Estimation of the Genome Sizes of Males and Females in the Marine Green Alga Monostroma angicava Using Flow Cytometry

Genome size provides important information in ecology and evolution as well as genomics. Genome size may be different between the sexes within a species. However, little information on the genome size of both sexes is available, particularly in ulvophycean marine green algae, because few methods of genome size estimation are suitable for these algae. We developed a method to examine the genome sizes of males and females in the dioicous ulvophycean marine green alga Monostroma angicava. We examined three methods to isolate haploid nuclei: 1) chopping of a haploid gametophyte; 2) homogenization of protoplasts made from haploid gametophyte cells; and 3) homogenization of gametes and found homogenization of gametes to be the most suitable method for isolation of nuclei in M. angicava. Isolated nuclei were stained with propidium iodide. We measured the fluorescence intensity of nuclei using flow cytometry and successfully estimated the genome sizes of males and females as 178.8 Mbp and 185.4 Mbp, respectively, using Arabidopsis thaliana and Brassica rapa as standard plants with an internal standard method. The genome size of males was slightly smaller than that of females. This may be due to the difference in the length of sex-specific genome regions.