Tuber

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Ulluku (Ullucus tuberosus) tubers Ullucus tuberosus (South Peru).jpg
Ulluku ( Ullucus tuberosus ) tubers

Tubers are enlarged structures used as storage organs for nutrients in some plants. They are used for the plant's perennation (survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing season, and as a means of asexual reproduction. [1] Stem tubers form thickened rhizomes (underground stems) or stolons (horizontal connections between organisms); well known species with stem tubers include the potato and yam. Some writers also treat modified lateral roots (root tubers) under the definition; these are found in sweet potatoes, cassava, and dahlias.

Contents

Terminology

The term originates from the Latin tuber, meaning "lump, bump, swelling". [2]

Some writers define the term "tuber" to mean only structures derived from stems; [3] others use the term for structures derived from stems or roots. [4]

Stem tubers

A stem tuber forms from thickened rhizomes or stolons. The top sides of the tuber produce shoots that grow into typical stems and leaves and the undersides produce roots. They tend to form at the sides of the parent plant and are most often located near the soil surface. The underground 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 (initiated below ground) rhizome. In the autumn the plant dies, except for the new offspring tubers, which have one dominant bud that 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 that act like seeds, producing small plants that resemble (in morphology and size) seedlings. Some stem tubers are long-lived, such as those of tuberous begonias, but many 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.

Flowers and tuber of Anredera cordifolia Starr 010725-9001 Anredera cordifolia.jpg
Flowers and tuber of Anredera cordifolia

Stem tubers generally start off as enlargements of the hypocotyl section of a seedling, but sometimes also include the first node or two of the epicotyl and the upper section of the root. The 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 tuber has an oblong rounded shape.

Tuberous begonias, yams, [5] [6] and cyclamens are commonly grown stem tubers. Mignonette vine ( Anredera cordifolia ) produces aerial stem tubers on 3.5-to-7.5-metre-tall (12 to 25 ft) vines; the tubers fall to the ground and grow. Plectranthus esculentus , of the mint family Lamiaceae, produces tuberous underground organs from the base of the stem, weighing up to 1.8 kg (3 lb 15 oz) per tuber, forming from axillary buds producing short stolons that grow into tubers. [7] Even though legumes are not commonly associated with forming stem tubers, Lathyrus tuberosus is an example native to Asia and Europe, where it was once grown as a crop. [8]

Potatoes

Potato plant with revealed tubers Amflora-Feldzerstorung Juli 2010.jpg
Potato plant with revealed tubers

Potatoes are stem tubers enlarged stolons thicken to develop into storage organs. [9] [10] [11] 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 tubers, and thus show the same apical dominance as a normal stem. Internally, a tuber is filled with starch stored in enlarged parenchyma-like cells. The inside of a 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 perennate the plant and as a means of propagation. When fall comes, the above-ground structure of the plant dies, but the tubers survive underground over winter until spring, when they regenerate new shoots that 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, which is involved in the control of potato tuber development.

The stolons are easily recognized when potato plants are grown from seeds. 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. Planting the pieces deeper creates 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

Freshly dug sweet potato plants with tubers Ipomoea batatasL ja01.jpg
Freshly dug sweet potato plants with tubers

A tuberous root or storage root is a modified lateral root, enlarged to function as a storage organ. The enlarged area of the tuber 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. Plants with tuberous roots include the sweet potato (Ipomoea batatas), cassava, and dahlia.

Root tubers are perennating organs, thickened roots that store nutrients over periods when the plant cannot actively grow, thus permitting survival from one year to the next. The massive enlargement of secondary roots typically represented by sweet potato have the internal and external cell and tissue structures of a normal root; they produce adventitious roots and stems, which again produce adventitious roots. [12]

In root tubers, there are no nodes and internodes or reduced leaves. The proximal end of the tuber, which was attached to the old plant, has crown tissue that produces buds which grow into new stems and foliage. [13] The distal end of the tuber normally produces unmodified roots. In stem tubers the order is reversed, with the distal end producing stems. Tuberous roots are biennial in duration: the plant produces tubers the first year, and at the end of the growing season, the shoots often die, leaving the newly generated tubers; the next growing season, the tubers produce new shoots. As the shoots of the new plant grow, the stored reserves of the tuber are consumed in the production of new roots, stems, and reproductive organs; any remaining root tissue dies concurrently to the plant's regeneration of the next generation of tubers.

Hemerocallis roots showing tuberous enlargement Hem Root.jpg
Hemerocallis roots showing tuberous enlargement

The Hemerocallis fulva daylily and a number of daylily hybrids have large root tubers; H. fulva spreads by underground stolons [14] that end with a new fan that grows roots that produce thick tubers and then send out more stolons. [8] [15]

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 are eaten by ducks. [16]

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

Related Research Articles

Root Part of a plant

In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the surface of the soil, but roots can also be aerial or aerating, that is, growing up above the ground or especially above water.

Rhizome Underground stem in which various plants asexually reproduce via budding

In botany and dendrology, a rhizome is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow horizontally. The rhizome also retains the ability to allow new shoots to grow upwards.

Root vegetable Plant root used as a vegetable

Root vegetables are underground plant parts eaten by humans as food. Although botany distinguishes true roots from non-roots, the term "root vegetable" is applied to all these types in agricultural and culinary usage.

Vegetative reproduction Asexual methods of reproduction

Vegetative reproduction is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or specialized reproductive structures, which are sometimes called vegetative propagules.

Corm Underground plant stem

A corm, bulbo-tuber, or bulbotuber is a short, vertical, swollen underground plant stem that serves as a storage organ that some plants use to survive winter or other adverse conditions such as summer drought and heat (perennation).

Clonal colony Genetically identical, single site plants, fungi, or bacteria

A clonal colony or genet is a group of genetically identical individuals, such as plants, fungi, or bacteria, that have grown in a given location, all originating vegetatively, not sexually, from a single ancestor. In plants, an individual in such a population is referred to as a ramet. In fungi, "individuals" typically refers to the visible fruiting bodies or mushrooms that develop from a common mycelium which, although spread over a large area, is otherwise hidden in the soil. Clonal colonies are common in many plant species. Although many plants reproduce sexually through the production of seed, reproduction occurs by underground stolons or rhizomes in some plants. Above ground, these plants most often appear to be distinct individuals, but underground they remain interconnected and are all clones of the same plant. However, it is not always easy to recognize a clonal colony especially if it spreads underground and is also sexually reproducing.

Aerial root Root which grows above the ground

Aerial roots are roots above the ground. They are almost always adventitious. They are found in diverse plant species, including epiphytes such as orchids (Orchidaceae), tropical coastal swamp trees such as mangroves, banyan figs, the warm-temperate rainforest rata, and pohutukawa trees of New Zealand. Vines such as Common Ivy and poison ivy also have aerial roots.

A storage organ is a part of a plant specifically modified for storage of energy (generally in the form of carbohydrates) 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 classification system. Storage organs often, but not always, act as perennating organs which enable plants to survive adverse conditions.

Stolon Horizontal connections between organisms

In biology, stolons, also known as runners, are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external skeletons.

Fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning, where an organism is split into fragments. Each of these fragments develop into mature, fully grown individuals that are clones of the original organism.

Edible plant stems are one part of plants that are eaten by humans. Most plants are made up of stems, roots, leaves, flowers, and produce fruits containing seeds. Humans most commonly eat the seeds, fruit, flowers, leaves, roots, and stems (e.g. [asparagus] of many plants. There are also a few edible petioles such as celery or rhubarb.

Secondary growth Type of growth in plants

In botany, secondary growth is the growth that results from cell division in the cambia or lateral meristems and that causes the stems and roots to thicken, while primary growth is growth that occurs as a result of cell division at the tips of stems and roots, causing them to elongate, and gives rise to primary tissue. Secondary growth occurs in most seed plants, but monocots usually lack secondary growth. If they do have secondary growth, it differs from the typical pattern of other seed plants.

Basal shoot

Basal shoots, root sprouts, adventitious shoots, and suckers are words for various kinds of shoots that grow from adventitious buds on the base of a tree or shrub, or from adventitious buds on its roots. Shoots that grow from buds on the base of a tree or shrub are called basal shoots; these are distinguished from shoots that grow from adventitious buds on the roots of a tree or shrub, which may be called root sprouts or suckers. A plant that produces root sprouts or runners is described as surculose. Water sprouts produced by adventitious buds may occur on the above-ground stem, branches or both of trees and shrubs. Suckers are shoots arising underground from the roots some distance from the base of a tree or shrub.

Plant reproduction is the production of new offspring in plants, which can be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from either parent. Asexual reproduction produces new individuals without the fusion of gametes. The resulting clonal plants are genetically identical to the parent plant and each other, unless mutations occur.

Underground stems are modified plants that derive from stem tissue but exist under the soil surface. They function as storage tissues for food and nutrients, propagation of new clones, and perennation. Types include bulbs, corms, rhizomes, stolons, and tubers.

This page provides a glossary of plant morphology. Botanists and other biologists who study plant morphology use a number of different terms to classify and identify plant organs and parts that can be observed using no more than a handheld magnifying lens. This page provides help in understanding the numerous other pages describing plants by their various taxa. The accompanying page—Plant morphology—provides an overview of the science of the external form of plants. There is also an alphabetical list: Glossary of botanical terms. In contrast, this page deals with botanical terms in a systematic manner, with some illustrations, and organized by plant anatomy and function in plant physiology.

Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. By contrast, an animal embryo will very early produce all of the body parts that it will ever have in its life. When the animal is born, it has all its body parts and from that point will only grow larger and more mature. However, both plants and animals pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.

This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary of leaf morphology. For other related terms, see Glossary of phytopathology and List of Latin and Greek words commonly used in systematic names.

Plant stem Structural axis of a vascular plant

A stem is one of two main structural axes of a vascular plant, the other being the root. It supports leaves, flowers and fruits, transports water and dissolved substances between the roots and the shoots in the xylem and phloem, stores nutrients, and produces new living tissue.

Ornamental bulbous plant Herbaceous perennials with underground storage parts grown for ornamental purposes

Ornamental bulbous plants, often called ornamental bulbs or just bulbs in gardening and horticulture, are herbaceous perennials grown for ornamental purposes, which have underground or near ground storage organs. Botanists distinguish between true bulbs, corms, rhizomes, tubers and tuberous roots, any of which may be termed "bulbs" in horticulture. Bulb species usually lose their upper parts during adverse conditions such as summer drought and heat or winter cold. The bulb's storage organs contain moisture and nutrients that are used to survive these adverse conditions in a dormant state. When conditions become favourable the reserves sustain a new growth cycle. In addition, bulbs permit vegetative or asexual multiplication in these species. Ornamental bulbs are used in parks and gardens and as cut flowers.

References

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