Phytoalexins from brassicas: overcoming plants' defenses
1997
Pedras, M.S.C. | Khan, A.Q. | Taylor, J.L.
In response to pathogen attack, plants synthesize phytoalexins, which are part of the plant's defense mechanism. Phytoalexins from brassicas have an indole ring and at least one sulfur atom as a common structural feature. Despite their close biogenetic relationship, these phytoalexins possess significantly different structures. Such structural differences suggest that brassica phytoalexins have different biological activity. We have determined that the virulence of the blackleg fungus, a fungal pathogen of brassicas, correlated with its ability to rapidly metabolize and detoxify the phytoalexin brassinin. This process appears to be a mechanism by which the pathogen overcomes the plant's chemical defenses. We have now compared the toxicity of three additional phytoalexins of brassicas, brassicanal A, brassilexin, and camalexin, and investigated their biotransformation by the blackleg fungus. Most interestingly, the biotransformation of brassicanal A was different from that of brassinin, and occurred at a much slower rate. Additionally, unlike brassinin, these phytoalexins did not significantly affect the synthesis of blackleg phytotoxins. Overall, these results suggest that the blackleg fungus does not have specific enzymes to carry out those biotransformations.
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