Background: The utilization of plant growth-promoting microbes is an environment friendly strategy to counteract stressful condition and encourage plants tolerance. In this regards, the current study was designed to isolate ACC deaminase and indole-3-acetic acid (IAA) producing halotolerant bacteria to promote tomato (Solanum lycopersicum L.) growth and tolerance against salinity stress.
Results: The selected bacterial isolate MO1 was identified as Leclercia adecarboxylata and IAA quantification results revealed that MO1 produced significant amount of IAA (9.815 ± 0.6293 μg mL- 1). The MO1 showed the presence of ACC (1-Aminocyclopropane-1-Carboxylate) deaminase responsible acdS gene and tolerance against salinity stress. A plant microbe interaction experiment using tomato (Solanum lycopersicum L.) with glycine betaine (GB) as a positive control was carried out to investigate the positive role MO1 in improving plant growth and stress tolerance. The results indicated that MO1 inoculation and GB application significantly increased growth attributes under normal as well as saline condition (120 mM NaCl). The MO1 inoculation and GB treatment approach conferred good protection against salinity stress by significantly improving glucose by 17.57 and 18.76%, sucrose by 34.2 and 12.49%, fructose by 19.9 and 10.9%, citric acid by 47.48 and 34.57%, malic acid by 52.19 and 28.38%, serine by 43.78 and 69.42%, glycine by 14.48 and 22.76%, methionine by 100 and 124.99%, threonine by 70 and 63.08%, and proline by 36.92 and 48.38%, respectively, while under normal conditions MO1 inoculation and GB treatment also enhanced glucose by 19.83 and 13.19%, sucrose by 23.43 and 15.75%, fructose by 15.79 and 8.18%, citric acid by 43.26 and 33.14%, malic acid by 36.18 and 14.48%, serine by 46.5 and 48.55%, glycine by 19.85 and 29.77%, methionine by 22.22 and 38.89%, threonine by 21.95 and 17.07%, and proline by 29.61 and 34.68% compared to levels in non-treated plants, respectively. In addition, the endogenous abscisic acid (ABA) level was noticeably lower in MO1-inoculated (30.28 and 30.04%) and GB-treated plants (45 and 35.35%) compared to their corresponding control plants under normal condition as well as salinity stress, respectively.
Conclusion: The current findings suggest that the IAA- and ACC-deaminase-producing abilities MO1 can improve plants tolerance to salinity stress.
Keywords: Metabolite regulation; NaCl; PGPR; Plant microbe interaction; Tomato.