Nitric oxide induces transcriptional activation of the nitric oxide-tolerant alternative oxidase in Arabidopsis suspension cells.

Nitric oxide (NO) is a double-edged sword - it can be either beneficial and activate defence responses in plants and animals or, together with reactive oxygen species, it can kill not only the pathogen but also the host. A prime target of NO is the cytochrome c-dependent respiration. Only plants possess alternative-pathway respiration with alternative oxidase (AOX) as a terminal electron acceptor. AOX has been suggested to be barely affected by NO. Here we show that NO affects cytochrome-dependent respiration in Arabidopsis thaliana (L.) Heynh. At the same time, treatment of Arabidopsis cell cultures with NO actually strongly induced AOX1a transcription, as determined by using a cDNA microarray and by Northern analysis. In accordance with transcript accumulation, NO treatment of suspension cells resulted in increased respiration through the alternative pathway. Addition of an AOX inhibitor to Arabidopsis cell cultures resulted in dramatically increased NO-sensitivity and cell death. In all, our data suggest that NO induces the AOX1a gene and that AOX may participate to counteract the toxicity of NO. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00425-002-0828-z.