Solanaceae


Solanaceae
Solanaceae
A flowering Brugmansia suaveolens
from the US Botanic Garden
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Solanales
Family: Solanaceae
Juss.
Subfamilies

Cestroideae
Goetzeoideae
Nicotianoideae
Petunioideae
Schizanthoideae
Schwenckioideae
Solanoideae[1]

Solanaceae are a family of flowering plants that include a number of important agricultural crops 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 soothing pharmacological properties of some of the psychoactive species of the family.

The family is also informally known as the nightshade - or potato family. The family includes Datura (Jimson weed), Mandragora (mandrake), Belladonna (deadly nightshade), Lycium barbarum (Wolfberry), Physalis philadelphica (Tomatillo) , Physalis peruviana (Cape gooseberry flower), Capsicum (paprika, chili pepper), Solanum (potato, tomato, eggplant), Nicotiana (tobacco), and Petunia. With the exception of tobacco (Nicotianoideae) and petunia (Petunioideae), most of the economically important genera are contained in the sub-family Solanoideae.

Solanaceae are characteristically ethnobotanical, that is, extensively utilized by humans. They are important sources 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.

Contents

Description

Plants are herbs, shrubs, trees, or sometimes vines. The flowers are usually actinomorphic. Flower shapes are typically rotate (radiately spreading in one plane with a short tube) or tubular (elongated cylindrical tube), with 4-5 petals that are usually fused. Leaves are alternate. The fruit has axile placentation and is a berry as in the case of the tomato or wolfberry, or a dehiscent capsule as in Datura. The seeds are usually round and flat, about 2–4 millimetres (0.079–0.16 in) in diameter. The stamens are epipetalous and are typically present in multiples of 4 or 5, most commonly four or eight. The ovary is superior.[2]

Genetics

Most Solanaceae have basically 12 chromosomes, a number that has increased due to polyploidy. Wild potatoes, of which there are approximately 200, are predominantly diploid (2 * 12 = 24 chromosomes) but triploid (3 * 12 =36 chromosomes), tetraploid (4 * 12 = 48 chromosomes), pentaploid (5 * 12 = 60) and even hexaploid (6 * 12 = 72 chromosome) species or populations exist. The cultivated species Solanum tuberosum has 4 * 12 = 48 chromosomes. Some capsicum species have 2 * 12 = 24 chromosomes, while others have 26 chromosomes.

Alkaloids

Solanaceae are known for possessing a diverse range of alkaloids. As far as humans are concerned, these alkaloids can be desirable, toxic, or both.

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 reflects its toxicity and lethality.

Tropane alkaloids are also found in the Datura, Mandragora, and Brugmansia genera, as well as many others in the Solanaceae family.[3] 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 dry mouth, dilated pupils, ataxia, urinary retention, hallucinations, convulsions, coma, and death.

Despite the extreme toxicity of the tropanes, they are useful drugs when administered in 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 ophthalmological 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.

An infamous alkaloid derived from Solanaceae 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 green potatoes.[4][5]

The chemical in chili peppers responsible for the burning sensation is capsaicin. Capsaicin affects only mammals, not birds. Pepper seeds can always survive the digestive tract of birds; their fruit becomes brightly colored once its seeds are mature enough to germinate thereby attracting the attention of birds who then distribute the seeds. Capsaicin extract is used to make pepper spray, a useful deterrent against aggressive mammals.

Selected genera

See also

References

Further reading

  • Hawkes, J. G., Lester, R. N., Skelding, A. D. (1979). The biology and taxonomy of the Solanaceae. Academic Press, London. ISBN 0-12-333150-1. 
  • 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. 

External links

Media related to Solanaceae at Wikimedia Commons