In the presence of either xenobiotic or endogenous reactive molecules, the synthesis of detoxifying enzymes and transporters is induced. The resulting metabolic processes, which facilitate the inactivation and elimination of these compounds, are divided into three discrete phases (Sandermann, 1992).
Phase I: Compounds are typically modified such that a functional group like e.g. a hydroxyl moiety is added or exposed through the action of hydrolases, cytochrome P450s, or peroxidases.
Phase II: Functional groups are conjugated to glycosyl, glutathione, and malonyl moieties. These reactions are catalyzed by specific glycosyltransferases, glutathione S-transferases, and less frequently, malonyltransferases.
Phase III: Conjugated forms of xenobiotics are recognized by specific membrane-associated transporters such as ABC transporters, resulting in their vacuolar sequestration or release into the apoplasmic space.
Induction of genes upon chemical stress is regulated by TGA transcription factors and SCL14 (Fode et al., 2008).