Genome size, heterochromatin organisation, and ribosomal gene mapping in four species of Ribes

Abstract

Four wild Ribes species (Ribes alpinum L., Ribes petraeum Wulf., Ribes rubrum L., and Ribes uva- crispa L.; all 2n = 2x = 16) were surveyed for their chromosome and genome organisation. Their genome size was assessed using flow cytometry. Ribes alpinum had 5.3% more nuclear DNA than did the three other species, whose average was 2C = 1.91 pg with 40.4% GC. In addition, GC- and AT-rich heterochromatin and rDNA (18S–5.8S–26S and 5S) patterns were studied using fluorochrome banding and double-target fluorescence in situ hybridization (FISH), respectively. Only GC-rich heterochromatin was detected, co-localizing with 18S–26S rDNA. Fluorochrome banding and FISH patterns revealed marked differences between species. Ribes alpinum and R. uva-crispa differed from R. rubrum and R. petraeum by the number of 18S–26S sites and the localization of 5S rDNA. Ribes alpinum and R. uva-crispa were differentiated by the number of 5S sites. Ribes rubrum and R. petraeum also differed by the number of 5S sites and by the size of the GC-rich band on the satellite chromosome pair. These results should contribute to a better understanding of phylogenetic relationships among these species.Key words: Ribes, flow cytometry, fluorochrome banding, FISH, rDNA, NORs.