The effects of various pre-treatments on the freeze-etching of root tips

Results of experiments on the pre-treatment of root tips for freeze-etching are outlined. Successful freeze-fixation of viable roots was obtained using seedlings of Avena, Triticum and Zea. The seeds were germinated in contact with water, then placed on top of tubes of filter paper impregnated with glycerol; this allowed aeration of the roots. Most roots grew slightly on exposure to glycerol and remained turgid. Avena and Triticum gave good freeze-fixation after 7 days in contact with 20% glycerol and after contact with 20% glycerol for 3 days followed by 25% glycerol for 3 days. Good preservation was also obtained with Zea but results were more variable than in Avena and Triticum. Root tips fixed in glutaraldehyde, either in glycerol or followed by glycerol, gave consistent freeze-fixation in all species. Results were comparable to those obtained from viable material. However, in some instances there was shrinkage of the organelles and the plane of fracture within certain membranes was altered.