Environmental stresses have been shown to induce strongly and transiently metabolism changes in plant cells such as ion fluxes and a so called oxidative burst. Hydrogen peroxide (H202), the major molecule produced by the oxidative burst was shown to play a dual role in both the induction of antioxidant genes and in the programmed cell death. This
H202-induced-programmed cell death suggests that H2r2 may also involved in down-regulating genes responsible for the cell-cycle progression. Using a synchronisable tobacco cell suspension, the present project aims to answer the following questions: (1) does H202triggers a common signal transduction pathway responsible for the induction of antioxidant genes and the inhibition of cell cycle progression genes ? (2) what are the key steps of this pathway and is it possible to modify them through transgenic approch ? (3) what are the molecular mecanisms involved in the regulation of transcription of the both types of genes ?