Kinetin

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Kinetin is a chemical analogue of cytokinins a class of plant hormone that promotes cell division. Kinetin was originally isolated by 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 hability to induce cell division, provided that auxin was present in the medium. It was shown later that kinetin is an artifact produced from the deoxyadenosine residues in DNA, which degrade on standing for long periods or when heated during the isolation procedure. Although kinetin doesn't occur naturally in plants, it has strong cytokinin activity and is often used in plant tissue culture for inducing formation of callus (in conjunction with auxin) and to regenerate shoot tissues from callus (with lower auxin concentration).

[edit] History

In 1939 P. A. C. Nobécourt (Paris) began the first permanent callus culture from root explants of carrot (Daucus carota). Such a culture can be kept forever by successive transplantations onto fresh nutrient agar. 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, is this not true for all. One reason for this is the aneuploidy of the nuclei and the thus caused unfavourable chromosome constellations.

J. van OVERBEEK (Rijksuniversiteit Utrecht) introduced in 1941 coconut milk as a new component of nutrient media for callus cultures. Coconut milk is liquid endosperm. In nature does it stimulate the embryo to grow which it supplies at the same time with food. 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 tumour tissue from isolated shoot parts of tobacco (Nicotiana tabacum). The thus developing callus grows when supplied with yeast 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. The substance was characterized. It is called kinetin and has been classified as a phytohormone.

The technique developed by F. Skoog proved to be ideal for the study of the regeneration capacity of callus cultures. Callus and tissue cultures can both be kept in light or in dark. Under light exposure produce the cells at the surface plastids, chlorophyll and carotenoids.

Callus cultures are useful for many purposes of pure and applied research. Among these are:

1) The production of secondary plant products and enzymes by tissue cultures.
2) Their use for the synthesis of starting compounds that are subsequently modified to yield the desired product.
3) Their use as starting material for the vegetative propagation of plants.
4) Their use as basic material fore high-yield cultivars (maintenance breeding).
5) Their reverting to tissue cultures allows the conservation of virus- or fungi-free and resistant cell lineages.

Kinetin is also claimed to have dermatologic effects and is used in some cosmetics.