Advances in Flavonoid Biosynthesis Research.docx
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Advances in Flavonoid Biosynthesis Research.docx
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AdvancesinFlavonoidBiosynthesisResearch
Contents
PARTI
AdvancesinFlavonoidBiosynthesisResearch····································································Ⅰ
PARTII
AbstractandKeywords············································································································Ⅰ
PARTIII
IIntroduction··························································································································1
IIFlavonoidsandblueflowercolour·················································································1
ⅢFlavonoidsandUV-Bprotectioninplants····································································2
ⅣMedicinalpropertiesofflavonoids··········································································3
4.1Antioxidantactivityofflavonoids·························································································3
4.2Vascularactivityofflavonoids·····························································································3
ⅤFlavonoidsbiosynthesis········································································································3
PARTIV
References·································································································································6
PARTV
Acknowledgements···················································································································7
AdvancesinFlavonoidBiosynthesisResearch
Abstract:
Theroleofanthocyaninsandflavonesinprovidingstableblueflowercoloursintheangiospermsisoutlined.ThecontributionofleafflavonoidstoUV-Bprotectioninplantsiscriticallydiscussed.Advancesinunderstandingthepathwayofflavonoidsbiosynthesisaredescribed.Thebiologicalpropertiesofflavonoidsareconsideredinanevaluationofthemedicinalandnutritionalvaluesofthesecompounds.
Keywords:
Flavonoid;Biosynthesis;UV-Bprotection;blueflowercolour
IIntroduction
Advancesinflavonoidresearchoverrecentdecadeshavebeenreviewedinaseriesoffourvolumes,beginningwithHarborneetal.(1975)andculminatinginHarborne.Sincethen,reviewsofnewstructuresintheanthocyaninandflavonoidfieldandwiththeisoflavoneshaveappeared;aswellasaccountsofisoprenylatedflavonoids.Anintroductiontoflavonoidshasbeenpublished(Bohm,1999).Thisisessentiallyalistingof6467knownflavonoidstructures,withformulae,referencesandinformationonbiologicalactivities.
Theroleofflavonoidsasthemajorred,blue,andpurplepigmentsinplantshasgainedthesesecondaryproductsagreatdealofattentionovertheyears.FromthefirstdescriptionofacidandbaseeffectsonplantpigmentsbyRobertBoylein1664tothecharacterizationofstructuralandregulatorygenesinthelate20thcentury,awealthofinformationhasbeencollectedonthestructures,chemicalactivities,andbiosynthesisofthesecompounds.Butbesidesprovidingbeautifulpigmentationinflowers,fruits,seeds,andleaves,flavonoidsalsohavekeyrolesinsignalingbetweenplantsandmicrobes,andinUVprotection.The“early”stepsinthepathwayarefoundeveninthebryophytes(mosses)andithasbeensuggestedthatsynthesisofflavones,flavanones,andflavonolsmayhaveevolvedfirsttoprovidechemicalmessengersandthenUVsunscreens(Stafford,1991).Flavonoidsarealsoaremarkablyd-iversegroupofsecondaryproductswithavastarrayofbiologicalfunctions,includingapparentrolesinstressprotection.Theflavonolsmaybeamongthemostimportantflavonoidsinthisregard;theyarethemostancientandwidespreadoftheflavonoids,synthesizedeveninmossesandferns,andhaveawiderangeofpotentphysiologicalactivities.
Perhapsthemostactiveareaofflavonoidresearchatthepresenttimeisinthepossiblemedicinalcontributionthatflavonoidsmaketohumanhealth.Recentresearchonthebiologicalpropertiesofflavonoidswillthereforebeafurthersubjectofthepresentreview.Progresscontinuestobemadeinunderstandingtherolesofflavonoidsinstressprotection,aswellasindefiningthemechanismsthatcontroltheamountsandvarietiesofflavonoidsthatareproducedinplantsinresponsetodiverseenvironmentalcues
IIFlavonoidsandblueflowercolour
Blueflowercolourisusuallyduetothepresenceinthepetalsofananthocyaninbasedondelphinidin.However,mostdelphinidinglycosidesaremauveincolourandtheshifttotheblueregionusuallyrequiresthepresenceofaflavonecopigment,andoccasionallyofoneormoremetalcations.Blueflowercolouristhepreferredattractantofbeepollinators,sothatevolutiontowardsbluecolourisapparentintemperatefloraswherebeepollinationisdominant.AsGottlieb(1982)haspointedout,blueflowercolourisrestrictedtothemorehighlyevolvedangiospermplantfamilies.Thus,manymoreprimitivefamilieshavefloralanthocyaninsbasedoncyanidin(intheredtomagentarange)andthisexplainswhyfamiliesliketheRosaceaeandgeneralikeRosalackdelphinidin-basedblueflowers.ThechemicalbasisofblueflowercolourwasfirstextensivelyinvestigatedinthecaseofCommelinacommunis.ThediscoverythatthebluepigmentofCommelinacommunishastwometalcations,ironandmagnesium,asessentialcomponentsoftheanthocyanin–flavonecomplex,suggestedatthetimethatmetalcationsmightbegenerallypresentinbluefloweredspecies.Thishas,however,notbeenborneoutbysubsequentexperimentation.Infact,theonlycomparablemetalcomplex,closelysimilartothatofCommelina,isthatofthebluecornflower,Centaureacyanus,wherethesametwometalsarepresentandwherethesameratio(6:
6:
1:
1)ofanthocyanintoflavonetoirontomagnesiumoccurs.TheonlyotherclearexampleofametalionbeingrequiredforblueflowercolouristhecaseoftheblueHydrangeamacrophyllawherethemetalisaluminium.
Finally,mentionshouldbemadeofsomeexperimentsonred–purpleandredflowercoloursinthecarnation,Dianthuscaryophyllus.Red–purplecarnationflowershaveyieldedcyanidin3,5-diglucoside-600,6000-malyldiester,thefirstmacrocyclicanthocyaninevertobecharacterised.Thesetwopigmentsareparticularlyunstableinacidicmediaandcanonlybeextractedifneutralsolventsareemployed.Invivo,thesetworarepigmentsappeartobestabilisedbycopigmentationwithassociatedflavones,aswiththemorefamiliarbluecopigmentcomplexesdiscussedabove.
ⅢFlavonoidsandUV-Bprotectioninplants
Ultravioletradiationisbyconventiondividedintothreebands,eachwithadierentenergyandwithdifferentecologicalsignificance.Ofthese,UV-B(280–315nm)isthebandoflowestwavelengthandhighestenergy.Itcanpenetratetheozonelayerinthestratosphereandhencepotentiallycausedamagetoplantlife.ResistancetoUV-Bmaytakemanyforms,butonetypeofresistancecouldlieintheflavonoidpigmentss.Theseflavonoidsgenerallyabsorbinthe280–315regionandthusarecapableofactingasUVfilters,therebyprotectingtheunderlyingphotosynthetictissuesfromdamage.
AseriesofexperimentsindierentlaboratoriesaroundtheworldhaveprovidedmoreconvincingevidencethatplantssubjectedartificiallytoUV-Bradiationrespondbychangesinthepathwayofflavonoidsynthesis.Changeshavebeenobservednotonlyinthelevelsofflavonoidsinepidermalcellsoftheadaxialleafsurface,butalsoinflavonoidsintheleafwaxandinleafhairs.ItisinterestingthatArabidopsismutantswhichareblockedinthebiosynthesisofrelatedphenylpropanoidsbasedonsinapicacid,arelessaectedbyUV-Bradiation.AlthoughArabidopsisisaspeciallyfavouredplantforgeneticstudies,mutantformsinotherplantsandespeciallyincerealscanbeobtainedbyappropriateexperimentation.Anothercerealinwhichmutantsaectingflavonoidsynthesisexistisbarley,Hordeumvulgare.Here,amutanthasbeenproducedwhichcontainsonly7%oftheflavonoids(mainlyglycoflavonesbasedonapigeninandluteolin)ofthewildtype.
ⅣMedicinalpropertiesofflavonoids
4.1Antioxidantactivityofflavonoids
Tournaireetal.(1993)havedevelopedanimprovedmethodtocomparetheantioxidantactivityof13selectedflavonoidsfromdierentclassesbymeasuringthequantumyieldsofsensitisedphoto-oxidationofindividualflavonoids.Thiswascoupledwithdeterminationofphoto-oxidationbasedonmeasuringthesingletoxygenluminescence.
Previousworkers(e.g.DasandPereira,1990)haveshownthatacarbonylgroupatC-4andadoublebondbetweenC-2andC-3arealsoimportantfeaturesforhighantioxidantactivityinflavonoids.Buteinandother3,4-dihydroxychalconesaremoreactivethananalogousflavonesbecauseoftheirabilitytoachievegreaterelectrondelocalisation(DziedzicandHudson,1983).Inmostrecentreportstheantioxidantactivityhasbeenmeasuredusingalipidperoxidationassay.Riosetal.(1992)foundthathypolaetin8-glucoside(8-hydro-xyluteolin8-glucoside)wasthemostpotentinhibitorofnon-enzymiclipidperoxidationamongsttheflavoneglycosidesintheaerialpartsofSideritishjavalambrensis(Labiatae).
4.2Vascularactivityofflavonoids
Inasurveyof65flavonoidsforprocoagulantactivity18werefoundtoinhibittheinterleukin1-inducedexpressionoftissuefactoronhumanmonocytesbutthemostactivewasthebiflavonoid,hinokiflavone(Laleetal.,1996).Tissuefactorisaglycoproteinthatinitiatesbloodcoagulationbutthisactivityisnotnormallyexpressedinmonocytesandendothelialcellsunlesstheyareexposedtoinflammatorymediatorswhichcausethemtoacquireprocoagulantproperties.Hinokiflavonewasfoundtoinhibitendoxin-andinterleukin-inducedt
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