Synergistic interactions between a saprophytic fungal consortium and Rhizophagus irregularis alleviate oxidative stress in plants grown in heavy metal contaminated soil

Accumulation of heavy metals in soil causes loss of cover vegetation and increases the production of reactive oxygen species (ROS). ROS accumulation induces the expression of genes encoding antioxidant enzymes and other proteins involved in redox homeostasis. This study aimed to evaluate the interaction between a saprophytic fungal consortium and mycorrhizal Rhizophagus irregularis with regard to the oxidative stress and molecular responses of Solanum lycopersicum L. grown in a soil contaminated with heavy metals. We determined the effects of the saprophytic fungal consortium (Bjerkandera adusta and Mortierella sp) and the mycorrhizal fungus Rhizophagus irregularis on the plant antioxidant response and the expression levels of genes encoding metallothioneins (MT), phytochelatins (PC), the NRAMP transporter and heat shock protein (HSP) in Solanum lycopersicum cultivated in a heavy metal-contaminated soil. The fungal consortium increased plant growth, and the co-inoculation with R. irregularis synergistically improved soil biochemical activities. Superoxide dismutase activity decreased in all treatments. Peroxidase activity (ascorbate and guaiacol) increased in plants inoculated with R. irregularis and the fungal consortium. Dual inoculation decreased the malondialdehyde content in the leaves and increased transcription of the NRAMP, GR, MT2b, PCS and HSP90 genes. Our results demonstrate that co-inoculation contributes to reduced plant stress by improving defence mechanisms and homeostasis