Gibberellins are modified by methylation in planta.

Methylation, the attachment of a methyl group in place of a hydrogen atom, is a common modification to numerous biological substrates. Almost all classes of plant metabolite are known to be methylated, including amino acids, alkaloids, phenylpropanoids, sugars, sterols, thiols, flavonoids, and purines (D’Auria et al., 2003). Methylation affects structural characteristics of these metabolites that impact their mobility, activity, and/or interactions with other molecules and therefore is often an important regulatory modification. The most widely used methyl donor in plant systems is S-adenosyl-L-methionine (SAM), and hundreds of SAM-dependent methyltransferases (MTs) have been identified. O-methylation (transfer of the methyl group to an oxygen atom) is the most common reaction that occurs among plant-specialized (i.e., secondary) metabolites, and O-methyltransferases (OMTs) constitute a large superclass of enzyme that contains numerous subgroups or families. Ibrahim et al. (1998) proposed a classification scheme for OMT depending on the substrate (e.g., whether they act on phenylpropanoids, flavonoids, alkaloids, or aliphatic substrates). However, a number of MTs have since been identified that do not fall into any of these classes, and it has been recognized that substrate is not necessarily a reliable predictor of MT provenance or phylogeny (D’Auria et al., 2003).