Two endophytic Bacillus strains from soybean nodules affect superoxide dismutase and peroxidase activities in soybean seedlings under salt stress

Abstract:

[Background] Salt stress affects the growth of soybean seedlings, while endophytic bacteria can improve the resistance of soybean seedlings to salt stress. [Objective] This study aims to investigate the effects of endophytic Bacillus subtilis 127 and B. proteolyticus 133 on the activities of superoxide dismutase (SOD) and peroxidase (POD) in soybean seedlings under salt stress. [Methods] Pot experiments were carried out with the soybean variety ‘Xudou 20’ in three groups: control group, salt stress group, and salt stress group with strain inoculation. Under artificial climatic conditions, the soybean seedlings were respectively treated with different concentrations (50, 100, 150, 200, 250 and 300 mmol/L) of NaCl solutions and inoculated with the bacterial suspensions at OD0.33, OD0.50 and OD0.75 (OD₆₀₀ value). [Results] After 14 days, the SOD activity was 1.04 U/g-FW in the soybean seedlings treated with 300 mmol/L or 100 mmol/L NaCl solution and inoculated with B. subtilis 127 suspension at OD0.33 or OD0.75; the POD activity was the highest (7 820 U/(g·min)) in the soybean seedlings treated with 300 mmol/L NaCl solution and inoculated with B. proteolyticus 133 suspension at OD0.50. After 28 days, the SOD activity was the highest (0.88 U/g-FW) in the soybean seedlings treated with 150 mmol/L NaCl solution and inoculated with B. subtilis 127 suspension at OD0.50; the POD activity was the highest (8 300 U/(g·min)) in the soybean seedlings treated with 100 mmol/L NaCl solution and inoculated with B. proteolyticus 133 suspension at OD0.50. [Conclusion] The optimum salt concentrations for endophytes B. subtilis 127 and B. proteolyticus 133 are different, and inoculation of endophytes can increase the SOD and POD activities in soybean seedlings exposed to salt stress. Both B. subtilis 127 and B. proteolyticus 133 can improve the salt tolerance of soybean seedlings.