Tuber
Overview
Tuber is Latin for "swelling", as also used for benign tumours such as in tuberous sclerosis
Tuberous sclerosis
Tuberous sclerosis or tuberous sclerosis complex is a rare multi-system genetic disease that causes non-malignant tumors to grow in the brain and on other vital organs such as the kidneys, heart, eyes, lungs, and skin. A combination of symptoms may include seizures, developmental delay, behavioral...


Tubers are various types of modified plant structures that are enlarged to store nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

s. They are used by plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s to survive the winter or dry months and provide energy and nutrients for regrowth during the next growing season and they are a means of asexual reproduction
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...

. There are both stem
Plant stem
A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...

and root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

tubers.

A stem tuber forms from thickened rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s or stolon
Stolon
In biology, stolons are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external skeletons.-In botany:...

s.
Encyclopedia
Tuber is Latin for "swelling", as also used for benign tumours such as in tuberous sclerosis
Tuberous sclerosis
Tuberous sclerosis or tuberous sclerosis complex is a rare multi-system genetic disease that causes non-malignant tumors to grow in the brain and on other vital organs such as the kidneys, heart, eyes, lungs, and skin. A combination of symptoms may include seizures, developmental delay, behavioral...


Tubers are various types of modified plant structures that are enlarged to store nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

s. They are used by plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s to survive the winter or dry months and provide energy and nutrients for regrowth during the next growing season and they are a means of asexual reproduction
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...

. There are both stem
Plant stem
A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...

and root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

tubers.

Stem tubers


A stem tuber forms from thickened rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s or stolon
Stolon
In biology, stolons are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external skeletons.-In botany:...

s. The tops or sides of the tuber produce shoots that grow into typical stems and leaves and the under sides produce roots. They tend to form at the sides of the parent plant and are most often located near the soil surface. The below-ground stem tuber is normally a short-lived storage and regenerative organ developing from a shoot that branches off a mature plant. The offspring or new tubers, are attached to a parent tuber or form at the end of a hypogeogenous rhizome. In the fall the plant dies except for the new offspring stem tubers which have one dominant bud, which in spring regrows a new shoot producing stems and leaves, in summer the tubers decay and new tubers begin to grow. Some plants also form smaller tubers and/or tubercules which act like seeds, producing small plants that resemble (in morphology and size) seedlings. Some stem tubers are long lived such as those of tuberous begonia
Begonia
Begonia is a genus in the flowering plant family Begoniaceae and is a perennial. The only other members of the family Begoniaceae are Hillebrandia, a genus with a single species in the Hawaiian Islands, and the genus Symbegonia which more recently was included in Begonia...

 but many tuberous plants have tubers that survive only until the plants have fully leafed out, at which point the tuber is reduced to a shriveled up husk.

Stem tubers generally start off as enlargements of the hypocotyl
Hypocotyl
The hypocotyl is the stem of a germinating seedling, found below the cotyledons and above the radicle .-Dicots:...

 section of a seedling but also sometimes include the first node or two of the epicotyl
Epicotyl
In plant physiology, the epicotyl is the embryonic shoot above the cotyledons. In most plants the epicotyl will eventually develop into the leaves of the plant. In dicots, the hypocotyl is what appears to be the base stem under the spent withered cotyledons, and the shoot just above that is the...

 and the upper section of the root. The stem tuber has a vertical orientation with one or a few vegetative buds on the top and fibrous roots produced on the bottom from a basal section, typically the stem tuber has an oblong rounded shape.

Tuberous begonia and Cyclamen are commonly grown stem tubers.
Mignonette vine (Anredera cordifolia
Anredera cordifolia
Anredera cordifolia, commonly known as the Madeira vine or mignonette vine, is a South American species of ornamental succulent vine of the family Basellaceae. The combination of fleshy leaves and thick aerial tubers makes this a very heavy vine...

) produces aerial stem tubers on 12 to 25 ft (3.7 to 7.6 m) vines, the tubers fall to the ground and grow. Plectranthus esculentus
Plectranthus esculentus
Plectranthus esculentus is a species of plant in the Lamiaceae family. It is indigenous to Africa, where it is grown for its edible tubers. It is more difficult to cultivate than Plectranthus rotundifolius, but able to give greater yields....

of the mint family Lamiaceae
Lamiaceae
The mints, taxonomically known as Lamiaceae or Labiatae, are a family of flowering plants. They have traditionally been considered closely related to Verbenaceae, but in the 1990s, phylogenetic studies suggested that many genera classified in Verbenaceae belong instead in Lamiaceae...

, produces tuberous under ground organs from the base of the stem, weighing up to 1.8 kg per tuber, forming from axillary buds producing short stolons that grow into tubers.

Potatoes

Potato
Potato
The potato is a starchy, tuberous crop from the perennial Solanum tuberosum of the Solanaceae family . The word potato may refer to the plant itself as well as the edible tuber. In the region of the Andes, there are some other closely related cultivated potato species...

es are stem tubers, which are the development of enlarged stolon
Stolon
In biology, stolons are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external skeletons.-In botany:...

s thickened into a storage organ
Storage organ
A storage organ is a part of a plant specifically modified for storage of energy or water. Storage organs often grow underground, where they are better protected from attack by herbivores. Plants that have an underground storage organ are called geophytes in the Raunkiær plant life-form...

.

The tuber has all the parts of a normal stem, including nodes and internodes, the nodes are the eyes and each has a leaf scar. The nodes or eyes are arranged around the tuber in a spiral fashion beginning on the end opposite the attachment point to the stolon. The terminal bud is produced at the farthest point away from the stolon attachment and tuber thus shows the same apical dominance
Apical dominance
In plant physiology, apical dominance is the phenomenon whereby the main central stem of the plant is dominant over other side stems; on a branch the main stem of the branch is further dominant over its own side branchlets....

 of a normal stem. Internally a tuber is filled with starch stored in enlarged parenchyma
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...

 like cells; also internally the tuber has the typical cell structures of any stem, including a pith, vascular zones and a cortex.

The tuber is produced in one growing season and used to perennialize the plant and as a means of propagation
Plant propagation
Plant propagation is the process of creating new plants from a variety of sources: seeds, cuttings, bulbs and other plant parts. Plant propagation can also refer to the artificial or natural dispersal of plants.-Sexual propagation :...

. When fall comes the above ground structure of the plant dies but the tubers survive over winter under ground until spring, when they regenerate new shoots which use the stored food in the tuber to grow. As the main shoot develops from the tuber, the base of the shoot close to the tuber produces adventitious roots and lateral buds on the shoot. The shoot also produces stolons that are long etiolated stems. The stolon elongates during long days with the presence of high auxins levels that prevent root growth off of the stolon. Before new tuber formation begins the stolon must be a certain age. The enzyme lipoxygenase makes a hormone, jasmonic acid
Jasmonic acid
Jasmonic acid is derived from the fatty acid linolenic acid. It is a member of the jasmonate class of plant hormones. It is biosynthesized from linolenic acid by the octadecanoid pathway....

, which is involved in the control of potato tuber development.

The stolons are easily recognized when potato plants are grown from seed, as the plants grow, stolons are produced around the soil surface from the nodes. The tubers form close to the soil surface and sometimes even on top of the ground. When potatoes are cultivated, the tubers are cut into pieces and planted much deeper into the soil. By planting the pieces deeper there is more area for the plants to generate the tubers and their size increases. The pieces sprout shoots that grow to the surface, these shoots are rhizome like and generate short stolons from the nodes while in the ground. When the shoots reach the soil surface they produce roots and shoots that grow into the green plant.

Root tubers


A tuberous root or storage root, is a modified lateral root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

, enlarged to function as a storage organ
Storage organ
A storage organ is a part of a plant specifically modified for storage of energy or water. Storage organs often grow underground, where they are better protected from attack by herbivores. Plants that have an underground storage organ are called geophytes in the Raunkiær plant life-form...

. The enlarged area of the root-tuber, or storage root, can be produced at the end or middle of a root or involve the entire root. It is thus different in origin but similar in function and appearance to a stem tuber. Examples of plants with notable tuberous roots include the sweet potato
Sweet potato
The sweet potato is a dicotyledonous plant that belongs to the family Convolvulaceae. Its large, starchy, sweet-tasting, tuberous roots are an important root vegetable. The young leaves and shoots are sometimes eaten as greens. Of the approximately 50 genera and more than 1,000 species of...

, cassava
Cassava
Cassava , also called yuca or manioc, a woody shrub of the Euphorbiaceae native to South America, is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, a major source of carbohydrates...

, yam
Yam (vegetable)
Yam is the common name for some species in the genus Dioscorea . These are perennial herbaceous vines cultivated for the consumption of their starchy tubers in Africa, Asia, Latin America and Oceania...

 and dahlia
Dahlia
Dahlia is a genus of bushy, tuberous, perennial plants native to Mexico, Central America, and Colombia. There are at least 36 species of dahlia, some like D. imperialis up to 10 metres tall. Dahlia hybrids are commonly grown as garden plants...

.

Root tubers are used to perennialize the plant, they store nutrients over periods when the plant can not actively grow, thus permitting survival from one year to the next.
The thickened roots are storage organs that differ from stem tubers. The massive enlargement of secondary roots typically represented by Sweet Potato (Ipomoea batatas), have the internal and external cell and tissue structures of a normal root, they produce adventitious roots and stems which again produce adventitious roots.

In root-tubers, there are no nodes and internodes or reduced leaves. Root tubers have one end called the proximal end, which is the end that was attached to the old plant; this end has crown tissue that produces buds which grow into new stems and foliage. The other end of the root tuber is called the distal end, and it normally produces unmodified roots. In stem tubers the order is reversed, with the distal end producing stems. Tuberous roots are biennial in duration, the first year the plant produces root-tubers, and at the end of the growing season, the plant often dies except for the newly generated tubers. The next growing season, the root-tubers produce a new plant. As the shoot(s) of the new plant grow, the stored reserves of the root-tuber are consumed in the production of new roots, stems, and in flowering; any remaining root tissue dies concurrently to the plants regeneration of next generation of root-tubers.

Hemerocallis fulva
Hemerocallis fulva
Hemerocallis fulva is a species of Hemerocallis, native to Asia from the Caucasus east through the Himalaya to China, Japan, Korea, and southeastern Russia.-Growth:...

plus a number of Daylily hybrids have large root-tubers, H. fulva spreads by underground stolons that end with a new fan that grows roots that produce thick root tubers and then send out more stolons.

Root tubers, along with other storage tissues that plants produce, are consumed by animals as a rich source of nutrients. The root-tubers of Arrowhead plants of the genus Sagittaria
Sagittaria
Sagittaria is a genus of about 30 species of aquatic plants whose members go by a variety of common names, including arrowhead, duck potato, iz-ze-kn, katniss, kuwai , swan potato, tule potato, and wapato...

are eaten by ducks.

Plants with root tubers are propagated in late summer to late winter by digging up the tubers and separating them, making sure that each piece has some crown tissue for replanting.

See also

  • Bulb
    Bulb
    A bulb is a short stem with fleshy leaves or leaf bases. The leaves often function as food storage organs during dormancy.A bulb's leaf bases, known as scales, generally do not support leaves, but contain food reserves to enable the plant to survive adverse conditions. At the center of the bulb is...

     – modified stems with a short fleshy vertical stem, covered by thick fleshy modified leaves that enclose a bud for the next season's growth.
  • Corm
    Corm
    A corm is a short, vertical, swollen underground plant stem that serves as a storage organ used by some plants to survive winter or other adverse conditions such as summer drought and heat ....

    – modified stems covered by dry scale-like leaves called a tunic, differing from true bulbs by having distinct nodes and internodes.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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