Inhibition Of Flavonoids On Growth And Photosynthetic Activity Of Phaeocystis Globosa And Its QSAR Modeling

In recent years,red tide in China's coastal areas has become more severe and has significant impact on the marine ecological environment,marine fisheries,marine economy and the development of offshore tourism,and also posed a threat to human health.Developing an effective and environmental friendly method to control the outbreak of red tide has become an urgent need for water resources management and maintaining aquatic ecosystem stability.Flavonoids,as allelochemicals,have remarkable effects on controlling cyanobacteria blooms,so we hypothesize that it also has great potential to inhibit the growth of red tide organisms.Therefore,in this thesis,the inhibitory effects of isoflavone,flavanone,flavone and dihydroflavones compounds(totally 19 flavonoid compounds)on Phaeocystis globosa,a typical species of red tide algae,were determined through lab experiments.An exploratory screening study on the inhibitory effect of flavonoids on the growth of red tide algae was carried out.Quantitative structure activity relationship(QSAR)modeling was used to study the quantitative relationship between the theoretical molecular structure of flavonoids and their algal inhibiting activities.It is of great significance to reveal the mechanism of the influence of the molecular structure of flavonoids on the algae inhibition properties.Natural chlorophyll fluorescence probe method was used to study the response of PS II photosynthetic reaction center excellent activity of two kinds of algal cells inhibited by two representative flavonoid compounds(quercetin and myricetin).This study is supposed to provide new insights for developing novel technologies for prevention and control of red tide outbreaks.The main findings were as follows:(1)Half inhibitory concentrations IC50,3d,IC50,5d and IC50?7d of 19 flavonoids were 0.001?5.517 mg L-1,0.068?3.065 mg L-1 and 0.025?3.135 mg L-1,respectively.All of these flavonoids could effectively inhibit the growth of Phaeocystis globosa.By increasing the concentration(0.5 mg L-1?16.0 mg L-1)of flavonoids,the inhibitory effect of flavonoids was also enhanced.For Phaeocystis globosa,flavonoids with strong algicidal activities mainly included quercetin,flavone,myricetin and chrysin,while the algicidal activities of flavanones such as 4',7-Dihydroxyisoflavone,5-hydroxyflavone,apigenin and 7-hydroxyflavone were weak.(2)The algicidal activity of flavonoids was related to the position of hydroxyl group in molecular structure.The introduction of 5-OH can improve the algicidal activity,while 4'-OH and 3'-OH can weaken the algae-inhibiting activity;the antialgal activity of flavonoids increased with the distance of hydroxyl group from carbonyl group.The compounds biological activity of dihydroflavones and methylated flavonoid were higher than that of flavone;and the inhibitory activity of flavone was better than that of isoflavones.(3)The QSAR model based on S-MLR has been tested both internally and externally,which showed that the model has high prediction ability.Molecular descriptor MR,partition coefficient PC,lowest unoccupied molecular orbital LUMO and highest occupied orbital HOMO were the key factors affecting the algae inhibition activity of flavonoids.(4)Flavonoids stressed the photosynthetic system of Phaeocystis globosa to a certain extent.The results showed that the maximum photochemistry quantum yield(Fv/Fm),actual photochemistry quantum(Yield),maximum relative electron transfer rate(rETRmax)and light energy utilization efficiency alpha(a)of quercetin were reduced by 18%,26%,29%and 28%,respectively.The effect of myricetin on photosynthetic activity of Phaeocystis globosa was not evident.