Defence responses of Arabidopsis thaliana during invasion and feeding site induction by the plant-parasitic nematode Heterodera glycines

The nature of local defence responses occurring during the infection of Arabidopsis thaliana by the soybean cyst nematode Heterodera glycines was analysed by light and electron microscopy. Arabidopsis thaliana is not a regular host of this nematode, but invasion, feeding site induction and in rare cases development of juveniles was observed. Compared to Heterodera schachtii, which interacts compatibly with A. thaliana, the period of invasion and migration was prolonged. During migration a strong hypersensitive response, characterized by extensive necroses, browning, autofluorescence and cell wall depositions, occurred in cells that were not in direct contact with the nematodes. Cells selected as initial syncytial cells were pierced with the stylet and, after having passed a preparation phase, secretions were released. The cells responded with rapid vacuolation and deposition of callose-like material around the styler and at the cell walls. and subsequent necrosis. In a very few cases the initial syncytial cells and neighbouring cells deposited callose-like material on their walls, but these cells remained intact so that functional syncytia developed, which allowed occasional nematode development.