Viticulture or winegrowing is the cultivation and harvesting of grapes. It is a branch of the science of horticulture. While the native territory of Vitis vinifera, the common grape vine, ranges from Western Europe to the Persian shores of the Caspian Sea, the vine has demonstrated high levels of adaptability to new environments. For this reason, viticulture can be found on every continent except Antarctica. Duties of the viticulturist include monitoring and controlling pests and diseases, irrigation, canopy management, monitoring fruit development and characteristics, deciding when to harvest, vine pruning during the winter months. Viticulturists are intimately involved with winemakers, because vineyard management and the resulting grape characteristics provide the basis from which winemaking can begin. A great number of varieties are now approved in the European Union as true grapes for winegrowing and viticulture; the earliest evidence of grape vine cultivation and winemaking dates back 7,000 years.
The history of viticulture is related to the history of wine, with evidence that humans cultivated wild grapes to make wine as far back as the Neolithic period. Evidence suggests that some of the earliest domestication of Vitis vinifera occurred in the area of the modern countries Georgia and Armenia; the oldest-known winery was discovered in the "Areni-1" cave in Armenia. Dated to c. 4100 BC, the site contained a wine press, fermentation vats and cups. Archaeologists found V. vinifera seeds and vines. Commenting on the importance of the find, McGovern said, "The fact that winemaking was so well developed in 4000 BC suggests that the technology goes back much earlier." There is evidence of grape domestication in the Near East in the early Bronze Age, around 3200 BC. Evidence of ancient viticulture is provided by cuneiform sources, plant remains, historical geography, archaeological excavations; the remnants of ancient wine jars have been used to determine the culture of wine consumption and cultivated grape species.
In addition to winemaking, grapes have been grown for the production of raisins. The earliest act of cultivation appears to have been the favoring of hermaphroditic members of the Vitis vinifera species over the barren male vines and the female vines, which were dependent on a nearby male for pollination. With the ability to pollinate itself, over time the hermaphroditic vines were able to sire offspring that were hermaphroditic. At the end of the 5th century BC, the Greek historian Thucydides wrote: The period that Thucydides was most referencing was the time between 3000 BC and 2000 BC, when viticulture emerged in force in Asia Minor and the Cyclades Islands of the Aegean Sea. During this period, grape cultivation developed from an aspect of local consumption to an important component of international economies and trade. From 1200 BC to 900 BC, the Phoenicians developed viticulture practices that were used in Carthage. Around 500 BC, the Carthaginian writer Mago recorded such practices in a two-volume work, one of the few artifacts to survive the Roman destruction of Carthage during the Third Punic War.
The Roman statesman Cato the Elder was influenced by these texts, around 160 BC he wrote De Agricultura, which expounded on Roman viticulture and agriculture. Around 65 AD, the Roman writer Columella produced the most detailed work on Roman viticulture in his twelve-volume text De Re Rustica. Columella's work is one of the earliest to detail trellis systems for raising vines off the ground. Columella advocated the use of stakes versus the accepted practice of training vines to grow up along tree trunks; the benefits of using stakes over trees was to minimize the dangers associated with climbing trees, necessary to prune the dense foliage in order to give the vines sunlight, to harvest them. Roman expansion across Western Europe brought Roman viticulture to the areas that would become some of the world's best-known winegrowing regions: the Spanish Rioja, the German Mosel, the French Bordeaux, Burgundy and Rhône. Roman viticulturists were among the first to identify steep hillsides as one of the better locations to plant vines, because cool air runs downhill and gathers at the bottom of valleys.
While some cool air is beneficial, too much can rob the vine of the heat it needs for photosynthesis, in winter it increases the risk of frost. In the Middle Ages, Catholic monks were the most prominent viticulturists of the time period. Around this time, an early system of Metayage emerged in France with laborers working the vineyards under contractual agreements with the landowners. In most cases, the prendeurs were given flexibility in selecting their crop and developing their own vineyard practice. In northern Europe, the weather and climate posed difficulties for grape cultivation, so certain species were selected that better suited the environment. Most vineyards grew white varieties of grape, which are more resistant to the damp and cold climates. A few species of red grape, such as the Pinot Noir, were introduced. Les Très Riches Heures du duc de Berry dates back to 1416 and depicts horticulture and viticulture in France; the images illustrate peasants bending down to prune grapes from vines behind castle walls.
Additional illustrations depict grape vines being harvested, with each vine being cut to three spurs around knee height. Many of the viticultural practices developed in this time period would become staples of European viticulture until the 18th century. Varietals were studied more intently to see which vines were the most suitable for a particular area. Around this
Vitis is a genus of 79 accepted species of vining plants in the flowering plant family Vitaceae. The genus is made up of species predominantly from the Northern hemisphere, it is economically important as the source of grapes, both for direct consumption of the fruit and for fermentation to produce wine. The study and cultivation of grapevines is called viticulture. Most Vitis varieties are wind-pollinated with hermaphroditic flowers containing both male and female reproductive structures; these flowers are grouped in bunches called inflorescences. In many species, such as Vitis vinifera, each pollinated flower becomes a grape berry with the inflorescence turning into a cluster of grapes. While the flowers of the grapevines are very small, the berries are big and brightly colored with sweet flavors that attract birds and other animals to disperse the seeds contained within the berries. Grapevines only produce fruit on shoots that came from buds that were developed during the previous growing season.
In viticulture, this is one of the principles behind pruning the previous year's growth that includes shoots that have turned hard and woody during the winter. These vines will be pruned either into a cane which will support 8 to 15 buds or to a smaller spur which holds 2 to 3 buds. Flower buds are formed late in the growing season and overwinter for blooming in spring of the next year, they produce leaf-opposed cymes. Vitis is distinguished from other genera of Vitaceae by having petals which remain joined at the tip and detach from the base to fall together as a calyptra or'cap'; the flowers are bisexual, with a hypogynous disk. The calyx is reduced or nonexistent in most species and the petals are joined together at the tip into one unit but separated at the base; the fruit is a berry, ovoid in shape and juicy, with a two-celled ovary each containing two ovules, thus producing four seeds per flower. Other parts of the vine include the tendrils which are leaf-opposed, branched in Vitis vinifera, are used to support the climbing plant by twining onto surrounding structures such as branches or the trellising of a vine-training system.
In the wild, all species of Vitis are dioecious, but under domestication, variants with perfect flowers appear to have been selected. Most Vitis species have but 40 in Vitis rotundifolia. Most Vitis species are found in the temperate regions of the Northern Hemisphere in North America and Asia with a few in the tropics; the wine grape Vitis vinifera originated in southern southwestern Asia. The species occur in different geographical areas and show a great diversity of form, their growth makes leaf collection challenging and polymorphic leaves make identification of species difficult. Mature grapevines can grow up to 48 cm in diameter at breast height and reach the upper canopy of trees more than 35 m in height. Many species are sufficiently related to allow easy interbreeding and the resultant interspecific hybrids are invariably fertile and vigorous, thus the concept of a species is less well defined and more represents the identification of different ecotypes of Vitis that have evolved in distinct geographical and environmental circumstances.
The exact number of species is not certain, with species in Asia in particular being poorly defined. Estimates range from 40 to more than 60; some of the more notable include: Vitis vinifera, the European grapevine. Native to the Mediterranean and Central Asia. Vitis labrusca, the fox grapevine, sometimes used for wine. Native to the Eastern United States and Canada. Vitis riparia, the riverbank grapevine, sometimes used for jam. Native to the entire Eastern U. S. and north to Quebec. Vitis aestivalis, the summer grape, native to the Eastern United States the Southeastern United States. Vitis rotundifolia, the muscadine, used for jams and wine. Native to the Southeastern United States from Delaware to the Gulf of Mexico. Vitis rupestris, the rock grapevine, used for breeding of Phylloxera resistant rootstock. Native to the Southern United States. Vitis coignetiae, the crimson glory vine, a species from East Asia grown as an ornamental plant for its crimson autumn foliage. Vitis amurensis, native to the Asian continent, including parts of China.
Vitis vulpina, the frost grape, native to the Eastern United States, from Massachusetts to Florida, west to Nebraska and Texas. Treated by some as a synonym of V. riparia. Vitis californica, the California wild grape, or Northern California grape, or Pacific grape, is a wild grape species widespread across much of California as well as southwestern Oregon. There are many cultivars of grapevines. Hybrid grapes exist, these are crosses between V. vinifera and one or more of V. labrusca, V. riparia or V. aestivalis. Hybrids tend to be less susceptible to frost and disease, but wine from some hybrids may have a little of the characteristic "foxy" taste of V. labrusca. The Latin word Vitis has feminine grammatical gender, therefore species names with adjectival specific epithets take feminine forms, such as V. vinifera. The fruit of several Vitis species are grown commercially for consumption as fresh grapes and for fermentation into wine. Vitis vinifera is the most important such species; the leaves of several species of grapevine are edible and are used in the production of dolmades and Vietnamese lot leaves.
According to the "Food and Agriculture Organization", 75,866 square kilometres of the world is dedicated to grapes. Approximate
Chardonnay is a green-skinned grape variety used in the production of white wine. The variety originated in the Burgundy wine region of eastern France, but is now grown wherever wine is produced, from England to New Zealand. For new and developing wine regions, growing Chardonnay is seen as a "rite of passage" and an easy entry into the international wine market; the Chardonnay grape itself is neutral, with many of the flavors associated with the wine being derived from such influences as terroir and oak. It is vinified in many different styles, from the lean, crisply mineral wines of Chablis, France, to New World wines with oak and tropical fruit flavors. In cool climates, Chardonnay wine tends to be medium to light body with noticeable acidity and flavors of green plum and pear. In warmer locations, the flavors become more citrus and melon, while in warm locations, more fig and tropical fruit notes such as banana and mango come out. Wines that have gone through malolactic fermentation tend to have softer acidity and fruit flavors with buttery mouthfeel and hazelnut notes.
Chardonnay is an important component of many sparkling wines around the world, including Champagne and Franciacorta in Italy. Chardonnay's popularity peaked in the late 1980s gave way to a backlash among those wine connoisseurs who saw the grape as a leading negative component of the globalization of wine. Nonetheless, it is one of the most planted grape varieties, with 210,000 hectares worldwide, second only to Airén among white wine grapes and fifth among all wine grapes. For much of its history, a connection was assumed between Pinot blanc. In addition to being found in the same region of France for centuries, ampelographers noted that the leaves of each plant have near-identical shape and structure. Pierre Galet disagreed with this assessment, believing that Chardonnay was not related to any other major grape variety. Viticulturalists Maynard Amerine and Harold Olmo proposed a descendency from a wild Vitis vinifera vine, a step removed from white Muscat. Chardonnay's true origins were further obscured by vineyard owners in Lebanon and Syria, who claimed that the grape's ancestry could be traced to the Middle East, from where it was introduced to Europe by returning Crusaders, though little external evidence supports that theory.
Another theory stated. Modern DNA fingerprinting research at University of California, now suggests that Chardonnay is the result of a cross between the Pinot noir and Gouais blanc grape varieties; the Romans are thought to have brought Gouais blanc from Croatia, it was cultivated by peasants in eastern France. The Pinot of the French aristocracy grew in close proximity to the Gouais blanc, giving both grapes ample opportunity to interbreed. Since the two parents were genetically distant, many of the crosses showed hybrid vigour and were selected for further propagation; these "successful" crosses included Chardonnay and siblings such as Aligoté, Aubin vert, Bachet noir, Franc Noir de la-Haute-Saône, Gamay Blanc Gloriod, Gamay noir, Knipperlé, Roublot and Dameron. As of 2006, 34 clonal varieties of Chardonnay could be found in vineyards throughout France, most of which were developed at the University of Burgundy in Dijon; the so-called "Dijon clones" are bred for their adaptive attributes, with vineyard owners planting the clonal variety best suited to their terroir and which will produce the characteristics that they are seeking in the wine.
Examples include the lower-yielding clones'Dijon-76','95' and'96' that produce more flavor-concentrated clusters.'Dijon-77' and'809' produce more aromatic wines with a "grapey" perfume, while'Dijon-75','78','121','124','125' and'277' are more vigorous and higher-yielding clones. New World varieties include the'Mendoza' clone, which produced some of the early California Chardonnays. The'Mendoza' clone is prone to develop millerandage known as "hens and chicks", where the berries develop unevenly. In places such as Oregon, the use of newer Dijon clones has had some success in those regions of the Willamette Valley with climates similar to that of Burgundy. Chardonnay has served as parent to several French-American hybrid grapes, as well as crossings with other V. vinifera varieties. Examples include the hybrid Chardonel, a Chardonnay and Seyval blanc cross produced in 1953 at the New York State Agricultural Experiment Station. Mutations of the Chardonnay grape include the rare pink-berried'Chardonnay Rose'.
Chardonnay Blanc Musqué is found around the Mâconnais village of Clessé and sometimes confused with the'Dijon-166' clone planted in South Africa, which yields Muscat-like aromas. In the 1930s, Chardonnay was crossed with a Seibel grape to create the hybrid grape Ravat blanc. Chardonnay has a wide-ranging reputation for relative ease of cultivation and ability to adapt to different conditions; the grape is "malleable", in that it reflects and takes on the impression of its terroir and winemaker. It is a vigorous vine, with extensive leaf cover which can inhibit the energy and nutrient uptake of its grape clusters. Vineyard managers counteract this with aggressive canopy management; when Chardonnay vines are planted densely, they are forced to compete for resources and funnel energy into their grape clusters. In certain conditions, the vines can be v
Sweetness is a basic taste most perceived when eating foods rich in sugars. Sweet tastes are regarded as a pleasurable experience, except in excess. In addition to sugars like sucrose, many other chemical compounds are sweet, including aldehydes and sugar alcohols; some are sweet at low concentrations, allowing their use as non-caloric sugar substitutes. Such non-sugar sweeteners include aspartame. Other compounds, such as miraculin, may alter perception of sweetness itself; the chemosensory basis for detecting sweetness, which varies between both individuals and species, has only begun to be understood since the late 20th century. One theoretical model of sweetness is the multipoint attachment theory, which involves multiple binding sites between a sweetness receptor and a sweet substance. Studies indicate that responsiveness to sugars and sweetness has ancient evolutionary beginnings, being manifest as chemotaxis in motile bacteria such as E. coli. Newborn human infants demonstrate preferences for high sugar concentrations and prefer solutions that are sweeter than lactose, the sugar found in breast milk.
Sweetness appears to have the highest taste recognition threshold, being detectable at around 1 part in 200 of sucrose in solution. By comparison, bitterness appears to have the lowest detection threshold, at about 1 part in 2 million for quinine in solution. In the natural settings that human primate ancestors evolved in, sweetness intensity should indicate energy density, while bitterness tends to indicate toxicity; the high sweetness detection threshold and low bitterness detection threshold would have predisposed our primate ancestors to seek out sweet-tasting foods and avoid bitter-tasting foods. Amongst leaf-eating primates, there is a tendency to prefer immature leaves, which tend to be higher in protein and lower in fibre and poisons than mature leaves. The'sweet tooth' thus has an ancient evolutionary heritage, while food processing has changed consumption patterns, human physiology remains unchanged. A great diversity of chemical compounds, such as aldehydes and ketones are sweet. Among common biological substances, all of the simple carbohydrates are sweet to at least some degree.
Sucrose is the prototypical example of a sweet substance. Sucrose in solution has a sweetness perception rating of 1, other substances are rated relative to this. For example, another sugar, fructose, is somewhat sweeter, being rated at 1.7 times the sweetness of sucrose. Some of the amino acids are mildly sweet: alanine and serine are the sweetest; some other amino acids are perceived as both bitter. A number of plant species produce glycosides; the most well-known example is glycyrrhizin, the sweet component of licorice root, about 30 times sweeter than sucrose. Another commercially important example is stevioside, from the South American shrub Stevia rebaudiana, it is 250 times sweeter than sucrose. Another class of potent natural sweeteners are the sweet proteins such as thaumatin, found in the West African katemfe fruit. Hen egg lysozyme, an antibiotic protein found in chicken eggs, is sweet; some inorganic compounds are sweet, including beryllium chloride and Lead acetate. The latter may have contributed to lead poisoning among the ancient Roman aristocracy: the Roman delicacy sapa was prepared by boiling soured wine in lead pots.
Hundreds of synthetic organic compounds are known to be sweet. The number of these that are permitted as food additives is, much smaller. For example, chloroform and Ethylene glycol are sweet, but toxic; as of 2005, seven artificial sweeteners are in widespread use: saccharin, aspartame, acesulfame potassium, sucralose and neotame. A few substances alter. One class of these inhibits the perception of sweet tastes, whether from sugars or from potent sweeteners. Commercially, the most important of these is lactisole, a compound produced by Domino Sugar, it is used in some jellies and other fruit preserves to bring out their fruit flavors by suppressing their otherwise strong sweetness. Two natural products have been documented to have similar sweetness-inhibiting properties: gymnemic acid, extracted from the leaves of the Indian vine Gymnema sylvestre and ziziphin, from the leaves of the Chinese jujube. Gymnemic acid has been promoted within herbal medicine as a treatment for sugar cravings and diabetes mellitus.
On the other hand, two plant proteins and curculin, cause sour foods to taste sweet. Once the tongue has been exposed to either of these proteins, sourness is perceived as sweetness for up to an hour afterwards. While curculin has some innate sweet taste of its own, miraculin is by itself quite tasteless. Despite the wide variety of chemical substances known to be sweet, knowledge that the ability to perceive sweet taste must reside in taste buds on the tongue, the biomolecular mechanism of sweet taste was sufficiently elusive that as as the 1990s, there was some doubt whether any single "sweetness receptor" exists; the breakthrough for the present understanding of sweetness occurred in 2001, when experiments with laboratory mice showed that mice possessing different versions of the gene T1R3 prefer sweet foods to different extents. Subsequent research has shown that the T1R3 protein forms a complex with a related protein, called T1R2, to form a G-protein coupled receptor, the sweetness receptor in mammals.
Human studies have shown that sweet taste receptors are not only found in tongue, but in the lining of gastrointestinal tract as well as na
A truffle is the fruiting body of a subterranean ascomycete fungus, predominantly one of the many species of the genus Tuber. In addition to Tuber, many other genera of fungi are classified as truffles including Geopora, Choiromyces and over a hundred others; these genera belong to the Pezizales order. There are several truffle-like basidiomycetes excluded from Pezizales including Rhizopogon and Glomus. Truffles are ectomycorrhizal fungi and are therefore found in close association with tree roots. Spore dispersal is accomplished through animals that eat fungi; these fungi have significant ecological roles in nutrient drought tolerance. Some of the truffle species are prized as food. French gourmet Jean Anthelme Brillat-Savarin called truffles "the diamond of the kitchen". Edible truffles are held in high esteem in French, Ottoman, Middle Eastern and Spanish cuisine, as well as in international haute cuisine. Truffles are cultivated agriculturally and are harvested from natural habitats; the first mention of truffles appears in the inscriptions of the neo-Sumerians regarding their Amorite enemy's eating habits and in writings of Theophrastus in the fourth century BCE.
In classical times, their origins were a mystery. Cicero deemed them children of the earth. Rome and Thracia in the Classical period produced three kinds of truffles: the Tuber melanosporum, the Tuber magnificanus and the Tuber magnatum; the Romans, did not use these and instead used a variety of fungus called Terfez sometimes called a "desert truffle." Terfez used in Rome came from Lesbos and Libya, where the coastal climate was less dry in ancient times. Their substance is pale. Unlike truffles, terfez have little inherent flavour; the Romans used the terfez as a carrier of flavour, because the terfez tend to absorb surrounding flavours. Indeed, Ancient Roman cuisine used many spices and flavourings, terfez were perfect in that context. Truffles were used during the Middle Ages. Truffle hunting is mentioned by Bartolomeo Platina, the papal historian, in 1481, when he recorded that the sows of Notza were without equal in hunting truffles, but they should be muzzled to prevent them from eating the prize.
During the Renaissance, truffles regained popularity in Europe and were honoured at the court of King Francis I of France. However, it was not until the 17th century that Western cuisine abandoned "heavy" oriental spices, rediscovered the natural flavour of foodstuffs. Truffles were popular in Parisian markets in the 1780s, they were imported seasonally from truffle grounds. Brillat-Savarin noted characteristically that they were so expensive they appeared only at the dinner tables of great nobles and kept women. A great delicacy was a truffled turkey. Truffles long eluded techniques of domestication, as Jean-Anthelme Brillat-Savarin noted: The most learned men have sought to ascertain the secret, fancied they discovered the seed, their promises, were vain, no planting was followed by a harvest. This is all right, for as one of the great values of truffles is their dearness they would be less esteemed if they were cheaper. However, truffles can be cultivated; as early as 1808, there were successful attempts to cultivate truffles, known in French as trufficulture.
People had long observed that truffles were growing among the roots of certain trees, in 1808, Joseph Talon, from Apt in southern France, had the idea of transplanting some seedlings that he had collected at the foot of oak trees known to host truffles in their root system. For discovering how to cultivate truffles, some sources now give priority to Pierre II Mauléon of Loudun, who began to cultivate truffles around 1790. Mauléon saw an "obvious symbiosis" between the oak tree, the rocky soil and the truffle, attempted to reproduce such an environment by taking acorns from trees known to have produced truffles, sowing them in chalky soil, his experiment was successful, with truffles being found in the soil around the newly grown oak trees years later. In 1847, Auguste Rousseau of Carpentras planted 7 hectares of oak trees, he subsequently obtained large harvests of truffles, he received a prize at the 1855 World's Fair in Paris. These successful attempts were met with enthusiasm in southern France, which possessed the sweet limestone soils and dry, hot weather that truffles need to grow.
In the late 19th century, an epidemic of phylloxera destroyed many of the vineyards in southern France. Another epidemic killed most of the silkworms there, making the fields of mulberry trees useless. Thus, large tracts of land were set free for the cultivation of truffles. Thousands of truffle-producing trees were planted, production reached peaks of hundreds of tonnes at the end of the 19th century. In 1890, there were 75,000 hectares of truffle-producing trees. In the 20th century, with the growing industrialization of France and the subsequent rural exodus, many of these truffle fields returned to wilderness; the First World War dealt a serious blow to the French countryside, killing 20% or more of the male working force. As a consequence, newly acquir
Carotenoids called tetraterpenoids, are organic pigments that are produced by plants and algae, as well as several bacteria and fungi. Carotenoids give the characteristic color to carrots, corn and daffodils, as well as egg yolks, rutabagas and bananas. Carotenoids can be produced from fats and other basic organic metabolic building blocks by all these organisms; the only animals known to produce carotenoids are aphids and spider mites, which acquired the ability and genes from fungi or it is produced by endosymbiotic bacteria in whiteflies. Carotenoids from the diet are stored in the fatty tissues of animals, carnivorous animals obtain the compounds from animal fat. There are over 1100 known carotenoids. All are derivatives of tetraterpenes, meaning that they are produced from 8 isoprene molecules and contain 40 carbon atoms. In general, carotenoids absorb wavelengths ranging from 400–550 nanometers; this causes the compounds to be colored yellow, orange, or red. Carotenoids are the dominant pigment in autumn leaf coloration of about 15-30% of tree species, but many plant colors reds and purples, are due to other classes of chemicals.
Carotenoids serve two key roles in plants and algae: they absorb light energy for use in photosynthesis, they protect chlorophyll from photodamage. Carotenoids that contain unsubstituted beta-ionone rings have vitamin A activity, these and other carotenoids can act as antioxidants. In the eye, meso-zeaxanthin, zeaxanthin are present as macular pigments whose importance in visual function remains under clinical research in 2017; the basic building blocks of carotenoids are isopentenyl dimethylallyl diphosphate. These two isoprene isomers are used to create various compounds depending on the biological pathway used to synthesis the isomers. Plants are known to use two different pathways for IPP production: the cytosolic mevalonic acid pathway and the plastidic methylerythritol 4-phosphate. In animals, the production of cholesterol starts by creating IPP and DMAPP using the MVA. For carotenoid production plants use MEP to generate IPP and DMAPP; the MEP pathway results in a 5:1 mixture of IPP:DMAPP.
IPP and DMAPP undergo several reactions, resulting in the major carotenoid precursor, geranylgeranyl diphosphate. GGPP can be converted into carotenes or xanthophylls by undergoing a number of different steps within the carotenoid biosynthetic pathway. Glyceraldehyde 3-phosphate and pyruvate, intermediates of photosynthesis, are converted to deoxy-D-xylulose 5-phosphate using the catalyst DXP synthase. DXP reductoisomerase reduces and rearranges the molecules within DXP in the presence of NADPH, forming MEP. Next, MEP is converted to 4--2-C-methyl-D-erythritol in the presence of CTP via the enzyme MEP cytidylyltransferase. CDP-ME is converted, in the presence of ATP, to 2-phospho-4--2-C-methyl-D-erythritol; the conversion to CDP-ME2P is catalyzed by the enzyme CDP-ME kinase. Next, CDP-ME2P is converted to 2-C-methyl-D-erythritol 2,4-cyclodiphosphate; this reaction occurs when MECDP synthase catalyzes the reaction and CMP is eliminated from the CDP-ME2P molecule. MECDP is converted to -4-hydroxy-3-methylbut-2-en-1-yl diphosphate via HMBDP synthase in the presence of flavodoxin and NADPH.
HMBDP is reduced to NADPH by the enzyme HMBDP reductase. The last two steps involving HMBPD synthase and reductase can only occur in anaerobic environments. IPP is able to isomerize to DMAPP via IPP isomerase. Two GGPP molecules condense via phytoene synthase; the subsequent conversion into all-trans-lycopene depends on the organism. Bacteria and fungi employ the bacterial phytoene desaturase for the catalysis. Plants and cyanobacteria however utilize four enzymes for this process; the first of these enzymes is a plant-type phytoene desaturase which introduces two additional double bonds into 15-cis-phytoene by dehydrogenation and isomerizes two of its existing double bonds from trans to cis producing 9,15,9’-tri-cis-ζ-carotene. The central double bond of this tri-cis-ζ-carotene is isomerized by the zeta-carotene isomerase Z-ISO and the resulting 9,9'-di-cis-ζ-carotene is dehydrogenated again via a ζ-carotene desaturase; this again introduces two double bonds. CRTISO, a carotenoid isomerase, is needed to convert the cis-lycopene into an all-trans lycopene in the presence of reduced FAD.
This all-trans lycopene is cyclized. There can be either a beta ring or an epsilon ring, each generated by a different enzyme. Alpha-carotene is produced when the all-trans lycopene first undergoes reaction with epsilon-LCY a second reaction with beta-LCY. Alpha- and beta-carotene are the most common carotenoids in the plant photosystems but they can still be further converted into xanthophylls by using beta-hydrolase and epsilon-hydrolase, leading to a variety of xanthophylls, it is believed that both DXS and DXR are rate-determining enzymes, allowing them to regulate carotenoid levels. This was discovered in an experiment where DXS and DXR were genetic