The level of chloroplast DNA has been estimated in bleached mutants of Euglena by the increase of the renaturation rate of a radioactive chloroplast DNA probe in response to the addition of total mutant DNA.
Two classes of bleached mutants differ from each other by their level of chloroplast DNA:– - a few bleached mutants contain chloroplast DNA in amounts similar to those of wild type strains; all sequences of the wild type chloroplast DNA seem to be present but in non stoechiometric proportions.
– - most bleached mutants have about 100 to 1,000 times less chloroplast DNA than wild type cells. In these mutants chloroplast DNA sequences form two frequency classes:
– - one class has about 5 to 12% of the complexity of the wild type genome; these sequences are reiterated from 30 to 160 times per cell and hybridize with wild type ribosomal cistrons. They are expressed as chloroplast ribosomal RNA in all bleached mutants analyzed so far.
– - the second class shows at least 40% of the complexity of the wild type genome; these sequences are present in 2 to 7 copies per cell.