Regulation of Plant Physiology and Antioxidant Enzymes for Alleviating Salinity Stress by Potassium-Mobilizing Bacteria

Abstract

Potassium (K) is among the most important essential macronutrients for plant growth. About 98 % of the potassium in the earth’s crust exists in insoluble forms as rocks and silicate minerals, resulting in very low concentrations of soluble potassium in the soil for plant growth and development. Rhizosphere bacteria are a group of metal-mobilizing, plant growth–promoting bacteria having the ability to solubilize potassium from insoluble potassium rocks. KSM (a potassium-solubilizing microorganism) is a metal-mobilizing, plant growth–promoting bacterium living symbiotically in/on the root surface and helps directly or indirectly in promoting plant growth via solubilization of insoluble minerals (K and P), assisting in resource acquisition (macro- and micronutrients), production of phytohormones and secretion of different regulatory chemicals in the purlieu of the rhizosphere of the plant root. KSM such as Bacillus spp. and Pseudomonas spp. are the most dominant plant growth–promoting bacteria (PGPB) of rhizospheric soils. Inoculation of KSM is found to be promising to induce growth of plants under 2.3–3.5 dSm−1 salinity levels and low availability of P and K, protecting the plants from salinity injury by enhancing their growth-related physiology and lipid peroxidation. These KSM help in the decrement of lipid peroxidation and enhance the stability of the plant cell membrane for the survival of the plant under salt stress. Inoculation of plants with such beneficial root-associated bacteria could provide salt tolerance to plants as these isolates also reside within the root, which is the plant part first directly in contact with saline soil. Hence it serves as a useful tool for alleviating salinity stress as well as in uptake of important mineral nutrients. The diversity of potassium-solubilizing microbes (KSM) and ability to mobilize important macronutrients from insoluble to soluble forms through biological conversion make them a good choice for agricultural use. Application of such efficient KSM aims to develop future prospects to provide a sustainable environmental system in different crop fields under both normal and stress conditions.