Soybean cultivar "Ludou 4" was inoculated with the AM fungus Glomus fasciculatus, soybean cyst nematode (SCN) Heterodera glycines race 4 and the AM fungus plus SCN. A number of coefficients such as mycorrhizal colonization, SCN infection rate, activities of chitinase and PAL and transcripts of the genes Chibl(Chitinase b1) and PAL5 in soybean roots were assayed. No significant effect of SCN was found on the colonization of G. Fasciculatum in soybean roots. On the other hand, the infection rate of SCN displayed a remarkable reduction in mycorrhizal soybean roots with G. Fasciculatum when compared with that in non-mycorrhizal soybean roots infected by the SCN. Furthermore, the activities of chitinase and PAL were strongly enhanced in mycorrhizal soybean roots infected by the SCN, and peaked at 3 d after inoculation with the SCN. In addition, time-course analysis of Chibland PAL5 transcripts in mycorrhizal soybean showed that the transcript levels of these two genes also peaked at 3 d after inoculation with the SCN, when the infection rate of SCN was remarkably reduced relative to that in non-mycorrhizal soybean roots challenged by the SCN, suggesting that expression of Chibl and PAL5 in mycorrhizal roots could be one of the defensive responses induced by the AM fungus against the SCN. Therefore, it was considered that Chiol and PAL5 may directly involve in the defense responses induced by the AM fungus G.fasciculatum against the SCN in soybean roots.%本研究系统分析了大豆(品种:‘鲁豆4’)接种AM真菌Glomusfasciculatum和胞囊线虫(SCN,Heterodera glycines)4号生理小种后各处理菌根和线虫侵染率、几丁质酶和苯丙氨酸解氨酶(PAL)活性及几丁质酶基因Chib1和苯丙氨酸解氨酶基因PAL5转录物的动态变化.结果表明,接种SCN对AM真菌的侵染率没有产生显著影响,但先接种AM真菌后接种SCN的大豆根内线虫侵染率明显低于只接种SCN的处理.另外,先接种AM真菌后接种SCN的大豆根内几丁质酶和PAL活性显著提高,活性高峰出现在接种线虫后的第3天.值得注意的是,先接种AM真菌后接种SCN的大豆根内两种基因Chtb1和PAL5转录物高峰也出现在接种SCN后的第3天,即AM真菌侵染率快速上升而SCN侵染率快速下降时期.所以Chib1和PAL5基因的表达可能是AM真菌诱导的抗大豆胞囊线虫病害防御反应的一种表现.因此推测Chib1和PAL5直接参与了AM真菌诱导大豆抗胞囊线虫病害的防御反应.
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