Phytoalexins, definition

De Novo Synthesis of Phytoalexins. Phytoalexins have been studied in great depth by plant pathologists. Excellent review papers are available in Hedin s ACS symposium volume. Host Plant Resistance to Plants (42), and more recently in the book edited by Horsfall and Cowling, Plant Disease (43). The antiherbivory effect of phytoalexins, however, is only now beginning to be fully appreciated. It is apparent that pathogen induced phytoalexins do have a definite effect on insect herbivores. There is mounting evidence that herbivore-inflicted injury may also result in the induction of phytoalexin production and accumulation. 

Compounds formed in response to stress may occur in at least two ways. In one response, the plant may form compounds throughout the tissue at a considerable distance from the infection site (Hammerschmidt, 1999). In another response, the plant may form compounds specifically at the infection site. This may include only a few cells and in rare cases, as few as one or two cells. (Snyder and Nicholson, 1990 Nicholson and Wood, 2001). In general, such compounds are referred to as either stress metabolites or more often as phytoalexins. By definition phytoalexins are formed in response to infection (Aguero et al., 2002 Lo et al., 2002 Hammerschmidt and Nicholson, 2001 Lo and Nicholson, 1998). Phytoalexins often exhibit toxicity to specific pathogens. In this case there is a genetic relationship between the expression of phytoalexin synthesis and the organism that induces that synthesis (Essenberg et al., 1985). 

Dakora, F.D., Phillips, D.A. Diverse functions of isoflavonoids in legumes transcend anti-microbial definitions of phytoalexins. Physiol Mol Plant Pathol 1996 49 1-20. 

Abiotic elicitors, examples, 48 Abscisic acid, plant-growth hormone inhibitor, I6f Active defense, definition, 37 Alfalfa, phytoalexins, 56 Allelochemicals... 

Phytoalexins. Let us now review the history of the term phytoalexin. An early definition stated that a phytoalexin was, "a chemical compound produced only when the living cells of the host are invaded by a parasite and undergo necrobiosis ... 

Paxton J 1980 A new working definition of the term phytoalexin. Plant Dis 64 734... 

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