The gene for alternative oxidase-2 (AOX2) from Arabidopsis thaliana consists of five exons unlike other AOX genes and is transcribed at an early stage during germination

We investigated the expressions of genes for alternative oxidase (AOX1a, AO X1b, AOX1c and AOX2) and genes for cytochrome c oxidase (COX5b and COX6b) d uring germination of Arabidopsis thaliana, and examined oxygen uptakes of t he alternative respiration and the cytochrome respiration in imbibed Arabid opsis seeds. A Northern blot analysis showed that AOX2 mRNA has already acc umulated in dry seeds and subsequently decreased, whereas accumulation of A OX1a mRNA was less abundant from 0 hours to 48 hours after imbibition and t hen increased. The increase of the capacity of the alternative pathway appe ared to be dependent on the expressions of both AOX2 and AOX1a. On the othe r hand, steady-state mRNA levels of COX5b and COX6b were gradually increase d during germination, and the capacity of the cytochrome pathway was correl ated with the increase of expressions of the COX genes. Antimycin A, the re spiratory inhibitor, strongly increased the expression of AOX1a but had no effect on the expression of AOX2. A 5'RACE analysis showed that AOX2 consis ts of five exons, which is different from the case of most AOX genes identi fied so far. Analysis of subcellular localization of AOX2 using green fluor escent protein indicated that the AOX2 protein is imported into the mitocho ndria.