1 Nadine Schubert Instituto de Ciencias del Mar y Limnología de la UNAM Unidad de Sistemas Arrecifales, Puerto Morelos, México Part 2: Photoacclimation and -adaptation 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)

5 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 ag DW Oxygen evolution Carbon fixation IIIII I- Light-limited region II- Light-saturated region III- Photoinhibition  EcEc EkEk P max RDRD I Area

8 Irradiance Photosynthesis High-light acclimation   antenna pigments    PSII    carotenoids    e - -transport components and Rubisco      P max DIFFERENCES IN PHOTOSYNTHESIS Low-light acclimation   antenna pigments    PSII    

9 Irradiance Photosynthesis E k1 E k2 DIFFERENCES IN PHOTOSYNTHESIS

10 Irradiance Photosynthesis E k1 E k2 DIFFERENCES IN PHOTOSYNTHESIS

11 Sagert et al. (1997) Chondrus crispus 3.5m depth8.5m depth Open symbols : diurnal cycle Closed symbols : recovery after 2h and 6.5h of light stress DIFFERENT SUSCEPTIBILITY TO LIGHT STRESS

12 Rodrigues et al. (2000) Laminaria digitata (intertidal) Laminaria abyssalis (60m) DIFFERENT SUSCEPTIBILITY TO LIGHT STRESS Data from Rodrigues et al. (2002) Photoprotective pigment pool

13 X Data PHOTOACCLIMATIVE CAPACITY Irradiance Photosynthesis The higher the photosynthetic plasticity (acclimative capacity) of an organisms the higher its distribution range. Low light condition High light condition

14 LIGHT ACCLIMATION – Ecklonia kelp bed Ecklonia radiata Pterocladia lucida Rhodymenia sonderi Acclimation to changes in light intensity depending on kelp density

15 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)

16 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

17 100% incident light 1% incident light (13m, Dean 1985) DIFFERENCES IN LIGHT ACCLIMATION (INTRASPECIFIC) M. pyrifera Wavelength (nm)Relative Absorbance Data from Colombo-Pallotta (2007) Differences in absorption

18 100% 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 Antenna pigment concentration Photoprotective pigments

19 Data from Colombo-Pallotta (2007) 100% incident light 1% incident light (13m, Dean 1985) DIFFERENCES IN LIGHT ACCLIMATION (INTRASPECIFIC) M. pyrifera sun shade Photosynthetic capacity Photoprotection

20 Chromatic Adaptation nm nm Adjustment of antenna pigment composition to light quality ACCLIMATION TO LIGHT QUALITY

21 PSII LHCII Cyt bfPSILHCI 2H 2 OO 2 + 4H + 2H + PQ PQH 2 2H + PC Fd NADP + H + NADPH H+H+ ATPase ADP + Pi ATP WHAT ABOUT OTHER STRESS FACTORS? It’s not what you get it’s what you feel!