ABSTRACT
This chapter provides an overview of the literature on biological effects of rhizobacteria on plant stress tolerance and the underlying mechanisms involved in rhizobacteria–plant symbiosis and growth regulation. A direct mechanism by which plant growth–promoting rhizobacteria can facilitate plant growth and tolerance to abiotic stress is through the increased acquisition of nutrients such as nitrogen, phosphorus, potassium, and iron. Bacteria produce diverse polysaccharides that coat their cell walls and are excreted into the environment. These substances are referred to as exopolysaccharides and play a valuable role in improving both bacterial and plant tolerance to various abiotic stresses, including drought and salinity, by effectively coating bacterial cells and plant tissues that are sensitive to desiccation in a polysaccharide film. Phytohormones, such as auxin, cytokinin, gibberellic acid, abscisic acid, and ethylene, can have various impacts on plant growth and stress tolerance. The crosstalk between hormones is known to play key roles in plant stress tolerance.
