With the seedlings of Lübachun No. 4, a
hypoxia-resistant cultivar, and Zhongnong No. 8, a
hypoxia-sensitive cultivar, as test materials, and by the method of
solution culture, this paper studied the effects of root zone
hypoxia on their roots' respiratory metabolism. The results showed that root zone
hypoxia inhibited the
tricarboxylic acid (TCA) cycle significantly, But accelerated the anaerobic respiration of cucumber roots. Under root zone
hypoxia stress, the decrement of
succinic dehydrogenase (SDH) and isocitric
dehydrogenase (IDH) activities and the increment of
lactate dehydrogenase (LDH) activity and
lactate and
pyruvate contents were lesser in Lübachun No. 4 than in Zhongnong No. 8 seedlings roots, but conversely, the increment of
pyruvate decarboxylase (PDC) and
alcohol dehydrogenase (ADH) activities and alcohol and
alanine contents in Lübachun No. 4 seedlings roots were higher than those in Zhongnong No. 8 seedlings roots. On the 8th day of
hypoxia stress, the ADH activity and alcohol and
alanine contents increased by 409.30%, 112.13% and 30.64% in Lübachun No. 4 roots and by 110.42%, 31.84% and 4.78% in Zhongnong No. 8 roots, respectively, compared with the control. No significant differences in the
alanine aminotransferase (AlaAT) activity and
acetaldehyde content were observed between the two cultivars. It was concluded that the acceleration of alcohol fermentation and the accumulation of
alanine were in favor of the enhancement of root zone
hypoxia tolerance of cucumber roots.