Chromosome number of Carex siderosticta in Korea (Cyperaceae)

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Korean J. Pl. Taxon. 2024;54(2):126-131

Publication date (electronic) : 2024 June 30

doi : https://doi.org/10.11110/kjpt.2024.54.2.126

Kyong-Sook CHUNG

Department of Medicinal Plant Science, Jungwon University, Goesan 28024, Korea

Corresponding author Kyong-Sook CHUNG E-mail: kchung@jwu.ac.kr

Received 2024 May 23; Revised 2024 June 10; Accepted 2024 June 15.

Abstract

INTRODUCTION

Carex siderosticta Hance (Cyperaceae) is described from Northern China (Hebei province) and occurs widely in Korea, China, Japan, and Russia (Hance, 1873; Hoshino et al., 2011; Park et al., 2016). It can be found in forests or margins of forests and flowers and fruits from April to May (Hoshino et al., 2011; Park et al., 2016). The species is characterized by its long rhizomes, broad leaves, androgynous inflorescences (bisexual spikes with female flowers on the top), 3-stigmas, and trigonous perigynia (Dai et al., 2010; Hoshino et al., 2011). In Korea, the species occurs throughout the peninsula (Park et al., 2016).

Four members in the Siderosticta clade are native to Korea: C. siderosticta, C. ciliatomarginata Nakai, C. okamotoi Ohwi, and C. splendentissima U. Kang & J. Chung (Chung et al., 2013; Yano et al., 2014; Park et al., 2016). Carex okamotoi and C. splendentissima are endemic to Korea, and C. ciliatomarginata occurs in Korea, Japan, and China (Park et al., 2016). Chromosome numbers of the four species were reported as diploids (2n = 2x = 12) (Chung et al., 2013, 2017).

Diploids (2n = 2x = 12) and tetraploids (2n = 4x = 24) of C. siderosticta have been reported. In Russia and China, several studies have reported tetraploids (Starodubtsev, 1989; Tang and Xiang, 1989; Hoshino et al., 1993; Probatova et al., 1998; Probatova, 2000; Yano et al., 2014). In Japan, both diploid and tetraploid populations have been found, though they were not morphologically distinguishable (Tanaka, 1939, 1940; Hoshino and Tanaka, 1977; Hoshino, 1981; Yano et al., 2014). Thus far, only diploids have been found in Korea (Chung et al., 2013, 2016, 2017; Yano et al., 2014).

As part of a comprehensive investigation of cytological studies of the Korean Carex (Chuang et al., 2013; Chung and Im, 2018, 2019, 2020; Chung and Chung, 2021; Chung et al., 2016, 2017, 2023; Lee and Chung, 2023), somatic chromosomes of C. siderosticta were examined and analyzed from various populations in Korea with an emphasis of the examination of its ploidy levels.

MATERIALS AND METHODS

From April 2022 to August 2023, field survey was conducted in various provinces in Korea and somatic chromosomes from 17 populations (one individual from each population) of C. siderosticta were counted (Table 1). The protocols in Yano et al. (2014) were utilized. Root tips were pretreated in 0.002 M 8-hydroxiquinoline about 8 h and then fixed in a mixture of ethanol and glacial acetic acid (3:1) for 12 h. After fixation, the root tips were preserved in 70% ethanol. To observe chromosome observation, the preserved root tips were macerated in 1 N HCl for 10 min and stained with 1% acetic-orcein. The stained root tips were squared and observed at 1,000× magnification (Nikon Eclipse 50i, Nikon, Tokyo, Japan). At least three mitotic cells per individual were analyzed to confirm the numbers. Spread somatic chromosomes were photographed for analyses. Voucher specimens were saved in the herbarium of the Korea National Institute of Biological Resources (KB).

Table 1.

Carex siderosticta voucher specimens and chromosome numbers.

RESULTS AND DISCUSSION

Somatic chromosomes in all samples exhibited diffuse centromeres (non-monocentric) and varied ca. 1.3–6.1 μm in length (Table 2). Chromosome numbers were 2n = 2x = 12 and 2n = 3x = 18 (Figs. 1, 2), and total chromosome lengths (average) were 35.4 μm and 54.5 μm, 2x and 3x, respectively (Table 1). For the first time, triploidy in C. siderosticta was observed (Fig. 2B, C). The triploidy population was not morphologically distinguishable from other populations and was distant from other diploid populations about 3–5 m. The population has been monitored and sampled for additional investigations.

Table 2.

Carex siderosticta karyotypes and ploidy levels.

Fig. 1.

Photomicrographs of somatic chromosomes of Carex siderosticta (2n = 12). A. Chung 9237. B. Chung 9239. C. Chun 9243. D. Chung 9501. E. Chung 9641. F. Chung 9657. G. Chung 9663. H. Chung 9669. I. Chung 9674. Scale bars = 10 μm.

Fig. 2.

Photomicrographs of somatic chromosomes of Carex siderosticta (2n = 12 and 18). A. Chung 9676. B, C. Chung 9677 (2n = 18). D. Chung 9685. E. Chung 9686. F. Chung 10047. G. Chung 10048. H. Chung Park 6. I. Chung Lee230512. Scale bars = 10 μm.

In the diploids and triploids, chromosomes could be categorized into three types in terms of the length. In the diploids, two large (more than ca. 4 μm long), six medium (less than ca. 4 μm long), and four small (less than 2 μm long) chromosomes were observed: 2n = 12 = 2L + 6M + 4S (Figs. 1, 2A, D–I). The triploids also exhibited chromosomes of three types of chromosomes three different lengths: three large, nine medium, and six small chromosomes: 2n = 18 = 3L + 9M + 6S (Fig. 2B, C). Based on the analyses, it can be hypothesized that triploidy may have derived from the fertilization of reduced and unreduced gametes of the diploids or reduced gametes of diploids and tetraploids.

Based on karyotype analyses, C. siderosticta tetraploids were hypothesized as autopolyploids although inconsistent karyotypes have been found (Table 2). Tanaka (1939, 1940) reported two levels of ploidy but with two types of karyotypes for C. siderosticta: x = 2L + 1Mt + 1M + 2S and x = 1Lt (with satellite) + 3L + 2S. Hoshino and Tanaka (1977) categorized chromosomes into four types for both diploids and tetraploids (x = 6L with two dark ends + 2S with one dark end + 2L without dark ends + 2S without dark ends). In addition, Hoshino (1981) documented chromosomes of the species for which 2n = 12 = 2L + 6M + 4S and 2n = 24 = 16L + 8S, reporting regular ploidy but not agmatoploidy. Karyotypes in the present study is congruent with types in Hoshino (1981), but are different from those in the other previous reports (Table 2). However, most chromosome reports pertaining to C. siderosticta found them to have three lengths. In Chinese populations, Hoshino et al. (1993) described tetraploid chromosomes with gradual variation in the length (from 1.3 μm to 2.4 μm) but did not categorize them. One of most distinct characteristics reported is satellites in long or medium chromosomes by Tanaka (1939, 1940). Further investigations of cytological characters should be conducted to clarify the various karyotypes in the species.

In Carex, intraspecific polyploidy has been reported in several species such as C. multifolia Ohwi, C. siderosticta, and C. grandiligulata Kük. (Tanaka, 1949; Yano et al., 2014). In C. multifolia, polyploidy and aneuploidy were reported (2n = 30, 60, 62, 64, 65, 66, 70) (Tanaka, 1949). However, the phenomenon is most significant in a basal group of the Carex, Siderostictae clade, showing the lowest chromosome number of 2n = 12 (Hoshino and Tanaka, 1977; Roalson, 2008; Yano et al., 2014). In the clade, C. siderosticta and C. grandiligulata have shown two ploidy levels, 2n = 12 and 24 (Tanaka, 1940; Yano et al., 2014). Carex grandiligulata has only been found in China thus far, and two chromosome numbers from two provinces (Zhejiang, 2n = 12; Shaanxi, 2n = 24) have been reported (Dai et al., 2010; Yano et al., 2014). Based on karyotype analyses, Tanaka (1939), Hoshino (1981), and Yano et al. (2014) hypothesized that the tetraploids may have derived from autopolyploidization. In Siderostictae clade, C. siderosticta is one of the most widely distributed species (Dai et al., 2010; Hoshino et al., 2011; Park et al., 2016).

The size of the genome of C. siderosticta has been estimated to be 1C = 0.77 ± 0.05 pg (Lee et al., 2019) and 1C = 1.2 pg (Nishikawa et al., 1984). Nishikawa et al. (1984) reported such values with a tetraploid, but Lee et al. (2019) did not state a ploidy level. Considering the average of the Carex C-value, 1 C = 0.44 ± 0.16 pg (Leitch et al., 2019), the C. siderosticta genome size is large in the genus. The Chromosome numbers vary greatly in the genus, from 2n = 12 to 2n = 136 (Roalson, 2008). The large genome and chromosome sizes with relatively few chromosomes in C. siderosticta support the basal phylogenetic position of the species. Based on total chromosome length data (Table 1), quantitative polyploidization is assumed although the genome sizes of the 17 C. siderosticta individuals are not available. However, there is a possibility of more complex, non-quantitative polyploidy associated with fission events due to holocentric chromosomes in the genus. Chromosome lengths and types various depending on samples (Table 2). Further cytogenetic experiments with expanded samples including closely related taxa should be conducted. Chromosome fission (fragmentation of chromosomes without DNA duplication, agmatoploidy) has been hypothesized as a cause of the rapid speciation in the genus (Hipp et al., 2009; Yano et al., 2014).

This finding of triploidy in C. siderosticta can enhance our understanding of polyploidization in Carex. Based on the chromosomes, it can be hypothesized that this instance of triploidy individuals from the fertilization of reduced and unreduced gametes of diploids or reduced gametes of diploids and tetraploids. Furthermore, triploid bridge can be postulated as one of potential roles of triploids. Triploids may produce tetraploid offspring through backcrosses with diploids or other triploids (Husband, 2004). These processes should be clarified by further molecular and cytological investigations.

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