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antenna sizes, the rate of electron transport away from ~, or the fraction of PS II traps
closed by continuous actinic illumination. It can also be used to quantify qp and 'IN directly.
As with the modulated technique, its main disadvantages are cost and complexity of the
apparatus.
The modulated fluorescence and double-flash techniques have the significant advantage that
they can easily be combined with simultaneous measurements of <>z evolution, a direct
measure of photosynthetic rate. The combination of fluorescence and photosynthetic rate data
derived from samples whose physiological state has been manipulated by light intensity, stress
conditions, metabolic inhibitors, etc., provides the most promising protocols for
understanding the processes that control photosynthesis and how best to use fluorescence
measurements to predict in vivo or in situ rates and physiological state.
FLUORFSCENCE MEASUREMENTS IN INDIVIDUAL CELL ANALYSES
The measurement and interpretation of chI fluorescence data described in the previous
sections rely on the assumption of a homogeneous sample, that the average fluorescence
properties measured simultaneously on a large number of cells is representative of the
properties of each individual cell. Unfortunately, natural phytoplankton populations are rarely
dominated by a single species, thus the heterogeneous nature of the sample must be
considered (Yentsch and Campbell, 1991). Within a heterogeneous population, individual
species may exhibit different growth rates, varying degrees of adaptation to the
physical/chemicallbiological environment at the time of sampling, and may have growth rates
limited by different environmental factors. Thus the fluorescence properties of the entire
sample may have little relationship to average photosynthetic rate of physiological properties
of the sample. More importantly, measurement of bulk sample fluorescence may mask critical
information of individual components of the population.
With the introduction of individual cell analysis into phytoplankton studies using flow
cytometric techniques, one may address the problem of heterogeneous natural samples
(Yentsch and Campbell, 1991; Olson et al., 1985; Legendre and Yentsch, 1989). In vivo
fluorescence from chIs and phycobilins are the major components of phytoplankton
antenna sizes, the rate of electron transport away from ~, or the fraction of PS II traps
closed by continuous actinic illumination. It can also be used to quantify qp and 'IN directly.
As with the modulated technique, its main disadvantages are cost and complexity of the
apparatus.
The modulated fluorescence and double-flash techniques have the significant advantage that
they can easily be combined with simultaneous measurements of <>z evolution, a direct
measure of photosynthetic rate. The combination of fluorescence and photosynthetic rate data
derived from samples whose physiological state has been manipulated by light intensity, stress
conditions, metabolic inhibitors, etc., provides the most promising protocols for
understanding the processes that control photosynthesis and how best to use fluorescence
measurements to predict in vivo or in situ rates and physiological state.
FLUORFSCENCE MEASUREMENTS IN INDIVIDUAL CELL ANALYSES
The measurement and interpretation of chI fluorescence data described in the previous
sections rely on the assumption of a homogeneous sample, that the average fluorescence
properties measured simultaneously on a large number of cells is representative of the
properties of each individual cell. Unfortunately, natural phytoplankton populations are rarely
dominated by a single species, thus the heterogeneous nature of the sample must be
considered (Yentsch and Campbell, 1991). Within a heterogeneous population, individual
species may exhibit different growth rates, varying degrees of adaptation to the
physical/chemicallbiological environment at the time of sampling, and may have growth rates
limited by different environmental factors. Thus the fluorescence properties of the entire
sample may have little relationship to average photosynthetic rate of physiological properties
of the sample. More importantly, measurement of bulk sample fluorescence may mask critical
information of individual components of the population.
With the introduction of individual cell analysis into phytoplankton studies using flow
cytometric techniques, one may address the problem of heterogeneous natural samples
(Yentsch and Campbell, 1991; Olson et al., 1985; Legendre and Yentsch, 1989). In vivo
fluorescence from chIs and phycobilins are the major components of phytoplankton