Antioxidative enzyme activities in Brassica juncea L. and Brassica oleracea L. plants under chromium stress

Abstract

Chromium (Cr) is one of the most common heavy-metal contaminant in groundwater, soil and sediments. Cr is a toxic element that occurs in highly variable oxidation states. Since Cr (VI) is a strong oxidant, it may cause severe oxidative stress in plant tissue. However, the antioxidative responses of plants to excess Cr have not been studied critically. Thus, the present study was undertaken to assess antioxidative responses of Brassica juncea L. and Brassica oleracea L. plants as models because of their phytoremediation capacity of metal enriched soils under different levels of Cr (VI) treatments. Seedlings were grown in 15 cm x 17 cm pots containing turf mixture in a greenhouse for 6 weeks. Then plants were irrigated with the solutions containing 0, 0.05, 0.25, 0.5 and 1 mM Cr (VI) for 10 weeks. Fully expanded leaves were collected from the plants at the end of the treatments for catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) analyses. Even though both species showed a similar trend in response to Cr (VI) treatments, the total enzyme activities were higher in Brassica oleracea L. than in Brassica juncea L. Cr (VI) treatments significantly decreased the activities of CAT depending on the Cr concentrations in both species. After the significant increase, a sharp decrease was observed in the activity of APX and GR in both species. Data indicated that a coordinated increase in APX and GR activities in both Brassica species under Cr stress played a role as signals to protect the plants from Cr-induced stress.