Mitotic karyotype stability and meiotic irregularities in the families Loranthaceae Juss. and Viscaceae Miq

Abstract

-Chromosome number, interphase nuclear structure, prophase chromosome condensation patterns, and meiotic behaviour were analysed in 14 Brazilian species within the families Loranthaceae and Viscaceae. All the species showed reticulate interphase nuclei and an uniform pattern of prophase chromosome condensation. The eleven species of Loranthaceae studied had 2n=16, whereas the three species of Viscaceae (Phoradendron) had 2n=28. The mitotic chromosome of only two species of Phoradendron revealed a significant karyotype asymmetry, while the remaining karyotypes were more symmetrical, and similar to each other. By contrast, the meiotic behaviour of ten species analysed exhibited several meiotic irregularities, characteristics of structural heterozygosis. In one sample of Struthanthus syringifolius, the majority of the meiocytes showed a ring tetravalent. The stability in mitotic karyotype associated with the meiotic irregularities observed in several genera of these families suggest that in spite of the structural changes orthoselection has preserved a diploid basal karyotype with large and symmetrical chromosomes. It is hypothesized that this karyotype was established before the diversification of these families and its large DNA amount has hindered the occurrence of polyploidy in these families.

IAPT chromosome data 35

“…The families presented new chromosome counts for almost all the analyzed species, in which 2n = 16 for Loranthaceae and 2n = 28 for Santalaceae were relatively more constant and conserved among their Neotropical representatives (Table 1). The obtained data in the present study support the basic number x = 8 for the Neotropical genera of Loranthaceae, as well as x = 14 for Santalaceae, suggesting dysploidy events (Andrade & al., 2005). Nevertheless, in Santalaceae, out of the eight analyzed species, only one was diploid (Phoradendron dipterum, with 2n = 16), which shows a numerical variability compatible with the incidence of disploidy by increasing a chromosome pair.…”

“…All previous counts using pollen grain stem cells were confirmed, as well as mitotic cell counts for Psittacanthus dichroos and Phoradendron perrottetii (Andrade & al., 2005). Struthanthus thyrsiflorus was the only species with two populations analyzed in this study, which presented 2n = 16 for the population of Morro do Chapéu -BA and 2n = 28 for the population of Simão Dias -SE.…”

“…Loranthaceae is quite diverse, has about 76 genera and 1050 species that occur in the Old and New World, rarely in temperate zones (Kuijt & Hansen, 2015;Christenhusz & Byng, 2016), while Santalaceae exhibit nearly 1000 species distributed in more than 43 genera, occurring in temperate, arid and tropical regions (Der & Nickrent, 2008;Nickrent & al., 2010;Christenhusz & Byng, 2016). Cytologically, these two families are poorly known, which most important contributions in terms of chromosome number records were Barlow (1963), Wiens (1968), , , Barlow & Martin (1984), Andrade & al. (2005) and Moraes & al.…”

IAPT chromosome data 39 – Extended version

“…On the other hand, the small chromosome size (Li & al., 2017) and the presence of repetitive and heterochromatic regions in Cactaceae increase the probability of hybridization and polyploidization (Eng & Ho, 2019;Madani & al., 2021;Heslop-Harrison & al., 2023). This is a positive situation for the expansion of chromosome sets as a whole (Gomes & al., 2012;Heslop-Harrison & al., 2023), but has a negative effect on dysploidy (Luceño & Guerra, 1996;Marinho & al., 2019). Some climatic factors, mainly temperature gradients, either in altitude or latitude, associated with both fragmentation and isolation of populations, have large impact on polyploidy in cacti, as this is an important response to the environment, especially when extreme factors limit taxa present there (Rice & al., 2019;Bauk & al., 2023).…”