Figure 1.

Major Routes for IAA Degradation in Arabidopsis.

Oxidation of IAA to oxIAA, and subsequent conjugation with Glc to form oxIAA-Glc, is a major route for IAA catabolism in Arabidopsis, based on feeding experiments with labeled precursors and mass spectrometry-based quantification of IAA metabolites (Östin et al., 1998; Kowalczyk and Sandberg, 2001; Kai et al., 2007; Kubeš et al., 2012; Peer et al., 2013). IAA can also be conjugated to either Glc or amino acids (AA), and these compounds can be further metabolized to oxIAA-Glc, 6-OH-IAA-AA, and oxIAA-AA. Some of these conjugates may act as reversible storage forms of IAA that can later be hydrolyzed to produce free IAA. The most abundant AA conjugates in Arabidopsis seedlings are normally IAA-Asp and IAA-Glu (Östin et al., 1998; Tam et al., 2000; Kowalczyk and Sandberg, 2001; Kai et al., 2007; Novák et al., 2012).