Effect of Cadmium Repartition on Nitrogen Metabolism in Tobacco Seedlings

摘要

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 CdCl2). Increasing Cd stress led to a gr a dual 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 (S1 leaves). Leaves from S1 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 S1 leaves despite of the high presence of Cd ions. At 100 μM Cd, glutamine synthetase activity (GS, EC 6.3.1.2) from S1 leaves rose to become 2 times more important than control. Western Blot analysis showed that S1 GS activity induction was correlated to the GS1 and GS2 protein accumulation. Young leaves (S3 leaves) were more affected by Cd stress than old leaves. The GS activity reduction in S3 leaves was correlated to GS2 protein decrease detected by western-blot analysis. So, tobacco plant accumulated Cd ions in old leaves (S1 leaves) to protect younger leaves which are more sensitive to Cd effects. Leaves from S1 are a target organ to verify an eventual soil contamination per cadmium. This leaves may evolve adaptive process to partially inactivate Cd ions and maintain stable rate of nitrogen metabolism.