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

Nitrate reductase, peroxidase, nitrate and sugar contents ofsugar beet leaves were increased by low NaCl concentrations.The salt was applied in the nutrient solution at concentrationsof 2, 4 and 10 mM and determinations were made at 24, 48, 72and 96 h after salt applications. Nitrate reductase was assayed both in vitro and in vivo. Inthe latter case maximum activity was attained in the first 24h for all salt concentrations after which there was a declineuntil control level was reached. Maximum nitrate content wasobserved at 48 h. It is suggested that in the first hours thesalt stimulated preferentially the flux of nitrate into theinducer nitrate pool. Maximum sugar content occurred in thefirst 24 h. This may be associated with the increase in nitratereductase activity as sugars are a source of reducing powerfor the enzyme and can supply energy and carbon skeletons forthe induction process. The salt treatments also stimulated peroxidase, maximum activitybeing reached at 48 h. Key words: Sugar beet, Sodium chloride, Nitrate reductase, Peroxidase