Determination of Volume ofDunaliellaCells by Lithium Dilution Measurements and Derivation of Internal Solute Concentrations

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Abstract
A method has been developed to measure the cell volume of the unicellular green alga Dunaliella parva 19/9 using Li+ measurements only. Concentrations of internal solutes can also be calculated if they are assayed in the same samples as Li+. We found that D. parva cells grown in 0.4 kmol m−3 NaCl have an average aqueous cell volume of 65.1 ±2.9 μm3, a K+ concentration of 126±6 mol m−3, a Na+ concentration of 11±11 mol m−3 and a glycerol concentration of 615±27 mol m−3 (n= 12). Algae grown in 1.5 kmol m−3 NaCl have an average aqueous cell volume of 131 ±7.5 μm3, a K+ concentration of 109±4 mol m−3, a Na+ concentration of 10±39 mol m−3 and a glycerol concentration of 1 425±59 mol m−3 (n = 12). These results indicate that D. parva cells adapted to high salinities have larger cell volumes than those adapted to lower salinities. However, there is no evidence for a significant difference in internal Na+ concentration, despite the almost 4-fold difference in the concentration of external NaCl. The intracellular glycerol concentration alone accounts for 65% and 54%, respectively, of the osmotic balance in low and high salt grown cells.