[Effect of sodium chloride on respiration and the activity of malate dehydrogenase in some halophytes and glycophytes].

This paper reports the effects of sodium chloride on the in vitro activity of malate dehydrogenase and on the specific activity of malate dehydrogenase isolated from various halophytes and glycophytes grown under saline and non-saline conditions. The influence of substrate salinity on respiration and dark CO2 fixation was also studied. The species used were the halophytesAster tripolium, Atriplex spongiosa, Mesembryanthemum crystallinum, Plantago maritima, Salicornia brachystachya, andSpergularia salina, and the glycophytesAster amellus, Plantago major, andSpergularia rubra.When added to the test solutions, sodium chloride stimulates the activity of malate dehydrogenase. Further addition of sodium chloride results in rapid decline of activity at salt concentrations which vary with the species. Malate dehydrogenase isolated from both glycophytes and halophytes do not show any significant difference in their response to sodium chloride, indicating salt tolerance. Enzyme isolated from halophytes grown under saline conditions is as sensitive to sodium chloride as enzymes isolated from the same plants grown in the absence of additional NaCl. A double reciprocal plot shows a competitive interaction between sodium chloride and oxaloacetate. The addition of sucrose during the in-vitro assay of malate dehydrogenase results in a stronger inhibition than that caused by isosmotic NaCl solutions.Enzymes extracted from seedlings of halophytes and glycophytes grown at various levels of sodium chloride showed important changes in specific activity of malate dehydrogenase (tested without additional sodium chloride in an in-vitro assay). In glycophytes, specific activity decreases with increasing substrate salinity, whereas in halophytes specific activity first increases, to a symptote and finally decreases. A double reciprocal plot shows a non-competitive interaction between sodium chloride and oxaloacetate indicating that the ratio of malate dehydrogenase to total extractable protein is altered by sodium chloride. The respiration of these seedlings runs parallels the specific activity of the malate dehydrogenase whereas CO2 dark fixation declines with increasing substrate salinity.The results are discussed with respect to compensatory reactions rather than compartmentalisation due to the addition of sodium chloride.