Metabolic Relationships of Putrescine, GABA and Alkaloids in Cell and Root Cultures of Solanaceae

Abstract

The diamine putrescine (1,4-diaminobutane) is the precursor of the polyamines spermidine (Spd) and spermine (Spm) in all living systems studied to date. In view of the functions that polyamines may have in plant growth and development (Smith 1985), it is of importance to understand the mechanisms that regulate the availability of precursor pools for the synthesis of these compounds. In most, if not all higher plants, putrescine is synthesized via two alternate routes: (1) decarboxylation of ornithine, which gives rise to putrescine directly; or(2) decarboxylation of arginine, with agmatine and N-carbamylputrescine as intermediates. The arginine decarboxylase pathway appears to be important under conditions of stress (Flores et al. 1985), whereas the ornithine decarboxylase pathway is closely correlated with rapid cell division (Cohen et al. 1982). Spd and Spm are formed by the transfer of one or two aminopropyl moieties, respectively, derived from decarboxylated S-adenosylmethionine (Tabor and Tabor 1984). There are, however, other possible metabolic fates of putrescine besides being a polyamine precursor.