Mint is a well-known herb that contains the aroma component menthol, a plant-specific metabolite that aids in the protection of plants against pests and pathogens. A research group led by Professor Gen-ichiro Arimura and others at the Faculty of Advanced Engineering at the Tokyo University of Science developed a safe and secure compound that activates the immunity of crops by focusing on menthol, which induces the defense response of different varieties of plants.

To determine its superior immunostimulatory ability, the research group synthesized compounds in which menthol was reacted with each of six amino acids, including valine, and examined the protective response of leaf vegetables exposed to the aqueous solutions of those compounds against pests.

In soybean leaves, significantly increased transcription of the defense genes was observed only in those exposed to "ment-Val," a conjugate of menthol with valine, and similar effects were observed in peas, turnips, tobacco, lettuce, and corn. This result shows the versatility of ment-Val as an immunostimulant for wide varieties of plants, including Leguminosae, Solanaceae, Asteraceae, and Gramineae. In addition, the exposure to the ment-Val solution lowered the area of soybean leaves preyed on by herbivorous Spodoptera litura larvae to approximately one-fifth of that of soybean leaves exposed to the control solution.

With growing interest in ecosystem protection, cultivation methods for environmentally friendly crops and highly safe production technologies have become a diet and health related subject. In response to this, ment-Val, which can enhance the natural immunity of various varieties of plants, is a promising candidate as an immunostimulant that can be used in plant factories and gardening farms in the future.

Fig. 1 Soybean leaves exposed to ment-Val solution were significantly less preyed on by Spodoptera litura larvae (in the starved state) than those exposed to the control or menthol solutions.