DNA barcoding is a modern molecular technique used for the identification and authentication of biological species by analyzing a short, standardized region of DNA called a DNA barcode.
In pharmacognosy, DNA barcoding is particularly useful for identifying medicinal plants and crude drugs, especially when the drug is:
- Dried
- Powdered
- Fragmented
- Difficult to identify morphologically
- Closely related to another species
- Suspected to be adulterated
Simple definition ⭐
DNA barcoding is a molecular identification technique in which a short, standardized DNA sequence is used to identify a species.
Why is DNA Barcoding Needed?
Traditional identification of medicinal plants is mainly based on:
- Morphology
- Organoleptic characters
- Microscopy
- Chemical constituents
However, these methods can become difficult when the plant material is powdered, processed, or highly fragmented.
For example, two plant species may look very similar but have different DNA sequences.
DNA barcoding can help distinguish between them.
Principle of DNA Barcoding
The basic principle is:
Different species have characteristic DNA sequences in specific regions of their genome.
A particular short DNA region is selected as a barcode region.
The DNA from the unknown sample is:
Extracted → Amplified → Sequenced → Compared with reference sequences → Species identified
Steps of DNA Barcoding
Step 1: Sample Collection
A sample of the plant or crude drug is collected.
The sample may be:
- Fresh plant material
- Dried material
- Powdered drug
- Herbal formulation
Step 2: DNA Extraction
DNA is isolated from the sample. The extracted DNA should be of sufficient quality and quantity for further analysis.
Step 3: PCR Amplification
The selected DNA barcode region is amplified using Polymerase Chain Reaction (PCR).
PCR: PCR produces millions of copies of the selected DNA region so that it can be analyzed.
Step 4: DNA Sequencing
The amplified DNA fragment is sequenced to determine its nucleotide sequence.
The sequence contains:
A – Adenine
T – Thymine
G – Guanine
C – Cytosine
Step 5: Sequence Comparison
The obtained DNA sequence is compared with sequences available in reference DNA databases. A close sequence match helps determine the identity of the species.
Step 6: Species Identification
Based on the sequence comparison, the unknown sample can be assigned to the most appropriate species.
Important DNA Barcode Regions ⭐
Different organisms require different barcode regions.
For plants, commonly used barcode regions include:
1. rbcL
The rbcL gene is located in the chloroplast genome.
Advantages:
- Relatively easy to amplify
- Good universality
- Useful for plant identification
Limitation: It may have relatively low discriminatory power between closely related species.
2. matK
matK is another chloroplast DNA barcode commonly used for plants. It generally provides better discrimination than rbcL for many plant groups.
Important:
rbcL + matK are widely used as core plant DNA barcode regions.
3. ITS / ITS2
ITS (Internal Transcribed Spacer) is a nuclear ribosomal DNA region. ITS2 is particularly useful for distinguishing many closely related medicinal plant species.
Advantages
- High discriminatory power in many groups
- Useful for medicinal plant authentication
Other regions
Depending on the plant group, other markers such as:
- trnH-psbA
- trnL-F
may also be used.
DNA Barcode vs DNA Barcoding
DNA Barcode: The short standardized DNA sequence used for identification.
DNA Barcoding: The complete process of using that DNA sequence to identify a species.
Applications in Pharmacognosy
DNA barcoding has several important applications.
1. Authentication of Medicinal Plants: It can confirm whether the plant material belongs to the claimed species.
2. Detection of Adulteration: It can identify substitute or adulterant species present in herbal drugs.This is particularly useful when the adulterant looks similar to the genuine drug.
3. Identification of Powdered Drugs: Morphological identification becomes difficult after grinding.DNA barcoding can sometimes identify the plant source even from powdered material.
4. Herbal Medicine Quality Control
It can be used as a tool for authentication and quality control of:
- Herbal drugs
- Herbal medicines
- Plant-based formulations
- Raw materials
5. Identification of Closely Related Species: Closely related species may be difficult to differentiate by morphology.DNA sequence differences can provide additional evidence for identification.
6. Detection of Substitution: A commercially supplied medicinal plant may be replaced with another species.DNA barcoding can help detect such substitution.
7. Conservation and Biodiversity Studies
DNA barcoding can also assist in:
- Species identification
- Biodiversity studies
- Conservation of medicinal plants
- Documentation of plant resources
Advantages of DNA Barcoding
- Highly specific molecular identification method.
- Can identify species from small biological samples.
- Useful for powdered and fragmented materials.
- Helps detect adulteration and substitution.
- Does not depend entirely on external morphology.
- Useful for closely related species.
- Can support quality control of herbal drugs.
- Results can be compared with reference DNA databases.
- Useful when diagnostic morphological characters are absent.
Limitations of DNA Barcoding
DNA barcoding is powerful, but it is not a perfect method.
1. Closely related species may have very similar barcode sequences: A single barcode may not always distinguish closely related species.
2. Hybridization: Hybrid plants can make species identification more complicated.
3. Processed materials
DNA may become degraded during:
- Heating
- Extraction
- Processing
- Long-term storage
Therefore, highly processed herbal products may be difficult to analyze.
4. Contamination: DNA from another organism can contaminate the sample and affect the result.
5. Reference database limitations: Correct identification depends on the availability and quality of authenticated reference sequences.
6. It may not determine chemical quality
This is a very important point:
DNA barcoding identifies biological origin, but it does not directly tell us the concentration of active chemical constituents.
Therefore, DNA barcoding should ideally be used along with microscopic, physicochemical and chemical evaluation.
DNA Barcoding in Drug Authentication
A simple example:
Suppose a crude drug is claimed to be Plant A.
Traditional method:
Examine:
Colour → Shape → Microscopy → Chemical tests
DNA barcoding:
Sample → DNA extraction → PCR → Sequencing → Database comparison → Species identification
If the DNA sequence matches Plant B instead of Plant A, the sample may be adulterated or substituted.
DNA Barcoding vs Traditional Evaluation
| Feature | Traditional Methods | DNA Barcoding |
| Basis | Morphological/chemical characters | DNA sequence |
| Fresh plant | Useful | Useful |
| Powdered drug | Sometimes difficult | Often useful |
| Closely related species | May be difficult | Can provide additional discrimination |
| Adulteration detection | Possible | Very useful |
| Chemical constituents | Can be evaluated | Not directly evaluated |
| Equipment | Often simple | Molecular laboratory required |
| Cost | Generally lower | Generally higher |
Editorial Note
This article has been carefully researched and written by Deepak Rajput with a focus on accuracy, clarity, and evidence-based healthcare information. Pharmaacademias.com
