Regular Articles
Cytological Study on Aspidistra from Thailand
2023 年 88 巻 1 号 p. 83-87
詳細
2023 年 88 巻 1 号 p. 83-87
Karyomorphological features of Aspidistra longifolia and A. subrotata from Thailand were here reported. The karyotype of A. longifolia is analyzed and confirmed as 2n=38=24m+2sm+12st in Doi Tung, Phu Hin Rong Kla National Park, and Nam Nao National Park. The tetraploid population of A. subrotata has been found in Phu Luang Wildlife Sanctuary, as the second tetraploid population reported for this species so far and the westernmost known record.
Aspidistra Ker Gawler (Asparagacae s.l.) is a large genus including more than 170 species occurring in China, Vietnam, Lao, Thailand, India, Malaysia, and Japan (Li 2004, Tillich 2014, The Angiosperm Phylogeny Group 2016, Nguyen et al. 2020, Deng et al. 2021). There are three species native to Thailand, i.e., A. sutepensis Larsen, endemic to N Thailand, as well as A. subrotata Y. Wan & C.C. Huang, and A. longifolia Hook.f., with wide distribution and variable morphology (Phonsena and de Wilde 2010).
Sixty-three Aspidistra species are confirmed as diploid with a chromosome number of 2n=36 in 25 species and 2n=38 in 38 species (Li 2004, Qiao et al. 2008, Gao and Liu 2011, 2012, Meng and Gao 2014, Gao et al. 2015), except for three tetraploid species with 2n=76, i.e., A. xilinensis Wan and Lu and A. cruciformis Wan and Lu and A. subrotata from China (Chen et al. 2017). So far only one hexaploid species with 2n=114, i.e., A. sutepensis, has been reported and its karyotype formula is 2n=72m+6sm+36st based on material collected during our first fieldwork in Thailand in 2014 (Gao et al. 2015).
A. subrotata var. angustifolia Phonsena was described as a new variety based on its leaf linear-lanceolate, 2–2.5 cm wide, and nerves not raised above. However, observations in Vietnamese and Laotian plants do not support the segregation of infraspecific taxa, i.e., A. subrotata var. carssinervis and A. subrotata var. angustifolia based on the leaf blade shape and character of its venation (Averyanov and Tillich 2017). Six tetraploid populations from Longzhou, China, and three diploid populations from Mt. Poman, Mt. Daqing, China, and Mt. Bavi, Vietnam have been found in A. subrotata (Chen et al. 2017). Combined the distribution and morphology, it shows that the leaf shape varies quantitatively between and within the diploid or tetraploid population(s) (Chen et al. 2017). A. subrotata was considered a widespread complex in southeast Asia with variety in leaf shape and two cytotypes (Chen et al 2017). There is a long-standing debate on the ecological success of polyploid relative diploids (Stebbins and Dawe 1987, Harbert et al. 2014). Being the westernmost known population, the karyological characterization of the Thai plants may provide a clear answer for that.
A. longifolia was placed into a single taxon with A. hainanensis W. Y. Chun et F. C. How, A. larutensis W. J. de Wilde & A. Vogel and A. yingjiangensis L. J. Peng (Phonsena and de Wilde 2010). However, A. longifolia was reported with a chromosome number of 2n=38 but no other karyotype features have been reported so far (Larsen 1963), while the chromosome of A. hainanensis and A. yingjiangensis were both reported 2n=36, with 2n=20m (2sat)+14st+2t and 2n=14m+6sm (2sat)+16st, respectively (Wang et al. 2001). Therefore, in 2018 we took the second filed work in Thailand in the framework of taxonomic revision and karyotype evolution study of Aspidistra. The chromosome numbers and karyotypes of A. longifolia and A. subrotata are reported in this study.
Plants were collected from the fieldwork in Thailand (Table 1, Fig. 1) and then cultivated in the experimental nursery of Guangxi Minzu University, Nanning, China.
| Species | Population | Voucher | Location | Latitude | Longitude |
|---|---|---|---|---|---|
| A. longifolia | L1 | Q. Gao QG707 | Chiang Rai, Doi Tung | 20°17′21.67″N | 99°48′39.99″E |
| L2 | Q. Gao QG1107 | Phitsanulok, Phetchaburi, Phu Hin Rong Kla NP. | 17°0′14.09″N | 100°59′39.29″E | |
| L3 | Q. Gao QG1109 | Phetchabun, Nam Nao NP. | 16°44′23.83″N | 101°34′25.39″E | |
| A. subrotata | S | Q. Gao QG1108 | Loei, Phu Luang WS. | 17°17′37.87″N | 101°33′18.21″E |
For chromosome observation, actively growing root tips were pretreated in 0.1% colchicine for 3–3.5 h at room temperature, and then fixed in Carnoy I (ethanol : glacial acetic acid=3 : 1) for 1 h above. Root tips were macerated in a 1 : 1 mixture of 1 M HCl and 45% acetic acid at 60°C for 4 min, stained, and squashed in 1% aceto-orcein.
More than 10 cells for each number were observed, and the karyotype formula was based on measurements of metaphase chromosomes taken from photographs. The nomenclature used to describe the karyotypes was followed by Levan et al. (1964). From the mean values of two to four individual karyotypes, the average chromosome length as well as the karyotype intrachromosomal index (A1) and interchromosomal asymmetry index (A2) (Zarco 1986) were calculated.
Plants of A. longifolia from three populations were observed and collected from Doi Tung, Chiang Rai, Phu Hin Rong Kla National Park, Phitsanulok, and Nam Nao National Park, Phetchabun, respectively (Table 1, Fig. 1).
All the plants investigated show a chromosome number of 2n=38 (Fig. 2A–C), and a karyotype formula 2n=24m+2sm+12st (Fig. 3A–C). The largest pair was median centromeric. Chromosomes II to VIII pairs were larger, of which one pair was submedian centromeric and the others were subterminal centromeric. The remaining chromosomes were smaller and median centromeric. The average chromosome length ranged from 5.86 to 6.10 µm, and the karyotype asymmetry indices A1 and A2 were from 0.43 to 0.44 and 0.53 to 0.55, respectively (Table 2).
| Species | Population | Karyotype formula | ALC (µm) | NCC | A1 | A2 | Figure |
|---|---|---|---|---|---|---|---|
| A. longifolia | L1 | 2n=38=24m+2sm+12st | 5.95±0.11 | 3 | 0.44±0.01 | 0.55±0.02 | 2A, 3A |
| L2 | 2n=38=24m+2sm+12st | 5.86±0.54 | 4 | 0.44±0.03 | 0.53±0.02 | 2B, 3B | |
| L3 | 2n=38=24m+2sm+12st | 6.10±0.22 | 4 | 0.43±0.02 | 0.53±0.03 | 2C, 3C | |
| A. subrotata | S | 2n=76=48m+4sm+24st | 5.21±0.10 | 2 | 0.44±0.01 | 0.58±0.01 | 2D, 3D |
A. subrotata was collected from Phu Luang Wildlife Sanctuary, Loei (Table 1, Fig. 1). The metaphase chromosomes were counted to be 2n=76 (Fig. 2D) and formulated as 2n=48m+4sm+24st (Fig. 3D). The largest pair was median centromeric. Chromosomes of II, IV to VIII pairs were subterminal centromeric. The III pair was submedian centromeric. The remaining chromosomes were small and median centromeric. The average chromosome length was 5.21 µm, and the average of karyotype asymmetry indices A1 and A2 were 0.44 and 0.58, respectively (Table 2).
Karyomorphological features were observed in A. longifolia and A. subrotata from Thailand (Table 2). Although the chromosome number of A. longifolia was counted to be 38 (Larsen 1963), the karyotype was first analyzed and confirmed as 2n=38=24m+2sm+12st in this study. It seems inappropriate to consider A. longifolia, A. hainanensis, and A. yingjiangensis as a single taxon by Phonsena and de Wilde (2010), according to the different chromosome numbers of 2n=36 reported for A. hainanensis and A. yingjiangensis (Wang et al. 2001). However, it is worth noting that plants of A. hainanensis reported with 2n=36, were collected from Jinxiu, Guangxi, where A. fasciaria G.Z. Li was also found and similar to A. hainanensis. Therefore, further cytological and morphological study on the plants of A. hainanensis from a typical locality should be carried out to clarify its taxonomic circumscription.
Different ploidy levels in A. subrotata have been reported by Chen et al. (2017). Diploid plants are distributed in Mt. Poman, Mt. Daqing, China, and Mt. Bavi Vietnam, with a chromosome number of 2n=38 and a karyotype formula 2n=22m+4sm+12st. The tetraploid plants of A. subrotata were considered to be only naturally distributed in China, with the easternmost known record of this species. However, another tetraploid population is reported in this study from Phu Luang Wildlife Sanctuary, Thailand, as the westernmost known record of A. subrotata. Therefore, from our results it seems that polyploids in A. subrotata have a larger range concerning diploids, a similar trend found also in other species (Stebbins and Dawe 1987, Dixit and Yadav 1989, Petit and Thompson 1999). Differently from Chinese tetraploid populations, plants of Thai populations show linear-lanceolate leaves (Phonsena and de Wilde 2010) and karyotypes of 2n=76=48m+4sm+24st with median centromeric chromosomes of IX pair. Further cytological studies on Laotian and Vietnamese plants and molecular studies on this complex may clarify the evolutionary origin and dynamics of natural polyploidization from the limestone area in southeast Asia.
The Aspidistra plants in Thailand, as the westernmost distribution of this genus (except A. longifolia in India), own the same base chromosome number of x=19 and three ploidy levels, i.e., diploidy, tetraploidy, and hexaploidy (Fig. 1). Meanwhile, only diploids with the chromosome base number of x=18 were found in A. attenuate Hayata and A. daibuensis Hayata and A. mushaensis from Taiwan, China (Chang and Hsu 1974), as the easternmost distribution of Aspidistra (except A. insularis Tillich with unknown chromosome number in Japan). It may shed some new light on the karyotypic evolution and polyploidization in this genus.
This work was supported by the National Natural Science Foundation of China under Grant 31560056, Guangxi University for Nationalities Research Funding Project under Grant 2018KJQD15, and the Guangxi Scholarship Fund of Guangxi Education Department under Grant 2020-61.
