Pollen Mitosis is a Good Choice for Gametophytic Chromosome Study in Higher Plants—Investigation with <i>Allium cepa</i> L. and <i>Aloe vera</i> L.

Abstract

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.