Effect of Bacteria from the Genus <i>Azospirillum</i> on Oxidative Stress Levels in Wheat <i>Triticum aestivum</i> L. in the Presence of Copper, Nickel, and Lead

Heavy metals (HMs) exert a negative impact on physiological processes in plants, which can adversely affect the productivity of agricultural crops. In this experiment, we assessed the potential to mitigate the toxic effects of HMs on soft wheat through the use of rhizospheric microorganisms from the genus <i>Azospirillum</i>. In the initial phase of the experiment, we identified the most resistant <i>Azospirillum</i> strains to Cu (from 1.5 to 15 mg/L), Ni (from 2 to 20 mg/L), and Pb (from 15.9 to 159.4 mg/L). Both Ni and Pb significantly inhibited bacterial growth and induced substantial oxidative stress in the majority of the studied strains. The strain <i>A. picis</i> B-2897^T exhibited the highest resistance to all HMs. The cultivation of wheat in soil supplemented with Cu led to an increased growth rate and enhanced wheat productivity. Conversely, Ni and Pb reduced wheat productivity by 65% and 27%, respectively. This was accompanied by chlorophyll depletion and a decrease in the expression of genes <i>NDOR</i> and <i>GST</i>, which are involved in xenobiotic detoxification. Pre-inoculation of seeds with <i>Azospirillum</i> led to a decrease in HM concentration in the plant seedlings; in particular, <i>A. picis</i> B-2897^T reduced the level of Ni from 0.005% to a concentration below the detectable level (i.e., below 0.001%), and Pb from 0.014% to 0.008%. The bacteria stimulated the expression of genes responsible for xenobiotic detoxification and contributed to the increased growth and productivity of wheat. Thus, <i>Azospirillum</i> can be utilized as a bioproduct to alleviate the toxic effects of HMs.