Karyomorphology, distribution of constitutive heterochromatin, and intrapopulation polymorphism of C-bands in a cross-pollinated population of Nigella sativa L. were studied. Enzymatic digestion of the cell wall allows cytoplasm-free chromosome preparation and enhances the stain resolution, thereby promoting accurate chromosome measurements and identification of chromosomal landmarks. The diploid chromosome number is 2n= 12, of which five pairs are moderately long and have median centromere, whereas one small pair has a subterminal centromere. Secondary constriction has been observed in two pairs of long chromosomes. Polymorphism of the C-band size in individuals of the same population and even between two homologous chromosomes of a single individual has been detected by the C-banding technique. Further, the absence of any DAPI-bands indicated that the DNA of C-band region is not AT-rich. The heterogeneity of C-bands in homologous pairs of a single individual is a consequence of cross-pollination where chromosomes come from two different parents. The pattern of heterochromatin distribution can serve as a unique marker that can enrich the karyosystematic database and prove useful in the breeding program of N. sativa.

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Coleus scutellarioides (L.) Benth. is a very popular ornamental plant with attractive colorful foliage and also has several medicinal properties. A detailed cytogenetical study was conducted in the ʻRed Trailing Queenʼ horticultural form of this species. Hitherto, elaborate cytogenetic studies in this species received less attention and all of the previous studies on chromosomes are decades old. Thus, a reassessment and detailed cytogenetic study of this species are necessary. The karyotype study revealed that somatic cells contain 2n=48 small chromosomes, classified into metacentric to submetacentric. Meiotic chromosomes stained with acetocarmine and 4′,6-diamidino-2-phenylindole (DAPI) revealed the occurrence of univalent, bivalent, and multivalent associations of chromosomes along with secondary associations. The result confirms the allopolyploid origin of this plant. Meiotic irregularities like laggard chromosomes and multipolarity movement have also been found. In addition to that, variation in the chromosome numbers within pollen mother cells (PMCs) has been observed frequently. Pollen viability has been determined by fluorescein diacetate (FDA) and found to be very low. Rosmarinic acid (RA) is a natural polyphenol utilized as an anti-microbial, immunomodulatory, anti-diabetic, anti-allergic, anti-inflammatory, hepato-protectant, and renal-protectant agent. The RA content has been quantified through high-performance liquid chromatography (HPLC) to find out the medicinal efficacy. The present investigation on detailed cytogenetics study along with the pollen viability will be beneficial in the breeding program and accordingly useful in further improvement of this ornamental medicinal plant.

In higher groups of plants, the somatic cells are conventionally used for karyomorphological studies, which contain a diploid (2n) set of chromosomes. Similar to diploid sporophytic cells, a chromosomal study in haploid (n) gametophytic cells is also necessary as it unfolds the karyomorphological status of germ cells. The mature male gametophytic plant body (i.e., pollen grain) is only two-or three-celled structures. This study focused on the first mitotic division in a microspore, popularly known as ʻpollen mitosis-I.ʼ Allium cepa L. and Aloe vera L. are two model species for karyomorphological study. Microspores of these species have been stained with 2.0% acetocarmine. The present finding reveals that the cell division in microspores of these two species is completely normal without any significant irregularities. As expected, the chromosome number of the microspores of Allium cepa is n=8 and Aloe vera is n= 7, exactly half the number of their sporophytic plants. The haploid karyotype of Allium cepa is the symmetric type with karyotype formula ʻ6m+2sm,ʼ whereas that of Aloe vera is between symmetric and asymmetric types with karyotype formula ʻ3sm+4st.ʼ This study not only enriches the chromosomal database of gametophytes of Allium cepa and Aloe vera, but also will encourage further research on this extremely neglected topic̶chromosome study in the gametophytic generation of flowering plants. As Allium cepa and Aloe vera are easily available and model species for karyomorphological study, and with two contrast karyotypes (i.e., symmetric and asymmetric), this article also helps numerous school/college teachers to teach their students about the structure and behavior of gametophytic chromosomes.

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