Karyotype characterization reveals active 45S rDNA sites located on chromosome termini in Smilax rufescens (Smilacaceae)

Abstract

ABSTRACT. The genus Smilax (Smilacaceae) includes species of medicinal interest; consequently, their identification is important for the control of raw material used in the manufacture of phytotherapeutic products. We investigated the karyotype of Smilax rufescens in order to look for patterns that would be useful for comparative studies of this genus. To accomplish this, we developed procedures to grow plants and optimize root pretreatment with mitotic fuse inhibitors to obtain metaphase spreads showing clear chromosome morphology. The karyotype, analyzed in Feulgen-stained preparations, was asymmetric, with N = 16 chromosomes gradually decreasing in size; the larger ones were subtelocentric and the smaller chromosomes were submetacentric or metacentric. Nearly terminal secondary constrictions were visualized on the short arm of chromosome pairs 7, 11, and 14, but they were clearly detected only in one of the homologues of each pair. The nucleolus organizer regions (NORs) were mapped by silver staining and fluorescent in situ hybridization of 45S rDNA probes. Silver signals (Ag-NORs) colocalized with rDNA loci were detected at the termini of the short arm of 6 chromosomes. The secondary constriction heteromorphism observed in Feulgen-stained metaphases suggests that differential rRNA gene expression between homologous rDNA loci can occur, resulting in different degrees of chromatin decondensation. In addition, a heteromorphic chromosome pair was identified and was interpreted as being a sex chromosome pair in this dioecious species.

Chromosomal localization of 45S rDNA, sex-specific C values, and heterochromatin distribution in Coccinia grandis (L.) Voigt

“…The CMA-positive signals are generally considered to represent GC-rich heterochromatin found mostly at NORs and also at proximal positions, coinciding with DAPI negativity (Guerra et al 2000). Such variations, though uncommon, have been found in a number of plant and animal species and has opened novel scopes to understand functional aspects of NOR regions (Cheng and Heneen 1995;Caperta et al 2002;Bi et al 2009;Pizzaia et al 2013). The proximal CMA +ve /DAPI −ve bands represent NOR-independent heterochromatic areas showing differential distribution between the male and female populations.…”

Karyotype structure and NOR activity in Brazilian Smilax Linnaeus, 1753 species (Smilacaceae)

“…Some polyploids (n= 32, 48 and 64) have been found in Asian species (Vijayavalli and Mathew 1989, Fu and Hong 1990, Fu et al 1993, 1995, Huang et al 1997, Kong et al 2007, Sun et al 2015). The karyotypes of the species analyzed were asymmetric and modal, with most chromosomes being submetacentric and subtelocentric and all of them gradually decreasing in size (Vijayavalli and Mathew 1989, Fu and Hong 1990, Fu et al 1993, 1995, Kong et al 2007, Pizzaia et al 2013). Smilax species are dioecious and heteromorphic chromosomes have been detected in some species, and are thought to be sexual chromosomes (Mangaly 1968, Vijayavalli and Mathew 1989, Fu et al1995, Pizzaia et al 2013).…”

“…The karyotypes of the species analyzed were asymmetric and modal, with most chromosomes being submetacentric and subtelocentric and all of them gradually decreasing in size (Vijayavalli and Mathew 1989, Fu and Hong 1990, Fu et al 1993, 1995, Kong et al 2007, Pizzaia et al 2013). Smilax species are dioecious and heteromorphic chromosomes have been detected in some species, and are thought to be sexual chromosomes (Mangaly 1968, Vijayavalli and Mathew 1989, Fu et al1995, Pizzaia et al 2013). Secondary constrictions and satellites were detected in few species (Vijayavalli and Mathew 1989, Fu et al 1995 and Pizzaia et al 2013).…”

“…Some studies on Smilax cytogenetics have reported chromosome numbers and karyotype characterization. Chromosome numbers of n = 16 were described for most species, but n = 13 and n = 15 were also recorded (Speese 1939, Mangaly 1968, Mehra and Sachdeva 1976, Vijayavalli and Mathew 1989, Fu and Hong 1990, Fu et al 1993, 1995, Huang et al 1997, Kong et al, 2007, Pizzaia et al 2013; Sun et al 2015). Some polyploids (n= 32, 48 and 64) have been found in Asian species (Vijayavalli and Mathew 1989, Fu and Hong 1990, Fu et al 1993, 1995, Huang et al 1997, Kong et al 2007, Sun et al 2015).…”

“…Smilax species are dioecious and heteromorphic chromosomes have been detected in some species, and are thought to be sexual chromosomes (Mangaly 1968, Vijayavalli and Mathew 1989, Fu et al1995, Pizzaia et al 2013). Secondary constrictions and satellites were detected in few species (Vijayavalli and Mathew 1989, Fu et al 1995 and Pizzaia et al 2013).…”