Abstract: The relative electrical conductivity, production rate, content of H₂O₂ and malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) activity were measured in potted poinsettia (Red Velvet) after treatment with high temperature in 45 ℃ /38 ℃ (day/ night) in artificial climatic chambers. The results showed that SOD, CAT and APX activity increased at first, and then decreased in 0.5 d, 1 d, 2 d, respectively, while POD activity increased all the time. Correspondingly, the membrane permeability increased a little within two days and then rose suddenly. The content of MDA firstly increased, then slightly deceased within two days, and then had a large scale rise after two days. At the same time, production rate and H2O2 content enhanced rapidly after two days.Therefore, two days maybe the time limit of tolerance of potted poinsettia (Red Velvet) to high temperature of 45 ℃ /38 ℃ (day/ night).

Key words: high temperature stress, poinsettia, membrane permeability, malondialdedyle, reactive oxygen species, defensive enzyme