| Abstract: | Plastid DNA band patterns generated by electrophoresis of endonuclease digests demonstrate remarkable conservation of DNA sequences at the species and subspecies level in flowering plants. Generally, patterns are identical or near-identical from different populations belonging to the same species. This methodology has now been applied to red algae to ascertain its value in systematic studies. Plastid DNA from nine bangiophycean and florideophycean red algae was isolated and cut with restriction endonucleases that recognize different 6-base pair sequences. The patterns generated upon the electrophoretic separation of digestion fragments show that within a species patterns are identical, but not within higher taxa. The proper identification of one Gracilaria population of uncertain taxonomic affinity was clearly established by this method of plastid DNA analysis. Differences between species in plastid DNA sequences were confirmed by probing blots of restriction fragments with known gene sequences. A number of heterologous plastid DNA probes were found to be sufficiently homologous to be useful in studying red algal DNA. Unexpectedly, supercoiled circular plasmids ranging in size from ca. 1.5–8 kb were found in some red algal species but not in others. The position of these plasmids in agarose gels following electrophoresis is uniform within a species but differs between different species of the same genus, contributing further patterns for taxonomic analysis. |
