Arbuscular mycorrhizal symbiosis mitigates oxidative injury in black locust under salt stress through modulating antioxidant defence of the plant

Excess salt in the soil induces oxidative injury in plant cells. Arbuscular mycorrhizal (AM) fungi can impart host plants salt tolerance and mitigate the oxidative injury in the plants exposed to salt stress. In order to clarify the effects of AM symbiosis on antioxidant activities in Robinia pseudoacacia under salt stress conditions and explore the molecular mechanisms involved, the biomass production and oxidative injury, concentrations of H2O2 and non-enzymatic antioxidants (ascorbate and glutathione), activities of antioxidant enzymes as well as expression of five antioxidant enzyme-encoding genes (RpCu/Zn-SOD, RpMn-SOD, RpAPX1, RpAPX2 and RpGR) in R. pseudoacacia inoculated with or without AM fungi under salt stress were analysed. The results showed that salinity reduced the biomass production in both NM and AM plants, but the reduction was lower in AM plants than in NM plants. In leaves, the levels of REL, MDA and H2O2 were reduced by AM symbiosis. Meanwhile, the activities of almost all enzymes tested (except for PDX, which was unaffected by AM symbiosis), the expression of five antioxidant enzyme-encoding genes and the concentrations of total, reduced and oxidized ascorbate and glutathione were increased by AM symbiosis. However, in roots, the H2O2 accumulation was upregulated by mycorrhizal colonization. Moreover, the activities of APX and MDHAR and concentrations of total, reduced and oxidized ascorbate were downregulated by AM symbiosis. In addition, the root MDA level was similar in NM and AM plants. The results of present study suggest that the mitigation of oxidative injury in R. pseudoacacia by AM symbiosis was more evident in leaves than in roots. The greater ability of AM plants to counteract oxidative stress resulted in the improved growth performance and salt tolerance of these plants under salt stress.