How to Test a Plant's DNA

While it may be difficult to tell the differences in plant varieties just by examining the seeds, deoxyribonucleic acid, or DNA, testing makes it possible to identify specific plant traits and to accurately identify each variety since the DNA of every plant is individualized. Knowing how to test a plant's DNA is significant in identifying specific genes, such as the drought-resistant varieties.

Things You'll Need

• Plant seedling (plant tissue)
• Liquid nitrogen
• Mortar and pestle
• CTAB Isolation Buffer (hexadecyltrimethylammonium bromide)
• Isopropanol or ethanol
• DNA polymerize
• Agarose gel/powdered agorose
• Gel slab
• CTAB Wash Buffer
• Ethidium bromide staining
• Nylon sheet
• X-ray film
• UV-transilluminator

Instructions

1. Freeze leaves (plant tissues) using liquid nitrogen flash freezing. Grind the frozen tissue using a mortar and pestle. Add CTAB Isolation Buffer to the solution to prevent the action of nucleases that would otherwise degrade the extracted DNA into nucleotides. Add cold isopropanol or ethanol to the solution to precipitate nucleic acids. Separate or extract the visible pellets that have formed -- the DNA pellets -- from the cellular components that make up the solution in the mortar.

2. Heat the DNA polymerize together with the DNA that you have extracted so that the nucleic acids can be amplified using the polymerase chain reaction. Separate and remove the amplified DNA strands that have formed. Since the DNA strands do not have a specific protein, the lengths of the amplified DNA strands differs in size and are also fragmented.

3. Separate the fragments of the nucleic acid on the basis of size and length using gel electrophoresis. Electrophoresis a process used to separate and identify the fragments of the DNA based on the sizes and electric charges of the fragments. Melt the powdered agarose in a buffered solution to ensure that it contains enough ions to conduct an electric current. Place a sample of the fragments of nucleic acids on a gel slab; the fragments will experience an electric current promoted by a negative pole at the top of the gel, and a positive pole at the bottom. Nucleic acids will as a result migrate in an electric field toward the positive electrode, separating the fragments across the gel in terms of similar lengths hence organizing them in a distinct pattern.

4. Place the nylon sheet next to the gel, and the pattern will be transferred to the nylon sheet. Radioactive DNA will as a result be introduced to the pattern on the nylon sheet. Expose the nylon sheet containing the radioactive probes to the X-ray film. Visualize the DNA molecules in the nylon sheet on the UV-transilluminator. The nitrogenous bases of the DNA will absorb UV light and pass the energy to the ethidium bromide. The ethidium bromide in turn will release this energy in the form of a red-orange fluorescence allowing the position of the DNA molecules in the gel to be identified. Dark bands that resemble a commercial bar code will develop at the probe sites in a pattern that is specific to the plant, since the DNA of each organism is unique.

References

• Virginia Tech: Fields of Fingerprints -- DNA Testing for Crops
• University of California; Genetic Engineering and testing Methodologies; McHughen Alan
• Purdue University; Forensic Biochemistry: DNA Testing of Plant Material; Wilson Anna, et al.
• DNA Junction: Electrophoresis
• University of Washington; DNA Testing: An Introduction For Non-Scientists; Riley Donald, Ph.D.