Effect of Piriformospora indica and nitric oxide on growth and some physiological-biochemical characteristics of proso millet (Panicum miliaceum) under zinc toxicity

Contamination of arable land with heavy metals is one of the important environmental problems that causes a reduction in plant growth and yield. Applying the biological potential of beneficial microorganisms and biochemical compounds that reduce oxidative stress are promising techniques to protect plants against heavy metal toxicity. Accordingly, a pot experiment was conducted as a factorial completely randomized design with three replicates to investigate the effects of four levels of zinc (0, 250, 500 and 750 mg/Kg soil), two levels of P. indica fungus (inoculation and non-inoculation) and two levels of foliar spraying (sodium nitroprusside and water). The results showed that root colonization of stressed plants by P. indica fungus and foliar spraying of sodium nitroprusside effectively reduced zinc content in the aerial parts of stressed plants. In addition, the highest chlorophyll content and root and shoot dry weight were obtained in the presence of the fungus and the simultaneous use of sodium nitroprusside. In proso millet plants subjected to zinc stress, P. indica inoculation and NO application boosted the activity of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) which was evident in the reduction of hydrogen peroxide and malondialdehyde content. In conclusion, the results of this experiment provide evidence that the utilization of synergistic effects between colonization of the endophytic fungus P. indica and foliar application of NO can be considered a proper approach to reducing the negative effects of zinc toxicity on plants.