PHOTOSYNTHETIC ACCLIMATION ABILITY OF CHLORELLA VULGARIS TO LOW TEMPERATURE TREATMENT ILLUSTRATED BY CHLOROPHYLL FLUORESCENCE

Abstract

The structural and functional alterations of photosynthetic apparatus of green algae Chlorella vulgaris grown at low temperature (10 degrees C) were investigated by chlorophyll (Chl) fluorescence. The results showed that 7 d of low temperature exposure didn't lead to a reduction of growth rate. The photosynthetic rate was stimulated under low temperature condition. F-v/F-m and MDA content showed no significant difference between 10 degrees C-and 25 degrees C-grown Chlorella cells. Cells grown at 10 degrees C had a significantly lower Chl a content, which would act to reduce the probability of light absorption. Measurements of electron transport rates [ETR(II)] and quantum yield of PSII [Y(II)] indicated that the cells grown at 10 degrees C maintained higher rates of electron transport of PSII than cells grown at 25 degrees C. Results from fast chlorophyll fluorescence transients further confirmed a very high potential of electron transport activity of PSII at 10 degrees C. Furthermore, non photochemical quenching (NPQ) was stimulated at 10 degrees C and the activation of NPQ played an important role in protecting PSII from stress of low temperature. Y(I) and ETR(I) did not showed no significant difference between low temperature and the control. Ultrastructure of chloroplast was not injured by low temperature, on the contrary, at low temperature more starch granules stored in chloroplasts, which might be used for supplying energy for maintenance of the cold acclimated state. All these results suggested that the Chlorella cells possess an ample acclimation ability to low temperature