Fluorescent Chromosome Banding and Genome Size Estimation in Three Species of Swertia

抄録

Chromosomal attributes of the critically endangered medicinal plant Swertia chirayita along with its allied species S. nervosa and S. bimaculata are precisely essential to assess phylogenetic relationships. The present study deals with karyomorphometric analysis based on patterns of fluorescence chromosome banding and nuclear genome size estimation by flow cytometry reported for the first time in S. chirayita (2n=26), S. nervosa (2n=26) and S. bimaculata (2n=26). Fluorescent banding revealed the distinct differences in chromosomal CMA^+ve/DAPI^−ve heterochromatic sites among the species. There were six chromosomes with CMA^+ve signals in S. chirayita and two chromosomes with CMA^+ve signals in S. bimaculata whereas all chromosomes of S. nervosa displayed CMA^+ve signals. Due to a difference in CMA banding pattern, proportion of GC rich regions differed among the chromosomes of S. chirayita (3.32%), S. nervosa (18.76%), and S. bimaculata (0.64%). S. bimaculata had the highest 2C DNA content (9.82 pg/2C) compared to S. nervosa (1.95 pg/2C) and S. chirayita (1.09 pg/2C). Lowest amount of GC-rich CMA sites along with highest DNA content distinguished S. bimaculata from the other two species. A nearly nine-fold difference in nuclear genome size among the homoploid species of Swertia (2n=26) and particular chromosomal discrimination by localized CMA bands allowed interpretation of karyotypic affiliations in the three species of Swertia.