Abstract
ABSTRACT Cactaceae species are karyotypically well-known with x = 11 and chromosome number variation due mainly to polyploidization. However, both assumptions are based on descriptive observations without taking an evolutionary framework of Cactaceae into account. Aiming to confirm these hypotheses in an evolutionary context, we obtained chromosome numbers for 20 species of Cactoideae, performed an extensive review of chromosome number for the family, and analyzed these data using a phylogenetic approach. The karyotypes presented here were characterized by CMA/DAPI banding, and for six species 5S and 45S rDNA sites were located. Our data, along with a survey of the literature, reinforce the long-standing hypothesis of a x = 11 as the base chromosome number for Cactaceae. They also reinforce the relevance of polyploidy in karyotype evolution of cacti, although polyploidy was important just after the diversification of subfamilies Maihuenioideae and Pereskioideae. Despite the homogeneous chromosome complements observed among cacti, chromosome banding and FISH techniques revealed informative characteristics, allowing the identification of chromosome synapomorphies, such as proximal CMA+ bands in Melocactus and proximal 5S rDNA in Pilosocereus, indicating the taxonomic potential of chromosome characterization in cacti.
Highlights
Cacti species have been important for humans for the past 9,000 years due to their frequent uses as food, medicine and, mainly and more recently, as ornamental plants (Russell & Felker 1987; Anderson 2001; García-Suárez et al 2007; Aragane et al 2011)
The terminal CMA+/DAPI– bands were always co-localized with 45S rDNA, and they were usually more intense when compared to proximal bands
Two terminal CMA+/ DAPI– bands were observed in diploid species with 2n = 22, whereas four bands were observed in the tetraploids, 2n = 44 (Figs. 1, 2)
Summary
Cacti species have been important for humans for the past 9,000 years due to their frequent uses as food, medicine and, mainly and more recently, as ornamental plants (Russell & Felker 1987; Anderson 2001; García-Suárez et al 2007; Aragane et al 2011). Three centers of diversity are proposed (Anderson 2001; Arakaki et al 2011): (1) arid regions in North America Most species of Cactaceae have showy flowers and exhibit adaptations to arid environments, the so-called succulent syndrome: shallow roots, thick and waxy cuticle and CAM photosynthesis (Anderson 2001; Arakaki et al 2011).
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