||After infected the plants of soybean, soybean mosaic virus ( SMV) will be transported between the cell through the plasmodesmata and complete the long distance transport via the sieve tubes of the phloem. There have been many investigations concerning the transportation through the plasmodesmata, but little known about the long distance transport because it is diffcult to let the SMV inoculate to the vascular.Preliminary work in our laboratory has showed that in the resistant varieties the modifications in the neck of the plasmodesmata restrict cell-to-cell transport through the plasmodesmata,blocking the SMV into the vascular for the long distance transport, which limited the virus to a small area within the inoculation region. So we propose that callose deposition in plasmodesmata plays an important role in SMV transport.In the present study, we has study the mode of the action of the callose in the long distance transport of the SMV,by inoculating the SMV to the vascular using grafting techniques, then observe the disease of the grafting leaf,detect the gene of the SMV coat protein(SMV-CP), fluorescence and pharmacological experiment using a specific dyeing on callose. The materials used in this study were soybean JD-7、JH-13 and nf-58. the soy bean mosaic virus were SC-8 and N3. Soybean JD-7 and JH-13 were susceptible to SMV SC-8 respectively, JD-7 was resistant to SMV N3 and nf-58. was susceptible to SMV N3. The results are as follows:1. The soybean JH-13 and nf-58 has been grafted to JD-7 sucessfully at the appropriate instar of the rootstock and the ingraftment and by controlling the temperature and humidity.2. The SMV SC-8 was inoculated to the JH-13 leaves, six days later the SMV-CP gene was detected in the stem and second leaves of JD-7 respectively, then symptom of disease appeared in the second leaves which showed that the SMV was inoculated to the vascular successfully. The SMV transport from the sieve tubes of the phloem.to the upper leaves because JD-7 are susceptible to SMV SC-8 .3. The SMV N3 was inoculate to the leaves of nf-58, six days later, the SMV-CP gene was not detected in the lobus superior of JD-7, also no symptom of disease was found,however,the SMV-CP gene was detected in the bottom of stem of JD-7, there is no CP gene in the superior part of stem. This has showed that the SMV was inoculated to the vascular successfully,but the SMV transport was blocked because the JD-7 is resistant to SMV N3.4. By staining with aniline blue,we also observed strong florescence spots due to callose formation on sieve plate in the bottom stem of JD-7 but no upper stem after SMV N3 was inoculated to the leaves of nf-58.Weak fluorescence or no fluorescence on sieve plate in the upper or bottom stem of JD-7 after SMV SC-8 was inoculated to the leaves of JH-13.5. To further examine whether the callose deposition observed in result 4 was involved in plant resistance against virus in phloem, inoculation experiments were performed by,prior to inoculation, injecting plant tissues with DDG which is a callose synthesis inhibitor. Injecting with 500μM DDG prior to inoculation found that the virus was unable to induce callose deposition on sieve plate, and the virus was able to transport via the sieve tubes of the phloem as judged by the appearance of foliar symptoms as well as by the expression of SMV-CP gene from the upper leaves.These results have showed that callose is the main factor in blocking the SMV into the vascular for the long distance transport.