Reduction of nitrate in leaves of tomato during vegetative growth

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Abstract
Activity of the enzyme nitrate reductase was shown to increase in young leaves of tomato until the leaves reached full expansion, and then it declined. The increase in activity was shown to be due both to an increase in enzyme activity per gram fresh weight and an increase in leaf weight, and the decline in activity was due to a decrease in activity per gram. Nitrate reductase is a key enzyme for the assimilation of nitrate by plants, and the decline in its activity in the older leaves was shown to be more than compensated for by the growth of new leaves. There was an exponential increase in the total activity of the enzyme in the whole leaf system during vegetative growth, when the leaf system itself was increasing in weight exponentially.