The form and position of these inclusions is somewhat different in the 

 various major physiological groups of phytoplankton. Polyphosphate bodies 

 in the blue-green algae may become large compared to the volume of the cell 

 within which they are contained and their position within the cell is highly 

 variable (Figure 5). In the green algae, as in most other eukaryotic cells, 

 polyphosphate bodies are restricted mainly to the vacuole. In the species 

 we have examined so far, there is considerable variation in the relative 

 size and position of the bodies present (Figures 6 and 7). 



In diatoms polyphosphate bodies are usually \/ery small (< 0.5 ym) (Fi- 

 gure 2) and are usually positioned near the vacuolar membrane inside the 

 vacuole, although they may become dispersed in the vacuole (Figures 2 and 

 8). 



Among the flagellate groups, polyphosphate bodies similar to those found 

 in diatoms have been noted in various members of the Chrysophyceae ( sens . 

 str . ) and the Prymnesiophyceae. Interestingly, they seem not to be present 

 in the Cryptophyceae and we have not found them in Euglenoids, although our 

 samples of these organisms are small, since they are very rare in the Great 

 Lakes. 



Since we had observed accumulation of Pb, but not other metals in field 

 samples, we decided to test for possible differential uptake of different 

 metals under controlled conditions. The metals tested were Pb and copper, 

 which is known to be rather acutely toxic to many species of algae 

 (Fitzgerald and Faust 1963). A unialgal culture of Diatoma tenue var. 

 elongatum Lyngb., originally isolated from Lake Michigan was grown in FM 

 medium. Since phosphorus limitation followed by phosphorus excess is one of 

 the conditions known to initiate polyphosphate body formation (Jensen and 

 Sicko 1974) phosphorus starvation and phosphorus excess were simulated in 

 the following manner. Four-day-old cultures which were in logarithmic 

 growth (controls) were packed by gentle centrifugation, washed twice with 

 sterile distilled water, then inoculated into a medium of the same composi- 

 tion of FM medium except that it lacked phosphate salts. Cells were incu- 

 bated in this medium for 3 days to induce phosphorus starvation. At the end 

 of the starvation period, during the fourth hour of the culture light cycle, 

 cells were again packed by centrifugation and resuspended in one of the 3 

 following media as treatments: 



1. Medium containing twice the phosphorus concentration of FM 

 medium with no other additions. 



2. Medium containing twice the phosphorus concentration of FM 

 medium + 0.05 yg-at/K. Pb. 



3. Medium containing twice the phosphorus concentration of FM 

 medium + 0.08 yg-at/2, Cu. 



Cells were incubated under normal culture conditions in these treatments 

 for 2 hours then fixed and prepared for electron microscopy along with con- 

 trol samples. Splits of the samples were also stained for polyphosphates 

 and prepared for observation under the light microscope. 



179 



