The determinants of specificity from Mycosphaerella species

以豌豆球腔菌疫病为研究对象，探讨了寄主-寄生物专一性的机理。用从豌豆黑胫病菌孢子萌发液中提取的高分子量激发子处理豌豆，可诱导豌豆产生两种类型的抗病性。pinodes。其中之一是生产pisatin，另一个是形成感染抑制剂。诱导子处理后6 h内，损伤组织中的Pisatin合成途径被激活，导致Pisatin积累。在处理后3 h内，该途径中的调控酶之一苯丙氨酸解氨酶（PAL）被激活，并在处理后1h内检测到PAL-和查尔酮解氨酶基因的表达。同时存在小分子量的抑制因子，该抑制因子分泌到M. pinodes，导致这些防御反应延迟至少3 h。另一种抑制M.处理后1-2小时，在置于未损伤组织上的激发子溶液中检测到pinodes。其他真菌诱导子也在处理的组织中诱导相同类型的排斥反应。这种类型的抗性也被抑制子与激发子的同时存在所否定。豌豆的一些非致病性真菌能够在抑制剂处理的组织上建立这些感染。对豌豆无毒的供试真菌不能产生对豌豆有效的抑制物。M.因此，pinodes似乎是决定豌豆-球腔菌pinodes系统专一性的主要原因。甜瓜也产生特异性决定簇，这些决定簇可能抵消各自寄主植物对诱导子诱导的防御反应。这些含有糖和肽的物质的提纯工作正在进行。

The mechanism of plant host-parasite specificity was investigated with a system of Mycosphaerella blight of pea. Two types of resistance were induced in pea tissues by the treatment with the high molecular weight elicitor prepared from the spore germination fluid of M. pinodes. One of them was pisatin production, and the other was the formation of infection inhibitors. Pisatin accumulation was caused by the activation of pisatin synthetic pathway in wounded tissues within 6 h after the eliciter-treatment. The activation of phenylalanine ammonia-lyase(PAL), one of regulatory enzymes in the pathway, was induced within 3 h, and the expressions of PAL- and chalcone synthase-gene were detected within 1 h after the treatment. The concomitant presence of the low molecular weight suppressor, which was secreated into spore germination fluid of M. pinodes, resulted in delay of these defense reactions for at least 3 h. Another substance which inhibits the penetration of M. pinodes was detected in the elicitor solution placed on uninjured tissues 1-2 h after the treatment. Other fungal elicitors also induced the same type of rejection reaction in the treated tissues. This type of resistance was also negated by the concomitant presence of suppressor with elicitor. Some nonpathogenic fungi of pea were able to establish these infection on the suppressor-treated tissues. The tested fungi avirulent to pea were not able to produce the suppressor effective to pea plant. The suppressor of M. pinodes, therefore, seems to be responsible for the determination of specificity in pea plant-Mycosphaerella pinodes system.Mycosphaerella ligulicola and My. melonis also produce the determinants of specificity which may negate the defense reaction of respective host plant induced by elicitor. The purification of these substances containing sugar and peptide is under way.