ABSTRACT
In 1968, 60 years after the original experiments of Bauer and Correns, the genetic autonomy of chloroplasts could be understood in molecular terms with the conclusive demonstration of the presence of DNA in chloroplasts. The success of the method depends upon the fact that higher plant chloroplasts can be obtained in relative intact condition, therefore, it is possible to remove contaminating nuclear DNA by treating with DNase. The molecular sizes of the higher plant Chloroplast (ctDNA)s have been determined by electron microscopy. The superhelix density of pea, lettuce, and spinach form ctDNA was determined by performing ethidium bromide sedimentation velocity titration. The studies on the molecular size of ctDNA by denaturation-renaturation experiments and electron microscopy indicated that the ctDNA consisted of homogeneous molecules with its entire information content present in the sequence of a circular DNA molecule. However, these techniques are only able to analyze the average properties of a very large number of molecules.
