131
the residence time of the cell in the illuminated volume and the rate of light absorption by the
antenna of each PS II reaction center. For a typical residence time of 1-20 Ils, the major
actinic effect should be due to photochemical quenching (electron transport from P680 to QJ;
all other reactions of electron transport and non-photochemical quenching occur on time
scales slower than 20 Ils. Essentially, the actinic effect determines how much ti>f will increase
as the cell traverses the illuminated volume due to closure of PS II traps. However, at
focused laser intensities, the possibility of excited-state annihilations cannot be neglected.
Clearly, the actual ti>f will be instrument-dependent and direct comparisons between different
instruments may be difficult.
Recently, a modification of the double-flash method has been applied successfully to
suspensions of higher plant chloroplasts and green algae to determine the rate of electron
transport away from ~ (Petit et ai., 1989). Here, the pump beam from one laser (closing
some fraction of PS II reaction centers) is positioned at a fixed distance upstream from the
probe (measuring) beam. By varying the flow rate, the delay time between the pump and
probe beams can be varied; fluorescence yield from the probe beam as a function of delay
time gives the kinetics of ~. oxidation. Additional modifications would permit the
quantification of qp and 'IN. Thus, with continued evolution of multiparametric analyses in
flow cytometry, it is likely that the properties of individual cells can be quantified sufficiently
to allow direct measurement of relative fluorescence yield.
CONCLUSIONS
Emission of chI fluorescence is a common characteristic of all photosynthetic organisms.
Measurement of in vivo fluorescence from phytoplankton samples, using a variety of
instruments, is sensitive and relatively straightforward. Based on both theoretical foundation
and correlative experiments, there is evidence that in vivo chI fluorescence can be useful in
predicting several important parameters including algal biomass, rates of photosynthesis, and
information on physiological state. This is of obvious importance to both laboratory and field
studies; fluorescence analyses require smaller samples and are considerably less time
consuming than direct measurement of these parameters.
the residence time of the cell in the illuminated volume and the rate of light absorption by the
antenna of each PS II reaction center. For a typical residence time of 1-20 Ils, the major
actinic effect should be due to photochemical quenching (electron transport from P680 to QJ;
all other reactions of electron transport and non-photochemical quenching occur on time
scales slower than 20 Ils. Essentially, the actinic effect determines how much ti>f will increase
as the cell traverses the illuminated volume due to closure of PS II traps. However, at
focused laser intensities, the possibility of excited-state annihilations cannot be neglected.
Clearly, the actual ti>f will be instrument-dependent and direct comparisons between different
instruments may be difficult.
Recently, a modification of the double-flash method has been applied successfully to
suspensions of higher plant chloroplasts and green algae to determine the rate of electron
transport away from ~ (Petit et ai., 1989). Here, the pump beam from one laser (closing
some fraction of PS II reaction centers) is positioned at a fixed distance upstream from the
probe (measuring) beam. By varying the flow rate, the delay time between the pump and
probe beams can be varied; fluorescence yield from the probe beam as a function of delay
time gives the kinetics of ~. oxidation. Additional modifications would permit the
quantification of qp and 'IN. Thus, with continued evolution of multiparametric analyses in
flow cytometry, it is likely that the properties of individual cells can be quantified sufficiently
to allow direct measurement of relative fluorescence yield.
CONCLUSIONS
Emission of chI fluorescence is a common characteristic of all photosynthetic organisms.
Measurement of in vivo fluorescence from phytoplankton samples, using a variety of
instruments, is sensitive and relatively straightforward. Based on both theoretical foundation
and correlative experiments, there is evidence that in vivo chI fluorescence can be useful in
predicting several important parameters including algal biomass, rates of photosynthesis, and
information on physiological state. This is of obvious importance to both laboratory and field
studies; fluorescence analyses require smaller samples and are considerably less time
consuming than direct measurement of these parameters.