Effects of water stress and arbuscular mycorrhizal fungi on reactive oxygen metabolism and antioxidant production by citrus (Citrus tangerine) roots

The effects of arbuscular mycorrhizal (AM) fungus Glomus versiforme on reactive oxygen metabolism and antioxidant production by citrus (Citrus tangerine) roots were investigated in pot culture under well-watered (WW) and water stress conditions. Seven-day-old citrus seedlings were transplanted into plastic pots containing with and without G. versiforme. After 97 days of acclimation, half of the seedlings were subjected to water stress and the other half were WW for 80 days. Regardless of water status, biomass yield, plant height, leaf number per plant and stem diameter were notably higher in AM than in non-AM seedlings. Whether water stressed (WS) or not but AM roots showed lower levels of malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide (O2.-). Under WW conditions, activities of superoxide dismutase (SOD), guaiacol peroxidase (G-POD) and glutathione reductase (GR) were significantly higher in AM than in non-AM roots. WS AM roots showed higher activities of SOD, catalase (CAT) and ascorbate peroxidase (APX) when compared with non-AM roots. WW AM roots had higher levels of soluble protein, glutathione (GSH) and oxidized glutathione (GSSG) on the other hand, WS AM roots also showed higher levels of ascorbate (ASC) and GSSG. The higher enzymatic and non-enzymatic antioxidant productions would partly alleviate oxidative damage. AM colonization was significantly positively correlated with GSH and negatively correlated with SOD, APX and H2O2. The data from the present study suggests that, AM symbiosis helps in increments of enzymatic and non-enzymatic antioxidant productions which in turn help AM plants to enhance drought tolerance.