Regulation by Azospirillum lectins of the activity of antioxidant enzymes in wheat seedling roots under short-term stresses

Azospirillum brasilense Tarrand, which has the potential to stimulate plant growth, belongs to plant-growth-promoting bacteria. Many species of azospirilla colonize the rhizosphere, the portion of soil attached to the root surface. Some species can also enter the host root system and enhance their beneficial effects with an endophytic lifestyle. Depending on the specific agroecological situation, the positive effect of Azospirillum on plants may be due to different mechanisms. Azospirilla can assist in mitigation of many kinds of abiotic stress. Although they can affect antioxidant enzyme activity in abiotically stressed plants, the underlying mechanisms are not fully understood. The surface lectins of A. brasilense strains Sp7 and Sp245 differ in carbohydrate specificity and in the mode of plant root colonization. They promote plant growth and enzyme activity, and they also can alter the plant cell content of stress metabolites, which attests that they can induce adaptation processes in wheat seedling roots. Here we comparatively investigated the ability of the Sp7 and Sp245 lectins (concentration, 5–40 µg ml−1) to regulate the activities of antioxidant enzymes in roots of 4-day-old seedlings of wheat subjected to hypothermic (5 °C) and hyperthermic (42 °C) stress. Both lectins increased peroxidase and superoxide dismutase activities and decreased catalase activity, but the effects lasted for different times and the concentrations involved were also different. We conclude that the Azospirillum lectins are involved in adaptational changes in wheat seedling roots and that this involvement promotes the normal course of metabolism and ensures regulation of the plant–Azospirillum interaction in a wider range of soil and climatic factors.