Mycorrhizal colonization alleviates drought-induced oxidative damage and lignification in the leaves of drought-stressed perennial ryegrass (Lolium perenne).

To investigate the effects of arbuscular mycorrhizal (AM) fungus Glomus intraradices on antioxidative activity and lignification under drought-stressed (DS) conditions, the enzyme activities, growth, lignin contents and some stress symptomatic parameters as affected by drought treatment were compared in AM colonized or non-colonized (non-AM) perennial ryegrass plants for 28 days. Drought significantly decreased leaf water potential (Ψ(w) ), photosynthesis rate and biomass. The negative impact of drought on these parameters was much highly relived in AM plants compared to non-AM ones. Drought increased H₂O₂, lipid peroxidation, phenol and lignin levels, with significantly higher in non-AM relative to AM plants at day 28 after drought treatment. The enhanced activation of guaiacol peroxidase (GPOX), coniferyl alcohol peroxidase (CPOX), syringaldazine peroxidase (SPOX) and polyphenol oxidase (PPO) was closely related with the decrease in Ψ(w) in both AM and non-AM plants. GPOX, CPOX, SPOX and PPO highly activated with a concomitant increase in lipid peroxidation and lignin as the Ψ(w) decreased below -2.11 MPa in non-AM plants, while much less activated by maintaining Ψ(w) ≥-1.15 MPa in AM ones. These results indicate that AM symbiosis plays an integrative role in drought stress tolerance by alleviating oxidative damage and lignification, which in turn mitigate the reduction of forage growth and digestibility under DS conditions.