Effect of low nocturnal temperature stress on fluorescence characteristics and active oxygen metabolism in leaves of Garcinia hanburyi seedlings grown under two levels of irradiance
夜间低温胁迫对两种生长光强下藤黄幼苗叶片荧光特征和活性氧代谢的影响

The fluorescence characteristics and active oxygen metabolism in leaves in Garcinia hanburyi seedlings grown under two irradiance levels (50% and 8% of full natural sunlight) and nocturnal low temperature (4 degrees C) were studied in Xishuangbanna. The results showed that the photochemical efficiency of PS II (Fv/Fm), the quantum yield of PS II linear electron transport (phi PS II) and non-photochemical quenching (NPQ) were decreased, but the initial fluorescence yield (F0) were increased with prolonged stress time of low temperature in leaves of Garcinia hanburyi grown under the two different irradiance levels. After three days of recovery treatment, the Fv/Fm and F0 of Garcinia hanburyi grown under 50% natural irradiance were not recovered completely, while those of the seedlings grown in 8% natural irradiance were recovered almost completely, which indicated that the photosynthetic apparatus of Garcinia hanburyi grown under 50% irradiance was injured by photooxidation, but that of seedlings grown in 8% irradiance was only reversibly inactivated by the nocturnal low temperature stress. In the mean time, although the activities of protective enzymes (SOD, CAT, and APX) increased, the O2-. production rate and H2O2 content also increased with the duration of the stress. The MDA also accumulated in leaves of Garcinia hanburyi grown under two different irradiance levels. After three day's recovery, much less active oxygen was produced in leaves of Garcinia hanburyi grown under 8% than that under 50% irradiance. The implication of the results for practice were also discussed.