CHANGES IN THE STRUCTURE OF ARABIDOPSIS-THALIANA ROOTS INDUCED DURINGDEVELOPMENT OF MALES OF THE PLANT-PARASITIC NEMATODE HETERODERA-SCHACHTII

Plant parasitic nematodes of the genus Heterodera show a high degree o f sexual dimorphism, which is reflected by different nutritional deman ds and differences in the structure of the induced specific syncytial feeding site in the plant. The determination of the sex of the nematod e Heterodera schachtii and other related species was repeatedly report ed to be dependent on trophic factors, which are provided by the induc ed syncytia. The structural differences of syncytia induced by H. scha chtii in roots of Arabidopsis thaliana were analysed at the anatomical and ultrastructural level. Syncytia of males were induced in the root pericycle. The developing syncytium then expanded into procambial or cambial cells of the vascular cylinder. Differentiated vascular elemen ts were not included. The expansion of the syncytium triggered the pro liferation of cambial and peridermal tissues, in a manner similar to s econdary growth, and the formation of additional xylem and phloem elem ents. In comparison to syncytia associated with females, syncytia asso ciated with males were less hypertrophied and were composed of more ce lls. Distinct cell wall openings were mostly found between the few str ongly hypertrophied syncytial elements at the actual feeding site in t he pericycle. The ultrastructure was very similar to female-associated syncytia but showed conspicuous differences in the structure and loca lization of cell wall ingrowths. These ingrowths were rare and weakly developed and occurred not only at the interface with xylem elements b ut also at the internal and external walls of the syncytia. After feed ing had ceased at the end of the third developmental stage the syncyti a degenerated.