In addition to serving as a precursor of spermidine and spermine, putrescine has three other metabolic fates; conjugation with hydroxycinnamic acids, metabolism to gamma-aminobutyrate (GABA), and utilization in alkaloid biosynthesis.

GABA can be derived from putrescine (via gamma-aminobutyraldehyde) through the reactions catalyzed by diamine oxidase [EC 1.4.3.6] and gamma-aminobutyraldehyde dehydrogenase (Flores et al, 1989). As noted in the discussion of Quaternary ammonium and tertiary sulfonium compounds, the latter enzyme may be the same as BADH involved in glycinebetaine synthesis (Trossat et al, 1997).

Putrescine serves as precursor of the nicotine and tropane alkaloids (Smith et al, 1979; Flores et al, 1989; Hashimoto and Yamada, 1994), which may play important roles in plant defense against herbivores.

Flores HE, Protacio CM, Signs MW 1989 Primary and secondary metabolism of polyamines in plants. In "Plant Nitrogen Metabolism" (JE Poulton, JT Romeo, EE Conn eds), Rec. Adv. Phytochem, Vol 23, Plenum Press, New York, pp. 329-393.

Hashimoto T, Yamada Y 1994 Alkaloid biogenesis: molecular aspects. Annu. Rev. Plant Physiol. Plant Mol. Biol. 45: 257-285.

Smith TA, Bagni N, Fracassini DS 1979 The formation of amines and their derivatives in plants. In (EJ Hewitt, CV Cutting eds) "Nitrogen Assimilation of Plants", Academic Press, New York, pp. 557-570.

Trossat C, Rathinasabapathi B, Hanson AD 1997 Transgenically expressed betaine aldehyde dehydrogenase efficiently catalyzes oxidation of dimethylsulfoniopropionaldehyde and omega-aminoaldehydes. Plant Physiol. 113: 1457-1461.