Specific mitochondrial proteins in pollen: presence of an additional ATP synthase beta subunit.

A protocol was designed to obtain a pure fraction of pollen mitochondria from the diploid species Nicotiana sylvestris, the female parent of the allotetraploid Nicotiana tabacum. Most organelles were morphologically intact and able to perform in organello mitochondrial (mt) protein synthesis. As revealed by two-dimensional protein electrophoresis, numerous quantitative differences exist between leaf and pollen mt proteins. Moreover, additional mt polypeptides, named R (for reproductive), encoded by either nuclear or mitochondrial genes, are found in pollen. The most abundant R polypeptide, R1 (M(r) 53,000, pI 5.6), is nuclearly encoded, is membrane bound, and cross-reacts with an antibody directed against the beta subunit of the mt ATP synthase (ATPase). N-terminal microsequence analysis showed that the two ATPase beta subunits present in leaves (beta 1 and beta 2) and the R1 pollen-specific subunit are encoded by distinct genes. A similar additional ATPase beta subunit was observed in pollen mitochondria from Petunia, suggesting that this polypeptide is of general importance for male gametophytic development in Solanaceaes.