ACC-Deaminase producing Pseudomonas putida RT12 inoculation: A promising strategy for improving Brassica juncea tolerance to salinity stress

Abstract

An important abiotic stressor that hinders plant growth, nutrient uptake, and global agricultural productivity is soil salinity. Among the different strategies to overcome the issue of salinity in agriculture sector, plant growth-promoting rhizobacteria (PGPR) have gained recognition as promising beneficial microbes that can improve plants’ response to biotic and abiotic stressors. The salinity tolerance and traits that promote plant growth of eight PGPR strains (RT1, RT2, RT3, RT4, RT5, RT7, and RT12) were evaluated in this study. During screening, one strain, RT12, had the highest plant growth-promoting activity and salt tolerance in the group. The strain when subjected to NaCl stress showed quantitative ACC-deaminase activity, in the presence of NaCl at various concentrations, demonstrating extraordinary tolerance to salt stress by withstanding doses of up to 3M NaCl. In order to further investigate the effects of salt stress on Brassica juncea (mustard), RT12, which was identified as Pseudomonas putida using 16s RNA sequencing, was inoculated. Two salt treatments (100 and 150 mM) were applied to the mustard variety ‘Mingora’ in a greenhouse. The results revealed that through ACC utilization, PGPR directly induced plant growth in salt-stressed mustard plants by lowering excess ethylene production. All plant parameters were negatively impacted by an increase in NaCl concentration in uninoculated plants. However, P. putida RT12 inoculation enhanced all growth parameters, antioxidant production, total soluble sugar (TSS), total protein (TP), proline, relative water content (RWC), chlorophyll contents, and nutrient uptake in salt-treated plants. The inoculation with P. putida also caused a marked decline in Na+ uptake and an increase in K+ uptake in the shoot. By maintaining a greater K+/Na+ ratio in the tissues of RT12-inoculated plants compared to controls, this change in ion uptake helped to maintain nutritional balance of the plants. The findings suggest that inoculating plants with ACC deaminase-producing PGPR, such as P. putida RT12, may boost growth and stress resistance.