Influence of lead on N03 uptake and reduction in cucumber seedlings

Abstract

The influence of PbCl<sub>2</sub> on NO<sub>3</sub>- uptake and activity level of nitrate (NR) and nitrite MR) reductases in cotyledons and roots of cucumber seedlings was studied. PbCl<sub>2</sub> in a 10<sup>-5</sup> M concentration decreased by 50 per cent N0<sub>3</sub> uptake and reduced NR and NiR activity <em>in vivo</em>. In <em>in vitro</em> experiments only high lead concentrations (10<sup>-3</sup> M) almost completely inhibited NR activity and reduced by 14-28 per cent that of NiR. Lower lead concentrations which inhibited <em>in vivo</em> NR activity did not affect enzyme induction, but depressed tissue hydration. These results indicate that lead in low concentrations (10<sup>-5</sup>, 10<sup>-4</sup> M) indirectly affected NR and NiR activity by producing water stress and reducing N0<sub>3</sub>- uptake, whereas the direct influence of lead on the proteins of the tested enzymes was noticeable at high concentrations.