Roles of Plant Growth-Promoting Rhizobacteria (PGPR) in Stimulating Salinity Stress Defense in Plants: A Review

Abstract

To date, soil salinity becomes a huge obstacle for food production worldwide since salt stress is one of the major factors limiting agricultural productivity. It is estimated that a significant loss of crops (20–50%) would be due to drought and salinity. To embark upon this harsh situation, numerous strategies such as plant breeding, plant genetic engineering, and a large variety of agricultural practices including the applications of plant growth-promoting rhizobacteria (PGPR) and seed biopriming technique have been developed to improve plant defense system against salt stress, resulting in higher crop yields to meet human’s increasing food demand in the future. In the present review, we update and discuss the advantageous roles of beneficial PGPR as green bioinoculants in mitigating the burden of high saline conditions on morphological parameters and on physio-biochemical attributes of plant crops via diverse mechanisms. In addition, the applications of PGPR as a useful tool in seed biopriming technique are also updated and discussed since this approach exhibits promising potentials in improving seed vigor, rapid seed germination, and seedling growth uniformity. Furthermore, the controversial findings regarding the fluctuation of antioxidants and osmolytes in PGPR-treated plants are also pointed out and discussed.

Microbial amelioration of salinity stress in HD 2967 wheat cultivar by up-regulating antioxidant defense

“…High α-tocopherol content in microbial inoculated plants lowers lipid peroxidation [ 26 ] as the α-tocopherol involves in scavenging lipid peroxyl radicals. PGPB enhanced salinity tolerance in plants by increasing the production of non- enzymatic antioxidants such as α-tocopherol, ascorbate, carotenoids and polyphenols [ 35 ]. P. indica colonization in maize plant decreased the level of MDA production by stimulating antioxidant enzymes [ 36 ].…”

The Contrivance of Plant Growth Promoting Microbes to Mitigate Climate Change Impact in Agriculture

“…Superoxidase dismutase (SOD, EC 1.15.1.1) is mainly involved as O 2 •− scavenger, which generates H 2 O 2 and O 2 . Therefore, H 2 O 2 can be scavenged by catalase (CAT EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11) and guaiacol peroxidase (GPX, EC 1.11.1.7) [ 65 , 87 ]. It has been reported that the increase in ABA production in plants under salinity stress induces antioxidant defense genes such as APX, SOD or CAT to remove ROS molecules [ 85 ].…”

Plant Growth-Promoting Rhizobacteria as a Green Alternative for Sustainable Agriculture

“…PGPR promote plant growth by associative nitrogen fixation, phosphate solubilization, phytohormone production, and volatile organic compounds [29][30][31][32]. PGPR also neutralize stress in plants created by biotic and abiotic factors by boosting nutrient uptake, osmolyte accumulation, enhanced production of antioxidant enzymes, and metabolites [33][34][35]. Among several abiotic stresses, salinization of soil increasing continuously and degraded lands all over the globe causes food insecurity by reducing crop productivity [36].…”