Abstract
The genus Smilax Linnaeus, 1753 (Smilacaceae) is a large genus of dioecious plants distributed in tropical, subtropical and temperate regions. Some Smilax species have medicinal importance and their identification is important for the control of raw material used in the manufacture of phytotherapeutical products. The karyotypes of seven Brazilian Smilax species were investigated. Mitotic metaphases of roots from young plants were analysed in Feulgen-stained preparations. The karyotypes were asymmetric and modal with 2n = 2x = 32 chromosomes gradually decreasing in size. In S. goyazana A De Candolle & C De Candolle, 1878, a polyploid species, 2n = 4x = 64. In all the species, the large and medium-sized chromosomes were subtelocentric and submetacentric and the small chromosomes were submetacentric or metacentric. Their karyotypes were quite similar, with differences in the arm ratio of some chromosomes. S. fluminensis Steudel, 1841 differed from the other species by having a large metacentric chromosome 1. These findings suggest that evolution occurred without drastic changes in the chromosomal structure in the species analyzed. Terminal secondary constrictions were visualized on the short arm of some chromosomes, but they were detected only in one homologue of each pair. Due to the terminal location and the degree of chromosome condensation, secondary constrictions were not visualized in some species. The nucleolus organizer regions (NORs) were mapped by silver-staining and fluorescent in situ hybridization (FISH) in S. rufescens Grisebach, 1842 and S. fluminensis. Silver-staining and FISH signals were colocalized on the short arms of six chromosomes in S. rufescens and four chromosomes in S. fluminensis. In FISH preparations, one of the largest chromosomes had the secondary constrictions highly decondensed in some cells. This finding and the heteromorphism observed in Feulgen-stained chromosomes suggest that differential rRNA gene expression between homologous rDNA loci can occur in some cells, resulting in different degrees of ribosomal chromatin decondensation. The presence of a heteromorphic chromosome pair in S. rufescens, S. polyantha Grisebach, 1842 and S. goyazana suggests a chromosomal sex determination in these dioecious species.
Highlights
The genus Smilax Linnaeus, 1753 (Smilacaceae) is a large genus of dioecious plants distributed in tropical, subtropical and temperate regions
In S. rufescens and S. fluminensis all the rDNA loci were active as demonstrated by silver-staining signals colocalized with the fluorescent in situ hybridization (FISH) signals
We concluded that differential expression of rDNA loci occurs in these species based on the observation of a distended secondary constriction in the largest nucleolus organizer regions (NORs) chromosome visualized in FISH preparations of some cells in both species
Summary
The genus Smilax Linnaeus, 1753 (Smilacaceae) is a large genus of dioecious plants distributed in tropical, subtropical and temperate regions. The genus has approximately 300 species, and their classification has been controversial (see Mangaly 1968). This genus had been assigned to the family Liliaceae, but for the past 20 to 30 years, botanists have accepted Smilacaceae as a distinct family belonging to the order Liliales according to APG III (The Angiosperm Phylogeny Group 2009). The genus has high variability in morphology, and morphological features were described for species in Brazil (Andreata 2009), North America (Mangaly 1968) and Asia (Koyama 1960, Fu et al 1995). Leaf morphology has been emphasized as an important feature for species identification by Mangaly (1968) and Andreata (2009). Reports on the morphoanatomy of vegetative organs (Martins and Appezzato-da-Gloria 2006, Martins et al 2010, 2012) and molecular phylogeny (Sun et al 2015) have contributed to species systematic
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