ABSTRACTThe most thoroughly investigated CMS type in sunflower is the PETI (or Leclercq) cytoplasm. The organization of the mtDNA of male sterile (PETI cytoplasm) and fertile lines differs only by an 11 kb inversion and a 5 kb insertion. Due to this insertion a new open reading frame. orfH522, is created in the 3'-flanking region of the atpA gene. The presence and transcription of the orfH522 correlates with the CMS phenotype. A homology to the 5 kb insertion could also he detected in another male sterile cytoplasm in sunflower, MAXI, and in one population of H. maximiliani (MAX30). However, in the MAXI cytoplasm the homologous region is not localized in the 3'-flanking region of the atpA gene. Sequence analysis of this region revealed that there exists a homology of about 90% to. both, the orfH522 and the orfH873.The mitochondrially encoded in organello translation products of male sterile, contrary to fertile lines, show an additional 16 kD polypeptide. In the other investigated male sterile cytoplasms ...