Main conclusion Arabidopsis wildtype plants suffer symptoms of stress at a sudden increase in CO 2 concentration, resulting from perturbation of photosynthetic electron transport. Defense-related gene induction includes increased methionine cycle and glucosinolates metabolism. Abstract Elevated CO 2 (eCO 2 ) increases photosynthetic performance of plants, but also leads to decreased nitrogen-to-carbon ratio and a long-term dec...