KARYOLOGY AND CYTOPHOTOMETRIC ESTIMATION OF INTERSPECIFIC AND INTRASPECIFIC NUCLEAR-DNA VARIATION IN 4 SPECIES OF PORPHYRA (RHODOPHYTA)

A cytogenetic investigation of four Porphyra species (Rhodophyta) from the temperate and tropical western Atlantic indicates that P. leucosticta Thuret in Le Jolis and P. spiralis Oliveira Filho et Coll var. amplifolia Oliveira Filho et Coll include populations with three and four chromosomes. Microspectrophotometry with the DNA-localizing fluorochrome hydroethidine was used to estimate nuclear genome sizes. Relative fluorescence (I(f)) values for the angiosperms Antirrhinum majus Linaeus and Arabidopsis thaliana (Linnaeus) Heynhold, and the green seaweed Cladophora albida (Hudson) Kutzing were plotted against their known DNA contents in order to derive a standard line. Mean nuclear DNA (I(f)) values for Porphyra spermatia were extrapolated to obtain estimates of their genome sizes. The results indicate a narrow range of relatively small values (0.93-1.18 pg/2 C genome) in the isolates that were examined. Similarities in nuclear genome size for both three- and four-chromosome populations of P. leucosticta and P. spiralis var. amplifolia suggest that fusion/translocation processes rather than chromosome loss/gain accompanied speciation in these entities.