Studies on Cytopathology of Viroid Infections

本研究旨在描述类病毒感染细胞中发生的细胞病变过程，并阐明类病毒感染特有的致病机制。利用柑橘裂皮类病毒(CEVd)、啤酒花矮化类病毒(HSVD)和苹果疤皮类病毒(ASSVd)，获得了如下结果。侵染CEVd的番茄叶片细胞病理变化表现为：顶生叶细胞壁起皱、叶绿体解体、线粒体解体等；第5叶叶片出现轻度卷曲症状，但未观察到特异性症状。感染HSVd的啤酒花树脂腺的细胞病变在啤酒花植株中形成两种树脂腺，即盘状腺和杯状腺。在感染的两个腺体的分泌细胞中，主要观察到典型的细胞壁扭曲和亚细胞器的紊乱。此外，在感染的细胞中，树脂物质(α-酸)不能完全释放到角质层下间隙，因此杯子不能充满晶格状结构，这表明细胞外α-酸的分泌减少。苹果果实受ASSVd侵染后，果皮细胞形态的变化。Indo)细胞严重扭曲，细胞壁呈波状，厚度不规则。在皮下各层中，果胶物质不能聚集到细胞间隙。从而导致皮下细胞扁平。综上所述，上述结果表明，叶细胞、分泌细胞和果皮细胞的细胞壁变形一致地导致了细胞骨架结构变形的顺序过程，而细胞骨架结构变形是类病毒侵染的结果。

The present study was undertaken to describe the cytopathic processes occurring in viroid-infected cells and to demonstrate the mechanism of pathogenesis specific to viroid infection. By using citrus exocortis viroid (CEVd), hop stunt viroid (HSVD) and apple scar skin viroid (ASSVd), following results are obtained.1. Cytopathic changes in CEVd-infected tomato leaf cells.Leaflets on terminal leaves bearing severe rugosity showed the undulated cell wall, disorganization of chloroplasts, mitochondrial disintegration etc. In the leaflets on 5th leaf bearing mild curling symptom, however, no specific symptoms were observed.2. Cytopathic changes in HSVd-infected resin glands of hops.In hop plants, there have been formed two kinds of resin glands, i. e., disk-shaped gland and cup-shaped gland. Typical cell wall distortion and disorganization of subcellular organella were predominatly observed in the infected secretory cells of both the glands. Moreover, it was evident in the infected cells that resinous substance (alpha acid) could not fully liberated into subcuticular space, thus the cup could not filled with lattice-like structure, suggesting the decrease in extracellular secretion of alpha acid.3. Cytopathic changes in ASSVd-infected fruit skin of apple.The cell shapes of fruit skin (epidermis and hypodermal layers) of the infected apple fruit (cv. Indo) were severely distorted and their cell walls were undulated with irregular thickness. In the hypodermal layers, it was noticeable that pectic substances could not accumulated into the intercellular space. thus resulting in the flattened hypodermal cells.4. To be summarized.The results mentioned above indicated to suggest that cell wall distortion in the leaf cells, secretory cells and fruit skin cells consistently leads to the sequential processes of the structural deformation of cell skeltones which are disturbed as a consequence of viroid infection.