Shimura Hanako, Sadamoto Mai, Matsuura Mayumi, Kawahara Takayuki, Naito Shigeo, Koda Yasunori
Laboratory of Crop Physiology, Graduate School of Agriculture, Hokkaido University, Kita-ku, Kita 9, Nishi 9, Sapporo, 060-8589, Japan.
Laboratory of Plant Pathology, Graduate School of Agriculture, Hokkaido University, Sapporo, 060-8589, Japan.
Mycorrhiza. 2009 Oct;19(8):525-534. doi: 10.1007/s00572-009-0251-4. Epub 2009 May 16.
We isolated Rhizoctonia-like fungi from populations of the threatened orchid Cypripedium macranthos. In ultrastructural observations of the septa, the isolates had a flattened imperforate parenthesome consisting of two electron-dense membranes bordered by an internal electron-lucent zone, identical to the septal ultrastructure of Rhizoctonia repens (teleomorph Tulasnella), a mycorrhizal fungus of many orchid species. However, hyphae of the isolates did not fuse with those of known tester strains of R. repens and grew less than half as fast as those of R. repens. In phylogenetic analyses, sequences for rDNA and internal transcribed spacer (ITS) regions of the isolates were distinct from those of the taxonomically identified species of Tulasnella. On the basis of the ITS sequences, the isolates clustered into two groups that corresponded exactly with the clades demonstrated for other Cypripedium spp. from Eurasia and North America despite the geographical separation, suggesting high specificity in the Cypripedium-fungus association. In addition, the two phylogenetic groups corresponded to two different plant clones at different developmental stages. The fungi from one clone constituted one group and did not belong to the other fungal group isolated from the other clone. The possibility of switching to a new mycorrhizal partner during the orchid's lifetime is discussed.
我们从濒危兰花大花杓兰种群中分离出类丝核菌。在隔膜的超微结构观察中，分离菌株有一个扁平的无孔膜孔，由两个电子致密膜组成，中间有一个电子透明区，这与许多兰花物种的菌根真菌立枯丝核菌（有性型为土氏菌属）的隔膜超微结构相同。然而，分离菌株的菌丝与已知的立枯丝核菌测试菌株的菌丝不融合，生长速度不到立枯丝核菌的一半。在系统发育分析中，分离菌株的核糖体DNA（rDNA）和内部转录间隔区（ITS）序列与已分类鉴定的土氏菌属物种的序列不同。基于ITS序列，分离菌株聚为两组，这两组与来自欧亚大陆和北美的其他杓兰属物种所显示的进化枝完全对应，尽管存在地理隔离，这表明杓兰与真菌的共生关系具有高度特异性。此外，这两个系统发育组对应于处于不同发育阶段的两个不同植物克隆。来自一个克隆的真菌构成一组，不属于从另一个克隆分离出的另一真菌组。本文讨论了兰花在其生命周期中切换到新的菌根伙伴的可能性。
