Genome size determination and chromosome characterization of Limosella aquatica L. (Scrophulariaceae) in Japan: Insights into Japanese population

Abstract

The genome size and karyomorphology of six accessions of Limosella aquatica L. in Japan were investigated. All six accessions had a chromosome number of 2n=40. The genome size of L. aquatica was estimated using flow cytometry (FCM) and 2C of the tetraploid genome size ranged from 1.38 pg in accession Shiranuka to 1.42 pg in accession Taiki (1,178–1,216 Mbp), with 1Cx estimated to be ca. 0.35 pg (300 Mbp). The GC contents of all accessions were less than 40%. The centromeres of all chromosomes were located at median positions, while secondary constrictions were found at the distal regions of two chromosomes, resulting in small chromatin segments as satellites. The chromosome complement showed a monomodal karyotype with a gradual decrease in the chromosome length, ranging from 1.3 to 0.6 µm. The average chromosome lengths of accessions in Hokkaido and Honshu were 0.9 and 1.0 µm, respectively. The accessions in Kumamoto were exceptions, showing chromosome lengths ranging from 1.6 to 0.8 µm. The DNA base-specific banding revealed that the pericentromeric regions of all chromosomes and the satellites were chromomycin A₃ positive and 4′,6-diamidino-2-phenylindole negative (CMA⁺DAPI⁻). The 18S rDNA fluorescence in situ hybridization (FISH) result also showed that the two signals were located at exactly the same positions as the CMA⁺DAPI⁻ satellites.