A comparison of computerized image analysis and stereology as tools for morphological study of algal cells

A computerized image analysis package (ImagePro+) was evaluated as an alternative method for morphometric analysis of electron micrographs of microalgal cells. The morphometric analysis was demonstrated with micrographs of the marine alga Nannochloropsis sp. grown under high and low light intensity. We applied the ImagePro+ package to estimate the relative volume of an organelle based on the ratio of perimeters of the organelle and the cell. The measurements included the volumes of chloroplasts, mitochondria, nuclei, vacuoles, and accumulation bodies, all relative to cell volume. The length of thylakoids was measured using the same package. The results obtained by ImagePro+ were compared to those of the traditional manual and laborious method involving the superimposition of an array of short lines on the micrograph. A high correlation between the methods was found. The following correlations were found for chloroplast, nucleus, and accumulation bodies: 0.96, 0.92, and 0.75, respectively. The correlation between length of thylakoids (ImagePro+) and surface area of thylakoids (superimposition) was 0.82.