Studies On Mutagenesis,screening And Traits Of A Photosynthetic Mutant Of Chlamydomonas Reinhardtii

The massive marine microalgae are important primary producer in ocean.Photosynthetic ability is directly related to the growth and metabolites production of microalgae.The study of photosynthetic mechanism in microalgae has been the main focus on microalgae research.In this study,a single-cell microalga,C.reinhardtii was selected as a model to study photosynthetic mechanism of microalgae,and expected the results would be completed and interpreted the existing research data.C.reinhardtii cultures were treated with different concentration of four common antibiotics,Ampicillin(Amp),kanamycin(Kan),chloramphenicol(Cmp),tetracycline(Tet),and then measured some parameters.The results showed that cell density and chlorophyll a content of C.reinhardtii increased in less than 100 ?g/ m L of Amp and 20 ?g/m L of Cmp treatment.However,cell density and chlorophyll a levels decreased in all treatments with Kan and Tet.The actual photosynthetic efficiency Y(II)and the relative electron transfer efficiency(r ETR)of C.reinhardtii raised first and then fell in treatments of 50 ?g/ m L Amp and 10 ?g/ m L Cmp.In contrast,the Y(II)and r ETR were decreased significantly in the treatments of Kan and Tet.Combined with the antibacterial effects of the four antibiotics,the concentration of 15?g/m L Cmp was selected to asepticize C.reinhardtii cultures and the sterilized culture was obtained.In order to get mutant,the sterilized C.reinhardtii were put under different dosage of UV irradiation to induce mutations,then Imaging-PAM was used to screen C.reinhardtii mutants whose photosynthetic parameters were significantly changed.One mutant was found with screening.The Y(II)of the mutant was significantly reduced and the Y(NO)of the mutant significantly increased.The fluorescence peak wavelength of chlorophyll a in the mutant was Ex440nm/Em682 nm,which decreased by 2 nm compared to wild type;The intensity of chlorophyll fluorescence in the mutant was significantly higher than that in wild type at the same cell density;The mutant grew slower and with longer life cycle.Meanwhile the growth of the mutant was strongly affected by light intensity fluctuations.High irradiation promoted the growth of mutant but inhibited the growth of the wild strain;Even though the Y(II)of the mutant significantly decreased,its ability of photoautotrophic still existed.Changes of cells and photosynthetic pigment content of the mutant were checked and the photosynthetic parameters under different irradiations of mutant and wild type were detected by using Multi-Color-PAM.The results showed that there was no difference in cell size between mutant and wild type,and there were less number of lipid spheres in the mutant than that in the wild type.The content of chlorophyll a of the mutant was only about 63% of wild-type.The content of chlorophyll b was about 84% of wild-type.The ratio of chlorophyll a to chlorophyll b was significantly lower than that of the wild strain in which it was 3: 1.The content of the carotenoid was about 70% of the wild strain.Regulatory energy dissipation(NPQ)of the mutant could function normally.However,the NPQ response of the mutant was delayed at low irradiation.The NPQ response of the mutant could achieve to the same level as that of the wild strain at high irradiation.By analyzing the results,the conclusion could be drown that the absorption and transduction of light energy of the C.reinhardtii mutant changed from state 2 to state 1 under normal conditions.Therefore,the mutant was an abnormal solar energy utilizing state mutagenesis.Further investigation of the mutant would find out the exact mutated site and helped to illustrate the mechanism of the light transformation.