Abstract: The aim of study was to elucidate the effects of low temperature above zero on ultrastructure and physiological characteristics of Taraxacum officinale F. H. Wigg.. T. officinale seedlings were treated with the low temperature stress of 4℃ at different time (0 h,3 h,6 h,12 h,24 h,48 h). Changes of leaves ultrastructure were observed,and the related physiological indexes were measured. With the extension of the low temperature treatments times,the results showed that the chloroplasts and vacuole membrane of T. officinale leaves were dissolved,the double-layer membrane structure appeared in the cytoplasm,and the number of starch grain and mitochondrion increased,the cytoplasmic separation was obvious. The initial fluorescence (Fo),the electron transport rate (ETR) and the non-photochemical fluorescence quenching (NPQ) increased at first,and then decreased,but maximum photochemical quantum yield (Fv/Fm),PSⅡ potential photochemical efficiency (Fv/Fo),PSⅡ actual photochemical quantum yield (ΦPSⅡ) attenuated. In addition,accumulation of proline and the activity of peroxidase (POD) was enhanced,the content of malondialdehyde (MDA) and electrolyte conductivity increased,however,the activity of superoxide dismutase (SOD) and catalase (CAT) was reduced. Under the condition of low temperature stress above zero,the leaves of T. officinale seedlings were damaged with the membrane permeability increased,the photosynthesis decreased and the submicroscopic structure damaged obviously.

Key words: Taraxacum officinale, Low temperature stress above zero, Ultrastructure, Chlorophyll fluorescence, Physiological characteristics

摘要： 为研究零上低温胁迫对药蒲公英（Taraxacum officinale F.H.Wigg.）亚显微结构与生理特性的影响，以药蒲公英幼苗为材料进行4℃不同时间（0 h，3 h，6 h，12 h，24 h，48 h）低温胁迫试验，观察叶片亚显微结构的变化，测量相关生理指标。结果表明：随着低温处理时间的延长，药蒲公英叶片中叶绿体、液泡膜逐渐溶解，细胞质出现未知双层膜结构，淀粉粒、线粒体数量增加，胞质分离明显；低温胁迫时，叶绿素初始荧光值（Initial fluorescence，Fo）、相对电子传递速率（Electron transport rate，ETR）和非光化学淬灭（Non-photochemical fluorescence quenching，NPQ）呈先上升后下降的趋势，最大光化学量子产量（Variable fluorescence/maximal fluorescence，Fv/Fm）、PSⅡ （Photosystem Ⅱ）潜在光化学效率（Fv/Fo）、实际光化学量子产量（PSⅡ actual photochemical quantum yield，ΦPSⅡ）下降；脯氨酸含量和过氧化物酶（Peroxidase，POD）活性增加，丙二醛（Malondialdehyde，MDA）含量和相对电导率升高，过氧化氢酶（Catalase，CAT）和超氧化物歧化酶（Superoxide dismutase，SOD）活性减小。零上低温胁迫下药蒲公英幼苗叶片受到损伤，膜透性增加，光合作用下降，亚显微结构遭到明显破坏。

关键词: 药蒲公英, 零上低温胁迫, 亚显微结构, 叶绿素荧光, 生理特性