Endophytic bacterial strains 72 and 146 affect catalase activity and proline content in soybean seedlings under salt stress

Abstract:

Objective To explore the effects of endophytic bacteria in soybean nodules on the growth of soybean seedlings under salt stress and provide reference for the high-quality development of crops in the Yellow River Basin.Methods A pot experiment was conducted with the soybean cultivar ‘Xudou 20’ under artificial climate conditions. Three groups were designed: control, salt stress, and salt stress inoculated with endophytic bacteria. The growth of soybean seedlings in each group was measured.Results Regarding strain 72, in the case of inoculation with the suspension at OD₆₀₀=0.75 (2:1) and the salt concentration of 200 mmol/L, the activity of catalase (CAT) in the seedlings of 21 days was the highest (2.010 0 U/g FW), which was 54.02% higher than that in the salt stress group; in the case of inoculation with the suspension at OD₆₀₀=0.33 (1:2) and the salt concentration of 300 mmol/L, the proline content was the highest (0.028 6 mg/g); in the case of inoculation with the suspension at OD₆₀₀=0.75 (2:1) and the salt concentration of 100 mmol/L, the proline content was 64.38% higher than that in the salt stress group. Regarding strain 146, the seedlings of 21 days in the case of inoculation with the suspension at OD₆₀₀=0.50 (1:1) and the salt concentration of 50 mmol/L had the highest CAT activity (1.350 0 U/g FW); the seedlings of 28 days in the case of inoculation with the suspension at OD₆₀₀=0.75 (2:1) and the salt concentration of 100 mmol/L had the CAT activity 272.73% higher than that in the salt stress group; the seedlings in the case of inoculation with the suspension at OD₆₀₀=0.75 (2:1) and the salt concentration of 150 mmol/L had the highest proline content of 0.147 0 mg/g, which was 860.78% higher than that in the salt stress group. The results indicated that inoculation with the endophytic bacterial strain 72 or 146 had a repairing effect. The increases in the CAT activity and proline content in the soybean seedlings inoculated with strain 146 over those in the salt stress group were generally higher than those in the case of inoculation with strain 72, indicating that the repairing effect of strain 146 was more obvious. The phylogenetic tree built based on 16S rRNA gene sequences showed that strains 72 and 146 had the highest similarity with Bacillus subtilis (99.45%) and B. protolyticus (100%), respectively.Conclusion Inoculating endophytic bacteria was of great significance for alleviating the effect of saline-alkali stress in the Yellow River Basin on the growth of soybean seedlings and developing biological repairing agents.