Metal Accumulation in Estuarine Plants: Investigating the Effect on the Levels of Non-protein Thiols in Roots of Different Salt Marsh Plants

Abstract

In natural environment, plants are exposed to constant biotic and abiotic stresses (including exposure to trace metals) which may unbalance their equilibrium. As a result, plants have developed important defense mechanisms as, for instance, the production of low molecular weight thiols such as cysteine (Cys) and reduced glutathione (GSH). Much effort has been put into studying the response of soil plants continuously exposed to metals, in terms of thiols production. However, research on this topic involving salt marsh plants is still relatively scarce. Therefore, more information is needed on the contents of thiol compounds as well as on the factors that influence their production in plants inhabiting estuarine environments. Therefore, the levels of non-protein thiols (NPT) (namely, cysteine (Cys), reduced glutathione (GSH), oxidized glutathione (GSSG)) and total acid-soluble SH compounds (Total Thiols) in roots of several salt marsh plants (Phragmites australis (Cav.) Trin. ex Steud., Juncus maritimus Lam., Triglochin striata Ruiz & Pav. and Halimione portulacoides L. Aelen) collected at two River estuaries subjected to different anthropogenic pressures were determined. A possible relationship between the content of each NPT in root tissues and that of a trace metal accumulated was also assessed. The content of thiolic compounds varied in function of the plant species and the sediment colonized by the plants. T. striata was the marsh plant presenting tendentiously higher contents of GSH and GSSG and containing the highest levels of Total Thiols (in specimens from both estuaries). Significant correlations were found between GSH and Cu concentration and between GSSG and Cd and Pb concentration. Results suggest that GSH plays a prominent role in the protection of salt marsh plants cells against metal toxicity, feature of great relevance for application of these plants in phytoremediation procedures.