Taste buds
Semidiagrammatic view of a portion of the mucous membrane of the tongue. Two fungiform papillæ are shown. On some of the filiform papillæ the epithelial prolongations stand erect, in one they are spread out, and in three they are folded in.
Latin	caliculus gustatorius
Gray's	subject #222 991
MeSH	Taste+Buds
Code	TH H3.04.01.0.02116 TH H3.04.01.0.03013

Taste buds contain the receptors for taste. They are located around the small structures on the upper surface of the tongue, soft palate, upper esophagus and epiglottis, which are called papillae.^[1] These structures are involved in detecting the five (known) elements of taste perception: salty, sour, bitter, sweet, and umami. Via small openings in the tongue epithelium, called taste pores, parts of the food dissolved in saliva come into contact with taste receptors. These are located on top of the taste receptor cells that constitute the taste buds. The taste receptor cells send information detected by clusters of various receptors and ion channels to the gustatory areas of the brain via the seventh, ninth and tenth cranial nerves.

On average, the human tongue has 2,000–8,000 taste buds.^[2]

Types of papillae[link]

This unreferenced section requires citations to ensure verifiability.

The majority of taste buds on the tongue sit on raised protrusions of the tongue surface called papillae. There are four types of papillae present in the human tongue:

• Fungiform papillae - as the name suggests, these are slightly mushroom-shaped if looked at in longitudinal section. These are present mostly at the apex (tip) of the tongue, as well as at the sides. Innervated by facial nerve.
• Filiform papillae - these are thin, long papillae "V"-shaped cones that don't contain taste buds but are the most numerous. These papillae are mechanical and not involved in gustation. They are characterized by increased keratinization.
• Foliate papillae - these are ridges and grooves towards the posterior part of the roof of the mouth found on lateral margins. Innervated by facial nerve (anterior papillae) and glossopharyngeal nerve (posterior papillae).
• Circumvallate papillae - there are only about 10 to 14 of these papillae on most people, and they are present at the back of the oral part of the tongue. They are arranged in a circular-shaped row just in front of the sulcus terminalis of the tongue. They are associated with ducts of Von Ebner's glands, and are innervated by the glossopharyngeal nerve.

It is generally accepted that there are four taste sensations:

• Sweet, bitter, and savory (now sometimes called umami), which work with a signal through a G protein-coupled receptor.
• Salty and sour, which work with ion channels.

Structure of taste buds[link]

Each taste bud is flask-like in shape, its broad base resting on the corium, and its neck opening, the gustatory pore, between the cells of the epithelium.

The bud is formed by two kinds of cells: supporting cells and gustatory cells.

The supporting (sustentacular) cells are mostly arranged like the staves of a cask, and form an outer envelope for the bud. Some, however, are found in the interior of the bud between the gustatory cells.

The gustatory (taste) cells, a chemoreceptor, occupy the central portion of the bud; they are spindle-shaped, and each possesses a large spherical nucleus near the middle of the cell.

The peripheral end of the cell terminates at the gustatory pore in a fine hair filament, the gustatory hair. Some early experimental studies (Kirk and Grills, 1992)it was shown that subjects who were genetically predisposed to baldness were found to be 78% more likely to experience taste loss sensations in 5 out of 5 taste trials.It was hypothesized that this was due to 'balding' of the tongue.

The central process passes toward the deep extremity of the bud, and there ends in single or bifurcated varicosities.

The nerve fibrils after losing their medullary sheaths enter the taste bud, and end in fine extremities between the gustatory cells; other nerve fibrils ramify between the supporting cells and terminate in fine extremities; these, however, are believed to be nerves of ordinary sensation and not gustatory.

The average life of a taste bud is 10 days.

See also[link]

• Taste
• Gustatory system

Additional images[link]

• 

  schematic drawing of a taste bud

• 

  taste bud (nerve missing)

References[link]

External links[link]

• Taste Perception: Cracking the Code
• Scientists Explore the Workings of Taste Buds from National Public Radio's Talk of the Nation, July 22, 2005
• http://kidshealth.org/kid/talk/qa/taste_buds.html For kids about taste buds!
• http://www.newser.com/story/103744/your-lungs-have-their-own-taste-buds.html
• http://en.wikipedia.org/wiki/Taste_bud#Types_of_papillae

Taste bud

Taste (also called smatch or gustation; adjectival form: gustatory) is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, poisons, etc.

Humans receive tastes through sensory organs called taste buds,^[1] or gustatory calyculi, concentrated on the top of the tongue.^[2] Taste is sensed through taste cells, which are known as taste buds. There are about 100,000 taste buds that are located on the back and front of the tongue. Others are located on the roof, sides and back of the mouth, and in the throat. The sensation of taste can be categorized into five basic tastes: sweet, bitter, sour, salty, and umami. “Umami” is originally the Japanese word for “meaty” or “savory”.^[3] Not surprisingly, it is characteristic of many Asian dishes.^[4] The amino acid glutamate produces a strong umami taste.^[5] The tongue is able to differentiate between the different tastes based on different molecules or ions that bind to the taste cell. Sweet, umami, and bitter taste is triggered by different molecules that bind to the G protein-coupled membrane receptors; while saltiness is from Na+ ions and sourness is from H+ ions entering the cell.^[6] As taste senses both harmful and beneficial things, all basic tastes are classified as either aversive or appetitive, depending upon the effect the things they sense have on our bodies.^[7] Sweetness helps to identify energy-rich foods, while bitterness serves as a warning sign of poisons.^[8]

The basic tastes contribute only partially to the sensation and flavor of food in the mouth — other factors include smell,^[1] detected by the olfactory epithelium of the nose;^[9] texture,^[10] detected through a variety of mechanoreceptors, muscle nerves, etc.;^[11] temperature, detected by thermoreceptors; and "coolness" (such as of menthol) and "hotness" (piquance), through chemesthesis.

Introduction[link]

As one of the senses, taste is an essential part of daily life.

History[link]

In the West, Aristotle, who postulated c. 350 BCE^[12] that the two most basic tastes were sweet and bitter,^[13] was one of the first to develop a list of basic tastes.^[14]

Ayurveda, an ancient Indian healing science, has its own tradition of basic tastes, comprising astringent, bitter, pungent, salty, sour, and sweet.^[15][16]

Recent discoveries[link]

The receptors for the basic tastes of bitter, sweet and umami have been identified. They are G protein-coupled receptors.^[17] The cells that detect sour have been identified as a subpopulation that express the protein PKD2L1. The responses are mediated by an influx of protons into the cells but the receptor for sour is still unknown . The receptor for amiloride-sensitive attractive salty taste in mice has been shown to be a sodium channel.^[18] There is some evidence for a sixth taste that senses fatty substances.^[19]

Basic tastes[link]

For a long period, it was commonly accepted^[who?] that there is a finite and small number of "basic tastes" of which all seemingly complex tastes are ultimately composed. Just as with primary colors, the "basic" quality of those sensations derives chiefly from the nature of human perception, in this case the different sorts of tastes the human tongue can identify. As of the early twentieth century, physiologists and psychologists believed there were four basic tastes: bitterness, saltiness, sourness, and sweetness. At that time umami was not proposed as a fifth taste^[20] but now a large number of authorities now recognize it as such.^{[citation needed]} In Asian countries within the sphere of mainly Chinese, Indian and Japanese cultural influence, piquance had traditionally been considered a fifth basic taste.^{[citation needed]}

Bitterness[link]

Bitterness is the most sensitive of the tastes, and many perceive it as unpleasant, sharp, or disagreeable. Common bitter foods and beverages include coffee, unsweetened cocoa, South American mate, marmalade, bitter gourd, beer, bitters, olives, citrus peel, many plants in the Brassicaceae family, dandelion greens, wild chicory, and escarole. Quinine is also known for its bitter taste and is found in tonic water.

Bitterness is of interest to those who study evolution, as well as various health researchers^[21][22] since a large number of natural bitter compounds are known to be toxic. The ability to detect bitter-tasting, toxic compounds at low thresholds is considered to provide an important protective function.^[21][22][23] Plant leaves often contain toxic compounds, yet even amongst leaf-eating primates, there is a tendency to prefer immature leaves, which tend to be higher in protein and lower in fiber and poisons than mature leaves.^[24] Amongst humans, various food processing techniques are used worldwide to detoxify otherwise inedible foods and make them palatable.^[25]

The threshold for stimulation of bitter taste by quinine averages a concentration of 0.000008 M .^{[clarification needed][21]} The taste thresholds of other bitter substances are rated relative to quinine, which is thus given a reference index of 1.^[21][26] For example, Brucine has an index of 11, is thus perceived as intensely more bitter than quinine, and is detected at a much lower solution threshold.^[21] The most bitter substance known is the synthetic chemical denatonium, which has an index of 1,000.^[26] It is used as an aversive agent that is added to toxic substances to prevent accidental ingestion. This was discovered in 1958 during research on lignocaine, a local anesthetic, by Macfarlan Smith of Edinburgh, Scotland.

Research has shown that TAS2Rs (taste receptors, type 2, also known as T2Rs) such as TAS2R38 coupled to the G protein gustducin are responsible for the human ability to taste bitter substances.^[27] They are identified not only by their ability to taste for certain "bitter" ligands, but also by the morphology of the receptor itself (surface bound, monomeric).^[28] The TAS2R family in humans is thought to comprise about 25 different taste receptors, some of which can recognize a wide variety of bitter-tasting compounds.^[29] Over 550 bitter-tasting compounds have been identified, of which about 100 have been assigned to one or more specific receptors.^[30] Recently it is speculated that the selective constraints on the TAS2R family have been weakened due to the relatively high rate of mutation and pseudogenization.^[31] Researchers use two synthetic substances, phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP) to study the genetics of bitter perception. These two substances taste bitter to some people, but are virtually tasteless to others. Among the tasters, some are so-called "supertasters" to whom PTC and PROP are extremely bitter. The variation in sensitivity is determined by two common alleles at the TAS2R38 locus.^[32] This genetic variation in the ability to taste a substance has been a source of great interest to those who study genetics.

Saltiness[link]

Saltiness is a taste produced primarily by the presence of sodium ions. Other ions of the alkali metals group also taste salty, but the further from sodium the less salty the sensation is. The size of lithium and potassium ions most closely resemble those of sodium and thus the saltiness is most similar. In contrast rubidium and cesium ions are far larger so their salty taste differs accordingly.^{[citation needed]} The saltiness of substances is rated relative to sodium chloride (NaCl), which has an index of 1.^[21][26] Potassium, as potassium chloride - KCl, is the principal ingredient in salt substitutes, and has a saltiness index of 0.6.^[21][26]

Other monovalent cations, e.g. ammonium, NH₄⁺, and divalent cations of the alkali earth metal group of the periodic table, e.g. calcium, Ca²⁺, ions generally elicit a bitter rather than a salty taste even though they, too, can pass directly through ion channels in the tongue, generating an action potential.

Sourness[link]

Look up sour in Wiktionary, the free dictionary.

Sourness is the taste that detects acidity. The sourness of substances is rated relative to dilute hydrochloric acid, which has a sourness index of 1. By comparison, tartaric acid has a sourness index of 0.7, citric acid an index of 0.46, and carbonic acid an index of 0.06.^[21][26]

Sour taste is detected by a small subset of cells that are distributed across all taste buds in the tongue. Sour taste cells can be identified by expression of the protein PKD2L1,^[33] although surprisingly this gene is not required for sour responses. There is evidence that the protons that are abundant in sour substances can directly enter the sour taste cells. This transfer of positive charge into the cell can itself trigger an electrical response. It has also been proposed that weak acids such as acetic acid, which are not fully dissociated at physiological pH values, can penetrate taste cells and thereby elicit an electrical response. According to this mechanism, intracellular hydrogen ions inhibit potassium channels, which normally function to hyperpolarize the cell. By a combination of direct intake of hydrogen ions (which itself depolarizes the cell) and the inhibition of the hyperpolarizing channel, sourness causes the taste cell to fire action potentials and release neurotransmitter. The mechanism by which animals detect sour is still not completely understood.

The most common food group that contains naturally sour foods is fruit, such as lemon, grape, orange, tamarind and sometimes melon. Wine also usually has a sour tinge to its flavor, and if not kept correctly, milk can spoil and develop a sour taste. Sour candy is popular in North America^[34] including Cry Babies, Warheads, Lemon drops, Shock tarts and Sour Skittles and Starburst. Many of these candies contain citric acid.

Sweetness[link]

Sweetness, usually regarded as a pleasurable sensation, is produced by the presence of sugars and a few other substances. Sweetness is often connected to aldehydes and ketones, which contain a carbonyl group. Sweetness is detected by a variety of G protein coupled receptors coupled to the G protein gustducin found on the taste buds. At least two different variants of the "sweetness receptors" must be activated for the brain to register sweetness. Compounds the brain senses as sweet are thus compounds that can bind with varying bond strength to two different sweetness receptors. These receptors are T1R2+3 (heterodimer) and T1R3 (homodimer), which account for all sweet sensing in humans and animals.^[35] Taste detection thresholds for sweet substances are rated relative to sucrose, which has an index of 1.^[21][26] The average human detection threshold for sucrose is 10 millimoles per liter. For lactose it is 30 millimoles per liter, with a sweetness index of 0.3,^[21] and 5-Nitro-2-propoxyaniline 0.002 millimoles per liter.

Umami[link]

Umami is an appetitive taste^[7] and is described as a savory^[36][37] or meaty^[37][38] taste. It can be tasted in cheese^[39] and soy sauce,^[40] and while also found in many other fermented and aged foods, this taste is also present in tomatoes, grains, and beans.^[39] Monosodium glutamate (MSG), developed as a food additive in 1908 by Kikunae Ikeda,^[5] produces a strong umami taste.^[40] See TAS1R1 and TAS1R3 pages for a further explanation of the amino-acid taste receptor. A loanword from Japanese meaning "good flavor" or "good taste",^[41] Umami (旨味^?) is considered fundamental to many Eastern cuisines^[42] and was first described in 1908,^[43] although it was only recently recognized in the West as a basic taste.^[40][44]

Some umami taste buds respond specifically to glutamate in the same way that "sweet" ones respond to sugar. Glutamate binds to a variant of G protein coupled glutamate receptors.^[45][46]

Measuring relative tastes[link]

Measuring the degree to which a substance presents one basic taste can be achieved in a subjective way by comparing its taste to a reference substance. Quinine, a bitter medicinal found in tonic water, can be used to subjectively rate the bitterness of a substance.^[47] Units of dilute quinine hydrochloride (1 g in 2000 mL of water) can be used to measure the threshold bitterness concentration, the level at which the presence of a dilute bitter substance can be detected by a human taster, of other compounds.^[47] More formal chemical analysis, while possible, is difficult.^[47]

Relative saltiness can be rated by comparison to a dilute salt solution.^[48]

The sourness of a substance can be rated by comparing it to very dilute hydrochloric acid (HCl).^[49]

Sweetness is subjectively measured by comparing the threshold values, or level at which the presence of a dilute substance can be detected by a human taster, of different sweet substances.^[50] Substances are usually measured relative to sucrose,^[51] which is usually given an arbitrary index of 1^[52][53] or 100.^[54] Fructose is about 1.4 times sweeter than sucrose; glucose, a sugar found in honey and vegetables, is about three-quarters as sweet; and lactose, a milk sugar, is one-half as sweet.^[b][50]

Functional structure[link]

Bitterness

Research has shown that TAS2Rs (taste receptors, type 2, also known as T2Rs) such as TAS2R38 are responsible for the human ability to taste bitter substances.^[55] They are identified not only by their ability to taste certain bitter ligands, but also by the morphology of the receptor itself (surface bound, monomeric).^[56]

Saltiness

Saltiness is a taste produced best by the presence of cations (such as Na⁺, K⁺ or Li⁺)^[57] and, like sour, it is tasted using ion channels.^[57]

Other ions of the alkali metals group also taste salty, but the less sodium-like the ion is, the less salty the sensation.^{[citation needed]} As the size of lithium and potassium ions is close to that of sodium, they taste similar to salt.^{[citation needed]} In contrast, the larger rubidium and cesium ions do not taste as salty.^{[citation needed]}

Other monovalent cations, e.g., ammonium, NH+
4, and divalent cations of the alkali earth metal group of the periodic table, e.g., calcium, Ca²⁺, ions, in general, elicit a bitter rather than a salty taste even though they, too, can pass directly through ion channels in the tongue.^{[citation needed]}

Sourness

Sourness is acidity,^[58][59] and, like salt, it is a taste sensed using ion channels.^[57] Hydrogen ion channels detect the concentration of hydronium ions that are formed from acids and water.^{[citation needed]} In addition, the taste receptor PKD2L1 has been found to be involved in tasting sour.^[60]

Sweetness

Sweetness is produced by the presence of sugars, some proteins, and a few other substances.^{[citation needed]} It is often connected to aldehydes and ketones, which contain a carbonyl group.^{[citation needed]} Sweetness is detected by a variety of G protein-coupled receptors coupled to a G protein that acts as an intermediary in the communication between taste bud and brain, gustducin.^[61] These receptors are T1R2+3 (heterodimer) and T1R3 (homodimer), which account for sweet sensing in humans and other animals.^[62]

Umami-ness

The amino acid glutamic acid is responsible for umami,^[63][64] but some nucleotides (inosinic acid^[42][65] and guanylic acid^[63]) can act as complements, enhancing the taste.^[42][65]

Glutamic acid binds to a variant of the G protein-coupled receptor, producing an umami taste.^[66][67]

Further sensations[link]

The tongue can also feel other sensations not generally included in the basic tastes. These are largely detected by the somatosensory system.

Calcium

In 2008, geneticists discovered a CaSR calcium receptor on the tongues of mice. The CaSR receptor is commonly found in the gastrointestinal tract, kidneys, and brain. Along with the "sweet" T1R3 receptor, the CaSR receptor can detect calcium as a taste. Whether closely related genes in mice and humans means the phenomenon exists in humans as well is unknown.^[68][69]

Coolness

Some substances activate cold trigeminal receptors even when not at low temperatures. This "fresh" or "minty" sensation can be tasted in spearmint, menthol, ethanol, and camphor. Caused by activation of the same mechanism that signals cold, TRPM8 ion channels on nerve cells, unlike the actual change in temperature described for sugar substitutes, this coolness is only a perceived phenomenon.

Dryness

Some foods, such as unripe fruits, contain tannins or calcium oxalate that cause an astringent or rough sensation of the mucous membrane of the mouth. Examples include tea, red wine, rhubarb, and unripe persimmons and bananas.

Less exact terms for the astringent sensation are "dry", "rough", "harsh" (especially for wine), "tart" (normally referring to sourness), "rubbery", "hard" or "styptic".^[70]

When referring to wine, dry is the opposite of sweet, and does not refer to astringency. Wines that contain tannins and so cause an astringent sensation are not necessarily classified as "dry," and "dry" wines are not necessarily astringent.

In the Indian Ayurvedic tradition, one of the six tastes is astringency (kasaaya).^[71]

Fattiness

Recent research reveals a potential taste receptor called the CD36 receptor that reacts to fat (fatty acids, more specifically).^[72] This receptor was found in mice.

Heartiness (kokumi)

Some Japanese researchers refer to the kokumi of foods laden with alcohol and thiol-groups in their amino acid extracts, and this sensation has also been described as mouthfeel.

Numbness

Both Chinese and Batak Toba cooking include the idea of 麻 (má or mati rasa), a tingling numbness caused by spices such as Sichuan pepper. The cuisines of Sichuan province in China and of the Indonesia province North Sumatra often combine this with chili pepper to produce a 麻辣 málà, "numbing-and-hot", or "mati rasa" flavor.^[73] These sensations although not taste fall into a category of Chemesthesis.

Spiciness

Substances such as ethanol and capsaicin cause a burning sensation called Chemesthesis, piquance, spiciness, hotness, or prickliness by inducing a trigeminal nerve reaction together with normal taste reception. The sensation of heat is caused by the food's activating nerves that express TRPV1 and TRPA1 receptors. Two main plant-derived compounds that provide this sensation are capsaicin from chili peppers and piperine from black pepper. The piquant ("hot" or "spicy") sensation provided by chili peppers, black pepper, and other spices like ginger and horseradish plays an important role in a diverse range of cuisines across the world—especially in equatorial and sub-tropical climates, such as Ethiopian, Peruvian, Hungarian, Indian, Korean, Indonesian, Lao, Malaysian, Mexican, Southwest Chinese (including Szechuan cuisine), Vietnamese, and Thai cuisines.

This particular sensation, called Chemesthesis, is not a taste in the technical sense, because the sensation does not arise from taste buds and a different set of nerve fibers carry it to the brain. Foods like chili peppers activate nerve fibers directly; the sensation interpreted as "hot" results from the stimulation of somatosensory (pain/temperature) fibers on the tongue. Many parts of the body with exposed membranes but no taste sensors (such as the nasal cavity, under the fingernails, surface of the eye ([cornea]) or a wound) produce a similar sensation of heat when exposed to hotness agents. Asian countries within the sphere of, mainly, Chinese, Indian, and Japanese cultural influence, traditionally consider piquance a sixth basic taste.

Temperature

Temperature can be an essential element of the taste experience. Food and drink that—in a given culture—is traditionally served hot is often considered distasteful if cold, and vice versa. For example, alcoholic beverages, with a few exceptions, are usually thought best when served cold, but soups—again, with exceptions—are usually only eaten hot. A cultural example is soda. In North America it is almost always preferred cold, regardless of season. In South America lukewarm soda is almost exclusively consumed in winter.^{[citation needed]}

Other concepts[link]

Supertasters[link]

A supertaster is a person whose sense of taste is significantly more sensitive than average. The cause of this heightened response is likely, at least in part, due to an increased number of fungiform papillae.^[74] Study have shown that supertasters require less fat and sugar in their food to get the same satisfying effects. However, contrary to what one might think, these people actually tend to consume more salt than the average person. This is due to their heightened sense of the taste of bitterness, and the presence of salt drowns out the taste of bitterness. (This also explains why supertasters prefer salted cheddar cheese over non-salted.)^[75]

Aftertaste[link]

Aftertastes arise after food has been swallowed. An aftertaste can differ from the food it follows. Medicines and tablets may also have a lingering aftertaste, as can certain artificial flavor compounds, such as aspartame (artificial sweetener).

Acquired taste[link]

Acquired taste is an appreciation for a food or beverage that one is likely to initially dislike. Many of the world's delicacies are considered acquired tastes.

Innervation[link]

Taste is brought to the brainstem by 3 different cranial nerves:

• Facial nerve for the anterior 2/3 of the tongue and soft palate.
• Glossopharyngeal nerve for the posterior 1/3 of the tongue.
• Vagus nerve for the small area on the epiglottis.

Disorders of taste[link]

• ageusia (complete loss of taste)
• dysgeusia (persistent abnormal taste)

See also[link]

Food portal

• Palatability
• Optimal foraging theory
• Vomeronasal organ
• BitterDB

Notes[link]

Footnotes[link]

Citations[link]

Reference #30 (Wooding et al.) is helpful, but it is incorrect. The discovery that variants in the TAS2R38 gene underlie the ability to taste PTC and PROP was reported a year earlier in: Kim, U.-K., Jorgenson, E., Coon, H., Leppert, M., Risch, N., and D. Drayna. Positional Cloning of the human quantitative trait locus underlying taste sensitivity to phenylthiocarbamide. Science 299:1221-1225 (2003). I was the senior and communicating author on both of these papers.

Dennis Drayna, PhD NIDCD/National Institutes of Health

Further reading[link]

• Bartoshuk, Linda M (June 1978), "The Psychophysics of Taste", American Journal of Clinical Nutrition 31 (6): 1068–1077, PMID 352127, http://www.ajcn.org/cgi/reprint/31/6/1068.pdf, retrieved 12 September 2010 
• Chandrashekar, Jayaram; Hoon, Mark A; Ryba , Nicholas J. P. & Zuker, Charles S (16 November 2006), "The receptors and cells for mammalian taste", Nature 444 (7117): 288–294, DOI:10.1038/nature05401, PMID 17108952, https://wiki.brown.edu/confluence/download/attachments/1444406/nature05401.pdf, retrieved 13 September 2010 
• Chaudhari, Nirupa & Roper, Stephen D (2010), "The cell biology of taste", Journal of Cell Biology 190 (3): 285–296, DOI:10.1083/jcb.201003144, PMC 2922655, PMID 20696704, http://jcb.rupress.org/content/190/3/285.full.pdf, retrieved 13 September 2010 
• Danker, W.H (1968), Basic Principles of Sensory Evaluation, Philadelphia: American Society for Testing and Materials, ISBN 978-0-8031-4572-6, http://books.google.com/?id=F_U5y5GkSToC&printsec=frontcover&dq=sensory+evaluation#v=onepage&q&f=false, retrieved 13 September 2010 
• Dulac, Catherine (March 17, 2000), "The Physiology of Taste, Vintage 2000", Cell 100 (6): 607–610, DOI:10.1016/S0092-8674(00)80697-2, PMID 10761926, http://www.biochem.arizona.edu/classes/bioc471/pages/Lecture14/t-Dulac.pdf, retrieved 13 September 2010 
• Finger, Thomas E, ed. (2009), International Symposium on Olfaction and Taste, Boston: Blackwell, for the New York Academy of Sciences, ISBN 1-57331-738-1, http://books.google.com/?id=KyOHZtkHulEC&printsec=frontcover&dq=International+Symposium+olfaction#v=onepage&q&f=false, retrieved 12 September 2010  Alternative ISBN 978-1-57331-738-2
• Hui, Y.H, ed. (2010), Handbook of Fruit and Vegetable Flavors, Hoboken, New Jersey: John Wiley & Sons, ISBN 978-0-470-22721-3, http://books.google.com/?id=XRVpfmrKpZkC&printsec=frontcover&dq=%22Handbook+of+Fruit+and+Vegetable+%22#v=onepage&q&f=false, retrieved 13 September 2010  See especially comments and key references in regards taste 
• Thomas Hummel & Antje Welge-Lüssen, ed. (2006), Tast and Smell: An Update, Advances in Oto-Rhino-Laryngolog, Vol.63, Basel, Switzerland: Karger, ISBN 3-8055-8123-8, http://books.google.com/?id=fuxS-p6bpuwC&printsec=frontcover&dq=Taste+smell#v=onepage&q&f=false, retrieved 12 September 2010 
• Lawless, Harry T., & Heymann, Hildegarde (1998), Sensory Evaluation of Food: Principles and Practices, New York: Kluwer Academic/Plenum Publishers, ISBN 0-8342-1752-X, http://books.google.com/?id=BTR7VEJPDWAC&printsec=frontcover&dq=sensory+evaluation+food#v=onepage&q&f=false, retrieved 13 September 2010 
• Macbeth, Helen, ed. (2006), Food Preferences and Taste: Continuity and Change, The Anthropology of Food and Nutrition, Vol.2, Providence, Rhode Island: Berghahn Books, ISBN 1-57181-958-4, http://books.google.com/?id=10yea7-5dQ0C&printsec=frontcover&dq=%22food+preferences+and+taste%22#v=onepage&q&f=false, retrieved 12 September 2010  Paperback ISBN 1-57181-970-3
• Patton, Harry D (March 1950), "Physiology of Smell and Taste", Annual Review of Physiology 12: 469–484, DOI:10.1146/annurev.ph.12.030150.002345, PMID 15411178, http://www.annualreviews.org/doi/abs/10.1146/annurev.ph.12.030150.002345, retrieved 12 September 2010 
• Reed, Danielle R; Tanaka, Toshiko; and McDaniel, Amanda H (June 30, 2006), "Diverse tastes: Genetics of sweet and bitter perception", Physiology & Behavior 88 (3): 215–226, DOI:10.1016/j.physbeh.2006.05.033, PMC 1698869, PMID 16782140 
• Reineccius, Gary, ed. (1999), Source Book of Flavours (2nd ed.), Gaithersburg, Maryland: Aspen, ISBN 0-8342-1307-9, http://books.google.com/?id=D9LBPoIe-F4C&printsec=frontcover&dq=source+book+flavours#v=onepage&q=source%20book%20flavours&f=false, retrieved 12 September 2010  Previously published 1994 by Chapman & Hall, New York ISBN 0-442-00376-5 
• Schiffman, Susan S (26 May 1983), "Taste and smell in disease (First of two parts)", The New England Journal of Medicine 308 (21): 1275–1279 
• Schiffman, Susan S; Schiffman, Susan S. (2 June 1983), "Taste and smell in disease (Second of two parts)", The New England Journal of Medicine 308 (22): 1337–1343, DOI:10.1056/NEJM198306023082207, PMID 6341845 
• Schiffman, S.S; Graham, B.G (2000), "Taste and smell perception affect appetite and immunity in the elderly" (PDF), European Journal of Clinical Nutrition 54 (Suppl. 3): S54–S63, PMID 11041076, http://www.healthmegamall.com/Articles/BabeskinArticle247.pdf, retrieved 16 June 2010 
• Seiden, Allen M, ed. (1997), Taste and Smell Disorders, Rhinology and Sinusology, New York: Thieme, ISBN 0-86577-533-8, http://books.google.com/?id=JSvZN3y9hSAC&printsec=frontcover&dq=Taste+smell#v=onepage&q&f=false, retrieved 12 September 2010  Alternative ISBN 3-13-107261-X
• Shallenberger, R.S (1993), Taste Chemistry, London & New York: Blackie Academic & Professional (imprint of Chapman & Hall), ISBN 0-7514-0150-1, http://books.google.com/?id=8_bjyjgClq0C&printsec=frontcover&dq=taste+chemistry#v=onepage&q&f=false, retrieved 12 September 2010 
• Svrivastava, R.C. & Rastogi, R.P (2003), "Relative taste indices of some substances", in ., Transport Mediated by Electrical Interfaces, Studies in interface science, vol.18, Amsterdam, Netherlands: Elsevier Science, ISBN 0-444-51453-8 B.V, http://books.google.com/books?id=hIyM_o4YFZ4C&pg=PA274&dq=%22same+concentration+(1M)%22&hl=en&ei=6yqRTIz4Ho-evQOM4dnBCw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCwQ6AEwAA#v=onepage&q=%22same%20concentration%20(1M)%22&f=false, retrieved 12 September 2010  Taste indices of table 9, p.274 are select sample taken from table in Guyton's Textbook of Medical Physiology (present in all editions) 
• Xiaodong Li, Lena Staszewski, Hong Xu, Kyle Durick, Mark Zoller, and Elliot Adler (April 2, 2002), "Human receptors for sweet and umami taste", Proceedings of the National Academy of Sciences 99 (7): 4692–4696, DOI:10.1073/pnas.072090199, PMC 123709, PMID 11917125, http://www.pnas.org/content/99/7/4692.full, retrieved 13 September 2010 

External links[link]

Look up sour in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Taste

• Researchers Define Molecular Basis of Human "Sweet Tooth" and Umami Taste
• Statistics on Taste at National Institute on Deafness and Other Communication Disorders. An informative overview with good list of references.
• The Science of taste at Kitchen Geekery. An informative article about the science behind taste. Written from a culinary science perspective.

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (June 2008)

Buds in the leaf axils of Populus tremula (aspen)

Bud of Ficus carica

Flower buds have not yet bloomed into a full-size flower

In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of the stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be specialized to develop flowers or short shoots, or may have the potential for general shoot development. The term bud is also used in zoology, where it refers to an outgrowth from the body which can develop into a new individual.

Overview[link]

The buds of many woody plants, especially in temperate or cold climates, are protected by a covering of modified leaves called scales which tightly enclose the more delicate parts of the bud. Many bud scales are covered by a gummy substance which serves as added protection. When the bud develops, the scales may enlarge somewhat but usually just drop off, leaving on the surface of the growing stem a series of horizontally-elongated scars. By means of these scars one can determine the age of any young branch, since each year's growth ends in the formation of a bud, the formation of which produces an additional group of bud scale scars. Continued growth of the branch causes these scars to be obliterated after a few years so that the total age of older branches cannot be determined by this means.

On the left is an opening inflorescence bud, that will develop like the one to the right.

In many plants scales are not formed over the bud, which is then called a naked bud.^[1] The minute underdeveloped leaves in such buds are often excessively hairy. Naked buds are found in some shrubs, like some species of the Sumac and Viburnums (Viburnum alnifolium and V. lantana)^[2] and in herbaceous plants. In many of the latter, buds are even more reduced, often consisting of undifferentiated masses of cells in the axils of leaves. A terminal bud occurs on the end of a stem and lateral buds are found on the side. A head of cabbage (see Brassica) is an exceptionally large terminal bud, while Brussels sprouts are large lateral buds.

Since buds are formed in the axils of leaves, their distribution on the stem is the same as that of leaves. There are alternate, opposite, and whorled buds, as well as the terminal bud at the tip of the stem. In many plants buds appear in unexpected places: these are known as adventitious buds.^[3]

Often it is possible to find a bud in a remarkable series of gradations of bud scales. In the buckeye, for example, one may see a complete gradation from the small brown outer scale through larger scales which on unfolding become somewhat green to the inner scales of the bud, which are remarkably leaf-like. Such a series suggests that the scales of the bud are in truth leaves, modified to protect the more delicate parts of the plant during unfavorable periods.

Types of buds[link]

Plant Buds classification

Buds are often useful in the identification of plants, especially for woody plants in winter when leaves have fallen.^[4] Buds may be classified and described according to different criteria: location, status, morphology, and function.

Botanists commonly use the following terms:

• for location:
  • terminal, when located at the tip of a stem (apical is equivalent but rather reserved for the one at the top of the plant);
  • axillary, when located in the axil of a leaf (lateral is the equivalent but some adventitious buds may be lateral too);
  • adventitious, when occurring elsewhere, for example on trunk or on roots (some adventitious buds may be former axillary ones reduced and hidden under the bark, other adventitious buds are completely new formed ones).

• for status:
  • accessory, for secondary buds formed besides a principal bud (axillary or terminal);
  • resting, for buds that form at the end of a growth season, which will lie dormant until onset of the next growth season;
  • dormant or latent, for buds whose growth has been delayed for a rather long time. The term is usable as a synonym of resting, but is rather employed for buds waiting undeveloped for years, for example epicormic buds;
  • pseudoterminal, for an axillary bud taking over the function of a terminal bud (characteristic of species whose growth is sympodial: terminal bud dies and is replaced by the closer axillary bud, for examples beech, persimmon, Platanus have sympodial growth).

• for morphology:
  • scaly or covered, when scales (which are in fact transformed and reduced leaves) cover and protect the embryonic parts;
  • naked, when not covered by scales;
  • hairy, when also protected by hairs (it may apply either to scaly or to naked buds).

• for function:
  • vegetative, if only containing vegetative pieces: embryonic shoot with leaves (a leaf bud is the same);
  • reproductive, if containing embryonic flower(s) (a flower bud is the same);
  • mixed, if containing both embryonic leaves and flowers.

Within zoology[link]

The term bud (as in budding) is used by analogy within zoology as well, where it refers to an outgrowth from the body which develops into a new individual. It is a form of asexual reproduction limited to animals or plants of relatively simple structure. In this process a portion of the wall of the parent cell softens and pushes out. The protuberance thus formed enlarges rapidly while at this time the nucleus of the parent cell divides (see: mitosis, meiosis). One of the resulting nuclei passes into the bud, and then the bud is cut off from its parent cell and the process is repeated. Often the daughter cell will begin to bud before it becomes separated from the parent, so that whole colonies of adhering cells may be formed. Eventually cross walls cut off the bud from the original cell.

References[link]

[[it:Gemma (botanica]