Analysis of plastid DNA-like sequences within the nuclear genomes of higher plants

A wide-ranging examination of plastid (pt)DNA sequence homologies withinhigher plant nuclear genomes (promiscuous DNA) was undertaken. Digestionwith methylation-sensitive restriction enzymes and Southern analysis wasused to distinguish plastid and nuclear DNA in order to assess the extentof variability of promiscuous sequences within and between plant species.Some species, such as Gossypium hirsutum (cotton), Nicotiana tabacum(tobacco), and Chenopodium quinoa, showed homogenity of these sequences,while intraspecific sequence variation was observed among differentcultivars of Pisum sativum (pea), Hordeum vulgare (barley), and Triticumaestivum (wheat). Hypervariability of plastid sequence homologies wasidentified in the nuclear genomes of Spinacea oleracea (spinach) and Betavulgaris (beet), in which individual plants were shown to possess a uniquespectrum of nuclear sequences with ptDNA homology. This hypervariabilityapparently extended to somatic variation in B. vulgaris. No sequences withptDNA homology were identified by this method in the nuclear genome ofArabidopsis thaliana.