Plant growth-promoting bacteria in regulation of plant resistance to stress factors

The review considers the mechanisms underlying the ability of plant growth-promoting bacteria (PGPB) to enhance plant tolerance to biotic and abiotic stresses. The improved tolerance is determined by a number of microbiological factors such as: supply of mineral nutrients; production of hormones and signaling metabolites; syntheses of antibiotics, biosurfactants, siderophores, chitinases, glucanases, proteases and lipases and other defence proteins; and induction of plant systemic resistance to pathogens and herbivores. Possible mechanisms of interactions in the plant-PGPB-pathogen (pest) system are considered. The PGPB may exert their role either directly, through elimination of harmful organisms by antimicrobial substances and hydrolytic enzymes, or indirectly, through activation of host defense systems and the induction of systemic resistance. New approaches to the design of broad-spectrum biopesticides on the basis of PGPB are considered.