Azotobacter vinelandii helps to combat chromium stress in rice by maintaining antioxidant machinery

Chromium (Cr) causes toxic effects in plants by generating reactive oxygen species (ROS) which create oxidative environment. Azotobacter vinelandii helps in growth and development of many crops; however, its role in Cr stress tolerance in rice has not been explored. Here, we report the new function of Azotobacter vinelandii strain SRI Az3 (Accession number JQ796077) in providing Cr stress tolerance in Oryza sativa (var. IR64). The efficiency of the strain was checked under different concentrations (50, 100, 150, 200 and 250 µM) of Cr stress and it was observed that it provides stress tolerance to rice plant up to 200 µM concentration. Different agronomic growth parameters were found to be better in this strain of Azotobacter vinelandii-inoculated rice plants as compared to un-inoculated one. The agronomic growth and photosynthetic characteristics such as net photosynthetic rate (PN), stomatal conductance (gs), intercellular CO₂ (Ci) were also found to be significantly increased with increasing concentration of Azotobacter vinelandii inoculation. The activities of antioxidant enzymes were significantly higher (35%) in rice plants inoculated with Azotobacter vinelandii as compared with un-inoculated rice plant. All these positive effects of Azotobacter vinelandii help rice to survive from the toxic effect of Cr.