The Inhibitory Effects Of Enhalus Acoroides On Phaeocystis Globosa And Its Antialgal Mechanism

The application of allelochemicals from aquatic plants to inhibit harmful algal blooms?HABs?is considered as an effective biological control method.Enhalus acoroides?E.acoroides?is one of the most common species in seagrass meadows which is widely distributed in the southeast coastal area of China.E.acoroides has large size,long service life,large coverage area.In this study,we used E.acoroides aqueous extract against harmful algae species Phaeocystis globosa?P.globosa?.?1?The results showed that E.acoroides aqueous extract could significantly inhibited the growth of P.globosa and the inhibition rate of 8g/L E.acoroides aqueous extract was98.02%at 96h.E.acoroides aqueous extract could decrease the chlorophyll-a content and photosynthetic efficiency?Fv/Fm?values of P.globosa,followed by destruction of organelles,plasmolysis,and vacuolization.?2?Ultraperformance liquid chromatography-high resolution mass spectrometry?UPLC-HRMS?was used to identify major chemical constituents in E.acoroides aqueous extract.We found fourteen major chemical constituents in E.acoroides aqueous extract.However,only twelve types of major chemical constituents were identified,including six flavonoids,two homocyclic peptides,two long-chain aliphatic amides,one tannin,and one nitrogen heterocyclic compound.The result revealed that flavonoids were the characteristic chemical constituents of E.acoroides aqueous extract and the antialgal activity of luteolin-7-O-glucuronide was then assessed.Luteolin 7-O-glucuronide could significantly inhibit the growth of P.globosa with 34.29?g/m L EC_{50–96 h} value and was one of the antialgal compounds of E.acoroides aqueous extract.However,its antialgal mechanism on P.globosa have not yet been elaborated in detail.?3?A liquid chromatography linked to tandem mass spectrometry?LC-MS/MS?-based untargeted metabolomic approach was applied to investigate changes in intracellular and extracellular metabolites of P.globosa after treated luteolin-7-O-glucuronide.There were significant differences in intracellular metabolites between the control group and the treatment group,but no significant differences in extracellular metabolites.For intracellular metabolite,the concentrations of luteolin,gallic acid,betaine and three fatty acids were increased,while the concentrations of?-Ketoglutarate and acetyl-Co A involved in tricarboxylic acid cycle,glutamate,and 11 organic acids were decreased.Luteolin increased the most in the treatment groups and had strong antialgal activity on P.globosa,showing that luteolin played a vital role in the antialgal mechanism.?-Ketoglutarate and acetyl-Co A were the most inhibited metabolites,indicating that luteolin-7-O-glucuronide inhibited the growth through disturbed the tricarboxylic acid cycle of P.globosa cells.In conclusion,our data can provide insights into controlling the growth of harmful algae by using E.acoroides.