The Halotolerant Rhizobacterium-Pseudomonas koreensis MU2 Enhances Inorganic Silicon and Phosphorus Use Efficiency and Augments Salt Stress Tolerance in Soybean (Glycine max L.).

Arjun Adhikari,Ko-Eun Lee,Sanjeev Dhungana,Muhammad Khan,In-Jung Lee,Sang-Mo Kang,Narayan Bhusal

doi:10.3390/microorganisms8091256

Arjun Adhikari, Ko-Eun Lee + Show 5 more

Open Access

https://doi.org/10.3390/microorganisms8091256

Copy DOI

Abstract

Optimizing nutrient usage in plants is vital for a sustainable yield under biotic and abiotic stresses. Since silicon and phosphorus are considered key elements for plant growth, this study assessed the efficient supplementation strategy of silicon and phosphorus in soybean plants under salt stress through inoculation using the rhizospheric strain—Pseudomonas koreensis MU2. The screening analysis of MU2 showed its high salt-tolerant potential, which solubilizes both silicate and phosphate. The isolate, MU2 produced gibberellic acid (GA1, GA3) and organic acids (malic acid, citric acid, acetic acid, and tartaric acid) in pure culture under both normal and salt-stressed conditions. The combined application of MU2, silicon, and phosphorus significantly improved silicon and phosphorus uptake, reduced Na+ ion influx by 70%, and enhanced K+ uptake by 46% in the shoots of soybean plants grown under salt-stress conditions. MU2 inoculation upregulated the salt-resistant genes GmST1, GmSALT3, and GmAKT2, which significantly reduced the endogenous hormones abscisic acid and jasmonic acid while, it enhanced the salicylic acid content of soybean. In addition, MU2 inoculation strengthened the host’s antioxidant system through the reduction of lipid peroxidation and proline while, it enhanced the reduced glutathione content. Moreover, MU2 inoculation promoted root and shoot length, plant biomass, and the chlorophyll content of soybean plants. These findings suggest that MU2 could be a potential biofertilizer catalyst for the amplification of the use efficiency of silicon and phosphorus fertilizers to mitigate salt stress.

Highlights

Exposures to salt stress are a major threat to sustainable agricultural production and food security [1]
Quantification of Organic and Gibberellic Acids. Organic acids such as malic, citric and acetic acid were significantly increased under salt-stress conditions; compared with the control, no significant difference was observed in tartaric acid
The current results suggest that the sole application of MU2, Si, and P improved plant growth, the combined application of MU2, Si, and P greatly promoted the morphological characteristics under stress conditions (Table 4)

Summary

Introduction

Exposures to salt stress are a major threat to sustainable agricultural production and food security [1]. Salt stress has adverse effects on plant metabolism, which include osmotic stress, ionic imbalance, oxidative damage, reduced water acquisition, damage of cellular structures, and declination in gas exchange rates, which leads to plant death [3,4]. Plants avoid the influx of Na+ and Cl−, which causes ionic toxicity and accumulation of K+ [5] This adverse effect on the ions-utilizing system alters the biochemical and metabolic processes of plants when the intake of Na+ exceeds its efflux through the plasma membrane channels [6]. The ionic system in plants has been reported to be extensively linked to the ideal concentration of phosphorus and silicon [7] Bargaz et al [8] reported that phosphorus (P) supplies induced salt tolerance in Phaseolus vulgaris through acquisition of K+ and Ca++. Proper utilization of Si and P can improve plant metabolism and growth under diverse environmental conditions

Methods

Results

Discussion

Conclusion