Stress Of Ag-NPs On Chlorella Pyrenoidosa Under The Modulation Of NO

Silver nanoparticles（Ag-NPs）inevitably enter the water environment in the process of production,transportation and use,which poses a potential threat to ecological security.Previous studies have investigated the toxic effects of Ag-NPs on algae,but there are relatively few studies on whether the toxicity of Ag-NPs on algae is attributable to the Ag⁺released by Ag-NPs,and the mechanism of biological toxic effects of Ag-NPs on algae under the regulation of NO and the response of algae to Ag-NPs stress.In this study,the 24 h EC₅₀ of Ag-NPs on Chlorella pyrenoidosa（C.pyrenoidosa）was used as the concentration of acute toxicity,the Ag⁺released from Ag-NPs in the BG11 medium was used as the control,and C.pyrenoidosa was used as the model organism to investigate whether the stress effect of Ag-NPs on C.pyrenoidosa was attributable to the Ag⁺released from the Ag-NPs.In addition,SNP and c-PTIO were used as NO donors and scavengers respectively to study the stress effects of Ag-NPs on C.pyrenoidosa under the modulation of NO.The main results of this paper are as follows:In this study,the stress effects of Ag-NPs and Ag⁺on C.pyrenoidosa were studied with Ag-NPs and Ag⁺as model organisms.Exogenous NO donors and scavengers were added to Ag-NPs and Ag⁺experimental groups to study the stress effect of Ag-NPs on C.pyrenoidosa under the modulation of NO.The main research results of this paper are as follows:（1）Ag-NPs and Ag⁺enrichment effects of C.pyrenoidosa were different.Ag-NPs and Ag⁺were adsorbed by chemisorption,and Ag⁺was adsorbed by combination of chemistry and physics.The amount of Ag internalized by algal cells under Ag-NPs and Ag⁺stress was higher than the extracellular loose adsorption amount.However,the amount of Ag in algal cells under Ag-NPs stress was 94.80 times that under Ag⁺stress,which indicated that Ag-NPs could destroy the cell structure more easily than Ag⁺.Ag-NPs increased the extracellular polysaccharide and extracellular protein content of algal cells,but Ag⁺did not affect the extracellular polymer content.Exogenous NO reduced the amount of Ag internalization by increasing the extracellular polymer content of algal cells under Ag-NPs stress.（2）The stress effects of Ag-NPs on growth characteristics and photosynthesis of algal cells were alleviated under the modulationof NO.The biomass inhibition rate of Ag-NPs group（44.84%）was higher than that of Ag⁺group（7.84%）.Compared with Ag⁺group,Ag-NPs inhibited the synthesis of photosynthetic pigments in C.pyrenoidosa and destroyed photosynthetic systemⅡmore seriously.Ag-NPs reduced cell size and increased cell complexity,while cell size increased and cell complexity did not change under Ag⁺.Exogenous NO decreased the inhibition rate of biomass and chlorophyll content in Ag-NPs group,while did not affect the algal cells under Ag⁺stress.（3）NO modulated the antioxidant system of algal cells under Ag-NPs so that the oxidative damage of Ag-NPs on algal cells was improved.Ag-NPs significantly increased the MDA content and the relative fluorescence content of cell membrane permeability by 217.60%.After EEM analysis,the intracellular material leakage occurred in Ag-NPs group,and the K⁺content in C.pyrenoidosa was significantly reduced by 57.81%.There was no significant difference in cell permeability between Ag⁺group and control group.Exogenous NO decreased the membrane permeability（37.99%）and the loss of intracellular K⁺under Ag-NPs.The SOD and POD activities increased by 120.95%and 192.07%,ASA content decreased by 42.70%,GSH content increased by 51.01%,DHAR activity decreased by 32.25%and proline content decreased by 20.86%in C.pyrenoidosa under Ag-NPs stress.Ag⁺did not significantly affect the antioxidant system of C.pyrenoidosa.Exogenous NO decreased the GSH content,SOD and POD activities in alga under Ag-NPs.The ASA content,DHAR activity,APX activity and proline content were positively modulated to alleviate the stress effect of Ag-NPs on alga.However,exogenous NO did not affect the oxidative stress of C.pyrenoidosa under Ag⁺.