The biological activity of the Sinorhizobium meliloti glucan

The study of the effect of the periplasmic glucan isolated from the root-nodule bacterium S. meliloti CXM1-188 on the symbiosis of another strain (441) of the same root-nodule bacterium with alfalfa plants showed that this effect depends on the treatment procedure. The pretreatment of alfalfa seedlings with the glucan followed by their bacterization with S. meliloti 441 insignificantly influenced the nodulation parameters of symbiosis (the number of root nodules and their nitrogen-fixing activity) but induced a statistically significant increase in the efficiency of symbiosis (expressed as the masses of the alfalfa overground parts and roots). At the same time, the pretreatment of S. meliloti 441 cells with the glucan brought about a considerable decrease in the nodulation parameters of symbiosis (the number of the root nodules and their nitrogen-fixing activity decreased by 2.5-11 and 7 times, respectively). These data suggest that the stimulating effect of rhizobia on host plants may be due not only to symbiotrophic nitrogen fixation but also to other factors. Depending on the experimental conditions, the treatment of alfalfa plants with the glucan and their bacterization with rhizobial cells enhanced the activity of peroxidase in the alfalfa roots and leaves by 10-39 and 12-27%, respectively.