The Role of Plant Growth-Promoting Rhizobacteria to Modulate Proline Biosynthesis in Plants for Salt Stress Alleviation

Abstract

Soil salinization causes serious problem to environmental resources and human health in many countries. Around 1.5 billion hectares of cultivated lands are present in the world. It is estimated that almost 5% of the cultivated land (77 million) and 6% of total surface land is affected by salinity. Agricultural crops and their productivity are severely affected by salt stress. Many physiological mechanisms within the plants are regulated when exposed to salt stress. The salinity tolerance measurement has a great demand to asses the regulatory variations, growth, and survival parameters. Microorganisms that colonize the roots could play a significant role in this aspect. Rhizobacteria which possess properties such as salt tolerance, nutrient uptake ability, synthesis of compatible solutes, production of plant growth-promoting hormones, biocontrol potential, and their interaction with crop plants is known as plant growth-promoting rhizobacteria (PGPRs). Proline is one of the essential compatible solute for both plant and bacteria to respond against osmotic imbalance and ionic toxicity. Proline biosynthesis occurs in cytosol and mitochondria of a cell and modulates their functions in various cellular physiological pathways. It can also influence the proliferation and apoptosis of cell and regulate specific gene expression to alleviate salt stress. Rhizobacteria having plant growth promoting characteristics can be used as a suitable bio-inoculant to promote growth and productivity through different mechanisms in addition to the accumulation of proline as osmoregulators.