Abstract: A hydroponic experiment was conducted to study the effects of exogenous calcium, LaCl₃, and trifluoperazine (TFP) on the abundance and activity of alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH) isoenzymes in cucumber seedlings under hypoxia stress. Hypoxia induced the formation of new ADH and LDH isoenzyme bands. Under hypoxia stress, the abundance and activity of ADH and LDH isoenzymes were significantly higher than those of the control. Increasing exogenous Ca²⁺ concentration was conducive to the Ca²⁺ signal formation and the adversity signal transduction. The application of 4 mmol CaCl₂·L^-1 alleviated the hypoxia stress significantly, and made the abundance and activity of ADH and LDH isoenzymes closed to the control level. La³⁺ inhibited the Ca²⁺ uptake and its in vivo transport. Applying 50 μmol·L^-1 of LaCl₃ decreased the abundance and activity of ADH and LDH isoenzymes significantly, inhibited the growth of cucumber seedlings, and made the plant biomass be significantly lower than that under hypoxia, implying that La³⁺ increased the hypoxia injury of cucumber seedlings. TFP inhibited the hypoxia signal transduction. Applying 20 μmol·L^-1 of TFP made the abundance and activity of ADH and LDH isoenzymes be significantly lower than those under hypoxia, inhibited the growth of cucumber seedlings, and decreased the hypoxia tolerance of the seedlings, which implied that TFP also increased the hypoxia injury of cucumber seedlings. Our results suggested that exogenous Ca²⁺ could regulate the anaerobic respiration process of cucumber roots under hypoxia stress. The exogenous Ca²⁺ increased the in vivo transport of Ca²⁺, alleviated the hypoxia injury, and enhanced the plant tolerance against hypoxia stress.

Key words: Phosphorus efficiency, Plant, High phosphorus use efficiency, Genotypes, Mechanism