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Stewart's Wilt

Stewart's Wilt

Stewart's Wilt is a bacterial disease caused by the bacterium Pantoea stewartii affecting plants, particularly maize. Its primary vector is the corn flea beetle, (Chaetocnema pulicaria). The bacterium lives in the gut of the beetle during the off season and is spread between plants when the beetle feeds on the seedlings. The bacterium can also be spread via the plant seed, but this is extremely rare and is insignificant compared to insect transmission. The disease manifests in two phases: seedling wilt, when the growing point dies; and leaf blight, white lesions on the leaves of older plants. Sweet corn is more susceptible than field corn. There are two subspecies:
- Pantoea stewartii subsp. stewartii
- Pantoea stewartii subsp. indologenes Category:Enterobacteria Category:Plant diseases

Bacterium

Actinobacteria
Aquificae
Bacteroidetes/Chlorobi
Chlamydiae/Verrucomicrobia
Chloroflexi
Chrysiogenetes
Cyanobacteria
Deferribacteres
Deinococcus-Thermus
Dictyoglomi
Fibrobacteres/Acidobacteria
Firmicutes
Fusobacteria
Gemmatimonadetes
Nitrospirae
Planctomycetes
Proteobacteria
Spirochaetes
Thermodesulfobacteria
Thermomicrobia
Thermotogae Bacteria (singular: bacterium) are a major group of living organisms. Most are microscopic and unicellular, with a relatively simple cell structure lacking a cell nucleus, and organelles such as mitochondria and chloroplasts. Their cell structure is further described in the article about prokaryotes, because bacteria are prokaryotes, in contrast to organisms with more complex cells, called eukaryotes. The term "bacteria" has variously applied to all prokaryotes or to a major group of them, otherwise called the eubacteria, depending on ideas about their relationships. In Wikipedia, bacteria is used specifically to refer to the eubacteria. Bacteria are the most abundant of all organisms. They are ubiquitous in soil, water, and as symbionts of other organisms. Many pathogens are bacteria. Most are minute, usually only 0.5-5.0 μm in their longest dimension, although giant bacteria like Thiomargarita namibiensis and Epulopiscium fishelsoni may grow past 0.5 mm in size. They generally have cell walls, like plant and fungal cells, but with a very different composition (peptidoglycans). Many move around using flagella, which are different in structure from the flagella of other groups.

History and taxonomy

The first bacteria were observed by Antony van Leeuwenhoek in 1683 using a single-lens microscope of his own design. The name bacterium was introduced much later, by Ehrenberg in 1828, derived from the Greek word βακτηριον meaning "small stick". Louis Pasteur (1822-1895) and Robert Koch (1843-1910) described the role of bacteria as conveyors and causes of disease or pathogens.

Metabolism

Bacteria show a wide variety of different metabolisms and can accordingly be classified into primary nutritional groups. The most common division is between heterotrophs, which depend on an organic source of carbon, and autotrophs, which are able to synthesize organic compounds from carbon dioxide and water. Autotrophs that obtain energy by oxidizing chemical compounds are called chemotrophs, and those that obtain their energy from light, via photosynthesis, are called phototrophs. There are many variations on this terminology such as chemoautotrophs and photosynthetic autotrophs and so on. In addition, bacteria are distinguished based on the source of reducing equivalents they are using. Those using inorganic compounds (e. g. water, hydrogen, sulfide or ammonia) for this purpose are called lithotrophs and others needing organic compounds (e. g. sugars or organic acids) and are called organotrophs. The metabolic modes of energy metabolism (phototrophy or chemotrophy), reducing equivalent sources (lithotrophy or organotrophy) and carbon sources (autotrophy or heterotrophy) can be combined differently in any single microorganism, and even shifting between different modes frequently occurs in many species. Other nutritional requirements include nitrogen, sulfur, phosphorus, vitamins and metallic elements such as sodium, potassium, calcium, magnesium, manganese, iron, zinc, cobalt, copper and nickel for normal growth. For some species, additional trace elements such as selenium, tungsten, vanadium or boron are needed. Based on their response to oxygen, most bacteria can be placed into one of three groups: Some bacteria can grow only in the presence of oxygen and are called aerobes; others can grow only in the absence of oxygen and are called anaerobes; and some can grow in the presence or absence of oxygen and are called facultative anaerobes.

Movement

Motile bacteria can move about, either using flagella, bacterial gliding, or changes of buoyancy. A unique group of bacteria, the spirochaetes, have structures similar to flagella, called axial filaments, between two membranes in the periplasmic space. They have a distinctive helical body that twists about as it moves. Bacterial flagella are arranged in many different ways. Bacteria can have a single polar flagellum at one end of a cell, clusters of many flagella at one end or flagella scattered all over the cell, as with Peritrichous. Many bacteria (such as E.coli) have two distinct modes of movement: forward movement (swimming) and tumbling. The tumbling allows them to reorient and introduces an important element of randomness in their forward movement. (see external links below for link to videos). Motile bacteria are attracted or repelled by certain stimuli, behaviors called taxes - for instance, chemotaxis, phototaxis, mechanotaxis and magnetotaxis. In one peculiar group, the myxobacteria, individual bacteria attract to form swarms and may differentiate to form fruiting bodies. The myxobacteria move only when on solid surfaces, unlike E. coli which is motile in liquid or solid media.

Groups and identification

myxobacteria Bacteria come in a variety of different shapes. Most are rod-shaped, sphere-shaped, or helix-shaped; these are respectively referred to as bacilli, cocci, and spirilla. An additional group, vibrios, are comma-shaped. Shape is no longer considered a defining factor in the classification of bacteria, but many genera are named for their shape (e.g. Bacillus, Streptococcus, Staphylococcus) and it is an important part in their identification. Another important tool is Gram staining, named after Hans Christian Gram who developed the technique. This separates bacteria into two groups, based on the composition of their cell wall. The first formal grouping of bacteria into phyla was based largely on this test:
- Gracilicutes - bacteria with a second cell membrane containing lipids, giving them Gram-negative stains
- Firmicutes - bacteria with a single membrane and thick peptidoglycan wall, giving them Gram-positive stains
- Mollicutes - bacteria with no second membrane or wall, giving them Gram-negative stains The archeabacteria were originally included as the Mendosicutes. As given, these phyla are no longer believed to represent monophyletic groups. The Gracilicutes have been divided into many different phyla. Most gram-positive bacteria are placed in the phyla Firmicutes and Actinobacteria, which are closely related. However, the Firmicutes have been redefined to include the mycoplasmas (Mollicutes) and certain Gram-negative bacteria.

Benefits and dangers

Bacteria are both harmful and useful to the environment, and animals, including humans. The role of bacteria in disease and infection is important. Some bacteria act as pathogens and cause tetanus, typhoid fever, pneumonia, syphilis, cholera, foodborne illness and tuberculosis. Sepsis, a systemic infectious syndrome characterized by shock and massive vasodilation, or localized infection, can be caused by bacteria such as streptococcus, staphylococcus, or many gram-negative bacteria. Some bacterial infections can spread throughout the host's body and become systemic. In plants, bacteria cause leaf spot, fireblight, and wilts. The mode of infection includes contact, air, food, water, and insect-borne microorganisms. The hosts infected with the pathogens may be treated with antibiotics, which can be classified as bacteriocidal and bacteriostatic, which at concentrations that can be reached in bodily fluids either kill bacteria or hamper their growth, respectively. Antiseptic measures may be taken to prevent infection by bacteria, for example, prior to cutting the skin during surgery or swabbing skin with alcohol when piercing the skin with the needle of a syringe. Sterilization of surgical and dental instruments is done to make them sterile or pathogen-free to prevent contamination and infection by bacteria. Sanitizers and disinfectants are used to kill bacteria or other pathogens to prevent contamination and risk of infection. In soil, microorganisms help in the transformation of nitrogen to ammonia with enzymes secreted by these microbes, which reside in the rhizosphere (a zone that includes the root surface and the soil that adheres to the root after gentle shaking). Some bacteria are able to use molecular nitrogen as their source of nitrogen, converting it to nitrogenous compounds, a process known as nitrogen fixation. Many other bacteria are found as symbionts in humans and other organisms. For example, the presence of the gut flora in the large intestine can help prevent the growth of potentially harmful microbes. The ability of bacteria to degrade a variety of organic compounds is remarkable. Highly specialized groups of microorganisms play important roles in the mineralization of specific classes of organic compounds. For example, the decomposition of cellulose, which is one of the most abundant constituents of plant tissues, is mainly brought about by aerobic bacteria that belong to the genus Cytophaga. This ability has also been utilized by humans in industry, waste processing, and bioremediation. Bacteria capable of digesting the hydrocarbons in petroleum are often used to clean up oil spills. Some beaches in Prince William Sound were fertilized in an attempt to facilitate the growth of such bacteria after the infamous 1989 Exxon Valdez oil spill. These efforts were effective on beaches that were not too thickly covered in oil. Bacteria, often in combination with yeasts and molds, are used in the preparation of fermented foods such as cheese, pickles, soy sauce, sauerkraut, vinegar, wine, and yogurt. Using biotechnology techniques, bacteria can be bioengineered for the production of therapeutic drugs, such as insulin, or for the bioremediation of toxic wastes.

Miscellaneous

Two organelles, mitochondria and chloroplasts, are generally believed to have been derived from endosymbiotic bacteria. Microorganisms are widely distributed and are most abundant where they have food, moisture, and the right temperature for their multiplication and growth. They can be carried by air currents from one place to another. The human body is home to billions of microorganisms; they can be found on skin surfaces, in the intestinal tract, in the mouth, nose, and other body openings. They are in the air one breathes, the water one drinks, and the food one eats. The great antiquity of the bacteria has enabled them to evolve a great deal of genetic diversity. They are far more diverse than, say, the mammals or insects. For instance, the genetic distance between E. coli and Thermus aquaticus is greater than the distance between humans and oak trees.

References

- Some text in this entry was merged with the Nupedia article entitled Bacteria, written by Nagina Parmar; reviewed and approved by the Biology group (editor: Gaytha Langlois, lead reviewer: Gaytha Langlois, lead copyeditors: Ruth Ifcher and Jan Hogle)
-

External links

- [http://www.dsmz.de/bactnom/bactname.htm Bacterial Nomenclature Up-To-Date from DSMZ]
- [http://www.sciencenews.org/pages/sn_arc99/4_17_99/fob5.htm The largest bacteria]
- [http://tolweb.org/tree?group=Eubacteria&contgroup=Life_on_Earth Tree of Life]
- [http://www.rowland.harvard.edu/labs/bacteria/index_movies.html Videos] of bacteria swimming and tumbling, use of optical tweezers and other fine videos.
- Category:Bacteriology ko:세균 ja:真正細菌 th:แบคทีเรีย

Maize

:This article is about the cereal. For the town, see Maize, Kansas. Maize (Zea mays ssp. mays) is a cereal grain that was domesticated in Mesoamerica. It is called corn in the United States, Canada, and Australia but there are further regional differences in terminology. While some maize varieties grow 7 m (23 ft) tall at certain locations, commercial maize has been bred for a high-end height of 2.5 m (9 ft). Sweet corn is usually shorter than field corn varieties.

Maize physiology

The stems look like bamboo cane and the joints (nodes) are about 40–50 cm (16–20 inches) apart. Maize has a very distinct growth form, the lower leaves being like broad flags, 50–100 cm long and 5–10 cm wide (2–4 feet by 2–4 inches); the stems are erect, from 2–3 m (7–10 feet) in height, with many nodes, casting off flag-leaves at every node. Under these leaves and close to the stem grows the corn, covered over by several layers of leaves, and so closed in by them to the stem, that it does not show itself easily till there bursts out at the end of the ear a number of strings, called silk, that look like tufts of horsehair, at first green, and afterwards red or yellow. The top of the stem ends in a flower, called the tassle. For each silk on which pollen from the tassle lands, one kernel of corn is produced. Young ears can be consumed raw, cob, silk, and all; as the plant matures (usually during the summer months) the cob toughens and the silk dries to inedibility. By late August the kernels have dried out and become difficult to chew without cooking them tender first in boiling water. The kernel of corn has a pericarp of the fruit fused with the seed coat, typical of the grasses. It is close to a multiple fruit in structure, except that the individual fruits (the kernels) never fuse into a single mass. The grains are about the size of peas, and adhere in regular rows round a white pithy substance, which forms the ear. An ear contains from two to four hundred grains, and is from 10–25 cm (4–10 inches) in length. They are of various colors, blackish, red, white and yellow. When ground into flour, it yields more flour, with much less bran, than wheat does. However, it lacks the protein gluten, and therefore makes baked goods with poor raising capability.

Genetics

Maize has 10 chromosomes (n=10). The combined length of the chromosomes is 1500 cM. Some of the maize chromosomes have what are know as "chromosomal knobs". They are highly repetitive heterochromatic domains that stain darkly. Individual knobs are polymorphic among strains of both maize and teosinte. Barbara McClintock used these knob markers to prove her transposon theory of "jumping genes".

Origin of maize

transposon Maize is a direct domesticate of the teosinte Zea mays ssp. parviglumis, native to the Balsas River Valley of southern Mexico, with up to 12% of its genetic material obtained from Zea mays ssp. mexicana through introgression. The term teosinte describes all species in the genus Zea, excluding Zea mays ssp. mays. Maize development is thought to have started from 7,500 to 12,000 years ago. The domestication of maize is of particular interest to researchers. It is unknown what precipitated its domestication, because the edible portion of the wild variety is too small to be worth cultivating. It would have taken many generations of selective breeding in order to produce a plant with cobs large enough to eat. Archaeological remains of the earliest maize cob, found at Guila Naquitz Cave in the Oaxaca Valley of Mexico, date back roughly 6,250 years. Maize was the staple food, or a major staple, of all the pre-Columbian Mesoamerican civilizations. During the 1st millenium CE, maize cultivation spread from Mexico across North America, transforming the landscape as Native Americans cleared large forest and grassland areas for the new crop. In the late 1930s, Paul Mangelsdorf suggested that domesticated maize was the result of a hybridization event between an unknown wild maize and Tripsacum. However, the proposed role of the related genus Tripsacum in the origins of maize has been refuted by modern genetic analysis.

Cultivation

Paul Mangelsdorf] Maize is widely cultivated throughout the world, and a greater weight of maize is produced each year than any other grain. While the United States produces almost half of the world's harvest, other top producing countries are as widespread as China, India, Brazil, France, Indonesia, and South Africa. Worldwide production was over 600 million metric tons in 2003, just slightly more than rice or wheat. Maize is planted in the spring to take advantage of spring rains. Its root system is shallow and the plant is dependent on steady rain or irrigation. In the United States, a good harvest was predicted traditionally if the corn was "knee-high by the Fourth of July", although modern hybrids often exceed this growth rate. Maize used as silage is harvested while the plant is green and the fruit unmatured. Otherwise, maize is left in the field very late in the autumn in order to dry thoroughly. In fact, it is sometimes not harvested until winter or even early spring. The importance of regular rain is shown in many parts of Africa, where periodic drought regularly causes famine by causing maize crop failure; the older traditional African native millet (which is however less palatable than maize, and much less productive in good years) would have survived and produced a small crop in these conditions. millet] Maize was planted by the Native Americans in hills, in a complex system known to some as the Three Sisters: beans used the corn plant for support, and squashes provided ground cover to stop weeds. This method was replaced by single species hill planting where each hill 60–120 cm (2–4 feet) apart was planted with 3 or 4 seeds, a method still used by the home gardener. A later technique was checked corn where hills were placed 40 inches apart in each direction, allowing cultivators to run through the field in two directions. In more arid lands this was altered and seed were planted in the bottom of 10–12 cm (4–5 inch) deep furrows to collect water. Modern technique plants maize in rows which allows for cultivation while the plant is young. In North America, fields are often planted in a two-crop rotation with a nitrogen-fixing crop, often soybeans. Sometimes a third crop, winter wheat, is added to the rotation. Fields are usually plowed each year, although no-till farming is increasing in use. Before about World War II, most maize was harvested by hand. This often involved large numbers of workers and associated social events. Some one- and two-row mechanical pickers were in use but the corn combine did not get adopted until after the War. By hand or mechanical picker, the entire ear is harvested which then requires a separate operation of a corn sheller to remove the kernels from the ear. Whole ears of corn were often stored in corn cribs which is a sufficient form for some livestock use. Some modern farms store maize in this manner and later shell it for sale in the off-season to capture better prices. The combine with a corn head (with points and snap rolls instead of a reel) cuts the stalk near the base and then separates the ear of corn from the stalk so that only the ear and husk enter the machinery. The combine separates the husk and the cob, keeping only the kernels.

Pests of maize

Insect pests

combine
- Corn earworm (Heliothis zea)
- Fall armyworm (Spodoptera frugiperda)
- Common armyworm (Pseudaletia unipuncta)
- Stalk borer (Papaipema nebris)
- Corn leaf aphid (Rhopalosiphum maidis)
- European corn borer (Ostrinia nubilalis) (ECB)
- Corn silkfly (Euxesta stigmatis)
- Lesser cornstalk borer (Elasmopalpus lignosellus)
- Corn delphacid (Peregrinus maidis) The susceptibility of maize to the European corn borer, and the resulting large crop losses, led to the development of transgenic corn expressing the Bacillus thuringiensis (Bt) toxin. Bt corn is widely grown in the United States and has been approved for release in Europe.

Diseases

- Corn smut or common smut (Ustilago maydis): a fungal disease, known in Mexico as huitlacoche, which is prized by some as a gourmet delicacy in itself.
- Maize Dwarf Mosaic Virus
- Stewart's Wilt (Pantoea stewartii)
- Common Rust (Puccinia sorghi)

Uses for maize

The primary use for corn (seed) in United States and Canada, is as a feed for livestock, while some is for the production of corn sweeteners like corn syrup, and the production of ethanol. Ethanol, a type of alcohol, is mostly used as an additive in gasoline to increase the octane rating. It is also used for making Bourbon whiskey. Bourbon whiskey Human consumption of corn and corn meal constitutes a staple food in many regions of the world. It is the main ingredient for tortilla and many other dishes of Mexican food. Maize can also be prepared as hominy, in which the kernels are bleached with lye; or grits, which are simply coarsely ground corn. These are commonly eaten in U.S. Southern States, foods handed down from Native Americans. Another common food made from maize is corn flakes. The flour of maize (cornflour or masa) is used to make cornbread and Mexican tortillas. Teosinte is used as fodder, and can also be popped as popcorn. As a food, maize (Zea mays ssp. mays) is used in various forms, with several major Cultivar Groups. The most important Cultivar Groups are:
- Flour corn - Zea mays L. subsp. mays Amylacea Group
- Popcorn - Zea mays L. subsp. mays Everta Group
- Dent corn - Zea mays L. subsp. mays Indentata Group
- Flint corn - Zea mays L. subsp. mays Indurata Group
- Sweetcorn - Zea mays L. subsp. mays Saccharata Group
- Pod corn - Zea mays L. var. tunicata Larrañaga ex A. St. Hil Many scientists speculate that fuel ethanol will mostly be produced from switchgrass and other biomass sources in the future. Corn cobs are also used as a biomass fuel source. Maize is relatively cheap and home heating furnaces have been developed which uses maize kernels as a fuel. They feature a large hopper which feeds the uniformly sized corn kernels (or wood pellets or cherry pits) into the fire. Some forms of the plant are occasionally grown for ornamental use in the garden. For this purpose, variegated and coloured leaf forms, as well as those with colourful cobs are used. Corncobs can be hollowed out and treated to make inexpensive smoking pipes, first manufactured in the United States in 1869. In 1983, Barbara McClintock received the Nobel Prize in Medicine for discovery of transposons while studying maize. Maize is still an imporant model organism for genetics and developmental biology today. In 2005, research by the USDA Forest Service indicated that the rise in maize cultivation 500 to 1,000 years ago in the southeastern United States contributed to the decline of freshwater mussels, which are very sensitive to environmental changes. [http://www.srs.fs.usda.gov/about/newsrelease/nr_2005-06-06-mussels.htm] An unusual use for maize prior to harvest is for a maze. In the U.S., these are called "corn mazes" and are popular in many farming communities. The first modern corn maze was designed by Adrian Fisher, who is in the Guiness Book of World Records for several of his maze designs. Mr. Fisher currently operates a company [http://www.mazemaker.com/ Adrian Fisher Mazes, Ltd.], specializing in mazes, including maize mazes.

References

- Ferro, D.N. and Weber, D.C. [http://www.eap.mcgill.ca/CPMP_1.htm Managing Sweet Corn Pests in Massachusetts]
- [http://www.itis.usda.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=42268 ITIS 42268] as of 2002-09-22
- [http://www.plantnames.unimelb.edu.au/Sorting/Zea.html Sorting Zea names]

External links

- [http://www.ncga.com/WorldOfCorn/main/index.htm NCGA Corn Industry Statistics]
- [http://caliban.mpiz-koeln.mpg.de/~stueber/thome/band1/tafel_088.html Image of Zea mays from Flora von Deutschland Österreich und der Schweiz]
- [http://www.pfaf.org/database/plants.php?Zea+mays&CAN=WIKPEDIA Zea mays at Plants For A Future]
- [http://www.iowacorn.org/cornuse/cornuse_3.html Usage of Iowa and U.S. Corn Crop]
- [http://www.kallipolis.com/diet/food.php?id=11168&w=3 Corn nutrition information]
- [http://maize.agron.iastate.edu/corngrows.html How a Corn Plant Develops]
- [http://www.maizegdb.org/ Maize Genetics/Genomics Database project]
- [http://www.cimmyt.org/ International Maize and Wheat Improvement Center]
- [http://www.howtocookcornonthecob.com How to cook corn on the cob]
- [http://www.milpa.nl Maize of Guatemala]

Food | List of fruits | List of vegetables Category:Vegetables Category:Cereals Category:Grains Category:Grasses Category:Fruits and vegetables of Mexico ms:Jagung ja:トウモロコシ zh-min-nan:Hoan-be̍h

Vector (biology)

Traditionally in medicine, a vector is an organism that does not cause disease itself but which spreads infection by conveying pathogens from one host to another. Species of mosquito, for example, serve as vectors for the disease-causing West Nile Virus; which the insects may ingest by feeding from an infected bird and regurgitate into a human, infecting him or her. This sense of "biological vector" is the primary one in epidemiology and in common speech. In gene therapy, a virus itself may serve as a vector, if it has been re-engineered and is used to deliver a gene to its target cell. A "vector" in this sense is a vehicle for delivering genetic material such as DNA to a cell. Finally, in genetics more generally, DNA by itself may be regarded as a vector, for example in particular when it is used for cell transformation. A vector in this sense is a DNA construct, such as a plasmid or a bacterial artificial chromosome, that contains an origin of replication. An appropriate replication origin causes a cell to copy the construct along with the cell's chromosomes and to pass it along to its progeny. A single cell that has been transformed with a vector will grow into an entire culture of cells, which all contain the vector, as well as any gene attached to it within the construct. Because the constructs can be extracted from the cells by purification techniques, transformation with a vector is a way of making a small number of DNA molecules in to a much larger one. There is a possibility for confusion between the use of "vector" in gene therapy and its use in molecular biology more generally. Some transformation technologies, such as lipofectamine, enable the direct delivery of a DNA construct as therapy in a tissue. In such a situation, a plasmid vector may be regarded as serving as its own gene-therapy vector. When a speaker calls it "a vector," they may be referring to either of its vector aspects or often both.

Epidemiology

- mosquito (malaria, St. Louis encephalitis, dengue fever)
- flea (bubonic plague)
- tick (Lyme disease, rocky mountain yellow-spotted fever)

Cell transformation and gene therapy

- adenovirus
- adeno-associated virus
- tobacco mosaic virus (plants)
- cytomegalovirus
- bacteriophage (bacteria)

DNA

- sv40
- plasmid
- yeast artificial chromosome (chromosome walking, positional cloning)
- bacterial artificial chromosome (shotgun sequencing)

Seed

A seed is the ripened ovule of gymnosperm or angiosperm plants. The importance of the seed relative to more primitive forms of reproduction and dispersal is attested to by the success of these two groups of plants in dominating the landscape.

Seed structure

A fertilized seed contains the embryo from which a new plant will grow under proper conditions. It also contains a supply of stored food and is wrapped in the seed coat or testa. The stored food begins as a tissue called endosperm derived from the parent plant. Endosperm becomes rich in oil or starch, and protein. In some species, the embryo is imbedded in the endosperm, which the seedling will use upon germination. In others, the endosperm is absorbed by the embryo as the latter grows within the developing seed, and the cotyledons of the embryo become filled with this stored food. At maturity, seeds of these species have no endosperm. Some common plant seeds that lack an endosperm are bean, pea, oak, walnut, squash, sunflower, and radish. Plant seeds with an endosperm include all conifers and most monocotyledons (e.g. grasses and palms), and also e.g. brazil nut, castor bean. castor bean See also: Hypocotyl The seed coat develops from tissues (called integument) originally surrounding the ovule. The seed coat in the mature seed can be a paper thin layer (as for example, in the peanut) or something more substantial (as for example, thick and hard in honey locust and coconut). The seed coat helps protect the embryo from mechanical injury and from drying out. In order for the seed coat to split, the embryo must imbibe (soak up water) which causes it to swell, splitting the seed coat. However, the nature of the seed coat determines how rapidly water can penetrate and subsequently initiate germination. For seeds with a very thick coat, scarification of the seed coat may be necessary before water can reach the embryo. Examples of scarification include: gnawing by animals, freezing and thawing, battering on rocks in a stream bed, or passing through an animal's digestive tract. In the latter case, the seed coat protects the seed from digestion, while perhaps weakening the seed coat such that the embryo is ready to sprout when it gets deposited (along with a bit of fertilizer) far from the parent plant. In species with thin seed coats, light may be able to penetrate into the dormant embryo. The presence of light or the absence of light may trigger the germination process, inhibiting germination in some seeds buried too deeply or in others not buried in the soil. Abscisic acid is usually the growth inhibitor in seeds. The seeds of angiosperms are contained in a hard or fleshy (or with layers of both) structure called a fruit. Gymnosperm seeds begin their development "naked" on the bracts of cones, although the seeds do become covered by the cone scales as they develop. An example of a hard fruit layer surrounding the actual seed is that of the so-called stone fruits (such as the peach).

Seed functions

Unlike animals, plants are limited in their ability to seek out favorable conditions for life and growth. Consequently, plants have evolved many ways to disperse and spread the population through their seeds (see also vegetative reproduction). A seed must somehow "arrive" at a location and be there at a time favorable for germination and growth. Those properties or attributes that promote the movement of the next generation away from the parent plant may involve the fruit more so than the seeds themselves. The function of a seed typically is one of serving as a delaying mechanism: a way for the new generation to suspend its growth and allow time for dispersal to occur or to survive harsh, unfavorable conditions of cold or dryness or both. In many if not most cases each plant species achieves success in finding ideal locations for placement of its seeds through the basic approach of producing numerous seeds. This is certainly the approach used by plants, such as ferns, that disperse by spores. However, seeds involve a considerably greater investment in energy and resources than do spores, and the payoff must come in achieving similar or greater success with fewer dispersal units.

External links

- [http://www.seedlab.co.nz/NAMESEED.HTM List of Common Botanical Seed Names]
- [http://theseedsite.co.uk/ The Seed Site]: collecting, storing, sowing, germinating, and exchanging seeds, with pictures of seeds, seedpods and seedlings. Category:Plants Category: plant morphology Category:Vegetables Category:Flowers ko:씨 ja:種子 simple:Seed

Lesion

A lesion is a non-specific term referring to abnormal tissue in the body. It can be caused by any disease process including trauma (physical, chemical, electrical), infection, neoplasm, metabolic and autoimmune. Not all lesions require treatment. Lesions can also be inflicted intentionally during surgery, for example to specific regions of the brain to treat epilepsy. Lesion is derived from a Latin word which means "injury." Category:Medical terms

Subspecies

In zoology, as in other branches of biology, subspecies is the rank immediately subordinate to a species. As an aside, do note that in botany a subspecies is only one of the ranks that will get a ternary name (see there), while in bacteriology, the terms subspecies and variety are usually interchangeable, see ICNB. The following applies to zoology only. In zoology, the scientific name of a subspecies is the binomen followed immediately by a subspecific name, e.g. Homo sapiens sapiens. The International Code of Zoological Nomenclature (4th edition, 2000) does not attempt to codify any "infrasubspecific entities". It should be noted that if a subspecies is indicated by the repetition of the specific name, it is known as the nominate subspecies. Thus Motacilla alba alba is the nominate subspecies of White Wagtail, Motacilla alba.

Criteria

Members of one subspecies differ morphologically from members of other subspecies of the species. Subspecies are defined in relation to species. It is not possible to understand the concept of a subspecies without first grasping what a species is. In the context of large living organisms like trees, flowers, birds, fish and humans, a species can be defined as a distinct and recognisable group that satisfies two conditions:
- Members of the group are reliably distinguishable from members of other groups. The distinction can be made in any of a wide number of ways, such as: differently shaped leaves, a different number of primary wing feathers, a particular ritual breeding behaviour, relative size of certain bones, different DNA sequences, and so on. There is no set minimum 'amount of difference': the only criterion is that the difference be reliably discernable. In practice, however, very small differences tend to be ignored.
- The flow of genetic material between the group and other groups is small and can be expected to remain so because even if the two groups were to be placed together they would not interbreed to any great extent. Note the key qualifier above: to be regarded as different groups rather than as a single varied group, the difference must be distinct, not simply a matter of continuously varying degree. If, for example, the population in question is a type of frog and the distinction between two groups is that individuals living upstream are generally white, while those found in the lowlands are black, then they are classified as different groups if the frogs in the intermediate area tend to be either black or white, but a single, varied group if the intermediate population becomes gradually darker as one moves downstream. This is not an arbitrary condition. A gradual change, called a cline, is clear evidence of substantial gene flow between two populations. A sharp boundary between black and white, or a relatively small and stable hybrid zone, on the other hand, shows that the two populations do not interbreed to any great extent and are indeed separate species. Their classification as separate species or as subspecies, however, depends on why they do not interbreed. If the two groups do not interbreed because of something intrinsic to their genetic make-up (perhaps black frogs do not find white frogs sexually attractive, or they breed at different times of year) then they are different species. If, on the other hand, the two groups would interbreed freely provided only that some external barrier was removed (perhaps there is a waterfall too high for frogs to scale, or the populations are far distant from one another) then they are subspecies. Note that the distinction between a species and a subspecies depends only on the likelihood that (absent external barriers) the two populations would merge back into a single, genetically unified population. It has nothing to do with 'how different' the two groups appear to be to the human observer. As knowledge of a particular group increases, its categorisation may need to be re-assessed. The Rock Pipit was formerly classed as a subspecies of Water Pipit, but is now recognised to be a full species. For an example of a subspecies, see Pied Wagtail.

Important difference between species and subspecies

Subspecies: a taxonomic subdivision of a species; a group of the organisms, which differ from other members of their species by genetically-encoded morphological and physiological characteristics, and by behavior. Members of different subspecies of the same species are potentially capable of breeding with each other, and production of fertile offspring. However, animals of the different subspecies of the same species might not interbreed even if geographical factor is removed. Differences in appearance and behavior rather often prevent the potential sex partners from recognizing each other as the sex partners. This is especially true for animals with complicated sexual rituals. Members of different species are incapable of reproduction, or produce an infertile offspring.

Category:Enterobacteria

Category:Proteobacteria

Lhommaizé

Lhommaizé è un comune francese di 686 abitanti situato nel dipartimento della Vienne nella regione di Poitou-Charentes. Lhommaize Lhommaize

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Stewart's Wilt

Bacterium

History and taxonomy

Metabolism

Movement

Groups and identification

Benefits and dangers

Miscellaneous

See also

References

Further reading

External links

Maize

Maize physiology

Genetics

Origin of maize

Cultivation

Pests of maize

Insect pests

Diseases

Uses for maize

See also

References

External links

Vector (biology)

Epidemiology

Cell transformation and gene therapy

DNA

See also

Seed

Seed structure

Seed functions

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External links

Lesion

Subspecies

Criteria

Important difference between species and subspecies

See also

Category:Enterobacteria

Lhommaizé

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