Cambridge Botanic Gardens: Plants: Nature's Great Chemists
|Author: Juliet Day, Development Officer, Cambridge Botanic Garden||Published: 8th August 2012 13:43|
Nicotiana tabacumPlants are nature's great chemists, producing a bewildering range of chemicals. Mostly these chemicals are toxins that deter feeding animals, from insects to grazing mammals. They can be found in all parts of a plant, most commonly in the leaves, but also in the roots and seeds. Many of these chemical compounds have been extracted for a wide variety of human uses, including for medicines, dyes, flavourings and foodstuffs. Lupins, for example, contain a range of bitter-tasting alkaloids that repel grazers, but the beans also contain the full range of essential amino acids and are a good source of protein and fat. They are grown as a food source in the Andes, although the poisonous alkaloids must be removed by soaking the beans in water.
Some plants, like spurges, Euphorbia sp, take a more mechanical approach. When the stem or leaf is chomped, a milky, sticky latex oozes out and congeals, effectively gumming up the mouthparts of insects attempting to graze. The latex becomes toxic once exposed to sunlight (phototoxic) and is irritating to the skin and mucous membranes.
The chemical melatonin is found in large quantities in the common garden plant feverfew, Tanacetum parthenium. Melatonin does not have a defence function, but regulates the plant's response to photoperiods (the length of night and day). In animals, melatonin is released into the blood by the pineal gland in the brain, and acts to regulate the sleep-wake cycle by chemically causing drowsiness and lowering body temperature. Melatonin can be used to treat circadian rhythm sleep disorders, some types of insomnia and to counter jet-lag and it is involved in the mechanism by which some reptiles and amphibians change colour.
At this time of year, with vegetable plots and allotments overflowing with bounty, it is interesting to reflect on the fine line between friend and foe in the plant world. The Solanaceae family contains some of our most important food crops: potatoes, tomatoes, peppers, aubergines and some quirkier goodies like Cape gooseberries. Cropping well at this time of year are the chillies, Capsicum annuum, from which capsaicin, the principal ingredient of pepper spray is derived. Capsaicin activates the same pain pathway as tarantula venom, stimulating the heat sensors in the body chemically, although body temperature is not actually raised. (Similarly, menthol, from mint, Mentha, in the Labiatae family activates the cold sensors in the body, without actually lowering the body temperature.) But Solanaceae members also include henbane, Hyoscyamus niger, which we grow at the Botanic Garden out of reach in the centre of the family beds on Systematics. It produces scopolamine, reputedly been used as a truth drug and in 1910, was detected in the remains of Cora Crippen, wife of Dr Crippen and was believed to be the cause of her death. Tobacco plant, Nicotiana tabacum, is another member of the potato family. It contains nicotine, an alkaloid which constitutes 0.6-3.0% of the dry weight of tobacco. It acts both as a stimulant and a relaxant. Initially, nicotine causes the release of adrenaline and may block the release of insulin and increase metabolic rate. Dopamine is also released which increases feelings of well-being. However, tobacco smoking is linked to increasing incidence of many diseases, including many cancers and circulatory and respiratory diseases. In the UK, an estimated 100,000 people per year die from smoking-related diseases.
In association with the Cambridge Crystallographic Data Centre, we have recently developed a new ‘Chemicals from Plants' trail at the Botanic Garden which explores just some of the chemical compounds found in plants. Full information can be found on the Botanic Garden's website, or borrow a trail to guide you round the selected plants from the ticket offices.
The Botanic Garden is open 10am - 6pm during September, October 10am - 5 pm, November- January 10am - 4pm. Adult admission is £4.50 (Giftaid admission £4.95) or join the Friends, get free admission & help the Garden grow! For news and events, detailed information about the Garden or to discover this week's Plant Picks from the Head of Horticulture, please visit the website at http://www.botanic.cam.ac.uk/
© Juliet Day, Development Officer, Cambridge Botanic Garden
(image supplied by Cambridge Botanic Garden)