Pipecolatebetaine is accumulated together with prolinebetaine in certain species; notably Medicago and Achillea (Wood et al, 1991; Bonham et al, 1995). Pipecolic acid is often accumulated to high levels by members of the Fabaceae (Stewart and Larher, 1980; Rosenthal, 1982), and indeed free pipecolic acid is a major constituent of the free amino acid pool of Medicago (Wood et al, 1991). It is not known whether the proline and N-methylproline N-methyltransferases have dual substrate specificity and are also capable of N-methylating pipecolic acid, and N-methylpipecolic acid, respectively.

Pipecolic acid is derived from lysine catabolism via alpha-aminoadipic semialdehyde (Goncalves-Butruille et al, 1996) which cyclizes to delta-1-piperideine-6-carboxylate. The latter can then be reduced to pipecolic acid in a reaction analogous to that catalyzed by P5CR (Stewart and Larher, 1980; Rosenthal, 1982; Galili, 1995) (see also Lysine catabolism under Branched chain amino acid and lysine synthesis).

Bonham CC, Wood KV, Yang W-J, Nadolska-Orczyk A, Samaras Y, Gage DA, Poupart J, Burnet M, Hanson AD, Rhodes D 1995 Identification of quaternary ammonium compounds by plasma desorption mass spectrometry. J. Mass Spectrom. 30: 1187-1194.

Galili G 1995 Regulation of lysine and threonine synthesis. Plant Cell 7: 899-906.

Goncalves-Butruille M, Szajner P, Torigoi E, Leite A, Arruda P 1996 Purification and characterization of the bifunctional lysine-ketoglutarate reductase-saccharopine dehydrogenase from maize. Plant Physiol. 110: 765-771.

Rosenthal GA 1982 Plant nonprotein amino and imino acids. Biological, Biochemical and Toxicological Properties. Academic Press, New York.

Stewart GR, Larher F 1980 Accumulation of amino acids and related compounds in relation to environmental stress. In "The Biochemistry of Plants" (BJ Miflin ed), Vol. 5, Academic Press, New York, pp. 609-635.

Wood KV, Stringham KJ, Smith DL, Volenec JJ, Hendershot KL, Jackson KA, Rich PJ, Yang W-J, Rhodes D 1991 Betaines of alfalfa: characterization by fast atom bombardment and desorption chemical ionization mass spectrometry. Plant Physiol. 96: 892-897.