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    山田胶锈菌与苹果叶互作的组织学及生理病理特征

    Histological and physiopathology characteristics in the interaction of Gymnosporangium yamadae and Malus domestica leaves

    • 摘要:
      目的 明确山田胶锈菌专性侵染苹果叶片的病理学过程,探究寄主受侵染后的生理代谢响应机制,为今后开展山田胶锈菌致病分子机理的研究奠定基础。
      方法 利用显微技术观察山田胶锈菌担孢子侵入感病苹果叶片的连续发育过程和寄主叶片细胞的结构变化;使用TU-1810型紫外可见分光光度计检测苹果叶片上产生褪绿花斑时以及在性孢子阶段和锈孢子阶段的过氧化氢、过氧化物酶(POD)及总酚含量。
      结果 山田胶锈菌的担孢子在苹果叶片上6 h后萌发产生芽管,12 h后由芽管直接侵入表皮细胞;24 h后在寄主细胞间隙产生初生胞间菌丝,72 h后观察到有隔膜的次生菌丝,7 d后由胞间菌丝或吸器母细胞形成的单核吸器进入寄主细胞;10 d后在叶片正面观察到性孢子器和性孢子形成,60 d时在叶片背面形成锈孢子器和锈孢子。在叶片表面出现褪绿花斑之前,寄主细胞的形态结构未发生明显变化;叶表出现明显花斑时,初生吸器大量形成,寄主细胞质染色变浅,细胞器形态发生扭曲。性孢子发育阶段,寄主细胞的细胞膜及细胞器开始消融;在锈孢子形成时期,寄主细胞出现坏死。随着锈菌侵染过程的推进,苹果叶片中过氧化氢含量先下降后略有上升,POD活性和总酚含量呈现不同幅度的上升趋势。
      结论 山田胶锈菌担孢子萌发后产生芽管和附着胞直接侵入叶表皮细胞(0 ~ 5 dpi),由胞间菌丝或吸器母细胞形成大量单核吸器与寄主建立活体营养寄生关系(5 ~ 10 dpi),最后发育产孢(10 dpi以后)生成性孢子和锈孢子。寄主细胞的感病反应从吸器进入叶肉细胞开始出现,细胞坏死发生于锈孢子形成时期。山田胶锈菌的侵染诱导苹果叶片中酚类物质的大量积累,可能在维持感病寄主体内低含量活性氧中发挥重要作用。

       

      Abstract:
      Objective The study aimed to determine the histopathological process of pathogen and investigate the physiological and metabolic response mechanisms of the host during specific infection of Gymnosporangium yamadae on apple (Malus domestica) leaves, and investigate the pathological mechanisms underlying the host-specific selection of the rust, so as to lay the groundwork for further research on pathogenetic molecular mechanisms of G. yamadae.
      Method After artificially inoculating apple leaves with G. yamadae basidiospores, the infection structures of pathogen and cytology changes of the host were observed continuously using microtechnic; the contents of hydrogen peroxide, peroxidase (POD) and total phenol of infected apple leaves showed chlorotic flecks and at the pycnium and aecium stages were determined using TU-1810 UV-visible spectrophotometer.
      Result G. yamadae basidiospores germinated and produced germ tubes after 6 hpi (hours past inoculation) and directly entered into apple leaf epidermal cells at 12 hpi, intercellular mycelia formed at 24 hpi and secondary mycelia with diaphragm were observed at 72 hpi. After 5 d, intercellular mycelia or haustorial mother cells entered into host cells, resulting in the formation of monokaryotic haustoria. After 10 dpi, the pycnium and pycniosporophores were observed on the surface of apple leaves and the aecium and aeciospores were formed on the undersides of apple leaves at 60 d. The morphological structure of host cells did not visually change before infected leaves showing chlorotic flecks. However, the cytoplasmic staining of the host cells lightened, and the morphology of organelles distorted when the host leaves showed chlorotic flecks (numbers of haustorium were formed and developed). In the spermogonial stage, host cell membranes and organelles became ablation. During the formation of aeciospores, host cells began to necrotic. The content of hydrogen peroxide decreased first and then increased slightly, while the activity of POD and the content of total phenol showed an increasing trend of different amplitude in infected apple leaves.
      Conclusion The basidiospores of G. yamadae germinate to produce germ tubes and appressorium directly enters the host epidermal cells (0−5 d post inoculation, dpi). The number of monokaryotic haustoria is formed by intercellular mycelia or haustorial mother cells to establish the biotrophic parasitic relationship with the host (5−10 dpi). Finally, the rust further develops to produce the spermatia and aeciospores (after 10 dpi). Susceptible reactions of the host cells begin with the haustorium entering mesophyll cells, and necrosis of the host cells occurres in the aecial stage. Furthermore, the infection of G. yamadae results in the considerable accumulation of phenols in apple leaves, which might play a crucial role in maintaining low reactive oxygen species in the host.

       

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