Feinstrukturelle Untersuchungen zur Entwicklung von Wurzel-Riesenzellen (Syncytien) induziert durch den Rübenzystennematoden Heterodera schachtii

Abstract

The ultrastructure and development of syncytia in rape roots, induced by the sugarbeet cyst nematode Heterodera schachtii in sterile agar culture was studied 60 h as well as 5, 7, 21 and 48 d after inoculation with infective larvae. 60 h after inoculation the cells at the permanent feeding site of the parasite within parenchymatous tissue of the vascular cylinder showed increased cytoplasmatic density due to marked increase of free ribosomes and the reduction of central vacuoles into numerous small vacuoles. First sign of cell wall dissolution became evident at this stage. At later stages wall breakdown was pronounced and the syncytia this formed were filled with smooth endoplasmatic reticulum, mitochondria and plastids. Tubules of smooth ER were frequently arranged in a parallel manner. Nuclei had increased in size, their envelope was distinctly lobed and they contained prominent nucleoli. Wall ingrowths, adjacent to xylem vessels, initiated 5 d after inoculation, were well developed in later stages. At a time when signs of cytoplasm degeneration became evident, the syncytium looked like a transfer cell. Exposure of infected roots to light led to the transformation of plastids into chloroplasts within the syncytia.