Transcript differences in photosynthesis

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
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ACCLIMATION versus ADAPTATION
Acclimation
Adaptation
Allen (1998)
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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..
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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)
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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)
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PHOTOACCLIMATION
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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
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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
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Ek1
Ek2
Photosynthesis
DIFFERENCES IN PHOTOSYNTHESIS
Irradiance
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Ek1
Ek2
Photosynthesis
DIFFERENCES IN PHOTOSYNTHESIS
Irradiance
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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
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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
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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
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LIGHT ACCLIMATION – Ecklonia kelp bed
Toohey et al. (2004)
Rhodymenia sonderi
Pterocladia lucida
Changes in photosynthesis between underneath
(shaded) and outside (unshaded) an Ecklonia
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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)
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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)
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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
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13
14
15
15
16
16
17
17
18
18
sun
19
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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)
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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+
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