Effect of exopolysaccharides of Paenibacillus polymyxa rhizobacteria on physiological and morphological variables of wheat seedlings

Paenibacillus polymyxa is a promising plant-growth-promoting rhizobacterium that associates with a wide range of host plants, including agronomically important ones. Inoculation of wheat seedlings with P. polymyxa strains CCM 1465 and 92 was found to increase the mitotic index of the root cells 1.2- and 1.6-fold, respectively. Treatment of seedlings with the exopolysaccharides (EPSs) of these strains increased the mitotic index 1.9-fold (P. polymyxa CCM 1465) and 2.8-fold (P. polymyxa 92). These increases indicate activation of cell division in the root meristems. Analysis of the morphometric variables of the seedlings showed that P. polymyxa CCM 1465, P. polymyxa 92, and their EPSs promoted wheat growth, increasing root and shoot length up to 22% and root and shoot dry weight up to 28%, as compared with the control. In addition, both strains were found to intensely colonize the seedling root surface. Thus, P. polymyxa EPSs are active metabolites that, along with whole cells, are responsible for the contact interactions of the bacteria with wheat roots and are implicated in the induction of plant responses to these interactions. The strains used in this work are of interest for further study to broaden the existing understanding of the mechanisms of plant-bacterial interactions and to develop effective biofertilizers for agricultural purposes.