Abstract:Lagotis brevituba, a typical alpine plant grown on Daban mountain(EL.4000 m),has higher photosynthetic capacity but lower quantum yield efficiency. The leaves of Lagotis brevituba possess well-developed palisade tissue, large intercellular spaces. The chloroplast structure is special,it has less grana. The special tissue and cell structure is the basis of the photosynthetic characteristics inLagotis brevituba. The photosynthetic apparent quantum yeild of Lagotis brevituba grown in the culture room (PAR:60～70 μmol·m-2·s-1; mean day/night temperature:15/10 ℃) was higher than that grown in the green house (PAR: highest 1*!250 μmol·m-2·s-1;mean day/night temperature:24/13 ℃),whereas the photosynthetic rate and Hill reaction rate were the opposite. Exposure of Lagotis brevituba to freezing stress resulted in declines of photosynthetic rate and apparent quantum yeild.The freezing stress was more inhibitive to the photosynthesis under light(90～100 μmol·m-2·s-1) than under the dark. Our experimental results indicate that Lagotis brevituba might possess particular freezing resistant mechanism and be a good plant for isolation and screening of freezing resistant genes.