关键词: 顶花板凳果, 冰冻胁迫, 差热分析, 胞外结冰

Abstract: [Objective] The freezing mode,namely intercellular or intracellular freezing, in an evergreen plant Pachysandra terminalis. was investigated with the differential thermal analysis and light microscopy.[Method] This study employed differential thermal analysis and microscopic observations to seek evidence of extracellular freezing in P. terminalis Sieb. et Zucc. duiring cooling and freezing.[Result] High resolution differential scanning calorimetry was used to detect the evidence of extracellular freezing in the P.terminalis leaves.The living leaves of the plants consistently exhibited biphasic freezing exotherms, i.e., an initial small exotherm followed by a slow but much larger exotherm. In contrast, the freeze-killed leaves, as well as the filter paper drenched with extracted tissue solutions from the leaves of the two plants, exhibited just one fast and large exotherm typical for a single phase freezing. The relaxation time of the freezing course was 195 seconds for the living leaves, and 73 seconds for the killed leaves; the supercooling degree was 5.05℃ for the living leaves and 5.45℃ for the freeze killed leaves. Colourless ice crystals were observed in the intercellular spaces in the living leaves, and however coloured ice crystals in killed leaves with a microscope, which was in agreement with the result from the differential thermal analysis.[Conclusion] Although differential thermal analysis has been used in analysing the phase change temperature and the saturation degree of membrane lipids, reports on the use of the technique in analysing the freezing mode of plant tissues has not yet been seen. The experiment provided another new approach to the researches on the mechanisms of freezing injury to plants.

Key words: Pachysandra terminalis, freezing stress, differential thermal analysis, extracelluar freezing