Calcium phosphate is the main component of our teeth and bones. And now researchers have found this tough mineral substance in the stinging hairs of South American plants from the rock nettle family. The findings were published in Scientific Reports last week.
Plants from the Loasaceae family are often well-equipped with a dense cover of barbed and extremely effective stinging hairs called trichomes. When an animal tries to eat one, the tips of the stinging hairs break off and toxins are injected into its tongue. These rock nettles are distantly related to the more famous stinging nettles, which fortify their needle-shape hairs with the glass-like mineral silica. Lots of plant surfaces rely on silica for defense against plant-eaters.
This process of biomineralization provides both plants and animals with resilient structures. And while calcium phosphate structures are well-known in the animal kingdom, it hasn’t been reported in higher plants, yet. Researchers have previously noticed the hypodermic syringe-like toughness of rock nettle hairs, but their chemical composition remained unknown. So, a team led by Maximilian Weigend of Universität Bonn cultivated a variety of biomineralized plants from the Loasaceae family at the Botanische Gärten der Universität Bonn and studied their stinging hairs.
Turns out, while stinging nettles have silica, rock nettles have calcium phosphate at the tips of their hairs. "The mineral composition of the stinging hairs is very similar to that of human or animal teeth," Weigend explained in a statement. Being densely encrusted with tiny calcium phosphate crystals renders the stinging hairs "unusually rigid." Some of them also have silica in the hooks.
It’s unclear why rock nettles evolved this particular type of biomineralization – with the calcium phosphate that makes up the teeth of those hoping to eat them. "At present we can only speculate about the adaptive reasons for this. But it seems that rock nettles pay back in kind," Weigend added. "A tooth for a tooth."
Image in the text: Blumenbachia insignis. Note the long, mineralized stinging trichomes. M. Weigend/Uni Bonn