Chloroplast and Mitochondrial DNA Variation in HORDEUM VULGARE and HORDEUM SPONTANEUM

Abstract

A survey of restriction fragment polymorphism in Hordeum vulgare and Hordeum spontaneum was made using 17 and 16 hexanucleotide restriction endonucleases on chloroplast (cp) and mitochondrial (mt) DNA, respectively. The plant accessions originated from various places throughout the Fertile Cresent and Mediterranean. The types of changes in cpDNA consisted of nucleotide substitutions and insertions and deletions on the order of 100 base pairs. In contrast, mtDNA has most likely undergone larger insertions and deletions of up to 20 kilobase pairs in addition to rearrangements. Grouping of mtDNA fragment data showed that in some cases geographical affinities existed between the two species, whereas in others there were no clear affinities. Nucleotide diversity estimates derived from the restriction fragment data were used in a number of comparisons of variability. Comparisons of overall mtDNA variability (nucleotide diversity = 9.68 x 10(-4)) with cpDNA variability (nucleotide diversity = 6.38 x 10(-4 )) indicated that the former are somewhat more variable. Furthermore, there was no indication that the wild H. spontaneum (cpDNA diversity = 5.57 x 10(-4); mtDNA diversity = 6.04 x 10( -4)) was more variable than the land races of H. vulgare (cpDNA diversity = 5.88 x 10(-4); mtDNA diversity = 9.79 x 10(-4)). In fact, on the basis of mtDNA diversity, H. vulgare was the more variable species. Comparison of organelle nucleotide diversity estimates with an estimate of nuclear nucleotide diversity derived from existing isozyme data provided evidence that both organelle genomes are evolving at a slower rate than the nuclear genome.