The Mechanisms of Sodium Chloride Stress Mitigation by Salt-Tolerant Plant Growth Promoting Rhizobacteria in Wheat

Zhen Huang,Yaxin Lu,Ying-Feng Lin,Jinhua Qiao,Qing Feng,Yuan Chang,Rey-May Liou,Chen Wang

doi:10.3390/agronomy12030543

Abstract

We investigated the growth-promoting mechanism of salt-tolerant plant growth promoting rhizobacteria (ST-PGPR) in wheat under sodium chloride (NaCl) stress by measuring the growth and physiological and biochemical responses of wheat plants inoculated with ST-PGPR under 0–400 mM NaCl. The results showed that ST-PGPR plays a significant role in the growth of wheat under NaCl stress. Under 300 mM NaCl, wheat plants inoculated with the three ST-PGPR strains increased in plant height, root length, dry weight, and fresh weight by 71.21%, 89.19%, 140.94%, and 36.31%, respectively, compared to the control group. The proline and soluble sugar contents of wheat inoculated with Bacillus thuringiensis increased by 38.8% and 21.4%, respectively. The average content of antioxidant enzymes increased by 13.89%, and compared with the control, in wheat inoculated with the three species of ST-PGPR, the average content of ethylene decreased 2.16-fold. In addition, a mathematical model based on the “interaction equation” revealed that the best results of mixed inoculation were due to the complementary strengths of the strains. The analysis of experimental phenomena and data revealed the mechanisms by which Brevibacterium frigoritolerans, Bacillus thuringiensis, and Bacillus velezensis alleviate NaCl stress in wheat: (1) by lowering of osmotic stress, oxidative stress, and ethylene stress in wheat and (2) by using root secretions to provide substances needed for wheat. This study provides a new approach for the comprehensive understanding and evaluation of ST-PGPR as a biological inoculant for crops under salt stress.

Highlights

Soil salinization is a worldwide ecological problem that severely limits the growth and yield of crops [1]
The roots obtained through show thatthat there werewere obvious ferences in wheatroots rootsbefore before inoculation with salt‐tolerant plant growth promoting rhizobacteria (ST‐PGPR), which indicate differences in the the wheat andand afterafter inoculation with salt-tolerant plant growth promoting rhizobacteria (ST-PGPR), which indicated that might have some connection with the roots of wheat
Studies b that ST-PGPR might have some connection with the roots of wheat (Figure 1)

Summary

Introduction

Soil salinization is a worldwide ecological problem that severely limits the growth and yield of crops [1]. It is estimated that 954 million hectares of land worldwide are threatened by salt stress [2,3]. 11.3% of China’s agricultural land is affected by salinization to varying degrees [4]. Wheat, as the most important agricultural crop that provides approximately one-third of China’s food source, is already severely affected by soil salinity [5]. NaCl stress is considered to be one of the main factors limiting wheat growth [6]. High salt (NaCl) concentrations disrupt the normal Na+ /K+ ratio, resulting in impaired osmotic phenomena in plants [7,8]. The presence of Na+ and Cl− can cause ion toxicity and nutrient deficiency, which affects the normal physiological activities of cells [9,10]

Methods

Results

Conclusion