Agar Analysis,nuclear genome quantification and characterization of four agarophytes (Gracilaria) from the Mexican Gulf Coast

DNA reassociation kinetics were used to determine nuclear genome organization and complexity in four species of Gracilaria (Gracilariales, Rhodophyta). In Gracilaria tikvahiae, G. caudata, G. cervicornis and G. divaricata, results indicate the presence of three second order components corresponding to fast, intermediate and slow fractions. Repetitive sequences varied from 13–46% and unique DNA ranged from 45–78%, Thermal denaturation (T _m) indicated guanine + cytosine (G + C) levels of 41.9–46.0 mol % G + C. Microspectrophotometry with the DNA-localizing fluorochrome DAPI was used to quantify nuclear DNA content. Comparisons of mean nuclear DNA (I _f) values to chicken erythrocytes (RBC) resulted in an estimate of 0.37–0.40 pg/2C genomes for the four Gracilaria species. Total agar content following alkaline pretreatment ranged from 7–15% dry weight. Gel strengths were generally below commercial levels, ranging from 40–260 g cm⁻² Nuclear genome profiles developed from information for genome size, organization and complexity are compared with data for agar quantity and quality. Gel quality and quantity do not appear to be correlated with either large repetitive fraction DNA or a high degree of genome complexity as previously speculated.