Specific checkpoints regulate plant cell cycle progression in response to oxidative stress

The effects of oxidative stress on plant cell cycle progression were studie d both in cell suspensions and in planta. Oxidative stress of variable seve rity was imposed by the addition of different concentrations of the methyl- quinone, menadione, into the growth media. In cell suspensions, flow cytome try analyses demonstrated that low concentrations (20-50 mu M) of menadione impaired the G1/S transition, slowed DNA replication, and delayed the entr y into mitosis. Furthermore, cells in G1 were more sensitive to menadione-m ediated oxidative stress than cells in S phase. Cell cycle arrest was assoc iated with an inhibition of the activity of cyclin-dependent kinases, cell cycle gene expression, and a concomitant activation of stress genes. Menadi one-mediated oxidative stress was shown to have very similar effects on tob acco plants, suggesting that a general regulation mechanism takes place in plants. These results define an oxidative stress checkpoint pathway that mo dulates both the expression of the core cell cycle genes and oxidative defe nce genes. Redox sensing could be of key importance in controlling cell cyc le progression in environmental stress conditions.