Abstract
Plant rhizosphere usually inhabits beneficial microorganisms distributed in the soil ecosystem, namely, arbuscular mycorrhizal fungi. The helpful fungi can form mycorrhizal associations with the plant roots, which help the host to uptake nutrient elements and water from the soils. ROS within plants is a very interesting field of research. ROS generated in the cell has negative impact on biomolecules and in severe case causes death of the cell. Relations between the mycorrhizal associations and ROS are widely concerned with plants. Mycorrhizal symbiosis generally restricts the oxidative burst under environmental stresses. As a result, arbuscule is associated with accumulation of H2O2, and more accumulation of H2O2 in arbuscules may predict the collapse or degradation of arbuscules during the mycorrhizal development. On the other hand, mycorrhizal association can enhance antioxidant enzyme activities and increase antioxidant contents of the host plant, thus partly alleviating oxidative stress. The mycorrhiza-mediated antioxidant defense systems may be dependent on both growth conditions and tissues of the host plant. Interestingly, arbuscular mycorrhizas themselves possessed various SOD genes to up-regulate stress tolerance, whereas the mycorrhizal mediation is fully known. In this chapter, we simply introduced mycorrhizal symbiosis, summarized the ROS occurrence under mycorrhizal symbiosis, and also clarified the roles of mycorrhizal association in antioxidant enzymes and antioxidants of the host plant. Relation of arbuscular mycorrhizas with ROS in plants in future is also discussed.