Desert Plant's Potent Chemical Cocktail Makes Mice Go 'Ptooey'

Desert Plant's Potent Chemical Cocktail Makes Mice Go 'Ptooey'
June 18, 2012
by Christopher Joyce

Next time you're in the Negev Desert and you come across a sweet mignonette bush, stop and listen. You might hear a tiny "Ptooey" from somewhere underneath.

In case you're not planning a trip to the Negev, then I'm here to tell you about something quite amazing that goes on between the plant and its pal, the spiny mouse that lives in the Middle Eastern deserts. The sweet mignonette (Ochradenus baccatus if you must know, and also called Taily Weed) has some nice little fleshy fruits growing on it. But you can't eat the fruit unless you do the "ptooey."

Here's how this bizarre twist of symbiotic behavior between mouse and mignonette works: The mignonette is as good a mixologist as you'll find in any trendy bar. It has two chemical weapons in its fruit: An enzyme in the flesh and a glucosinolate inside the fruit's seeds. Rule number one with these chemicals: DO NOT MIX! As you would when, say, you bite into the fruit and break open a seed inside. Because when that happens, the chemicals combine to create what is called a "mustard oil bomb."

The mustard oil bomb "has more punch than Grey Poupon," says Denise Dearing from the University of Utah, who did the study in Israel. It's potent. And it keeps most animals from chowing down on this tiny fruit. But not the spiny mouse. (See this video of the seed-spitting mouse in action.)

Dearing and scientists from the University of Utah and Israel observed the mouse delicately chewing the fruit and spitting out the seeds, unscathed. They're very, very careful about that. And that's exactly what the plant wants, if it can be said that plants "want" things. Unbroken seeds propagate more plants, broken ones don't. So the plant needs a predator that knows how to "ptooey" in order to disperse its seeds.
Spiny mice eat the fruit of the mignonette bush but spit out the seeds
Michal Samuni-Blank/Technion-Israel Institute of Technology.

Spiny mice eat the fruit of the mignonette bush but spit out the seeds

The research paper appears in the latest edition of Current Biology.

The mouse-mignonette bush discovery is only the latest round of plants training animals to help them procreate. There are other plants that that tailor their seeds for a particular animal. The majestic Guanacaste tree in Central America has large, tough seeds. They have to go through a big herbivore's gut before they'll germinate. Not just any herbivore...horses teeth and stomachs ruin them. Cows are just right though. And there's no "ptooey" required.