Allelochemicals Biologica... - Name

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ANA LUISA ANAYA
isopimaric acid, a mixture of two diterpenols: sandaracopimaradien-19-ol and
akhdarenol, α-amyrin, and the flavone salvigenin. The phytotoxicity exhibited by
several fractions and the full extract almost disappeared when pure compounds were
evaluated on the test plants, suggesting a synergistic or additive effect. Akhdarenol,
α-amyrin and isopimaric acid methyl ether had antifeedant effects on Leptinotarsa
decemlineata. Alpha-amyrin was most toxic to this insect. No correlation was found
between antifeedant and toxic effects on this insect, suggesting that different modes
of action were involved. All the test compounds were cytotoxic to insect Sf9 cells
while salvigenin, akhdarenol, and isopimaric acid also affected mammalian Chinese
Hamster Ovary (CHO) cells. Alpha-amyrin showed the strongest selectivity against
insect cells (Anaya et al., 2003). In this study the authors emphasized that
allelochemicals involved in allelopathic interactions often have multiple functionality.
Sesquiterpene lactones (SL) occur in over 15 plant families, predominantly in
the Asteraceae, and represent with about 3,500 naturally occurring compounds, one
of the largest groups of natural products. It has been demonstrated that some
sesquiterpene lactones exhibit a broad spectrum of biological activities including
phytotoxic and plant growth regulatory properties, cytotoxicity and antitumor
properties, antimicrobial, insecticidal, molluscicidal and antimalarial activity (Fischer,
1986). Phytotoxic terpenoids and their possible involvement in allelopathy were covered
in reviews on mono- and sesquiterpenes (Evenari, 1949; Fischer, 1986, 1991, 1994)
and biological activities of SL were reviewed by Stevens and Merrill (1985), Picman
(1986) and Elakovich (1988). Seedlings of Ambrosia cumanensis are inhibited by
leachates of the adult plants and residues in soils. Some SL of this species have been
implicated in this autototoxic mechanism (Anaya and del Amo, 1978). In the same
way, parthenin and coronopilin of Parthenium hysterophorus also exhibited autotoxicity
toward seedlings and older plants, this fact possibly reveal a mechanism of intraspecific
population regulation (Picman and Picman, 1984). Axivalin and tomentosin from the
seeds of Iva axillaris were inhibitory toward the germination and growth of Abutilon
theophrasti (velvetleaf) (Spencer et al., 1984). The germacranolide-type SL represented
by dihydrotartridin B significantly inhibited the root growth of Brassica rapa var.
pervidis (Sashida et al., 1983). The α-methylene-γ-lactone group is present in many
of the isolated natural sesquiterpene lactones, and has been proposed as one of the
factors which can determine their allelopathic activity, in particular, as well as their
biological activity in general. The different spatial arrangements that a molecule of
SL can adopt is the other factor that has been related with the potential allelopathic
activity of this type of secondary compounds (Macias et al., 1992). Data of several
studies on the allelopathic potential of SL clearly demonstrated that they can selectively
promote or inhibit germination or growth at concentrations as low as 1 µM. It is
reasonable to assume that rain washes transport SL from the source plant or
decomposing litter into the soil where they can reach significant concentration levels.
In the case of isoalantolactone, it has been demonstrated that it can persist in mineral
and organic soil for 3 months, supporting the assumption that SL play a significant
role in allelopathic interactions in the environment (del Amo and Anaya, 1976; Stevens
and Merril, 1985; Picman, 1986; Fischer, 1991).