芜菁花叶病毒外壳蛋白在寄主植物叶绿体中的积累及其对光系统ll活性的影响

分别以接种感染芜菁花叶病毒(TuMV)和健康对照的青菜苏州青品种(Brassica chinens L．cv．Suzhou)和芥菜温州芥菜品种(B，jucea L．cv．Wenzhou)叶片为材料提取完整叶绿体，用胰蛋白酶消除其表面蛋白后，抽提总蛋白，经SDS—PAGE电泳和Western blot检测，发现TuMV的外壳蛋白(CP)存在于感病寄主的叶绿体中。免疫金标记电镜实验显示TuMV—CP定位在感病青菜和芥菜的细胞质和叶绿体中。对两种寄主植物叶片的叶绿素荧光动力学参数测定结果显示，青菜、芥菜的Fv／Fo、Fv／Fm、φpsⅡ、qp值都有不同程度的降低，qn值增大。实验结果表明TuMV侵染后在寄主细胞叶绿体中积累的CP，抑制了光系统Ⅱ(PS Ⅱ)的光化学活性，这可能是影响寄主植物光合作用的一个重要原因。

Accumulation of coat protein of Turnip mosaic virus in host chloroplasts and its effect on PS II activity.]

Intact chloroplasts were isolated from Chinese cabbage (Brassica chinensis L. cv. Suzhou) and mustard (B. juncea L. cv. Wenzhou) leaves inoculated with Turnip mosaic virus (TuMV). The proteins attached to the surface of chloroplasts were digested, then the total proteins of chloroplasts were extracted. By analysis of the SDS-PAGE pattern, one extra protein band with the same mobility and molecular weight as TuMV-coat protein was found in the chloroplasts of infected leaves. Results of Western blotting showed that this band was highly reactive to the antiserum against TuMV-CP. The detection of immunogold-particles also showed the presence of TuMV-CP in chloroplasts of both host plant species as compared with the healthy control plant. Electron microscopic photograph showed some virus particles and cylindrical inclusions in the cytoplasm of host plants. Some chloroplasts showed abnormalities, including inhibited lamellar development, swollen and rounded, membrane vesiculation and disintegration. On the tenth day after TuMV inoculation, F(v) /F(o), F(v)/ F(m), Phi(PS II) and q(P) values all became lower, but the q(N) values were higher, as compared with the healthy control plants. The results provided the evidence for the presence of TuMV-CP in the diseased chloroplasts. It suggests that the accumulation of TuMV-CP inside chloroplasts affect photosynthesis in virus-infected plants by inhibiting the PS II activity.