Cryofixation of plant tissues without pretreatment

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Abstract
SUMMARY: Root tips from Sorghum and Dahlia were frozen without cryoprotection by dipping into nitrogen slush, rapid immersion in liquid propane and by the high‐pressure method. Structural preservation of the samples was studied using freeze‐fracture (FF) and freeze‐substitution (FS) techniques for electron microscopy. It was found that most of the organelles were disrupted by freezing in nitrogen slush and that only the boundary beween the cytoplasm and the vacuole remained visible. If the samples were frozen by rapid immersion in liquid propane, small membraneous organelles, such as dictyosomes, were preserved in peripheral regions of the rhizodermal cells up to 10 μm below the surface of the tissue. Specimens frozen by the high‐pressure freezing technique showed good ultrastructural preservation throughout the tissues up to a depth of more than 100 μm.