The mode of action, and mechanism of resistance of many antibiotics are known since antibiotic resistance markers are commonly used in microbial genetics. Some of them, such as streptomycin, kanamycin and chloramphenicol selectively inhibit protein synthesis on the ''bacterial type'' ribosomes of the chloroplasts and mitochondria. Resistance to these antibiotics is, in some cases, coded by the organellar DNA, so these mutations are convenient markers in studies on organelle segregation, recombination and function in fungi and a 1 gae 1 The need for marker mutations in plant cell genetics, and our interest in cytoplasmic organelles, suggested to us the selection of antibiotic resistant cell lines in cell cultures of two species belonging to the genus Nicotiana~ N. tabacum and N. sylvestris. Streptomycin, kanamycin and chloramphenicol resistant lines described in flowering plants (N. tabacum~ N. sylvestris~ Petunia hybrida) and the moss, Physcomitrella patens~ have been reviewed. In the next sections some recent results on streptomycin, chloramphenicol and kanamycin resistance from our laboratory will follow.