Cellular and molecular cytogenetics of Safed Musli (Chlorophytum): gaps and the way forward

Chlorophytum (Asparagaceae) is an Old World genus known for its medicinally important saponins. The genus has two basic chromosome numbers, i.e. x = 7 and x = 8. Of the 202 recognized taxa, only 49 (24%) have been studied cytogenetically. Most of the cytogenetical data come from the Asian taxa, particularly, the Indian subcontinent. We examined the cellular cytogenetics of five Chlorophytum species, namely C. bharuchae (2n = 16), C. borivilianum (2n = 28), C. comosum (2n = 28), C. laxum (2n = 32) and C. tuberosum (2n = 16). Comparative karyotypes of these taxa revealed majority of the chromosomes with submedian and median region centromeres. A few sub-telomeric chromosomes were seen in C. comosum and C. bharuchae. Male meiosis in the pollen mother cells (PMCs) was normal except for C. comosum and C. tuberosum that exhibited non-disjunction, stickiness, precocious separation, laggards, bridges and spindle mis-orientation. Fluorescent in-situ hybridization (FISH) of 5S rDNA on C. comosum chromosomes revealed five loci on the interphase nucleus and mitotic metaphase whereas six loci were observed for 45S rDNA on the mitotic metaphase on different chromosome sets (somatic cells). Genomic in-situ hybridization (GISH) showed that the DNA of diploid species, viz. C. heynei and C. filipendulum subsp. amaniense hybridised with the DNA of C. comosum non-specifically, indicating gross similarity in the genomes of diploid species. Chlorophytum on account of its large-sized chromosomes and owing to the presence of different ploidy levels (diploid to dodecaploid) is an ideal material to apply molecular cytogenetic techniques and flow cytometry to understand role of chromosomes in speciation.