[The influence of sodium and potassium ions on the photophosphorylation in Ankistrodesmus braunii].
During short-time experiments (30 sec to 60 min) sodium ions stimulate the phosphate uptake and especially the (32)P-labelling of the organic TCA-soluble phosphate compounds up to 1,500% (K(+)=100%). The labelling is maximally stimulated in the light and in the dark at concentrations of about 5×10(-3) mol/l Na(+) and at pH 8. Lithium ions stimulate (32)P-labelling in a similar but less effective way. In comparison, in the presence of potassium ions the (32)P-label decreases.It was investigated whether sodium ions specifically stimulate the ATP-synthesis or some reaction of the photosynthetic carbon reduction cycle or whether they only enhance the (32)P-labelling of phosphorylated compounds.Separation by thin-layer chromatography of the MCF-soluble phosphate fraction showed that labelling of all compounds investigated was stimulated by Na(+) to a similar extent.Experiments performed in red and far-red light (683 and 712 nm) under nitrogen and in the presence of various DCMU-concentrations, as well as in the presence of antimycin A and CCCP showed that Na(+) exerts no specific influence either on the cyclic or on the non-cyclic photophosphorylation in vivo.ATP-dependent reactions such as (14)CO2-fixation or glucose uptake are not influenced by Na(+).Since Na(+) does not change the size of phosphate pools in a different way from K(+), there is no evidence for the assumption that the Na(+)-dependent increase in the (32)P-labelling is due to its action on the chloroplast membrane in increasing its permeability to orthophosphate ions. This is supported by the lack of any effect of sodium plus phosphate ions on the CO2-fixation.Therefore the results give no evidence that sodium acts directly on phosphorus metabolism inside the cell. It is suggested that its action is localised at the phosphate-transporting site of the plasmalemma.
Botanisches Institut I der Universität Würzburg, Würzburg, Deutschland.
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Ullrich-Eberius
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Simonis