| The fossil energy dry up continuously and the energy crisis is getting worse with the development of human socity.We want to find a new renewable energy sources to replace fossil energy sources.The new energy include water energy,solar energy,wind energy and so on.The biomass energy is one of the important new energy sources that have been widely concerned.Researchers generally believe that microalgae is the main raw material for the industrial production of biodiesel in the future.Microalgae has the features of rapid propagation,simple cultivation,rich in triglyceride?TAG?and photosynthesis.It has good development prospects.Studies have shown that microalgae can promote the oil content after being stressed by rare earth elements.In this experiment,the Nannochloropsis oculata was treated with different concentrations of cerium.We detected the biomass,oil content,activity of antioxidant enzymes,indicators of photosystem II and genes involved in lipid metabolism of Nannochloropsis oculata.The results were showed as following:1.The staining conditions of Nile red staining method were optimized for the detection of intracellular lipid content.First of all,we designed four single factor experiments.The four single factor included dimethyl sulfoxide?DMSO?concentrations,pretreatment temperature,the concentration of Nile red and dyeing time.Then the orthogonal experiments were designed.The optimal dyeing conditions were as following:DMSO concentration of 20%,pretreatment temperature of 35?,Nile red concentration of1.5?g·mL-11 and the dyeing time of 10 min.At the same time,the linear relationship between the oil content(mg·L-1)and fluorescence value was constructed.The content of lipid was detected by the optimal dyeing conditions to be514 mg·L-1.2.The low concentration group had no effect on biomass of Nannochloropsis oculata,but had significantly inhibition in high concentration group.The oil content of N.oculata was the highest in the 52.6?mol·L-11 of cerium concentration.There were 38%increase compared to the control.The cerium element in the cells was localized by transmission electron microscopy.The cerium was mainly concentrated in the intercellular space,endoplasmic reticulum,vacuoles and chloroplasts.3.The activity of CAT,SOD and the content of MDA in N.oculata cells increased during the exponential and stationary phase.The N.oculata was treated with cerium.It indicated that the rising of oxygen radicals and superoxide anions affected the normal function of intracellular organelles and caused cellular injury.The content of chlorophyll-a showed an increase at low cerium concentrations and a decrease at high cerium concentrations during the exponential phase.It decreased continuously during the stationary phase with the increasing of cerium concentrations.About the energy conversion of the photosystem II,the energy absorption of the donor side and heat dissipation has increased while the energy reception of the acceptor side has decreased during the exponential phase.However,during the stationary phase,it was not change significantly in the energy absorption of the donor side and the energy reception of the acceptor side.But the heat dissipation has decreases.4.The treatment group of 52.6?mol·L-11 cerium and the control group were sent to the sequencing company for RNA-seq analysis.A total of 55,609 unigenes were annotated to GO term.A total of 25039 unigenes were assigned by KEGG pathway analysis.The main metabolic pathways involved carbohydrate metabolism?2224 genes?,amino acid metabolism?1726 genes?,lipid metabolism?1198 genes?,energy metabolism?1111 genes?.The enzyme of the lipid metabolism mainly included pyruvate dehydrogenase complex 1,acyl-CoA oxidase,glycerol kinase with the analysis of differential genes.The levels of pyruvate dehydrogenase complex 1 and glycerol kinase in treated group were as high as5.26 times and 1.14 times of control group by real-time PCR.The levels of acyl-CoA oxidase in treated group was as down as 0.68 times of control group by real-time PCR..The results were consistent with the results of RNA-seq.We determined the oil content,antioxidant system,photosystem II and genes of lipid metabolism in N.oculata which being treated with cerium.We have identified initially the mechanism of lipid synthesis.These findings provide theoretical support of making biodiesel by N.oculata. |
PDF Full Text Request