Effect of Low Salt Concentrations on Nitrate Reductase and Peroxidase of Sugar Beet Leaves

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Abstract
Nitrate reductase, peroxidase, nitrate and sugar contents of sugar beet leaves were increased by low NaCl concentrations. The salt was applied in the nutrient solution at concentrations of 2, 4 and 10 mM and determinations were made at 24, 48, 72 and 96 h after salt applications. Nitrate reductase was assayed both in vitro and in vivo. In the latter case maximum activity was attained in the first 24 h for all salt concentrations after which there was a decline until control level was reached. Maximum nitrate content was observed at 48 h. It is suggested that in the first hours the salt stimulated preferentially the flux of nitrate into the inducer nitrate pool. Maximum sugar content occurred in the first 24 h. This may be associated with the increase in nitrate reductase activity as sugars are a source of reducing power for the enzyme and can supply energy and carbon skeletons for the induction process. The salt treatments also stimulated peroxidase, maximum activity being reached at 48 h.