The Role Of Callose Deposition At Plasmodesma In Soybean Against With Soybean Mosaic Virus

The role played by callose (β-1,3-Glucan) to protect plants against virus has gained more and more attentions, however, its exact effect to keep soybean away from soybean mosaic virus (SMV) infection is relatively little known. In this experiment, the soybean (Jidou 7) and SMV strain SC-8 and N3 were formed compatible combination and incompatible combination respectively, by inoculating virus with pointion inoculation method, then studied the effect of callose formation on the intercellular transfer of SMV in the soybeans plants was studied by using diameter measurement of hypersensitive necrosis spot, callose specified aniline blue fluorescent dye staining, callose immunogold and SMV coat protein gene test as well as fluorescent microscope or electron microscope observation.The results showed that, in incompatible combination, we could observed that plenty of callose fluorescence in inoculation sites before and after the forming of hypersensitive necrosis spots, which was firstly observed in 2 hours after inoculation and reached to strongest intensity in 96 hours after inoculation; the immunogold and RT-PCR results showed that callose located in the neck of plasmodesmata and CP gene was not observed in leaves above inoculated leaves respectively; while in compatible combination, callose fluorescence was not observed before and after the forming of hypersensitive spots; callose labeled by gold particle was also not found in the neck of plasmodesmata; and SMV CP gene could be observed in the upper leaves in 42 hours after the inoculation, which indicated that virus has been transferred to the upper leaves. Compared with compatible combination, diameters of necrosis spots in incompatible combination were obviously longer than the compatible one, and the diameter in 168 hours after inoculation was 1mm longer than that in 96 hours. In incompatible combination, through virus CP gene test of the inoculation sites showed that the virus CP gene was restricted in the necrosis spots and 1mm around in 96 hours after inoculation and disappeared in 168 hours after inoculation. The above results indicated that callose might involve in SMV resistance of soybeans before the forming of necrosis spot (in the early stage of virus infection) and play an important role in blocking the virus intercellular spread. In order to further confirm the effect of callose on the virus-resistance of the host, injecting 2-deoxy-D-glucose (2-DDG, an inhibitors of callose synthesis) of different concentration to the incompatible combination. In the concentration of 500μmol/L, SMV CP gene in upper leaves were observed and no callose fluorescent in the necrosis spots and surrounding healthy cells were founded in 4 days after inoculation, and vein necrosis and necrosis spots appeared in upper leaves after 8 days.In summary, while soybean infects SMV and generates hypersensitive necrosis spots, callose can modify the neck of plasmodesmata, by which it can prevent virus intercellular transfer, so the virus can not be long-distance transport.