美国依利诺依大学著名光合作用教授Govindjee的光合作用讲座.pdf

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1、Photosynthesis WorkshopJanuary 14,2005Bloemfontein,South AfricaBasics of Oxygenic PhotosynthesisGovindjeeOxygenic Photosynthesis(source:several text books:thanks to Vineet Soni)The process by which plants,algae,and some colored bacteria use solar energy to drive the synthesis of organic molecules(e.

2、g.sugars,starch,etc.)from carbon dioxide(CO2)and water(H2O).Source:LarcherHistory of the AutotrophsfsFromPhotonsto aPlantpsns smsshrwkyrEXCITED STATECHROMOPHOREREACTION CENTERMEMBRANECHLOROPLASTLEAFPLANTGOV 924eC2H5VHCHHCH3CH3NNMgNNHCH3CHLight absorptionPrimary photochemistryElectron transportO2 evo

3、lutionCO2 fixationMetabolismProductivity?Photosynthesis can be broadlyseparated into:Light reactions-light dependent,but only two reactions are really light-requiring all others can occur in dark.Dark reactions-light independent,but cannot go on in darkness asthey need light-activated enzymes,and pr

4、oducts made in light.Light reactions,that occur in Photosystems I and II,are the initial reactions that lead to:the oxidation of water to oxygen reduction of NADP+to NADPH and ATP,both of the latter,in principle,can occur in darkness.By convention,the term Dark reactions,that occur in the stromamatr

5、ix of chloroplasts,have been associated with:the fixation of CO2into CH2O,using ATP and NADPH,made in light.However,many of the enzymes need to be activated by light;and thesedark reactions cannot proceed without this and the products(ATP and NADPH)made in light.On thylakoid membranes,the followingp

6、rocesses take place:1.Light absorption2.Excitation energy transfer3.Primary photochemistry4.Electron transport leading tooxygen evolutionproduction of reducing power,NADPH;and proton translocation5.Formation of ATPPhotosynthetically Active Radiation(PAR):400 to 700 nm.Absorption spectra of several p

7、lant pigments Image from Purves et al.,Life:The Science of Biology,4th Edition,by Sinauer AssociatesChlorophylls a&b,beta carotene and phycocyanin(source:several text books)Reflects bluebluelight;absorbs restReflects yellowyellowlight;absorbs restReflects greengreenlight;absorbs restStructure of Lig

8、ht-harvesting Complex:Crystal structure of spinach major light-harvesting complex at 2.72 A resolutionby Zhenfeng LIU,Hancchl YAN,Keblan WANG,Tingyun KUANG,Jiping ZHANG,Lulu GUL,Xiomin AN andWenrui CHANG Nature 428:287-292,2004From Liu et al.(2004)Nature,428:287-292From Liu et al.(2004)Photosyntheti

9、c Unit:Excitation Energy Transfer to the Reaction CenterSource:Photosystem IIJohn Whitmarsh and GovindjeeEncyclopedia of Life Sciences/2001Nature Publishing Group;Macmillan Publishers;EnglandSource:Photosystem IIJohn Whitmarsh and GovindjeeEncyclopedia of Life Sciences/2001Nature Publishing Group;Ma

10、cmillan Publishers;EnglandThe Z-Scheme Diagram of Photosynthesis4 Protein Complexes of Thylakoids:The two mobile carriers:PQ;and PC(Source:Govindjee,2000:http:/www.life.uiuc.edu/govindjee)Overview of photosynthetic processesas they occur in plants,algae,and cyanobacteriaFluorescence:90%PSII683-685nm

11、 variable int.;up to 2ns(Vibr.720-735nm)10%PSI 705-715nm constant int.;=0.1 nsThe Complex Architecture of Oxygenic Photosynthesis N.Nelson and A.Ben-Shem(2004)Nature Reviews:Molecular cell Biology,Volume 5,pp.1-12Architecture of Oxygenic Photosynthesis:The 4 ComplexesPhotosystem II Structure,Ferreir

12、a et al.(2004)pp.534Photosystem II:another version?Transfers electrons from water to plastoquinone(oxidizing water to O2)?Generates proton(H+)gradient between thylakoid lumen and stroma Bruce A.Diner and Fabrice Rappaport(2002)“Structure,Dynamics and Energetics of the Photochemistry of Photosystem I

13、I of Oxygenic Photosynthesis”,Annu.Rev.Plant Biol.53:55180.Thylakoid membraneCytochrome b6/f Complex(Popot and co-workers;Cramer and co-workers,2003)pp.537Photosystem IThylakoid membrane?Generates reduced ferredoxin?Through FNR(Ferredoxin-NADP reductase protein),it reduces NADP+to NADPH.A model for

14、the interaction of plant photosystem I with its electron donors/acceptors and the pathways forlight-induced electron transport.A Model for ATPSynthase(Wayne Frasch,ASU,Tempe)In stroma matrix:1.CO2fixation by RUBISCO(Ribulose bisphosphate carboxylase-oxygenase)in C3and C4plants,and Phosphoenolpyruvat

15、e carboxylase in C4plants.2.Reduction and phosphorylation of phosphoglyceric acid to triose phosphate using NADPH and ATP.3.Regeneration of receptor of CO24.Formation 6-C sugars and starchCARBOXYLATIONSucroseStarchRubiscoGOV94REDUCTION&PhosphoglycericacidRibulose 1,5-bisphosphateTriosephosphateREGEN

16、ERATIONRibulose 5-monophosphatePHOSPHOR YLATIONPHOSPHOR YLATIONRUBISCOIt is a notoriously inefficient enzymeAbout 107tons of this enzyme is present on Earth;this amounts to 29 kilograms of this enzyme per person on Earth!The active site,i.e.,where CO2and O2are added,is in the large subunit;it is for

17、med at the interface between two large subunits.The enzyme RUBISCO in higher plants is made up of 8 large(53 kilodaltons)and 8 small(13 kilodaltons)subunits.Ribulose-1,5-bisphosphatecarboxylase/oxygenase(Rubisco)RuBP Carboxylase in plants is a complex(L8S8)of:8 large catalytic subunits(L,477 amino a

18、cid residues)8 small subunits(S,123 amino acid residues).Rubisco is also one of thelargest enzymes in nature,with a molecular mass of 560 kDa.Photorespiration results from the oxygenation reactioncatalyzed by ribulose-bisphosphate carboxylase/oxygenaseO2O2RibulosebisphosphateCH2O PCH2O PHCOHHCOHC OH

19、2O,CO2,POHPhosphoglycerateHCOHH2CO PPhosphoglycolateO=CO-CH2O PO=CO-P=PO32-http:/treebiol.forest.wisc.edu/forestry415/TreeStructure/leaves/darkReactions/photoresp.htmPhotorespirationThe relationship of photosynthetic rateto leaf temperature in two desert ephemeralsPhotosyntheticrate(mmolCO2 m-1s-1)L

20、eaf temperature(C)C4 PlantC3 Plant8060402001020304050Quantumyield,mol CO2 perabsorbedeinstein0.080Leaf temperature,C0.040.020.064010Normal air2030012004008002%O221%O2C3C3C42%or 21%O2CO2 intercellular,bar1600C4Maximum short-term crop growth rateas function of latitudeAnnualproduction(tons hectare-1)L

21、atitude(N)C4 PlantC3 Plant0.40.30.20.1102030405060EquatorCrassulacean Acid Metabolism(CAM)http:/www.teaching-biomed.man.ac.uk/student_projects/2000/mnby7lmg/lectures/cam.htmlComparison of C-3,C-4 and CAM PlantsC-3SoybeanC-4MaizeCAMPineappleAnatomyspongy and palisade cellsmesophyll and bundle sheath

22、cellscells with large vacuolesGrowth rates(gdm-2day-1)140.02Stomatesopen in dayclosed at nightopen in dayclosed at nightclosed in dayopen at nightComparison of C-3,C-4 and CAM PlantsWater useefficiencygCO2kg-1H2OMaxphotosyntheticrate(5 range)+Optimum temperatureC-3Soybean1-330mgCO2dm-2hr-120-30oCC-4

23、Maize2-560mgCO2dm-2hr-130-45oCCAMPineapple10-403mgCO2dm-2hr-130-45oCComparison of C-3,C-4 and CAM PlantsCompensation point:CO2conc.when there is no net photosynthesisPhotorespirationKeycarboxylatingenzymeC-3Soybean50 ppmHighRUBISCOonlyC-4Maize5 ppmLowPEPCaseRUBISCOCAMPineapple2 ppm(in dark)LowPEPCas

24、eRUBISCOInfluence of different parameters on the efficiency of the carbon dioxide uptake(ordinate)of a C3plant(Atriplex patula,yellow line)and a C4plant(Atriplex rosea,green line).Measured parameters(from left to right):light intensity,leaf temperature and concentration of carbon dioxide within the intercellular space(according to O.BJRKMAN and J.BERRY,1973).http:/www.rrz.uni-hamburg.de/biologie/b_online/e24/24b.htm#cam