In November 2019, a study published in Scientific Reports showed a fascinating defense mechanism possessed by a certain variety of sweet potato named TN 57, which was known to be much more resistant to pests than other strains. Researchers found that when one of the plant’s leaves is attacked by insects, or damaged in any other way, it releases a strong odour that serves to alert the rest of the affected plant’s leaves, as well as those of neighbouring plants, that danger is nearby. This odourous mixture, which contains many chemicals, fills the surrounding air, and triggers a defensive response in the undamaged leaves. One of these compounds is DMNT, (for the chemically curious, (E)-4,8–dimethyl–1,3,7-nonatriene), a volatile plant hormone that is thought to be the sole initiator of this response.
Stimulated by DMNT, the leaves increase their production of a protein known as “sporamin”, the same protein that makes it difficult for us humans to digest uncooked sweet potato. Increased levels of sporamin result in the leaves becoming much harder for insects to digest, thereby discouraging them from nibbling.
In the study, when an untouched plant was placed in the same enclosed space as one whose leaves had been punctured with tweezers, the undamaged leaves of both plants reported high levels of sporamin within 24 hours.
For now, this ability to warn neighbouring leaves through the air has only been observed in the TN 57 variety of sweet potato. Another variety known as TN 66, which is much less resistant to pests, was also examined, and unsurprisingly was not found to produce any DMNT.
Such research is more than just of academic interest. Choosing to grow the TN 57 variety allows farmers to increase yields while reducing the use of insecticides. And this increases the availability of a tuber that is rich in beta-carotene, a compound the body converts into vitamin A.
Caitlin Bard is completing her Bachelor of Science with a major in neuroscience at McGill University.