Immunolabelling of cell surfaces of Arabidopsis thaliana roots following infection by Meloidogyne incognita (Nematoda)

Studies of the migration of second stage juveniles (JJ2) of the root-knot nematode Meloidogyne incognita in Arabidopsis roots were made at the cellular level using immunolabelling techniques. A panel of antibodies that recognize epitopes present in the plant extracellular matrix (JIMs) and the nematode cuticle (PC245) were used. The normal route for the juvenile (J2) has been reconfirmed for both in vitro and in vivo conditions. Histological studies show that, during migration towards the root meristem, juveniles (JJ2) sometimes break the physico-chemical barrier of the endodermis and establish close contact with the central cylinder. Despite this, the juveniles continue their intercortical migration towards the root meristem. When the endodermis is breached, hyperplasia and hypertrophy occur and a premature gall is formed. Ultrastructural observations confirmed that loosening of the middle lamella occurs during progress through the cortex. Differences in the patterns of labelling of healthy and infected roots were revealed when the antipolygalacturonic acid antibody, JIM5, was applied; epitopes recognized by this antibody are mainly located on the triple junctions between cells. Some of the antibodies used proved very useful in illustrating the intercellular migration of JJ2 in the vascular cylinder, where they move in the vicinity of the protoxylem and future metaxylem cells. An envelope surrounding the nematodes, but located specifically on plant cell walls, was observed when infected rootsections were probed with PC245. This material at this interface appears to be of nematode origin. Characterization of the molecules involved is currently under investigation.