Inoculation with Rhizobacteria Enhanced Tolerance of Tomato (Solanum lycopersicum L.) Plants in Response to Cadmium Stress

In this study, cadmium (Cd)-tolerant bacteria Serratia sp. D23 (D23) and Sphingomonas sp. D36 (D36) were isolated from Cd-contaminated rhizospheric soil. Both strains have indole-3-acetic acid production, phosphate solubilization and siderophores production ability. A hydroponic experiment was performed to evaluate the effect of D23 and D36 on Cd toxicity and Cd content in tomato plants. The results indicated that under Cd-stressed condition, D23 and D36 inoculation increased photosynthetic pigment content in tomato leaves and decreased malonyldialdehyde level in tomato roots (p < 0.05). Both strains could alleviate Cd-induced inhibition of dry mass accumulation, D23 inoculation increased the root and leaf dry mass by 44.95% and 99.13%, while D36 treatment increased the root and leaf dry mass by 41.56% and 46.81%, respectively. Besides, D23 treatment reduced the Cd content in tomato root by 46.70%, and D36 inoculation reduced the Cd content in root and leaf by and 27.63% and 35.41%. Moreover, the expression of stress-related genes, including Hsp90, MT2 and Nramp3 were enhanced by bacterial inoculation. The subcellular localization of Cd and the activity of antioxidant enzyme were also influenced by D23 and D36 colonization. Taken together, rhizobacteria D23 and D36 could alleviate Cd toxicity and reduce Cd concentration in tomato plants via alleviating oxidative stress, modulating Cd subcellular localization and upregulating stress-related gene expression. This study provides evidence of enhancing Cd tolerance in tomato plants via rhizosphere bacteria and will be helpful to establish bacterial-assisted approach for alleviating heavy metal toxicity in plants.