Cucumber yield and nitrogen metabolism in response to nitrogen supply

Cucumber plants (Cucumis sativus L. cv. Brunex) were grown under controlled conditions in an experimental greenhouse and treated with four rates of N in the form of KNO3 (N1, 5 g/m(2); N2, 10 g/m(2); N3, 20 g/m(2); and N4, 40 g/m(2)). The intermediate N rates (N2 and N3) gave higher utilization of NO3- in the leaves (highest NR activities) than treatment N1 (inadequate) and N3 (excessive). This latter rate (N4) appears to result in excessive foliar assimilation of NO3-, thereby increasing amino acids and proteins and inhibiting or reducing NR activity. N2 and, especially, N3 treatments strengthened the translocation of organic nitrogenous compounds (amino acids) towards the fruit, which enhanced the commercial yield. (C) 1999 Elsevier Science B.V. All rights reserved.