by Yan HONG
, 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 mainstream medicine.
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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