Effect of High Sodium Chloride Concentrations in the Growth Medium on the Activity of Glucose-6-Phosphate Dehydrogenase From Pea Roots

The experiments reported in this paper examined discrepant results, obtained in earlier investigations, concerning the effects of NaCl in the growth medium of vascular plants on the specific activity of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) extracted from the plants. NaCl at 120 mM or higher concentrations increased the specific activity of the enzyme in extracts from roots of germinating peas. However, this effect of NaCl was only clearly expressed when 0.1M phosphate was the buffer used to extract the enzyme. When organic buffers were used the observed increase in enzyme activity was either much smaller or absent. Increases in specific activity of glucose-6-phosphate dehydrogenase were only found in extracts from roots that showed severely retarded growth and some brown discoloration. No increase in activity was found either when 120 mM NaCl was added to the growth medium after seedling establishment, or if seeds were germinated in 75 mM NaCl. These observations account for the discrepancies reported in the literature.