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Plants That Sting
by George Shiflet
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Australia is well-known for its natural beauty and also its poisonous animals. Besides these animals, there are plants in the forests of eastern Australia that produce poison (Figure 1). These plants, belonging to the nettle family (Urticaceae), may be shrubs or very tall trees. The poison is associated with small, stiff hairs (trichomes) on the leaf or stem surfaces that release a host of chemicals when touched. Physical contact with these plants can lead to excruciating pain as well as other symptoms, some of which may be prolonged. In extreme cases, people contacting these plants have been treated in critical care facilities. Scientists in Australia, some of whom have had their own unpleasant experiences with these stinging plants, have attempted to determine which chemicals in the mix are responsible for the extremely painful outcome.
Figure 1. Leaf of a stinging plant
Copyright © CSIRO at https://commons.wikimedia.org/wiki/File:CSIRO_ScienceImage_4541_Leaf_of_the_GympieGympie_one_of_the_stinging_trees.jpg
After analyzing the chemical mix in the hairs from leaves and stems of two species of trees of the genus Dendrocnide, scientists found a number of molecules that could cause inflammation and irritation, but they have now focused on a group of small proteins (peptides) that bind to and activate sensory neurons in mice, while also inhibiting their deactivation (prolonging pain). Interestingly, these peptides show a striking structural similarity to neurotoxins found in some spiders and in cone snails. Cone snails are predaceous molluscs that possess a set of hollow teeth that can pierce prey animals, injecting the venom and paralyzing them immediately. Scientists who study evolution call the presence of similarly developed features in essentially non-related organisms an interesting example of convergent evolution.
Pain is a characteristic of many diseases and injuries. Understanding how these venoms work may lead scientists to understand better how pain is stimulated. Better understanding of such mechanisms may help treatment and management of pain, particularly in diseases like cancer.