Many plants use toxins as a defense against being eaten. But why do these toxins not harm the plants themselves? Scientists at the Max Planck Institute for Chemical Ecology and the University of Münster have investigated the mechanisms involved in defensive toxins in plants, and their findings may lead to new treatments for human diseases.
Wild Tobacco - Image Credit: Sunbunny Studio via Shutterstock / HDR tune by Universal-Sci
Defensive toxins are common in plants, but little is known about how they produce and store these chemicals without harming themselves. The researchers chose to investigate terpene glycosides, a toxin found in a species of wild tobacco plant [Nicotiana attenuate]. These plants also produce nicotine as a defense against herbivores. Nicotine is a neurotoxin and, since plants do not have nervous systems, it can be stored in the leaves without harming the plant. The researchers want to know if there was a similar mechanism at work regarding terpene glycosides.
The scientists identified two proteins involved in the biosynthesis and storage of terpene glycosides. They modified plants so that they could not produce these proteins, to see what effect this had on them. The plants became unwell and could not grow properly. They also lost the ability to reproduce and showed all the signs of being poisoned by the terpene glycosides. Experiments revealed the absence of the two proteins allowed the terpene glycosides to attack elements of the plant's cell membranes called sphingolipids.
A detailed chemical analysis of larval frass (small black ball) revealed how toxins are activated in the caterpillars, providing clues to the biosynthesis of the toxins in the plant, the reversed process in comparison to digestion, or as the scientists called it: the "digestive duet". - Image Credit: Anna Schroll
Tripping the defenses
Sphingolipids are found in all living cells. The experiments the scientists conducted indicate the terpene glycosides specifically attack a cell's sphingolipid metabolism. They discovered that the job of the proteins [that they had deactivated in their test-plants] is to add a molecule to the terpene glycosides during biosynthesis, rendering the toxin inert while in storage. Once an insect or animal eats the plant, this extra molecule is detached during the digestive process, thus activating the toxin.
A possible new treatment
This surprising discovery could hold hope for potential new treatments for many human ailments. Shuging Xu, a member of the research team at the University of Münster, explains, "Diterpene glycosides and their derivatives can have broad defensive functions against many agricultural pests and pathogenic fungi. At the same time, many human diseases, such as diabetes, cancers and some neurodegenerative diseases are also associated with elevated sphingolipid metabolisms". This could be a major development for medical researchers who are investigating ways to treat disease by inhibiting the sphingolipid metabolism.
If you would like to learn more about the study, be sure to check out the paper published in Science listed below.
Further reading:
FEATURED ARTICLES: