Abstract:

In this paper, two muskmelon cultivars, `Xiyu 1' with low hypoxia-resistance and `Dongfangxingguang' with high hypoxia-resistance, were used to study the changes in the activities in PDC, ADH, LDH and MDH under hypoxia stress. (DO at 2±0.20 mg·L^-1). When seedlings grew to 3rd euphylla, they were cultured in a Hoagland nutrient solution and divided into two sets. One set of seedlings was exposed to normal dissolved oxygen levels (DO) using vigorous aeration to maintain DO levels at 8.0-8.5 mg·L^-1, and the other set was treated with hypoxia stress using a DO analyzer (QUANTUM-25) to keep levels at 2.0±0.2 mg·L^-1. The results showed that seedling growth of both cultivars were significantly inhibited and the root activity increased under hypoxic conditions. The PDC activity in roots of both seedlings increased significantly under hypoxia stress, but there were no obvious differences between the two cultivars. The MDH activity in roots of both seedlings decreased significantly under hypoxia stress and the decrease of activity of `Xiyu 1' was much more than that of `Dengfangxingguang'. The activities of ADH and LDH of both seedlings increased significantly under hypoxia stress. The increase in the activity of ADH in `Dongfangxingguang' was more than that of `Xiyu 1', while the increase of the activity of LDH in `Xiyu 1' was more than that of `Dongfangxingguang'. The results suggested that `Dongfangxingguang' could maintain high levels of aerobic respiration, and ethanol fermentation was the primary pathway of anaerobic respiration under hypoxic stress whereas lactate fermentation was the leading pathway of anaerobic respiration under hypoxia stress in `Xiyu 1'.

Key words: Hypoxia stress, Muskmelon (Cucumis melo var. raticulalus), Anaerobic respiration