Effects of Phytohormone-Producing Rhizobacteria on Casparian Band Formation, Ion Homeostasis and Salt Tolerance of Durum Wheat

Elena Martynenko,Vera Safronova,Ilshat Galin,Tatiana Arkhipova,Zarina Akhtyamova,Dmitry Veselov,Guzel Kudoyarova,Oksana Seldimirova,Ruslan Ivanov

doi:10.3390/biom12020230

Abstract

Inoculation with plant growth-promoting rhizobacteria can increase plant salt resistance. We aimed to reveal bacterial effects on the formation of apoplastic barriers and hormone concentration in relation to maintaining ion homeostasis and growth of salt-stressed plants. The rhizosphere of a durum wheat variety was inoculated with cytokinin-producing Bacillus subtilis and auxin-producing Pseudomonas mandelii strains. Plant growth, deposition of lignin and suberin and concentrations of sodium, potassium, phosphorus and hormones were studied in the plants exposed to salinity. Accumulation of sodium inhibited plant growth accompanied by a decline in potassium in roots and phosphorus in shoots of the salt-stressed plants. Inoculation with both bacterial strains resulted in faster appearance of Casparian bands in root endodermis and an increased growth of salt-stressed plants. B. subtilis prevented the decline in both potassium and phosphorus concentrations and increased concentration of cytokinins in salt-stressed plants. P. mandelii decreased the level of sodium accumulation and increased the concentration of auxin. Growth promotion was greater in plants inoculated with B. subtilis. Increased ion homeostasis may be related to the capacity of bacteria to accelerate the formation of Casparian bands preventing uncontrolled diffusion of solutes through the apoplast. We discuss the relative impacts of the decline in Na accumulation and maintenance of K and P content for growth improvement of salt-stressed plants and their possible relation to the changes in hormone concentration in plants.

Highlights

Excessive salt concentrations in a soil solution negatively affect plant growth and productivity
Our results indicate that maintaining concentrations of potassium and phosphorus, detected in salt-stressed plants inoculated with B. subtilis IB-22, may be more important for promotion of plant growth under salinity than a decline in the accumulation of sodium per se
A recent review showed that Casparian bands play a key role in salt tolerance [20]

Summary

Introduction

Excessive salt concentrations in a soil solution negatively affect plant growth and productivity. These effects arise as a result of water scarcity due to a decrease in the availability of water from saline soil solution and accumulation of sodium ions, being toxic for plants at high concentrations. The areas of saline arable land are growing steadily all over the world, due to increasing climate aridity and expansion of irrigated agriculture [1,2,3]. This determines the search for approaches to increase salt tolerance of plants, i.e., the ability to maintain productivity under salt stress. To select more promising strains and optimize biotechnology of their use as regulators of plant salt tolerance, it is important to clearly

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