Abstract: Chloroplast DNA (ctDNA)from the rape (Brassica napus) and tobacco (Nicotiana tabacum) has been isolated using a intact pure chloroplast lysis methed followed by discontinute sucrose gradient centrifugation and DNase treatment. Our electron microscopic observation on the chloroplast DNAs revealed clearly flowerlike configurations made up of many “petal-loops” linked together in the middle to forming one “central-loop”. The number of petal-loops per molecule varies from 5 to 50, usually about 7 or 8. The size of the petal-loops is not much different, being 1.52 ± 0.48μm and 1.28 ± 0.37μm in average length for rape and tobacco respactively. Some petal-loops appear attached to membrane protein, indicating the possibility that ctDNAs may have a similar organization as chromosome. Besides, some configurations are quite large with a total of over 50 petal-loops including 2 or 3 molecules linked together by petal-loops, and some rather small ones with a single circular molecule, the size of which is about to 1–2 petal-loops in length. Such variation in the size of ctDNA may suggest the possibility of hithly organized internal molecular arragement of the ctDNA and occurrence of intramolecular of intermolecular recombination.

Key words: Chloroplast DNA, DNA form, DNA loop, Rape, Tobacco