382
these cells showed responses similar to that of the photosynthetic capacity as determined by
1 4 C uptake experiments (Fig. 19). The green fluorescein fluorescence does not interfere with
red chlorophyll fluorescence, so both biomass (from chlorophyll fluorescence) and viability
(from FDA activity) can be determined simultaneously on a cell-by-cell basis. The authors
point out that FDA could also be useful for examining the metabolic activity of heterotrophic
cells, but caution that we still do not understand all of the physiological properties that
influence FDA activity.
Fluorescein diacetate is just one example of fluorescent probes being developed for a myriad
of molecules within cells (Haugland 1989). As methods are adapted from epifluorescence
microscopy to flow cytometry, these probes will make it possible to monitor the levels of
other molecules within individual phytoplankton cells. Each new probe allows us to investigate
how another cell component or property changes in response to environmental stresses and
provides more hints on how cells deal with changing growth conditions.
Future Research Directions
The proliferation of both custom-built and commercial flow cytometers, combined with
improvements in technology, continue to expand the scope of individual cell analyses in
oceanography. Improvements in our ability to recognize and discriminate among different
particles, to make sensitive and reproducible measurements, and to analyze the large amounts
of data acquired are growing continually. Discussed below are some of the areas in which
these improvements might lead to further advances in the near future.
Physical Processes: The biological responses of phytoplankton cells to changes in their
environment can be used to provide information on physical processes such as water column
mixing and nutrient supply. If we know how fast cells can respond to changes in light levels,
we can get an idea from the depth distribution of their properties how fast they have been
moved from one depth to another. A variety of bulk water parameters, such as photosynthesis
vs. irradiance characteristics (Falkowski 1983) and carbon:chlorophyll ratio (Cullen and Lewis
1988), have been proposed as potential candidates for investigating vertical mixing. Flow
these cells showed responses similar to that of the photosynthetic capacity as determined by
1 4 C uptake experiments (Fig. 19). The green fluorescein fluorescence does not interfere with
red chlorophyll fluorescence, so both biomass (from chlorophyll fluorescence) and viability
(from FDA activity) can be determined simultaneously on a cell-by-cell basis. The authors
point out that FDA could also be useful for examining the metabolic activity of heterotrophic
cells, but caution that we still do not understand all of the physiological properties that
influence FDA activity.
Fluorescein diacetate is just one example of fluorescent probes being developed for a myriad
of molecules within cells (Haugland 1989). As methods are adapted from epifluorescence
microscopy to flow cytometry, these probes will make it possible to monitor the levels of
other molecules within individual phytoplankton cells. Each new probe allows us to investigate
how another cell component or property changes in response to environmental stresses and
provides more hints on how cells deal with changing growth conditions.
Future Research Directions
The proliferation of both custom-built and commercial flow cytometers, combined with
improvements in technology, continue to expand the scope of individual cell analyses in
oceanography. Improvements in our ability to recognize and discriminate among different
particles, to make sensitive and reproducible measurements, and to analyze the large amounts
of data acquired are growing continually. Discussed below are some of the areas in which
these improvements might lead to further advances in the near future.
Physical Processes: The biological responses of phytoplankton cells to changes in their
environment can be used to provide information on physical processes such as water column
mixing and nutrient supply. If we know how fast cells can respond to changes in light levels,
we can get an idea from the depth distribution of their properties how fast they have been
moved from one depth to another. A variety of bulk water parameters, such as photosynthesis
vs. irradiance characteristics (Falkowski 1983) and carbon:chlorophyll ratio (Cullen and Lewis
1988), have been proposed as potential candidates for investigating vertical mixing. Flow