ABSTRACT
ABSTRACT Important changes in vegetation types occur along elevational gradients. The genus Gymnocalycium is endemic to southern South America, and its species are distributed along elevational gradients. In particular, Gymnocalycium quehlianum is a globular cactus endemic to the Sierras de Córdoba. Studying cytogenetic aspects and DNA content in populations throughout their distribution is key to understanding the species. DNA content and cytogenetic characteristics were analyzed in four populations of G. quehlianum (615, 744, 948 and 1257 masl). The genome size in the four populations varied between 3.55 and 4.30 pg. The populations were diploid (2n = 22). All populations showed the karyotype formula of 10 metacentrics (m) + 1 submetacentric (sm). The species presented symmetrical karyotypes and constitutive heterochromatin CMA+/DAPI- associated with nucleolar organizing regions, always found in the first pair of m chromosomes. The 18-5.8-26S rDNA locus is found in the terminal regions of the first pair of chromosomes m, and the 5S locus is adjacent to the 18-5.8-26S locus. A tendency for DNA content to decrease with increasing altitude was observed.
RESUMEN A lo largo de los gradientes altitudinales se producen cambios importantes en los tipos de vegetación. El género Gymnocalycium es endémico del sur de América del Sur y sus especies se distribuyen en gradientes altitudinales. En particular, Gymnocalycium quehlianum es un cactus globular endémico de las Sierras de Córdoba. Estudiar aspectos citogenéticos y de contenido de ADN en las poblaciones a lo largo de su distribución es clave para comprender a la especie. En cuatro poblaciones de G. quehlianum (615, 744, 948 y 1257 msnm) se analizaron el contenido de ADN y las características citogenéticas. El tamaño del genoma en las cuatro poblaciones varió entre 3,55 y 4,30 pg. Las poblaciones resultaron diploides (2n=22). Todas las poblaciones presentaron la fórmula del cariotipo de 10 metacéntricos (m) + 1 submetacéntrico (sm). La especie presentó cariotipos simétricos y heterocromatina constitutiva CMA+/DAPI- asociados con regiones organizadoras nucleolares, que siempre se encontraban en el primer par de cromosomas m. El locus de ADNr 18-5.8-26S se encuentra en las regiones terminales del primer par de cromosomas m y el locus de 5S está adyacente al locus 18-5.8-26S. Se observó una tendencia del contenido de ADN a disminuir con el aumento de la altitud.
ABSTRACT
Karyotype analyses in members of the four Cactaceae subfamilies were performed. Numbers and karyotype formula obtained were: Pereskioideae = Pereskiaaculeata(2n = 22; 10 m + 1 sm), Maihuenioideae = Maihuenia patagonica (2n = 22, 9 m + 2 sm; 2n = 44, 18 m + 4 sm), Opuntioideae = Cumulopuntia recurvata(2n = 44; 20 m + 2 sm), Cactoideae = Acanthocalycium spiniflorum (2n = 22; 10 m + 1 sm),Echinopsis tubiflora (2n = 22; 10 m + 1 sm), Trichocereus candicans (2n = 22, 22 m). Chromosomes were small, the average chromosome length was 2.3 mum. Diploid species and the tetraploid C. recurvata had one terminal satellite, whereas the remaining tetraploid species showed four satellited chromosomes. Karyotypes were symmetrical. No CMA(-)/DAPI(+) bands were detected, but CMA(+)/DAPI(-) bands associated with NOR were always found. Pericentromeric heterochromatin was found in C. recurvata, A. spiniflorum, and the tetraploid cytotype of M. patagonica. The locations of the 18S-26S rDNA sites in all species coincided with CMA(+)/DAPI(-) bands; the same occurred with the sizes and numbers of signals for each species. This technique was applied for the first time in metaphase chromosomes in cacti. NOR-bearing pair no.1 may be homeologous in all species examined. In Cactaceae, the 18S-26S loci seem to be highly conserved.
