111
and phycobilins in the green region of the spectrum is central to the success of aquatic algae.
Finally, antenna complexes serve several regulatory functions which optimize the overall
efficiency of photosynthesis under conditions of varying light intensity and spectral quality
(Fork and Satoh, 1986). As we shall see, these regulatory functions can also be detected as
changes in chI fluorescence.
Source olin vivo fluorescence. Equations 2-4 describe the factors that determine the quantum
yield of fluorescence for individual isolated pigments in a dilute solution. Photosynthetic
systems are considerably more complex because of the large and heterogeneous aggregate of
coupled pigments and because of the additional processes that are competing for excitation
energy. However, both the rate constant and lifetime formulations of fluorescence yield can
be useful when appropriately applied to the large antenna systems. A useful starting point is
a comparison of the contributions of PS I and PS II to total fluorescence emission. It has long
been known that nearly all of the room temperature fluorescence from ~-evolving organisms
is derived from PS II pigments. Recent excitation lifetime measurements on PS I and PS II
from green algae and higher plant chloroplasts provide a straightforward explanation for this
observation: the lifetime of excitations in PS I is about 70-90 x 10"12 s, a factor of five shorter
than that measured in PS II (Holzwarth, 1987). In addition, there are about twice as many
PS II as PS I pigments, with the net result that PS I contributes only about 5 % of the total
steady state fluorescence. Thus, the direct contribution of PS I to fluorescence at
physiological temperatures can be essentially ignored. (At cryogenic temperatures,
fluorescence emission is dominated by PS I emission at 710-740 nm; Butler, 1978).
The relative contribution of accessory pigments to total fluorescence is also an important
consideration. The ability to detect emission from accessory pigments could be useful in
determining the taxonomic characteristics of a sample by detection of emission from pigments
unique to a particular group of algae. Unfortunately, most of the accessory pigments
contribute very little to the total fluorescence of a sample under physiological conditions. For
accessory chIs and carotenoids, the rate constant for excitation transfer to chi a is thought to
be on the order of 10 12 S-I • Adding this term into the denominator of equation 2 gives a
fluorescence yield of about 0.02%. Thus, even if the accessory chIs accounted for 50% of
the cellular pigment, they would not contribute significantly to total fluorescence emission.
and phycobilins in the green region of the spectrum is central to the success of aquatic algae.
Finally, antenna complexes serve several regulatory functions which optimize the overall
efficiency of photosynthesis under conditions of varying light intensity and spectral quality
(Fork and Satoh, 1986). As we shall see, these regulatory functions can also be detected as
changes in chI fluorescence.
Source olin vivo fluorescence. Equations 2-4 describe the factors that determine the quantum
yield of fluorescence for individual isolated pigments in a dilute solution. Photosynthetic
systems are considerably more complex because of the large and heterogeneous aggregate of
coupled pigments and because of the additional processes that are competing for excitation
energy. However, both the rate constant and lifetime formulations of fluorescence yield can
be useful when appropriately applied to the large antenna systems. A useful starting point is
a comparison of the contributions of PS I and PS II to total fluorescence emission. It has long
been known that nearly all of the room temperature fluorescence from ~-evolving organisms
is derived from PS II pigments. Recent excitation lifetime measurements on PS I and PS II
from green algae and higher plant chloroplasts provide a straightforward explanation for this
observation: the lifetime of excitations in PS I is about 70-90 x 10"12 s, a factor of five shorter
than that measured in PS II (Holzwarth, 1987). In addition, there are about twice as many
PS II as PS I pigments, with the net result that PS I contributes only about 5 % of the total
steady state fluorescence. Thus, the direct contribution of PS I to fluorescence at
physiological temperatures can be essentially ignored. (At cryogenic temperatures,
fluorescence emission is dominated by PS I emission at 710-740 nm; Butler, 1978).
The relative contribution of accessory pigments to total fluorescence is also an important
consideration. The ability to detect emission from accessory pigments could be useful in
determining the taxonomic characteristics of a sample by detection of emission from pigments
unique to a particular group of algae. Unfortunately, most of the accessory pigments
contribute very little to the total fluorescence of a sample under physiological conditions. For
accessory chIs and carotenoids, the rate constant for excitation transfer to chi a is thought to
be on the order of 10 12 S-I • Adding this term into the denominator of equation 2 gives a
fluorescence yield of about 0.02%. Thus, even if the accessory chIs accounted for 50% of
the cellular pigment, they would not contribute significantly to total fluorescence emission.