| Abstract: | Three strains of Scenedesmus acutus f. alternans Hortobagyi with markedly different sensitivities to copper were examined to determine the relative importance of cellular polyphosphate content on acute copper toxicity to photosynthesis. By manipulating the phosphate concentration in semicontinuous cultures, the response of each strain was assessed at three cellular phosphorus states: P-loaded, P-sufficient, and P-deficient. The results demonstrated the importance of cellular polyphosphate content in reducing the toxic effect of copper on photosynthesis; the greater the cellular P content, the less inhibition of photosynthesis occurred during copper exposure. This relationship was evident for both Cu-tolerant strains (XCu and B-4) and a Cu-sensitive strain (X72). The ranges of response to 9.9 μM Cu (measured as the percentage of control rate of photosynthesis within strains) were, from P-loaded to P-deficient cells, X72, 78–54%; XCu, 95–77%; and B-4, 99–94%. The data suggest that polyphosphate plays a passive role in protecting cells from copper; however, with respect to the mechanism of Cu tolerance, polyphosphate appeared to be relatively unimportant because the sensitivity of the Cu-tolerant strains showed less dependence on cellular polyphosphate than did the Cu-sensitive strain. |
