The absorption of nitrate and the activity of nitrate reductase were much lower in Ca-deficient plants ofCururbita pepo L., cv. ‘Kveta’ than in normal plants grown in complete nutrient solution for a period of 8 days. After the addition of nitrate to the nutrient medium, nitrate reductase activity in the roots of NO3-deficient plants sharply rose during the first 6 h and then remained constant during the following 6 h; the content of endogenous NO3− rose slowly and continuously. These processes were depressed in (Ca, NO3)-deficient plants independently of the addition of Ca2+ to the medium in the variant with NO3−. Thus it seems that the whole nitrogen metabolism,i.e. both NO3− absorption and the synthesis of nitrate reductase, is impaired in Ca-deficient plants.
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