1Nadine SchubertInstituto de Ciencias del Mar y Limnología de la UNAM Unidad de Sistemas Arrecifales, Puerto Morelos, México

Part 2:Part 2: Photoacclimation and -adaptation Photoacclimation and -adaptation

PHOTOBIOLOGY PHOTOBIOLOGY

2

ACCLIMATION versus ADAPTATION

Allen (1998)

Acclimation

Adaptation

3

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..

4

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)

PHOTOACCLIMATION (at organismal level)

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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)

6

PHOTOACCLIMATION

7

PHOTOSYNTHESIS vs. LIGHT-CURVE (P-E curve)

E

P

Chl a g DW

Oxygen evolutionCarbon fixation

II III

I- Light-limited regionII- Light-saturated regionIII- Photoinhibition

Ec Ek

Pmax

RD

I

Area

8

Irradiance

Ph

oto

syn

the

sis

High-light acclimation

antenna pigments

PSII

carotenoids

e--transport components

and Rubisco

Pmax

DIFFERENCES IN PHOTOSYNTHESIS

Low-light acclimation

antenna pigments

PSII

9

Irradiance

Ph

oto

syn

the

sis

Ek1

Ek2

DIFFERENCES IN PHOTOSYNTHESIS

10

Irradiance

Ph

oto

syn

the

sis

Ek1

Ek2

DIFFERENCES IN PHOTOSYNTHESIS

11

Sagert et al. (1997)

Chondrus crispus

3.5m depth 8.5m depth

Open symbols : diurnal cycle

Closed symbols : recovery after 2h and 6.5h of light stress

DIFFERENT SUSCEPTIBILITY TO LIGHT STRESS

12Rodrigues et al. (2000)

Laminaria digitata (intertidal)

Laminaria abyssalis (60m)

DIFFERENT SUSCEPTIBILITY TO LIGHT STRESS

Data from Rodrigues et al. (2002)

L. digitata L. abyssalis

Xan

thop

hyll

cycl

e pi

gmen

ts (

% o

f to

tal p

igm

ents

)

0

2

4

6

8

10

Photoprotective pigment pool

13X Data

PHOTOACCLIMATIVE CAPACITY

Irradiance

Ph

oto

syn

the

sis

The higher the photosynthetic plasticity (acclimative capacity) of an organisms the higher its distribution range.

Low light condition

High light condition

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LIGHT ACCLIMATION – Ecklonia kelp bed

Ecklonia radiata

Pterocladia lucida

Rhodymenia sonderi

Acclimation to changes in light intensity depending on kelp density

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Pterocladia lucida

Rhodymenia sonderi

LIGHT ACCLIMATION – Ecklonia kelp bed

Changes in absorption between underneath (shaded) and outside

(unshaded) an Ecklonia kelp canopy

Toohey et al. (2004)

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Toohey et al. (2004)

Pterocladia lucida

Rhodymenia sonderi

LIGHT ACCLIMATION – Ecklonia kelp bed

Changes in photosynthesis between underneath (shaded) and outside (unshaded) an Ecklonia

kelp canopy

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100% incident light

1% incident light(13m, Dean 1985)

DIFFERENCES IN LIGHT ACCLIMATION (INTRASPECIFIC)

M. pyrifera

Wavelength (nm)

Re

lativ

e A

bso

rba

nce

Data from Colombo-Pallotta (2007)

Differences in absorption

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Pigment concentration ( of canopy value)

0 50 100 150 200 250

De

pth

(m

)

0

5

10

15

20

Chl a+cFucoxanthinZeaxanthin

100% incident light

1% incident light(13m, Dean 1985)

DIFFERENCES IN LIGHT ACCLIMATION (INTRASPECIFIC)

M. pyrifera

Data from Colombo-Pallotta (2007)

Differences in pigment concentration

sun

shade

Ant

enna

pig

men

t con

cent

ratio

n

Photoprotective pigm

ents

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Gros Photosynthesis (mol O2 m-2 s-1)

12 13 14 15 16 17 18 19

Dep

th (

m)

0

5

10

15

20

Data from Colombo-Pallotta (2007)

Gros Photosynthesis (mol O2 m-2 s-1)

12 13 14 15 16 17 18 19

Dep

th (

m)

0

5

10

15

20

NPQ

0 2 4 6 8 10

100% incident light

1% incident light(13m, Dean 1985)

DIFFERENCES IN LIGHT ACCLIMATION (INTRASPECIFIC)

M. pyriferasun

shade

Pho

tosy

nthe

tic c

apac

ity

Photoprotection

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Chromatic Adaptation

550-630nm 495-570nm

Adjustment of antenna pigment composition to light quality

ACCLIMATION TO LIGHT QUALITY

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PSIILHCII Cyt bf PSI LHCI

2H2O O2+ 4H+

2H+

PQ

PQH2

2H+

PC

Fd

NADP + H+ NADPH

H+

ATPase

ADP + Pi ATP

WHAT ABOUT OTHER STRESS FACTORS?

It’s not what you get it’s what you feel!