PHYTOALEXINS: What Have We Learned After 60 Years?

Abstract

One of the best and longest-studied defense response of plants to infection is the induced accumulation of antimicrobial, low-molecular-weight secondary metabolites known as phytoalexins. Since the phytoalexin hypothesis was first proposed in 1940, a role for these compounds in defense has been revealed through several experimental approaches. Support has come, for example, through studies on the rate of phytoalexins in relation to cessation of pathogen development, quantification of phytoalexins at the infection site, and relationship of pathogen virulence to the phytoalexin tolerance. Evidence in support of phytoalexins in resistance as well some recent advances in phytoalexin biosynthesis are reviewed. Criteria for evaluating a role for phytoalexins in disease resistance are also discussed.

A Multidrug Resistance–Associated Protein Involved in Anthocyanin Transport in Zea mays

“…Recent work on the last genetically defined step in this pathway (Marrs et al, 1995;Alfenito et al, 1998) has also identified anthocyanin biosynthesis as an important model for studying the mechanisms for the detoxification and vacuolar sequestration of heterocyclic organic anions. In addition to anthocyanins, this class of compounds includes a vast array of endogenous and xenobiotic chemicals involved in pest and disease resistance, pigmentation, UV protection, intracellular and extracellular signaling, and weed control (Abell et al, 1993;Shirley, 1996;Hammerschmidt, 1999). Understanding the molecular mechanisms involved in transporting these molecules to the correct cellular locations represents a fundamental, yet poorly understood, problem in biology.…”

A fungal-responsive MAPK cascade regulates phytoalexin biosynthesis in Arabidopsis

“…Phytoalexins are defined as low-molecular-weight antimicrobial compounds produced by plants after exposure to pathogens (15,16). Phytoalexins are an integral part of induced plant disease resistance.…”

“…Engineeringenhanced phytoalexin production can lead to increased disease resistance (15). Phytoalexin induction is associated with the activation of genes encoding biosynthetic enzymes (15,16,21,22). However, the signaling pathway(s) leading to activation of these genes are poorly understood.…”

La résistance induite : une nouvelle stratégie de défense des plantes contre les agents pathogènes

“…Les phytoalexines sont des métabo-lites secondaires de faible poids molé-culaire (composés phénoliques) qui sont synthétisés par la plante en réponse à l'infection (Hammerschmidt 1999). Ces petites molécules, à potentiel fortement antimicrobien, s'accumulent dans des zones localisées près des sites d'infection.…”

“…La structure chimique des phytoalexines identifiées jusqu'à présent d'une grande variété de plantes est extrêmement diversifiée. Bien que leur fongitoxicité in planta reste encore à démontrer, plusieurs travaux suggèrent que les phytoalexines jouent un rôle majeur dans l'expression de la résis-tance chez les plantes (Hammerschmidt 1999). …”