Bioaccumulation du Cd et du Zn chez les plants de tomates (Lycopersicon esculentum L.)

Abstract

This work aims at evaluating the accumulation of cadmium (Cd) and zinc (Zn) (trace elements) in the organs of young tomato plants (Lycopersicon esculentum L. var. Rio Grande) and their effects on the rate of chlorophyll and enzyme activities involved in the antioxidant system: catalase (CAT), glutathion-S-transferase (GST) and peroxysase ascorbate (APX). Plants previously grown on a basic nutrient solution were undergoing treatment for 7 days, either by increasing concentrations of CdCl2 or ZnSO4 (0, 50, 100, 250, 500μM) or by the combined concentrations of Cd and Zn (100/50, 100/100, 100/250, 100/500μM). The results concerning the determination of metals in the various compartments of tomato plants as a function of increasing concentrations of Cd or Zn, suggest a greater accumulation of Cd and Zn in the roots compared to leaves. The combined treatment (Cd/Zn) interferes with the absorption of the two elements according to their concentrations in the culture medium. The presence of Zn at low concentrations (50μM of Zn/100μM Cd) has little influence on the accumulation of Cd in the roots and leaves, while the absorption of these two elements in the leaves increases and decreases in roots when their concentrations are equivalent (100/100μM) compared to treatment alone. When the concentration of Zn is higher than that of Cd (500μM of Zn/100μM Cd) absorption of the latter is inhibited in the roots while increasing their translocation to the leaves. Meanwhile, the dosage of chlorophylls shows that they tend to decrease in a dose-dependent for both treatments (Cd or Cd/Zn), however, treatment with low concentrations of Zn (50 and 100μM) stimulates chlorophyll synthesis. However, treatment with different concentrations of Cd seems to induce the activity of the enzymes studied (CAT, APX, GST). It is the same for treatment with different concentrations of Zn and this particularly for the highest concentrations. Finally, the combined treatment (Zn/Cd) also appears to cause enzyme inductions: CAT, APX and GST.