Vegetarians Watch Out: Some Plants Have Teeth to Bite BackJun 29, 2016, by
Many vegetarians will argue that it’s a moral decision to eat plants instead of animals, but this is in direct contradiction to the fact that plants obviously don’t want to be eaten. Many of them go to great lengths to ensure they don’t get eaten, though this sometimes backfires. For example, capsaicin was developed by peppers to keep mammals from eating their fruits, since their seeds can’t pass safely through our digestive tract. How ironic it is, then, that we now eat pepper specifically because of their capsaicin (and even use it to cure headaches!).
But there are some plants that have gone so far to avoid being eaten that they have developed teeth to bite back against plant-eating animals. Researchers have confirmed for the first time that some plants make their spines out of crystalline hydroxyapatite, the same material as tooth enamel. Researchers are hoping it will give them a new angle to develop biomimetic materials that can be used for bone and tooth regrowth.
Most Plants Don’t Have Teeth
The use of hydroxyapatite for materials like teeth and bones is primarily an animal characteristic.
When plants need to make hard structures they use what are described as phytoliths–plant stones–that are made mostly of silica (SiO2–glass, basically) and calcium carbonate (CaCO3, limestone, but also used in mollusc shells and the homes of coral). But they also make hard structures known as mineralized trichomes, basically hard plant hairs that serve to injure would-be predators. These structures are designed to break off in the mouth of herbivores, inflicting tiny wounds that are then filled with painful chemicals released from inside the plant.
A Tale of Two Nettles
Up here we are all familiar the stinging nettle which is found in the Dallas area, and the terrible rashes they can give. But these nettles don’t actually have teeth. Instead, they use the usual silica to make their stinging hairs. It’s the South American rock nettle that has the distinction of being the first plant to have actual teeth. Although it’s structurally very similar to the stinging nettle, instead of using silica or calcium carbonate, the rock nettle uses calcium hydroxyapatite, a much more complicated structure. Researchers say that the mineral composition is very similar to that of animal teeth.
What researchers don’t know is just why this plant has chosen to use calcium hydroxyapatite to make its stinging hairs. Usually, they assume that plants do it because they can’t make the other materials. But in this case, it seems that the rock nettle uses plenty of silica, sometimes side-by-side with calcium hydroxyapatite. With no good reason why the rock nettles have developed the teeth, saying only that it allows the nettles to respond in kind to its predators–”a tooth for a tooth.”
Researchers note that this discovery is interesting not just for its novelty but also because it gives us another pathway to understand biomineralization–the way that living organisms can grow and develop mineral tissues. This is obviously a challenge, especially when it comes to teeth. If animal models are unable to help us develop ways to grow replacement teeth, perhaps plant models will help us understand the essentials better.
And we may be growing more than just replacement teeth. In addition to teeth, researchers compared the stressed structures of the rock nettles to reinforced concrete. It may be that some day we will grow structural elements, rather than having to build them. Even if these aren’t appropriate for large-scale constructions, it may some day be used for small-scale applications.
Of course, speculations about growing teeth are all very well, but until they become practical, we have a very good option for tooth replacement. Dental implants are very close to natural teeth and offer many benefits.