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Chromosome Counts in Six Species of Acanthaceae from China
2023 Volume 88 Issue 2 Pages 105-109
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2023 Volume 88 Issue 2 Pages 105-109
Chromosome numbers of one species of Eranthemum (E. macrophyllum Wall. ex Nees) and five species of Strobilanthes [S. affinis (Griff.) Terao ex J. R. I. Wood et J. R. Benett., S. biocullata Y. F. Deng & J. R. I. Wood, S. dimorphotricha Hance, S. heteroclita D. Fang et H. S. Lo and S. pseudocollina K. J. He et D. H. Qin] in the family Acanthaceae from China have been reported for the first time. The chromosome numbers were determined as 2n=4x=44 in E. macrophyllum, 2n=2x=30 in S. affinis, S. biocullata and S. heteroclita, 2n=2x=18 in S. dimorphotricha and 2n=2x=32 in S. pseudocollina.
Acanthaceae is a pantropical family comprising about 230 genera and 4,000 species and widely distributed in the tropical and subtropical regions of the world (Scotland and Vollesen 2000, Mabberley 2008, Hu et al. 2011, Manzitto-Tripp et al. 2021). Forty-two genera and 304 species are recognized in China of which two genera and 134 species are endemic (Hu et al. 2011, Deng et al. 2016, Deng and Gao 2020). Many species in Acanthaceae are very important sources of medicines, dyes, beverages, ornamentals, and so on (Hu et al. 2011). Because members of the family show a great diversity in morphological characteristics, habitats, and biogeographic patterns (McDade et al. 2000a, b, 2008), there has been considerable disagreement about its taxonomic system (Nees von Esenbeck 1847, Bentham 1876, Lindau 1895, Bremekamp 1965a, b, Devi and Mathew 1991, Scotland and Vollesen 2000). In order to establish a more accurate and reliable classification system, scholars have tried to obtain classification basis from different disciplines, such as morphology (Ahmad 1978, Inamdar et al. 1990), cytology (Grant 1955, Bir and Saggoo 1981, Devi and Mathew 1997, Daniel and Chuang 1998), palynology (Lindau 1895, Raj 1961, Scotland and Vollesen 2000), and molecular phylogeny (McDade et al. 2000a, b, 2005, Scotland and Vollesen 2000, Tripp 2007, Wenk and Daniel 2009, Tripp et al. 2013).
Plant cytology is used chromosomal data to explore taxonomic problems (Hong 1990). Karyological data such as chromosome number can provide evidence for biosystematics classification at the level of family, genus, and species (Hong 1990, Guerra 2008, Soltis 2014, Joshi et al. 2016). Besides, understanding the variation of chromosome number in a group is of great significance for exploring the evolutionary mechanism of the group (Hong 1990). However, less than 12% of the cytological data of Acanthaceae has been reported worldwide (Daniel et al. 2000). Moreover, in China, only 16 species were studied, i.e., Andrographis paniculata Nees (Chen et al. 2002), Peristrophe japonica (Thunb.) Bremek. (Ge et al. 1989), P. baphica Merr. (Chen et al. 2009), Rungia flaviflora Z. L. Lin & Y. F. Deng (Lin and Deng 2018), R. hirpex Benoist (Lin et al. 2016), S. cusia (Nees) Kuntze (Ge et al. 1989, Chen et al. 2009, Wu 2010), S. aprica (Hance) T. Anderson ex Benth. (Chen et al. 2009), S. tomentosa (Nees) J.R.I. Wood (Chen et al. 2009), Ruellia simplex C.Wright (Cai and Zhou 2012), Ru. elegans Poir. (Cai and Zhou 2012), S. bantonensis Lindau, S. compacta D. Fang et H. S. Lo, S. hongi Y. F. Deng & F. L. Chen, S. longzhouensis H. S. Lo & D. Fang, S. reptans (G. Forster) Moylan ex Y. F. Deng & J. R. I. Wood and S. retusa D. Fang (Wang et al. 2022). The taxonomic usability of chromosome numbers in the family has been ignored in China.
The purpose of this work is to contribute the chromosome numbers of six species in two genera of Acanthaceae from China to expand the chromosomal information of Acanthaceae.
The studied specimens of six Acanthaceae species were collected from natural habitats in China in 2020 (Table 1). Eight individuals of each species were investigated. All fresh specimens were transplanted to the greenhouse of the South China Botanical Garden (SCBG), Chinese Academy of Sciences, China. Voucher specimens were deposited in South China Botanical Garden Herbarium (IBSC).
| Taxon | Locality | Voucher | 2n |
|---|---|---|---|
| Eranthemum L. | |||
| E. macrophyllum Wall. ex Nees | Yingjiang, Yunnan, China | Y. F. Deng & G. H. Xu 27509 | 44 |
| Strobilanthes Bl. | |||
| S. affinis (Griff.) Terao ex J. R. I. Wood et J. R. Benett. | Menghai, Yunnan, China | Y. F. Deng et al. 29232 | 30 |
| S. biocullata Y. F. Deng & J. R. I. Wood | Fuchuan, Guangxi, China | Z. Y. Niu & Q. Wang NW20 | 30 |
| S. dimorphotricha Hance | Luzhai, Guangxi, China | Y. F. Deng & S. Wang YQ20190416 | 18 |
| S. heteroclita D. Fang et H. S. Lo | Longan, Guangxi, China | Q. Wang et al. WW04 | 30 |
| S. pseudocollina K. J. He et D. H. Qin | Yangshuo, Guangxi, China | Q. Wang WJ04 | 32 |
The studied materials were root tips from mature plants. Healthy root tips of 0.5–1 cm length were cut off between 8 a.m. and 9 a.m. Then samples were preprocessed with a pretreatment agent (0.1% colchicine : 2 mM 8-hydroxyquinoline=1 : 1, v : v) at room temperature for 2.5–3 h under dark conditions, fixed in Carnoy fixative (ethanol : acetic acid=3 : 1, v : v) in a 4°C refrigerator for 2–24 h, hydrolyzed in 1 M HCl at 37°C for 45 min, and stained in carbol fuchsin at room temperature for 1.5–4 h. Between every two deals, root tips were washed in distilled water three times. Lastly, the root tips were squashed gently in a drop of 45% acetic acid on a glass slide and observed under an Olympus BX43 microscope equipped with a digital camera. At least 30 well-spread metaphase plates for each species were photographed to determine the chromosome number (Li and Chen 1985).
The chromosome numbers and mitotic-metaphase chromosome plates of the six species belonging to two genera of Acanthaceae from China are presented in Table 1 and Fig. 1. This is the first report for these species.
The genus Eranthemum has about 40 species distributed in tropical and subtropical regions of Asia, and four species and one variety recorded in China (Hu et al. 2011, Deng 2020, Gong et al. 2020). In the present study, one species E. macrophyllum was newly reported its chromosome number from China (Gong et al. 2020). The chromosome number of E. macrophyllum was determined to be 2n=4x=44 with basic chromosome number x=11 (Fig. 1A).
Including E. macrophyllum, the chromosome numbers of seven species of Eranthemum have been reported, including 2n=22, 24, 30, 34, 40, 42, 44, 84 (Table 2). Nevertheless, the numbers in three species were controversial, i.e., E. capense, E. pulchellum and E. variegatum. So, in this genus, further cytological studies are needed to confirm the controversial species and explore the basic numbers.
| Taxon | 2n | References |
|---|---|---|
| E. capense | 30 | Ranganath (1981), Krishnappa and Ranganat (1982) |
| 40 | Gosavi et al. (2015) | |
| 44 | Saggoo and Bir (1982, 1986), Saggoo (1983) | |
| E. macrophyllum | 44 | Present study |
| E. pulchellum | 22 | Bala and Gu (2011) |
| 42 | Pathak and Singh (1949), Kaur (1970), Sarkar et al. (1978), Govindarajan and Subramanian (1985) | |
| 44 | Grant (1955), Saggoo (1983), Bala and Gu (2012) | |
| E. purpurascens | 84 | Kaur (1970) |
| E. roseum | 30 | Narayanan (1951) |
| E. splendens | 24 | Nanda (1962) |
| E. variegatum | 34 | Narayanan (1951) |
| 42 | Pathak and Singh (1949) |
The Strobilanthes is the third largest genus in the family Acanthaceae and consists of about 400 species distributed in tropical and subtropical regions of Asia with some species extending to the Pacific Islands (Hu et al. 2011, Deng 2020, Deng and Gao 2020). In China, 131 species have been reported mainly in the south of Changjiang Valley (Hu et al. 2011). In the present study, the chromosome numbers of five species in Strobilanthes were counted. The chromosome numbers of S. affinis, S. biocullata and S. heteroclita are 2n=2x=30 (Fig. 1B, C, E). The chromosome number of S. dimorphotricha is 2n=2x=18 (Fig. 1D). The chromosome number of S. pseudocollina is 2n=2x=32 (Fig. 1F).
By integrating the present and previous chromosome count data of Strobilanthes, the chromosome numbers of 48 species have been obtained (Wang et al. 2022). However, nine species had inconsistent chromosome numbers according to different research, including S. atropurpurea, S. atropurpureus var. atropurpurea, S. callosus, S. cusia, S. dalhousieanus, S. glutinosus, S. lawsoni, S. persicifolia, and S. urticifolia. For S. callosus, Saggoo and Bir (1982) and Saggoo (1983) reported 2n=28, while Mane et al. (2018) found 2n=30. The two extra chromosomes might be miscounted or B chromosomes because of their dispensable propety within species (Hong 1990). For S. cusia, Hsu (1968) counted 2n=16, but Ge et al. (1989) and Iwatsubo et al. (1993), and Hu et al. (2011) reported 2n=32. Perhaps the former counted the chromosome numbers in gametophytes, while the latter in sporophytes. Same reason for S. urticifolia and S. dalhousieanus. On account of the change in taxonomic position and the lack of micrographs, the chromosome numbers of these species require further confirmation.
As shown in the previous work (Wang et al. 2022), Strobilanthes has a diverse chromosome number, involving 2n=16, 18, 20, 22, 26, 28, 30, 32, 40, 42, and 60. Excluding nine species with inconsistent chromosome numbers, the most common numbers are 2n=32 (43%) and 2n=30 (32%). In addition, 2n=16 is the lowest number in Strobilanthes, so we suggest x=8 as the basic number for this genus, which agrees with the result of Daniel and Chuang (1998). Other chromosome numbers might be produced by the aneuploidy and polyploidy of x=8. For example, x=8 evolved to n=9, 10, 11, 13, 14, 15 by the ascending aneuploidy. Then polyploidy occurred in some of these numbers, producing n=16, 20, and 30. Therefore, aneuploidy and polyploidy may promote the evolution of the genus Strobilanthes.
This work was financially supported by the National Natural Science Foundation of China (grant nos. 32170213).
