Allelochemicals Biologica... - Name

ALLEOPATHIC ORGANISMS AND
MOLECULES
3.1. Terpenoids and sesquiterpene lactones
Vokou et al. (2003) compared the potential allelopathic activity of 47 monoterpenoids
of different chemical groups, by estimating their effect on seed germination and
subsequent growth of Lactuca sativa seedlings. Apart from individual compounds,
eleven pairs at different proportions were also tested. As a group, the hydrocarbons,
except for (+)-3-carene, were the least inhibitory. Of the oxygenated compounds, the
least inhibitory were the acetates; whenever the free hydroxyl group of an alcohol
turned into a carboxyl group, the activity of the resulting ester was markedly lower
(against both germination and seedling growth). Twenty-four compounds were
extremely active against seedling growth (inhibiting it by more than 85%), but only
five against seed germination. The compounds that were most active against both
processes belonged to the groups of ketones and alcohols; they were terpinen-4-ol,
dihydrocarvone, and two carvone stereoisomers. These authors used a model to
investigate whether compounds acted independently when applied in pairs. The
combined effect varied. In half of the cases, it followed the pattern expected under the
assumption of independence; in the rest, either synergistic or antagonistic interactions
were found in both germination and elongation. However, even in cases of synergistic
interactions, the level of inhibition was not comparable to that of a single extremely
active compound, unless such a compound already participated in the combination.
The effect of the sesquiterpene cacalol and extracts (water and petroleum ether)
derived from the roots of Psacalium decompositum (Asteraceae) on the germination
and radicle growth of two plants, Amaranthus hypochondriacus (Amaranthaceae)
and Echinochloa crus-galli (Poaceae), and the radial growth of four phytopathogenic
fungi was described (Anaya et al., 1996). The activity of two cacalol derivatives (methyl
cacalol and cacalol acetate) was also investigated. Germination of A. hypochondriacus
was inhibited by almost all the treatments. The extracts and cacalol produced a
significant inhibition of radicle growth of A. hypochondriacus and E. crus-galli.
Cacalol acetate showed a specific inhibition on E. crus-galli, and methyl cacalol
inhibited significantly the growth of A. hypochondriacus. In general, antifungal activity
depended upon the target fungi and the concentration of each treatment. Cacalol had
also effects on the morphology and coloration of the fungal mycelium. The bioactivity
shown by the extracts of Psacalium decompositum on the tested seeds and fungi is
mainly due to their content in cacalol.
The allelochemical potential of Callicarpa acuminata (Verbenaceae) was
investigated using a biodirected fractionation study as part of a long-term project to
search for bioactive compounds among the rich biodiversity of plant communities in
the Ecological Reserve El Eden, Quintana Roo, Mexico. Aqueous leachate, chloroformmethanol
extract, and chromatographic fractions of the leaves of the plant species
inhibited the root growth of Amaranthus hypochondriacus, Echinochloa crus-galli,
and tomato (23% , 59%, and 70% respectively). Some of these treatments caused a
moderate inhibition of the radial growth of two phytopathogenic fungi,
Helminthosporium longirostratum and Alternaria solani (18% to 31%). The
chloroform-methanol (1:1) extract prepared from the leaves rendered five compounds:
37