A Cytological Study on three Species of Colocasia (Araceae) from Yunnan

Transcription

1 CARYOLOGIA Vol. 56, no. 3: , 2003 A Cytological Study on three Species of Colocasia (Araceae) from Yunnan ZHIYUN YANG, TINGSHUANG YI, HENG LI and XUN GONG* Kunming Institute of Botany, Chinese Academy of Sciences, Kunming Yunnan , China. Abstract - Chromosome numbers and karyotypes of three Colocasia species from Yunnan were reported. Their karyotypes were as follows: 2n=2x=28=22m(1sat)+6sm for C. gongii; 2n=2x=28=20m+8sm for C. gaoligongensis; 2n=2x=28=20m+8sm for C. gigantea. Common karyomorphological characteristics of three species examined were: (1) the simple chromocenter type of the resting chromosomes and the proximal type of the mitotic prophase chromosomes; (2) the chromosome number 2n=28 and (3) the chromosome complement of m- and sm-chromosomes. x=14 was confirmed as the basic chromosome number of Colocasia. There were differences among species in the number of m- and sm-chromosomes as well as satellite. Key words: C. gongii; C. gaologongensis; C. gigantea; basic chromosome number; karyomorphology. INTRODUCTION Colocasia Schott, a small genus of family Araceae, comprising about 13 species, is widely distributed in tropical and subtropical Asia (MAYO et al. 1997). 11 species are currently recognized in China (LI 1986; LI and LONG 1999; LONG and LI 2000; LONG and LIU 2001). Some species, such as C. esculenta, are widely cultivated in tropical, subtropical and temperate area as an important food crop. Since NAKAJIMA (1936) did the chromosome study on Colocasia esculenta, abundant cytological data were reported for Colocasia (KURAKUBO 1940; ITO 1942; RAO 1947; DELAY 1951; SHARMA and DAS 1954; MOOKERJEA 1955; PFITZER 1957; FUKUSHIMA et al. 1962; YEN and WHEELER 1968; BAI et al. 1971; KAWAHARA 1978; KURUVILLA et al. 1981; COASTES et al. 1988; OKADA and HAMBALI 1989; PETERSEN 1989; SREEKUMARI and MATHEW, 1991a, b; KOKUBUGATA and KONISHI 1999), but * Corresponding author: fax ; gongxun@mail.kib.ac.cn cytological data are mainly associated with different populations of C. esculenta for its variation of chromosome numbers. Although most species of Colocasia are distributed in China, and 4 new species, C. heterchroma, C. gaoligongensis, C. gongii and C. lihengiae, were recently described from Yunnan Province, China (LI and WEI 1993; LI and LONG 1999; LONG and LI 2000; LONG and LIU 2001), there was no cytological study on these species up to the present time. This paper deals with karyomorphological aspects of 3 species in Colocasia from Yunnan Province, China. Of them, C. gongii and C. gaoligongensis were recently described (LI and LONG 1999; LONG and LI 2000). MATERIAL AND METHODS The materials for cytological analysis were introduced from following sites and cultivated in Kunming Botanical Garden. Voucher specimens were deposited at the herbarium of Kunming Institute of Botany, Chinese Academy of Sciences (KUN).

2 324 YANG, YI, LI and GONG C. gaoligongensis: Hills at south end of Tenghong valley, Tengchong county, Yunnan, SW China, 3700m a. s. l. Yi Tingshuang C. gongii: Kagang, Jiemao in Yingjiang county, Yunnan, SW China, 760m a. s. l., Long Chun-lin C. gigantea: Pingbian county, Yunnan, SW China. Yi Tingshuang For the observations of somatic chromosomes, the growing root tips were pretreated in 0.1% colchicine solution at room temperature for 2.5 hours, and were then fixed in acetic alcohol (3:1=absolute ethanol and glacial acetic) at 4 C for 30 minutes. They were macerated in 1:1 mixture of 1 mol/l hydrochloric acid and 45% acetic acid at 60 C for 4 to 5 minutes and then were stained and squashed in 1% aceto-orcein solution before observation. Karyomorphological observations were made on chromosomes at resting stage and mitotic prophase and metaphase, and their classifications followed TANAKA (1971, 1977). Karyotype formulas were derived on measurements of metaphase chromosomes from photomicrographs. The nomenclature used to describe the karyotype followed LEVAN et al. (1964). The classification of karyotype asymmetry followed STEBBINS (1971). RESULTS The chromosomes at resting stage and mitotic prophase and metaphase of the three species examined are shown in Fig. 1. Their chromosome number is 2n=28. The karyomorphological characteristics are summarized in Table 1. In the nuclei at resting stage, several darkly stained heteropycnotic bodies, which were irregularly protruded, were clearly observed. The other region was just very dilutely stained, so the boundary of the bodies was rather distinct (Fig. 1A). Karyomorphology of the nuclei at resting stage was categorized to be simple chromocentre type. In the mitotic prophase chromosomes, heteroand euchromatic segments were distinguishable, and heterochromatic segments were mainly distributed in the proximal regions (Fig. 1B). The morphology of mitotic-prophase chromosomes was categorized to be the proximal type. The chromosome length of C. gongii ranged from 3.49 to 1.67 µm (Fig. 1D). The total length of chromosomes at metaphase was µm. The chromosome complement metaphase consisted of 22 metacentrics (m) and 6 submetacentrics (sm) chromosomes, and a satellite was observed on the short arm of one chromosome of the 13th pair of 13. Karyotype asymmetry was estimated as Stebbins 1A-type. The chromosome length of C. gaoligongensis ranged from 3.60 to 2.23 µm (Fig. 1E). The total length of chromosomes at metaphase was µm. The chromosome complement at metaphase consisted of 20 m- and 8 sm-chromosomes. Karyotype asymmetry was estimated as Stebbins 1Atype. The chromosome number of C. gigantea agreed with the previous reports (KURAKUBO 1940; ITO 1942; HOTTA 1971; RAMACHANDRAN 1978; OKADA et al. 1989). The chromosomes ranged in length from µm (Fig. 1C). The total length of chromosomes at metaphase was µm. The chromosome complement at Table 1 Measurements of somatic chromosome at metaphase in the representative karyotypes in C. gongii, C. gaoligongensis and C. gigantea. C. gongii C. gaoligongensis C. gigantea K=2n=2x=28=22m(1sat)+6sm K=2n=2x=28=20m+8sm K=2n=2x=28=20m+8sm Chrom. RL AR PC RL AR PC RL AR PC m m m m m sm m m m m m m m sm m m m m m m m sm m m m m m m m m* sm sm m m sm sm m* m sm sm sm sm RL: relative length; AR: arm ratio; PC: position of centromere; * satellite-chromosomes.

3 325 CYTOLOGICAL STUDY ON COLOCASIA FROM YUNNAN a c b d e E D C Fig. 1 The resting nuclear, prophase and somatic metaphase chromosome of three species in Colocasia. a) Resting nuclear of C. gongii; b) Prophase of C. gongii; metaphase plates and karyotypes respectively of C. gigantea (c and C), C. gongii (d and D) and C. gaoligongensis (e and E).

4 326 YANG, YI, LI and GONG metaphase consisted of 20 m- and 8 sm-chromosomes. Karyotype asymmetry was estimated as Stebbins 1A-type. DISCUSSION Previous cytological studies on Colocasia indicated some confusion concerning the basic chromosome number of the genus, and some different chromosome numbers were estimated, such as 2n=28,36 and 42, and x=7, 12 and 14 were suggested as the basic chromosome number of Colocasia by some previous researchers (RAO 1947; DELY 1951; DARLINGTON et al. 1955; MARCHANT 1971; RAMACHANDRAN 1978; COATES et al. 1988; OKADA et al. 1989). But, wild Calocasia species, except C. antiquorum, possess the same chromosome number, 2n=28. According to chromosome behaviours in meiosis (VIJAYA et al. 1971; OKADA et al. 1989), the basic chromosome number of Colocasia is x=14. The populations of C. esculenta with 42 chromosomes are triploid, 3x=42. The fact that plants with 42 chromosomes are sterile is one of evidences. x=12 was suggested as a basic chromosome number of Colocasia based on the observations of RAO (1947) and DELY (1951). However, none of the more recent studies on Colocasia have confirmed x=12 as a base number. It therefore seems that the plants observed with a base number of 12 were either misidentified as Colocasia species, or that the chromosome counts were inaccurate. Three species studied in this paper are diploid with 2n=2x=28. C. esculenta is the only species in Colocasia with various chromosome number and various basic chromosome number. The populations with chromosome number of 2n=42 were triploid with a basic chromosome number of x=14 but were not hexaploid with a basic chromosome number of x=7. The chromosome number of populations cultivated of C. esculenta may vary due to long history and the various conditions of cultivation. The karyomorphological characters of three species studied here were almost the same to each other, such as the chromosome complements only consisting of m- and sm-type of chromosomes, karyotype asymmetry of 1A-type. But, there are differences in the numbers of m- and sm-chromosomes as well as satellite-chromosomes among species. C. gongii is different from C. gigantea by tubiform convolute and golden yellow spathe blade which usually gapes at anthesis. C. gaoligongensis is different from C. esculenta by the widely obovate blade and spadix without appendix. In our study, the chromosome complement of C. gongii was different from that of C. gigantea by the number of m- and sm-chromosomes as well as satellite. The former possessed 22 m- and 6 sm-chromosomes, and lower asymmetry s index with The latter possessed 20 m- and 8 sm-chromosome?mand higher asymmetry s index of C. esculenta showed diversity not only in the chromosome number but also in karyotypes. Five karyotypes in C. esculenta were reported (SREEKUMARI and MATHEW 1991). So, karyotypes cannot be compared between C. gaoligongensis and C. esculenta. It is very necessary to study China s other species in Colocasia for revealing phylogenetic relationships of whole genus. REFERENCES BAI V.K., MAGOON, M.L. and KRISHNAN R., 1971 Meiosis and pollen mitosis in diploid and triploid Colocasia Antiquorum Schott. Genetica, 42: COATES D.J., YEN D.E. and GAFFEY P.M., 1988 Chromosome variation in Taro, Colocasia esculenta: Implications for origin I the pacific. Cytologia, 53, DARLINGTON C.D. and WYLIE A.P., 1955 Chromosome Atlas of Flowering Plants. George Allen and Unwin Ltd., London. DELAY J., 1951 Nombres chromosomiques chez les phanéorgames. Rev. Cytol. Biol. Végétales, 12: FUKUSHIMA E., IWASA S., TOKUMASU S. and IWA- MASA M., 1962 Chromosome numbers of the taro varieties cultivated in Japan. Chromosome Information Service, 3: HOTTA M., 1971 Study of the Family Araceae. Men. Coll. Sci. Univ. Kyoto, series B: ITO T., 1942 Chromosomen und Sexualität von der Araceae I. Somatische Chromosomenzahlen einiger Arten. Cytologia, 12: KAWAHARA T., 1978 Chromosome number of Taros in Nepal and India. Chromosome Information Services, 24: 4-5. KRISHNAN R. and MAGOON M.L., 1977 Edible aroids-new insights into phylogeny. In: C.L.A. LeaLiuy (Ed.), Proc. 3rd Int. Symp. Trop. Root Crops, pp Int. Inst. Tropical Agric., Ibadan, Nigeria. KURAKUBO Y., 1940 Über die chromosomenzahlen von Araceae-Arten. Bot. and Zool. (Tokyo), 8: 1492.

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