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The effects of cadmium (Cd) uptake on ultrastructure and lipid composition of chloroplasts were investigated in 28-day-old tomato plants (Lycopersicon esculentum var. Ibiza F1) grown for 10 days in the presence of various concentrations of CdCl2. Different growth parameters, lipid and fatty acid composition, lipid peroxidation, and lipoxygenase activity were measured in the leaves in order to assess the involvement of this metal in the generation of oxidative stress. We first observed that the accumulation of Cd increased with external metal concentration, and was considerably higher in roots than in leaves. Cadmium induced a significant inhibition of growth in both plant organs, as well as a reduction in the chlorophyll and carotenoid contents in the leaves. Ultrastructural investigations revealed that cadmium induced disorganization in leaf structure, essentially marked by a lowered mesophyll cell size, reduced intercellular spaces, as well as severe alterations in chloroplast fine structure, which exhibits disturbed shape and dilation of thylakoid membranes. High cadmium concentrations also affect the main lipid classes, leading to strong changes in their composition and fatty acid content. Thus, the exposure of tomato plants to cadmium caused a concentration-related decrease in the fatty acid content and a shift in the composition of fatty acids, resulting in a lower degree of fatty acid unsaturation in chloroplast membranes. The level of lipid peroxides and the activity of lipoxygenase were also significantly enhanced at high Cd concentrations. These biochemical and ultrastructural changes suggest that cadmium, through its effects on membrane structure and composition, induces premature senescence of leaves.

Cells of Catharanthus roseus (L.) G. Don were maintained and sub-cultured in the absence of NaCl (control) or were sub-cultured for 7 days in the presence of 50 ("50") or 100 ("100") mM NaCl, or were maintained and sub-cultured for 8 months in the continuous presence of 50 mM NaCl ("50T" or salt-adapted cells). Exposure to salt treatment reduced growth in a concentration-dependent manner. Salt-treated cells strongly accumulated Na + and, to a lesser extent, Cl -. However, no significant change in Claccumulation was observed in 50T cells.Salt progressively increased superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities whereas a strong increase in catalase (CAT) activity was only obtained in 50 and 50T cells. SOD activity was lower in 50T than in 50 cells, whereas the opposite was observed for APX activity.After native polyacrylamide gel electrophoresis (PAGE) analysis, five SOD isoenzymes were detected and the increase in SOD activity observed in salt-treated cells seemed to be mainly due to isoenzymes (SOD 1, 2 and 3). Three APX isoenzymes (APX 1, 2 and 3) were detected markedly, especially in salt-adapted cells. Salt strongly induced CAT 2 isoenzyme in 50 cells and CAT 1 isoenzyme in 50T cells. These data suggest that salt treatment provoked an oxidative stress in C. roseus cells, as shown by the increase in lipid peroxidation, in spite of the induction of antioxidant enzymes. This increase in lipid peroxidation was paralleled by a rise in lipoxygenase (LOX) activity.Increases in antioxidant activities could also be a response to the cellular damage provoked by NaCl. Probably, this increase could not stop the deleterious effects of salt, but reduced stress severity thus allowing cell growth to occur. On the other hand, and although no JA measurements has been carried out, the antioxidant enzymes could me mediated, at least 3 partially, by an LOX-mediated JA increase in salt-treated C. roseus cells. SALEM: Please penser si on laisse ce paragraph or no

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