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Australia is well known for having many of the most poisonous creatures in the world, ranging from snakes, spiders, jellyfish, centipedes, fish, ticks, bees, and ants. 21 of the 25 most poisonous snakes in the world are all from Australia. The country is also home to dangerous plants, such as the Australian stingy tree.
Close up of the heart-shaped leaf of the most toxic of Australia’s stinging tree species, Dendrocnide moroides, also known as scrub, gympie stinger, moonlight plant among others. Image Credit: Victoria Tucholka / Shutterstock
Now, a team of researchers at the University of Queensland in Brisbane examined toxins produced by two species of Australian stinging trees: the bush-sized Gympie-Gympie (Dendrocnide moroides) and the Australian giant treeDendrocnide excelsa).
Leaves of the fearsome giant tree, Dendrocnide excelsa. Image Credit: Lakeview Images
The Gympie-Gympie bite tree is one of the most toxic plants in the world and can cause excruciating and long-lasting pain. From these plants, the researchers found a new family of toxins, which they called “gympietides” after the tree’s name. These trees are typically found in the Northern Rivers region of New South Wales and at the tip of the Cape York peninsula.
“Our research on the poison of Australian trees, found in the northeast of the country, shows that these dangerous plants can inject unsuspecting vagrants with chemicals much like those found in scorpion, spider and cone snail bites. “the researchers said.
Lasting pain
The Australian tree is covered in hollow needle-like hairs called trichomes, which are reinforced with silica. Like common nettles, the hairs contain toxins and substances that can induce extreme pain.
Scientists reported that biting trees produce extremely persistent and painful stings when their trichomes come into contact with mammalian skin. The pain usually lasts for several hours and intermittent painful flare-ups may appear for days and weeks.
“Australian biting tree species are particularly notorious for producing an excruciatingly painful sting, which unlike those of their European and North American relatives can cause symptoms that last for days or weeks,” Irina Vetter, associate professor at the Institute for Molecular Bioscience at the UQ said.
“Like other stinging plants, such as nettles, the giant tree is covered in needle-like appendages called trichomes that are around five millimeters long; the trichomes look like fine hairs, but act like hypodermic needles that inject toxins when come into contact with skin, “he added.
The team reported that the pain and stinging sensation may be related to small molecule neurotransmitters and inflammatory mediators. However, these compounds cannot explain the sensory effects observed.
In the study, published in the journal Scientific advances, the team showed that poisons from stinging trees contain unknown pain-inducing peptides.
Discovering gympietides
To arrive at the study’s findings, the team studied the stinging hairs of the Australian giant tree and obtained an extract from them. They separate them into their unique molecular contents. The substances produced extreme pain responses when tested in the laboratory.
The team discovered that the extract contains a small family of mini proteins. In addition, the team examined the genes found in Gympie-Gympie leaves to find out which one might produce the toxin. From there, the team revealed molecules that can reproduce the pain response even when synthetically developed in the laboratory.
Gympietides contain an intricate three-dimensional structure held by bonds within the molecule that form a knotted shape. Thus, the toxin remains stable, which remains intact for a long time once it is injected into the victim. The structure of gympietides is similar to toxins from cone snail, scorpion, and spider venom, which affect ion channels in nerve cells that are known as pain mediators.
“The 3D structure of these gympietides is reminiscent of toxins in animal venom that target the same receptors, representing a remarkable case of convergent evolution between kingdoms of animal and plant venoms,” the researchers wrote in the paper.
“Our work clarifies the molecular basis of pain caused by these plants while allowing studies of structure-activity and convergent evolution to define how ancestrally different peptides in venoms can elicit the same response in pain receptors,” they added.
The researchers hope the toxins will provide new information about how pain-sensitive nerves work, paving the way for the development of new pain relievers.
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