Antioxidant characteristics of symbiotic association of soybean and different Bradyrhizobium japonicum strains

The ability of legume plants to fix atmospheric nitrogen in symbiotic association with nodule bacteria, have great environmental and agricultural significance. Bradyrhizobium japonicum is the most common soybean microsymbiont. In order to overcome the negative effects of drought, more tolerant crops genotypes are created and agricultural practices are improved. Selection of effective strains of rhizobia more tolerant to water deficit is certainly a measure that can increase nitrogen fixation and improve soybean production under drought conditions. This study was focused on the impact of drought on antioxidant characteristics of symbiotic communities of soybean and different Bradyrhizobium japonicum strains from the collection of Institute of Field and Vegetable Crops. Drought stress conditions increased the activity of the soluble and ionically cell wall-bound peroxidases in plant roots and nodules. The antioxidant activities in the roots and nodules as well as the content of soluble proteins were significantly increased under conditions of water deficit. Increased protein content in stress conditions can be explained by the synthesis of proteins involved in antioxidant response and accumulation of plant proteins involved in adaptation to drought, as confirmed by a significant correlation between protein content and the activities of peroxidase in roots and nodules. The applied strain significantly affected the activity of soluble and cell wall-bound peroxidase, antioxidant activity and the content of soluble proteins. The applied strain had a greater impact on the studied parameters in plants that were exposed to water deficit compared to plants that were provided optimum water. Significant correlations between antioxidant activity and the activity of soluble and bound peroxidases in nodules and roots indicated a linked antioxidant response of plant and bacteria under stress