Arginine decarboxylase (ADC) (a chloroplast localized enzyme (Borrell et al, 1995)) is induced by a variety of stresses (most notably potassium deficiency; Watson and Malmberg, 1996) and is thought to be the enzyme primarily responsible for environmental stress-induced putrescine accumulation (Galston and Sawnhey, 1990):

Arginine decarboxylase of oats is clipped from a precursor into two polypeptides found in the soluble enzyme (Malmberg et al, 1992). The two polypetides are linked by disulfide bonds to form the active enzyme (Watson and Malmberg, 1996).

The oat (Bell and Malmberg, 1990), tomato (Rastogi et al, 1993), and Arabidopsis arginine decarboxylase (Watson and Malmberg, 1996) genes have been cloned.

In Arabidopsis, arginine decarboxylase enzyme levels do not correspond to ADC protein amounts, suggesting post-translational modification of the enzyme in response to potassium deficiency (Watson and Malmberg, 1996). In osmotically stressed oat leaves spermine inhibits post-translational processing of the ADC precursor, with subsequent decreases in mature ADC (Borrell et al, 1996).

Loss of regeneration capacity of rice in long term culture is associated with massive accumulation of putrescine due to an increase in arginine decarboxylase activity. Difluoromethylarginine, an inhibitor or arginine decarboxylase, restored regeneration capacity to long-term cultures (Bajaj and Rajam, 1996). Spermidine treatment also caused a reduction in putrescine content and arginine decarboxylase activity and restoration of plant regeneration ability (Bajaj and Rajam, 1996). In contrast, putrescine promotes and difluoromethylarginine inhibits somatic embryogenesis in eggplant (Yadav and Rajam, 1998).

The alternative, more direct pathway of synthesis of putresine via ornithine decarboxylation catalyzed by cytosolic ornithine decarboxylase (ODC) [EC 4.1.1.17] is proposed to be of little importance in stress-induced putrescine accumulation, but may be critical in regulation of developmental processes (Galston and Sawhney, 1990; Walden et al, 1997). Increased putrescine biosynthesis catalyzed by ornithine decarboxylase promotes somatic embryogenesis in carrots (Bastola and Minocha, 1995). Increased production of putrescine in carrot cells expressing mouse ODC is accompanied by increased putrescine catabolism (Andersen et al, 1998).

Levels of putrescine are higher in a drought tolerant wheat cultivar in comparison to a drought suceptible wheat cultivar. These wheat cultivars also differ for oxidant stress resistance as assayed by resistance to paraquat (Ye et al, 1997). Constitutively elevated levels of Arg decarboxylase and Orn decarboxylase are correlated with paraquat resistance in Conzya bonariensis (Ye et al, 1997). Arg decarboxylase and Orn decarboxylase are differentially regulated in Conzya bonariensis, with only the former detectable in 2 week-old plants. Orn decarboxylase becomes more abundant than Arg decarboxylase in 10 week-old plants (Ye et al, 1997). Exogenously supplied putrescine prevents oxidative damage in paraquat-resistant C. bonariensis (Ye et al, 1997). In part this may be due to inhibition of paraquat uptake by putrescine (Hart et al, 1993). Ye et al (1997) suggest that putrescine and other polyamines could function directly or indirectly as free radical scavengers.

Andersen SE, Bastola DR, Minocha SC 1998 Metabolism of polyamines in transgenic cells of carrot expressing a mouse ornithine decarboxylase cDNA. Plant Physiol. 116: 299-307.

Bajaj S, Rajam MV 1996 Polyamine accumulation and near loss of morphogenesis in long-term callus cultures of rice: restoration of plant regeneration by manipulation of cellular polyamine levels. Plant Physiol. 112: 1343-1348.

Bastola DR, Minocha SC 1995 Increased putrescine biosynthesis through transfer of mouse ornithine decarboxylase cDNA in carrot promotes somatic embryogenesis. Plant Physiol. 109: 63-71.

Bell E, Malmberg RL 1990 Analysis of a cDNA encoding arginine decarboxylase from oat reveals similarity to the Escherichia coli arginine decarboxylase and evidence of protein processing. Mol. Gen. Genet. 224: 431-436.

Borrell A, Besford RT, Altabella T, Masgrau C, Tiburcio AF 1996 Regulation of arginine decarboxylase by spermine in osmotically stressed oat leaves. Physiol. Plant. 98: 105-110.

Galston AW, Sawhney RK 1990 Polyamines in plant physiology. Plant Physiol. 94: 406-410.

Hart JJ, DiTomaso JM, Kochian LV 1993 Characterization of paraquat transport in protoplasts from maize (Zea mays L.) suspension cells. Plant Physiol. 103: 963-969.

Malmberg RL, Smith KE, Bell E, Cellino ML 1992 Arginine decarboxylase of oats is clipped from a precursor into two polypeptides found in the soluble enzyme. Plant Physiol. 100: 146-152.

Rastogi R, Dulson J, Rothstein SJ 1993 Cloning of tomato (Lycopersicon esculentum Mill.) arginine decarboxylase gene and its expression during fruit ripening. Plant Physiol. 103: 829-834.

Walden R, Cordeiro A, Tiburcio AF 1997 Polyamines: small molecules triggering pathways in growth and development. Plant Physiol. 113: 1009-1013.

Watson MB, Malmberg RL 1996 Regulation of Arabidopsis thaliana (L.) Heynh arginine decarboxylase by potassium deficiency stress. Plant Physiol. 111: 1077-1083.

Yadav JS, Rajam MV 1998 Temporal regulation of somatic embryogenesis by adjusting cellular polyamine content in eggplant. Plant Physiol. 116: 617-625.

Ye B, Muller HH, Zhang J, Gressel J 1997 Constitutively elevated levels of putrescine and putrescine-generating enzymes correlated with oxidant stress resistance in Conzya bonariensis and wheat. Plant Physiol. 115: 1443-1451.