Serratia liquefaciens KM4 Improves Salt Stress Tolerance in Maize by Regulating Redox Potential, Ion Homeostasis, Leaf Gas Exchange and Stress-Related Gene Expression.

Mohamed El-Esawi,Saud Alzahrani,Ibrahim Alaraidh,Margaret Ahmad,Abdulaziz Alsahli,Aisha Alayafi,Hayssam Ali

doi:10.3390/ijms19113310

Abstract

High salinity mitigates crop productivity and quality. Plant growth-promoting soil rhizobacteria (PGPR) improve plant growth and abiotic stress tolerance via mediating various physiological and molecular mechanisms. This study investigated the effects of the PGPR strain Serratia liquefaciens KM4 on the growth and physiological and molecular responsiveness of maize (Zea mays L.) plants under salinity stress (0, 80, and 160 mM NaCl). High salinity significantly reduced plant growth and biomass production, nutrient uptake, leaf relative water content, pigment content, leaf gas exchange attributes, and total flavonoid and phenolic contents in maize. However, osmolyte content (e.g., soluble proteins, proline, and free amino acids), oxidative stress markers, and enzymatic and non-enzymatic antioxidants levels were increased in maize under high salinity. On the other hand, Serratia liquefaciens KM4 inoculation significantly reduced oxidative stress markers, but increased the maize growth and biomass production along with better leaf gas exchange, osmoregulation, antioxidant defense systems, and nutrient uptake under salt stress. Moreover, it was found that all these improvements were accompanied with the upregulation of stress-related genes (APX, CAT, SOD, RBCS, RBCL, H+-PPase, HKT1, and NHX1), and downregulation of the key gene in ABA biosynthesis (NCED). Taken together, the results demonstrate the beneficial role of Serratia liquefaciens KM4 in improving plant growth and salt stress tolerance in maize by regulating ion homeostasis, redox potential, leaf gas exchange, and stress-related genes expression.

Highlights

Soil salinity stress affects crops growth and performance, and represents a main threat to the sustainable agricultural development worldwide [1,2,3]
Maximum decrease in maize growth and biomass was recorded at the high salt concentration (160 mM NaCl) as compared with control plants
Zhang et al [43] indicated that B. subtilis GB03 inoculation enhanced salinity stress tolerance in Arabidopsis thaliana by inducing HKT1 gene expression in shoots

Summary

Introduction

Soil salinity stress affects crops growth and performance, and represents a main threat to the sustainable agricultural development worldwide [1,2,3]. It severely affects the physiological processes in plants, including lipid metabolism, protein synthesis, ion homeostasis, photosynthesis, and nitrogen fixation [3,4]. It minimizes water uptake by roots and causes over-production of toxic ions [5], resulting in the generation of toxic free radicals that cause oxidative damage [6]. To mitigate the oxidative damage and negative impacts of salt stress, crops have developed various self-defense mechanisms such as compartmentalization of ions, production of compatible osmolytes, regulation of photosynthetic pathways, induction of phytohormones, and upregulation of antioxidants such as catalase (CAT), ascorbic acid (AsA), glutathione reductase (GR), proline, peroxidase (POD), and superoxide dismutase (SOD) [6,11,12,13,14]

Methods

Results

Conclusion