Root

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Primary and secondary roots in a cotton plant Primary and secondary cotton roots.jpg
Primary and secondary roots in a cotton plant
Root system of adult Araucaria heterophylla Profile of an adult Araucaria heterophylla with its roots system, Auckland-New Zealand, hand drawing Axel Aucouturier.jpg
Root system of adult Araucaria heterophylla

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. [1] 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.

Contents

Function

The root's major functions are absorption of water and plant nutrition and anchoring of the plant body to the ground. [2]

Anatomy

The cross-section of a barley root CSIRO ScienceImage 11626 Barley root.jpg
The cross-section of a barley root

Root morphology is divided into four zones: the root cap, the apical meristem, the elongation zone, and the hair. [3] The root cap of new roots helps the root penetrate the soil. These root caps are sloughed off as the root goes deeper creating a slimy surface that provides lubricant. The apical meristem behind the root cap produces new root cells that elongate. Then, root hairs form that absorb water and mineral nutrients from the soil. [4] The first root in seed producing plants is the radicle, which expands from the plant embryo after seed germination.

When dissected, the arrangement of the cells in a root is root hair, epidermis, epiblem, cortex, endodermis, pericycle and, lastly, the vascular tissue in the centre of a root to transport the water absorbed by the root to other places of the plant.[ clarification needed ]

Ranunculus Root Cross Section Ranunculus Root Cross Section.png
Ranunculus Root Cross Section

Perhaps the most striking characteristic of roots that distinguishes them from other plant organs such as stem-branches and leaves is that roots have an endogenous [5] origin, i.e., they originate and develop from an inner layer of the mother axis, such as pericycle. [6] In contrast, stem-branches and leaves are exogenous, i.e., they start to develop from the cortex, an outer layer.

In response to the concentration of nutrients, roots also synthesise cytokinin, which acts as a signal as to how fast the shoots can grow. Roots often function in storage of food and nutrients. The roots of most vascular plant species enter into symbiosis with certain fungi to form mycorrhizae, and a large range of other organisms including bacteria also closely associate with roots. [7]

Large, mature tree roots above the soil Kiental entre Herrsching y Andechs, Alemania 2012-05-01, DD 12.JPG
Large, mature tree roots above the soil

Root system architecture (RSA)

Tree roots at Cliffs of the Neuse State Park Tree Roots at Riverside.jpg
Tree roots at Cliffs of the Neuse State Park

Definition

In its simplest form, the term root system architecture (RSA) refers to the spatial configuration of a plant's root system. This system can be extremely complex and is dependent upon multiple factors such as the species of the plant itself, the composition of the soil and the availability of nutrients. [8] Root architecture plays the important role of providing a secure supply of nutrients and water as well as anchorage and support.

The configuration of root systems serves to structurally support the plant, compete with other plants and for uptake of nutrients from the soil. [9] Roots grow to specific conditions, which, if changed, can impede a plant's growth. For example, a root system that has developed in dry soil may not be as efficient in flooded soil, yet plants are able to adapt to other changes in the environment, such as seasonal changes. [9]

Terms and components

The main terms used to classify the architecture of a root system are: [10]

Branch magnitudeNumber of links (exterior or interior)
TopologyPattern of branching (Herringbone, Dichotomous, Radial)
Link lengthDistance between branches
Root angleRadial angle of a lateral root's base around the parent root's circumference, the angle of a lateral root from its parent root, and the angle an entire system spreads.
Link radiusDiameter of root

All components of the root architecture are regulated through a complex interaction between genetic responses and responses due to environmental stimuli. These developmental stimuli are categorised as intrinsic, the genetic and nutritional influences, or extrinsic, the environmental influences and are interpreted by signal transduction pathways. [11]

Extrinsic factors affecting root architecture include gravity, light exposure, water and oxygen, as well as the availability or lack of nitrogen, phosphorus, sulphur, aluminium and sodium chloride. The main hormones (intrinsic stimuli) and respective pathways responsible for root architecture development include:

Auxin Lateral root formation, maintenance of apical dominance and adventitious root formation.
Cytokinins Cytokinins regulate root apical meristem size and promote lateral root elongation.
Ethylene Promotes crown root formation.
Gibberellins Together with ethylene, they promote crown primordia growth and elongation. Together with auxin, they promote root elongation. Gibberellins also inhibit lateral root primordia initiation.

Growth

Roots of trees Root of a Tree.JPG
Roots of trees

Early root growth is one of the functions of the apical meristem located near the tip of the root. The meristem cells more or less continuously divide, producing more meristem, root cap cells (these are sacrificed to protect the meristem), and undifferentiated root cells. The latter become the primary tissues of the root, first undergoing elongation, a process that pushes the root tip forward in the growing medium. Gradually these cells differentiate and mature into specialized cells of the root tissues. [12]

Growth from apical meristems is known as primary growth, which encompasses all elongation. Secondary growth encompasses all growth in diameter, a major component of woody plant tissues and many nonwoody plants. For example, storage roots of sweet potato have secondary growth but are not woody. Secondary growth occurs at the lateral meristems, namely the vascular cambium and cork cambium. The former forms secondary xylem and secondary phloem, while the latter forms the periderm.[ citation needed ]

In plants with secondary growth, the vascular cambium, originating between the xylem and the phloem, forms a cylinder of tissue along the stem and root.[ citation needed ] The vascular cambium forms new cells on both the inside and outside of the cambium cylinder, with those on the inside forming secondary xylem cells, and those on the outside forming secondary phloem cells. As secondary xylem accumulates, the "girth" (lateral dimensions) of the stem and root increases. As a result, tissues beyond the secondary phloem including the epidermis and cortex, in many cases tend to be pushed outward and are eventually "sloughed off" (shed).[ citation needed ]

At this point, the cork cambium begins to form the periderm, consisting of protective cork cells. The walls of cork cells contains suberin thickenings, which is an extra cellular complex biopolymer. [13] The suberin thickenings functions by providing a physical barrier, protection against pathogens and by preventing water loss from the surrounding tissues. In addition, it also aids the process of wound healing in plants. [14] It is also postulated that suberin could be a component of the apoplastic barrier (present at the outer cell layers of roots) which prevents toxic compounds from entering the root and reduces radial oxygen loss (ROL) from the aerenchyma during waterlogging. [15] In roots, the cork cambium originates in the pericycle, a component of the vascular cylinder. [15]

The vascular cambium produces new layers of secondary xylem annually.[ citation needed ] The xylem vessels are dead at maturity but are responsible for most water transport through the vascular tissue in stems and roots.[ citation needed ]

Tree roots at Port Jackson Tree branches and roots.jpg
Tree roots at Port Jackson

Tree roots usually grow to three times the diameter of the branch spread, only half of which lie underneath the trunk and canopy. The roots from one side of a tree usually supply nutrients to the foliage on the same side. Some families however, such as Sapindaceae (the maple family), show no correlation between root location and where the root supplies nutrients on the plant. [16]

Regulation

There is a correlation of roots using the process of plant perception to sense their physical environment to grow, [17] including the sensing of light, [18] and physical barriers. Plants also sense gravity and respond through auxin pathways, [19] resulting in gravitropism. Over time, roots can crack foundations, snap water lines, and lift sidewalks. Research has shown that roots have ability to recognize 'self' and 'non-self' roots in same soil environment. [20]

The correct environment of air, mineral nutrients and water directs plant roots to grow in any direction to meet the plant's needs. Roots will shy or shrink away from dry [21] or other poor soil conditions.

Gravitropism directs roots to grow downward at germination, the growth mechanism of plants that also causes the shoot to grow upward. [22]

Research indicates that plant roots growing in search of productive nutrition can sense and avoid soil compaction through diffusion of the gas ethylene. [23]

Fluorescent imaging of an emerging lateral root. ArabidopsisLatRoot.jpg
Fluorescent imaging of an emerging lateral root.

Shade avoidance response

In order to avoid shade, plants utilize a shade avoidance response. When a plant is under dense vegetation, the presence of other vegetation nearby will cause the plant to avoid lateral growth and experience an increase in upward shoot, as well as downward root growth. In order to escape shade, plants adjust their root architecture, most notably by decreasing the length and amount of lateral roots emerging from the primary root. Experimentation of mutant variants of Arabidopsis thaliana found that plants sense the Red to Far Red light ratio that enters the plant through photoreceptors known as phytochromes. [24] Nearby plant leaves will absorb red light and reflect far- red light which will cause the ratio red to far red light to lower. The phytochrome PhyA that senses this Red to Far Red light ratio is localized in both the root system as well as the shoot system of plants, but through knockout mutant experimentation, it was found that root localized PhyA does not sense the light ratio, whether directly or axially, that leads to changes in the lateral root architecture. [24] Research instead found that shoot localized PhyA is the phytochrome responsible for causing these architectural changes of the lateral root. Research has also found that phytochrome completes these architectural changes through the manipulation of auxin distribution in the root of the plant. [24] When a low enough Red to Far Red ratio is sensed by PhyA, the phyA in the shoot will be mostly in its active form. [25] In this form, PhyA stabilize the transcription factor HY5 causing it to no longer be degraded as it is when phyA is in its inactive form. This stabilized transcription factor is then able to be transported to the roots of the plant through the phloem, where it proceeds to induce its own transcription as a way to amplify its signal. In the roots of the plant HY5 functions to inhibit an auxin response factor known as ARF19, a response factor responsible for the translation of PIN3 and LAX3, two well known auxin transporting proteins. [25] Thus, through manipulation of ARF19, the level and activity of auxin transporters PIN3 and LAX3 is inhibited. [25] Once inhibited, auxin levels will be low in areas where lateral root emergence normally occurs, resulting in a failure for the plant to have the emergence of the lateral root primordium through the root pericycle. With this complex manipulation of Auxin transport in the roots, lateral root emergence will be inhibited in the roots and the root will instead elongate downwards, promoting vertical plant growth in an attempt to avoid shade. [24] [25]

Research of Arabidopsis has led to the discovery of how this auxin mediated root response works. In an attempt to discover the role that phytochrome plays in lateral root development, Salisbury et al. (2007) worked with Arabidopsis thaliana grown on agar plates. Salisbury et al. used wild type plants along with varying protein knockout and gene knockout Arabidopsis mutants to observe the results these mutations had on the root architecture, protein presence, and gene expression. To do this, Salisbury et al. used GFP fluorescence along with other forms of both macro and microscopic imagery to observe any changes various mutations caused. From these research, Salisbury et al. were able to theorize that shoot located phytochromes alter auxin levels in roots, controlling lateral root development and overall root architecture. [24] In the experiments of van Gelderen et al. (2018), they wanted to see if and how it is that the shoot of Arabidopsis thaliana alters and affects root development and root architecture. To do this, they took Arabidopsis plants, grew them in agar gel, and exposed the roots and shoots to separate sources of light. From here, they altered the different wavelengths of light the shoot and root of the plants were receiving and recorded the lateral root density, amount of lateral roots, and the general architecture of the lateral roots. To identify the function of specific photoreceptors, proteins, genes, and hormones, they utilized various Arabidopsis knockout mutants and observed the resulting changes in lateral roots architecture. Through their observations and various experiments, van Gelderen et al. were able to develop a mechanism for how root detection of Red to Far-red light ratios alter lateral root development. [25]

Types

A true root system consists of a primary root and secondary roots (or lateral roots).

Specialized

Stilt roots of Maize plant Prop roots of Maize plant.jpg
Stilt roots of Maize plant
Roots forming above ground on a cutting of an Odontonema ("Firespike") Adventitious roots on Odontonema aka Firespike.jpg
Roots forming above ground on a cutting of an Odontonema ("Firespike")
Aerating roots of a mangrove Mangroves.jpg
Aerating roots of a mangrove
The growing tip of a fine root Root tip.JPG
The growing tip of a fine root
Aerial root Aerial root.jpg
Aerial root
The stilt roots of Socratea exorrhiza Socratea exorriza2002 03 12.JPG
The stilt roots of Socratea exorrhiza
Visible roots Visible roots.jpg
Visible roots

The roots, or parts of roots, of many plant species have become specialized to serve adaptive purposes besides the two primary functions[ clarification needed ], described in the introduction.

Depths

Cross section of a mango tree Exposed mango tree roots.jpg
Cross section of a mango tree

The distribution of vascular plant roots within soil depends on plant form, the spatial and temporal availability of water and nutrients, and the physical properties of the soil. The deepest roots are generally found in deserts and temperate coniferous forests; the shallowest in tundra, boreal forest and temperate grasslands. The deepest observed living root, at least 60 metres below the ground surface, was observed during the excavation of an open-pit mine in Arizona, USA. Some roots can grow as deep as the tree is high. The majority of roots on most plants are however found relatively close to the surface where nutrient availability and aeration are more favourable for growth. Rooting depth may be physically restricted by rock or compacted soil close below the surface, or by anaerobic soil conditions.

Records

Ficus Tree with buttress roots Tree roots2.jpg
Ficus Tree with buttress roots
SpeciesLocationMaximum rooting depth (m)References [29] [30]
Boscia albitrunca Kalahari desert68Jennings (1974)
Juniperus monosperma Colorado Plateau61Cannon (1960)
Eucalyptus sp.Australian forest61Jennings (1971)
Acacia erioloba Kalahari desert60Jennings (1974)
Prosopis juliflora Arizona desert53.3Phillips (1963)

Evolutionary history

The fossil record of roots—or rather, infilled voids where roots rotted after death—spans back to the late Silurian, about 430 million years ago. [31] Their identification is difficult, because casts and molds of roots are so similar in appearance to animal burrows. They can be discriminated using a range of features. [32] The evolutionary development of roots likely happened from the modification of shallow rhizomes (modified horizontal stems) which anchored primitive vascular plants combined with the development of filamentous outgrowths (called rhizoids) which anchored the plants and conducted water to the plant from the soil. [33]

Environmental interactions

Coralloid roots of Cycas revoluta Cycas revoluta coralloid roots.JPG
Coralloid roots of Cycas revoluta

Light has been shown to have some impact on roots, but its not been studied as much as the effect of light on other plant systems. Early research in the 1930s found that light decreased the effectiveness of Indole-3-acetic acid on adventitious root initiation. Studies of the pea in the 1950s shows that lateral root formation was inhibited by light, and in the early 1960s researchers found that light could induce positive gravitropic responses in some situations. The effects of light on root elongation has been studied for monocotyledonous and dicotyledonous plants, with the majority of studies finding that light inhibited root elongation, whether pulsed or continuous. Studies of Arabidopsis in the 1990s showed negative phototropism and inhibition of the elongation of root hairs in light sensed by phyB. [34]

Certain plants, namely Fabaceae, form root nodules in order to associate and form a symbiotic relationship with nitrogen-fixing bacteria called rhizobia. Owing to the high energy required to fix nitrogen from the atmosphere, the bacteria take carbon compounds from the plant to fuel the process. In return, the plant takes nitrogen compounds produced from ammonia by the bacteria. [35]

Soil temperature is a factor that effects root initiation and length. Root length is usually impacted more dramatically by temperature than overall mass, where cooler temperatures tend to cause more lateral growth because downward extension is limited by cooler temperatures at subsoil levels. Needs vary by plant species, but in temperate regions cool temperatures may limit root systems. Cool temperature species like oats, rapeseed, rye, wheat fare better in lower temperatures than summer annuals like maize and cotton. Researchers have found that plants like cotton develop wider and shorter taproots in cooler temperatures. The first root originating from the seed usually has a wider diameter than root branches, so smaller root diameters are expected if temperatures increase root initiation. Root diameter also decreases when the root elongates. [36]

Plant interactions

Plants can interact with one another in their environment through their root systems. Studies have demonstrated that plant-plant interaction occurs among root systems via the soil as a medium. Researchers have tested whether plants growing in ambient conditions would change their behavior if a nearby plant was exposed to drought conditions. [37] Since nearby plants showed no changes in stomatal aperture researchers believe the drought signal spread through the roots and soil, not through the air as a volatile chemical signal. [38]

Soil interactions

Soil microbiota can suppress both disease and beneficial root symbionts (mycorrhizal fungi are easier to establish in sterile soil). Inoculation with soil bacteria can increase internode extension, yield and quicken flowering. The migration of bacteria along the root varies with natural soil conditions. For example, research has found that the root systems of wheat seeds inoculated with Azotobacter showed higher populations in soils favorable to Azotobacter growth. Some studies have been unsuccessful in increasing the levels of certain microbes (such as P. fluorescens ) in natural soil without prior sterilization. [39]

Grass root systems are beneficial at reducing soil erosion by holding the soil together. Perennial grasses that grow wild in rangelands contribute organic matter to the soil when their old roots decay after attacks by beneficial fungi, protozoa, bacteria, insects and worms release nutrients. [4]

Scientists have observed significant diversity of the microbial cover of roots at around 10 percent of three week old root segments covered. On younger roots there was even low coverage, but even on 3-month-old roots the coverage was only around 37%. Before the 1970s, scientists believed that the majority of the root surface was covered by microorganisms. [4]

Nutrient absorption

Researchers studying maize seedlings found that calcium absorption was greatest in the apical root segment, and potassium at the base of the root. Along other root segments absorption was similar. Absorbed potassium is transported to the root tip, and to a lesser extent other parts of the root, then also to the shoot and grain. Calcium transport from the apical segment is slower, mostly transported upward and accumulated in stem and shoot. [40]

Researchers found that partial deficiencies of K or P did not change the fatty acid composition of phosphatidyl choline in Brassica napus L. plants. Calcium deficiency did, on the other hand, lead to a marked decline of polyunsaturated compounds that would be expected to have negative impacts for integrity of the plant membrane, that could effect some properties like its permeability, and is needed for the ion uptake activity of the root membranes. [41]

Economic importance

Roots can also protect the environment by holding the soil to reduce soil erosion Roots and Soil Erosion.jpg
Roots can also protect the environment by holding the soil to reduce soil erosion

The term root crops refers to any edible underground plant structure, but many root crops are actually stems, such as potato tubers. Edible roots include cassava, sweet potato, beet, carrot, rutabaga, turnip, parsnip, radish, yam and horseradish. Spices obtained from roots include sassafras, angelica, sarsaparilla and licorice.

Sugar beet is an important source of sugar. Yam roots are a source of estrogen compounds used in birth control pills. The fish poison and insecticide rotenone is obtained from roots of Lonchocarpus spp. Important medicines from roots are ginseng, aconite, ipecac, gentian and reserpine. Several legumes that have nitrogen-fixing root nodules are used as green manure crops, which provide nitrogen fertilizer for other crops when plowed under. Specialized bald cypress roots, termed knees, are sold as souvenirs, lamp bases and carved into folk art. Native Americans used the flexible roots of white spruce for basketry.

Tree roots can heave and destroy concrete sidewalks and crush or clog buried pipes. [42] The aerial roots of strangler fig have damaged ancient Mayan temples in Central America and the temple of Angkor Wat in Cambodia.

Trees stabilize soil on a slope prone to landslides. The root hairs work as an anchor on the soil.

Vegetative propagation of plants via cuttings depends on adventitious root formation. Hundreds of millions of plants are propagated via cuttings annually including chrysanthemum, poinsettia, carnation, ornamental shrubs and many houseplants.

Roots can also protect the environment by holding the soil to reduce soil erosion. This is especially important in areas such as sand dunes.

Roots on onion bulbs OnionBulbRoots.jpg
Roots on onion bulbs

See also

Related Research Articles

Vascular cambium Main growth tissue in the stems, roots of plants

The vascular cambium is the main growth tissue in the stems and roots of many plants, specifically in dicots such as buttercups and oak trees, gymnosperms such as pine trees, as well as in certain other vascular plants. It produces secondary xylem inwards, towards the pith, and secondary phloem outwards, towards the bark.

Meristem Type of plant tissue involved in cell proliferation

The meristem is a type of tissue found in plants. It consists of undifferentiated cells capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells continue to divide until a time when they get differentiated and then lose the ability to divide.

Plant hormone Chemical compounds that regulate plant growth and development

Plant hormones are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from embryogenesis, the regulation of organ size, pathogen defense, stress tolerance and through to reproductive development. Unlike in animals each plant cell is capable of producing hormones. Went and Thimann coined the term "phytohormone" and used it in the title of their 1937 book.

Auxin Plant hormone

Auxins are a class of plant hormones with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essential for plant body development. The Dutch biologist Frits Warmolt Went first described auxins and their role in plant growth in the 1920s. Kenneth V. Thimann became the first to isolate one of these phytohormones and to determine its chemical structure as indole-3-acetic acid (IAA). Went and Thimann co-authored a book on plant hormones, Phytohormones, in 1937.

Cytokinin Class of plant hormones promoting cell division

Cytokinins (CK) are a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots. They are involved primarily in cell growth and differentiation, but also affect apical dominance, axillary bud growth, and leaf senescence.

Coleoptile Protective sheath in certain plants

Coleoptile is the pointed protective sheath covering the emerging shoot in monocotyledons such as grasses in which few leaf primordia and shoot apex of monocot embryo remain enclosed. The coleoptile protects the first leaf as well as the growing stem in seedlings and eventually, allows the first leaf to emerge. Coleoptiles have two vascular bundles, one on either side. Unlike the flag leaves rolled up within, the pre-emergent coleoptile does not accumulate significant protochlorophyll or carotenoids, and so it is generally very pale. Some preemergent coleoptiles do, however, accumulate purple anthocyanin pigments.

Casparian strip Thickening in the root endodermis of vascular plants

The Casparian strip is a band-like thickening in the center of the root endodermis of vascular plants. The composition of the region is mainly lignin, and its width varies between species. The Casparian strip is impervious to water so can control the transportation of water and inorganic salts between the cortex and the vascular bundle, preventing water and inorganic salts from being transported to the stele through the apoplast, so that it must enter the cell membrane and move to the stele through the symplastic pathway, blocking the internal and external objects of the cell. The function and function of mass transportation are similar to that of animal tissues.. The development of the Casparian strip is regulated by transcription factors such as SHORT-ROOT (SHR), SCARECROW (SCR) and MYB36, as well as polypeptide hormone synthesised by midcolumn cells.

Gravitropism

Gravitropism is a coordinated process of differential growth by a plant in response to gravity pulling on it. It also occurs in fungi. Gravity can be either "artificial gravity" or natural gravity. It is a general feature of all higher and many lower plants as well as other organisms. Charles Darwin was one of the first to scientifically document that roots show positive gravitropism and stems show negative gravitropism. That is, roots grow in the direction of gravitational pull and stems grow in the opposite direction. This behavior can be easily demonstrated with any potted plant. When laid onto its side, the growing parts of the stem begin to display negative gravitropism, growing upwards. Herbaceous (non-woody) stems are capable of a degree of actual bending, but most of the redirected movement occurs as a consequence of root or stem growth outside. The mechanism is based on the Cholodny–Went model which was proposed in 1927, and has since been modified. Although the model has been criticized and continues to be refined, it has largely stood the test of time.

The pericycle is a cylinder of parenchyma or sclerenchyma cells that lies just inside the endodermis and is the outer most part of the stele of plants.

Vascular tissue Conducting tissue in vascular plants

Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue: the vascular cambium and the cork cambium. All the vascular tissues within a particular plant together constitute the vascular tissue system of that plant.

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.

Primordium Organ in the earliest recognizable stage of embryonic development

A primordium in embryology, is an organ or tissue in its earliest recognizable stage of development. Cells of the primordium are called primordial cells. A primordium is the simplest set of cells capable of triggering growth of the would-be organ and the initial foundation from which an organ is able to grow. In flowering plants, a floral primordium gives rise to a flower.

Lateral root Plant root

Lateral roots, emerging from the pericycle, extend horizontally from the primary root (radicle) and over time makeup the iconic branching pattern of root systems. They contribute to anchoring the plant securely into the soil, increasing water uptake, and facilitates the extraction of nutrients required for the growth and development of the plant. Lateral roots increase the surface area of a plant's root system and can be found in great abundance in several plant species. In some cases, lateral roots have been found to form symbiotic relationships with rhizobia (bacteria) and mycorrhizae (fungi) found in the soil, to further increase surface area and increase nutrient uptake.

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.

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.

Plant tissue culture is a collection of techniques used to maintain or grow plant cells, tissues or organs under sterile conditions on a nutrient culture medium of known composition. It is widely used to produce clones of a plant in a method known as micropropagation. Different techniques in plant tissue culture may offer certain advantages over traditional methods of propagation, including:

Phototropism Phototropism is the growth of an plant in response to a light stimulus

Phototropism is the growth of an organism in response to a light stimulus. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light contain a hormone called auxin that reacts when phototropism occurs. This causes the plant to have elongated cells on the furthest side from the light. Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Growth towards a light source is called positive phototropism, while growth away from light is called negative phototropism. Negative phototropism is not to be confused with skototropism which is defined as the growth towards darkness, whereas negative phototropism can refer to either the growth away from a light source or towards the darkness. Most plant shoots exhibit positive phototropism, and rearrange their chloroplasts in the leaves to maximize photosynthetic energy and promote growth. Some vine shoot tips exhibit negative phototropism, which allows them to grow towards dark, solid objects and climb them. The combination of phototropism and gravitropism allow plants to grow in the correct direction.

Biomass partitioning is the process by which plants divide their energy among their leaves, stems, roots, and reproductive parts. These four main components of the plant have important morphological roles: leaves take in CO2 and energy from the sun to create carbon compounds, stems grow above competitors to reach sunlight, roots absorb water and mineral nutrients from the soil while anchoring the plant, and reproductive parts facilitate the continuation of species. Plants partition biomass in response to limits or excesses in resources like sunlight, carbon dioxide, mineral nutrients, and water and growth is regulated by a constant balance between the partitioning of biomass between plant parts. An equilibrium between root and shoot growth occurs because roots need carbon compounds from photosynthesis in the shoot and shoots need nitrogen absorbed from the soil by roots. Allocation of biomass is put towards the limit to growth; a limit below ground will focus biomass to the roots and a limit above ground will favor more growth in the shoot.

A canopy root, also known as an arboreal root, is a type of root that grows out of a tree branch underneath an epiphytic mat. These adventitious roots form in response to moist, dark, nutrient-rich conditions that are found in “canopy soils”. Canopy roots have been found in species of maple, poplar, alder, myrtle, beech, and spruce, among many others. They are structurally similar to roots found on the forest floor and likely serve a similar purpose for water and nutrient uptake, though their specific functions are still being studied.

Phenotypic plasticity is the ability of an individual organism to alter its behavior, morphology and physiology in response to changes in environmental conditions. Root phenotypic plasticity enables plants to adapt to an array of biotic and abiotic constraints that limit plant productivity. Even though the exploitation of soil resources through root activity is energetically costly, natural selection favors plants that can direct root activity to exploit efficiently the heterogeneous distribution of soil resources.

References

  1. Harley Macdonald & Donovan Stevens (3 September 2019). Biotechnology and Plant Biology. EDTECH. pp. 141–. ISBN   978-1-83947-180-3.
  2. "Plant parts=Roots". University of Illinois Extension.
  3. Yaacov Okon (24 November 1993). Azospirillum/Plant Associations. CRC Press. pp. 77–. ISBN   978-0-8493-4925-6.
  4. 1 2 3 "Backyard Gardener: Understanding Plant Roots". University of Arizona Cooperative Extension.
  5. Gangulee HC, Das KS, Datta CT, Sen S. College Botany. Vol. 1. Kolkata: New Central Book Agency.
  6. Dutta AC, Dutta TC. BOTANY For Degree Students (6th ed.). Oxford University Press.
  7. Sheldrake, Merlin (2020). Entangled Life. Bodley Head. p. 148. ISBN   978-1847925206.
  8. Malamy JE (2005). "Intrinsic and environmental response pathways that regulate root system architecture". Plant, Cell & Environment. 28 (1): 67–77. doi: 10.1111/j.1365-3040.2005.01306.x . PMID   16021787.
  9. 1 2 Caldwell MM, Dawson TE, Richards JH (January 1998). "Hydraulic lift: consequences of water efflux from the roots of plants". Oecologia. 113 (2): 151–161. Bibcode:1998Oecol.113..151C. doi:10.1007/s004420050363. PMID   28308192. S2CID   24181646.
  10. Fitter AH (1991). "The ecological significance of root system architecture: an economic approach". In Atkinson D (ed.). Plant Root Growth: An Ecological Perspective. Blackwell. pp. 229–243.
  11. Malamy JE, Ryan KS (November 2001). "Environmental regulation of lateral root initiation in Arabidopsis". Plant Physiology. 127 (3): 899–909. doi:10.1104/pp.010406. PMC   129261 . PMID   11706172.
  12. Russell PJ, Hertz PE, McMillan B (2013). Biology: The Dynamic Science. Cengage Learning. p. 750. ISBN   978-1-285-41534-5. Archived from the original on 2018-01-21. Retrieved 2017-04-24.
  13. "Suberin – an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2021-08-31.
  14. "Suberin Form & Function – Mark Bernards – Western University". www.uwo.ca. Retrieved 2021-08-31.
  15. 1 2 Watanabe, Kohtaro; Nishiuchi, Shunsaku; Kulichikhin, Konstantin; Nakazono, Mikio (2013). "Does suberin accumulation in plant roots contribute to waterlogging tolerance?". Frontiers in Plant Science. 4: 178. doi: 10.3389/fpls.2013.00178 . ISSN   1664-462X. PMC   3683634 . PMID   23785371.
  16. van den Driessche, R. (1974-07-01). "Prediction of mineral nutrient status of trees by foliar analysis". The Botanical Review. 40 (3): 347–394. doi:10.1007/BF02860066. ISSN   1874-9372. S2CID   29919924 via Springer.
  17. Nakagawa Y, Katagiri T, Shinozaki K, Qi Z, Tatsumi H, Furuichi T, et al. (February 2007). "Arabidopsis plasma membrane protein crucial for Ca2+ influx and touch sensing in roots". Proceedings of the National Academy of Sciences of the United States of America. 104 (9): 3639–44. Bibcode:2007PNAS..104.3639N. doi: 10.1073/pnas.0607703104 . PMC   1802001 . PMID   17360695.
  18. UV-B light sensing mechanism discovered in plant roots, San Francisco State University, December 8, 2008
  19. Marchant A, Kargul J, May ST, Muller P, Delbarre A, Perrot-Rechenmann C, Bennett MJ (April 1999). "AUX1 regulates root gravitropism in Arabidopsis by facilitating auxin uptake within root apical tissues". The EMBO Journal. 18 (8): 2066–73. doi:10.1093/emboj/18.8.2066. PMC   1171291 . PMID   10205161.
  20. Hodge A (June 2009). "Root decisions". Plant, Cell & Environment. 32 (6): 628–40. doi: 10.1111/j.1365-3040.2008.01891.x . PMID   18811732.
  21. Carminati A, Vetterlein D, Weller U, Vogel H, Oswald SE (2009). "When roots lose contact". Vadose Zone Journal. 8 (3): 805–809. doi:10.2136/vzj2008.0147. S2CID   128600212.
  22. Chen R, Rosen E, Masson PH (June 1999). "Gravitropism in higher plants". Plant Physiology. 120 (2): 343–50. doi:10.1104/pp.120.2.343. PMC   1539215 . PMID   11541950.
  23. Pandey, Bipin K.; Huang, Guoqiang; Bhosale, Rahul; Hartman, Sjon; Sturrock, Craig J.; Jose, Lottie; Martin, Olivier C.; Karady, Michal; Voesenek, Laurentius A. C. J.; Ljung, Karin; Lynch, Jonathan P. (2021-01-15). "Plant roots sense soil compaction through restricted ethylene diffusion". Science. 371 (6526): 276–280. Bibcode:2021Sci...371..276P. doi:10.1126/science.abf3013. ISSN   0036-8075. PMID   33446554. S2CID   231606782.
  24. 1 2 3 4 5 Salisbury FJ, Hall A, Grierson CS, Halliday KJ (May 2007). "Phytochrome coordinates Arabidopsis shoot and root development". The Plant Journal. 50 (3): 429–38. doi: 10.1111/j.1365-313x.2007.03059.x . PMID   17419844.
  25. 1 2 3 4 5 van Gelderen K, Kang C, Paalman R, Keuskamp D, Hayes S, Pierik R (January 2018). "Far-Red Light Detection in the Shoot Regulates Lateral Root Development through the HY5 Transcription Factor". The Plant Cell. 30 (1): 101–116. doi:10.1105/tpc.17.00771. PMC   5810572 . PMID   29321188.
  26. 1 2 Nowak EJ, Martin CE (1997). "Physiological and anatomical responses to water deficits in the CAM epiphyte Tillandsia ionantha (Bromeliaceae)". International Journal of Plant Sciences. 158 (6): 818–826. doi:10.1086/297495. hdl: 1808/9858 . JSTOR   2475361. S2CID   85888916.
  27. Nadkarni NM (November 1981). "Canopy roots: convergent evolution in rainforest nutrient cycles". Science. 214 (4524): 1023–4. Bibcode:1981Sci...214.1023N. doi:10.1126/science.214.4524.1023. PMID   17808667. S2CID   778003.
  28. Pütz N (2002). "Contractile roots". In Waisel Y., Eshel A., Kafkafi U. (eds.). Plant roots: The hidden half (3rd ed.). New York: Marcel Dekker. pp. 975–987.
  29. Canadell J, Jackson RB, Ehleringer JB, Mooney HA, Sala OE, Schulze ED (December 1996). "Maximum rooting depth of vegetation types at the global scale". Oecologia. 108 (4): 583–595. Bibcode:1996Oecol.108..583C. doi:10.1007/BF00329030. PMID   28307789. S2CID   2092130.
  30. Stonea EL, Kaliszb PJ (1 December 1991). "On the maximum extent of tree roots". Forest Ecology and Management. 46 (1–2): 59–102. doi:10.1016/0378-1127(91)90245-Q.
  31. Retallack GJ (1986). "The fossil record of soils" (PDF). In Wright VP (ed.). Paleosols: their Recognition and Interpretation. Oxford: Blackwell. pp. 1–57. Archived (PDF) from the original on 2017-01-07.
  32. Hillier R, Edwards D, Morrissey LB (2008). "Sedimentological evidence for rooting structures in the Early Devonian Anglo–Welsh Basin (UK), with speculation on their producers". Palaeogeography, Palaeoclimatology, Palaeoecology. 270 (3–4): 366–380. Bibcode:2008PPP...270..366H. doi:10.1016/j.palaeo.2008.01.038.
  33. Amram Eshel; Tom Beeckman (17 April 2013). Plant Roots: The Hidden Half, Fourth Edition. CRC Press. pp. 1–. ISBN   978-1-4398-4649-0.
  34. Kurata, Tetsuya (1997). "Light-stimulated root elongation in Arabidopsis thaliana". Journal of Plant Physiology. 151 (3): 345–351. doi:10.1016/S0176-1617(97)80263-5. hdl: 2115/44841 .
  35. Postgate, J. (1998). Nitrogen Fixation (3rd ed.). Cambridge, UK: Cambridge University Press.
  36. Encyclopedia of Soil Science
  37. Chamovitz, Daniel. (21 November 2017). What a plant knows : a field guide to the senses. ISBN   9780374537128. OCLC   1041421612.
  38. Falik O, Mordoch Y, Ben-Natan D, Vanunu M, Goldstein O, Novoplansky A (July 2012). "Plant responsiveness to root-root communication of stress cues". Annals of Botany. 110 (2): 271–80. doi:10.1093/aob/mcs045. PMC   3394639 . PMID   22408186.
  39. Bowen GD, Rovira AD (1976). "Microbial Colonization of Plant Roots". Annu. Rev. Phytopathol. 14: 121–144. doi:10.1146/annurev.py.14.090176.001005.
  40. Plant Roots and their Environment. Elsevier. 1988. p. 17.
  41. Plant Roots and their Environment. Elsevier. 1988. p. 25.
  42. Zahniser, David (February 21, 2008) "City to pass the bucks on sidewalks?" Archived 2015-04-17 at the Wayback Machine Los Angeles Times

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