Application of Halotolerant Bacteria to Restore Plant Growth Under Salt Stress

Abstract

High salinity abolishes several stages of plant life ranging from the seed germination step to maturity. Many processes are inhibited, such as phytohormone synthesis and regulation, normal root and shoot development, nutrient uptake, photosynthesis, and DNA replication. Plant growth promoting bacteria (PGPB) are naturally colonizing plants and occur in the rhizosphere or non rhizosphere soil and benefit plant growth by numerous processes. The importance of halotolerant PGPB resides in their ability to adapt to increased salinity by efficient osmoregulatory mechanism to be able to continue regular cell functions. Thus, halotolerant PGPB are able to provide plants with their activities to challenge osmotic stress by supporting them in the restoration of essential activities, e.g., in their hormonal balance. Halotolerant PGPB stimulate plant growth under high salinity by using similar mechanisms like halosensitive PGPB, such as synthesis of indole acetic acid (IAA), gibberellins (GA), cytokinins (CK), abscisic acid (ABA), solubilization of insoluble phosphate, synthesis and excretion of siderophores, and production of ACC-deaminase to reduce high growth inhibitory levels of ethylene occurring in plants at salt stress conditions. Furthermore, some halotolerant PGPB are even able to colonize plants endophytically, produce various antimicrobial metabolites against pathogenic fungi and bacteria, support plant health by improving systemic resistance and contribute to soil fertility and remediation.