44 植物病原菌Alternaria alternataが生産する宿種特異的AF及びAK毒素の生合成及び毒素生成失活機構に関する一考察(口頭発表の部)

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AF- and AK-toxins are host-selective toxins produced by Alternaria alternata strawberry pathotype and Japanese pear pathotype, respectively, and express different toxicities to the host-plants (Table 1). We have already succeeded in structure determinations of AF-toxins and total syntheses (Scheme 1) of AF-and AK-toxins. Here, we wish to report recent studies on the cultivation condition of AK-toxin producer, the biosynthesis of AK-toxin I (4) and the mechanism of toxinless mutation of A.alternata pathogens. Various 2'-acyl derivatives 9-11 were prepared from AF-toxin II (2) as shown in Scheme 1. All of those acyl derivatives are toxic to both Japanese pear and strawberry similarly to AF-toxin I (1) and III (3) as shown in Table 3. Those host-selectivities demonstrated our hypothesis concerning structure-activity relationships. By examination of varirous cultivation conditions of A. alternata Japanese pear pathotype, we succeeded in harvesting AK-toxin I about 10 times much than before. Since it was found that decatrienoic acid 12 is about 10 times of AK-toxin I in the culture (Figure 2), it was suggested that 12 is a precursor of AK-toxins. When 3H-labeled decatrienoic acid 12 (Scheme 3) was fed to the culture of AK-toxin producer, radioactivity was incorporated into AK-toxin I. Thus, the decatrienoic acid (12) was proved to be a biosynthetic precursor of AK-toxins (Scheme 2). Various A. alternata mutants losting their pathogenicities produce neither host-selective toxins nor their precursor decatrienoic acid 12 as shown in Table 4. This result suggests that the machanism of toxinless mutation is luck of enzyme system for the initial step in the biosynthesis of host-selective toxins.
天然有機化合物討論会の論文
1988-09-26

44 植物病原菌Alternaria alternataが生産する宿種特異的AF及びAK毒素の生合成及び毒素生成失活機構に関する一考察(口頭発表の部)

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