by Yan HONG
"Fingerprinting" the genetic makeup of plants is being applied in authentication and quality control of medical herbs, protection of property rights for new plant varieties, and many other exciting uses.
, or deoxyribonucleic acid, is the fundamental building
components of all living cells. The specific arrangement
of DNA base-pair sequences guides the production
of proteins and enzymes. These in turn decide features such as
leaf shape and flower colour, as well as direct synthesis of a wide
range of phytochemicals in plants.
DNA fingerprinting refers to the use of techniques based on
polymerase chain reaction (PCR) -- a system for the amplification
of DNA -- to reveal the specific DNA profile for a particular
organism which is as unique as a fingerprint. A DNA fingerprint is
generally independent of environment, and is consistent throughout
different parts and developmental stages of the organism.
Similarity of DNA fingerprints depends on genetic closeness of
tested samples. DNA fingerprinting can distinguish plants from
different families, genera, species, cultivars (cultivated variety),
and even sibling plants. Clones have the same DNA fingerprint
as their mother plant. Over the years, scientists have developed many DNA fingerprinting techniques with variation in complexity,
setting-up cost, throughput, operation cost, and reliability.
Amplified Fragment Length Polymorphism and Simple Sequence
Repeat (microsatellite) are gaining popularity for their high level
of resolution, throughput, and reliability.
Botanical products are gaining popularity worldwide for
human well-being and healthcare. In 2001, Americans spent
US$4.2 billion on herbs and other botanicals, accounting for
over half of the total nutraceuticals consumer sales. According
to a report in the journal Trends in Pharmacological Sciences,
the worldwide market for Chinese herbal medicine is projected to
worth US$400 billion by 2010.
There is a growing trend that physicians are seriously considering
botanic products as complementary and alternative medicine.
In June 2004, the US Food and Drug Administration (FDA) issued
the "Guidance for Industry Botanical Drug Products." Taking certain
unique characteristics of botanical drug product into consideration, the guidelines make it non-essential for a botanical drug to
identify the active constituents. Instead, FDA requires various tests
to be conducted throughout all manufacturing processes, from
raw material to products, to ensure the identity, purity, quality,
strength, potency, and consistency of botanical drugs.
Despite consumers acceptance, rising sales, and exciting opportunity
for botanical drug products, botanical products are
beleaguered by the issue of product quality and safety. Several
accidents, which involved botanical products, became the targets
of negative media attention.
In one case, two women were hospitalised with symptoms of
poisoning from digoxin, a poisonous preparation from foxglove
used to treat congestive heart failure or irregular heartbeat. Analysis
of serum samples confirmed the presence of significant blood levels
of digoxin. The source of digoxin was finally traced to the foxglove
Digitalis lanata that was accidentally mixed with plantain,
a component of a herbal combination that they both took.
In another instance, a number of participants in a clinical
study of a weight-loss Chinese herbal product developed serious
kidney poisoning, to the extent that some required replacement
of the organ. Continuous monitoring of the study population
revealed a higher rate of kidney tumours. It was determined that
this incident was caused by inappropriate substitution of the
expected Stephania tetrandra by Arastolochia fangchi, probably
because of the confusion arising from the similar Chinese names
(Han Fang Ji vs Guang Fang Ji).
The two incidents highlighted the situation that harvested
herbs, cultivated or wild, could be intentionally or unwittingly
mixed with other plant species, resulting in diluted physiological
effect or worse, dire consequences. A recent survey by a group of
researchers at Temasek Life Sciences Laboratory on several herbs
sold in Singapore found that some herbs of different genetic
identities were sold under the same generic names. The finding
is not totally surprising because same generic names have been
associated with different plants in different herbal books and
regions. Such situation is exemplified by the finding that as many
as 31 different plants species were used under the generic name
Guanzhong (). These findings show that reliable authentication
and quality control for herbal materials are becoming critical
for the protection of consumers, for the sustainable development
of the industry, and for the integration of folk medicine into
DNA fingerprinting will provide an objective evaluation of
genetic identity of plants based on species, cultivars, or geographic
origin. It can ensure genetic uniformity of raw herbal materials. For
medical herbs, synthesis and accumulation of chemical constituents
rely on both genetic makeup and environmental conditions.
Chromatographic techniques such as High Performance Thin-Layer
Chromatography and High Performance Liquid Chromatography
provide chemical fingerprinting or the profiling of various chemical
constituents of a herb. Combining the use of DNA fingerprinting
and chemical fingerprinting will be an effective tool in authentication and quality control of herbs.
Plant breeding takes much time and effort. With the absence
of property rights for new varieties, breeders derive little benefit since new plant varieties can be easily multiplied by seeds
or vegetative propagation. However, the requirement of World
Trade Organization on member states to provide protection for
new plant varieties is changing this situation. New plant varieties
can now get protection in many more countries. With the ability
of getting highly specific DNA profile for a single plant, DNA
fingerprint can prove that a new variety satisfies necessary criteria
for granting protection. These criteria may include novelty, distinctiveness,
uniformity, and stability. For administrators of plant
property rights, DNA fingerprinting can help select most suitable
reference varieties for morphological comparison and save cost. It
is most effective in enforcing protection by proving infringement
of property rights.
The technique has been applied in the matching of DNA
fingerprints of tree stumps and logs to confirm and incriminate
illegal logging in Canada. DNA fingerprinting has been used on
residues of orange to establish the substitution of premium citrus
fruits with those from lower-quality variety by an orange juice
manufacturer in Britain. It was also adopted in France to ascertain
the fraudulent adulteration of Chianti wines with inferior-quality
grapes. The method also facilitates the management of biodiversity.
Several international plant resource germplasm (genetic material)
collection centres are exploiting DNA fingerprinting to help them
focus their limited resources on maintaining and propagating
those unique collections.
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