Ultrastructure of feeding plugs and feeding tubes formed by Heterodera schachtii

The development of feeding plugs and feeding tubes formed in syncytia induc ed by the cyst-forming nematode Heterodera schachtii in roots of Arabidopsi s thaliana was examined at the ultrastructural level. The feeding plug was first observed 24 h after selection of the initial syncytial cell (ISC) and was present throughout the entire nematode life cycle. In later stages of nematode development the feeding plug became increasingly robust and infilt rated by fibrillar syncytial wall material while the central part, through which the nematode stylet was inserted, retained an amorphous structure. Ne ither the feeding plug nor the nematode stylet were observed to penetrate t he plasmalemma of the syncytium. After the nematode completed the preparati on phase for feeding, the first secretions were released from the stylet or ifice and emitted through the plasmalemma into the cytoplasm. They formed u niformly osmiophilic wavy tubes without an electron translucent lumen. The first typical feeding tubes were found 24 h after ISC selection and were co mposed of an electron dense wall and an electron translucent lumen. The siz e of a single feeding tube was about 1 x 4 mu m. No difference occurred bet ween feeding tubes formed by male and female juveniles. Frequently, membran es of the endoplasmic reticulum were connected to the wall of feeding tubes . After the nematode completed feeding, the tubes were disassociated from t he styler orifice and were dispersed in the syncytial cytoplasm. The feedin g tube lumen was filled with cytoplasm and the wall gradually degraded.