Islam Md Tofazzal
Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
Z Naturforsch C J Biosci. 2008 Mar-Apr;63(3-4):233-40. doi: 10.1515/znc-2008-3-413.
The motile zoospores of the damping-off pathogen Aphanomyces cochlioides aggregate on host plants (e.g., sugar beet, spinach) guided by the host-specific plant signal cochliophilin A before infection. To assess the potential role of secondary metabolites in nonhost resistance, acetone extracts of 200 nonhost traditional medicinal plants from Chinese and Bangladeshi origins were tested for the motility behaviour of A. cochlioides zoospores using a particle bioassay method. Nearly one third of the tested plant extracts exhibited diverse deleterious activities such as repellent, stimulant, motility halting and lysis against A. cochlioides zoospores. Among these active plants, an extract of the Chinese medicinal plant Dalbergia odorifera displayed potent repellent activity toward zoospores. Chromatographic separation of D. odorifera constituents revealed that the repellent activity was regulated by the cumulative effect of three motility-affecting isoflavonoids, viz. (+/-)-medicarpin (repellent at 150 microg/ml), (-)-claussequinone (stimulant at 100 microg/ml) and formononetin (stimulant and attractant at 50 microg/ml). A mixture (1:1:1, w/w/w) of these three compounds exhibited only repellent activity toward zoospores at a concentration lower than 50 microg/ml. These results suggest that nonhost plants might possess potential bioactive secondary metabolites to ward off zoosporic phytopathogens.
猝倒病病原菌刺腐霉的游动孢子在感染前会在宿主特异性植物信号耳蜗亲和素A的引导下聚集在宿主植物（如甜菜、菠菜）上。为了评估次生代谢产物在非寄主抗性中的潜在作用，使用颗粒生物测定法，对来自中国和孟加拉国的200种非寄主传统药用植物的丙酮提取物进行了刺腐霉游动孢子运动行为的测试。近三分之一的测试植物提取物对刺腐霉游动孢子表现出多种有害活性，如驱避、刺激、运动停止和裂解。在这些活性植物中，中国药用植物降香檀的提取物对游动孢子表现出强烈的驱避活性。对降香檀成分进行色谱分离后发现，驱避活性受三种影响运动的异黄酮类化合物的累积效应调节，即（±）-紫穗槐二氢黄酮（150微克/毫升时具有驱避作用）、（-）-克劳喹酮（100微克/毫升时具有刺激作用）和芒柄花素（50微克/毫升时具有刺激和吸引作用）。这三种化合物的混合物（1:1:1，w/w/w）在浓度低于50微克/毫升时对游动孢子仅表现出驱避活性。这些结果表明，非寄主植物可能拥有潜在的生物活性次生代谢产物来抵御游动孢子植物病原体。
