Effect Of UV Radiation On Photosynthetic Performance And Lipid Accumulation Of Chlorella Vulgaris

Under the ultraviolet radiation dose conditions of 0-80 m J/cm²,the effects of ultraviolet radiation on physiology,photosynthesis and lipid accumulation of Chlorella vulgaris were investigated.The expression of genes related to lipid synthesis in algae cells was analyzed by fluorescence quantitative PCR.The optimal radiation dose was determined.The mortality rate was 81.5%at the dosage of 40 m J/cm²,indicating it had good mutagenicity.The algae cells were broken and aggregated after ultraviolet radiation.After 28 days of cultivation,the dry weight of algae cells was 513 mg/L under normal culture conditions.Under the dosages of 20 m J/cm²,40 m J/cm²,60 m J/cm²and 80m J/cm²,the dry weights of algae cells were 530 mg/L,515 mg/L,448 mg/L and 336mg/L,respectively.When the doses weren't higher than 40 m J/cm²,the growth rate and biomass of algae cells were close to those under normal culture conditions,and when the doses were higher than 40 m J/cm²,the growth rate and biomass of algae cells were lower than those under normal culture conditions.After ultraviolet radiation,the contents of polysaccharides and proteins in algae cells decreased in varying degrees,but still accorded with the composition of nutrients in algae cells.Under the dose of 20 mJ/cm²,the Fv/Fm and Y(?)values were stable in the range of 0.56-0.60 and 0.58-0.62,respectively.Under the dose of 40 m J/cm²,Fv/Fm and Y(?)values were stable in the range of 0.54-0.58 and 0.56-0.60,respectively.Under the doses of 20 m J/cm²and 40 m J/cm²,r ETR reached the normal range of 20-25umolm^-2s^-1,the values of chlorophyll fluorescence parameters were similar to those under normal culture conditions,which showed that the photosynthetic performance was good.Under the dose of 60 m J/cm²,the values of Fv/Fm and Y(?)were with in0.50-0.55 and 0.52-0.56,respectively.Under the dose of 80 m J/cm²,the values of Fv/Fm and Y(?)were within 0.50-0.53 and 0.52-0.54,respectively.Under the doses of 60 m J/cm²and 80 m J/cm²,r ETR did not exceed 20 umolm^-2s^-1,and the chlorophyll fluorescence parameters were much different from those under normal culture conditions,indicating that the photosynthetic performance deteriorated.Under the dose of 20 mJ/cm²,the lipid production reached 41%,and the lipid content was 217 mg/L,which was 27.45%higher than that under normal culture conditions.Under the dose of 40 m J/cm²,the lipid production reached 46%and the greatest lipid content was 237 mg/L,which was 39.22%higher than that under normal culture conditions.At 60 m J/cm²,the lipid production was 39%,and the lipid content was 175 mg/L,which only increased by 2.94%.At 80 m J/cm²,the lipid production and the lipid content were not increased,the lipid production was 32%and the lipid content was 108 mg/L.The relative expressions of acc D and gap A genes in algae cells at different doses were higher than those in normal culture conditions,depending on the dose.The relative expressions of acc D and gap A genes increased by 2.5 and 5 times at 40 m J/cm²,respectively.The relative expressions of acc D and gap A genes increased by 2.2 and 4.5times at 80 m J/cm².At the doses of 20 m J/cm²and 60 m J/cm²,the relative expressions of acc D gene were nearly doubled,and the relative expressions of gap A gene were increased by 0.5 and 3 times,respectively.For the Me gene,the relative expressions of20 m J/cm²and 40 m J/cm²doses were basically the same as those at normal culture conditions,the relative expression at 60 m J/cm²was nearly twice as much as that under normal culture conditions,while the relative expression was significantly reduced at 80 m J/cm².For the Pk gene,under the dose of 40 m J/cm²,the relative expression was basically the same as that at normal culture condition,while the relative expression decreased significantly at other doses.Concluding the measurement results of various parameters,40m J/cm²was determined as the optimal ultraviolet radiation dose.Under the optimal dose,the Chlorella vulgaris had good mutagenicity,the biomass is not significantly reduced,the fluorescence parameters were maintained at a high level.The lipid accumulation had been greatly increased,and the relative expression levels of the target genes were increased as well.