The dependence of nitrate reductase activity on the level of soluble sugars in wheat and cucumber roots growing in the presence of simazine, in light or in darkness

Abstract

At concentrations of 25 and 5 µM, simazine inhibited nitrate reductase activity in wheat and cucumber roots, respectively. It also lowered the content of soluble sugars and decreased the activities of NADH malate dehydrogenase and NADP⁺ glucose-6-phosphate dehydrogenase. The inclusion of 50 mM glucose into the medium partially reversed the inhibitory effect of simazine on the activity of nitrate reductase in cucumber roots and slightly increased the activity of this enzyme in wheat roots These results suggest a complex influence of the herbicide on the activity of nitrate reductase: simazine lowers the level of soluble sugars in roots and decreases the activity of the dehydrogenases supplying the reduced nucleotides indispensable for reduction of nitrates.