Signs of oxidative stress in the chlorotic leaves of iron starved plants

Studies were made to relate signs of oxidative stress in chlorotic and non-chlorotic leaves of plants receiving deficient supply, either nil (chlorotic leaves) or 10 μM (non-chlorotic leaves) of Fe, with thiobarbituric acid reactive substance (TBARS) and Fe status of leaf tissues. Total Fe concentration in the young leaves of mulberry, maize and cauliflower plants supplied deficient Fe did not show any significant change. Deficient supply of Fe caused decreases in the activities of catalase, peroxidase and ascorbate peroxidase and increases in the activity and number of isoforms of superoxide dismutase (SOD), accumulation of superoxide anion radical (O2−) and concentration of H2O2 in the young leaves of each mulberry, maize or cauliflower plants. While the chlorotic leaves of Fe-starved mulberry, maize and cauliflower plants had significantly lower TBARS compared to green leaves of the controls or non-chlorotic leaves of cauliflower plants supplied low Fe (10 μM). While TBARS concentration in the young leaves of these plants was well correlated with the concentrations of chloroplastic pigments, and activities of catalase and ascorbate peroxidase, its relationship with leaf tissue Fe or H2O2 concentration was rather poor. Progressive increase in the activity and induction of new isoforms of SOD and higher accumulation H2O2 and O2− may be considered as signs of oxidative stress, whereas, increased ascorbate content along with lower mole fraction of ascorbic acid/total ascorbate are indicative of disturbed cellular redox environment in Fe-starved plants. It is concluded that chlorotic leaves of Fe-starved plants though have elevated titre of reactive oxygen species they are less susceptible to oxidative damage probably due to lower chloroplastic pigments/or low functional Fe in the tissue.