effect of water stress on nitrogen fixation of sinorhizobium and compatible solutes accumulation in alfalfa (medicago sativa cv. bami)

abstract osmoreguolation is a physiological processes that plant cell uses to maintain water balance and it is generally caused by metabolite accumulation inside the cell. inoculated legumes by some drought tolerant sinorhizobium isolates helps osmoreguolation by increasing biological nitrogen fixation. in order to find some drought tolerant sinorhizobium isolates, 80 isolates were isolated and purified from different parts of kerman province. they were tested for drought tolerant in liquid trypton yeast medium with different water potential (0, -1, -2 and -3.5 mpa using peg 6000) and then they were classified into tolerant and sensitive groups. four out of eighty isolates of sinorhizobium (two from each group) were selected for a greenhouse experiment. the experiment was carried out in a factorial arrangement with a completely randomized design. the results showed that in water stress condition, inoculated plant substantially increased the nitrogenase activity, shoot dry weight, proline content, root soluble sugars, soluble protein concentration, k/na in shoot and root by 2, 3, 2.7, 1.7, 1.1, 3 and 2 times, respectively.