Aluminium effect on nitrate assimilation in cucumber (Cucumis sativus L.) roots

In vivo effect of aluminium on nitrate uptake and reduction by cucumber seedlings was investigated. The high-performance liquid chromatography was used to analyse the rate of nitrate uptake. Low (0.5 mM) concentration of AlCl3 in the nutrient solution stimulated nitrate uptake during the first 3 h. On the other hand, 6 h exposure of the cucumber seedlings to 1 or 5 mM of AlCl3 resulted in inhibition of nitrate uptake and at 5 mM concentration of AlCl3 the efflux of nitrate was observed. Furthermore, the amount of nitrate accumulated in cucumber roots after aluminium treatment was decreased. The noteworthy fact was observed, that at all concentrations of aluminium tested on increase of the nitrate reductase activity. This stimulation was concentration depended, but independent of the source of the enzyme. The activity of both the cytosolic and the plasma membrane bound nitrate reductase activity was enhanced in vivo. On the other hand, AlCl3 applied in vitro only slighty decreased nitrate reductase activity.