Comparative ultrastructure of conventionally fixed and high-pressure frozen chloroplasts of Vitis vinifera

Abstract

Chemical fixation of biological samples for transmission electron microscopy is still the most widely used method because of the availability of low cost chemicals and universal knowledge of the fixation protocol. Microscopists are very familiar with images of the chemically fixed cell with its irregular membranes, flattened Golgi cisternae, elongated mitochondria and football-shaped chloroplasts. But the advent of high quality ultra-rapid freezing techniques in the past decade or so has greatly increased our knowledge of cellular ultrastructure and altered our perception of biological material preserved in a “lifelike” state. While many of the best freezing techniques achieve a depth of well frozen tissue to only 10-40μm, the high pressure freezing method (HPM) yields well preserved tissue samples to approximately 600μm. Although the HPM is becoming more popular, it is still a relatively novel technique.