Background High (intense) light stress causes the formation of oxygen radicals in chloroplasts and has the potential to damage them. However, plants are able to respond to this stress and protect the chloroplasts by various means, including transcriptional regulation in the nucleus. Although the corresponding signalling pathway is largely unknown, the high light response in the expression of the Arabidopsis APX2 gene is reported to be mediated by hydrogen peroxide.

Results We characterized light stress signalling by analysing expression profiles of another high light-inducible gene of Arabidopsis, ELIP2, with the aid of an ELIP2 promoter-luciferase gene fusion. The established ELIP2::LUC transgenic Arabidopsis showed activation by high light, but not by hydrogen peroxide. On the other hand, the native ELIP2 gene as well as the APX2 gene was activated by the hydrogen peroxide. The activation of ELIP2::LUC by intense light was not inhibited by K252a but by okadaic acid.

Conclusion The light stress signalling from the chloroplast to the nucleus is revealed to be mediated through at least two pathways: both hydrogen peroxide-dependent and –independent. The latter pathway is thought to be mediated by the protein phosphatase 2A/1 activity that is suppressed by okadaic acid.