THE DETERMINATION OF VOLUME OF DUNALIELLA CELLS BY TRANSMISSION ELECTRON-MICROSCOPY AND IMAGE-ANALYSIS

A method has been developed to measure the cell volume of the unicellular, green alga Dunaliella bioculata 19/4 during salt stress conditions, where shape change in the alga becomes problematic and the cells can no longer be recognised as ‘prolate ellipsoids’, by using image analysis of transmission electron micrographs. The image analysis of the micrographs employs a specialised numerical integration programme or ‘variable frames analysis’ for unicellular microorganisms which possess a single axis of symmetry. Basic mathematics was used to determine: (a) the functional dependence of the calculated volume on the angle of the cut to the axis of symmetry and the distance of the origin of the cut from the centre of mass; (b) errors resulting from the orientation of the longest axis off-vertical for image analysis; (c) the uppermost range of calculated volumes obtained which represent the ‘true’ volumes within required confidence levels. The procedure was applied to a series of experiments on the effects of salt stress on Dunaliella bioculata cells. © 1994 Annals of Botany Company.