Abstract: Gas exchange, chlorophyll fluorescence and activities of anti-oxidant enzymes were investigated to study the responses of photosynthetic characteristics and photoprotective mechanisms to various temperatures （25 ℃, 32 ℃, 38 ℃ and 44 ℃） in 'Leishan 1' and 'Sayaka' of Lilium× formolongo seedlings. In this study, the results showed that the temperatures from 25 ℃ to 38 ℃ led to only slight decrease in photosynthetic rate (Pn), but the 44 ℃ induced a significant reduction in the values of Pn. Along with the decrease in photosynthetic capacity, stomatal conductance (Gs) decreased considerably; during this process, the stomatal limitation value (Ls) decreased gradually and clearly. The measurement of chlorophyll fluorescence showed that the initial fluorescence yield (Fo) was not effected by the raising temperatures, while the maximum fluorescence yield (Fm) and the maximal quantum yield of photosystem II photochemistry (Fv/Fm) went down slightly with temperature increasing in the two lily varieties. The actual efficiency of PSⅡ(ΦPSⅡ) reduced distinctly along with the increase of temperature, while non-photochemical quenching (NPQ) strikingly increased. Moreover, the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and peroxidases (POD) were enhanced with the temperature increasing. According to our data, we suggest that Lilium × formolongo is able to tolerate mild high temperatures; Non-photochemical quenching and the anti-oxidant enzymes are the main mechanisms in the two lily varieties seedlings, which can effectively protect its photosynthetic apparatus against high temperatures.

Key words: LILY, Lilium × formolongo, heat tolerance, gas exchange, chlorophyll fluorescence, anti-oxidant enzymes