Low oxygen concentration is a normal natural environmental stress during kiwifruit cultivating. Under root zone of hypoxia stress, pH and reduction potential would become much lower around the plants' roots. Under this condition, Mn4 + would be deoxygenized to Mn²⁺, which is the form of manganese absorbed by plants in the soil. If hypoxia soil keeps the low reducing and pH conditions for a long time, Mn²⁺ will be accumulated to a high concentration, and Mn²⁺ toxicity to plants may occur. So in this paper, changes of antioxidant enzyme activities of different resistant kiwifruit seedlings (Actinidia. deliciosa var. Qinmei & Actinidia. chinensis var.Qinmei rufopulpa) are evaluated under hypoxia stress with different levels of Mn²⁺ . Activities of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxide (APX), glutathione reductase (GR), catalase (CAT), the contents of H₂O₂, ascorbic (AsA) and malondialdehyde (MDA) are studied to understand how active oxygen damages the membrane lipid under hypoxia stress. Two species' seedlings were planted in hydroponics. Nutrient solutions including different levels of Mn²⁺ (10, 200, 400 and 600 μmol/L) were aerated with nitrogen in order to induce root zone of hypoxia stress. Eight days later, when symptoms were obvious, antioxidant enzyme activities, contents of H₂O₂ and malondialdehyde (MDA) were investigated. It is concluded that the right amount of Mn²⁺ could reduce damages of active oxygen from hypoxia stress, however, a high level of Mn²⁺ is only to aggravate the damage. The two different resistant kiwifruit species have similar physiological mechanisms, but the A. deliciosa var. seedling is superior to that of A. chinensis var. rufopulpa in terms of anti-active oxygen abilities.

kiwifruit  /  hypoxia stress  /  Mn  /  anti-oxidative system