12 Purification of Mitochondrial DNA from Green Tissues of Arabidopsis

Plant mttochondrtal genomes vary m size and complextty. Both can be rapidly estimated by analysis of the restriction pattern of purified mitochondrial DNA (mtDNA). A prerequisite to purify mtDNA with little contamination of nuclear and also of plastid DNA is the isolatton of mitochondrta from cells. Mitochondria from green plants are generally dtfticult to purify because of the low amount of these organelles and the high number of chloroplasts m photosynthetic tissues. For a large number of plants, rt 1s possible to isolate comparatively pure mitochondria from nonphotosynthetic tissues (1 ) or cell cultures (2 ). The absence of mature chloroplasts reduces the plastid contamination and increases the purification rate. In many investigations, however, it is necessary to use green tissues such as leaves as sources, when as for Arabidopsis, only few nonphotosynthetic tissues or certain cell cultures are available. Furthermore, tissue cultures are not always the ideal source for mvestigations of mitochondrial genome structure, since frequent reorganizattons have been reported for such tissue cultures, which distort the inplanta structure of these genomes (3 ,4 ).