1Nadine Schubert

Instituto de Ciencias del Mar y Limnología de la UNAM Unidad de Sistemas Arrecifales, Puerto Morelos, México

PHOTOBIOLOGY PHOTOBIOLOGY

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WHAT DOES PHOTOBIOLOGY MEAN?

Photosynthesis Photomorphogenesis Cirvadian Rhythm Ultraviolet Radiation

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PHOTOBIOLOGY PHOTOBIOLOGY

Part 1: Photosynthesis and FluorescencePart 1: Photosynthesis and Fluorescence

Part 2: Photoacclimation/-adaptationPart 2: Photoacclimation/-adaptation

Part 3: PhotoprotectionPart 3: Photoprotection

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Part 1:Part 1: Photosynthesis and Fluorescence Photosynthesis and Fluorescence

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PHOTOSYNTHESIS

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LIGHT ABSORPTIONLIGHT ABSORPTION

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THE PHOTOSYNTHETIC APPARATUSTHE PHOTOSYNTHETIC APPARATUS

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THE PHOTOSYNTHETIC APPARATUSTHE PHOTOSYNTHETIC APPARATUS

PSIILHCII Cyt bf PSI LHCIATPase

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LIGHT ABSORPTION

Photochemistry

Antenna pigments

PS II

Photochemistry

Antenna pigments

PS II

The absorbed light energy is

funneled by excitation transfer

into the RC’s, where energy

conversion by charge

separation takes place.

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excited state

ground state

molecule absorbs photon

photon

Incr

easi

ng e

nerg

y

LIGHT ABSORPTIONLIGHT ABSORPTION

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EXCITATION ENERGY TRANSFER

Light

Reaction Center

Antenna

Excitation transfer Electron transfer

Donor

Acceptor

e-

e-

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PSIILHCII Cyt bf PSI LHCI

2H2O O2+ 4H+

2H+

PQ

PQH2

2H+

PC

FdNADP + H+ NADPH

H+

ATPase

ADP + Pi ATP

ELECTRON TRANSFER

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LIGHT ABSORPTION AND ENERGY TRANSFER

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PHOTOSYNTHESIS AND FLUORESCENCE

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excited state

ground state

molecule absorbs photon

photonexcited state

ground state

Photochemistry

Fluorescence

Heat

PHOTOSYNTHESIS AND FLUORESCENCE

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Heat Fluorescence

Photochemistry

Antenna pigments

PS II

PHOTOSYNTHESIS AND FLUORESCENCE

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Heat Fluorescence

Photochemistry

Antenna pigments

PS II

Non-light -tress conditions

PHOTOSYNTHESIS AND FLUORESCENCE

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Whitmarsh & Govindjee (2002)

Photochemistry = 1Fluorescence = 0

Photochemistry = 0Fluorescence = 1

PHOTOSYNTHESIS AND FLUORESCENCE

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PS = 0NPQ = 0

PS = 1NPQ = 0

CHLOROPHYLL FLUORESCENCE MEASUREMENT

Fv/Fm = (Fm-Fo)/Fm

Fm = maximum fluorescence (RC’s closed)Fo = minimum fluorescence (RC’s open)

(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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Chondrus crispus

Hanelt et al. (1992)

Fv/Fm – Diurnal and spatial variation

Dep

th (m

)

Macrocystis pyrifera

Colombo-Pallotta (2007)

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Littoral

Littoral

Sublittoral

SublittoralSublittoral

Sublittoral

van de Poll et al. (2001)

Fv/Fm – Comparison of stress responses between species

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1 PS 01 NPQ 0

CHLOROPHYLL FLUORESCENCE MEASUREMENT

Fv/Fm F/Fm’PS = 01 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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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).

ELECTRON-TRANSPORT RATE (ETR)– CURVES

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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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Macrocystis pyrifera

Colombo-Pallotta et al. (2006)

ETR– CURVES AS AN ANALOGUE TO P-E- CURVES

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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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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

FLUOROMETERS

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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)

Pulse-Amplitude-Modulated Fluorometers

Distinguish between fluorescence and ambient light

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Pulse-Amplitude-Modulated Fluorometers

MINI-PAM

DUAL-PAM

IMAGE-PAM

DIVING-PAM XE-PAM