| Abstract: | The chromosome numbers and karyotypes of 7 species of Smilax L. in Liliaceae (s. 1.) are cytotaxonomically studied in this work. Their karyotypic characters, distinction between the species and the chromosomal basis of sexual differentiation are discussed. The karyotypes of most species are first reported. The results are shown as follows (see Tables1-4 for the chromosome parameters and the karyotype constitution; Fig. 1 for their idiograms): 1. Smilax nipponica Miq. The species is one of the herbaceous species distributed in East Asia. Two karyotypes, 2n = 26(type A) and 2n = 32 (type B), are found in the species (Plate 1: 1-7). The karyotype of No. 88032 (uncertain of -L--M--S- sexuality) is 2n = 26 = 2m + 6st + 6m + 4sm + 6sm + 2st. The karyotype has 4 pairs of L chromosomes, of which the first three pairs are subterminal, and the 4this median. The karyotype belongs to 3B. No. 88045 (the male) and No. 88046(the female) have 2n = 32. Their karyotypes are basically uniform, and both are -L--M-- S2n=32= 2m+4sm+ 2st+ 2m+4sm+ 6m+ 10sm + 2st, also with 4 pairs of Lchromosomes, but the 2nd pair is median, and thus different from the type A. Thekaryotype belongs to 3B. The first pair of chromosomes of the male are distinctlyunequal in length, with the D. V. (0.93) of relative length between them obviouslygreater than that of the female (0.1). The pair seems to be of sex-chromosomes.Sixteen bivalents (n= 16) were observed at PMCs MI of No. 88045 (Plate 1: 4).The major difference between the karyotypes A and B are greater relative lengthof L chromosomes in the type A than in the type B, and the increase of chromosome number in the karyotype B mainly due to the increase of st chromosomes. Nakajima (1937)reports 2n= 30 for S. hederacea var. nipponica (=S. nipponica,Wang and Tang, 1980). 2. S. riparia A. DC. This species is also herbaceous, distributed in East Asia. Thirty chromosomes were found in root-tip cells (uncertain of sexuality). The kar -L--M--S-yotype is 2n = 30 = 8st + 6sm + 2st + 6m + 6sm + 2st (Plate 3: 1, 5), consistingmainly of sm and st chromosomes. There are 4 pairs of L chromosomes which areall subterminal and the m chromosomes appear to fall all into S category. Thoughthe karyotype belongs to 3B, it is less symmetrical than that of S. nipponica. Thespecies is karyologically rather different from S. nipponica, therefore. The first pairof chromosomes of this material are unequal in length, and it may be a male. Thekaryotype of this species is first reported. 3. S. sieboldii Miq. The species is a thorny climbing shrub, distributed inEast Asia. At PMCs All, 16 chromosomes (n= 16) were found (Plate 2: 6), inaccordance with Nakajima's (1933) report for a Japanese material. 4. S. china L. This species, a thorny climbing shrub, is of a wide distribution range mainly in East Asia and Southeast Asia. Two karyotypes were observedin different populations. (1) The population from Xikou has 2n = 96(6x) = 20st+L- -M- 6t + 6sm + 12st + 52(S) (Plate 3:7), of which the first three pairs of chromosomes are terminal, different from those in the other species. The arm ratios ofboth L and M chromosomes are larger than 2.0, which resembles those of S. davidiana. (2) PMCs MI of the population from Shangyu shew 15 chromosomes (n15). The hexaploid of the species is recorded for the first time. Hsu (1967,1971)reported 2n = 30 from Taiwai and Nakajima (1937) recorded n = 30 from Japan,which indicates that the karyotype of the species varies not only in ploidy, butalso in number. 5. S. davidiana A. DC. The somatic cells were found to have 32 chromosomes, and PMCs MI shew 16 bivalents (Plate 2: 1-5). The karyotype is 2n = 32=-L- -M- -S 8st + 4sm + 4st + 8sm + 8st. The karyotype belongs to 3B, and is less symmetrical than those in herbaceous species. The D. V. (0.20) of relative length betweenthe two homologues of the first pair is slightly larger in the male than in the female (0.14), and it is thus difficult to determine whether they are sexual chromosomes or not. 6. S. glabra Roxb. The species is a non-thorny climbing shrub, distributedin East Asia and Southeast Asia. 32 chromosomes were found in somatic cells. The -L- -M- - Skaryotype is 2n= 32= 8st + 10st+6sm+8st (Plate 3: 2, 6),with only 3 pairsof sm chromosomes (12, 13 and 16th). The karyotype is more asymmetric thanthat of S. davidiana, although it is also of 3B (Table 1). The karyotype is firstreported for the species. 7. S. nervo-marginata Hay. var. liukiuensis (Hay.) Wang et Tang The varietyhas a relatively narrow distribution range, mainly occurring in eastern China. Thechromosomal number of somatic cells is 2n= 32 (Plate 3: 3-4). The karyotype is -L- -M- -S2n = 32 = 2sm + 6st + 2sm + 2st + 2m + 6sm + 12st, evidently different from thatof S. glabra. The first pair of chromosomes are submedian, and much longer thanthe 2nd to 4th pairs. The ratio in length of the largest chromosome to the smallestone is 4.3. The symmetric degree is of 3C, a unique type. The karyotype of thespecies is reported for the first time. In Smilax, the known basic numbers are 13, 15, 16 and 17. The two herbaceous speciesdistributed in East Asia have three basic numbers: 13, 15 and 16, while the woody species studied mainly have 16, with no 13 recorded. Mangaly (1968) studied 8 herbaceous species in NorthAmerica and reported 2n=26 for them except S. pseudo-china with 2n=30. Mangaly considered that a probably ancestral home of Smilax, both the herbaceous and woody, is in SoutheastAsia and the eastern Himalayas, and speculated that the ancestral type of Sect. Coprosmanthus is possibly an Asian species, S. riparia. The karyotypes of the two herbaceous species inEast Asia consist mostly of sm and m chromosomes, whereas those for the North Americanspecies are all of st chromosomes. Based on the general rule of karyotypic evolution, i.e. fromsymmetry to asymmetry, his speculation seems reasonable. Researches on sex-chromosomes of Smilax have been carried out since 1930 (Lindsay, 1930;Jensen, 1937; Nakajima, 1937; Mangaly, 1968), and they are generally considered to be thelargest pair, but there is still no adequate evidence. The result of our observation on S. nipponicamay confirm that the first pair of chromosomes of this species is XY type of sex-chromosomes. Chromosomes of the genus are small and medium-sized, varying between 1-6 μm, slightlylarger in herbaceous species than in woody ones, larger in the karyotype of 2n=26 than inthat of 2n=32. Based on karyotype constitution of the above 5 species, the karyotype in thegenus is characterized by 4 pairs of L chromosomes and 2-5 pairs of M chromosomes, andmostly st and sm chromosomes, and by rather asymmetrical 3B type. The degree of symmetryin the above 5 species is from Sect. Coprosmanthus to Sect. Coilanthus, and herbaceous species towoody ones. |
