Exopolysaccharides of rhizobacteria Paenibacillus polymyxa in the antioxidant protection of wheat seedlings under osmotic stress

The effect of phytostimulating rhizobacteria Paenibacillus polymyxa CCM 1465 (P. polymyxa) and their exopolysaccharides (EPS) on the functioning of the pro-/antioxidant system of wheat seedlings was studied under optimal growth conditions and under osmotic stress (20% of polyethyleneglycol-6000 (PEG), 3 days). It was found that under the optimal culture conditions, the activity of catalase and peroxidase in the experimental plant leaves was practically not distinct from the controls (plants untreated with either bacteria or EPS). The malondialdehyde (MDA) content, as an indicator of oxidative stress in plants, under optimal growth conditions did not change when wheat seedlings were inoculated with the bacteria P. polymyxa, and even decreased when the roots were treated with EPS of these bacteria. Osmotic stress inhibited catalase activity in both controls and plants treated with bacteria or EPS. Stress conditions increased peroxidase activity in the experimental variants. In the course of repair, catalase activity enhanced and leveled off towards controls not exposed to stress, while peroxidase activity remained at a higher level in bacterized and EPS-treated plants. The antioxidant enzymes activity alteration contributed to lowering MDA level in wheat seedling leaves after having gone through stress and repair, that ameliorated the oxidative stress-induced impact on plants, and promoted their rapid recovery after stress.