Plant carotene

Daucus carota L. subsp. sative Hoffm. Nan He Chi (Carrot) (whole plant) Carotenes, lycopene, phytofluere, umbelliferone, alpha-pinene, camphene, myrcene, daucol, alpha-phellandrene, bisabolene, luteolin-7-glucoside, daucine, pyrrolidine, geraniol, citronellol, carotol, citral, caryophyllene, p-cymene, asarone, daucosterol, petroselinic acid.48 For chronic dysentery, worms, carminative, diuretic, emmenagogue, lower blood sugar, prevent cancer, diabetes, dyspepsia and gout. 

Two major groups of carotenoids are synthesized by higher plants carotenes, which are cyclized or uncyclized hydrocarbons, and xanthophylls, which are oxygenated derivatives of carotenes. 

In green plants / carotene is the major carotenoid pigment. 

Carotene is found in plant chioroplasts. When ingested into animals it serves as a precursor of vitamin A (the transformation occurs in the liver). 

Carotenoids are natural pigments characterized by a tail to tail linkage between two C20 units and an extended conjugated system of double bonds They are the most widely dis tributed of the substances that give color to our world and occur m flowers fruits plants insects and animals It has been estimated that biosynthesis from acetate produces approximately a hundred million tons of carotenoids per year The most familiar carotenoids are lycopene and (3 carotene pigments found m numerous plants and easily isolable from npe tomatoes and carrots respectively... 

Section 26 16 Carotenoids are tetraterpenes They have 40 carbons and numerous dou ble bonds Many of the double bonds are conjugated causing carotenes to absorb visible light and be brightly colored They are often plant pigments... 

An important function of certain carotenoids is their provitamin A activity. Vitamin A may be considered as having the stmcture of half of the P-carotene molecule with a molecule of water added at the end position. In general, all carotenoids containing a single unsubstituted P carotene half have provitamin A activity, but only about half the activity of P carotene. Provitamin A compounds are converted to Vitamin A by an oxidative enzyme system present in the intestinal mucosa of animals and humans. This conversion apparendy does not occur in plants (see Vitamins, VITAMIN a). 

Animals cannot synthesize vitamin A-active compounds and necessary quantities are obtained by ingestion of vitamin A or by consumption of appropriate provitamin A compounds such as P-carotene. Carotenoids are manufactured exclusively by plants and photosynthetic bacteria. Until the discovery of vitamin A in the purple bacterium Halobacterium halobium in the 1970s, vitamin A was thought to be confined to only the animal kingdom (56). Table 4 Hsts RDA and U.S. RDA for vitamin A (67). 

In addition to the U.S. certified coal-tar colorants, some noncertified naturally occurring plant and animal colorants, such as alkanet, annatto [1393-63-17, carotene [36-884] C qH, chlorophyll [1406-65-17, cochineal [1260-17-9] saffron [138-55-6] and henna [83-72-7], can be used in cosmetics. In the United States, however, natural food colors, such as beet extract or powder, turmeric, and saffron, are not allowed as cosmetic colorants. 

An alkene, sometimes caJled an olefin, is a hydrocarbon that contains a carbon-carbon double bond. Alkenes occur abundantly in nature. Ethylene, for instance, is a plant hormone that induces ripening in fruit, and o-pinene is the major component of turpentine. Life itself would be impossible without such alkenes as /3-carotene, a compound that contains 11 double bonds. An orange pigment responsible for the color of carrots, /3-carotene is a valuable dietary source of vitamin A and is thought to offer some protection against certain types of cancer. 

Terpenoids are classified according to the number of five-carbon multiples they contain. Monoterpenoids contain 10 carbons and are derived from two isopentenyl diphosphates, sesquiterpenoids contain 15 carbons and are derived from three isopentenyl diphosphates, diterpenoids contain 20 carbons and are derived from four isopentenyl diphosphates, and so on, up to triterpenoids (C30) and tetraterpenoids (C40). Monoterpenoids and sesquiterpenoids are found primarily in plants, bacteria, and fungi, but the higher terpenoids occur in both plants and animals. The triterpenoid lanosterol, for example, is the precursor from which steroid hormones are made, and the tetraterpenoid /3-carotene is a dietary source of vitamin A (Figure 27.6). 

Annatto is a colored pigment that is extracted from the Central and South American plant Bixa orellana. The color comes from the resinous outer covering of the seeds of the plant, which is composed of the carotenoid pigments bixin and norbixin and their esters. The central portion of those molecules is the same as that of the molecule beta-carotene, and the yellow-orange color of annatto comes from the same physical chemistry origins as the orange color of beta-carotene. 

Vitamin A (retinol), present in carnivorous diets, and the provitamin (P-carotene), found in plants, form retinaldehyde, utilized in vision, and retinoic acid, which acts in the control of gene expression. Vitamin D is a steroid prohormone yielding the active hormone derivative calcitriol, which regulates calcium and phosphate metaboUsm. Vitamin D deficiency leads to rickets and osteomalacia. 

Alkenes with many double bonds in a row are colored. Some plant pigments are alkenes of this kind. One example is )S-carotene, which gives carrots their distinctive orange color. Animals break down )S-carotene into vitamin A, which is essential for vision. Xanthin molecules, relatives of j6-carotene that contain oxygen atoms, occur in com, orange juice, and shellfish. The xanthin below makes the flamingo pink. 

The antioxidant activities of carotenoids and other phytochemicals in the human body can be measured, or at least estimated, by a variety of techniques, in vitro, in vivo or ex vivo (Krinsky, 2001). Many studies describe the use of ex vivo methods to measure the oxidisability of low-density lipoprotein (LDL) particles after dietary intervention with carotene-rich foods. However, the difficulty with this approach is that complex plant foods usually also contain other carotenoids, ascorbate, flavonoids, and other compounds that have antioxidant activity, and it is difficult to attribute the results to any particular class of compounds. One study, in which subjects were given additional fruits and vegetables, demonstrated an increase in the resistance of LDL to oxidation (Hininger et al., 1997), but two other showed no effect (Chopra et al, 1996 van het Hof et al., 1999). These differing outcomes may have been due to systematic differences in the experimental protocols or in the populations studied (Krinsky, 2001), but the results do indicate the complexity of the problem, and the hazards of generalising too readily about the putative benefits of dietary antioxidants. 

Tomato CrtL-h, sense and antisense Pds Increased (up to 7-fold) P-carotene in sense plants Rosati et al., 2000... 

The first reports of genetic manipulation of a crop plant were using the carrot. The introduction of crt genes from Erwinia herbicola by a group from Amoco (Ausich etal, 1991 Hauptmann etal.,1991) resulted in elevated levels of P-carotene. 

ALBRECHT M, KLEIN A, HUGUENEY p, SANDMANN G and KUNTZ M (1995) Molecular cloning and functional expression in E. coli of a novel plant enzyme mediating -carotene desaturation , FEES Lett, 372, 199-202. 

ISAACSON T, RONEN G, ZAMIR D and HIRSCHBERG J (2002) Cloning of tangerine from tomato reveals a carotenoid isomerase essential for production of 3-carotene and xanthophyUs in plants . Plant Cell, 14, 333-42. 

LINDEN H, MISAWA N, SAITO T and SANDMANN G (1994) A uovel caroteuoid biosynthesis gene coding for -carotene desaturase functional expression, sequence and phylogenetic origin . Plant Mol Biol, 24, 369-79. 

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