Solanaceae

Solanaceae

The Solanaceae is a family of flowering plants, that contains a number of important agricultural plants as well as many toxic plants. The name of the family comes from the Latin Solanum "the nightshade plant", but the further etymology of that word is unclear. Most likely, the name comes from the perceived resemblance that some of the flowers bear to the sun and its rays, and in fact a species of Solanum (Solanum nigrum) is known as the sunberry. Alternatively, it has been suggested the name originates from the Latin verb solari, meaning "to soothe". This presumably refers to alleged soothing pharmacological properties of some of the psychoactive species of the family.

The family is also informally known as the nightshade family or potato family. The family includes the Datura or Jimson weed, mandrake, deadly nightshade or belladonna, capsicum (paprika, chili pepper), potato, tobacco, tomato, eggplant and petunia.

The Solanaceae family is characteristically ethnobotanical, that is, extensively utilized by humans. It is an important source of food, spice and medicine. However, Solanaceae species are often rich in alkaloids whose toxicity to humans and animals ranges from mildly irritating to fatal in small quantities.

Description

Flowers are typically conical or funnel in shape, with five petals, usually fused. The leaves are alternate, often with a hairy or clammy surface. Solanaceous plants produce a fruit that is either a berry, as in the case of the tomato or wolfberry, or is dehiscent capsule (breaks open upon drying, or dehiscing, releasing the seeds) as in the case of Datura. The seeds are usually round and flat, being 2-4 millimeters in diameter. The stamens are usually present in multiples of four (most commonly four or eight). The ovaries are superior. The hypogynus gynoecium is a syncarp located obliquely in relation to the median.

Alkaloids

The Solanaceae are known for possessing a diverse range of alkaloids. As far as humans are concerned, these alkaloids can be desirable, toxic, or both, though they presumably evolved because they reduce the tendency of animals to eat the plants.

One of the most important groups of these compounds is called the tropane alkaloids. The term "tropane" comes from a genus in which they are found, Atropa (the belladonna genus). The belladonna genus is so named after the Greek Fate, Atropos, who cut the thread of life. This nomenclature betrays the toxicity and lethality that has long been known to be characteristic of these compounds.

Tropane alkaloids are also found in the Datura, Mandragora, and Brugmansia genera, as well as many others in the Solanaceae family. Chemically, the molecules of these compounds have a characteristic bicyclic structure and include atropine, scopolamine, and hyoscyamine. Pharmacologically, they are the most powerful known anticholinergics in existence, meaning they inhibit the neurological signals transmitted by the endogenous neurotransmitter, acetylcholine. Symptoms of overdose may include mouth dryness, dilated pupils, ataxia, urinary retention, hallucinations, convulsions, coma, and death.

Despite the extreme toxicity of the tropanes, they are important drugs when administered in appropriate (and extremely small) dosages. They can reverse cholinergic poisoning, which can be caused by overexposure to pesticides and chemical warfare agents such as sarin and VX. More commonly, they can halt many types of allergic reactions. Scopolamine, a commonly used ophthamological agent, dilates the pupils and thus facilitates examination of the interior of the eye. They can also be used as antiemetics in people prone to motion sickness or receiving chemotherapy. Atropine has a stimulant effect on the central nervous system and heart, whereas scopolamine has a sedative effect.

A famous alkaloid from the Solanaceae family is nicotine. Like the tropanes, its pharmacology acts on cholinergic neurons, but with the opposite effect (it is an agonist as opposed to an antagonist). It has a higher specificity for nicotinic acetylcholine receptors than other ACh proteins. Its effects are well known. Nicotine occurs naturally in the Nicotiana or Tobacco genus.

Another class of toxic substances found in this family are the glycoalkaloids, for example solanine which has occasionally been responsible for poisonings, in people who ate berries from species such as Solanum nigrum or Solanum dulcamara, or spoiled potatoes.

Nutritional importance

The most important species of this family for the global diet is the potato or Solanum tuberosum, whose carbohydrate-rich tubers have been a staple food in many times and places, and which is one of the most grown crops today. In many genera, the fruits are the desirable item, for example, tomatoes, tomatillos, eggplants, uchuva, and peppers.

Some people experience sensitivity or allergy-like symptoms in response to nightshade plants.

References

External links

See also

Additional reading

D'Arcy, William G. (1986). Solanacea. Columbia University Press. ISBN 0-231-05780-6. Radford, Albert E. (1986). Fundamentals of Plant Systematics. Harper & Row, Publishers, Inc.. ISBN 0-06-045305-2.

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