Mechanism of Light Acclimation in
Marine Phytoplankton
Uriel Aparicio
Dr. Allen Milligan
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
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.
Background
Fluor
Absorb Light~Incident
Light
Fluor~Absorbed Light?
NO!
Fluorescence
saturates
Why?
Energy is
being lost to
some other
pathway
Energy Pathways
Photochemistry
Fluorescence
Non-Photochemical
quenching (NPQ)
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
Objective
Test NPQ
response of
phytoplankton
under different
light conditions
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.
Methodology
Methodology
Measure the natural fluorescence
Measure the NPQ
Fluorescence Yield
High acclimated
cells have a
greater
fluorescence yield
than the low
acclimated cells.
NPQ Measurements
(FmFm’)/Fm’
Averaged
the last 4
data
points
Results
Low Light Acclimated NPQ: 0.69
High Light Acclimated NPQ: 0.35
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
Maps derived from
Satellite Data
Acknowledgements
Howard Hughes Medical Institute
NASA
Dr. Allen Milligan
Dr. Michael Behrenfeld
Dr. Kevin Ahern
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
Hypothesis
A. NPQ is perfectly
efficient at dissipating light
energy
B. Fluorescence yield is
dependent on the ratio of
PSII : PSI

iPAR
C. Fluorescence yield is
dependent on the
photoacclimation state