HORT640 - Metabolic Plant Physiology
Polyamines, nonprotein amino acids and alkaloids
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(see also Secondary products derived from aromatic amino acids)
The diamine putrescine, the triamine spermidine and the tetramine spermine are ubiquitous in plant cells (Smith et al, 1979; Bagni and Pistocchi, 1992). They occur as free cations and as conjugates with phenolic acids and macromolecules (Galston and Sawnhey, 1990). Their levels increase greatly in response to environmental stresses, most notably under conditions of potassium deficiency, water deficits, salinity stress, anaerobiosis and acid stress (Flores et al, 1989). Because polyamines are synthesized by amino acid decarboxylation reactions which consume H+, polyamine accumulation may function as part of a homeostatic mechanism to keep intracellular pH at a constant value (Flores et al, 1985). Polyamines may also play a role in the regulation of DNA replication and cell division, and are implicated in the control of senescence and morphogenesis (Evans and Malmberg, 1989; Galston and Sawnhey, 1990). It has been proposed that polyamines could be part of an intrinsic signaling network of the extracellular matrix (Messiaen et al, 1997). Polyamines also serve as precursors of several classes of alkaloids (Smith et al, 1979; Flores et al, 1989; Hashimoto and Yamada, 1994) which may play important roles in plant defense against herbivores.
Over 250 nonprotein amino acids have been identified in plants (Swain, 1977). A number of these compounds are intermediates in the synthesis and catabolism of the protein amino acids (Lea and Norris, 1976). However, many of these non-protein amino acids may play roles as defensive agents.
Alkaloids are nitrogenous compounds which belong to a broad category of secondary plant metabolites; over 10,000 alkaloids have been isolated and their structures elucidated. These compounds may play an important role in defense of the plant against pathogenic organisms, herbivores and insects (Swain, 1977).
Bagni N, Pistocchi R 1992 Polyamine metabolism and compartmentation in plant cells. In "Nitrogen Metabolism of Plants" (K Mengel, DJ Pilbeam eds), Clarendon Press, Oxford, pp. 229-248.
Evans PT, Malmberg RL 1989 Do polyamines have roles in plant development? Annu. Rev. Plant Physiol. Plant Mol. Biol. 40: 235-269.
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.
Flores HE, Young ND, Galston AW 1985 Polyamine metabolism and plant stress. In "Cellular and Molecular Biology of Plant Stress" (JL Key, T Kosuge eds), Alan R. Liss, Inc., New York, pp. 93-114.
Galston AW, Sawhney RK 1990 Polyamines in plant physiology. Plant Physiol. 94: 406-410.
Hashimoto T, Yamada Y 1994 Alkaloid biogenesis: molecular aspects. Annu. Rev. Plant Physiol. Plant Mol. Biol. 45: 257-285.
Lea PJ, Norris RD 1976 The use of amino acid analogues in studies of plant metabolism. Phytochem. 15: 585-595.
Messiaen J, Cambier P, Van Cutsem P 1997 Polyamines and pectins. I. Ion exchange and selectivity. Plant Physiol. 113: 387-395.
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.
Swain T 1977 Secondary compounds as protective agents. Annu. Rev. Plant Physiol. 28: 479-501.