Palliating Salt Stress in Mustard through Plant-Growth-Promoting Rhizobacteria: Regulation of Secondary Metabolites, Osmolytes, Antioxidative Enzymes and Stress Ethylene

Abstract

The severity of salt stress is alarming for crop growth and production and it threatens food security. Strategies employed for the reduction in stress are not always eco-friendly or sustainable. Plant-growth-promoting rhizobacteria (PGPR) could provide an alternative sustainable stress reduction strategy owning to its role in various metabolic processes. In this study, we have used two strains of PGPR, Pseudomonas fluorescens (NAIMCC-B-00340) and Azotobacter chroococcum Beijerinck 1901 (MCC 2351), either singly or in combination, and studied their effect in the amelioration of salt toxicity in mustard cultivar Pusa Jagannath via its influence on plants’ antioxidants’ metabolism, photosynthesis and growth. Individually, the impact of Pseudomonas fluorescens was better in reducing stress ethylene, oxidative stress, photosynthesis and growth but maximal alleviation was observed with their combined application. MDA and H2O2 content as indicator of oxidative stress decreased by 27.86% and 45.18% and osmolytes content (proline and glycine-betaine) increased by 38.8% and 26.3%, respectively, while antioxidative enzymes (SOD, CAT, APX and GR) increased by 58.40, 25.65, 81.081 and 55.914%, respectively, over salt-treated plants through the application of Pseudomonas fluorescens. The combined application maximally resulted in more cell viability and less damage to the leaf with lesser superoxide generation due to higher antioxidative enzymes and reduced glutathione formation (GSH). Considering the obtained results, we can supplement the PGPR in combination to plants subjected to salt stress, prevent photosynthetic and growth reduction, and increase the yield of plants.

Evaluation of the growth-inducing efficacy of various Bacillus species on the salt-stressed tomato (Lycopersicon esculentum Mill.)

“…Our results corroborate those of Gururani et al (2013), who discovered that PGPR-treated potato plants exposed to various stressors had increased activity of ROS-scavenging enzymes like APX, CAT, DHAR, GR, and SOD (salt, drought, and heavy metals). Khan et al (2023) also found that antioxidative enzymes (SOD, CAT, APX and GR) increased by 58.40, 25.65, 81.081 and 55.914%, respectively, over salt-treated plants through the application of Pseudomonas fluorescens. Additionally, salt-stressed okra plants treated with the PGPR Enterobacter sp.…”

Synergistic action of Pseudomonas fluorescens with melatonin attenuates salt toxicity in mustard by regulating antioxidant system and flavonoid profile

“…In our investigation, P. fluorescens inoculation to mustard plants improved growth characteristics, such as RL, SL, plant height, DW, FW, leaf area, and leaf number, as also demonstrated in Pisum sativum by Sofy et al (2021). Overall, the enhancement of growth parameters in mustard plants in the presence of PGPR can be attributed to their plant growth promotion traits, such as IAA production, ACC deaminase activity, siderophore production, and solubilization of mineral nutrients (Khan et al, 2023). To boost plant growth under stressful conditions, PGPR secretes IAA, which results in an increase in root surface area and eventually improves nutrient absorption by the plant (Yasmin et al, 2017).…”

“…P. fluorescens strain (NAIMCC‐B‐00340) was obtained from the National Bureau of Agriculturally Important Microorganisms (NBAIM), Mau, India. This strain has previously been characterized for salinity tolerance (Khan et al, 2023).…”

“…P. fluorescens N21.4 was found to increase the expression of some flavonoid biosynthetic genes and their concentration in blackberries (Garcia-Seco et al, 2015). It was found to increase the total flavonoid content (TFC) in B. juncea under salt stress (Khan et al, 2023).…”

“…P. fluorescens N21.4 was found to increase the expression of some flavonoid biosynthetic genes and their concentration in blackberries (Garcia‐Seco et al, 2015). It was found to increase the total flavonoid content (TFC) in B. juncea under salt stress (Khan et al, 2023). Similarly, among the various growth regulators, melatonin (MT) has recently gained substantial attention, because of its pleiotropic nature and direct function as an antioxidant.…”