PHOTOBIOLOGY
Part 2:
Photoacclimation and -adaptation
Nadine Schubert
Instituto de Ciencias del Mar y Limnología de la UNAM
Unidad de Sistemas Arrecifales, Puerto Morelos, México
1
ACCLIMATION versus ADAPTATION
Acclimation
Adaptation
Allen (1998)
2
PHOTOADAPTATION (at population level)
Adaptive responses occur over time scales covering multiple generations
of a population. Evolutionary changes in genotypes may occur (ie. natural
selection) adapting a population to a modified environment. In essence
evolutionary adaptation reflects the close correspondence between
organisms and their environment.
Adaptive responses may involve phenology, growth and development,
morphology, biochemistry etc..
3
PHOTOACCLIMATION (at organismal level)
Balance between energy derived from the light reactions and the amount
of energy used during carbon fixation etc...
 changes in environmental conditions cause an imbalance:
- to maintain constant photosynthetic efficiency under a variety of light
intensities the organisms have to adjust their capacity to harvest
and utilize light

Photoacclimation
(complex light response that changes cellular activities on many time scales)
4
PHOTOACCLIMATION = at the organismal level
Short-term photoacclimation (sec-min): responses to environmental changes that
are easily reversible, involving preexisting components within a biochemical pathway
(e.g. increases in enzyme activity within the Calvin cycle in response to temperature
increase)
Long-term photoacclimation (hours-days):
-changes in enzyme activity/concentration and gene expression (alterations of the
concentration of photosynthetic complexes, changes in antenna composition and
photosystem stoichiometry)
-morphological change (not immediately reversible) that lead to the development of
a visually different phenotype (e.g. larger blades of algae growing in shade)
5
PHOTOACCLIMATION
6
PHOTOSYNTHESIS vs. LIGHT-CURVE (P-E curve)
P
I
II
Pmax
III
Oxygen evolution
Carbon fixation
Chl a
g DW
a
Area
Ec
RD
Ek
E
I- Light-limited region
II- Light-saturated region
III- Photoinhibition
7
DIFFERENCES IN PHOTOSYNTHESIS
High-light acclimation
 antenna pigments
 PSII
a
Photosynthesis
 carotenoids
 e--transport components
 Pmax
and Rubisco
Low-light acclimation
Irradiance
 antenna pigments
 PSII
a
8
Ek1
Ek2
Photosynthesis
DIFFERENCES IN PHOTOSYNTHESIS
Irradiance
9
Ek1
Ek2
Photosynthesis
DIFFERENCES IN PHOTOSYNTHESIS
Irradiance
10
DIFFERENT SUSCEPTIBILITY TO LIGHT STRESS
Chondrus crispus
3.5m depth
8.5m depth
Sagert et al. (1997)
Open symbols : diurnal cycle
Closed symbols : recovery after 2h and 6.5h of light stress
11
DIFFERENT SUSCEPTIBILITY TO LIGHT STRESS
Laminaria digitata (intertidal)
Laminaria abyssalis (60m)
Xanthophyll cycle pigments (% of total pigments)
Photoprotective pigment pool
10
8
6
4
2
0
L. digitata
L. abyssalis
Data from Rodrigues et al. (2002)
Rodrigues et al. (2000)
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PHOTOACCLIMATIVE CAPACITY
The higher the photosynthetic plasticity (acclimative capacity) of an
organisms the higher its distribution range.
Photosynthesis
High light condition
Low light condition
Irradiance
X Data
13
LIGHT ACCLIMATION – Ecklonia kelp bed
Ecklonia radiata
Acclimation to changes in light intensity
depending on kelp density
Rhodymenia sonderi
Pterocladia lucida
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LIGHT ACCLIMATION – Ecklonia kelp bed
Toohey et al. (2004)
Rhodymenia sonderi
Pterocladia lucida
Changes in absorption between
underneath (shaded) and outside
(unshaded) an Ecklonia kelp canopy
15
LIGHT ACCLIMATION – Ecklonia kelp bed
Toohey et al. (2004)
Rhodymenia sonderi
Pterocladia lucida
Changes in photosynthesis between underneath
(shaded) and outside (unshaded) an Ecklonia
16
kelp canopy
DIFFERENCES IN LIGHT ACCLIMATION (INTRASPECIFIC)
100% incident light
M. pyrifera
Relative Absorbance
Differences in absorption
Wavelength (nm)
1% incident light
(13m, Dean 1985)
Data from Colombo-Pallotta (2007)
17
DIFFERENCES IN LIGHT ACCLIMATION (INTRASPECIFIC)
100% incident light
Differences in pigment
concentration
M. pyrifera
sun
0
50
100
150
200
Depth (m)
5
10
15
Chl a+c
Fucoxanthin
Zeaxanthin
Photoprotective pigments
0
250
Antenna pigment concentration
Pigment concentration ( of canopy value)
20
Data from Colombo-Pallotta (2007)
1% incident light
(13m, Dean 1985)
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shade
DIFFERENCES IN LIGHT ACCLIMATION (INTRASPECIFIC)
100% incident light
M. pyrifera
-2 ss-1
-1))
Photosynthesis (mol
(mol O
O22 m
m-2
Gros Photosynthesis
12
13
14
15
15
16
16
17
17
18
18
sun
19
19
Depth (m)
Depth
(m)
5
10
15
Photoprotection
Photosynthetic capacity
0
20
0
2
4
6
8
10
NPQ
1% incident light
(13m, Dean 1985)
19
Data from Colombo-Pallotta (2007)
shade
ACCLIMATION TO LIGHT QUALITY
Chromatic Adaptation
550-630nm
495-570nm
Adjustment of antenna pigment composition to light quality
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WHAT ABOUT OTHER STRESS FACTORS?
ATP
ADP + Pi
NADP + H+
2H+
NADPH
Fd
ATPase
PQH2
LHCII
PSII
Cyt bf
PSI
LHCI
PQ
2H2O
O2+ 4H+
PC
2H+
It’s not what you get it’s what you feel!
H+
21