High Stability in Chromosomal Traits of <i>Chamaelirium japonicum</i> and <i>C. koidzuminum</i> (Melanthiaceae) with Holocentric Chromosomes

Abstract

Chromosome number, morphology, and behavior in the mitotic cycle were examined for 334 individuals from 34 local populations of Chamaelirium japonicum, including two infraspecific taxa so far chromosomally uninvestigated, and for 20 individuals from three populations of C. koidzumianum, including one variety cytologically unexplored to date. All of the individuals proved to have holocentric chromosomes, and 351 out of the 354 individuals exhibited 2n=24=4L+20S (where L and S denote long and short, respectively) and were regarded as diploids (2x). Of the other three individuals of C. japonicum ssp. japonicum, two were triploids (3x) with 2n=36=6L+30S, and one was a hyperploid (2x+1) with 2n=25=4L+19S+2f, of which the two small chromosomes (f) presumably arose by fission in one short chromosome. The triploid and the hyperploid showed lower pollen stainability (16.3 and 71.7%, respectively) with cotton blue than normal diploids (98.0-99.5%). Factors leading to the high stability of chromosomal traits in the two species are suggested.

Chromosomal Variation in Populations of <i>Chamaelirium hisauchianum</i> (Melanthiaceae) with Holocentric Chromosomes

“…2C, Table 3). As two other species of the same subsection, C. japonicum and C. koidzumianum, are diploid, having 2n=24 with the base number (x) 12 (Tanaka and Tanaka 1979, 1980, Tanaka 2020, subsp. kurohimense with 2n= 44 is interpreted as a hypotetraploid (4x 4) if assumed to share the same base number with the two diploids.…”

“…Root tip meristematic cells were used to observe chromosome traits. The method for making chromosomal preparations is the same as stated in Tanaka (2020). For observation of meiosis, very young spikes were excised and fixed in a 2 : 1 : 1 mixture of ethanol, acetic acid, and chloroform for over 1 h. A few immature anthers fixed were placed onto a glass slide, squeezed with a dissecting needle tip, stained with 1 or 2% aceto-orcein, and carefully pressed after a coverslip was mounted on the samples.…”

“…For observation of meiosis, very young spikes were excised and fixed in a 2 : 1 : 1 mixture of ethanol, acetic acid, and chloroform for over 1 h. A few immature anthers fixed were placed onto a glass slide, squeezed with a dissecting needle tip, stained with 1 or 2% aceto-orcein, and carefully pressed after a coverslip was mounted on the samples. For the method for investigating pollen stain- ability with cotton blue and the information about the microscope and camera used, see Tanaka (2020).…”

“…hisauchianum and minoense have 2n= 42, thus markedly differing from C. japonicum and C. koidzumianum that possess 2n=24 (e.g. Hara and Kurosawa 1962, 1979, Tanaka 2020. Except for subsp.…”

“…In species having holocentric chromosomes, chromosomal variants originated by chromosomal fission are expected to occur, for fragmented chromosomes are likely to survive through mitoses and gametes with such fragments may participate in sexual reproduction. This deduction has recently been explored for C. japonicum and C. koidzumianum (Tanaka 2020), but not yet for C. hisauchianum that is contrastingly distinct from them in the mating system as well as some chromosomal traits such as karyotype and ploidy level. To fill this lack of knowledge, many individuals of C. hisauchianum were sampled from different local populations and their chromosomal traits and variation were investigated.…”