Chloroplast nucleoids in large number and large DNA amount with regard to maternal inheritance inChlamydomonas reinhardtii

Summary We studied the maternal chloroplast inheritance ofChlamydomonas reinhardtii by epifluorescence microscopy after staining with DNA specific fluorochrome DAPI and by genetic methods, using wild type cells and cells containing previously isolated mutation of cond-1 and cond-2. Wild type cells contained about 7 chloroplast (cp) nucleoids, while mutants, cond-1(+) and cond-2(+), contained about 14 and 23 cp nucleoids, respectively, after one week culture on agar plates. The total cpDNA contents were almost proportional to the numbers of cp nucleoids. When cells containing cond-1 or cond-2 mutation were used as a parental source to cross with wild type cells of the other parent, preferential digestion of cp nucleoids from male parent (mt^–) origin occurred in the zygotes, although the frequencies of the digestion were slightly lower than that in the zygotes from the cross between wild type cells. Western blot analysis of the protein ofzyslB gene, which has been found related to preferential digestion of mt^– origin cp-nucleoids DNA, showed that a high amount of this protein was detected with the initiation of preferential digestion of mt^– cp nucleoids and disappeared with the completion of the digestion. Cp genetic markers for antibiotic resistance were maternally inherited in all crosses. These results showed that although the preferential digestion of cp nucleoids consisting of large number and large cpDNA amount requires a slightly longer period to complete, this high ploidy of the cp nucleoids does not disturb maternal inheritance.