Light-dependent Reactions Of Photosynthesis
Light-dependent reactionsof photosynthesisTom Donald 2015 American Society of Plant Biologists
Lesson outline Photosynthesis overviewEvolution and diversity of photosynthesisLight and pigmentsThe light response curve and quantum efficiencyPlastids and chloroplastsStructure and function of photosynthetic complexesPathways of electron transportDamage avoidance and repair: Acclimations to lightMonitoring light reactionsOptimizing and improving photosynthesisArtificial photosynthesisPhotosynthetic fungi and animals 2015 American Society of Plant Biologists
Overview: Photosynthesis captures lightenergy as reduced carbon“Highenergy”,reducedcarbonEnergy inputfrom sunlightLight-dependent reactionsThe first step is the capture oflight energy as ATP andreducing power, NADPHATP“Low energy”,oxidized carbonin carbondioxideOxygen isreleased asa byproductNADPHLight-independent reactionsThe second step is the transfer ofenergy and reducing power fromATP and NADPH to CO2, to producehigh-energy, reduced sugars6 CO2 6 H2O C6H12O6 6 O2 2015 American Society of Plant Biologists
Photosynthesis is two sets of connectedreactions2 NADPHe 2 H 2 NADP 2 H2OO2 2 H 2 e ADPATPChloroplastH The LIGHT reactions take place inthe thylakoid membranesThe CARBON-FIXINGreactions take place inthe chloroplast stromaAdapted from Kramer, D.M., and Evans, J. R. (2010). The importance of energy balance in improving photosynthetic productivity. Plant Physiol.155: 70–78. 2015 American Society of Plant Biologists
Light reactions (usually) take place inthylakoid membranesProkaryotesGloeobacter violaceus,the only cyanobacteriumwithout ii, a modelgreen algaeSynechocystis spp. PCC6803,a model plastidChloroplastReproduced with permission Annual Reviews of Plant Biology Nickelsen, J. and Rengstl, B. (2013).Photosystem II assembly: From cyanobacteria to plants. Annu. Rev. Plant Biol. 64: 609-635. 2015 American Society of Plant Biologists
Light reactions produce O2, ATP andNADPH2 NADPHThe reactionsrequire severallarge multi-proteincomplexes: twolight harvestingphotosystems (PSIand PSII), thecytochrome b6fcomplex, and ATPsynthaseCytochromeb6f complexADP ATP2 H2OO2 2 H 2 e Photosystem II (PSII)e 2 H 2 NADP PhotosystemI (PSI)H ATP synthaseAdapted from Kramer, D.M., and Evans, J. R. (2010). The importance of energy balance in improving photosynthetic productivity. Plant Physiol.155: 70–78. 2015 American Society of Plant Biologists
Chlorophyll captures light energy toinitiate the light reactionsFirst step ofphotochemistryChl*Chlorin ringcaptures photonse PhotonH H2OChlorophyll isheld in pigmentproteincomplexes in ahighly organizedmannerChlPhoton capture bychlorophyll excites thechlorophyll (Chl*). Chl*can lose an electron tobecome oxidizedchlorolphyll (Chl )Chl e O2Chl is reduced bystripping an electronfrom water, releasingoxygen and protonsBuchanan, B.B., Gruissem, W. and Jones, R.L. (2015) Biochemistry and Molecular Biology of Plants. American Society of Plant Physiologists. 2015 American Society of Plant Biologists
Excited chlorophyll can release energy inseveral waysChl*PhotonPhotochemistry (first step in photosynthesis)FluorescenceNon-photochemical quenching (e.g., heat)3Chl*Alternatively, it can convert to a damaging triplet stateChlThe fate of captured light energy and photosynthetic efficiencydepend on many factors including temperature, water availability,nutrient availability, stress etc. 2015 American Society of Plant Biologists
Heat, drought, & other stresses affectphotosynthetic efficiencyLight reactionsADP ATPNADP NADPHCarbon-fixing reactionsThe light reactionsand carbon-fixingreactions are linkedthrough pools ofATP/ADP andNADPH/NADP For example . High temperature affects protein complex stability and thylakoid membrane fluidity Low temperatures slow enzyme-catalyzed reactions Drought causes stomata to close, lowering CO2 uptake and carbon-fixing reactions Nutrient deficiency or toxicity can affect electron transfer machinery 2015 American Society of Plant Biologists
Oxygenic photosynthesis requires TWOphotosystemsStrong 1.5reductantPSIIP700*EnergyRedox potential eVReductants donateelectrons to other 1.0speciesP680*e 0.5NADP NADPH0.00.5StrongoxidantP700* is a very strongreductant – strongenough to donateelectrons to NADP PSI1.0Oxidizers removeelectrons from otherspeciesP700 P700 2 H2O 4 e4 H O 2P680 P680P680 is a very strongoxidant – strong enough topull electrons from H2O 2015 American Society of Plant Biologists
PSI & PSII are connected by an electrontransport chainStrong 1.5reductantP700*EnergyRedox potential eVReductants donateelectrons to other 1.0speciesP680* 0.5e PQNADP PC 2 H2O 4 e1.0Oxidizers removeelectrons from otherspeciesNADPHCyt b6f0.00.5StrongoxidantPSIPSII4H O2P680 P680P700 P700The electron transport chaingenerates proton-motive force thatdrives ATP production 2015 American Society of Plant Biologists
This diagram is known as a Z-schemeStrong 1.5reductantP700*EnergyRedox potential eVReductants donateelectrons to other 1.0speciesP680* 0.5e PQNADP PC 2 H2O 4 e1.0Oxidizers removeelectrons from otherspeciesNADPHCyt b6f0.00.5StrongoxidantPSIPSII4H O2P680 P680P700 P700The electron transport chaingenerates proton-motive force thatdrives ATP production 2015 American Society of Plant Biologists
PSI can function without PSII, but itdoesn’t produce oxygen or NADPHPSICyclic electron transport: Involves PSI Does not involve PSII Involves the electron transport chain Results in ATP production Does not liberate O2 Does not produce NADPHP700*PQCyt b6fPCP700 P700The electron transport chaingenerates proton-motive force thatdrives ATP production 2015 American Society of Plant Biologists
The photosystems are embedded inthylakoid membranesPlastidSTROMASTROMA4 H O2LUMENe 2 H 2 NADP Cyt b6fPQThylakoidMembrane 2 H2O 4 e2 NADPHCytochrome b6f(Cyt b6f) is a Plastoquinone (PQ) isa small molecule andmobile electron carrierPQPlastocyanin (PC) is asmall protein andmobile electron carrier 2015 American Society of Plant Biologists
Electrical and H gradients drive ATPsynthesis2 NADPH2 H H 4 H O2ADP Pi2 NADP ATPSynthaseATPCyt b6fThylakoidMembrane 2 H2O 4 ee PSIIPSI[H ]Protongradientfrom high(in) to low(out) 2015 American Society of Plant Biologists
Products of the light-dependent reactionsdrive carbon-fixationLight-dependent reactionsADP ATPEach CO2 fixedrequires 3 ATPand 2 NADPHCarbon-fixing sphateNADPHH H NADP RegenerationCalvinBensonCycleGlyceraldehyde 3phosphate (GAP)For every 3 CO2 fixed, oneGAP is produced forbiosynthesis and energyATPADP PiNADPH1 x GAPNADP H EnergyinputReducingpower inputAdapted from: Buchanan, B.B., Gruissem, W. and Jones, R.L. (2000) Biochemistry and Molecular Biology of Plants. American Society of Plant Physiologists. 2015 American Society of Plant Biologists
Lesson outline Photosynthesis overviewEvolution and diversity of photosynthesisLight and pigmentsThe light response curve and quantum efficiencyPlastids and chloroplastsStructure and function of photosynthetic complexesPathways of electron transportDamage avoidance and repair: Acclimations to lightMonitoring light reactionsOptimizing and improving photosynthesisArtificial photosynthesisPhotosynthetic fungi and animals 2015 American Society of Plant Biologists
Evolution and diversity ofphotosynthesisMostphotosyntheticprokaryotes useonly a singletype of reactioncenter and donot releaseoxygenNote thatoxygenicphotosynthesisrequires Type I& Type IIreaction centersworking in seriesThere are two types of reaction centers, Type I & Type IIEach type is found in various photosynthetic bacteriaBoth types are found in cyanobacteria and chloroplastsType II are pheophytinquinone reaction centersType I are iron-sulfurreaction centersPSIPSIIO2Reprinted from Allen, J.P. and Williams, J.C. (1998). Photosynthetic reaction centers. FEBS Letters. 438: 5-9 with permission from Elsevier. 2015 American Society of Plant Biologists
Type I & Type II reaction centers arebroadly distributed in prokaryotesCyanobacteria,chloroplastsType I Type IIType IIType ISeveral bacterial lineageshave some photosyntheticmembers, indicating thatlateral gene transfer hasplayed an important role in theevolution of photosynthesis.Type IType IType IIReprinted from Macalady, J.L., Hamilton, T.L., Grettenberger, C.L., Jones, D.S., Tsao, L.E. and Burgos, W.D. (2013). Energy, ecology and the distribution of microbial life. Phil. Trans. Roy. Soc. B: 368: 20120383. bypermission of the Royal Society. See also Blankenship, R.E. (2010). Early evolution of photosynthesis. Plant Physiol. 154: 434–438; 2015 American Society of Plant Biologists
Prokaryotic photosynthetic obacteria1800sType I Type IIChl a,b,c,dProteobacteria1800sType IIBChl a,b1906Type IBChl a,c, d, e; Chl a1974Type IIBChl a,c1983Type IBChl g; Chl a2007Type IBChl a,cColloquial namePurple sulfur / nonsulfur bacteriaChlorobiGreen sulfur bacteriaChloroflexiFilamentous anoxygenic pted from Raymond, J. (2008). Coloring in the tree of life. Trends Microbiology. 16: 41-43. 2015 American Society of Plant Biologists
Type I may be the ancestral reactioncenterA proposed scenario for the initial evolutionof photosynthetic reaction orobiProteobacteriaCyanobacteriapastGene duplication: PsA PsaBAncestralreactioncenterFe-S cluster as electron acceptorWith kind permission from Springer Science Business Media Nelson, N. (2013). Evolution of photosystem I and the control of global enthalpy in an oxidizing world. Photosynth. Res. 116: 145-151. 2015 American Society of Plant Biologists
Oxygenic photosynthesis evolved atleast 2.5 billion years tesCyanobacteriaPhototropic bacteria?LifeOrigin ofEarth43210Billion years before presentStromatolites are nearly 3billion years old and mayhave been formed by oxygenproducing cyanobacteriaAdapted from Des Marais, D.J. (2000). When did photosynthesis emerge on Earth? Science. 289: 1703-1705 and Xiong, J. and Bauer, C.E. (2002). Complex evolution of photosynthesis. Annu. Rev. Plant Biol. 53: 503-521. NASA; Ruth Ellison 2015 American Society of Plant Biologists
Eukaryotic photosynthesis is derivedfrom endosymbiosisA single primaryendosymbiotic event* about1.5 billion years ago gave riseto chloroplasts inchlorophytes (green algaeand plants), red algae, andglaucophytes*A second more recent event thatgave rise to Paulinellachromatophora is described sChlorophytesGreen plantsBrown algae,diatoms,dinoflagellates,euglenoids .Secondary, tertiaryendosymbiosisThis lesson focuses onphotosynthesis as itoccurs in plants, greenalgae and cyanobacteriaReprinted with permission from Rumpho, M.E., Pelletreau, K.N., Moustafa, A. and Bhattacharya, D. (2011). The making of a photosynthetic animal. J. Exp. Biol. 214: 303-311. 2015 American Society of Plant Biologists
Secondaryendosymbiosisled to morephotosyntheticeukaryotesA huge variety of photosyntheticeuglenoids, diatoms, dinoflagellatesand other algae are products ofsecondary (or tertiary) endosymbiosis;the engulfment of a primary (orsecondary) endosymbiontReproduced with permission Annual Reviews from Keeling, P.J. (2013). The number, speed, and impact of plastid endosymbioses in eukaryotic evolution. Annu. Rev. Plant Biol. 64: 583-607. 2015 American Society of Plant Biologists
A recent independent endosymbioticevent: Paulinella chromatophora0.06 billion years ago1.5 billion years agoFree-livingα-CyanobacteriumGlaucophytesPrimary eukaryotic hostPlastidEukaryoticamoeba hostNucleuschromatophoresRhodophytes(Red algae)MitochondrionFree-livingβ-Cyanobacterium5 μmChlorophytes(Green algae)PlantsPhotosynthetic amoebaPaulinella chromatophoraReprinted by permission from Macmillan Publishers Ltd: from Gould, S.B. (2012). Evolutionary genomics: Algae's complex origins. Nature. 492: 46-48. Reproduced with permission Annual Reviews Gould, S.B., Waller, R. F., and McFadden, G. (2008).Plastid evolution. Annu. Rev. Plant Biol. 59: 491 – 517; See also Mackiewicz, P., Bodył, A. and Gagat, P. (2012). Possible import routes of proteins into the cyanobacterial endosymbionts/plastids of Paulinella chromatophora. Theory in Biosciences. 131: 1-18. 2015 American Society of Plant Biologists
Summary: Evolution and diversity etic bacteriaAnoxygenicOxygenic (H2O aselectron riaBrown algae,diatoms,dinoflagellates,euglenoids .Rhodophytes,Primaryendosymbiosis glaucophytes,Viridiplantae (plants,chlorophytes)Secondary, tertiaryendosymbiosis 2015 American Society of Plant Biologists
Lesson outline Photosynthesis overviewEvolution and diversity of photosynthesisLight and pigmentsThe light response curve and quantum efficiencyPlastids and chloroplastsStructure and function of photosynthetic complexesPathways of electron transportDamage avoidance and repair: Acclimations to lightMonitoring light reactionsOptimizing and improving photosynthesisArtificial photosynthesisPhotosynthetic fungi and animals 2015 American Society of Plant Biologists
Light and pigmentsLight travels at a fixed speed,c (3 x 108 m/sec).Frequency (ν) is inverselyproportional to wavelength (λ):ν c/λWavelengthGamma raysEnergy is proportional to frequency: E hν andinversely proportional to wavelength.Therefore, shorter wavelength light (e.g., UV)has higher energy than longer wavelength light1 nmUVX rays1 mmIR400500nm1mRadio wavesMicrowavesVisibleWavelength nmHigh energyHigh frequencyShort wavelength1 μm600nmLow energyLow frequencyLong wavelength 2015 American Society of Plant Biologists
Spectra of light hitting leaf(μmol photos / m2-sec)Light that hits a leaf is mainly light in thevisible spectrum (400 – 700 nm)The sun emits light at arange of differentwavelengths, but much ofthe very short wavelengthlight is absorbed by velength (nm)The earth’satmosphere blocksmuch of the shortwavelength lightNASA 2015 American Society of Plant Biologists
Absorption spectra of photosyntheticpigments300Chlorophyll cessorypigmentsChlorophyll aAbsorption spectra ofphotosynthetic pigments(normalized)All chlorophyll-basedphotosynthesis systems usechlorophyll aDifferent antenna systems usedifferent subsets of accessorypigments which expand the range oflight absorbed Chlorophyll b is found in landplants, green algae andcyanobacteria Carotenoids are found in allchlorophyll-based photosynthesissystems Phycoerythrin are found incyanobacteria and non-greenalgae, and phycocyanin incyanobacteria800Wavelength (nm) 2015 American Society of Plant Biologists
Accessory pigments are in antennacomplexes next to reaction centersIn cyanobacteria,accessory pigmentsare arranged inphycobilisomesAntenna pigmentstransfer lightenergy to thereaction centerAntenna complexPhotosystemAntenna complexIn green algae andplants accessorypigments areembedded in thethylakoid membranesGovindjee and Shevela, D. (2011). Adventures with cyanobacteria: a personal perspective. Frontiers in Plant Science. 2: 28; Reprinted by permission from Macmillan Publishers Ltd: Scholes, G.D., Fleming, G.R.,Olaya-Castro, A. and van Grondelle, R. (2011). Lessons from nature about solar light harvesting. Nat. Chem. 3: 763-774. 2015 American Society of Plant Biologists
Absorbance spectrum of photosynthesisin a green plantAbsorbancespectrum of agreen plantAbsorbancespectraChlorophyll aChlorophyll bβ -carotene300The photosynthetic actionspectrum shows the rate ofphotosynthesis that occurswhen a single wavelengthof light shines on a plantA different action spectrum can bemeasured in other organisms as afunction of their accessory pigments400500600Wavelength (nm)700800Reaction center chlorophylls absorb maximally at 680and 700 nm. Longer wavelength light does not havesufficient energy to drive photosynthesis in plants 2015 American Society of Plant Biologists
Pigments are characterized by networksof double bondsTetrapyrrole ringwith Mg in center300Chlorophyll cessorypigmentsAbsorption spectra ofphotosynthetic pigmentsChlorophyll aChlorophyll a800Wavelength (nm)Phycocyanobilin(linear tetrapyrrole)β-carotene 2015 American Society of Plant Biologists
Bacteriochlorophylls are related but havedifferent absorption spectraSpectra of light hitting leaf(μmole photons / m2-sec)Bacteriochlorophyll aBacteriochlorophyll bMg300400500600700800Wavelength (nm)Small changes in side chains aresufficient to change the absorptionspectra of (bacterio)chlorophylls 2015 American Society of Plant Biologists
Chlorophyll biosynthesisProtoporphyrin IX is a precursorof Mg-containing chlorophyll andFe-containing l tailChlorophyllsynthaseRissler, H.M., Collakova, E., DellaPenna, D., Whelan, J. and Pogson, B.J. (2002). Chlorophyll biosynthesis. Expression of a second Chl I gene of magnesium chelatase in Arabidopsis supports only limited chlorophyllsynthesis. Plant Physiol. 128: 770-779; Yamazaki, S., Nomata, J. and Fujita, Y. (2006). Differential operation of dual protochlorophyllide reductases for chlorophyll biosynthesis in response to environmental oxygenlevels in the cyanobacterium Leptolyngbya boryana. Plant Physiol. 142: 911-922. 2015 American Society of Plant Biologists
Lesson outline Photosynthesis overviewEvolution and diversity of photosynthesisLight and pigmentsThe light response curve and quantum efficiencyPlastids and chloroplastsStructure and function of photosynthetic complexesPathways of electron transportDamage avoidance and repair: Acclimations to lightMonitoring light reactionsOptimizing and improving photosynthesisArtificial photosynthesisPhotosynthetic fungi and animals 2015 American Society of Plant Biologists
The light response curve and quantumefficiencyAt low lightintensities therelationshipbetween CO2consumptionand lightintensity islinear. Why?Why does the rate ofCO2 consumption leveloff at higher lightintensities?At low light intensities,why is there is aproduction (negativeconsumption) of CO2?Skillman, J.B. (2008). Quantum yield variation across the three pathways of photosynthesis: not yet out of the dark. J. Exp. Bot. 59: 1647-1661 by permission of Oxford University Press . 2015 American Society of Plant Biologists
Quantifying photosynthesis: The lightresponse curveAt low light intensities,photosynthesis is lightlimited, so as morephotons are absorbedmore CO2 is fixedPlants have mitochondriaand respire, consuming O2and producing CO2. In thelight they are net CO2consumers, but in the darkproduction is greater thanconsumptionAs light intensity increasesabove the light saturationpoint, photosynthetic reactionrate is determined by lightindependent reactionsThis is the light compensation point:The amount of light needed to balance photosynthetic CO2consumption to respiratory CO2 productionSkillman, J.B. (2008). Quantum yield variation across the three pathways of photosynthesis: not yet out of the dark. J. Exp. Bot. 59: 1647-1661 by permission of Oxford University Press . 2015 American Society of Plant Biologists
Quantum Yield: Moles CO2 fixed or O2produced per moles photonsIn this study, the quantumyield is 0.05 mol CO2 fixedper mol absorbed photons(the slope of the line)What factorsinfluencequantum yield?Note that the quantumyield can only bemeasured in lightlimiting conditions wherethe relationship betweenabsorbed light and CO2fixation is linearSkillman, J.B. (2008). Quantum yield variation across the three pathways of photosynthesis: not yet out of the dark. J. Exp. Bot. 59: 1647-1661 by permission of Oxford University Press . 2015 American Society of Plant Biologists
Quantum Yield: Moles CO2 fixed or O2produced per moles photonsIn this study, the quantumyield is 0.05 mol CO2 fixedper mol absorbed photons(the slope of the line)Note that the quantumyield can only bemeasured in lightlimiting conditions wherethe relationship betweenabsorbed light and CO2fixation is linearWhat factorsinfluencequantum yield? Light absorbance byphotosynthetic vsnon-photosyntheticpigments Balance in excitationenergy between PSIand PSII (For CO2 yield,activities ofdownstreamprocesses) TemperatureSkillman, J.B. (2008). Quantum yield variation across the three pathways of photosynthesis: not yet out of the dark. J. Exp. Bot. 59: 1647-1661 by permission of Oxford University Press . 2015 American Society of Plant Biologists
Lesson outline Photosynthesis overviewEvolution and diversity of photosynthesisLight and pigmentsThe light response curve and quantum efficiencyPlastids and chloroplastsStructure and function of photosynthetic complexesPathways of electron transportDamage avoidance and repair: Acclimations to lightMonitoring light reactionsOptimizing and improving photosynthesisArtificial photosynthesisPhotosynthetic fungi and animals 2015 American Society of Plant Biologists
Plastids and chloroplasts: Essentialorganelles for most plant cellsPlant cell (outlined) withmany green chloroplastsA single chloroplastEnvelope (doublemembrane, resemblesprokaryotic membranes) withspecialized transportersStromaThylakoid membranesBesides photosynthesis,several metabolic pathwaysoccur in plastids including Nand S assimilation, and thesynthesis of secondarymetabolites, pigments, andhormonesKristian Peters; Louisa Howard, Dartmouth microscopy facility; and3k and caper437 2015 American Society of Plant Biologists
In plants, plastids divide by fission anddifferentiateSeeds, embryonic,meristems andreproductivetissuesDark grownphotosynthetictissueLeafFlower,fruitStorage of starch, oils and proteinsImmage credit LadyofHats; see also Sakamoto W., Miyagishima S., and Jarvis P. (2008). Chloroplast Biogenesis: Control of PlastidDevelopment, Protein Import, Division and Inheritance. The Arabidopsis Book 6:e0110. doi:10.1199/tab.0110 2015 American Society of Plant Biologists
Chlamydomonas cells have a single largechloroplastflagellaThese images show the thylakoids (green),chloroplast starch grains (brown) and a special regioncalled the pyrenoid (py) in which carbonfixing reactions take placenucleuspyEngel, B.D., Schaffer, M., Kuhn Cuellar, L., Villa, E., Plitzko, J.M. and Baumeister, W. (2015). Native architecture of the Chlamydomonas chloroplast revealed by in situ cryo-electron tomography. eLife. 4: e04889. 2015 American Society of Plant Biologists
Light induces conversion from etioplastto chloroplastLIGHTDARKProlamellar bodyin etioplastTransition tolamellar layersPrimary lamellarlayersGrana layersPribil, M., Labs, M. and Leister, D. (2014). Structure and dynamics of thylakoids in land plants. J. Exp. Bot. 65: 1955-1972 by permission of OxfordUniversity Press . Von Wettstein, D., Gough, S. and Kannangara, C.G. (1995). Chlorophyll biosynthesis. Plant Cell. 7: 1039-1057. 2015 American Society of Plant Biologists
Land plants have distinctive grana stacksin the thylakoidsGranaGrana stacksMembranes at the margins are nonappressed (green) and those within thegrana stacks (red) are appressed. Differentcomplexes are found in appressed vs nonappressed regions of the thylakoidsLouisa Howard, Austin, J.R., et al and Staehelin, L.A. (2006). Plastoglobules Are lipoprotein subcompartments of the chloroplast that are permanently coupled to thylakoid membranes and contain biosynthetic enzymes.Plant Cell. 18: 1693-1703; see also Staehelin, L.A. (1976). Reversible particle movements associated with unstacking and restacking of chloroplast membranes in vitro. J. Cell Biol. 71: 136-158. 2015 American Society of Plant Biologists
Appressed and non-appressedthylakoids have different functionslumenPSII packing into appressed membranesPSII is mainly found inappressed regions,ATP synthase and PSI inunappressed regions, andCyt b6f is distributed throughoutState 1Cyt b6fPSIILHCIIGranaATP synthaseCyt b6fPSI-LHCIsupercomplexDaum, B., et al., (2010). Arrangement of Photosystem II and ATP synthase in chloroplast membranes of spinach and pea. Plant Cell. 22: 1299-1312; Nagy, G., et al. and Minagawa, J. (2014). Chloroplast remodeling duringstate transitions in Chlamydomonas reinhardtii as revealed by noninvasive techniques in vivo. Proc. Natl. Acad. Sci. USA. 111: 5042-5047. 2015 American Society of Plant Biologists
Summary: Light, pigments, quantumefficiency and chloroplastsThe first step of photosynthesis is light capture bypigments in thylakoid membranes of chloroplasts.β-carotene 2015 American Society of Plant Biologists
Lesson outline Photosynthesis overviewEvolution and diversity of photosynthesisLight and pigmentsThe light response curve and quantum efficiencyPlastids and chloroplastsStructure and function of photosynthetic complexesPathways of electron transportDamage avoidance and repair: Acclimations to lightMonitoring light reactionsOptimizing and improving photosynthesisArtificial photosynthesisPhotosynthetic fungi and animals 2015 American Society of Plant Biologists
Structure and function of photosyntheticcomplexesStroma(electronegative side)Lumen(electropositive side)Photosystem IICytochromeb6f complexPhotosystem IReprinted by permission from Baniulis, D., Yamashita, E., Zhang, H., Hasan, S.S. and Cramer, W.A. (2008). Structure–Function of the Cytochrome b6f Complex†. Photochemistry and Photobiology. 84: 1349-1358. 2015 American Society of Plant Biologists
Linear electron transport involves threecomplexes, PSII, Cyt b6f & PSIe e e e H2OH e O2Photosystem IICytochromeb6f complexPhotosystem IReprinted by permission from Baniulis, D., Yamashita, E., Zhang, H., Hasan, S.S. and Cramer, W.A. (2008). Structure–Function of the Cytochrome b6f Complex†. Photochemistry and Photobiology. 84: 1349-1358. 2015 American Society of Plant Biologists
Structure and function ofPhotosystem II – LHCII complexPSII is a multi-proteincomplex that functions as adimer. This diagramrepresentsa monomerConservedreactioncenter coreCP43D2CP47The conservedreaction centercore is made ofup proteins D1and D2, andinner-antennaproteins CP43and CP47Dimer structure of PSIIH2O1/2 O2 2 H D1The oxygen-evolvingMn4CaO5 cluster is on theluminal side and shieldedby the more divergentextrinsic proteinsDivergent extrinsic proteinsReprinted by permission from Calderone, V., Trabucco, M., Vujičić, A., Battistutta, R., Giacometti, G.M., Andreucci, F., Barbato, R. and Zanotti, G. (2003). Crystal structure of the PsbQ protein of Photosystem II fromhigher plants. EMBO reports. 4: 900-905; Reprinted with permission Annual Reviews Nickelsen, J. and Rengstl, B. (2013).Photosystem II assembly: From cyanobacteria to plants. Annu. Rev. Plant Biol. 64: 609 – 634. 2015 American Society of Plant Biologists
Conserved cores, variable lightharvesting structuresCyanobacteria & redalgae harvest lightthrough peripheralantenna systemsThe peripheralantenna and lightharvesting complex(LHC) are differentbetweencyanobacteria andchloroplastsSame corePlants and green algaeharvest light throughmembrane-embedded lightharvesting complexesLHCIIReprinted with permission Annual Reviews Nickelsen, J. and Rengstl, B. (2013).Photosystem II assembly: From cyanobacteria to plants. Annu. Rev. Plant Biol. 64: 609 – 634. 2015 American Society of Plant Biologists
Proteins in PSII can be characterized bySGC, SDS-PAGE and EMThe subunit composition of eachband is determined by SDS-PAGELighterProtein complexes canbe separated by sucrosegradient centrifugationHeavierEM can also reveal complex compositionReprinted with permission from Caffarri, S., Kouřil, R., Kereïche, S., Boekema, E.J. and Croce, R. (2009). Functional architecture of higher plantPhotosystem II supercomplexes. EMBO J. 28: 3052-3063. 2015 American Society of Plant Biologists
Proteins’ roles are to orient and positionpigment moleculesNumerouschlorophylls,β carotenes andother smallmolecules are held inposition by PSIIproteinsNeveu,Curtis 2015 American Society of Plant Biologists
Electron transfer in PSII(1) Light converts reaction center chlorophyll (P680)to excited form P680*(2) Electron leaves P680*, forming P680 (photooxidation, charge separation)(3) The electron is transferred to Pheophytin(Pheo), forming Pheo (4) Pheo passes the electron to QA to produce QA (5) QA passes the electron to QB to produce QB (5)QB Q B e (4)QA Q A e (3)Pheo Pheo e P680 P680* P680 (1)(2)STROMAPSII(4)(5)(3)LUMEN 2015 American Society of Plant Biologists
Plastoquinone/ plastoquinol is a carrierof electrons and protons2 H 2 e Plastoquinone (PQ)at QB site of PSIIPlastoquinonol (PQH2)Plastoquinone (PQ) at the QB siteis reduced to PQ2 which picksup to protons from the stroma toform PQH2 (plastoquinol)Diffusion through lipidbilayer to Cyt b6fPQH2 diffusesthrough the lipidbilayer, carryingprotons andelectrons.See Cramer, W. A., Hasan, S.S., and Yamashita, E. (2011). The Q cycle of cytochrome bc complexes: A structure perspective. Biochim. Biophys. Acta - Bioenerg. 1807: 788–802. 2015 American Society of Plant Biologists
The oxygen-evolving complex (OEC)resides on PSII luminal surfaceThe OEC’s catalytic center core is an inorganicMn4CaO5 cluster which performs themechanistically-challenging reaction ofremoving four tightly-bound electrons and fourprotons from water
Oxygenic photosynthesis evolved at least 2.5 billion years ago Adapted from Des Marais, D.J. (2000). When did photosynthesis emerge on Earth? Science. 289: 1703-1705 and Xiong, J. and Bauer, C.E. (2002). Complex evolution of photosynthesis. Annu. Rev. Plant Biol. 53: 503-521. NASA; Ruth Ellison Eukaryotes 4 3 2 1 0 Billion years before present
Overview of Photosynthesis * . 2 The wTo Parts of Photosynthesis Photosynthesis takes place in two sequential stages: the light-dependent reactions and the light independent-reactions. In the light-dependent reactions ,
Photosynthesis overview worksheet key Page ID8997 Contributed by BoundlessGeneral Microbiology at Boundless Light-dependent and light-independent reactions are two successive reactions that occur during photosynthesis. In light-dependent reactions, the energy from sunlight is
d. What is the energy source for photosynthesis? sunlight 4. Photosynthesis occurs in 2 parts – the light-dependent reactions and the light-independent reactions. a. What is another name for the light-independent reactions? Calvin cycle b. In what part of the chloroplast do the li
Photosynthesis takes place in autotrophs. [brown] Oxygen is a product of photosynthesis. [black] Photosynthesis takes place in the nucleus of plantcells. [blue] 12. Which of the followingstatements is true? Photosynthesis takes place primarily in plant leaves. [light red] Plants obtain their ”food” from the soil. [red] Photosynthesis .
UNIT 1 PHOTOSYNTHESIS AND RESPIRATION Photosynthesis is the process whereby plants use carbon dioxide, water and light energy in a series of chemical reactions to produce glucose (food). Photosynthesis Microorganisms Interactions and interdependencies Life and living Photosynthesis and respiration Photosynthesis Respiration
photosynthesis 1/2-5/2 8/2 S1-5 Picnic Day 9/2-19/2 Lunar New Year Holiday photosynthesis 11A 4/6 Chapter 21 Photosynthesis o Basic concepts of photosynthesis o Requirements for photosynthesis o Site of The process of photosynthesis oPre Lesson Worksheet o Communication s
Photosynthesis Chapter 8 2 Photosynthesis Overview Energy for all life on Earth ultimately comes from photosynthesis. 6CO 2 12H 2O C 6H 12O 6 6H 2O 6O 2 Oxygenic photosynthesis is carried out by: cyanobacteria, 7 groups of algae, all land plants 3 Photosynthesis Overview Photosynt
In this live Gr 11 Life Sciences show we take a look at Photosynthesis. In this lesson we study the process of photosynthesis looking at the light and dark phases. We discuss the importance of photosynthesis as well as consider the effects of varying amou nts of light, carbon dioxide and temperature on the rate of photosynthesis.
