Biochemistry and Cell Biology of Secondary Metabolites
Many secondary metabolites in plants promote human health not only as pharmaceuticals
but also as dietary supplements and functional foods (Askin
et al., 2002; Briskin, 2000). Plant-produced recombinant proteins are also important as
botanical therapeutics (Askin
et al., 2002). As suggested by their diverse functions, secondary metabolites are structurally divergent (see Croteau
et al., 2000 or other
chapters) and are usually classified into several major groups. Terpenoids and
steroids, which are formed from isoprenoid moieties, include the antineoplastic
diterpene paclitaxel, from
T. brevifolia Nutt; the antimalarial sesquiterpene artemisinin,
isolated from
Artemisia annua L.; diosgenin, a precursor for oral contraceptives
and hormonal drugs, from
Dioscorea spp.; and the cardiotonic steroidal
glycoside digoxin, from
Digitalis spp. Phenylpropanoids, derived from the
shikimate pathway, include the antineoplastic lignan, podophyllotoxin, from
Podophyllum peltatum L. Alkaloids, which are a diverse family of alkaline
nitrogen-containing compounds, include many biologically active chemicals
such as caffeine, coniine, morphine, nicotine, and strychnine. We focus here on
the alkaloids, justified by their relatively high beneficial biological activities, and
especially the isoquinoline alkaloids, the terpenoid indole alkaloids, and the
tropane alkaloids, which are currently the subjects of intensive study (De Luca
and Laflamme, 2001; Facchini, 2001; Facchini and St-Pierre, 2005; Hashimoto and
Yamada, 2003; Kutchan, 2005a,b; Verpoorte and Memelink, 2002; Zhao
et al., 2005). Excellent reviews of the potential of lignans in cell cultures (Petersen and
Alfermann, 2001), as well as monoterpenes (Lange and Croteau, 1999) and taxol
(Jennewein and Croteau, 2001), have already been published.