Scanning electron microscopy of syncytial transfer cells induced in roots by cyst-nematodes

Syncytia induced by cyst-nematodes form by wall dissolution and fusion of cell protoplasts. The patterns and extent of wall perforations of syncytia induced in soybean by Heterodera glycines and in tobacco by Heterodera tabacum were examined by scanning electron microscopy after removal of the cytoplasm. Wall perforations appear to form at sites formerly occupied by pit fields. The origin and control of enzymes responsible for dissolving the walls to form these perforations are discussed. It is concluded that these enzymes are of plant origin

Cellular alterations induced in soybean roots by three endoparasitic nematodes

The cellular alterations induced in soybean roots by three endoparasitic nematodes, Meloidogyne incognita, Heterodera glycines and Rotylenchulus reniformis, were examined by light microscopy Particular reference was made to altered cell walls. No wall gaps were evident in mature giant cells induced by M. incognita; extensive wall gaps were present in syncytia induced by H. glycines and smaller wall gaps occurred in syncytia induced by R. reniformis. In cells altered by all three nematodes some of the walls were evenly thickened. Wall in-growths characteristic of transfer cells were present adjacent to vascular elements in giant cells induced by M. incognita and syncytia induced by H. glycines, but not in syncytia induced by R. reniformis. This difference is discussed in terms of the surface to volume relationships of the altered cells. Clear areas in the cytoplasm of giant cells induced in coleus roots by M. arenaria were interpreted as nematode “saliva”

Scanning electron microscopy in nematode-induced giant transfer cells

A study of giant cells induced by the root-knot nematode, Meloidogyne incognita, in roots of Impatiens balsamina was made by scanning electron microscopy. The cytoplasmic contents of giant cells were removed by a procedure based on KOH digestion, to reveal inner wall structure. Wall ingrowths typical of transfer cells are present in giant cells from six days onwards after induction. They develop on walls adjacent to vascular tissues, and their distribution and development was examined. Pit fields contianing plasmodesmata become elaborated in walls between giant cells, but pit fields are lost between giant cells and cells outside them. The distribution of plasmodesmata in pit fields suggests that de novo formation of plasmodesmata occurs in walls between giant cells. Various aspects of giant cell formation and function are discussed and wall ingrowth development is compared in giant cells and normal transfer cells

Transmembrane potentials of parenchyma cells and nematode-induced transfer cells

A comparison of transmembrane potential (pd) properties of parenchyma cells and giant transfer cells induced by a root-knot nematode in the roots ofImpatiens balsamina has been made. Apart from some differences in rate of response to a few treatments, parenchyma and giant cells had similar pd values; active and passive components of the pd (cyanide, azide); responses to total ion concentration, pH and potassium concentration; responses to protein synthesis inhibitors (puromycin, cycloheximide and actinomycin D) and responses to sugars. Both parenchyma cells and giant cells are depolarized by puromycin, cycloheximide and actinomycin D. The cells recover from the depolarization in the presence of cycloheximide, suggesting that this presumed protein synthesis inhibitor does not act in a straight-forward manner. The cells do not recover in the presence of puromycin or actinomycin D. Parenchyma cells and giant cells clearly have different metabolic rates and ion fluxes, but their pd responses are the same. This suggests that the pd does not reflect metabolic activity or ion fluxes of a cell, but is strictly controlled in itself. Part of this control may be via a feedback mechanism acting on an electrogenic pump. The depolarization caused by glucose is induced by aging the cells after excision. The effect is discussed in terms of an H+ dependent cotransport system and an ATPase permease system. The apparent normality of pd responses of nematode-induced giant transfer cells suggests that they may be a useful model system for experiments on higher plant cells