Plant growth promoting bacteria (PGPR) induce antioxidant tolerance against salinity stress through biochemical and physiological mechanisms

Salinity is one of the most severe abiotic stress in the world. Also, the irrigated lands have been treated with second salinity. Canola is one of the most important industrial crops for oil production all over the world which is affected by salinity. Salt stress causes imbalanced ion hemostasis (Na+ and K+) and interrupted mineral absorption in canola. Also, salinity stress leads to oxidative stress (production and accumulation of reactive oxygen species (ROS). Accumulation of ROS is extremely dangerous and lethal for plants. As a consequence, canola production is reduced under salinity stress. So, a suitable approach should be found to deal with salinity stress and prevent the loss of production oilseed. Plant growth-promoting rhizobacteria (PGPR) can colonize on the plant root surface and alleviate the salt stress effect by providing minerals like nitrogen, phosphate, and potassium. Also, they alleviate salt stress by phytohormones like auxin (IAA), cytokinin (CK), and abscisic acid (ABA). This study focus on physiological parameters like leaf area (LA), root length (RL), shoot length (SL), chlorophyll fluorescence indexes (Fv/Fm and Fv/F0), relative water content (RWC), electrolyte leakage index (ELI), photosynthesis pigments (chlorophyll a, b, and carotenoids), Na+, and K+; and biochemical parameters like malondialdehyde (MDA) content, hydrogen peroxide content (H2O2), total protein content, proline, antioxidant capacity, and antioxidant enzyme activities in canola through the inoculation with Enterobacter sp. S16-3 and Pseudomonas sp. C16-2O. This study showed that LA, RL, SL, chlorophyll fluorescence indexes, RWC were significantly increased and ELI was significantly decreased in bacteria inoculated treatments. Also, MDA, H2O2 were decreased, and antioxidant capacity, proline, and antioxidant enzymes were increased due to inoculation with these bacteria. Besides, the amount of K+ as an index of salinity tolerance significantly increased, and leaf Na+ content was significantly decreased.