DNA Bar-coding

DNA barcoding is a taxonomic method used to identify plants by extracting DNA from a tiny sample of plant material. DNA barcodes are small sections of DNA code (between 400 and 800 base pairs) that are identifiable as belonging to a particular species. In land plants, standardised regions of DNA found on genes in the chloroplasts, are typically used. DNA barcoding offers a quick and accurate analysis of plant samples, allowing the user to retrieve information about known plant species.
The main problem with identifying plants using anatomical characteristics is the limitations of identifying plant samples correctly in a quick and repeatable manner. Plants of the same species can differ dramatically in their appearance depending on their stage of life, condition, habitat etc, so this adds to the difficulty in identifying plants based on their anatomy.
DNA barcoding was initially developed as a taxonomic tool to counteract the limitations faced in order to facilitate species identification. DNA barcoding makes it possible to identify a plant species at all life stages, for example through sampling a fruit, seed, immature plant and mature plant. It can also be used to analyse plant samples that are damaged and may otherwise be unidentifiable. Furthermore, DNA barcoding may even be used to identify species in the gut contents and faeces of animals. 

Process of using DNA barcoding for plant identification

Using DNA barcoding as a method to identify plants requires the following:
Known plant species are recorded in a database that serves as a DNA barcode library. 

  • Examples of a DNA barcoding library may be plant species within a specific geographic location, plant species within a particular taxonomic group, target plant species for a particular study e.g. medicinal herbs. 
  • Multiple specimens of each plant species should be used to allow for variation within species and safeguard against any errors. 
  • Tissue for DNA analysis may be extracted from specimens in herbaria or collected from fresh specimens from the field. 

The DNA barcode of a plant specimen that requires identification is matched against the DNA barcode library.

  • Tissue for DNA analysis is then extracted from the unknown plant samples. 
  • The DNA barcodes generated from these samples can then be compared with the those of the known species in the DNA barcode library in order to find a match and identify the plant species. 

Applications of DNA barcoding

Using DNA barcoding as a taxonomic tool has many applications including: 

  • Identification of species of interest e.g. protected species, pest species, regulated species.
  • Testing products containing plants e.g. medicinal herbs, supplements.
  • Conservation and ecological applications e.g. manipulation of plant assemblages in plant communities, identifying the extent of specialisation in plant and animal interactions, protecting habitats of evolutionary significance.

A problem with DNA barcoding at the time of writing is that not all species are in the barcode library and so a negative result may be interpreted as a new species.

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