Etude des enzymes de stress oxydatif chez Hedysarum pallidum Desf.et Lygeum spartum L. en réponse à la pollution du sol par l'antimoine.

Abstract

"The aim of this study is to evaluate the oxidative stress' level and antioxidant defense systems of plants growing in antimony (Sb) and arsenic (As) contaminated soil, and to analyze the expression of GST genes. For this, two species Hedysarum pallidum Desf. and Lygeum spartum L. were collected from different areas around an old mine of antimony located in Jebel Hamimat (Algeria), according to a concentration gradient of Sb and As in soil, and act as the subject of analysis related to the oxidative stress markers (malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) and glutathione-S-transferase (GST)). Both species accumulate differently Sb and As in their aerial and underground parts. The results show that the oxidative stress level indicator, the MDA, in both plants, increases significantly with increasing concentrations of Sb and As in the soil, although it is significantly higher in H. pallidum. The activities of antioxidant enzymes vary from plant to plant and also from one zone to another. The activities of SOD, APX and GST are the highest in the most polluted zone in the two parts of H. pallidum. The inhibition of CAT activity in H. pallidum roots, in all the contaminated zones, is concomitant with the induction of POD activity in the same tissue. In L. spartum the APX of the upper parts, the CAT and the GST of the upper parts and the roots are increased to the maximum at zone 5 (the most polluted zone). However, the activities' decline of SOD and POD in the tissues due to the high concentrations of Sb and As on the soil , was also observed.. These results suggest that MDA can be used as a potential soil pollution biomarker by Sb and As for both plants. Seeds In-vitro culture of two populations of H. pallidum has allowed the cloning and sequencing of three fragments of actin gene and two of GST tau. The percent identity between the two genes of GST (tau1 et tau2) is 53% at the nucleotide level and 46% at the protein level. The analysis of the expression of the two genes by semi-quantitative PCR, in response to increasing concentrations of Sb in the breeding ground, shows that the expression of GST tau1 is at its maximum with low concentrations of Sb for the two populations. GST tau2 concentration is more expressed in the population of spoil mine and its expression becomes more important when the concentration of Sb increases. This allows to deduce that every GST tau is specific to a substrate and also that GST tau2 has a specific H domain linked to antimony. This metalloid participates in activation of gene expression that intensifies with increasing concentration. The results of the GST and the analysis of the expression of both genes of GST tau in H. pallidum show that all GST are expressed at low quantities in the absence of the metal stress. In the metal stress moment, only the GST tau having a specific domain for binding to the metal are overexpressed."