When in vitro plantlets developed under low light conditions are exposed to high light upon transfer to ex vitro, it is common to observe symptoms of oxidative stress. In order to unravel more of what takes place in this phase of transition, paramount for plant survival, the present study focused on the expression of genes coding for proteins related with the metabolic pathways most affected upon transfer to ex vitro and monitored their expression in response to hormones and chemicals inducing alternative sinks for photosynthetic electron transport (PET) and reactive oxygen species (ROS) production. The expression of eight genes was significantly downregulated after all the treatments: catalase, beta-glucosidase, cytochrome P450, vegetative storage protein 2, wak1, a calcium binding protein, a meprin and TRAF homology domain-containing protein and a serine/threonine kinase. It was possible to verify that abscisic acid (ABA) was able to revert light induced gene expression and that the PET inhibitors DCMU and DPI had the same effect as ABA. ABA and jasmonic acid showed parallel effects, as both induced the expression of the same set of genes. Finally, exogenous cytokinin, instead of enhancing the plant´s response to high light led to the downregulation of light-responsive genes
