ANALYSIS OF PLASTID DNA-LIKE SEQUENCES WITHIN THE NUCLEAR GENOMES OF HIGHER-PLANTS

A wide-ranging examination of plastid (pt)DNA sequence homologies with in higher plant nuclear genomes (promiscuous DNA) was undertaken. Dige stion with methylation-sensitive restriction enzymes and Southern anal ysis was used to distinguish plastid and nuclear DNA in order to asses s the extent of variability of promiscuous sequences within and betwee n plant species. Some species, such as Gossypium hirsutum (cotton), Ni cotiana tabacum (tobacco), and Chenopodium quinoa showed homogenity of these sequences, while intraspecific sequence variation was observed among different cultivars of Pisum sativum (pea), Hordeum vulgare (bar ley), and Triticum aestivum (wheat). Hypervariability of plastid seque nce homologies was identified in the nuclear genomes of Spinacea olera cea (spinach) and Beta vulgaris (beet), in which individual plants wer e shown to possess a unique spectrum of nuclear sequences with ptDNA h omology. This hypervariability apparently extended to somatic variatio n in B. vulgaris. No sequences with ptDNA homology were identified by this method in the nuclear genome of Arabidopsis thaliana.