Karyology and cytophotometric estimation of inter- and intraspecific nuclear DNA variation in four species of Porphyra (Rhodophyta)

Abstract

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 Coli var. amplifolia Oliveira Filho et Coli 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 Linnaeus and Arabidopsis thaliana (Linnaeus) Heynhold, and the green seaweed Cladophora albida (Hudson) Kützing 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.