Effect of Bacillus subtilis on Some Physiological and Biochemical Processes in Barley (Hordeum vulgare L.) Plant Grown under Salt Stress

THE GOAL of this study was to explore the effect of salinity on some growth parameters, changes in some physiological and biochemical reactions, particularly those associated with nitrogen metabolism, in barley plant (Hordeum vulgare L.). Also, to determine the effect of plant growth-promoting bacteria (PGPB), Bacillus subtilis, to alleviate the inhibitory effect of salt on plant growth and development. Addition of 100mM NaCl to hydroponic growth cultures significantly suppressed the growth of barley plants. This was accompanied with a significant increase of osmoregulatory components including sucrose, trehalose and proline. There was a significant accumulation of ethylene in salt stressed barley plants. Moreover, salinity stress resulted in a significant decline of nitrate content and nitrate assimilating enzymes activity; nitrate reductase (NR) and glutamine synthetase (GS) while ammonia content was significantly increased in the roots. Inoculation of plants with Bacillus subtilis mainly improved the growth of salt stressed barley plants via protecting the cellular membranes integrity and increasing NR and GS activities as well as supplying a growth hormone indole-3-acetic acid/indole acetic acid (IAA) to the cultures and reducing the generation of ethylene under salt stress through the secretion of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which might increase nutrient uptake and growth. Hence, B. subtilis could promote the growth of barley plants under salinity through secretion of extra amount of IAA.