Comparison of antioxidant enzyme activities in leaves stems and roots of Sorghum (Sorghum bicolor L.) exposed to Chromium (VI)

Abstract

This study was conducted to determine the response between different organs to assess which one was more severely affected. Thus, we exposed sorghum (Sorghum bicolor L.) to five level 0, 30, 60, 100 and 130 mg/L concentration of chromium (Cr) VI during two weeks and measuring the activity of glutathione-s-transferase (GST), glutathione reductase (GR), glutathione peroxidase (GPX), catalase (CAT), total glutathione (GSG) and lipid peroxidation (LPO) in upper, middle and lower leaves, stems and roots of sorghum plants. Reduction in dry matter of roots, stem and leaves was noticed in Cr (VI) stress. GST and Cr (VI) activities were induced in all organs of the exposed plant, but was inhibited in 130 mgL-1 Cr (VI). GPX and CAT activities wereinduced in all the organs at all studied concentrations, whereas inhibited was observed in the roots and higher leaves above 100 and 130 mgL-1. Significant increases in lipid peroxidation in plants exposed to 100 and 130 mgL-1.These results suggest that in roots and upper leaf of sorghum the tolerance to Cr (VI) toxicity is more dependent on the activities of GST and GR than other enzyme activities. Hyperactivity of the GR and GST indicated that these enzymes played an important role in protecting the sorghum fromCr (VI) toxicity. However, GPX took a little part in detoxification of Cr (VI). Furthermore,the conjugation of GSH with Cr (VI) ions by GST helped them to sequester into vacuole. GR participates in the GSG biosynthesis and might build up a reduced form GSG against poisoning of the Cr (VI). This might be a part of defense strategy adapted by S. bicolor against chromium toxicity to protect themselves. We find that the roots and upper leaves, often considered as a first biomarker for Cr (VI) treated plants organ compared to the other organs. A higher level of LPO was correlated with lower CAT andGPX activities. Therefore, hyperactivities of GST and GR in roots and upper leaves might be attributed to the strategies adopted by S. bicolor to overcome the toxicity of theCr (VI). Key words: Hyperactivity, GST, CAT, GR. activities and Sorghum bicolor, LPO.