Alterations in the mineral nutrition of pea seedlings exposed to cadmium

A study was made of the effects of different levels of cadmium (Cd) in the nutrient solution (0.0, 1.5, and 6.0 mg/L Cd) on the assimilation of nitrate (NO3-) and the uptake and distribution of cationic nutrients in pea (Pisum sativum cv. Argona) seedlings. Cadmium treatment resulted in an accumulation of NO3- in the root, indicating an alteration in NO3- translocation to the shoot. This was related to a decrease in the nitrate reductase (NR) activity in the shoot, severely inhibiting NO3- assimilation, and associated to a reduction in fresh tissue weight and in their relative water content. The concentration of potassium (K) decreased in both root and shoot, but its relative distribution between those tissues was not affected by the presence of Cd Among other cationic nutrients, manganese (Mn) was the most affected, its concentration constantly decreased concomitantly with the increase in Cd supply. The distribution of Mn between shoot and root revealed that more was accumulated in the shoot than in the root, opposite to the distribution of NO3-. The 'shock' addition of 6.0 mg/L Cd in a short-term experiment confirmed that the transport of NO3- to the aerial part was reduced after 72 h of treatment and Cd displaced Mn from its physiological positions in root tissues.