Involvement of glutathione metabolism in Eichhornia crassipes tolerance to arsenic

Abstract

Aquatic macrophytes are potential useful for phytoremediation programs in environments contaminated by arsenic (As). Biochemical and physiological modification analyses in different plant parts are important to understand As tolerance mechanisms. 2. The objective was to evaluate glutathione metabolism in leaves and roots of Eichhornia crassipes (Mart.) Solms plants subjected to As. Specimens of Eichhornia crassipes plants were cultured for three days in Clark's nutrient solution containing 7 μM of As. The enzymes ATP sulfurylase (ATPS), glutathione reductase (GR), glutathione peroxidase (GSH‐Px), glutathione sulfotransferase (GST) and γ‐glutamylcysteine (γ‐ECS) synthetase activity, the glutathione contents, total proteic and non‐proteic thiols were evaluated. 3. The ATPS activity increased in roots. The GR activity in leaves and GSH‐Px in roots were lower. GST activity was higher in roots and lower in leaves and γ‐ECS activity was higher in this plant's leaves. Glutathione levels were lower, total thiols levels were higher and non proteic levels presented no change in E. crassipes leaves and roots. Exposure to As increased the enzyme activity involved with sulfur metabolism, such as ATPS. Higher GR activity and lower GSH‐Px indicates a greater glutathione conjugation to As, due to the greater GSH availability. The greater GST activity indicates its participation in As detoxification and accumulation, through As GSH conjugation. Changes in the glutathione and thiol levels suggest high phytochelatin synthesis. 4. In conclusion, the increment in ATPS, GR, GST and γ‐ECS activity indicates that these enzymes are involved in GSH metabolism and are part of the E. crassipes As detoxification mechanism.