Nad6 orf, encoded in the sunflower mitochondrial genome in single copy contains a non-conserved 3'-extension. The transcription of the nad6 locus generates a highly complex pattern. Three main transcripts of 1240, 960 and 870 nt have been characterized by different approaches. The two smaller ones are apparently the most abundant of the steady-state RNA population and are generated as primary transcription products as well as by processing of the 1240 nt transcript. Their 5'-UTRs are absent or very short. Whereas the 3'-ends of the 960 nt transcripts contain a TGA codon the shorter one terminates at positions excluding the stop codon. The fate of transcripts to promote the synthesis of NAD6 sunflower protein seems, thus, to rely on the occurrence of mechanisms yet to be identified.