ELEMENTAL COMPOSITION, CORRELATIONS, AND RATIOS WITHIN A POPULATION OF STAURASTRUM-PLANCTONICUM (ZYGNEMATALES) - AN X-RAY MICROANALYTICAL STUDY

Individual cells of Staurastrum planctonicum (Teil.) within a mixed fr eshwater phytoplankton sample were analyzed by scanning electron micro scope, X-ray microanalysis to determine their elemental composition. X -ray emission spectra routinely showed clear peaks of P, S, and Cl, pl us monovalent (Na, K) and divalent (Mg, Ca) cations. Si and Cu were al so present in lower quantities. Concentrations of individual elements (expressed as mmol . kg(-1) dry weight) varied widely among cells, wit h values over the sample population approximating to a normal distribu tion. Although intracellular anion and cation levels varied considerab ly, significant correlations occurred between concentrations of monova lent and divalent cations (mean ratio 1.4), major diffusible anions an d cations (mean ratio 1.2), and total levels of electropositive and el ectronegative elements (mean ratio 1.2). The monovalent cations of K a nd Na occurred at a mean ratio of 1.2 and were not significantly corre lated. Concentrations of individual elements (except Si) showed clear positive correlations within the analyses, with 12 highly significant (99% probability) correlations out of 36 possible combinations. Princi pal factor analysis showed that elemental correlations were determined by true major factors. With two resulting groups of elements-(Na, S, Cl, Ca, Cu) and (Mg, P, K). Statistical relationships between elements followed a clear correlation pattern, which retained its characterist ics men when elemental concentrations were expressed per unit P rather than per unit dry weight. Elemental concentrations were closely simil ar in matching, but not nonmatching, semicells. The statistical patter n of elemental associations noted in Staurastrum parallels that seen i n X-ray microanalytical studies of other algae but differs in detail. This pattern of statistical associations has biological implications i n terms of cell compartmentation, characterization of different cell t ypes, and cell interactions with their environment.