Photosynthetic Response Of Photosystem ? In Phosphorus Absorption And Metabolism By Chlorella Vulgaris Under The Stress Of Silver Nanoparticles

The environmental behavior and biological effects of nanomaterials have become one of the hot issues in the field of environmental chemistry in recent years.Among which,silver nanopartiles(Ag NPs)is one of the most widely used nanomaterials.Due to their fast growth and reproduction rate,ease of cultivation,and their photosystem II(PSII)sensitivity to environmental stress,algae are generally regarded as model organisms to evaluate the environmental biological effects of pollutants.By evaluating the effect of Ag NPs on the PSII system of chloroplast,the key mechanism of phosphorus absorption in algal cells,it is helpful to understand the effect of Ag NPs on aquatic organisms and its potential ecological risks.By investigating the photosynthetic response of PSII system,the key mechanism of phosphorus adsorption and mechanism by algal cells under the stress of Ag NPs,it is helpful to deeply understand the impact of Ag NPs on aquatic organisms and its potential ecological risks.In this paper,Chlorella vulgaris(C.vulgaris),a common single-celled green alga in aquatic environment,was used as the experimental algal species.The changes of cell and photosynthetic ultrastructure of chlorella under Ag NPs stress were observed The photosynthetic response parameters of chlorella under different phosphorus concentrations were determined,such as chlorophyll spontaneous fluorescence and PSII photosynthetic oxygen releasing activity,etc.,and the effects of Ag NPs on photosynthetic parameters of chlorella in phosphorus absorption were evaluated.On this basis,metabolomics was employed to investigate the phosphorus metabolomics of chlorella under Ag NPs stress.The research conclusions of this paper are as follows:(1)Ag NPs stress reduced the size of chlorella cells,and the cell walls were folded and indented.The results of atomic force microscope(AFM)and transmission electron microscopy(TEM)showed that compared with the control group,with the increase of Ag NPs concentration,the grana stacked loosely or unstacked in chloroplast,the number of PSII particles decreased,the diameter decreased and the arrangement was disordered.There was a clear phenomenon of plasmural separation in algal cells.Ag NPs adversely affected the number and arrangement of PSII particles on thylakoid and damaged the ultrastructure of algal cells and chloroplasts.(2)With the concentration of Ag NPs(0-0.20 mg /L)increasing,the algal growth was obvious inhibited in the experimental period(7 days),however the inhibition was alleviated in the high-phosphorus medium(2 mg/L).The algae grew hardly in the absence of phosphorus,indicating that phosphorus is an necessary nutrient element for algal growth.Under the stress of 0.20mg/L Ag NPs,the content of chlorophyll a on the 7th day in the high phosphorus culture(2 mg /L)was 19 % less than that in the OECD normal phosphorus medium(0.36 mg/L),indicating that high phosphorus promoted the absorption of light energy by the algal cells.After the treatment of 0.20 mg/L Ag NPs,the chlorophyll spontaneous fluorescence intensity of the algae was reduced by 60%(high phosphorus)and 73%(normal phosphorus)respectively compared with that of the control group(0 mg/L Ag NPs)on the 7th day,indicating that high phosphorus promote the generation of chlorophyll.The activity of acid phosphatase decreased by about 69% compared with the control group,indicating that Ag NPs inhibited the activity of acid phosphatase and interfered with the physiological and related metabolic functions in the algal cells.The inhibition rate of hydrogen-ATPase activity(high phosphorus)was 55%,which was 11% lower than that of normal phosphorus.Hydrogen-ATPase played an energy supply role in phosphorus transport and absorption,indicating that the algae had higher abilities to selectively absorb nutrients under high phosphorus medium under Ag NPs stress.The content of adenosine triphosphate(ATP)in the high-phosphorus media was significantly higher than that in the normal phosphorus media,and the inhibition rate of energy charge AEC(high phosphorus)was 30% and 17% lower than that of AEC(normal phosphorus),indicating as an important nutrient for cell energy metabolism,and the high phosphorus alleviated the effect of Ag NPs on metabolism of the algae.(3)Under the stress of Ag NPs,33 metabolites with significant changes were identified in the algal cells.Among which,glucose,fructose,inositol and glycine were relatively high contents metabolites.Compared with the control group,glucose,sucrose and glycine increased,however the content of chlorophyll decreased and inositol decreased most by up to 75%.Ag NPs significantly disturbed the metabolism pathway of C.vulgaris,metabolism of phosphoinositol,porphyrin and chlorophyll,and metabolism of glycine,serine and threonine were down-regulated.By destroying the synthesis of chlorophyll,Photosynthetic response of PSII,and the morphology and parameters of thylakoid membrane,Ag NPs affect the absorption and metabolism of phosphorus in algae cells,and eventually lead to the inhibition of the growth of algae cells.