Ultrastructural effects of PVYNTN infection of <em>Capsicum annuum</em> L. cv. Yolo Wonder generative organs; a first step in describing seed transmission

Abstract

Potato virus Y ^NTN (PVY^NTN), a member of the family Potyviridae, is one of the most important plant viruses. Despite common occurrence of seed transmission process in the Potyviridae, the number or routes of virion entry into seeds are still unclear. Embryos could probably be infected either through host embryogenesis processes or via infection of reproductive tissues, therefore both processes of virus transmission in seeds and pollen grains are likely to be related. Infection by PVY has been studied in detail in host vegetative organs. We investigated, for the first time the impact of infection by the necrotic strain of PVY on Capsicum annuum reproductive organs. We found PVY^NTN particles inside C. annuum pollen grains and on the exine surfaces, and PVY epitopes were also found in pollen tubes. We postulate that the male gametophyte in C. annuum could be a source of PVY infection, which may have significance in self-pollinated hosts. We also demonstrated that PVY^NTN particles could be detected inside C. annuum seeds on embryo surfaces, while particles and Potyvirus inclusion bodies were observed in endothelium layers. These were mainly detected inside ovarian tissues, that is, in the ovular integuments and nucelli. Changes in both gametophytes strongly indicate that generative organs were a source of PVY^NTN infection. Furthermore, we have demonstrated that in C. annuum, PVY was transmitted vertically via seeds.