Abstract: The effect of Ca²⁺ on respiratory metabolism in two cucumber cultivars (Cucumis sativus L. )‘Zhongnong 8’( the hypoxia-sensitive cultivar) and‘Lübachun 4’ ( the hypoxia-tolerant cultivar) seedling roots was investigated under hypoxia stress in nutrient solution. The results showed that compared with ‘Zhongnong 8’ seedling roots, the decrease of activities of succinic dehydrogenase ( SDH) and isocitric dehydrogenase ( IDH) wasweaker and the increase of alcohol dehydrogenase (ADH) activitywas greater, the increase of lactate dehydrogenase (LDH) activity was weaker, and lactate contentwas lower in ‘Lübachun 4’seedling roots. The activities of SDH, IDH and ADH were promoted, while LDH activity was inhibited, the
accumulation of lactate was depleted in cucumber seedling roots under the calcium sufficient hypoxic treatment, but that showed inverse results under the calcium deficient hypoxic treatment. The results suggested that exogenous calcium could increase the capacity of ethanol fermentation and decrease the capacity of lactate fermentation and maintain aerobic respiration for cucumber seedling roots, which was beneficial to improve the resistance to hypoxia stress for cucumber seedlings.

Key words: Ca²⁺, Cucumber, Hypoxia stress, Aerobic respiration, Anaerobic respiration