Mechanism of Light Acclimation in Marine Phytoplankton

1. Mechanism of Light Acclimation in Marine Phytoplankton • Uriel Aparicio • Dr. Allen Milligan

2. Relevance • 50% of net photosynthesis of the earth comes from marine phytoplankton. • Primary production is sensitive to climate variability • To understand these changes and to be able to predict future changes we need to understand factors that influences phytoplankton growth. Example: limiting nutrients

3. Background • Fluorescence can be used to indicate physiological status of the phytoplankton. example: high fluorescence=iron limited phytoplankton • In 2002, NASA launched its AQUA satellite with MODIS(MODerate-resolution Imaging Spectroradiometer). • MODIS is an instrument that can measure the fluorescence of marine phytoplankton.

4. Background Fluor

5. Absorb Light~Incident Light • Fluor~Absorbed Light?

6. NO! • Fluorescence saturates

7. Why?

8. Energy is being lost to some other pathway

9. Energy Pathways Photochemistry Fluorescence Non-Photochemical quenching (NPQ)

10. Light availability and nutrient stress can have an effect on the fluorescence through NPQ • Low light acclimated cells have more chlorophyll than high light acclimated cells and therefore absorb more energy. (Greater NPQ) • To detect nutrient stress, fluorescence must be corrected for light dependent NPQ response • So far the corrections to fluorescence data have assumed a single photoacclimation state

11. Objective • Test NPQ response of phytoplankton under different light conditions

12. Hypothesis • Low light acclimated cells will demonstrate a stronger NPQ response than the high light acclimated cell. • Low light acclimated cells have more chlorophyll and therefore absorb more energy when they are at the surface.

13. Methodology

14. Methodology • Measure the natural fluorescence • Measure the NPQ

15. Fluorescence Yield • High acclimated cells have a greater fluorescence yield than the low acclimated cells.

16. NPQ Measurements • (Fm-Fm’)/Fm’ • Averaged the last 4 data points

17. Results • Low Light Acclimated NPQ: 0.69 • High Light Acclimated NPQ: 0.35

18. Prior research has concluded the opposite of our research(Garcia-Mendoza and Colombo-Pallotta 2007; Niyogi et al. 1997a) • These studies (and others) acclimated their organisms to high and low constant light

19. Maps derived from Satellite Data

20. Acknowledgements • Howard Hughes Medical Institute • NASA • Dr. Allen Milligan • Dr. Michael Behrenfeld • Dr. Kevin Ahern

21. Background • Global climate change can change the availability of nutrients that are limiting in the ocean • Previous studies have been done on iron limitation in the ocean but are limited to bottles or iron addition to surface water. • New techniques with satellites can cover the entire ocean by measuring fluorescence of phytoplankton. • The amount of fluorescence emitted indicates the physiological state of the phytoplankton

22. φ iPAR Hypothesis • A. NPQ is perfectly efficient at dissipating light energy • B. Fluorescence yield is dependent on the ratio of PSII : PSI • C. Fluorescence yield is dependent on the photoacclimation state