Ion Homeostasis, Osmotic Adjustment, and ROS Detoxification Underlie Pea Salinity Tolerance Induced by Pseudomonas putida RT12

In saline soil, legumes are restricted in their growth potential by osmotic stress, ion toxicity, and oxidative damage. We evaluated five halotolerant plant growth-promoting bacteria and selected Pseudomonas putida RT12 for its exceptional EPS production, tolerance to 600 mM NaCl, strong biofilm development, and plant growth-promoting traits (ACC-deaminase 2.86 µM·mg−1; IAA 144 µM·mL−1). RT12 was evaluated on two varieties of peas (peas2009 and 9800-10) with and without inoculation at 0, 75, and 150 mM NaCl concentrations. RT12 markedly protected growth under severe salinity: at 150 mM, shoot length rose to 23.13 cm (peas2009) and 17.44 cm (9800-10), in contrast to 11.18 cm and 12.32 cm in uninoculated specimens; root length and dry weight demonstrated comparable recovery (root length increased from 11.00 to 22.25 cm; dry weight of peas2009 from 0.15 to 0.17 and 0.41 to 0.71 g). RT12 sustained photosynthesis (total chlorophyll increased from 43.5 to 54.5), enhanced relative water content (to 94.1% and 97.2%), elevated osmolytes (total soluble proteins rose from 7.34 to 18.12 µg·g−1 FW; total soluble sugars increased from 19.1 to 41.3 mg·g−1 FW), and augmented antioxidant activities (catalase increased from 2.11 to 4.70; superoxide dismutase rose from 1.20 to 4.83; peroxidase increased from 0.08 to 0.18), while reducing malondialdehyde/hydrogen peroxide levels. RT12 was significant as it inhibited the accumulation of Na+ (from 23.95 to 16.32 mg·g−1 DW), elevated K+ levels (from 17.76 to 29.12 mg·g−1 DW), and restored the K+/Na+ ratio to normal (from 0.74 to 1.59) in inoculated plants compared to non-inoculated ones. A multivariate analysis linked growth protection to ionic homeostasis, osmotic control, and the detoxification of reactive oxygen species (ROS). RT12 is a promising bioinoculant for cultivating peas in saline-affected soils.