Phytoalexins: Defence or just a response to stress?

Inducible plant defence responses include antimicrobial compounds called phytoalexins, lytic enzymes, oxidizing agents, cell wall lignification and a number of pathogenesis related proteins. The antimicrobial properties of phytoalexins suggest that they are an important component of plant defence. A role for these compounds in defence has been revealed through several experimental approaches. Data have 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. Although there are some evidence suggesting a role for phytoalexins accumulation in resistance, there are also examples against it. Progress in the development of our understanding of the role of phytoalexins in resistance is discussed in this review.