Callus (cell biology)
Encyclopedia
Plant callus is a mass of undifferentiated cells derived from plant tissue (explants) for use in biological research and biotechnology. In plant biology, callus cells are those cells that cover a plant wound. To induce callus formation, plant tissues are surface sterilized and then plated onto in vitro tissue culture medium. Plant hormones, such as auxin
s, cytokinin
s, and gibberellin
s, are supplemented into the medium to initiate callus formation or somatic embryogenesis
. Callus tissue initiation has been described for a number of plant taxonomic divisions:
s for the given cell type. There are several types of basal salt mixtures used in plant tissue culture, but most notably modified Murashige and Skoog medium
, White's medium, and woody plant medium. Vitamins are also provided to enhance growth such as Gamborg B5 vitamins. For plant cells, enrichment with nitrogen
, phosphorus
, and potassium
is especially important.
tissues. The tissues used to initiate callus formation depends on plant species and which tissues are available for explant culture
. The cells that give rise to callus and somatic embryos usually undergo rapid division or are partially undifferentiated such as meristem
atic tissue. In alfalfa, Medicago truncatula
, however callus and somatic embryos are derived from mesophyll cells that undergo dedifferentiation. Plant hormones are used to initiate callus growth. Specific auxin
to cytokinin
ratios in plant tissue culture medium give rise to an unorganized growing and dividing mass of callus cells. Callus cultures are often broadly classified as being either compact or friable. Friable calluses fall apart easily, and can be used to generate cell suspension cultures. Callus can directly undergo direct organogenesis
and/or embryogenesis
where the cells will form an entirely new plant. Callus can brown and die during culture, but the causes for callus browning are not well understood. In Jatropha curcas
callus cells, small organized callus cells became disorganized and varied in size after browning occurred. Browning has also been associated with oxidation and phenolic compounds in both explant tissues and explant secretions.
Plant calli can differentiate into a whole plant, a process called regeneration, through addition of plant hormones in culture medium. This ability is known as totipotency. Regeneration of a whole plant from a single cell allows researchers to recover whole plants that have a copy of the transgene in every cell. Regeneration of a whole plant that has some genetically transformed cells and some untransformed cells is called a chimera
. In general, chimeras are not useful for genetic research or agricultural applications.
Genes can be inserted into callus cells using biolistic bombardment, also known as a gene gun
, or Agrobacterium tumefaciens
. Cells that receive the gene of interest can then be recovered into whole plants using a combination of plant hormone
s. The whole plants that are recovered can be used for experiment to determine gene function(s), or to enhance crop plant traits for modern agriculture.
Callus tissue is of particular use in micropropagation
where it can be used to grow genetically identical copies of plants with desirable characteristics.
Henri-Louis Duhamel du Monceau
investigated wound-healing responses in elm trees, and was the first to report formation of callus tissue on live plants.
In 1908, E. F. Simon was able to induce callus from poplar stems that also produced roots and buds. The first reports of callus induction in vitro came from three independent researchers in 1939. P. White induced callus derived from tumor-developing procambial tissues of hybrid Nicotiana glauca
that did not require hormone supplementation. Gautheret and Nobecourt were able to maintain callus cultures of carrot using auxin hormone additions.
Auxin
Auxins are a class of plant hormones with some morphogen-like characteristics. Auxins have a cardinal role in coordination of many growth and behavioral processes in the plant's life cycle and are essential for plant body development. Auxins and their role in plant growth were first described by...
s, cytokinin
Cytokinin
Cytokinins are a class of plant growth substances 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...
s, and gibberellin
Gibberellin
Gibberellins are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence....
s, are supplemented into the medium to initiate callus formation or somatic embryogenesis
Somatic Embryogenesis
Somatic embryos are mainly produced in vitro and for laboratory purposes, using either solid or liquid nutrient media which contain plant growth regulators . The main PGRs used are auxins but can contain cytokinin in a smaller amount. Somatic embryogenesis is a process where a plant or embryo is...
. Callus tissue initiation has been described for a number of plant taxonomic divisions:
- MarchantiophytaMarchantiophytaThe Marchantiophyta are a division of bryophyte plants commonly referred to as hepatics or liverworts. Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information....
- Anthocerotophyta
- BryophytaMossMosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
- LycopodiophytaLycopodiophytaThe Division Lycopodiophyta is a tracheophyte subdivision of the Kingdom Plantae. It is the oldest extant vascular plant division at around 410 million years old, and includes some of the most "primitive" extant species...
- Pteridophyta
- Cycadophyta
- Ginkophyta
- PinophytaPinophytaThe conifers, division Pinophyta, also known as division Coniferophyta or Coniferae, are one of 13 or 14 division level taxa within the Kingdom Plantae. Pinophytes are gymnosperms. They are cone-bearing seed plants with vascular tissue; all extant conifers are woody plants, the great majority being...
- GnetophytaGnetophytaThe plant division Gnetophyta or gnetophytes consists of three genera of woody plants grouped in the gymnosperms. The living Gnetophyta consists of around 70 species across the three genera Gnetum , Welwitschia , and Ephedra .The gnetophytes differ from other gymnosperms The plant division...
- Magnoliophyta
Callus Induction and Tissue Culture
A callus cell culture is usually sustained on gel medium. Callus induction medium consists of agar and a mixture of macronutrients and micronutrientMicronutrient
Micronutrients are nutrients required by humans and other living things throughout life in small quantities to orchestrate a whole range of physiological functions, but which the organism itself cannot produce. For people, they include dietary trace minerals in amounts generally less than 100...
s for the given cell type. There are several types of basal salt mixtures used in plant tissue culture, but most notably modified Murashige and Skoog medium
Murashige and Skoog medium
Murashige and Skoog medium or is a plant growth medium used in the laboratories for cultivation of plant cell culture. MSO was invented by plant scientists Toshio Murashige and Folke K. Skoog in 1962 during Murashige's search for a new plant growth regulator...
, White's medium, and woody plant medium. Vitamins are also provided to enhance growth such as Gamborg B5 vitamins. For plant cells, enrichment with nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, and potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
is especially important.
Morphology
Plant callus is usually derived from somaticSomatic
The term somatic means 'of the body',, relating to the body. In medicine, somatic illness is bodily, not mental, illness. The term is often used in biology to refer to the cells of the body in contrast to the germ line cells which usually give rise to the gametes...
tissues. The tissues used to initiate callus formation depends on plant species and which tissues are available for explant culture
Explant culture
In biology, explant culture is a technique used for the isolation of cells from a piece or pieces of tissue. Tissue harvested in this manner is called an explant...
. The cells that give rise to callus and somatic embryos usually undergo rapid division or are partially undifferentiated such as meristem
Meristem
A meristem is the tissue in most plants consisting of undifferentiated cells , found in zones of the plant where growth can take place....
atic tissue. In alfalfa, Medicago truncatula
Medicago truncatula
Medicago truncatula is a small legume native to the Mediterranean region that is used in genomic research. It is a low-growing, clover-like plant 10–60 cm tall with trifoliate leaves. Each leaflet is rounded, 1–2 cm long, often with a dark spot in the center...
, however callus and somatic embryos are derived from mesophyll cells that undergo dedifferentiation. Plant hormones are used to initiate callus growth. Specific auxin
Auxin
Auxins are a class of plant hormones with some morphogen-like characteristics. Auxins have a cardinal role in coordination of many growth and behavioral processes in the plant's life cycle and are essential for plant body development. Auxins and their role in plant growth were first described by...
to cytokinin
Cytokinin
Cytokinins are a class of plant growth substances 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...
ratios in plant tissue culture medium give rise to an unorganized growing and dividing mass of callus cells. Callus cultures are often broadly classified as being either compact or friable. Friable calluses fall apart easily, and can be used to generate cell suspension cultures. Callus can directly undergo direct organogenesis
Organogenesis
In animal development, organogenesis is the process by which the ectoderm, endoderm, and mesoderm develop into the internal organs of the organism. Internal organs initiate development in humans within the 3rd to 8th weeks in utero...
and/or embryogenesis
Embryogenesis
Embryogenesis is the process by which the embryo is formed and develops, until it develops into a fetus.Embryogenesis starts with the fertilization of the ovum by sperm. The fertilized ovum is referred to as a zygote...
where the cells will form an entirely new plant. Callus can brown and die during culture, but the causes for callus browning are not well understood. In Jatropha curcas
Jatropha curcas
Jatropha curcas is a species of flowering plant in the spurge family, Euphorbiaceae, that is native to the American tropics, most likely Mexico and Central America. It is cultivated in tropical and subtropical regions around the world, becoming naturalized in some areas...
callus cells, small organized callus cells became disorganized and varied in size after browning occurred. Browning has also been associated with oxidation and phenolic compounds in both explant tissues and explant secretions.
Uses
Callus cells are not necessarily genetically homogeneous because a callus is often made from structural tissue, not individual cells. Nevertheless, callus cells are often considered similar enough for standard scientific analysis to be performed as if on a single subject. For example, an experiment may have half a callus undergo a treatment as the experimental group, while the other half undergoes a similar but non-active treatment as the control group.Plant calli can differentiate into a whole plant, a process called regeneration, through addition of plant hormones in culture medium. This ability is known as totipotency. Regeneration of a whole plant from a single cell allows researchers to recover whole plants that have a copy of the transgene in every cell. Regeneration of a whole plant that has some genetically transformed cells and some untransformed cells is called a chimera
Chimera (plant)
Chimeras in botany are usually single organisms composed of two genetically different types of tissue. They occur in plants, on the same general basis as with animal chimeras...
. In general, chimeras are not useful for genetic research or agricultural applications.
Genes can be inserted into callus cells using biolistic bombardment, also known as a gene gun
Gene gun
A gene gun or a biolistic particle delivery system, originally designed for plant transformation, is a device for injecting cells with genetic information. The payload is an elemental particle of a heavy metal coated with plasmid DNA...
, or Agrobacterium tumefaciens
Agrobacterium tumefaciens
Agrobacterium tumefaciens is the causal agent of crown gall disease in over 140 species of dicot. It is a rod shaped, Gram negative soil bacterium...
. Cells that receive the gene of interest can then be recovered into whole plants using a combination of plant hormone
Plant hormone
Plant hormones are chemicals that regulate plant growth, which, in the UK, are termed 'plant growth substances'. Plant hormones are signal molecules produced within the plant, and occur in extremely low concentrations. Hormones regulate cellular processes in targeted cells locally and, when moved...
s. The whole plants that are recovered can be used for experiment to determine gene function(s), or to enhance crop plant traits for modern agriculture.
Callus tissue is of particular use in micropropagation
Micropropagation
Micropropagation is the practice of rapidly multiplying stock plant material to produce a large number of progeny plants, using modern plant tissue culture methods....
where it can be used to grow genetically identical copies of plants with desirable characteristics.
History
Henri-Louis Duhamel du Monceau
Henri-Louis Duhamel du Monceau , was a French physician, naval engineer and botanist. As a botanist his standard abbreviation is Duhamel...
investigated wound-healing responses in elm trees, and was the first to report formation of callus tissue on live plants.
In 1908, E. F. Simon was able to induce callus from poplar stems that also produced roots and buds. The first reports of callus induction in vitro came from three independent researchers in 1939. P. White induced callus derived from tumor-developing procambial tissues of hybrid Nicotiana glauca
Nicotiana glauca
Nicotiana glauca is a species of wild tobacco known by the common names tree tobacco and incorrectly also Mustard tree. Its leaves are attached to the stalk by petioles , and its leaves and stems are neither pubescent nor sticky like Nicotiana tabacum...
that did not require hormone supplementation. Gautheret and Nobecourt were able to maintain callus cultures of carrot using auxin hormone additions.
See also
- Embryo RescueEmbryo RescueEmbryo Rescue is one of the earliest and successful forms of in-vitro culture techniques that is used to assist in the development of plant embryos that might not survive to become viable plants. Embryo rescue plays an important role in modern plant breeding, allowing the development of many...
- Somatic EmbryogenesisSomatic EmbryogenesisSomatic embryos are mainly produced in vitro and for laboratory purposes, using either solid or liquid nutrient media which contain plant growth regulators . The main PGRs used are auxins but can contain cytokinin in a smaller amount. Somatic embryogenesis is a process where a plant or embryo is...
- Chimera (plant)Chimera (plant)Chimeras in botany are usually single organisms composed of two genetically different types of tissue. They occur in plants, on the same general basis as with animal chimeras...
- HyperhydricityHyperhydricityHyperhydricity is a physiological malformation that results in excessive hydration, low lignification, impaired stomatal function and reduced mechanical strength of tissue culture-generated plants. The consequence is poor regeneration of such plants without intensive greenhouse acclimation for...