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Coral bleaching and thermal stress: The first step is not damage to Photosystem II. Ove Hoegh-Guldberg School of Biological Sciences University of Sydney. Outline. Elevated temperature and coral-dinoflagellate symbioses. - PowerPoint PPT Presentation
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Coral bleaching and thermal Coral bleaching and thermal stress: The first step is not stress: The first step is not damage to Photosystem II.damage to Photosystem II.
Ove Hoegh-GuldbergOve Hoegh-Guldberg
School of Biological SciencesSchool of Biological Sciences
University of SydneyUniversity of Sydney
OutlineOutlineElevated temperature and Elevated temperature and
coral-dinoflagellate symbioses.coral-dinoflagellate symbioses.
Light, photoinhibition and photoprotectionLight, photoinhibition and photoprotection
Primary effects of temperature: A modelPrimary effects of temperature: A model
Take home message: Take home message: Bleaching is due to a lowering Bleaching is due to a lowering of the threshold for photoinhibition.of the threshold for photoinhibition.
Stylophora pistillataStylophora pistillata
Seriatopora hystrixSeriatopora hystrix
Hoegh-Guldberg and Smith (1989)Hoegh-Guldberg and Smith (1989)
Hoegh-Guldberg and Smith (1989)Hoegh-Guldberg and Smith (1989)
S. pistillata S. hystrix S. pistillata S. hystrix
Photosynthetic ratePhotosynthetic rate Respiratory rateRespiratory rate
Hoegh-Guldberg and Smith (1989)Hoegh-Guldberg and Smith (1989)
OutlineOutlineElevated temperature and Elevated temperature and
coral-dinoflagellate symbioses.coral-dinoflagellate symbioses.
Light, photoinhibition and photoprotectionLight, photoinhibition and photoprotection
Primary effects of temperature: A modelPrimary effects of temperature: A model
Take home message: Take home message: Bleaching is due to a lowering Bleaching is due to a lowering of the threshold for photoinhibition.of the threshold for photoinhibition.
Classic photoinhibition.Classic photoinhibition.Classic photoinhibition.Classic photoinhibition.
-40
-20
0
20
40
60
80
100
0 500 1000 1500 2000 2500
PhotoinhibitionPhotoinhibition
IrradianceIrradianceNet
Pho
tosy
nthe
t ic R
ate
Net
Pho
tosy
nthe
t ic R
ate
Rub
isco
Rub
isco
LHC LHC
Higher Plants: Low light and Normal COHigher Plants: Low light and Normal CO2 2 Fixation Fixation
e-
PSII
PSI COCO22
H+
HH++
POOLPOOL
Organic COrganic C(Dark Reactions)(Dark Reactions)
StromaStromaLumenLumen
OO22
HH22OO
NADPNADP
NADPHNADPH + ATP+ ATP
ATPATPATPATP
ADPADPADPADP
DARK REACTIONSDARK REACTIONSDARK REACTIONSDARK REACTIONS
Thylakoid membraneThylakoid membraneThylakoid membraneThylakoid membrane
LHC LHC PSII
PSI
HH++
POOLPOOL
DVE
ZeaxanthinZeaxanthin
NPQ
ViolaxanthinViolaxanthin
OO22
HH22OOStimulatedStimulatedas as pH builds pH builds due to due to reduction of Oreduction of O22
OO22
OO2 2 --
Mehler
H+
e-
Violaxanthin and Zeaxanthin are higher Violaxanthin and Zeaxanthin are higher plant xanthophylls. In dinoflagellates, plant xanthophylls. In dinoflagellates, monoepoxide diadinoxanthin and monoepoxide diadinoxanthin and diatoxanthin probably perform thediatoxanthin probably perform thesame roles.same roles.
Violaxanthin and Zeaxanthin are higher Violaxanthin and Zeaxanthin are higher plant xanthophylls. In dinoflagellates, plant xanthophylls. In dinoflagellates, monoepoxide diadinoxanthin and monoepoxide diadinoxanthin and diatoxanthin probably perform thediatoxanthin probably perform thesame roles.same roles.
NADPNADP
NADPHNADPH
Photoprotection Photoprotection against the effects against the effects of high irradiance.of high irradiance.
Photoprotection Photoprotection against the effects against the effects of high irradiance.of high irradiance.
SOD
SOD
APO
APO
HH22OO22
HH22O + OO + O22+ MDA+ MDA
Rub
isco
Rub
isco
LHCLHC
Higher Plants: High light and photo-oxidation Higher Plants: High light and photo-oxidation
e-
PSII
PSI COCO22
H+
HH++
POOLPOOL
Organic COrganic C(Dark Reactions)(Dark Reactions)
StromaStromaLumenLumen
OO22
HH22OO
NADPNADP
NADPHNADPH + ATP+ ATP
OO22
OO2 2 --
Mehler
Active oxygenActive oxygenActive oxygenActive oxygen
Mehler Reaction:Mehler Reaction:Electrons donated Electrons donated from near PS I to from near PS I to oxygen => superoxide.oxygen => superoxide.
Chronic photoinhibitionChronic photoinhibitionChronic photoinhibitionChronic photoinhibition
Singlet oxygen Singlet oxygen originating from originating from electron donation at electron donation at or near PS IIor near PS II
Fo
qP
qN
Ft
FV’/FM
Time (min)
Pulsed Amplitude Modulated (PAM) Pulsed Amplitude Modulated (PAM) fluorescence analysisfluorescence analysisPulsed Amplitude Modulated (PAM) Pulsed Amplitude Modulated (PAM) fluorescence analysisfluorescence analysis
Pulsed amplitude modulated Pulsed amplitude modulated (PAM) Fluorometry(PAM) FluorometryPulsed amplitude modulated Pulsed amplitude modulated (PAM) Fluorometry(PAM) Fluorometry
Chl Chl aa (PSII) (PSII)Chl Chl aa (PSII) (PSII)
LHC LHC PSII
PSI
HH++
POOLPOOL
DVE
ZeaxanthinZeaxanthin
NPQ
ViolaxanthinViolaxanthin
OO22
HH22OOStimulatedStimulatedas as pH builds pH builds due to due to reduction of Oreduction of O22
OO22
OO2 2 --
Mehler
H+
e-
NADPNADP
NADPHNADPH
PAM Fluorometer PAM Fluorometer measures efficiency measures efficiency of light utilisation of of light utilisation of Photosystem II Photosystem II
PAM Fluorometer PAM Fluorometer measures efficiency measures efficiency of light utilisation of of light utilisation of Photosystem II Photosystem II
SOD
SOD
APO
APO
HH22OO22
HH22O + OO + O22+ MDA+ MDA
PSII
NPQ - heat
Phot
osyn
th
Photochemistry versus heatPhotochemistry versus heat
Fo
qP
qN
Ft
FV’/FM
Porites cylindrica (June 1997)Porites cylindrica (June 1997)
DarkDark 800 umol m-2 s-1800 umol m-2 s-1
11 22 33 44
Yield versus time of day
0.400
0.450
0.500
0.550
0.600
0.650
0.700
0.750
0.800
0 5 10 15 20 25
Time
Yie
ld
Pink Sp
Brow n Sp
PoritesSunriseSunrise SunsetSunset
YesYes
Yield versus time of day
0.400
0.500
0.600
0.700
0.800
0 20 40 60 80
Time
Yie
ldPink Sp
Brow n Sp
Porites
Dynamic PhotoinhibitionDynamic Photoinhibition
OutlineOutlineElevated temperature and Elevated temperature and
coral-dinoflagellate symbioses.coral-dinoflagellate symbioses.
Light, photoinhibition and photoprotectionLight, photoinhibition and photoprotection
Primary effects of temperature: A modelPrimary effects of temperature: A model
Take home message: Take home message: Bleaching is due to a lowering Bleaching is due to a lowering of the threshold for photoinhibition.of the threshold for photoinhibition.
Stylophora pistillataStylophora pistillataOne Tree IslandOne Tree IslandFeb ‘97Feb ‘97
Stylophora pistillataStylophora pistillataOne Tree IslandOne Tree IslandFeb ‘97Feb ‘97Normal Normal Normal Normal Normal (28Normal (28ooC)C)Normal (28Normal (28ooC)C)
Electron flow in heat stressed zooxanthellae is oxygen dependent(I.e. MP pathway)
Electron flow in heat stressed zooxanthellae is oxygen dependent(I.e. MP pathway)
Calvin cycle doesn’t turn on. qN has to continuedumping heat.
Calvin cycle doesn’t turn on. qN has to continuedumping heat.Heat stressed Heat stressed
(32(32ooC, 4 h)C, 4 h)measured in measured in presence presence of oxygen.of oxygen.
Heat stressed Heat stressed (32(32ooC, 4 h)C, 4 h)measured in measured in presence presence of oxygen.of oxygen.
Heat stressed Heat stressed (32(32ooC, 4 h)C, 4 h)measured in measured in absence absence of oxygen.of oxygen.
Heat stressed Heat stressed (32(32ooC, 4 h)C, 4 h)measured in measured in absence absence of oxygen.of oxygen.
Effects of heat on zooxanthellae:Effects of heat on zooxanthellae:
• Primary effectPrimary effect is to stall the flow of electrons to is to stall the flow of electrons to dark reactions of photosynthesis. The first step is dark reactions of photosynthesis. The first step is not to disrupt the light harvesting reactions as not to disrupt the light harvesting reactions as previously thought.previously thought.
• PhotoprotectionPhotoprotection is induced as dark reactions fail is induced as dark reactions fail through oxygen dependent electron flow (Mehler through oxygen dependent electron flow (Mehler Reactions). Reactions).
Rub
isco
Rub
isco
LHCLHC
Zooxanthellae: High light and Normal COZooxanthellae: High light and Normal CO2 2 Fixation Fixation
e-
PSII
PSI COCO22
H+
HH++
POOLPOOL
Organic COrganic C(Dark Reactions)(Dark Reactions)
Ascorbate Ascorbate PoolPool
DVE
DiatoxanthinDiatoxanthin
NPQ
StromaStromaLumenLumen
SOD = Superoxide dismutaseSOD = Superoxide dismutaseAPO = Ascorbate peroxidaseAPO = Ascorbate peroxidaseDVE = Violaxanthin deepoxidase DVE = Violaxanthin deepoxidase
DiadinoxanthinDiadinoxanthin
OO22
HH22OO
NPQ reducesNPQ reduces possibility of possibility of singlet oxygen singlet oxygen formation. formation. Singlet oxygen Singlet oxygen promotes promotes degradation of degradation of D1 protein and D1 protein and damage to reaction damage to reaction centre componentscentre components
StimulatedStimulatedas as pH builds pH builds due to due to reduction of Oreduction of O22
OO22
OO2 2 --
Mehler O2 -
SOD
SOD
APO
APO
HH22OO22 (Stromal SOD and APO not shown)
NADPNADP
NADPHNADPH + ATP+ ATP
HH22O + OO + O22+ MDA+ MDA
Rub
isco
Rub
isco
LHCLHC
New model (step 1): reduced CONew model (step 1): reduced CO2 2 FixationFixation
e-
PSII
PSI CO2
H+
HH++
POOLPOOL
Organic C(Dark Reactions)
Ascorbate Ascorbate PoolPool
DDE
DiatoxanthinDiatoxanthin
NPQ
StromaStromaLumenLumen
DiadinoxanthinDiadinoxanthin
OO22
HH22OO
Capacity of NPQ Capacity of NPQ to quench PS IIto quench PS IIexceeded. exceeded.
StimulatedStimulatedas as pH builds pH builds due to due to reduction of Oreduction of O22
OO22
OO2 2 --
Mehler O2 -
SOD
SOD
APO
APO
HH22OO22 (Stromal SOD and APO not shown)
NADPNADP
NADPHNADPH + ATP+ ATP
HH22O + OO + O22+ MDA+ MDA
O2 -
O2 -
OO2 2 --
1. Calvin cycle begins to fail1. Calvin cycle begins to fail Electron pressure builds.Electron pressure builds.2. NPQ then MP pathways2. NPQ then MP pathways come into play come into play 3. Quantum yield still in 3. Quantum yield still in tact as electrons aretact as electrons are passed to oxygenpassed to oxygen
1. Calvin cycle begins to fail1. Calvin cycle begins to fail Electron pressure builds.Electron pressure builds.2. NPQ then MP pathways2. NPQ then MP pathways come into play come into play 3. Quantum yield still in 3. Quantum yield still in tact as electrons aretact as electrons are passed to oxygenpassed to oxygen
Rub
isco
Rub
isco
LHCLHC
e-
PSII
PSI
H+
HH++
POOLPOOL
Ascorbate Ascorbate PoolPool
DDE
NPQ
StromaStromaLumenLumen
OO22
HH22OO
NPQ reducesNPQ reduces possibility of possibility of singlet oxygen singlet oxygen formation. formation. Singlet oxygen Singlet oxygen promotes promotes degradation of degradation of D1 protein and D1 protein and damage to reaction damage to reaction centre componentscentre components
StimulatedStimulatedas as pH builds pH builds due to due to reduction of Oreduction of O22
OO22
OO2 2 --
Mehler O2 -
SOD
SOD
APO
APO
HH22OO22 (Stromal SOD and APO not shown)
HH22O + OO + O22+ MDA+ MDA
O2 -
OO2 2 --
1O2
OO2 2 --
OO2 2 --
OO2 2 --
OO2 2 --
OO2 2 --
OO2 2 --OO2 2
--
OO2 2 --
OO2 2 --
11OO22
DiatoxanthinDiatoxanthin
DiadinoxanthinDiadinoxanthin
4. MP pathway cannot 4. MP pathway cannot absorb all singlet oxygenabsorb all singlet oxygen5. Singlet oxygen and 5. Singlet oxygen and superoxide builds upsuperoxide builds up and photosystems and and photosystems and general p/syn components general p/syn components are damagedare damaged6. Oxygen evolution reduced6. Oxygen evolution reduced
4. MP pathway cannot 4. MP pathway cannot absorb all singlet oxygenabsorb all singlet oxygen5. Singlet oxygen and 5. Singlet oxygen and superoxide builds upsuperoxide builds up and photosystems and and photosystems and general p/syn components general p/syn components are damagedare damaged6. Oxygen evolution reduced6. Oxygen evolution reduced
New model (step 2): redox buildupNew model (step 2): redox buildup
Rub
isco
Rub
isco
LHCLHC
Zooxanthellae: High light and Normal COZooxanthellae: High light and Normal CO2 2 Fixation Fixation
e-
PSII
PSI COCO22
H+
HH++
POOLPOOL
Organic COrganic C(Dark Reactions)(Dark Reactions)
Ascorbate Ascorbate PoolPool
DVE
DiatoxanthinDiatoxanthin
NPQ
StromaStromaLumenLumen
SOD = Superoxide dismutaseSOD = Superoxide dismutaseAPO = Ascorbate peroxidaseAPO = Ascorbate peroxidaseDVE = Violaxanthin deepoxidase DVE = Violaxanthin deepoxidase
DiadinoxanthinDiadinoxanthin
OO22
HH22OO
NPQ reducesNPQ reduces possibility of possibility of singlet oxygen singlet oxygen formation. formation. Singlet oxygen Singlet oxygen promotes promotes degradation of degradation of D1 protein and D1 protein and damage to reaction damage to reaction centre componentscentre components
StimulatedStimulatedas as pH builds pH builds due to due to reduction of Oreduction of O22
OO22
OO2 2 --
Mehler O2 -
SOD
SOD
APO
APO
HH22OO22 (Stromal SOD and APO not shown)
NADPNADP
NADPHNADPH + ATP+ ATP
HH22O + OO + O22+ MDA+ MDA
0
200
400
600
800
0 50 200 800 1600
PAR (µmol quanta m-2 s-1)
dar
k-ad
apte
d F
v/F
m
Upper surface Lower surface
0
200
400
600
800
0 50 200 800 1600
(a) 28ºC
(b) 33ºC
The interaction of light and temperature may explain some of the differences in bleaching on the upper versus lower surfaces of corals.
The interaction of light and temperature may explain some of the differences in bleaching on the upper versus lower surfaces of corals.
Upper surfaceUpper surface
Lower surfaceLower surfaceLi
ght
Ligh
t
Rub
isco
Rub
isco
LHCLHC
e-
PSII
PSI CO2
H+
HH++
POOLPOOL
Organic C(Dark Reactions)
Ascorbate Ascorbate PoolPool
DDE
DiatoxanthinDiatoxanthin
NPQ
DiadinoxanthinDiadinoxanthin
OO22
HH22OO
OO22
OO2 2 --
Mehler O2 -
SOD
SOD
APO
APO
HH22OO22
NADPNADP
NADPHNADPH + ATP+ ATPO2
-
O2 -
OO2 2 --
XX
OutlineOutlineElevated temperature and Elevated temperature and
coral-dinoflagellate symbioses.coral-dinoflagellate symbioses.
Light, photoinhibition and photoprotectionLight, photoinhibition and photoprotection
Primary effects of temperature: A modelPrimary effects of temperature: A model
Take home message: Take home message: Bleaching is due to a lowering Bleaching is due to a lowering of the threshold for photoinhibition.of the threshold for photoinhibition.