Colonization of arbuscular mycorrhizal fungi Glomus mosseae or exogenous salicylic acid (SA) treatment can increase Avena nuda plant tolerance to elevated NO(2) exposure. The combination of the two factors, namely application of SA to the mycorrhizal plants, further promoted NO(2) tolerance, as indicated by an alleviated plant biomass decrease compared to the respective treatment. The analysis of antioxidant capacity, redox status and photon energy utilization showed that the increased NO(2) tolerance in the treated plants may be associated, at least in part, with scavenging reactive oxygen species, maintaining CO(2) assimilated rate and reducing conditions in cells.