Photoperiodicity is the physiological reaction of organisms to the length of day or night. It occurs in plants Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants, bryophytes, ferns and fern allies. As of 2004, and animals Animals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also.
Contents |
In plants
Many flowering plants The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Together with gymnosperms, they are the only extant groups of seed-producing plants, but they can be distinguished from the gymnosperms by a series of synapomorphies (derived characteristics). These characteristics include flowers, use a photoreceptor protein, such as phytochrome Phytochrome is a photoreceptor, a pigment that plants use to detect light. It is sensitive to light in the red and far-red region of the visible spectrum. Many flowering plants use it to regulate the time of flowering based on the length of day and night and to set circadian rhythms. It also regulates other responses including the germination of or cryptochrome, to sense seasonal changes in night length, or photoperiod, which they take as signals to flower. In a further subdivision, obligate photoperiodic plants absolutely require a long or short enough night before flowering, whereas facultative photoperiodic plants are more likely to flower under the appropriate light conditions, but will eventually flower regardless of night length.
Photoperiodic flowering plants are classified as long-day plants or short-day plants, though the regulatory mechanism is actually governed by hours of darkness, not the length of the day.
Modern biologists believe[citation needed] that it is the coincidence of the active forms of phytochrome or cryptochrome, created by light during the daytime, with the rhythms of the circadian clock A circadian rhythm is a roughly 24-hour cycle in the biochemical, physiological, or behavioural processes of living entities, including plants, animals, fungi and cyanobacteria . The term "circadian" comes from the Latin circa, "around", and diem or dies, "day", meaning literally "approximately one day". The that allows plants to measure the length of the night. Other than flowering, photoperiodism in plants includes the growth of stems or roots during certain seasons, or the loss of leaves.
Long-day plants
A long-day plant requires fewer than a certain number of hours of darkness in each 24-hour period to induce flowering. These plants typically flower in the northern hemisphere The Northern Hemisphere is the half of a planet that is north of equator—the word hemisphere literally means 'half sphere'. It is also that half of the celestial sphere north of the celestial equator. Earth's northern hemisphere contains most of its land area and most of its human population during late spring or early summer as days are getting longer. In the Northern Hemisphere, the longest day of the year is on or about 21 June (solstice A solstice is an astronomical event that happens twice each year when the Sun's apparent position in the sky reaches its northernmost or southernmost extremes. The name is derived from the Latin sol and sistere (to stand still), because at the solstices, the Sun stands still in declination; that is, the apparent movement of the Sun's path north or). After that date, days grow shorter (i.e. nights grow longer) until 21 December (solstice). This situation is reversed in the Southern Hemisphere (i.e. longest day is 21 December and shortest day is 21 June). In some parts of the world, however, "winter" or "summer" might refer to rainy versus dry seasons, respectively, rather than the coolest or warmest time of year.
Some long-day obligate plants are:
- Carnation Dianthus caryophyllus is a species of Dianthus. It is probably native to the Mediterranean region but its exact range is unknown due to extensive cultivation for the last 2,000 years. It is the wild ancestor of the garden Carnation (Dianthus)
- Henbane Henbane , also known as stinking nightshade, is a plant of the family Solanaceae that originated in Eurasia, though it is now globally distributed (Hyoscyamus)
- Oat The common oat is a species of cereal grain grown for its seed, which is known by the same name (usually in the plural, unlike other grains). While oats are suitable for human consumption as oatmeal and rolled oats, one of the most common uses is as livestock feed. Oats make up a large part of the diet of horses and are regularly fed to cattle as (Avena)
- Ryegrass Ryegrass is a genus of nine species of tufted grasses, family Poaceae. Also called tares (even though there is no firm evidence that this is the same as the plant given that name in English language translations of the Bible - vetches are another candidate), these plants are native to Europe, Asia and northern Africa, but are widely cultivated and (Lolium)
- Clover Clover , or trefoil, is a genus of about 300 species of plants in the pea family Fabaceae. The genus has a cosmopolitan distribution; the highest diversity is found in the temperate Northern Hemisphere, but many species also occur in South America and Africa, including at high altitudes on mountains in the tropics. They are small annual, biennial, (Trifolium)
- Bellflower (Campanula carpatica)
Some long-day facultative plants are:
- Pea A pea is most commonly the small spherical seed or the seed-pod of the legume Pisum sativum. Each pod contains several peas. Peapods are botanically a fruit, since they contain seeds developed from the ovary of a flower. However, peas are considered to be a vegetable in cooking. The name is also used to describe other edible seeds from the (Pisum sativum)
- Barley Barley is a cereal grain derived from the annual grass Hordeum vulgare (Hordeum vulgare)
- Lettuce Lettuce is a temperate annual or biennial plant of the daisy family Asteraceae. It is most often grown as a leaf vegetable. In many countries, it is typically eaten cold, raw, in salads, sandwiches, hamburgers, tacos, and in many other dishes. In some places, including China, lettuce is typically eaten cooked and use of the stem is as important as (Lactuca sativa)
- Wheat Wheat is a grass, originally from the Fertile Crescent region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize (784 million tons) and rice (651 million tons). Globally, wheat is the leading source of vegetable protein in human food, having a (Triticum aestivum, spring wheat cultivars)
- Turnip The turnip or white turnip is a root vegetable commonly grown in temperate climates worldwide for its white, bulbous taproot. Small, tender varieties are grown for human consumption, while larger varieties are grown as feed for livestock (Brassica rapa)
- Arabidopsis thaliana Arabidopsis thaliana , is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, Arabidopsis is popular as a model organism in plant biology and genetics. Its genome is one of the smallest plant genomes and was the first plant genome to be sequenced. Arabidopsis is a popular (model organism)
Short-day plants
Short-day plants flower when the night is longer than a critical length. They cannot flower under long days or if a pulse of artificial light is shone on the plant for several minutes during the middle of the night; they require a consolidated period of darkness before floral development can begin. Natural nighttime light, such as moonlight or lightning, is not of sufficient brightness or duration to interrupt flowering.
In general, short-day (i.e. long-night) plants flower as days grow shorter (and nights grow longer) after 21 June in the Northern Hemisphere, which is during summer or fall. The length of the dark period required to induce flowering differs among species and varieties of a species.
Photoperiod affects flowering when the shoot is induced to produce floral buds instead of leaves and lateral buds. Note that some species must pass through a "juvenile" period during which they cannot be induced to flower—common cocklebur is an example of a plant species with a remarkably short period of juvenility and plants can be induced to flower when quite small.
Some short-day obligate plants are:
- Chrysanthemum Chrysanthemums, often called mums or chrysanths, are a genus of about 30 species of perennial flowering plants in the family Asteraceae, native to Asia and northeastern Europe
- Coffee Coffee is a brewed drink prepared from roasted seeds, commonly called coffee beans, of the coffee plant. They are seeds of coffee cherries that grow on trees in over 70 countries. Green unroasted coffee is one of the most traded agricultural commodities in the world. Due to its caffeine content, coffee can have a stimulating effect in humans
- Poinsettia Euphorbia pulcherrima, commonly known as poinsettia, is a species of flowering plant indigenous to Mexico and Central America. The name "poinsettia" is after Joel Roberts Poinsett, the first United States Minister to Mexico, who introduced the plant into the US in 1828. It is also called the Atatürk flower
- Strawberry The garden strawberry is a common plant of the genus Fragaria cultivated worldwide for its fruit, the strawberry. The fruit is widely appreciated, mainly for its characteristic aroma but also for its bright red color, and it is consumed in large quantities, either fresh or in prepared foods such as preserves, fruit juice, pies, ice creams, and
- Tobacco Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as an organic pesticide and, in the form of nicotine tartrate, it is used in some medicines. It is most commonly used as a recreational drug, and is a valuable cash crop for countries such as Cuba, China and United States, var. Maryland Mammouth
- Common duckweed Duckweeds, or water lentils, are aquatic plants which float on or just beneath the surface of still or slow-moving fresh water bodies. They arose from within the arum or aroid family, , and therefore, often are classified as the subfamily Lemnoideae within the Araceae. Classifications created prior to the approximate end of the twentieth century, (Lemna minor)
- Cocklebur Cockleburs are a genus of flowering plants in the family Asteraceae, native to the Americas and eastern Asia (Xanthium)
- Maize Maize is a grass domesticated by indigenous peoples in Mesoamerica in prehistoric times. The Aztecs and Mayans cultivated it in numerous varieties throughout central and southern Mexico, to cook or grind in a process called nixtamalization. Later the crop spread through much of the Americas. Between 1250 A.D. and 1700 A.D. nearly the whole - tropical cultivars only
Some short-day facultative plants are:
- Hemp Hemp is the name of the soft, durable fibre that is cultivated from plants of the Cannabis genus, cultivated for commercial use (Cannabis)
- Cotton Cotton is a soft, fluffy staple fiber that grows in a boll around the seeds of the cotton plant. The plant is a shrub native to tropical and subtropical regions around the world, including the Americas, Pakistan, India and Africa. The fiber most often is spun into yarn or thread and used to make a soft, breathable textile, which is the most widely (Gossypium)
- Rice Rice is the seed of the monocot plant Oryza sativa. As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East, South, Southeast Asia, the Middle East, Latin America, and the West Indies. It is the grain with the second highest worldwide production, after maize
- Sugar cane Sugarcane is any of six to thirty-seven species of tall perennial grasses of the genus Saccharum (family Poaceae, tribe Andropogoneae). Native to warm temperate to tropical regions of Asia, they have stout, jointed, fibrous stalks that are rich in sugar, and measure two to six meters (six to nineteen feet) tall. All sugar cane species interbreed,
Day-neutral plants
Day-neutral plants, such as cucumbers The cucumber is a widely cultivated plant in the gourd family Cucurbitaceae, which includes squash, and in the same genus as the muskmelon, roses and tomatoes, do not initiate flowering based on photoperiodism at all; they flower regardless of the night length. They may initiate flowering after attaining a certain overall developmental stage or age, or in response to alternative environmental stimuli, such as vernalization Vernalization is the acquisition of the competence to flower in the spring by exposure to the prolonged cold of winter. The word vernalization comes from the Latin word vernus, meaning of the spring (a period of low temperature), rather than in response to photoperiod.
In animals
Daylength, and thus knowledge of the season of the year, is vital to many animals. A number of biological and behavioural changes are dependent on this knowledge. Together with temperature changes, photoperiod provokes changes in the colour of fur and feathers, migration, entry into hibernation, sexual behaviour, and even the resizing of sexual organs.
Birds', such as the canary, singing frequency depends on the photoperiod. In the spring when the photoperiod increases (more daylight), the male canary's testes grow. As the testes grow, more androgens are secreted and song frequency increases. During autumn when the photoperiod decreases (less daylight), the male canary's testes regress and androgen levels dramatically drop resulting in decreased singing frequency. Not only is singing frequency dependent on the photoperiod but also song repertoire. The long photoperiod of spring results in a greater song repertoire. Autumn's shorter photoperiod results in a reduction in song repertoire. These behavioral photoperiod changes in male canaries are caused by changes in the song center of the brain. As the photoperiod increases so does the high vocal center HVC is a nucleus in the brain of the songbirds (order passeriformes) necessary for both the learning and the production of bird song. It is located in the lateral caudal nidopallium and has projections to both the direct and the anterior forebrain pathways (HVC) and the robust nucleus of the archistriatum (RA). When the photoperiod decreases these areas of the brain regress.[1]
In mammals daylength is registered in the suprachiasmatic nucleus The suprachiasmatic nucleus or nuclei, abbreviated SCN, is a tiny region on the brain's midline, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms. The neuronal and hormonal activities it generates regulate many different body functions in a 24-hour cycle, using around 20,000 neurons (SCN), which is informed by retinal light-sensitive ganglion cells Photosensitive ganglion cells, also called photosensitive Retinal Ganglion Cells , intrinsically photosensitive Retinal Ganglion Cells (ipRGC) or melanopsin-containing ganglion cells, are a recently discovered type of nerve cell in the retina of the mammalian eye which, unlike other retinal ganglion cells, are intrinsically photosensitive. This, which are not involved in vision. The information travels through the retinohypothalamic tract The retinohypothalamic tract is a photic input pathway involved in the circadian rhythms of mammals. The origin of the retinohypothalamic tract is the intrinsically photosensitive Retinal Ganglion Cells , which contain the photopigment melanopsin. The axons of the ipRGCs belonging to the retinohypothalamic tract project directly to the (RHT). Some mammals are highly seasonal while humans' seasonality is largely evolutionary baggage.[2]
See also
- Chronobiology Chronobiology is a field of biology that examines periodic phenomena in living organisms and their adaptation to solar and lunar related rhythms. These cycles are known as biological rhythms. "Chrono" pertains to time and "biology" pertains to the study, or science, of life. The related terms chronomics and chronome have been
- Florigen
- Scotobiology
References
- ^ Nelson Randy J. (2005) An Introduction to Behavioral Endocrinology (p.189). Sunderland, MA: Sinauer Associates.
- ^ Foster, Russell; Williams, Robyn (5). "Extra-retinal photo receptors" (Interview). Science Show. ABC Radio National. http://www.abc.net.au/rn/scienceshow/stories/2009/2762261.htm. Retrieved 2010-05-28. "…we have the evolutionary baggage of showing seasonality but we're not entirely sure what the mechanism is."
Related reading
- D.E. Fosket, Plant Growth & Development, A Molecular Approach. Academic Press, San Diego, 1994, p. 495.
- B. Thomas and D. Vince-Prue, Photoperiodism in plants (2nd ed). Academic Press, 1997.
Categories: Zoology | Animals Animals are a major group of organisms, classified as the kingdom Animalia. This category includes animals, their study, and their classification | Botany | Plant physiology Plant physiology is the study of the function, or physiology of plants. Fundamental processes such as photosynthesis, respiration, transpiration, and floral inducation are studied by plant physiologists | Circadian rhythms | Biology terminology
