Polymerase Chain Reaction: A New Method For The Identification Of Aloe Vera

 

Polymerase chain reaction is a laboratory technique that allows the DNA from a selected region of a genome to be amplified a billionfold so that it may be detected and compared against known DNA sequences for identification of its origin. This method is being used for the medical diagnosis of genetic diseases, forensic science, and as a standard molecular biology tool.

 

We have developed this technique for the detection and identification of aloe DNA. Three different DNA markers were developed (rbcL, the defined chloroplast DNA marker for ribulose 1,5-biophosphate carboxylase; species-specific tRNA genes; and RAPD primers) that are specific for aloe and are reproducible at low concentration without spurious artifacts. Extraction of DNA from aloe leaves and processed aloe was optimal using guanidine thiocyanate followed by isopropanol precipitation. The yield of DNA varied from 10 ug/g of fresh leaf tissue to as low as 1 pg/ml from 10 ml of 1:1 decolorized gel or retail drink products.

 

It was possible to increase the total amount of extracted DNA by increasing the amount of sample being processed. Also, it was found that industrial processing greatly affects the final content of DNA in processed aloe, e.g., decolorization with carbon decreased DNA content by 100-1,000 fold, and storage of raw gel or whole leaf for several hours permits significant nuclease enzyme degradation of aloe DNA. While the yield of DNA from aloe products could be variable, the PCR technique was able to detect aloe DNA in all samples, and it was capable of identifying the species of aloe from which the material originated. In challenge tests, this method differentiated between Aloe capensis, Aloe aborescens and Aloe barbadensis. The gene sequences of the DNA from each of these plants used as primers in the PCR test have been identified and found to be unique to each type of plant. No homology was evident with any other plant or animal DNA on the basis of a GENBANK search. This method provides an unequivocal detection of aloe and identification of its plant origin.

By Dr. Steve Orndorff, Ph.D.

Univera Phytoceuticals, Inc.

 

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