Effect of Cadmium Repartition on Nitrogen Metabolism in Tobacco Seedlings

Abstract

Thirty-day-old tobacco seedlings (Nicotiana tabaccum, Bureley v) were subjected during one week to increasing cadmium (Cd) concentrations (0, 10, 20, 50 and 100 µM CdCl 2). Increasing Cd stress led to a gradual decrease of dry weight (DW) production, water and nitrate contents. More than the half of Cd accumulated per plant was sequestered in the oldest leaf stage (S 1 leaves). Leaves from S 1 were the least affected by Cd stress. The activities of nitrate reductase (NR, EC 1.6.1.6), nitrite reductase (NiR, EC 1.7.7.1) were the least reduced in S 1 leaves despite of the high presence of Cd ions. At 100 µM Cd, glutamine synthetase activity (GS, EC 6.3.1.2) from S 1 leaves rose to become 2 times more important than control. Western Blot analysis showed that S 1 GS activity induction was correlated to the GS 1 and GS 2 protein accumulation. Young leaves (S 3 leaves) were more affected by Cd stress than old leaves. The GS activity reduction in S 3 leaves was correlated to GS 2 protein decrease detected by western-blot analysis. So, tobacco plant accumulated Cd ions in old leaves (S 1 leaves) to protect younger leaves which are more sensitive to Cd effects. Leaves from S 1 are a target organ to verify an eventual soil contamination per cadmium. This leaves may evolve adaptive process to partially inacti-vate Cd ions and maintain stable rate of nitrogen metabolism.