Detection of Chloroplast DNA by Using Fluorescent Monoclonal Anti-Bromodeoxyuridine Antibody and Analysis of Its Fate During Zygote Formation in Chlamydomonas Reinhardtii

A monoclonal anti-bromodeoxyuridine antibody conjugated to fluorescein was used to detect the chloroplast nucleoids after specific incorporation of bromodeoxyuridine (BUdR) into the chloroplast DNA of Chlamydomonas reinhardtii. The incorporation of BUdR was enhanced by simultaneous treatment with fluorodeoxyuridine (FUdR). The method was applied to analyze the fate of chloroplast DNA in zygotes resulting from mating between BUdR-treated gametes (mt+ or mt-) and untreated gametes of opposite mating-type. In crosses between wild-type strains, the nucleoids of mt+ origin remained in the large majority of zygotes whereas those of mt- origin most often disappeared within the first hours following copulation. In crosses of the type mat-3 mt+ x wild-type mt- (the mat-3 mutation permits a high transmission of chloroplast genes from the mt- parent), the nucleoids of mt- origin were generally not eliminated which indicates that the mat-3 mutation prevents the selective destruction of paternal chloroplast DNA in the zygote.