Chromium effect on ROS generation and detoxification in pea (Pisum sativum) leaf chloroplasts

Pea plants were exposed to 0, 20, 50, and 100 microM chromium [Cr(VI)] to investigate oxidative stress in isolated chloroplasts. Leaf area and biomass accumulation were significantly reduced at higher Cr supply. Generation of superoxide, hydrogen peroxide, and *OH radical generation was enhanced in the chloroplasts isolated from Cr-exposed pea plants. Cr(VI) significantly reduced F(v)/F(m) ratio of chlorophyll (Chl) fluorescence, Chl content, and whole chain electron transport rate. Superoxide dismutase (SOD) activity increased at lower Cr supply while it decreased at higher Cr supply. Ascorbate peroxidase (APX) was found to be most sensitive to Cr stress. Monodehydroascorbate reductase activity remained higher at 20 and 50 microM Cr but decreased at 100 microM Cr. Increased activities of dehydroascorbate reductase (DHAR) and glutathione reductase (GR) in the isolated chloroplasts were observed during the initial 3 days of Cr exposure of pea plants. Activities of DHAR and GR were increased up to day 3 only. Ascorbate and glutathione (GSH) pools showed similar decrease that was more evident in the GSH pool as the duration of Cr treatment increased. Observed changes in reactive oxygen species concentration, photosynthetic characteristics, and antioxidant system indicate that chloroplasts in Cr-exposed pea plants are an important target of oxidative stress.