CYTOPHOTOMETRIC ESTIMATION OF INTERPACIFIC AND INTRASPECIFIC NUCLEAR-DNA CONTENT VARIATION IN GRACILARIA AND GRACILARIOPSIS (GRACILARIALES, RHODOPHYTA)

Microspectrophotometry with the DNA-localizing fluorochrome hydroethidine was used to estimate nuclear genome sizes in three geographic isolates of Gracilaria tikvahiae, Gracilaria sp. (cultivar G-6), G. blodgettii and Gracilariopsis lemanieformis. Relative fluorescence (I(f)) values for the angiosperm Antirrhinum majus and the green alga Cladophora albida were plotted against their known DNA contents to derive a standard line. Mean 2 C nuclear DNA I(f) values for Gracilaria and Gracilariopsis were extrapolated to obtain estimates of their genome sizes. Results indicate a narrow range of relatively small values (0.35-0.45 pg) in isolates examined. All Gracilaria species had similar nuclear genomes, within the range of 0.40-0.45 pg, while a smaller genome of 0.35 pg was indicated for Gracilariopsis lemanieformis. Variations in genome size and previously determined differences in nucleotide base pair compositions suggest genome repatterning processes which may have accompanied speciation in these taxa.