Allelochemicals Biologica... - Name

THE ALLELOPATHIC POTENTIAL OF GINSENOSIDES 161
shown to be biologically active at their ecologically relevant concentration. Lastly,
the allelopathic role of the compounds has to be demonstrated at the field level.
3.1. The Host Plant
3. GINSENG AND GINSENG SAPONINS
American ginseng (Panax quinquefolius L.) is a native North American member of
the Araliaceae, a family whose more than 800 species are found mostly in the tropics
(Lawrence, 1951). Panax quinquefolius is a perennial understory herb that is associated
with deciduous forests (Fountain, 1986; Anderson et al., 1993) and ranges from
Ontario and Quebec, south to northern Florida and west to Minnesota (Small and
Catling, 1999). The aboveground tissues senesce at the end of each growing season
and estimates of the maximum age of this plant are 23-30 yr (Anderson et al., 1993)
to >50 yr (Lewis and Zenger, 1982). Ginseng typically has one aerial stem, with
three to five palmately compound leaves and an umbelliferous inflorescence. The
main pollinators of the small greenish-white to greenish-yellow flowers are bees
(Catling and Spicer, 1995) and the mature red fruits usually contain two seeds, but
range from one to three seeds (Anderson et al., 1993; Schlessman, 1985). Before
germinating, the seeds of American ginseng require an after-ripening period of one
to two winters (Lewis and Zenger, 1982; Anderson et al., 1993). Panax quinquefolius
is threatened in Canada (Small and Catling, 1999), probably due to over-collection of
the root for economic gain.
The main commercial product from ginseng is the taproot, which is sought for its
purported medicinal properties. Commercially, the roots are harvested after 3-5 yr of
intensive cultivation. American ginseng has been commercially cultivated in Canada
since the late nineteenth century (Proctor and Bailey, 1987), under artificial shade or
in interplanted woodlands. In 2002 Ontario, which is one of Canada’s largest provincial
producers, exported over one thousand metric tons of ginseng root representing a
value of almost $ 40 million (OMAF, 2003). However, commercial productivity is
hindered by susceptibility to several fungal diseases of the leaves, stem, fruit and
roots.
3.2. Ginsenoside Structure and Biosynthetic Origins
Ginsenosides are triterpenoid saponins primarily based on two tetracyclic dammarane
ring structures: (20S)-protopanaxadiol and (20S)-protopanaxatriol (Figure 1), with
one representative (Ro) derived from oleanoic acid. While more than 25 ginsenoside
structures have been identified in Panax spp. (Fuzzati et al., 1999), six are considered
major: the (20S)-protopanaxadiol-derived Rb 1 , Rb 2 , Rc and Rd and the (20S)protopanaxatriol-derived
Re and Rg 1 . With the exception of a few monodesmosidic
compounds (e.g., Rh 2 , Rg 3 , Rh 1 , Rf and Rg 2 ), ginsenosides are generally bisdesmosidic.
(20S)-Protopanaxadiols are 3-O and 20-O diglycosides, while (20S)-protopanaxatriols