Organism of the week #13 – Unlucky for some

I’m a sucker for things that are both poisonous and pretty. Datura metel definitely meets both criteria.

These photos were taken in southern Spain, where this purple variety of the plant seemed to have naturalised itself out from someone’s garden .

Datura metel is closely related to Atropa belladonna, the deadly nightshade, and – like it – the plant contains high concentrations of atropine and scopolamine. If eaten, these chemicals clog up receptors in the nervous system, the normal job of which is to cause the body to “rest and digest“. By blocking these receptors, high doses of atropine or scopolamine cause a “flight or fight” response: increased heart rate, dry mouth, reduced gut movement, and dilated pupils. The last of these effects is the source of the belladonna (‘beautiful lady’) of Atropa belladonna: juice from deadly nightshade was used cosmetically during the middle ages to dilate the pupils alluringly – and, one suspects – alarmingly.

Atropine and scopolamine are still used medically, but in standardised and pure form rather than as the random rag-bag of assorted poisons used by mediaeval herbalists. Atropine is used to speed up dangerously slow heart beats, and as a treatment for organophosphate poisoning, where it counteracts the excessive “rest and digest” symptoms caused by nerve agents and accidental consumption of some insecticides. Atropine is no longer used to dilate pupils for eye examinations as it is too long-lasting in its effects (days to weeks!) Scopolamine is mostly used in the treatment of motion sickness: it reduces nausea by reducing motion of the gut.

The fruit of the Datura is called a thorn-apple, but I would certainly not recommend baking them into pies. In Datura stramonium, the fruit varies markedly in its shape if it carries an extra copy of one of its chromosomes. Extra chromosomes (up to and including a whole extra set, or four, or even eight!) are quite well tolerated by plants, although they can lead to fertility issues. However, in humans, most (but not all) changes to chromosome number are lethal. Quite why plants are more tolerant than humans of this sort of large-scale chromosomal change is not well understood. On the other hand, doubling of chromosome number has occurred at least twice in the evolutionary history of human beings, and our own chromosome 2 is the product of fusion of two smaller chromosomes (which are retained in our nearest relatives), so these events – whilst rare – are not unheard of in mammals.