PHOTOBIOLOGY
Nadine Schubert
Instituto de Ciencias del Mar y Limnología de la UNAM
Unidad de Sistemas Arrecifales, Puerto Morelos, México
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WHAT DOES PHOTOBIOLOGY MEAN?
Photosynthesis
Photomorphogenesis
Cirvadian Rhythm
Ultraviolet Radiation
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PHOTOBIOLOGY
Part 1: Photosynthesis and Fluorescence
Part 2: Photoacclimation/-adaptation
Part 3: Photoprotection
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Part 1:
Photosynthesis and Fluorescence
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PHOTOSYNTHESIS
5
LIGHT ABSORPTION
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THE PHOTOSYNTHETIC APPARATUS
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THE PHOTOSYNTHETIC APPARATUS
ATPase
LHCII
PSII
Cyt bf
PSI
LHCI
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LIGHT ABSORPTION
The absorbed light energy is
funneled by excitation transfer
into the RC’s, where energy
Antenna
Antenna
pigments
pigments
conversion by charge
separation takes place.
PSPS
II II
Photochemistry
Photochemistry
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LIGHT ABSORPTION
photon
molecule
absorbs
photon
ground
state
Increasing energy
excited
state
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EXCITATION ENERGY TRANSFER
Excitation transfer
Electron transfer
Acceptor
Light
e-
Reaction
Center
eDonor
Antenna
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ELECTRON TRANSFER
ATP
ADP + Pi
NADP + H+
2H+
NADPH
Fd
ATPase
PQH2
LHCII
PSII
Cyt bf
PSI
LHCI
PQ
2H2O
O2+ 4H+
PC
2H+
H+
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LIGHT ABSORPTION AND ENERGY TRANSFER
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PHOTOSYNTHESIS AND FLUORESCENCE
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PHOTOSYNTHESIS AND FLUORESCENCE
photon
excited
state
molecule
absorbs
photon
excited
state
Photochemistry
Fluorescence
Heat
ground
state
ground
state
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PHOTOSYNTHESIS AND FLUORESCENCE
Antenna pigments
Heat
Fluorescence
PS II
Photochemistry
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PHOTOSYNTHESIS AND FLUORESCENCE
Antenna pigments
Non-light -tress
conditions
Heat
Fluorescence
PS II
Photochemistry
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PHOTOSYNTHESIS AND FLUORESCENCE
Photochemistry = 1
Fluorescence = 0
Photochemistry = 0
Fluorescence = 1
Whitmarsh & Govindjee (2002)
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CHLOROPHYLL FLUORESCENCE MEASUREMENT
PS = 0
NPQ = 0
Fv/Fm = (Fm-Fo)/Fm
Fm = maximum fluorescence (RC’s closed)
Fo = minimum fluorescence (RC’s open)
PS = 1
NPQ = 0
(higher plants – 0.85, macroalgae usually lower)
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Fv/Fm – MAXIMUM QUANTUM YIELD
Quantum yield: Probability that the energy of a photon
absorbed will be used for photosynthesis (i.e. enters in the
e- - transport chain)

Indicator of photosynthetic efficiency
Maximum quantum yield: requires complete relaxation of the
competing mechanisms with the photochemical energy conversion
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Fv/Fm – Diurnal and spatial variation
Depth (m)
Chondrus crispus
Macrocystis pyrifera
Colombo-Pallotta (2007)
Hanelt et al. (1992)
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Fv/Fm – Comparison of stress responses between species
Littoral
Sublittoral
Littoral
Sublittoral
Sublittoral
Sublittoral
van de Poll et al. (2001)
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CHLOROPHYLL FLUORESCENCE MEASUREMENT
Fv/Fm
PS = 0
1  NPQ  0
F/Fm’
1  PS  0
1  NPQ  0
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F/Fm’ – EFFECTIVE QUANTUM YIELD
Used to describe the variation in the photochemical
efficiency of PSII under illuminated conditions.
Measurement of this parameter at certain irradiance
value.

Indicator of the ability of an organism to move electrons
beyond PSII (ETR)
F/Fm’ = (Fm’-F)/Fm’
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ELECTRON-TRANSPORT RATE (ETR)– CURVES
ETR = Irradiance  F/Fm’  0,5  Absorptance (Genty et al. 1989)
F/Fm’ = effective quantum yield (under light)
0,5 = Assumption that 50% of these quanta are absorbed by PSII
Absorptance = fraction of incident light that is absorbed by the photosynthetic tissue. Not the
same as absorbance (quantifies how much of the incident light is absorbed by an object).
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ELECTRON-TRANSPORT RATE (ETR)– CURVES
ETR = Irradiance  F/Fm’  0,5  Absorptance
Relative ETR = Irradiance  F/Fm’  0,5 (Ralph et al. 2002)
-ETR: when absorption characteristics change between species, acclimations,
seasons…
- rel. ETR: use only when it is sure that there are no differences in the absorption
characteristics
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ETR– CURVES AS AN ANALOGUE TO P-E- CURVES
Macrocystis pyrifera
Colombo-Pallotta et al. (2006)
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CHLOROPHYLL FLUORESCENCE
EXTENSIVELY USE DUE TO:
• NON-DESTRUCTIVE
• NON-INVASIVE
• RAPID
• SENSITIVE
• IN REAL-TIME
Since 1995 the number of articles published applying
chlorophyll fluorescence on the analysis of the
photosynthetic performance in macroalgae and seagrasses
has increased more than five times.
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FLUOROMETERS
The Chl fluorometer should be capable of measuring the fluorescence yield in
a non-intrusive way:
 very low measuring light (i.e. exciting light) intensity for assessment of the
fluorescence yield of a dark-adapted sample
 the detection system has to be very selective to distinguish between
fluorescence excited by the measuring light and the much stronger signals
caused by ambient and actinic light (full sun light, saturating light pulses for
assessment of maximum fluorescence)
 fast time response to resolve the rapid changes in fluorescence yield upon
dark-light and light-dark transitions
PAM fluorometers: Pulse-Amplitude-Modulated fluorometers
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Pulse-Amplitude-Modulated Fluorometers
Distinguish between fluorescence and ambient light
 Allows measurement of fluorescence in the presence of actinic
light (light absorbed by the photosynthetic apparatus to drive
photosynthesis)
How? – Measuring light is modulated and the fluorescence
amplifier is highly selective for the modulated signal (yield of
chlorophyll fluorescence)
- pulse-modulated measuring light can be generated either by a
light-emitting diode (LED; most PAM fluorometers) or a flash
discharge lamp (i.e. XE-PAM)
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Pulse-Amplitude-Modulated Fluorometers
DUAL-PAM
IMAGE-PAM
MINI-PAM
DIVING-PAM
XE-PAM
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