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Leishmania amazonensis
and
Leishmania
donovani
promastigotes with 100% lysis at
100 mg/ml. The cytotoxicities (IC
50
) of embe-
lin and the mentioned AR on human lung
fibroblasts were 739 and 366 mM, respec-
tively. Embelin was the main active con-
stituent isolated. Because
O. erythrorhiza
is
used to treat heart complaints, a symptoma-
tology related to Chagas' disease, a possible
link between the traditional use of the plant
extract and the trypanocidal effect was sug-
gested. Phenolic lipids associated with
the antioxidant activity were also detected
in
Chenopodium pallidicaule
, an Andean
pseudocereal (Peñarrieta
et al.
, 2008).
production, which may allow the possibil-
ity of transgenic manipulation of the lipid
resorcinol pathway (Dayan
et al.
, 2005).
10.9.2 Promotive biotic
and abiotic factors
Biotic and abiotic factors can induce the
synthesis of phenolic compounds, which is
sometimes related to activation of responses
in plant defence (Daniel
et al
., 1999). This
premise led to
in vitro
assays where the
influence of physical and chemical factors
was evaluated on the accumulation of
ARs in rye and rice. Seedlings of these
cereals grown under light accumulate less
ARs than those kept in the dark (Suzuki
et al
., 1996; Magnucka
et al.
, 2007a). As
previously mentioned, the synthesis of ARs
was related to mitochondrial and plastidial
compartments, and higher contents in etio-
lated plants were attributed to a higher
number of plastids in etiolated seedlings
(Deszcz and Kozubek, 2000). The decrease
in temperature stimulates the accumulation
of ARs in rye seedlings, with a higher par-
ticipation of unsaturated ARs. Seedlings
grown in solutions containing fungicides
(benomyl or Carbendazin) or herbicides
(lenacil, chloridazon or norflurazon) pro-
vided at 10 ppm enhanced the levels of
ARs, although it was not clear how these
biocides exert their effect on AR metabo-
lism (Magnucka
et al.
, 2001; Magnucka
et al.
, 2007a,b). These results are promis-
ing, but further research is needed in field
conditions to know the real impact of these
chemicals on AR contents in rye.
The synthesis of ARs in response to
biotic factors was also investigated in bar-
ley. Barley grains were inoculated with
Pseudomonas fluorescens
PsR21 before
sowing in field plots (Zarnowski
et al
.,
2000b). Inoculation significantly increased
the crop yield at harvest, compared with
control plants. Infections with phytopatho-
genic fungi were apparently decreased. Both
control and inoculated plants contained
comparable amounts of ARs. Plants treated
with the bacterium as well as control plants
biosynthezised the same homologues with
10.9 Potential Uses of
ARs in Agriculture
The accumulation of ARs in cereal plants
may increase their resistance against nox-
ious organisms. This should reduce the
input of, and dependence on, synthetic agro-
chemicals (Gealy
et al.
, 2003). Several strate-
gies were proposed to achieve a high content
of ARs in cereal plants, as described below.
10.9.1
Breeding improvement
Although the determination of AR content
was suggested as a valid indicator of disease
resistance in cereal grains (García
et al
.,
1997), there is no breeding programme ori-
ented to select crop varieties with enhanced
AR accumulation. Most knowledge on AR
content and composition is currently
restricted to cereal kernels. AR composition
is species dependent, whereas both envi-
ronment and cultivars determine the total
content (Ross
et al.
, 2003b, 2004a; Zarnowski
and Suzuki, 2004). Root exudation of AR
glycosides and derivatives (i.e. sorgoleone)
was related to rice and sorghum allelopathy,
respectively (Kong
et al
., 2002; Dayan
et al
.,
2005). Identification and characterization
of enzymes involved in the biosynthesis
of these metabolites are in progress.
Nevertheless, much remains to be done to
fully understand not only the synthesis of
ARs but also the factors regulating their
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