Cell size as a morphological marker to calculate the mitotic index and ploidy level of citrus callus

Abstract

We have developed a new method for calculating the mitotic index (MI) and ploidy level of citrus callus. The first step was to symbolize the diameters of new daughter cells and metaphase cells with RD and RM, respectively. The formula RD=0.7937 RM was subsequently established. The validity of this hypothesis was verified by morphological, cytological and fluorescent observations as well as by a protoplast electrofusion test. The MI and the ploidy level of a cell population were then calculated according to this formula. As a final step, tetraploid and hexaploid cell lines were produced from a mixoploid cell population, and somatic embryos were regenerated from these cell lines. These results suggest that cell size can be used as a morphological marker to calculate MI and ploidy level of citrus callus.