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Plant Stress Next assignment for Friday, Feb 22: presenting an abiotic plant stressor, what is known about it, and how it might affect plants in an ~ 10 minute presentation.
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/ 18 Content / 2 Organization? / 1 Introduction?
/ 5 Quantity of material presented? / 5 Quality of material presented? / 2 Clarity? / 1 Understanding? / 2 use of images / 7 Mechanics / 1 Confidence /1 Diction & volume / 1 Interaction with audience / 1 Pace / 1 poise, mannerisms / 1 Time? / 1 Quality of answers Total: /25 = pts
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We have chosen the following stresses:
Yelling Shaking Elevated CO2 Fungal stress N and S deprivation High Temp Predation Flooding Each of you will make presentations and write a 5 page paper about something to do with the project. Grading Proposal:
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Converts light to chemical energy
Photosynthesis Converts light to chemical energy 6 CO2 + 6 H2O + light energy <=> C6H12O6 + 6 O2
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Photosynthesis 1) Light rxns use light to pump H+ use ∆ pH to make ATP by chemiosmosis 2) Light-independent (dark) rxns use ATP & NADPH from light rxns to make organics only link: each provides substrates for the other
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Light Rxns 3 stages 1) Catching a photon (primary photoevent) 2) ETS 3) ATP synthesis by chemiosmosis
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Catching photons photons: particles of energy that travel as waves Energy inversely proportional to wavelength () visible light ranges from nm
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Catching photons Photons: particles of energy that travel as waves caught by pigments: molecules that absorb light
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Accessory Pigments action spectrum shows use of accessory pigments l used for photosynthesis plants use entire visible spectrum l absorbed by chlorophyll work best
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4 fates for excited e-: 1) fluorescence 2) transfer to another molecule 3) Returns to ground state dumping energy as heat 4) energy is transferred by inductive resonance excited e- vibrates and induces adjacent e- to vibrate at same frequency
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Photosystems Pigments are bound to proteins arranged in thylakoids in photosystems arrays that channel energy absorbed by any pigment to rxn center chlorophylls
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Photosystems Arrays that channel energy absorbed by any pigment to rxn center chls 2 photosystems : PSI & PSII PSI rxn center chl a dimer absorbs 700 nm = P700 PSII rxn center chl a dimer absorbs 680 nm = P680
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Photosystems Each may have associated LHC (light harvesting complex) (LHC can diffuse within membrane) PSI has LHCI: ~100 chl a, a few chl b & carotenoids PSII has LHCII: ~250 chl a, many chl b & carotenoids Proteins of LHCI & LHCII also differ
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cyclic photophosphorylation
Absorbs photon & transfers energy to P700 transfers excited e- from P700 to fd fd returns e- to P700 via PQ, cyt b6/f & PC
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Cyclic photophosphorylation
first step is from P700 to A0 (another chlorophyll a) next transfer e- to A1 (a phylloquinone) next = 3 Fe/S proteins finally ferredoxin
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Cyclic photophosphorylation
Ferredoxin reduces PQ-, forms PQH2 (H+ from stroma) 2) PQH2 reduces cyt b6 and Fe/S, releases H+ in lumen since H+ came from stroma, transports 2 H+ across membrane (Q cycle)
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Cyclic photophosphorylation
5) PC (Cu+) diffuses to PSI, where it reduces an oxidized P700
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Cyclic photophosphorylation
Limitations Only makes ATP Does not supply electrons for biosynthesis = no reducing power
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Photosystem II Evolved to provide reducing power -> added to PSI
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PSI and PSII work together in the “Z-scheme”
General idea: ∆ redox potential from H2O to NADP+ is so great that must boost energy of H2O e- in 2 steps each step uses a photon
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PSI and PSII work together in the “Z-scheme”
General idea: ∆ redox potential from H2O to NADP+ is so great that must boost energy of H2O e- in 2 steps each step uses a photon 2 steps = 2 photosystems
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PSI and PSII work together in the “Z-scheme”
1) PSI reduces NADP+
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PSI and PSII work together in the “Z-scheme”
1) PSI reduces NADP+ e- are replaced by PSII
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PSI and PSII work together in the “Z-scheme”
2) PSII gives excited e- to ETS ending at PSI
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PSI and PSII work together in the “Z-scheme”
2) PSII gives excited e- to ETS ending at PSI Each e- drives cyt b6/f
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PSI and PSII work together in the “Z-scheme”
2) PSII gives excited e- to ETS ending at PSI Each e- drives cyt b6/f Use PMF to make ATP
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PSI and PSII work together in the “Z-scheme”
2) PSII gives excited e- to ETS ending at PSI Each e- drives cyt b6/f Use PMF to make ATP PSII replaces e- from H2O forming O2
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PSI and PSII work together in the “Z-scheme”
Light absorbed by PS II makes ATP Light absorbed by PS I makes reducing power
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Ultimate e- source None water O2 released? No yes
cyclic non-cyclic Ultimate e- source None water O2 released? No yes Terminal e- acceptor None NADP+ Form in which energy is ATP ATP & temporarily captured NADPH Photosystems required PSI PSI & PSII
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Z-scheme energetics
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Physical organization of Z-scheme
PS II consists of: P680 (a dimer of chl a) ~ 30 other chl a & a few carotenoids > 20 proteins D1 & D2 bind P680 & all e- carriers
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Physical organization of Z-scheme
PSII has 2 groups of closely associated proteins 1) OEC (oxygen evolving complex) on lumen side, near rxn center Ca2+, Cl- & 4 Mn2+
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Physical organization of Z-scheme
PSII also has two groups of closely associated proteins 1) OEC (oxygen evolving complex) on lumen side, near rxn center Ca2+, Cl- & 4 Mn2+ 2) variable numbers of LHCII complexes
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Physical organization of Z-scheme
D1 & D2 bind P680 & all e- carriers Synechoccous elongatus associates phycobilisomes cf LHCII with PSII
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Physical organization of Z-scheme
D1 & D2 bind P680 & all e- carriers Synechoccous elongatus associates phycobilisomes cf LHCII with PSII
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Physical organization of Z-scheme
2 mobile carriers plastoquinone : lipid similar to ubiquinone
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Physical organization of Z-scheme
2 mobile carriers 1) plastoquinone : lipid similar to ubiquinone “headgroup” alternates between quinone & quinol
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Physical organization of Z-scheme
2 mobile carriers 1) plastoquinone : lipid similar to ubiquinone “headgroup” alternates between quinone & quinol Carries 2 e- & 2 H+
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Physical organization of Z-scheme
2 mobile carriers 1) plastoquinone : hydrophobic molecule like ubiquinone “headgroup” alternates between quinone and quinol Carries 2 e- & 2 H+ diffuses within bilayer
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Physical organization of Z-scheme
2 mobile carriers 1) plastoquinone 2) plastocyanin (PC) : peripheral membrane protein of thylakoid lumen
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Physical organization of Z-scheme
2) plastocyanin (PC) : peripheral membrane protein of thylakoid lumen Cu is alternately oxidized & reduced carries 1 e- & 1 H+
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Physical organization of Z-scheme
3 protein complexes (visible in EM of thylakoid) 1) PSI 2) PSII 3) cytochrome b6/f 2 cytochromes & an Fe/S protein
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Physical organization of Z-scheme
2 mobile carriers 1) plastoquinone 2) plastocyanin (PC) 3 protein complexes 1) PSI 2) PSII 3) cytochrome b6/f ATP synthase (CF0-CF1 ATPase) is also visible in E/M
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Physical organization of Z-scheme
Complexes are arranged asymmetrically! PSII is in appressed regions of grana
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Physical organization of Z-scheme
Complexes are arranged asymmetrically! PSII is in appressed regions of grana PSI and ATP synthase are found in exposed regions (ends & margins of grana, and stromal lamellae)
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Physical organization of Z-scheme
Complexes are arranged asymmetrically! PSII is in appressed regions of grana PSI and ATP synthase are in exposed regions cytochrome b6/f, PC and PQ are evenly dispersed
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Physical organization of Z-scheme
Complexes are arranged asymmetrically! PSII is in appressed regions of grana PSI and ATP synthase in exposed regions cytochrome b6/f, PC and PQ are evenly dispersed why PC and PQ must be mobile
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Physical organization of Z-scheme
Complexes are arranged asymmetrically! PSII is in appressed regions of grana PSI and ATP synthase in exposed regions cytochrome b6/f, PC and PQ are evenly dispersed why PC and PQ must be mobile why membrane must be very fluid
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PSII Photochemistry 1) LHCII absorbs a photon 2) energy is transferred to P680
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PSII Photochemistry 3) P680* reduces pheophytin ( chl a with 2 H+ instead of Mg2+) = primary electron acceptor
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PSII Photochemistry 3) P680* reduces pheophytin ( chl a with 2 H+ instead of Mg2+) = primary electron acceptor charge separation traps the electron
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PSII Photochemistry 4) pheophytin reduces PQA (plastoquinone bound to D2) moves electron away from P680+ & closer to stroma
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PSII Photochemistry 5) PQA reduces PQB (forms PQB- )
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PSII Photochemistry 6) P680+ acquires another electron , and steps 1-4 are repeated
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PSII Photochemistry 7) PQA reduces PQB - -> forms PQB2-
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PSII Photochemistry 8) PQB2- acquires 2 H+ from stroma forms PQH2 (and adds to ∆pH)
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PSII Photochemistry 9) PQH2 diffuses within bilayer to cyt b6/f - is replaced within D1 by an oxidized PQ
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Photolysis: Making Oxygen
1) P680+ oxidizes tyrZ ( an amino acid of protein D1)
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Photolysis: Making Oxygen
2) tyrZ + oxidizes one of the Mn atoms in the OEC Mn cluster is an e- reservoir
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Photolysis: Making Oxygen
2) tyrZ + oxidizes one of the Mn atoms in the OEC Mn cluster is an e- reservoir Once 4 Mn are oxidized replace e- by stealing them from 2 H2O
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Shown experimentally that need 4 flashes/O2
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Shown experimentally that need 4 flashes/O2
Mn cluster cycles S0 -> S4 Reset to S0 by taking 4 e- from 2 H2O
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Electron transport from PSII to PSI
1) PQH2 diffuses to cyt b6/f 2) PQH2 reduces cyt b6 and Fe/S, releases H+ in lumen since H+ came from stroma, transports 2 H+ across membrane (Q cycle)
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Electron transport from PSII to PSI
3) Fe/S reduces plastocyanin via cyt f cyt b6 reduces PQ to form PQ-
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Electron transport from PSII to PSI
4) repeat process, Fe/S reduces plastocyanin via cyt f cyt b6 reduces PQ- to form PQH2
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Electron transport from PSII to PSI
4) PC (Cu+) diffuses to PSI, where it reduces an oxidized P700
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Electron transport from PSI to Ferredoxin
1) LHCI absorbs a photon 2) P700* reduces A 3) e- transport to ferredoxin via A0, A1 & 3 Fe/S proteins
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Electron transport from Ferredoxin to NADP+
2 Ferredoxin reduces NADP reductase
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Electron transport from Ferredoxin to NADP+
2 Ferredoxin reduces NADP reductase reduces NADP+
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Electron transport from Ferredoxin to NADP+
2 Ferredoxin reduces NADP reductase reduces NADP+ this also contributes to ∆pH
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Overall reaction for the Z-scheme
8 photons + 2 H2O + 10 H+stroma + 2 NADP+ = 12 H+lumen + 2 NADPH + O2
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Chemiosmotic ATP synthesis
PMF mainly due to ∆pH is used to make ATP
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Chemiosmotic ATP synthesis
PMF mainly due to ∆pH is used to make ATP -> very little membrane potential, due to transport of other ions
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Chemiosmotic ATP synthesis
PMF mainly due to ∆pH is used to make ATP -> very little membrane potential, due to transport of other ions thylakoid lumen pH is < 5 cf stroma pH is 8
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Chemiosmotic ATP synthesis
PMF mainly due to ∆pH is used to make ATP -> very little membrane potential, due to transport of other ions thylakoid lumen pH is < 5 cf stroma pH is 8 pH is made by ETS, cyclic photophosphorylation,water splitting & NADPH synth
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Chemiosmotic ATP synthesis
Structure of ATP synthase CF1 head: exposed to stroma CF0 base: Integral membrane protein
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a & b2 subunits form stator that immobilizes a & b F1 subunits
a is also an H+ channel c subunits rotate as H+ pass through g & e also rotate c, g & e form a rotor
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Binding Change mechanism of ATP synthesis
H+ translocation through ATP synthase alters affinity of active site for ATP
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Binding Change mechanism of ATP synthesis
H+ translocation through ATP synthase alters affinity of active site for ATP ADP + Pi bind to subunit then spontaneously form ATP
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Binding Change mechanism of ATP synthesis
H+ translocation through ATP synthase alters affinity of active site for ATP ADP + Pi bind to subunit then spontaneously form ATP ∆G for ADP + Pi = ATP is ~0 role of H+ translocation is to force enzyme to release ATP!
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Binding Change mechanism of ATP synthesis
1) H+ translocation alters affinity of active site for ATP 2) Each active site ratchets through 3 conformations that have different affinities for ATP, ADP & Pi due to interaction with the subunit
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Binding Change mechanism of ATP synthesis
1) H+ translocation alters affinity of active site for ATP 2) Each active site ratchets through 3 conformations that have different affinities for ATP, ADP & Pi 3) ATP is synthesized by rotational catalysis g subunit rotates as H+ pass through Fo, forces each active site to sequentially adopt the 3 conformations
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Evidence supporting chemiosmosis
1) ionophores (uncouplers) 2) can synthesize ATP if create ∆pH a) Jagendorf expt: soak cp in pH 4 in dark, make ATP when transfer to pH 8
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Evidence supporting chemiosmosis
Racker & Stoeckenius (1974) reconstituted bacteriorhodopsin and ATP synthase in liposomes Bacteriorhodopsin uses light to pump H+ make ATP only in the light
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Evidence supporting “rotational catalysis”
Sambongi et al experiment a) reconstituted ATPase & attached a subunits to a slide b) attached actin filament to c subunit & watched it spin
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Regulating Light reactions
Regulate partitioning of light energy between PSI and PSII by phosphorylating LHCII complex ordinarily is associated with PSII.
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Regulating Light reactions
Regulate partitioning of light energy between PSI and PSII by phosphorylating LHCII complex ordinarily is associated with PSII. if PSI falls behind PSII LHCII is kinased
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Regulating Light reactions
if PSI falls behind PSII LHCII is phosphorylated increased negative charge forces it out of appressed stacks
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Regulating Light reactions
if PSI falls behind PSII LHCII is phosphorylated increased negative charge forces it out of appressed stacks it then associates with PSI & boosts PSI cyclic activity
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Regulating Light reactions
if PSI falls behind PSII LHCII is phosphorylated increased negative charge forces it out of appressed stacks it then associates with PSI & boosts PSI cyclic activity sensor is PQ: when highly reduced it indirectly activates a protein kinase that kinases LHCII
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Regulating Light reactions
sensor is PQ: when highly reduced it indirectly activates a protein kinase that kinases LHCII elevated PQH2 means PSI is falling behind
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Regulating Light reactions
sensor is PQ: when highly reduced it indirectly activates a protein kinase that kinases LHCII elevated PQH2 means PSI is falling behind Allows plants to adjust relative ATP & NADPH syn
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Regulating ATP synthase
in dark, ATP synthase could run backwards and consume ATP to make a PMF
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Regulating ATP synthase
in dark, ATP synthase could run backwards and consume ATP to make a PMF 2 mechanisms prevent this 1) ATP synthase needs a pH gradient to be active
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Regulating ATP synthase
in dark, ATP synthase could run backwards and consume ATP to make a PMF 2 mechanisms prevent this 1) ATP synthase needs a pH gradient to be active 2) ATP synthase must be reduced by ferredoxin (via thioredoxin) to be active becomes oxidized (therefore inactive) in the dark
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