Nuclear DNA amounts in Macaronesian angiosperms

Abstract

Nuclear DNA contents for 104 Macaronesian angiosperms, with particular attention on Canary Islands endemics, were analysed using propidium iodide flow cytometry. Prime estimates for more than one-sixth of the whole Canarian endemic flora (including representatives of 11 endemic genera) were obtained. The resulting 1C DNA values ranged from 0.19 to 7.21 pg for Descurainia bourgeauana and Argyranthemum frutescens, respectively (about 38-fold difference). The majority of species, however, possessed (very) small genomes, with C-values <1.6 pg. The tendency towards small nuclear DNA contents and genome sizes was confirmed by comparing average values for Macaronesian and non-Macaronesian representatives of individual families, genera and major phylogenetic lineages. Our data support the hypothesis that the insular selection pressures in Macaronesia favour small C-values and genome sizes. Both positive and negative correlations between infrageneric nuclear DNA amount variation and environmental conditions on Tenerife were also found in several genera.

Fig. 1. 1C DNA amount distribution (pg means) of 104 Macaronesian species investigated.

Fig. 2. Flow‐cytometric histograms showing the difference in 2C nuclear DNA content for species with the smallest DNA amounts, Descurainia bourgeauana and D. lemsii (A), and species with the highest DNA amounts, Argyranthemum haouarytheum and A. frutescens (B). Nuclei of both species in the genus were isolated and stained with propidium iodide simultaneously. Small G2 peaks represent the nuclei of Descurainia with doubled (4C) nuclear DNA content.

Fig. 3. Flow‐cytometric histogram obtained after simultaneous analysis of propidium iodide‐stained nuclei of Lycopersicum esculentum (L.e.; internal standard) and Rumex maderensis. Occurrence of nuclei with 2C, 4C and 8C DNA amounts indicates endoreduplication.