Betalain

Betalains are a class of red and yellow indole-derived pigments found in plants of the Caryophyllales. They are most often noticeable in the petals of flowers, but may color the fruits, leaves, stems, and roots of plants that contain them.

Description

The name "betalain" comes from the Latin name of the common beet ("Beta vulgaris"), from which betalains were first extracted. The deep red color of beets, bougainvillea, amaranth, and many cacti results from the presence of betalain pigments.cite book
last= Robinson
first= Trevor
year=1963
title=The Organic Constituents of Higher Plants
pages=292
location= Minneapolis
publisher= Burgess Publishing ] The particular shades of red to purple are distinctive and unlike that of anthocyanin pigments found in most plants. Betalains may occur in any part of the plant, including the petals of flowers, fruits, leaves, stems, and roots.

There are two categories of betalains:cite book
last= Salisbury
first= Frank B.
coauthors=Cleon W. Ross
year=1991
title=Plant Physiology
edition=4th
pages=325-326
location= Belmont, California
publisher= Wadsworth Publishing
id=ISBN 0-534-15162-0 ]
* Betacyanins include the reddish to violet betalain pigments.
* Betaxanthins are those betalain pigments which appear yellow to orange.

Among the betaxanthins present in plants include vulgaxanthin, miraxanthin and portulaxanthin, and indicaxanthin.

Plant physiologists are uncertain of the function that betalains serve in those plants which possess them, but there is some preliminary evidence that they may have fungicidal properties. [cite journal
last= Kimler
first= L. M.
year=1975
title=Betanin, the red beet pigment, as an antifungal agent
journal= Botanical Society of America, Abstracts of papers
volume= 36 ]

Chemistry

It was once thought that betalains were related to anthocyanins, the reddish pigments found in most plants. Both betalains and anthocyanins are water-soluble pigments found in the vacuoles of plant cells. However, betalains are structurally and chemically unlike anthocyanins. For example, betalains contain nitrogen whereas anthocyanins do not.

It is now known that betalains are aromatic indole derivatives synthesized from tyrosine. They are not related chemically to the anthocyanins and are not even flavonoids. [cite book
last= Raven
first= Peter H.
coauthors = Ray F. Evert, Susan E. Eichhorn
year=2004
title=Biology of Plants
edition=7th
pages=465
location= New York
publisher= W. H. Freeman and Company
id=ISBN 0-7167-1007-2 ] Each betalain is a glycoside, and consists of a sugar and a colored portion. Their synthesis is promoted by light.

The most heavily studied betalain is betanin, also called beetroot red after the fact that it may be extracted from red beet roots. Betanin is a glucoside, and hydrolyzes into the sugar glucose and betanidin. It is used as a food coloring agent, and the color is sensitive to pH. Other betalains known to occur in beets are isobetanin, probetanin, and neobetanin.

Other important betacyanins are amaranthine and isoamaranthine, isolated from species of "Amaranthus".

Taxonomic significance

Betalain pigments occur only in the Caryophyllales and some Basidiomycota (mushrooms).cite book
last= Cronquist
first= Arthur
year=1981
title=An Integrated System of Classification of Flowering Plants
pages=235-239
location= New York
publisher= Columbia University Press
id=ISBN 0-231-03880-1 ] Where they occur in plants, they sometimes coexist with anthoxanthins (yellow to orange flavonoids), but never occur in plant species with anthocyanins.

Among the flowering plant order Caryophyllales, most members produce betalains and lack anthocyanins. Of all the families in the Caryophyllales, only the Caryophyllaceae (carnation family) and Molluginaceae produce anthocyanins instead of betalains. The limited distribution of betalains among plants is a synapomorphy for the Caryophyllales, though their production has been lost in two families.

Recently, betalain-like compounds have been discovered in carnivorous plants that were not previously considered related to the Caryophyllales, but which have been added to that order under the APG II system. Betalains are now known from species of "Drosera" (sundew) and "Nepenthes".fact|date=September 2007

Economic uses

Betanin is commercially used as a natural food dye. It can cause beeturia (red urine and faeces) in some people who are unable to break it down. The interest of the food industry in betalains has grown since they were identified as natural antioxidants [cite journal
last=Escribano
first=J.
coauthors= M. A. Pedreño, F. García-Carmona, R. Muñoz
year=1998
title=Characterization of the antiradical activity of betalains from "Beta vulgaris" L. roots
journal=Phytochem. Anal.
volume=9
pages=124–127
doi=10.1002/(SICI)1099-1565(199805/06)9:3<124::AID-PCA401>3.0.CO;2-0
doilabel=10.1002/(SICI)1099-1565(199805/06)9:3124::AID-PCA4013.0.CO;2-0 ] which may have positive health effects in humans.cite journal
last=Tesoriere
first=Luisa
coauthors=Mario Allegra, Daniela Butera, and Maria A. Livrea
title=Absorption, excretion, and distribution of dietary antioxidant betalains in LDLs: potential health effects of betalains in humans
journal=American Journal of Clinical Nutrition
year=2004
volume=80
issue=4
pages=941–945
url=http://www.ajcn.org/cgi/content/abstract/80/4/941
pmid=15447903] Betalians may exhibit anti-cancer activity. Betalains from the prickly pear showed considerable free radical scavenger and antioxidant properties "in vitro" to protect endothelium from cytokine-induced redox state alteration, through ICAM-1 inhibition. [ [http://lib.bioinfo.pl/pmid:15650274 Antioxidant betalains from cactus pear (Opuntia ficus-indica) inhibit endothelial ICAM-1 expression. [My paper] C Gentile, L Tesoriere, M Allegra, M A Livrea, P D'Alessio Dipartimento Farmacochimico, Tossicologico e Biologico, Università di Palermo, Italy.] ]

The 'Hopi Red Dye' amaranth produces red flowers which the Hopi Amerindians used as the source of a deep red dye.

ee also

* Biological pigment
* Caryophyllales
* Glycoside

References

External links

* [http://www.botgard.ucla.edu/html/botanytextbooks/generalbotany/shootfeatures/generalstructure/leafcolor/a0896tx.html Betalain synthesis diagram]