Phytoalexin

Phytoalexins ( gr phytos = plant, alekein = " ward " ) are low molecular weight, antimicrobial and antioxidant activity at least in some cases, chemical compounds that immediately after infection by microorganisms ( such as bacteria or fungi ), are produced by the plant, to inhibit the propagation, growth or reproduction in said plant. They are about 24 h after infection in the affected plant tissues and reach detectable after about 3 days, a maximum concentration. Important to mention here is that the phytoalexins exclusively in the affected areas of micro-organisms and the immediate vicinity (a few mm) are produced. The substances that act as phytoalexins, there is a variety of compounds from various substance classes such as flavonoids, terpenoids, alkaloids, stilbenoids, polyacetylenes, isoflavones, etc. phytoalexins belong to the secondary plant substances.

Phytoalexins were in the 1940s, based on studies on the response of different potato cultivars on pathogenic and non- pathogenic strains of the fungus Phytophthora sp. postulated and about 1960 for the first time actually proven. Meanwhile, several hundred different phytoalexins from more than 15 plant families are known, within most families more than a phytoalexin is (partly also from various substance classes derived ) produced. Typically, the phytoalexins a particular plant species of a class of substances belonging to the type or family (also constitutively present) is characteristic without this. So, for example, polyacetylenes and sesquiterpene lactones found in the Asteraceae, isoflavonoids in the Fabaceae, coumarins and polyacetylenes in Apiaceae, Phenanthrene and stilbenes in the Orchidaceae, etc. phytoalexins generally have no high specificity ( few exceptions ), but on the contrary quite unspecific effective against a variety of invading microorganisms. Phytoalexins should not be confused with other plant ingredients, which ( etc. insects, worms, grazing animals ) are about the plant to ward off predators available. This term is applied exclusively to de novo formed substances for defense against microorganisms.

Phytoalexins are always only after the penetration of microorganisms in plant tissue to fight off the same newly produced ( de novo ) and are not normally found in healthy parts of the plant detectable. Except by microorganisms, the production of phytoalexins can also be triggered by a variety of others, even abiotic factors, such as UV radiation, heavy metals, temperature shock, tissue injury, etc. This discovery has also meant that the original concept of Müller & Boerger was completely softened and followed numerous phytonutrients were published as phytoalexins, which did not deserve this attribute, as these often only induced by heavy metal salts and their antimicrobial properties have not been verified.

Clearly distinguishing (also called phytoanticipins; eg glucosinolates ) phytoalexins are in any case of so-called constitutive plant defense compounds, which holds always ready to defend the plant and are akkummuliert in diverse areas ( glands secretion transitions, vacuoles, etc.). Phytoalexins other hand, are produced only when needed and in a very limited range ( only at the site of infection ) and environmental or energy, they provide a good protection of the plant at relatively low energy expenditure. This does not mean that phytoalexin - producing plants renounce completely constitutive defense compounds!

As a start signal for the production of phytoalexins of the plant are called elicitors ( inter alia by enzymes cut out substances from the cell wall of the challenge microorganisms ) that bind to receptors and pass through a complex signaling cascade the information to the cell nucleus. To elicitors, which are recognized by the plant, include polysaccharides and bacterial and fungal proteins and glycoproteins.

In biochemistry, genetics, and evolution of phytoalexins is highly topical areas of research.