Solanaceae
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 A flowering Brugmansia x insignis from the US Botanic Garden | ||||||||||
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| Acnistus
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The Solanaceae is a family of flowering plants, many of which are edible, while others are poisonous (some have both edible and toxic parts). The name of the family comes from the Latin Solanum "the nightshade plant", but the further etymology of that word is unclear; it has been suggested it originates from the Latin verb solari, meaning "to soothe". This would presumably refer to alleged soothing pharmacological properties of some of the psychoactive species found in the family. It is more likely, however, that 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. The family is also informally known as the nightshade or potato family. The family includes the Datura or Jimson weed, eggplant, mandrake, deadly nightshade or belladonna, capsicum (paprika, chile pepper), potato, tobacco, tomato, 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 alkaloidal glucosides that can range in their toxicity to humans and animals from mildly irritating to fatal in small quantities.
Flowers are typically conical or funnelform 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 a dehiscent (breaks open upon drying, or dehiscing, releasing the seeds) capsule 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 inferior. The hypogynus gynoecium is a syncarp located obliquely in relation to the median.
Alkaloids
The Solanaceae are known for possessing a diverse range of alkaloidal glucosides, or simply alkaloids. As far as humans are concerned, these alkaloids can be desirable, toxic, or both, though they presumably evolved because they reduced 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 opthamalic 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.
Cocaine is also considered a tropane alkaloid due to its structural similarity to the aforementioned compounds. Its pharmacology, however, is radically different, and it does not occur in the Solanaceae family.
The most 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.
Capsaicin is structurally unrelated to nicotine or the tropanes, and is found in the genus Capsicum, which includes chile peppers such as Tabasco peppers and habaneros. The compound is not appreciably toxic to animals. However, it stimulates specific pain receptors in most mammals, those which sense heat, in the oral mucosa as well as many other epithelial tissues. This causes a sensation of burning not unlike an actual heat or chemical burn. It is used in high concentration as a deterrent in pepper sprays, and sought after for many culinary dishes for its "spiciness". It is thought that the reason one would deliberately induce pain while eating is the rewarding release of endorphins it has been shown to induce. The "hotness" of capsaicin products and foods is expressed in Scoville units. A scoville unit is the factor by which the capsaicin-containing substance must be diluted to render the resulting solution imperceptible to a tester (for example, a teaspoon of a 5,000 Scoville unit hot sauce would have to be diluted with 4,999 teaspoons of a sugar water solution to negate its potential to cause a sensation on the palate).
Nutritional importance
The most important species of this family for the global diet is the potato or Solanum tuberosum. Although this plant itself is generally considered toxic, swollen subterranean sections of modified stem known as tubers generally possess no toxicity. Instead, the tubers contain a copious store of carbohydrates that both the plant and humans can use to obtain energy. However, the tubers may become toxic if allowed to sprout. Green areas on a potato indicate new growth, which may indicate the presence of chaconine and [[ solanine]]. These glycoalkaloid compounds can be in sufficient concentrations in a single potato serving to be poisonous to humans. In many genera, the fruits are the desirable item, for example, tomatoes, tomatillos, eggplants, and peppers. Some people experience sensitivity or allergy-like symptoms in response to nightshade plants.
External links
- SOL Genomics Network
- Solanaceae Network - pictures of plants
- Solanaceae Source - more pictures
- Solanaceae in L. Watson and M.J. Dallwitz (1992 onwards). The families of flowering plants: descriptions, illustrations, identification, information retrieval. http://delta-intkey.com
- Solanace in USDA Plants Database.
- http://personal.denison.edu/~kuhlman/WOL/plants.html
Additional reading
D'Arcy, William G. (1986). Solanacea. Columbia University Press. ISBN 0-231-05780-6.
