Abstract
A potted experiment was carried out to study the effect of an arbuscular mycorrhizal fungus (Diversispora versiformis) and arbuscular mycorrhizal like fungus (Piriformospora indica) on antioxidant enzyme defense system of Satsuma orange (Citrus sinensis cv. Oita 4) grafted on Poncirus trifoliata under favourable temperature (25 degrees C) and cold temperature (0 degrees C) for 12 h. Such short-term treatment of cold temperature did not cause any significant change in root fungal colonization and spore density in soil. Under cold stress, D. versiformis inoculation did not change the activity of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) in leaves and roots, whereas P. indica inoculation significantly increased the activity of CAT in roots and POD in leaves only. In addition, inoculation of two mycorrhizal fungi under cold stress significantly increased the relative expression levels of PtPOD and PtF-SOD in leaves, P. indica up-regulated the expression levels of PtCu/Zn-SOD in leaves, and D. versiformis also induced the expression levels of PtMn-SOD and PtCAT1 in leaves. In addition, inoculated Oita 4 trees maintained significantly lower hydrogen peroxide levels and malondialdehyde contents in leaves and roots under cold temperature, suggesting induced the expression of antioxidant enzyme genes, depending on the fungal species, and thus mitigated oxidative damage for higher cold resistance in inoculated plants.