Plasmodesmal modifications and distribution of tospovirus in potato and tomato

The tospovirus isolate on tomato was found to be systemic while the one on potato was non-systemic. The virus was present in all the tissues except xy lem vessels in tomato, while it was often found only in the cortical cells of potato stems. Virions were detected in all cells of phloem tissue in tom ato, while none were present in the case of potato. Plasmodesmata were pres ent between phloem parenchyma and the phloem sieve tubes in infected tomato but none were present in infected potato. There were pronounced plasmodesm al changes in response to infection in tomato. These included dissolution o f the desmotubule (central rod-like structure), making the plasmodesmata po re-like structures with a diameter of ca. 45 nm, which contained electron-d ense material, presumably ribonucleoprotein of the virus. No such changes w ere found in infected potato. These results of comparative studies suggeste d that the virus was non-systemic in potato due to its non-loading into the phloem and consequently lacked long distance transport.