Studies on Infection and Multiplication of Plant VIruses in Variegated Tobacco Plants (2) : Infection and Multiplication of Tobacco Mosaic Virus in Variegated Leaves of Tobacco Cultivar Samsun Nc

Abstract

The sensitivity of withe (W) and green (G) areas of variegated tobacco leaves (NIcotiana tabacum cv. Samsun Nc) to infection and multiplication of tobacco mosaic virus (TMV) was compared. 1. The number of local lesions produced on W was double of that on G. 2. The enlargement of local lesions was relatively faster on W, however, TMV concentration at 3-4 days after inoculation was 2-6 times higher in the lesions produced on G as compared to that in the lesions on W. 3. The central and marginal tissues of local lesions developed on W and G were observed by electron microscopy to clarify the processes of collapse and necrotization of cells in relation to TMV amultiplication. The results are as follows. 1) In the central tissues of lesions on both areas of W and G, all cellsd were completely collapsed, shrinked and star-shaped. In these cells, TMV particles were aggregated in crystalline form in altered electron-dense cytoplasm. The size and number of the virus-aggregates in G cells were greater than those in W cells. 2) In marginal tissues of the lesions, various stages of cell necrotization were observed. The first events of cell necrotization were plasmolysis and rupturing of tonoplast. Following these events, the plastids or chloroplasts burst and the continuity in the cytoplasmic membrane occurred earlier than bursting of plastids. TMV particles were scattered in the cytoplasm with bursting of the tonoplast in W and G cells. 3) No remarkable difference was observed in the ultrastructure of margins of the lesions from W and G. TMV particles were observed in the cytoplasm of several cells beyond the necrotic region. 4. From these results, the fact that TMV concentration in local lesions on W is lower than that in the lesions on G, contrasting to highersensitivity (in terms of lesion formation) of the former than the latter, may be attributed to the rapid cell necrotization in W cell as compared to that in G cells resulting in early inhibition of virus multiplication.タバコ(Nicotiana tabacum cv. Samsun Nc)の斑入り葉の白色部と緑色部とにおけるTMV の感染･増殖を比較した.1. TMV局部病斑は白色部において多く現われ,その数は線色部における病斑数の約2倍であった.2. 局部病斑の拡大は白色部においてやや速やかであったが,接種3, 4日目の病斑部から回収されるTMV量は緑色部の病斑において高く,白色部の病斑から回収される量の2-6倍であった.3. 白色部と緑色部とにおける4日目の局部病斑の内部およびその周縁部組織を電顕観察して,細胞え死に伴う崩壊過程とTMV粒子の存在状態を詳細に比較した結果次のような所見が得られた.1) 白色および線色両組織における局部病斑内部の細胞は完全に崩壊し,収縮して屋形を呈した.これらの細胞においてはTMV粒子は変質した細胞質内に結晶状に集合した状態で存在し,白色細胞より緑色細胞でより大きな集団を形成し,またその数も緑色細胞で多かった.2) 病斑周縁部の組織においては細胞え死化の種々の段階の像が見られ,え死化の第1段階は原形質分離とtonoplastの崩壊であった. これに続いてplastidまたは葉緑体と細胞質膜の崩壊が起こった.細胞質膜の連続性は緑色組織より白色組織でより早く失われた.TMV粒子は白色および緑色細胞のいずれにおいてもtonoplastの崩壊によって細胞質内に散在していた.3) 病斑を取り巻く細胞内で見られる形態的変化においては白色,緑色両組織の間に顕著な差異が認められなかった.TMV粒子はえ死細胞の数層外側の細胞においても見られた.4) 以上の結果から,白色部のTMV感受性(柄斑形成数)は緑色部のそれに比べて高いにもかかわらず白色病斑部のTMV量が緑色病斑部の量に比べて低い原因はウイルス増殖に伴う細胞え死化が白色細胞において緑色細胞におけるよりもより早く現れ,TMVが十分に増殖する前に細胞機能の低下を引き起こすためと考えられる