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Gayana Bot. v.63 n.1 Concepción 2006
Gayana Bot. 63(1): 115-118 2006. Comunicación Breve
CHROMOSOME NUMBERS OF CHILEAN PTERIDOPHYTES: FIRST CONTRIBUTION
NUMEROS CROMOSOMICOS DE PTERIDOFITOS CHILENOS: PRIMERA CONTRIBUCION
Pedro Jara-Seguel1, Mario Romero-Mieres1 & Claudio Palma-Rojas2
1Escuela de Ciencias Biológicas y Químicas, Facultad de Recursos Naturales, Universidad Católica de Temuco, Casilla 15-D, Temuco-Chile. email@example.com
2Departamento de Biología, Facultad de Ciencias, Universidad de La Serena, Casilla 599, La Serena-Chile.
Mitotic chromosome counts in Chilean pteridophytes confirm the diploidy described for Equisetum L. (2n = 216) and Blechnum L. (2n = 66), as well as the tetraploidy of Asplenium L. (2n = 144). Megalastrum spectabile (Kaulf.) A.R.Sm. et R.C.Moran is diploid (2n = 82), while in metaphases of Polystichum subintegerrimum (Hook. et Arn.) R.A.Rodr. chromosome numbers from ca. 311 to 328 were counted. Tetraploidy was also described in Adiantum chilense Kaulf. (2n = 116).
The analysis of chromosome numbers represents an important step in studies of genetic variation, phylogeny, taxonomy and evolution, as well as in studies on the structure and diversity of the genomes (e.g., genome sizes, ploidy levels, nuclear architecture).
In pteridophytes, chromosome numbers have been documented by Manton (1950), Tryon et al. (1975), Löve et al. (1977), Smith & Mickel (1977), Walker (1985), Dawson et al. (2000), Bennett & Leitch (1997, 2001), Yatabe et al. (2001), Widén et al. (2001), Hanson & Leitch (2002), Obermayer et al. (2002), Tindale & Roy (2002), Buarque et al. (2003), Windham & Yatskievych (2003), Perrie et al. (2003), Buarque et al. (2005), Bennert et al. (2005). Others important contributions are available but are not cited here. Based on all these references, we compiled information on chromosome numbers for at least 641 species (7.12% of the species recognized), which inhabit in Europe, Oceania, North America, Asia and Caribbean Island. In South America, chromosome data for 27 species (included in the total above) have been documented for taxa from Amazonia and north-eastern Brazil (Tryon et al. 1975, Buarque et al. 2003, Buarque et al. 2005). However, species from other South American countries have not been analysed.
Among the South American undersampled taxa are the Chilean pteridophytes. These taxa are all homosporous, and although they are a minor component of the biodiversity of Chilean vascular plants (about 2.3% of vascular plants) (Marticorena 1990), are important due to that historically have been used as medical (Looser & Rodríguez 2004) and ornamental (Macaya 2004) resources. Despite of that, the structure and diversity of their genomes have not been still studied.
In this work chromosome numbers for nine native Chilean species belonging to six genera and five families are shown. Chromosome numbers may be used in first instance to elaborate a chromosome index for Chilean pteridophytes, which may be the basis for future studies on structure, diversity and evolution of the genomes of these vascular plants.
Sporophytes of one accession of each species were obtained from naturally growing populations, and voucher specimens were deposited in the no official herbarium (UCT) of the Escuela de Ciencias Biológicas y Químicas of the Universidad Católica de Temuco (Table I). The taxonomic identification was based on Gunckel (1984) and Rodríguez (1995). In the laboratory, plants were kept with their rhizomes submerged in water subject to constant aeration, in order to favor active growth of adventitious roots. After ten to fifteen days, 5 mm-long root tips were excised from the rhizomes and treated in a solution of 2 mM 8-hydroxiquinoline for 1 h at room temperature followed by 23 h at 8ºC (Buarque et al. 2003). They were then fixed in ethanol_acetic acid (3:1 v/v) for at least 24 h, placed in 70% ethanol, and stored at 4ºC until required. The mitotic chromosomes were obtained by squashing of root tips previously stained with the Feulgen reaction, and photographed with a digital camera OLYMPUS C-5050 connected to microscope OLYMPUS CX31. The chromosome counts were made on magnified printed photograph.
The chromosome numbers are presented in Table I, and metaphases of four species are shown in Fig. 1.
The results of chromosome count for species of each genus are described as follow:
Adiantum L. (Adiantaceae): A tetraploid number 2n = 116 was described for Adiantum chilense Kaulf. var. chilense, and its base number x = 29 is similar to that documented for A. pedatum L. (Haufler & Soltis 1986). The chromosome numbers described for these two species are the sole recorded for the genus.
Asplenium L. (Aspleniaceae): The tetraploidy documented previously for species of Asplenium (Herrero et al. 2001, Van den Heede et al. 2004) was also found for A. dareoides Desv. (2n = 144). The base number for the genus is x = 36. Inter-specific variations in chromosome numbers in this genus have been compiled by Dawson et al. (2000) for New Zealand taxa, whose larger value was recorded for a hexaploid cytotype of A. trichomanes L. (2n = 216).
Blechnum L. (Blechnaceae): The four species analysed showed a diploid chromosome number 2n = 66, which is similar to the described for fifteen New Zealand species. Besides, a high variation in 2n numbers has been compiled by Dawson et al. (2000), with 2n values from 56 chromosomes for three species (x = 28) to 132 for a tetraploid accession of B. fluviatile (R.Br.) Salomon (x = 33). However, the most frequent base number for the genus is x = 33.
Figure 1. Mitotic metaphases of (a) Blechnum mochaenum var. mochaenum 2n = 66, (b) Megalastrum spectabile var. spectabile 2n = 82, c) Asplenium dareoides 2n = 144, and d) Polystichum subintegerrimum 2n = ca. 311. Bar = 10 µm.
Figura 1. Metafases mitóticas de (a) Blechnum mochaenum var. mochaenum 2n = 66, (b) Megalastrum spectabile var. spectabile 2n = 82, c) Asplenium dareoides 2n = 144 y d) Polystichum subintegerrimum 2n = ca. 311. Barra = 10 µm.
Equisetum L. (Equisetaceae): The diploid chromosome number of Equisetum bogotense Kunth. (2n = 216) was similar to that described for others species of the Subgenus Equisetum (Obermayer et al. 2002). Additionally, all species of this Subgenus checked to date are uniform with a high base number x = 108, which is unusual within the pteridophyta. This base number is also presents in hybrid species of the Subgenus Hyppochaete (J.Milde) Baker which were found to be triploid with 2n = 324 chromosomes (Bennert et al. 2005).
Megalastrum Holtt. (Dryopteridaceae): The diploid chromosome number 2n = 82 described for Megalastrum spectabile (Kaulf.) A.R.Sm. et R.C.Moran was similar to that documented previously for its sister genus Dryopteris Adans. (Widén et al. 2001). The base number for these two genera is x = 41.
Polystichum Roth (Dryopteridaceae): Meta-phases with 2n numbers from ca. 311 to 328 chromosomes were observed in Polystichum subintegerrimum (Hook. et Arn.) R.A.Rodr. This high 2n number is nearby to that described previously for the octoploid Polystichum neozelandicum Fée, with n = ca. 164 bivalents in diakinesis (2n = ca. 328) (Perrie et al. 2003). Furthermore, Perrie et al. (2003) pointed out that others species have been described as tetraploid with 2n = ca. 164 chromosomes. The base number for the genus is x = 41. The remarkable similitude in the base number x = 41 among Megalastrum, Dryopteris and Polystichum, suggest a constancy of base chromosome number in the family Dryopteridaceae.
The high chromosome number described for nine Chilean species of pteridophytes is a typical character for homosporous, whose lowest record is x = 27 (Windham & Yatskievych 2003). On the other hand, the allopolyploidy described in many species (Herrero et al. 2001, Van den Heede et al. 2004, Perrie et al. 2003) together with the different diploid numbers reported, may be evidence of a high genome diversity in these vascular plants. However, with aprox. 116 species of pteridophytes recognized for continental Chile, much remains to be done. Further studies in others Chilean families will be reported in the future, thus increasing the information on chromosome numbers in homosporous pteridophytes.
We are grateful to Dr. Julio R. Gutiérrez for reading the manuscript. Financed by DGIUCT Project 2005-4-02.
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