In vivo nitrate reductase activity in the roots of seven day old wheat (Tritkum aestivum L.) seedlings was decreased when different concentrations of NiCl2, Pb (NO3)2, CdSO4 and CuSO4 were added in the plant growth or enzyme assay medium. Nitrate uptake by the roots was also decreased with the heavy metal salt treatment. The level of inhibition, was more at higher concentration of the heavy metal salts. Addition of 1 mM dithiothreitol ameliorated the inhibitory effect of heavy metals on nitrate reductase as well as nitrate uptake. Toxic effect of the heavy metals on these two processes was presumably due to an interaction of the heavy metal ions with the -SH groups of the respective proteins.
