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United States Department of Agriculture

Agricultural Research Service

Title: A Comparison of Cryofixation and Chemical Fixation for Viewing Nematode Faces

Authors
item Carta, Lynn
item Wergin, William
item Erbe, Eric -
item Murphy, Charles

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2002
Publication Date: N/A

Interpretive Summary: Plant-parasitic nematodes are microscopic worms that annually cause crop losses of ten billion dollars in the United States. One problem with identifying them is the very small number of anatomical features that do not vary among different specimens of the same nematode species or among different methods of preparation for examination in a powerful microscope called the scanning electron microscope. Therefore, this paper examines the anatomical variations among the faces of nematodes prepared by chemical methods versus a new low-temperature method involving specimens prepared in a natural state within a frozen specimen holder. Three destructive species of nematodes called lesion nematodes were selected for study. The major finding was that lesion nematodes prepared with the low- temperature technique showed six sectors within their lips that were absent in chemically prepared specimens. These lips are important features for identifying species. In addition, sensory pore secretions occurred in the majority of chemically prepared nematodes, but not in those prepared with the new method. The results are significant because nematode faces are more life-like with this new method and are thus more useful as features for nematode identification. This information will be used by other scientists studying nematode anatomy or identifying nematode species in order to determine which are causing crop losses.

Technical Abstract: Faces of the lesion nematodes Pratylenchus teres (populations RTB and JK) and P. zeae or the bacterivore Distolabrellus veechi were observed as frozen specimens with low temperature scanning electron microscopy (SEM), and as chemically fixed specimens with conventional (ambient temperature) SEM. Amphidial secretions occurred in chemically fixed but not cryofixed lesion nematodes. Overhanging liplets of chemically fixed Distolabrellus veechi when cryofixed appeared as variably filled mostly empty membranes, and may be artifactual. The frozen lesion nematodes exhibited six sectors of variable prominence within the diagnostically useful lips that were absent in chemically fixed specimens. The variable sectoring observed in Pratylenchus spp. is proposed to be due to different degrees of muscle contraction that were captured during cryofixation, which occurs in microseconds. This is the first evidence that rarely observed lip sectors in Pratylenchus may be something other than an artifact of shrinkage.

Last Modified: 7/22/2014
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