102
It is not my intent that this report serve as an exhaustive review of application and
interpretation of in vivo fluorescence measurements in phytoplankton studies. Rather, I hope
to present a description of our present knowledge concerning the source of in vivo
fluorescence the physiological processes that regulate the yield of fluorescence, and their
relationship to primary photochemistry, electron transport and the dark reactions of
photosynthesis. At present, most of this knowledge is derived from studies on higher plant
chloroplasts or green algae; the latter only occasionally dominates natural phytoplankton
communities. Very little is known about analogous processes in other algal classes. The level
of this knowledge is not sufficient, even in green algae, to provide the mechanistic description
linking fluorescence with the reactions of photosynthesis. However, this knowledge is
sufficient to demonstrate the complexity of processes contributing to the regulation of
fluorescence yield and the general ties between these processes and the component reactions
of photosynthesis. Most importantly, I hope that this report provides a minimal foundation
for understanding fluorescence measurements and sets some significant goals for future
research in this area.
IN VITRO FLUORESCENCE
When a photosynthetic pigment in its lowest energy (ground) state absorbs a photon of visible
light, the pigment is raised to an electronically excited state. For chI molecules, the major red
(560-680 nm) and blue (400-480 nm) absorptions correspond to transitions from the ground
state to the four lowest energy excited states (Figure 1). Absorption is restricted to photons
whose energy exactly matches the energy difference between the initial (ground) and final
(excited) states
(1)
where h is Planck's constant, c is the speed of light and A is the wavelength of the photon.
It is not my intent that this report serve as an exhaustive review of application and
interpretation of in vivo fluorescence measurements in phytoplankton studies. Rather, I hope
to present a description of our present knowledge concerning the source of in vivo
fluorescence the physiological processes that regulate the yield of fluorescence, and their
relationship to primary photochemistry, electron transport and the dark reactions of
photosynthesis. At present, most of this knowledge is derived from studies on higher plant
chloroplasts or green algae; the latter only occasionally dominates natural phytoplankton
communities. Very little is known about analogous processes in other algal classes. The level
of this knowledge is not sufficient, even in green algae, to provide the mechanistic description
linking fluorescence with the reactions of photosynthesis. However, this knowledge is
sufficient to demonstrate the complexity of processes contributing to the regulation of
fluorescence yield and the general ties between these processes and the component reactions
of photosynthesis. Most importantly, I hope that this report provides a minimal foundation
for understanding fluorescence measurements and sets some significant goals for future
research in this area.
IN VITRO FLUORESCENCE
When a photosynthetic pigment in its lowest energy (ground) state absorbs a photon of visible
light, the pigment is raised to an electronically excited state. For chI molecules, the major red
(560-680 nm) and blue (400-480 nm) absorptions correspond to transitions from the ground
state to the four lowest energy excited states (Figure 1). Absorption is restricted to photons
whose energy exactly matches the energy difference between the initial (ground) and final
(excited) states
(1)
where h is Planck's constant, c is the speed of light and A is the wavelength of the photon.