The red colour of tomato fruit is due mainly to a carotenoid called lycopene. There have been many studies linking lycopene with potential health benefits including reducing the risk of certain cancers. Other studies have shown that cooking tomato fruit helps increase their nutritional value since your body is better able to absorb lycopene from cooked tomatoes. Lycopene is not the only pigment found in tomato plants. Chlorophylls are obviously present in all green plants and in tomato leaves. When the leaves become old and are ready to fall off, the chlorophylls break down and the yellow carotenoids become visible. This is just like the colour change we can observe in some autumn leaves. Other than lycopene, other carotenoids present in tomatoes include beta-carotene and xanthophylls. When consumed, these pigments in tomato fruit act as antioxidants to protect your cells. Unlike in the related eggplant and pepper fruits, tomato fruit do not usually produce anthocyanins, but anthocyanins are present in tomato leaf tissue.
Chlorophyll a and b both absorb in the blue and red regions of the spectrum but have their peak absorption at different wavelengths. Chlorophylls do not absorb strongly in the green region (490 to 550 nanometers (nm)). The green wavelength is reflected which is why plant leaves appear as green to us.
There are two main types of carotenoids: carotenes and xanthophylls. Carotenes are molecules containing hydrogen and carbon atoms. In addition to carbon and hydrogen atoms, xanthophylls also contain oxygen atoms. Carotenoids have two main functions. First, they play a part in photosynthesis by transferring some of the light energy they absorb to chlorophylls. Second, they protect the plant from photodamage by releasing the excess energy in the form of heat. Carotenoids are formed in the plastids (chloroplasts and chromoplasts) of plant cells. Carotenoids absorb at wavelengths ranging from 400 to 550 nm. Carotenoids primarily absorb in the blue wavelengths but reflect the wavelengths producing the yellow, orange, and red colors. A common carotenoid, beta-carotene, is produced in the chromoplasts of sunflower petals to produce the bright yellow and orange colors we associate with these flowers. Beta-carotene is also responsible for the orange color in carrots and sweet potatoes. In autumn leaves, carotenoids are revealed when chlorophyll is broken down in response to shorter daylight hours.
The tomato (/təmeɪtoʊ/ or /təmɑːtoʊ/) is the edible berry of the plant Solanum lycopersicum, commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word tomatl gave rise to the Spanish word tomate, from which the English word tomato derived. Its domestication and use as a cultivated food may have originated with the indigenous peoples of Mexico. The Aztecs used tomatoes in their cooking at the time of the Spanish conquest of the Aztec Empire, and after the Spanish encountered the tomato for the first time after their contact with the Aztecs, they brought the plant to Europe, in a widespread transfer of plants known as the Columbian exchange. From there, the tomato was introduced to other parts of the European-colonized world during the 16th century. Tomatoes are a significant source of umami flavor. They are consumed in diverse ways: raw or cooked, and in many dishes, sauces, salads, and drinks. While tomatoes are fruits—botanically classified as berries—they are commonly used culinarily as a vegetable ingredient or side dish. Numerous varieties of the tomato plant are widely grown in temperate climates across the world, with greenhouses allowing for the production of tomatoes throughout all seasons of the year. Tomato plants typically grow to 1–3 meters (3–10 ft) in height. They are vines that have a weak stem that sprawls and typically needs support. Indeterminate tomato plants are perennials in their native habitat, but are cultivated as annuals. (Determinate, or bush, plants are annuals that stop growing at a certain height and produce a crop all at once.) The size of the tomato varies according to the cultivar, with a range of 1–10 cm (1⁄2–4 in) in width.
The poor taste and lack of sugar in modern garden and commercial tomato varieties resulted from breeding tomatoes to ripen uniformly red. This change occurred after discovery of a mutant "u" phenotype in the mid-20th century, so named because the fruits ripened uniformly. This was widely cross-bred to produce red fruit without the typical green ring around the stem on uncross-bred varieties. Prior to general introduction of this trait, most tomatoes produced more sugar during ripening, and were sweeter and more flavorful.
Evidence has been found that 10–20% of the total carbon fixed in the fruit can be produced by photosynthesis in the developing fruit of the normal U phenotype. The u genetic mutation encodes a factor that produces defective chloroplasts with lower density in developing fruit, resulting in a lighter green color of unripe fruit, and repression of sugars accumulation in the resulting ripe fruit by 10–15%. Perhaps more important than their role in photosynthesis, the fruit chloroplasts are remodelled during ripening into chlorophyll-free chromoplasts that synthesize and accumulate the carotenoids lycopene, β-carotene, and other metabolites that are sensory and nutritional assets of the ripe fruit. The potent chloroplasts in the dark-green shoulders of the U phenotype are beneficial here, but have the disadvantage of leaving green shoulders near the stems of the ripe fruit, and even cracked yellow shoulders, apparently because of oxidative stress due to overload of the photosynthetic chain in direct sunlight at high temperatures. Hence genetic design of a commercial variety that combines the advantages of types u and U requires fine tuning, but may be feasible.
Furthermore, breeders of modern tomato cultivars typically strive to produce tomato plants exhibiting improved yield, shelf life, size, and tolerance/resistance to various environmental pressures, including disease. However, these breeding efforts have yielded unintended negative consequences on various tomato fruit attributes. For instance, linkage drag is a phenomenon that has been responsible for alterations in the metabolism of the tomato fruit. Linkage drag describes the introduction of an undesired trait or allele into a plant during backcrossing. This trait/allele is physically linked (or is very close) to the desired allele along the chromosome. In introducing the beneficial allele, there exists a high likelihood that the poor allele is also incorporated into the plant. Thus, breeding efforts attempting to enhance certain traits (for example: larger fruit size) have unintentionally altered production of chemicals associated with, for instance, nutritional value and flavor.
Breeders have turned to using wild tomato species as a source of alleles for the introduction of beneficial traits into modern tomato varieties. For example, wild tomato relatives may possess higher amounts of fruit solids (which are associated with greater sugar content) or resistance to diseases caused by microbes, such as resistance towards the early blight pathogen Alternaria solani. However, this tactic has limitations, for the incorporation of certain traits, such as pathogen resistance, can negatively impact other favorable phenotypes, such as fruit production.
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