Soybean leaf lipoxygenases (LOX) are involved with several important physiological processes including a defense mechanism. LOX is used as part of the soybean's mechanism for controlling pathogen growth. This study was done to determine if wound-induced LOX had antimicrobial properties, and whether LOX acts directly on the pathogen's cell membrane or if it acts indirectly by converting free fatty acids into fatty acid hydroperoxides that are toxic to the pathogens. It also allowed us to determine if the LOX defense system is more effective against Gram negative or Gram positive bacteria. LOX enzymes were extracted from soybean leaves. After extraction and purification, the activity of LOX was analyzed for both wound-induced and control plants. Different concentrations of LOX were added to Escherichia coli, Bacillus cereus and Pseudomonas fluorescens. The lowest concentration of LOX enzyme that inhibited growth was the minimum inhibitory concentration. The samples that contained no growth were plated on nutrient agar. In plates that did not contain any growth after incubation, the LOX enzyme had killed the bacteria. The lowest concentration of enzyme that was needed to kill the bacterial was the minimum bactericidal concentration. This process was repeated with hydroperoxides formed by the reaction of LOX with linoleic acid. Different concentrations of the hydroperoxides were incubated with the bacteria. Again, minimum inhibitory and minimum bactericidal concentrations were determined.
Rustad, Keean. "Antimicrobial Properties of Lipoxygenases Enzymes in Wound Induced Soybean Leaves." Undergraduate Research Symposium, Mankato, MN, April 16, 2013.