Insights into the Bacterial and Nitric Oxide-Induced Salt Tolerance in Sugarcane and Their Growth-Promoting Abilities.

Anjney Sharma,Krishan K Verma,Naeem Khan,Yang-Rui Li,Pratiksha Singh,Mukesh Kumar Malviya,Anukool Vaishnav,Xiu-Peng Song,Prakash Lakshmanan,Rajesh Kumar Singh,Dong-Ping Li,Dao-Jun Guo

doi:10.3390/microorganisms9112203

Abstract

Soil salinity causes severe environmental stress that affects agriculture production and food security throughout the world. Salt-tolerant plant-growth-promoting rhizobacteria (PGPR) and nitric oxide (NO), a distinctive signaling molecule, can synergistically assist in the alleviation of abiotic stresses and plant growth promotion, but the mechanism by which this happens is still not well known. In the present study, in a potential salt-tolerant rhizobacteria strain, ASN-1, growth up to 15% NaCl concentration was achieved with sugarcane rhizosphere soil. Based on 16S-rRNA gene sequencing analysis, the strain ASN-1 was identified as a Bacillus xiamenensis. Strain ASN-1 exhibits multiple plant-growth-promoting attributes, such as the production of indole-3-acetic acid, 1-aminocyclopropane-1-carboxylate deaminase, siderophores, HCN, ammonia, and exopolysaccharides as well as solubilized phosphate solubilization. Biofilm formation showed that NO enhanced the biofilm and root colonization capacity of the PGPR strain ASN-1 with host plants, evidenced by scanning electron microscopy. The greenhouse study showed that, among the different treatments, the combined application of PGPR and sodium nitroprusside (SNP) as an NO donor significantly (p ≤ 0.05) enhanced sugarcane plant growth by maintaining the relative water content, electrolyte leakage, gas exchange parameters, osmolytes, and Na+/K+ ratio. Furthermore, PGPR and SNP fertilization reduced the salinity-induced oxidative stress in plants by modulating the antioxidant enzyme activities and stress-related gene expression. Thus, it is believed that the acquisition of advanced information about the synergistic effect of salt-tolerant PGPR and NO fertilization will reduce the use of harmful chemicals and aid in eco-friendly sustainable agricultural production under salt stress conditions.

Highlights

Abiotic stresses are the most common environmental constraints to agricultural production and food security around the world
The results showed that a significant improvement in Relative Water Content (RWC), by 91.8%, was observed in sugarcane plants treated with the plant-growth-promoting rhizobacteria (PGPR) and sodium nitroprusside (SNP), alone or in combination, had significant positive effects on RWC under normal non-stressed and salt-stressed conditions
The results showed that, under normal non-stressed conditions, the application of PGPR and SNP remarkably regulated the expression of these stress-tolerant genes in sugarcane plants

Summary

Introduction

Abiotic stresses are the most common environmental constraints to agricultural production and food security around the world. It is estimated that environmental abiotic stresses such as salt, drought, high/low temperature, heavy metals, and chemical pesticides affect 90% of all arable land [1]. Among these abiotic stresses, soil salinity, caused mainly by groundwater irrigation, is one of the most serious abiotic stresses for plant growth and agricultural production [2]. As a result of soil salinity and sodicity, about 70% of plant growth and production loss have been documented in various crops [6]. The major cations, such as Na+ (sodium), Ca2+ (calcium), and Mg2+ (magnesium), and anions, such as

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