Kinetin (/'kaɪnɪtɪn/) is a type of

cytokinin 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 le ...

, a class of

plant hormone Plant hormone (or phytohormones) 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, pa ...

that promotes

cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...

. Kinetin was originally isolated by Carlos Miller and Skoog ''et al.'' as a compound from autoclaved herring sperm DNA that had cell division-promoting activity. It was given the name kinetin because of its ability to induce

, provided that

auxin Auxins (plural of auxin ) are a class of plant hormones (or plant-growth regulators) with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essenti ...

was present in the medium. Kinetin is often used in

plant tissue culture 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 ...

for inducing formation of

callus A callus is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, but they may o ...

(in conjunction with

) and to regenerate

shoot In botany, a plant shoot consists of any plant stem together with its appendages, leaves and lateral buds, flowering stems, and flower buds. The new growth from seed germination that grows upward is a shoot where leaves will develop. In the spri ...

tissues from callus (with lower

concentration). For a long time, it was believed that kinetin was an artifact produced from the deoxyadenosine residues in DNA, which degrade on standing for long periods or when heated during the isolation procedure. Therefore, it was thought that kinetin does not occur naturally, but, since 1996, it has been shown by several researchers that kinetin exists naturally in the DNA of cells of almost all organisms tested so far, including human and various plants. The mechanism of production of kinetin in DNA is thought to be via the production of furfural — an oxidative damage product of deoxyribose sugar in DNA — and its quenching by the adenine base's converting it into N6-furfuryladenine, kinetin. Kinetin is also widely used in producing new plants from tissue cultures.

History

In 1939 P. A. C. Nobécourt (Paris) began the first permanent callus culture from root explants of carrot (''

Daucus carota ''Daucus carota'', whose common names include wild carrot, European wild carrot, bird's nest, bishop's lace, and Queen Anne's lace (North America), is a flowering plant in the family Apiaceae. It is native to temperate regions of the Old Wor ...

''). Such a culture can be kept forever by successive transplantations onto fresh nutrient

agar Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from ogonori (''Gracilaria'') and "tengusa" (''Gelidiaceae''). As found in nature, agar is ...

. The transplantations occur every three to eight weeks. Callus cultures are not cell cultures, since whole tissue associations are cultivated. Though many cells keep their ability to divide, this is not true for all. One reason for this is the

aneuploidy Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more complete sets of chromosomes. A cell with any ...

of the nuclei and the resultant unfavourable chromosome constellations. In 1941 J. van Overbeek (Rijksuniversiteit Utrecht) introduced coconut milk as a new component of nutrient media for callus cultures.

Coconut milk Coconut milk is an opaque, milky-white liquid extracted from the grated pulp of mature coconuts. The opacity and rich taste of coconut milk are due to its high oil content, most of which is saturated fat. Coconut milk is a traditional food i ...

is liquid endosperm. It stimulates the embryo to grow when it is supplied with food at the same time. Results yielded from callus cultures showed that its active components stimulate the growth of foreign cells too. In 1954 F. Skoog (University of Wisconsin, Madison) developed a technique for the generation and culture of wound

tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

tissue from isolated shoot parts of tobacco (''

Nicotiana tabacum ''Nicotiana tabacum'', or cultivated tobacco, is an annually grown herbaceous plant of the ''Nicotiana'' genus. The plant is tropical in origin, is commonly grown throughout the world, and is often found in cultivation. It grows to heights bet ...

''). The developing callus grows when supplied with

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...

extract, coconut milk, or old DNA preparations. Freshly prepared DNA has no effect but becomes effective after autoclaving. This led to the conclusion that one of its breakdown products is required for cell growth and division. This characterized substance was named ''kinetin'', and was classified as a

phytohormone Plant hormone (or phytohormones) 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, pat ...

References

* * * {{Use dmy dates, date=March 2018 2-Furyl compounds Cytokinins Purines