Responses of growth and antioxidant system to root-zone hypoxia stress in two Malus species

Responses of growth and antioxidant system to root-zone hypoxia stress were comparatively studied in two Malus species (M. hupenensis and M. toringoides) differing in hypoxia tolerance. 50-day-old seedlings were hydroponically grown for 20 days in normoxic and hypoxic nutrient solutions. Hypoxia stress inhibited the growth of both species. Compared with M. hupenensis, M. toringoides was more responsive to hypoxia stress, resulting in larger decreases in leaf number, root length, plant height, and biomass production. The contents of superoxide radicals (O(2)radical anion) and hydrogen peroxide (H2O2) significantly increased in roots of both species exposed to hypoxia stress, and resulted in lipid peroxidation, which was indicated by accumulated concentration of malonaldehyde (MDA). In addition, a significant increase in O(2)radical anion, H2O2 and MDA contents was found in M. toringoides under hypoxia stress. In responses to hypoxia stress, peroxidse (POD), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) activities increased during the early part of the hypoxia stress, but decreased in the late period; the activities of SOD, POD and APX were more increased in M. hupenensis than in M. toringoides. Ascorbic acid (AsA) and glutathione (GSH) accumulation was also higher in M. hupenensis than in M. toringoides in the early period under hypoxia stress. These results suggest that the hypoxia-tolerant M. hupenensis has a larger protective capacity against oxidative damage by maintaining higher induced activities of antioxidant system than the hypoxia-sensitive M. toringoides.