Measuring the plants gene expression response:

The results of the plant response and the insect feeding experiments demonstrated a physiological link between JAR1 enzyme activity and the insect feeding response. Extending the experiments to coi1 mutants suggested that multiple genes drove the JA response pathway.  Direct study of the expression and control of these genes was possible. The Staswick team wanted to understand some details of the JAR1 gene expression that led to these JA modification differences. A method they could use to document gene expression difference was a northern blot hybridization. The northern blot hybridization is a method of measuring the amount of a specific mRNA molecule in a sample. The specific mRNA is detected by binding it to a special membrane, then probing it with radioactive DNA copies of the specific gene. DNA from the gene binds to the mRNA that was encoded by the gene during the transcription process. Therefore, northern blots reveal if a specific gene was transcribed or expressed in a sampled tissue and generally if the expression was at a high level (lots of radioactive signal on the blot) or low level (little signal on the blot). There are other methods plant biologists can use to obtain a mRNA level that can be quantified with a number.