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(Last modification:
13. May 2010)
Proposal for STS-type Reaction: Anacardic Acids and Urushiols
Anacardiaceae: An excellent overview of the secondary compounds in this family
can be found here:
more...
Setup of this page
Well-known, at least to the Americans, are probably the
urushiols: they are the main
reason for the strong allergenic properties of
poison ivy (Rhus
radicans, Toxidodendron radicans),
poison oak (Rhus toxidodendron),
poison alder (Rhus
vernix), and other plants of the family Anacardiaceae.
They were also described very early (Symes
and Dawson, 1954) because of the medical importance.
According to the summary in the Wikipedia entry (Urushiol),
urushiol is a mixture of several closely related organic
compounds. Each consists of a catechol, i.e. an aromatic ring of 6 carbon atoms
with attachment of two neighboring hydroxyl groups, and a side chain that has
15 or 17 carbon atoms. The side chain may be saturated or unsaturated, and the exact
mixture depends on the plant species. For example, poison oak urushiol
contains mostly catechols with C17 side chains, but poison ivy and
poison sumac contain mostly catechols with C15 side chains. The
allergic potential is dependent on the degree of unsaturation of the alkyl chain.
Less than half of the general population reacts with the saturated urushiol
alone, but over 90% react with urushiol containing at least two double bonds. Wikipedia also provides an overview of the
allergenic effects and their treatments (Urushiol-induced contact dermatitis).
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Name |
Rest (R ) |
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Urushiol I |
-(CH2)14-CH3 |
|
Urushiol II |
-(CH2)7-CH=CH-(CH2)5-CH3 |
|
Urushiol III |
-(CH2)7-CH=CH-CH2-CH=CH-(CH2)2-CH3 |
|
Urushiol IV |
-(CH2)7-CH=CH-CH2-CH=CH-CH=CH-CH3 |
|
Urushiol V |
-(CH2)7-CH=CH-CH2-CH=CH-CH2-CH=CH2 |
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Anacardic acids
occur in a number of plants, most often in Anacardiaceae, and
that is where the name is derived from. The most well-known example
is probably the nut shells of
cashew
(Anacardium
occidentale; syn. Anacardium curatellifolium A.St.-Hil.)
(Izzo
and Dawson, 1949; Paul and
Yeddanapalli, 1956;
Trevisan et al., 2006), and Wikipedia has a special chapter on
cashews.
The cashew nutshell liquid (CNSL)
or cashew shell oil is a natural resin found in the honeycomb
structure of the cashew nutshell. It consists of about 90% anacardic
acids and 10% cardol; it also contains apparently urushiols. All substances are dermatogenic, similarly to the
oils of the
poison ivy, and present danger during manual cashew processing. |
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Such compounds have also been described in other plant
families, e.g. in leaves and seeds of
Ginkgo biloba (Ginkgoales) (Wikipedia:
English -
German) (Gellerman
et al., 1976; Adawadkar
and El Sohly, 1981). With respect to the biosynthesis (discussed below) it
is noteworthy that this plant also contains urushiols (Schötz,
2004), alkylresorcinols (Zarnowska
et al., 2000) and other related substances (see below). Extracts from leaves are widely used for medical
purposes, for example in preventing dementia or the onset of Alzheimer's
disease, or for prevention of memory loss or as concentration enhancer.
However, that has been disputed (more...),
and the results from many studies are controversial. There are also a number of
possible side effects (more...).
The potential of anacardic acids and urushiols as allergenic compounds is a
possible concern for the use of such extracts, but there seems no reason to
worry about this point in the modern standardized preparations (Van
Beek and Montoro, 2009). Click here for an excellent and comprehensive
review on Ginkgo biloba.
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Overview of compounds in Ginkgo biloba |
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Left: What only few
people seem to know: the peels of
Mango fruits ( (Mangifera
indica, also belongs to the Anacardiaceae)
(Wikipedia: English
- German) also contain
urushiols
(Oka
et al., 2004; Hershko et al.,
2005).
Right: Other plants with anarcadic acids are the geranium
species (e.g. the
Garden geranium, Pelargoníum x hortorum)
(Walters
et al., 1990; Grazzini et
al., 1999). Most people have heard that geranium can be very allergenic, but
many do not know that anacardic acids are the reason. Their biological
purpose, however, is in providing resistance against all sorts of pests
(Yerger et al., 1992;
Schultz et al., 1996,
2006).
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The principle of
the biosynthesis: a proposal
From all the previously published data on the
biosynthesis, it is very likely that anacardic acids, urushiol, and the other
compounds are derived
from the same biosynthetic pathway. The key reaction should be a polyketide
synthase reaction, with a long-chain acyl-CoA as substrate (the length and
degree of saturation are variable), three condensation
reactions, followed by an aldol condensation. These are the basics; in addition
to that, tailoring reactions are included, e.g. decarboxylations, reduction
steps, hydroxylations; these lead to the variations in the compounds.
The biosynthetic scheme:
Actually, almost all of the reactions proposed here
are known to be carried out by type III PKS in other plants. A few comments:
-
Anacardic acids
- the
biosynthesis corresponds to the reactions of the stilbenecarboxylate synthases
in Hydrangea macrophylla, including the reduction step (more...) that has to be
postulated (more...),
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Cardanols
- their formation,
including the reduction step (more...), corresponds to the sequence of the reactions in
the biosynthesis of lunularin in the liverwort Marchantia polymorpha: the
type III PKS reaction to prelunularic acid, aromatization to lunularic acid, and
decarboxylation to
lunularin (more...).
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Resorcylic acids
- that should be just about the same as that postulated for the biosynthesis of
olivetolic acid in Cannabis sativa (more...), which also uses an aliphatic
starter CoA-ester (hexanoyl-CoA).
-
Resorcinols
- that is the standard stilbene synthase reaction (more...).
Actually, with the long-chain acyl-CoAs as starters, it is exactly the
reaction carried out by the type III PKS in the biosynthesis of sorgoleone
in Sorghum bicolor (more...),
and by the orphan PKS in Physcomitrella patens (more...).
In the case of the resorcinols discussed here (the cardols) it is not known,
however, whether the decarboxylation is integrated in the overall reaction
mechanism, and it cannot be excluded at this point that the resorcylic acid
is a detectable precursor. There is at least one example with contradictory
results (an enzyme from Neurospora crassa), and interestingly, this
is a case of a type III PKS using long-chain acyl-CoAs as substrate: one
group found resorcinols as product, while another group detected resorcylic
acids as major products (more...).
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Urushiols: it seems
pretty obvious that anacardic acids are the biosynthetic precursors, but the
sequence of the reactions to the urushiols (a decarboxylation and a
hydroxlation) is unknown.
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Direct links to other enzymes with aldol condensations
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Other type III PKS
with substrate preferences for long-chain CoA-esters
in plants and bacteria
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-
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Alkylresorcinols
and
long-chain pyrones in the bacterium Azotobacter vinelandii:
more...
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Alkylresorcinol
Streptomyces
griseus: more...
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Pyrone synthases in the bacteria
Mycobacterium tuberculosis and
Bacillus subtilis: more...
Return to
top
References
-
Ginkgo
biloba (2000),
Series: Medicinal and Aromatic Plants - Industrial Profiles, Vol 12.
Editor: Van Beek, T.A.; Publisher: Harwood Academic Publishers.
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Adawadkar, P. D., El
Sohly, M. A., 1981. Isolation, purification and antimicrobial activity of
anacardic acids from Ginkgo biloba fruits. Fitoterapia 53, 129-135.
No Abstract.
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Austin, M. B., Bowman, M.
E., Ferrer, J.-L., Schröder, J., Noel, J. P., 2004. An aldol switch
discovered in stilbene synthases mediates cyclization specificity of type
III polyketide synthases. Chemistry & Biology 11, 1179-1194.
Stilbene synthase (STS) and chalcone synthase (CHS) each catalyze the
formation of a tetraketide intermediate from a CoA-tethered phenylpropanoid
starter and three molecules of malonyl-CoA, but use different cyclization
mechanisms to produce distinct chemical scaffolds for a variety of plant
natural products. Here we present the first STS crystal structure, and
identify, by mutagenic conversion of alfalfa CHS into a functional stilbene
synthase, the structural basis for the evolution of STS cyclization
specificity in type III polyketide synthase (PKS) enzymes. Additional
mutagenesis and enzymatic characterization confirms that electronic effects
rather than steric factors balance competing cyclization specificities in CHS
and STS. Finally, we discuss the problematic in vitro reconstitution of
plant stilbenecarboxylate pathways, using insights from existing biomimetic
polyketide cyclization studies to generate a novel mechanistic hypothesis to
explain stilbenecarboxylate biosynthesis.
Request a reprint
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Dewick, P. M., 1997. Medicinal
Natural Products - A Biosynthetic Approach. John Wiley & Sons, Chichester.
No Abstract.
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Gellerman, J. L.,
Anderson, W. H., Schlenk, H., 1976. Synthesis of anacardic acids in seeds
of Ginkgo biloba. Biochimica et Biophysica Acta 431, 16-21.
Anacardic
(6-alkylsalicylic) acids and common lipids are efficiently synthesized
by immature seeds of Ginkgo biloba. The seeds were incubated with
14C-labeled acetic, malonic and palmitoleic acids, glucose, and other
potential precursors. Levels of 14C in common lipids and in anacardic
acids, and the distribution of 14C in anacardic acids were determined.
The results show that the salicylic moiety is synthesized by a
polyketide pathway via malonic acid. The chain moiety for anacardic acid
synthesis is in a different state of activation and/or site than chains
that are used for synthesis of the common lipids. Labeled shikimic acid
did not contribute 14C to anacardic acids, nor to other lipids,
and palmitoleic acid was incorporated only into common lipids.
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Grazzini, R. A., Paul, P.
R., Hage, T., Cox-Foster, D. L., Medford, J. I., Craig, R., Mumma, R. O.,
1999. Tissue-specific fatty acid composition of glandular trichomes of
mite-resistant and -susceptible Pelargonium xhortorum. Journal of
Chemical Ecology 25, 955-968.
Anacardic acids,
alkyl phenolic acids excreted by tall glandular trichomes of the garden
geranium, Pelargonium xhortorum, confer small-pest resistance. Up
to 90% of the trichome exudate from mite-resistant P. x hortorum
inbreds consists of an unusual anacardic acid with an unsaturated
omega-5 (delta5) alkyl chain. As fatty acids are biochemical precursors
to anacardic acids, we examined by GC the fatty acid composition of
leaves, pedicels, petals, sepals, mature seeds, and glandular trichomes
from pest-resistant and pest-susceptible Pelargonium inbred lines
to determine the localization of delta5-fatty acids within plant tissues.
The fatty acid composition of lipid classes (galactolipids,
phospholipids, and neutral lipids) extracted from glandular trichomes
from mite-resistant pedicels were also examined. delta5-Fatty acids
(16:1, 11 and 18:1, 13) were found only in the glandular trichomes from
pest-resistant geraniums (27.2% in trichomes of pedicels) and were
localized predominantly in the phospho- and galactolipids (phosphatidylinositol,
25.9%; phosphatidylcholine, 18.2%; monogalactosyldiglyceride, 15.5%; and
diglactosyldiglyceride, 14.0%).
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Izzo, P. T., Dawson, C. R.,
1949. Cashew nut shell liquid. VI. The olefinic nature of anacardic acid.
Journal of Organic Chemistry 14, 1039-1047.
It has been
established that the anacardic acid component of the oil of the shell of
the cashew nut Anacardium occidentale, is not a homogeneous
compound having the structure of a 3-pentadecadienylsalicyclic acid as
heretofore believed. The anacardic acid as it occurs naturally in the
cashew nut shell and which may be obtained from such shells by cold
solvent-extraction, has been found to consist of a mixture of several
olefinic components possessing an average unsaturation equivalent to
about two double bonds. It has been estimated that at least 25% of the
anacardic acid is a monoolefinic component. Using conditions throughout
which would not be expected to alter the olefinic nature of the
anacardic acid, the free acid was first methylated with diazomethane and
the resulting dimethyl-ether-ester, possessing an average unsaturation
equivalent to two double bonds, was hydroxylated using a mixture of 30%
hydrogen peroxide-formic acid at low temperatures. The resulting mixture
of glycols was partially separated by molecular distillation and a pure
monoglycol was obtained. The crystalline monoglycol on cleavage with
periodic acid yielded n-heptaldehyde, thereby establishing the
monoolefin present in the natural anacardic acid mixture as
1-hydroxy-2-carboxy-3-(8'-pentadecenyl)benzene. The higher-boiling
glycol fraction yielded formaldehyde on cleavage with periodic acid or
lead tetraacetate, thereby establishing the existence of a terminal
olefinic linkage in one or more of the higher olefinic components of
anacardic acid.
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Paul, V. T., Yeddanapalli, L.
M., 1956. On the olefinic nature of anacardic acid from indian cashew nut
shell liquid. Journal of the American Chemical Society 78, 5675-5678.
The anacardic
acid isolated from the solvent-extracted liquid from Indian cashew nut
shells has been separated by low-temperature fractional crystallization
into a saturated component and a mono-, di- and triolefin which have
been identified by analysis of their permanganate oxidation products,
respectively, as 1-hydroxy-2-carboxy-3-pentadecyl benzene,
1-hydroxy-2-carboxy-3-(8'-pentadecenyl)-benzene,
1-hydroxy-2-carboxy-3-(8'11'-pentadecadienyl)-benzene and
1-hydroxy-2-carboxy-3-(8',11',14'-pentadecatrienyl)-benzene.
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Schötz, K., 2004.
Quantification of allergenic urushiols in extracts of Ginkgo biloba
leaves, in simple one-step extracts and refined manufactured material (EGb
761). Phytochemical Analysis 15, 1-8.
Extracts of leaves of Ginkgo biloba (family Ginkgoaceae), widely
used in the treatment of peripheral and cerebral circulatory disorders
as well as for dementia of different aetiology, contain long chain
alkylphenols (with allergenic, cytotoxic, mutagenic and tumour-promoting
properties) together with the extremely potent allergens, the urushiols.
Such hazardous compounds can be present only in very low concentrations
in phytopharmaceutical preparations and hence, for the purposes of drug
safety, techniques must be available for the identification and
quantification of these allergens at extremely low levels in refined
manufactured materials. GC-MS analysis of samples collected at various
stages during the production process of a standardised extract of G.
biloba (EGb 761) demonstrated that all alkylphenols present in the
primary acetone extracts were removed in parallel with the same
efficiency irrespective of their aromatic substitution pattern.
Furthermore, in the final product the content of urushiols was generally
below the detection limit of 0.03 ppm. Therefore, it is concluded that
demonstrating the absence of the predominant, and easily quantifiable,
ginkgolic acids provides a reliable means for the control of
pharmaceutical quality of the final product.
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Symes, W. F., Dawson, C. R.,
1954. Poison ivy "urushiol". Journal of the American Chemical Society 76,
2959-2963.
The toxic
principle of poison ivy has an olefinic unsaturation of about two double
bonds and possesses the carbon skeleton of 3-pentadecylcatechol. It has
been found that the dimethyl ether can be separated by chromatography on
alumina into four pure components which vary only in their degree of
unsaturation in the side chain. One of the components has a completely
reduced side chain. The other three contain one, two and three olefinic
bonds, respectively. The structures proposed for the olefinic components
on the basis of ozonolysis and oxidative degradation experiments are as
follows: a monoolefin, 1,2-dihydroxy-3-(pentadecenyl-8')-benzene; a
diolefin, 1,2-dihydroxy-3-(pentadecadienyl-8',11')-benzene and a
triolefin, 1,2-dihydroxy-3-(pentadecatrienyl-8',11',14')-benzene.
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Trevisan, M. T. S.,
Pfundstein, B., Haubner, R., Würtele, G., Spiegelhalder, B., Bartsch, H.,
Owen, R. W., 2006. Characterization of alkyl phenols in cashew (Anacardium
occidentale) products and assay of their antioxidant capacity. Food
and Chemical Toxicology 44, 188-197.
In this study the content of anacardic acids, cardanols and cardols in
cashew apple, nut (raw and roasted) and cashew nut shell liquid (CNSL)
were analysed. The higher amounts (353.6 g/kg) of the major alkyl
phenols, anacardic acids were detected in CNSL followed by cashew fibre
6.1 g/kg) while the lowest (0.65 g/kg) amounts were detected in roasted
cashew nut. Cashew apple and fibre contained anacardic acids exclusively,
whereas CNSL also contained an abundance of cardanols and cardols.
Cashew nut (raw and roasted) also contained low amounts of hydroxy alkyl
phenols. Cashew nut shell liquid was used for a basic fractionation of
the alkyl phenol classes and the individual anacardic acids, major
cardanols and cardols were purified to homogeneity from these fractions
by semi-preparative HPLC and definitively identified by nano-ESI-MS-MS,
GC-MS and NMR analyses. The hexane extracts (10 mg/ml) of all cashew
products tested plus CNSL, displayed significant antioxidant capacity.
Cashew nut shell liquid was the more efficient (inhibition = 100%)
followed by the hexane extract of cashew fibre (94%) and apple (53%).
The antioxidant capacity correlated significantly (P < 0.05) with the
concentration of alkyl phenols in the extracts. A mixture of anacardic
acids (10.0 mg/ml) showed the higher antioxidant capacity (IC 50 = 0.60
mM) compared to cardols and cardanols (IC50 > 4.0 mM). The data shows
that of these substances, anacardic-1 was by far the more potent
antioxidant (IC50 = 0.27 mM) compared to cardol-1 (IC50 = 1.71 mM) and
cardanol-1 (IC50 > 4.0 mM). The antioxidant capacity of anacardic acid-1
is more related to inhibition of superoxide generation (IC50 = 0.04 mM)
and xanthine oxidase (IC 50 = 0.30 mM) than to scavenging of hydroxyl
radicals. At present a substantial amount of cashew fibre is mostly used
in formulations of animal or poultry feeds. The data presented in this
study, indicates that this waste product along with CNSL, both of which
contain high contents of anacardic acids, could be better utilized in
functional food formulations and may represent a cheap source of cancer
chemopreventive agents.
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Van Beek, T. A., Montoro, P.,
2009. Chemical analysis and quality control of Ginkgo biloba
leaves, extracts, and phytopharmaceuticals. Journal of Chromatography A
1216, 2002-2032.
The chemical analysis and quality control of Ginkgo leaves, extracts,
phytopharmaceuticals and some herbal supplements is comprehensively
reviewed. The review is an update of a similar, earlier review in this
journal [T.A. van Beek, J. Chromatogr. A 967 (2002) 21-55]. Since 2001
over 3000 papers on Ginkgo biloba have appeared, and about 400 of
them pertain to chemical analysis in a broad sense and are cited herein.
The more important ones are discussed and, where relevant, compared with
the best methods published prior to 2002. In the same period over 2500
patents were filed on Ginkgo and the very few related to analysis are
mentioned as well. Important constituents include terpene trilactones,
i.e. ginkgolide A, B, C, J and bilobalide, flavonol glycosides,
biflavones, proanthocyanidins, alkylphenols, simple phenolic acids,
6-hydroxykynurenic acid, 4-O-methylpyridoxine and polyprenols. In the
most common so-called "standardised" Ginkgo extracts and
phytopharmaceuticals several of these classes are no longer present.
About 130 new papers deal with the analysis of the terpene trilactones.
They are mostly extracted with methanol or water or mixtures thereof.
Supercritical fluid extraction and pressurised water extraction are also
possible. Sample clean-up is mostly by liquid-liquid extraction with
ethyl acetate although no sample clean-up at all in combination with
LC/MS/MS is gaining in importance. Separation and detection can be
routinely carried out by RP-HPLC with ELSD, RI or MS, or by GC/FID or
GC/MS after silylation. Hydrolysis followed by LC/MS allows the
simultaneous analysis of terpene trilactones and flavonol aglycones. No
quantitative procedure for all major flavonol glycosides has yet been
published because they are not commercially available. The quantitation
of a few available glycosides has been carried out but does not serve a
real purpose. After acidic hydrolysis to the aglycones quercetin,
kaempferol and isorhamnetin and separation by HPLC, quantitation is
straightforward and yields by recalculation an estimation of the
original total flavonol glycoside content. A profile of the genuine
flavonol glycosides can detect poor storage or adulteration. Although
the toxicity of Ginkgo alkylphenols upon oral administration has never
been undoubtedly proven, most suppliers limit their content in extracts
to 5 ppm and dozens of papers on their analysis were published. One
procedure in which a methanolic extract is directly injected on a C8
HPLC column appears superior in terms of sensitivity (<5 ppm),
separation, simplicity and validation and will be incorporated in the
European Pharmacopoeia. Alternatively GC/MS and ELISA methods can be
used. A sharp contrast to the plethora of papers on terpene trilactones,
flavonol glycosides, and ginkgolic acids forms the low number of papers
on biflavones, proanthocyanidins, simple phenolics, simple acids, and
other constituents that make up the remaining 70% of Ginkgo standardised
extracts. More research in this direction is clearly needed. For the
analysis of Ginkgo proanthocyanidins (7%) for instance, no reliable
assays are yet existing. Finally the growing literature on
pharmacokinetic and fingerprinting studies of Ginkgo is briefly
summarised.
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Walters, D. S., Craig, R., Mumma, R. O.,
1990. Fatty acid incorporation in the biosynthesis of anacardic acids of
geraniums. Phytochemistry 29, 1815-1822.
Geraniums,
Pelargonium x hortorum, have been shown to possess tall glandular
trichomes which secrete anacardic acids, a viscous, sticky exudate which
provides defence against small pest species. Pest-resistant geraniums
possess primarily C22- and C24-unsaturated (-5) anacardic acids with
lesser amounts of the C22- and C24-saturated side chain structures.
Previous workers have suggested that anacardic acids are biosynthesized
from fatty acids by addition of two carbon units. To investigate this
hypothesis, [14C]lauric, -myristic, -palmitic, -stearic and -oleic acids
were administered to leaves and floral buds of pest-resistant geraniums.
Palmitate and stearate were shown to be the respective precursors for
C22 and C24 anacardic acids with saturated side chains. A major portion
of the applied [14C]stearate was degraded and subsequently incorporated
into the C22- and C24-saturated and unsaturated (-5) anacardic acids
indicating an indirect pathway of biosynthesis also exists. Therefore,
the -5 anacardic acids must be the result of -5 fatty acid precursors
rather than the desaturation of saturated anacardic acids. Data supports
the hypothesis that anacardic acids are biosynthesized from saturated
and -5 unsaturated C16 and C18 fatty acids by chain elongation through
the addition of three acetate groups, which then undergo partial
reduction and dehydration, followed by intramolecular aldol condensation,
to give the aromatic ring in a manner similar to that proposed for the
biosynthesis of salicylic acid.
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Yerger, E. H., Grazzini, R. A., Hesk, D.,
Cox-Foster, D. L., Craig, R., Mumma, R. O. , 1992. A rapid method
for isolating glandular trichomes. Plant Physiology 99, 1-7.
A physical method is described for the rapid isolation of plant
trichomes, with emphasis on stalked glandular types. The technique
involved breaking frozen trichomes with powdered dry ice and collection
of glandular heads by sieving from larger tissue fragments. This method
was applied to several plants that bear similar stalked trichomes:
geranium (Pelargonium), potato (Solanum tuberosum), tomato
(Lycopersicon esculentum), squash (Cucurbita pepo), and
velvetleaf (Abutilon theophrasti). The tissue preparation was of
sufficient quality without further purification for biochemical and
molecular studies. The preparation maintained the biochemical integrity
of the trichomes for active enzymes and usable nucleic acids. A large
quantity of tissue can be harvested; for example, 351 milligrams dry
weight of glandular trichomes were harvested from geranium pedicels in
12 hours. The utility of the technique was demonstrated by examining the
fatty acid composition of tall glandular trichomes of geraniums,
Pelargonium x hortorum L.H. Bailey. These purified cells
contained high concentrations of unusual
w5-unsaturated fatty
acids, proportionally 23.4% of total fatty acids in the trichomes. When
the trichomes were removed, the supporting tissue contained no w5-fatty acids,
thereby unequivocally localizing w5-fatty
acids to the trichomes. Because w
5-fatty acids are unique precursors for the biosynthesis of w5-anacardic acids,
we conclude that anacardic acid synthesis must occur in the glandular
trichomes.
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Schultz, D. J., Cahoon, E. B., Shanklin,
J., Craig, R., Cox-Foster, D. L., Mumma, R. O., Medford, J. I. ,
1996. Expression of a D9
14:0-acyl carrier protein fatty acid desaturase gene is necessary for
the production of w5
anacardic acids found in pest-resistant geranium (Pelargonium
xhortorum). Proceedings of the National Academy of Sciences of the
United States of America 93, 8771-8775.
Anacardic acids, a class of secondary compounds derived from fatty acids,
are found in a variety of dicotyledonous families. Pest resistance (e.g.,
spider mites and aphids) in Pelargonium xhortorum (geranium) is
associated with high levels (approximately 81%) of unsaturated 22:1
omega 5 and 24:1 omega 5 anacardic acids in the glandular trichome
exudate. A single dominant locus controls the production of these omega
5 anacardic acids, which arise from novel 16:1 delta 11 and 18:1 delta
13 fatty acids. We describe the isolation and characterization of a cDNA
encoding a unique delta 9 14:0-acyl carrier protein fatty acid
desaturase. Several lines of evidence indicated that expression of this
desaturase leads to the production of the omega 5 anacardic acids
involved in pest resistance. First, its expression was found in
pest-resistant, but not suspectible, plants and its expression followed
the production of the omega 5 anacardic acids in segregating populations.
Second, its expression and the occurrence of the novel 16:1 delta 11 and
18:1 delta 13 fatty acids and the omega 5 anacardic acids were specific
to tall glandular trichomes. Third, assays of the recombinant protein
demonstrated that this desaturase produced the 14:1 delta 9 fatty acid
precursor to the novel 16:1 delta 11 and 18:1 delta 13 fatty acids.
Based on our genetic and biochemical studies, we conclude that
expression of this delta 9 14:0-ACP desaturase gene is required for the
production of omega 5 anacardic acids that have been shown to be
necessary for pest resistance in geranium.
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Schultz, D. J., Olsen, C., Cobbs, G. A.,
Stolowich, N. J., Parrott, M. M. , 2006. Bioactivity of anacardic
acid against colorado potato beetle (Leptinotarsa decemlineata)
larvae. Journal of Agricultural and Food Chemistry 54, 7522-7529.
Anacardic acid (2-hydroxy-6-alkylbenzoic acid) produced and secreted
from glandular trichomes of zonal geranium (Pelargonium x
hortorum; Geraniaceae family) provides resistance to small pests (aphids
and spider mites). To assess the potential bioactivity of anacardic acid
against larger insect pests and to determine if an alternate mode of
application (ingestion rather than the topical application) could impart
resistance to pests, the effects of anacardic acid consumption on the
development of Colorado potato beetle larvae were tested. Analysis of
dose-response curves indicated a significant effect on weight gain and
mortality. Assessment of food preference (treated versus untreated)
indicated larvae avoid food containing anacardic acid and have a lower
feeding rate on food containing anacardic acid. On the basis of these
results, it is suggested that anacardic acid, applied as a chemical
spray or through bioengineering production in crop plants, may provide a
new tool in the arsenal to minimize damage to plants caused by pests.
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Hershko, K., Weinberg, I., Ingber, A. ,
2005.
Exploring the mango-poison ivy connection: the riddle of discriminative plant
dermatitis. Contact Dermatitis 52, 3-5.
A relationship between sensitivity to poison oak or poison ivy and mango
dermatitis has been suggested by previous publications. The observation that
acute allergic contact dermatitis can arise on first exposure to mango in
patients who have been sensitized beforehand by contact with other
urushiol-containing plants has been documented previously. We report 17 American
patients employed in mango picking at a summer camp in Israel, who developed a
rash of varying severity. All patients were either in contact with poison ivy/oak
in the past or lived in areas where these plants are endemic. None recalled
previous contact with mango. In contrast, none of their Israeli companions who
had never been exposed to poison ivy/oak developed mango dermatitis. These
observations suggest that individuals with known history of poison ivy/oak
allergy, or those residing in area where these plants are common, may develop
allergic contact dermatitis from mango on first exposure. We hypothesize that
previous oral exposure to urushiol in the local Israeli population might
establish immune tolerance to these plants.
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Oka, K., Saito, F., Yasuhara, T., Sugimoto, A. ,
2004. A study of cross-reactions between mango contact allergens and urushiol.
Contact Dermatitis 51, 292-296.
The allergens causing mango dermatitis have long been suspected to be alk(en)yl
catechols and/or alk(en)yl resorcinols on the basis of observed
cross-sensitivity reactions to mango in patients known to be sensitive to poison
ivy and oak (Toxicodendron spp.). Earlier, we reported the 3 resorcinol
derivatives: heptadecadienylresorcinol (I), heptadecenylresorcinol (II) and
pentadecylresorcinol (III); collectively named 'mangol', as mango allergens. In
this study, we extracted the 1st 2 components (I and II) from the Philippine
mango, adjusted them to 0.05% concentration in petrolatum and patch tested the
components on 2 subjects with mango dermatitis. Both subjects reacted to I. 1
subject also elicited a weaker positive reaction to II. To investigate the
cross-reaction between mangol and urushiol, we also patch tested the same
subjects with urushiol. The subject sensitive to II reacted to urushiol. 6
subjects with a history of lacquer contact dermatitis and positive reactions to
urushiol were similarly patch tested. 5 persons reacted to I. 2 subjects also
exhibited a slower but positive reaction to II. This is the 1st report in which
heptadec(adi)enyl resorcinols known to be present in mango have been shown to
elicit positive patch test reactions in mango-sensitive patients.
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Zarnowska, E. D., Zarnowski, R., Kozubek, A.,
2000. Alkylresorcinols in fruit pulp and leaves of Ginkgo biloba L.
Zeitschrift für Naturforschung 55c, 881-885.
These studies were undertaken to characterise resorcinolic lipids
(5-n-alk(en)ylresorcinols) composition and to determine their seasonal
fluctuations in fruit pulp and leaves of Ginkgo biloba L. Resorcinolic
lipid concentrations were consistently higher in fruit pulp than in leaves. In
pulp, several mono- and di-unsaturated homologs of alkylresorcinols were the
predominant group of analysed lipids. Contrary to the fruit pulp, only
5-n-pentadecylresorcinol was demonstrated in leaves. Initially, the
alkylresorcinol's content both in pulp and leaves increased until June - July
and decreased following seeds ripening. This trend continued until senescence of
leaves in late September and October.
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