To keep its strain alive in the desert, an Israeli shrub known as sweet mignonette or taily weed has developed a ‘toxic mustard oil bomb’ which causes animals that feed on it to spit out the seeds and help with germination.
A joint US-Israel study says this is the first known case within a single species of “directed deterrence” that “the fruit is trying have itself eaten by the right consumer — one that will spread its seeds,” says Denise Dearing, a co-author of the study and professor of biology at the University of Utah.
“It adds a new dimension to our understanding of the ongoing battle between plants and animals,” she says. “In this case, the plants have twisted the animals to do their bidding, to spread their progeny.”
According to the study, the mustard oil bomb produced by the shrub is activated when an animal eating the plant’s small berries chews the seed as well as the fruity pulp. Enzymes (myrosinases) in the seed activate toxic substances (glucosinolates, or GLSs) in the pulp, which otherwise would be harmless.
The reaction produces chemicals named thiocyanate, isothiocyanates and nitriles. Isothiocyanates are responsible for the characteristic hot flavor of mustard.
The chemical reaction in the shrub is “encouraging seed dispersal via seed spitting by rodents,” the researchers wrote.
“It’s not that these mice have poor table manners,” Dearing says. “They deliberately wiggle the seed out of the pulp of the fruit like a person does when eating watermelon. This removal of the seed keeps the toxins in the pulp from being activated.”
Dearing conducted the research with first author and doctoral student Michal Samuni-Blank and Professor Zeev Arad, ecologists at Technion-Israel Institute of Technology in Haifa; Professor Ido Izhaki and graduate student Alon Lotan, ecologists at University of Haifa; lecturer Yoram Gerchman and technician Beny Trabelcy, biochemists at University of Haifa at Oranim; and wildlife ecology Professor William Karasov at the University of Wisconsin, Madison.
The study was published online in the journal Current Biology.