low ionic strength was separated from ribosomes, deoxyribonucleic acid, and associated polyamines by centrifugation, and from many ions by ultrafiltration and fractionation on Sephadex G-100. Addition of Na(+) and K(+) salts to 200 mm was markedly inhibitory. The combined reductions both in synthesis of the inhibitor spermidine and in intracellular ionic strength may explain the in vivo activation of this enzyme.

Arginine↗