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 benefi t plant growth by numerous processes. The importance of halotolerant PGPB resides in their ability to adapt to increased salinity by effi cient 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 ACCdeaminase 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 .

Halotolerant Rhizobacteria Promote Growth and Enhance Salinity Tolerance in Peanut

“…Use of halophilic or salt tolerant PGPR is an effective approach that has been employed successfully in various crops to improve their growth and tolerance under salt stress condition. The halotolerant bacteria are able to withstand high salt concentration because of their capability to accumulate compatible osmolyte to maintain intracellular osmotic balance (Nabti et al, 2015 ). These bacteria are positive for multiple stress-related traits that may facilitate plants to survive under growth inhibitory levels of salt (Rohban et al, 2009 ; Siddikee et al, 2010 ; Bharti et al, 2013 ).…”

Mining Halophytes for Plant Growth-Promoting Halotolerant Bacteria to Enhance the Salinity Tolerance of Non-halophytic Crops

“…Like halophytic plants, salt-tolerant rhizobacteria have evolved various strategies to live in high saline environments. An important strategy is the ability to accumulate compatible osmolytes to maintain intracellular osmotic balance (Nabti et al, 2015 ; Sharma et al, 2016 ). These bacteria exhibit multiple stress-related traits that may contribute to their plant protective capabilities under growth inhibiting levels of salt (Rohban et al, 2009 ; Siddikee et al, 2010 ; Bharti et al, 2013 ; Sharma et al, 2016 ).…”

Bacillus subtilis HG-15, a Halotolerant Rhizoplane Bacterium, Promotes Growth and Salinity Tolerance in Wheat (Triticum aestivum)

“…In addition, inoculation with ABA-producing PGPB often decreases the accumulation and concentration of ABA in roots and significantly alters the long distance signaling of shoot-to-root ABA transport in the phloem and the root-to-shoot ABA transport in the xylem [7,37]; the resulting changes in ABA levels may mitigate the plant's sensitivity to water scarcity. PGPB promote the ability of plants to accumulate compatible solutes to maintain intracellular osmotic balance [10]. Inoculation with the HG-15 strain resulted in an increase in certain osmolytes, such as TSS, total protein content, and a decrease in MDA content.…”