Plant toxicity

Scrolling through Google news yesterday, I came across an item about a four-year-old girl in Bolton who had brushed against giant hogweed and developed huge blisters on her hand.

Giant hogweed is from the Caucasus, and in ideal conditions it can reach five metres in height. It is recognised by the purple blotches on its stems and flowers that look like cow parsley. The plant was brought to Britain to Kew and distributed as an ornamental plant until its danger was recognised.

The sap of giant hogweed contains furanocoumarins. On contact with human skin which is then exposed to sunlight, these chemicals cause phytophotodermatitis. That is, it causes inflammation because the sap prevents skin from protecting itself from sunlight which then leads to bad sunburn.

Furocoumarins enter the nucleus of epithelial cells and form a bond with the DNA when exposed to UV light, and that kills the cell, and that causes inflammation. The chemical mechanism known as the arachidonic acid cascade involves prostaglandin hormones that are found throughout the body and are involved in many inflammatory processes.

Certain furanocoumarins are toxic to fungi, which is interesting because of the role that fungi play in plant growth of very many other families of plants.

I happened to go to the plant day at the Botanic Garden and spoke with a researcher at the Cambridge University Department of Plant Sciences. She explained how most plant families regulate their intake of nutrients by a relationship with fungi in an around their roots and between plants.

The relationship, known as arbuscular mycorrhiza, is where a fungus penetrates the cells of the roots of a plant leading to a continuous orchestration of signals to benefit both the plant and the fungus.

She explained that some plants – I think she mentioned the carrot family – do not have this relationship, and neither do plants that live in water.

That fits because Giant Hogweed is in the umbelliferae family of celery, carrot, parsley etc. Umbelliferae are easily recognised by the circular flower heads a circle made up of tiny flowers on short stalks around a central stalk.