Ultrastructural changes during desiccation of the anhydrobiotic nematode Ditylenchus dipsaci

Ultrastructural changes during desiccation of the anhydrobiotic nematode Ditylenchus dipsaci were followed and quantified after preparation of material at different levels of hydration using freeze substitution techniques. Some shrinkage was caused by processing in the more hydrated specimens but the changes observed correspond to those observed in live nematodes by light microscopy, indicating that the technique is useful for following changes during desiccation. The overall pattern of changes was a rapid decrease in the magnitude of the measured parameter during the first 5 min of desiccation, followed by a slower rate of decrease upon further desiccation. This was observed in the cuticle, the lateral hypodermal cords and the muscle cells and is consistent with the pattern of water loss of the nematode. The contractile region of the muscle cells, however, proved an exception and the muscle fibres appear to resist shrinkage and packing until water loss becomes severe. The mitochondria swell and then shrink during desiccation, which may indicate disruption of the permeability of the mitochondrial membrane. A decrease in the thickness of the cortical zone was the most prominent change in the cuticle and this may be related to the permeability slump which occurs during the first 5 min of desiccation.