Australia may be notorious for its venomous animals, such as and , but the country is also home to dangerous plants. Some produce toxins that look very similar at the molecular level to spider and scorpion venom.
Irina Vetter at the University of Queensland in Brisbane and her colleagues examined the toxins produced by two species of Australian stinging trees: the giant Australian stinging tree (Dendrocnide excelsa), which can grow to be up to 35 metres high, and the shrub-sized gympie gympie (Dendrocnide moroides), which is the most toxic of the six Dendrocnide species found in .
Both of these species, commonly found in rainforests in eastern Australia, are covered with felt-like hairs that can penetrate human skin and deliver the toxin 鈥� which can hospitalise people and reportedly kill horses who have brushed up against the plants.
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鈥淭he pain can last for such a long time,鈥� says Vetter. 鈥淎t a minimum, it lasts for 6 to 8 hours from personal experience, but it can persist and keep flaring up for days, weeks.鈥�
The team identified the trees鈥� primary pain-causing toxins as a group of peptides consisting of 36 amino acids. The toxins have a 3-dimensional knot-like structure that resembles the venoms found in spiders and scorpions.
鈥淭hey鈥檙e very dissimilar to anything we鈥檝e seen before [in plants],鈥� says Vetter.
The researchers studied the effect of the stinging tree toxins on mice sensory neurons. They found that the toxins bind to ion channels, resulting in activation of . 鈥淵ou require very little input and they will fire like crazy,鈥� says Vetter.
Stinging trees may have developed these animal-like toxins as a defence mechanism against mammals.聽They are likely to be insecticidal too, says Vetter, but some species aren鈥檛 affected. 鈥淨uite often, you find plants that are completely chewed apart,鈥� she says.
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