Changes in the lipophilicity of the surfaces of Meloidogyne incognita and Haemonchus contortus during exposure to host signals

The surfaces of plant and animal parasitic nematodes share certain lipids, which seem to be important in the infection process. The surfaces of 2 para sitic nematodes, Meloidogyne incognita and Haemonchus contortus, were activ ated by different pH buffers to allow the insertion of different fluorescen t probes. The lipid analogue PKH26 and the surface charge indicator, cation ized ferritin, were used as probes with these nematodes but labelled only t he retaining 2nd-stage moulted cuticle of H. contortus 3rd-stage larvae (L- 3). Shedding of the second moult of H. contortus L-3 was also visualized wi th PKH26 and cationized ferritin. The fluorescent anionic lipid probe 5-N-( octadecanoyl)-aminofluorescein (AF18) was inserted into the epicuticle laye r of M. incognita 2nd-stage juveniles (J(2)) and H. contortus L-3, and also of the second moult of H. contortus L-3. Incubation with tomato root diffu sate caused modifications of the M. incognita surface allowing the insertio n of AF18. Fluorescence with AF18 was significantly decreased after treatin g M. incognita J(2) with amiloride, a potent blocker of hydrogen and sodium (H+/Na+) antiporter. No surface fluidity was observed in M. incognita J(2) and H. contortus L-3 pre-treated with alkaline buffer when the lipid analo gue AF18 was used in fluorescence recovery after photobleaching experiments . The significance of these findings to host infection processes is discuss ed.