EFFECT OF CHILLING ON NITRATE REDUCTASE IN THE LEAVES AND ROOTS OF CUCUMBER (CUCUMIS-SATIVUS L)

Intact plants of cucumber (C. sativus) were exposed to low temperature treatment (+0.5, +2 or +3.degree. C) for a different length of time (16-84 h) either in the light or in the darkness. Under such conditions, nitrate reductase (EC 1.6.6.1) activity determined in vivo at the end of exposition to the chilling conditions was not inhibited. The combination chilling conditions plus light and chilling conditions plus darkness had a different effect on nitrate reductase activity. After the chilling treatment, an increase in nitrate content of plant organs occurred. Differences in enzyme activities in plant organs (leaves, roots) occurred as a response of the plant to the stress evoked by the low temperature. Nitrate reductase induction by nitrate was followed in the light and in the darkness at the temperature close to zero (0.5, + 2.degree. C). The induction was sensitive to the presence of molybdate or tungstate and to several proteosynthesis inhibiting antibiotics. Tungstate cause a partial increase of nitrate content in the tissue of the studied plants.