[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.