359
cytometer "sees" only total fluorescence from a particle within relatively broad spectral bands
determined by the optical filters.
Field Studies
The relatively low concentrations of the larger phytoplankton in natural ocean waters, and
conversely, the relatively high concentrations of picoplankters, have defined the applications
of commercially available flow cytometers for field studies to date. Typical sample flow rates
are a fraction of a milliliter per minute, which limits efficient analysis to those types of cells
whose abundance is in accord with reasonable sample analysis times. The picoplankters
Synechococcus and prochlorophytes fit this category and thus have been most extensively
studied using flow cytometric methods. In fact, the latter were effectively discovered using
flow cytometry (Chisholm et al. 1988). As is discussed below, larger and less abundant cells
can be studied using this technology and with some minor technological advances we will be
able to analyze them as readily as the smaller cells.
Synechococcus: Synechococcus has been a prime target of study using flow cytometry since
the first open ocean seawater samples were analyzed using this method (Yentsch et al. 1983;
Olson et al. 1985). These cells have very distinctive signatures because they are very small
(about 1 pm) and contain phycoerythrin, which fluoresces brightly in the orange (570 nm)
region of the spectrum. They are found in surface waters of all the warm oceans at
concentrations high enough (1()3-HP ml- I ) to analyze rapidly with standard commercial flow
cytometers.
Synechococcus was discovered using epifluorescence microscopy (Waterbury et al. 1979;
Johnson and Sieburth 1979), and the general distribution of these cells has been fairly well
established using this technique (Waterbury et al. 1986; Glover et al. 1986; Glover 1985;
Iturriaga and Marra 1988). Flow cytometry, in addition to making more detailed sampling
possible, has enabled us to quantify the optical characteristics of the cells, such as
fluorescence intensity and cell size, and to do more detailed studies of the factors that regulate
the distribution and abundance of various pigment types (Olson et al. 1988, 1990a).
cytometer "sees" only total fluorescence from a particle within relatively broad spectral bands
determined by the optical filters.
Field Studies
The relatively low concentrations of the larger phytoplankton in natural ocean waters, and
conversely, the relatively high concentrations of picoplankters, have defined the applications
of commercially available flow cytometers for field studies to date. Typical sample flow rates
are a fraction of a milliliter per minute, which limits efficient analysis to those types of cells
whose abundance is in accord with reasonable sample analysis times. The picoplankters
Synechococcus and prochlorophytes fit this category and thus have been most extensively
studied using flow cytometric methods. In fact, the latter were effectively discovered using
flow cytometry (Chisholm et al. 1988). As is discussed below, larger and less abundant cells
can be studied using this technology and with some minor technological advances we will be
able to analyze them as readily as the smaller cells.
Synechococcus: Synechococcus has been a prime target of study using flow cytometry since
the first open ocean seawater samples were analyzed using this method (Yentsch et al. 1983;
Olson et al. 1985). These cells have very distinctive signatures because they are very small
(about 1 pm) and contain phycoerythrin, which fluoresces brightly in the orange (570 nm)
region of the spectrum. They are found in surface waters of all the warm oceans at
concentrations high enough (1()3-HP ml- I ) to analyze rapidly with standard commercial flow
cytometers.
Synechococcus was discovered using epifluorescence microscopy (Waterbury et al. 1979;
Johnson and Sieburth 1979), and the general distribution of these cells has been fairly well
established using this technique (Waterbury et al. 1986; Glover et al. 1986; Glover 1985;
Iturriaga and Marra 1988). Flow cytometry, in addition to making more detailed sampling
possible, has enabled us to quantify the optical characteristics of the cells, such as
fluorescence intensity and cell size, and to do more detailed studies of the factors that regulate
the distribution and abundance of various pigment types (Olson et al. 1988, 1990a).