Higher Plants - Roots
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Frozen hydrated root hairs
One of the most delicate structures borne on higher plants is the root hair. This is simply a projection of the outer tangential wall of the epidermis of the root, and has a mechanical function as well as a physiological one.
Because root hairs are over 90% water, conventional preparation methods - such as air or critical point drying - always result in considerable collapse, distortion and shrinkage of these structures. Low-temperature SEM, on the other hand, provides good preservation of structure without any collapse.
Root hairs illustrated here still have a thin layer of water (ice) on their surface, verifying their true frozen hydrated nature. If the ice proves to obscure important detail, it can be removed by careful sublimation.
Bar: 50um (inset: 25um)
Freeze-dried root hairs
Carefully controlled freeze-drying can often prove a useful method for preparing soft biological tissue. Root hairs, however, are very sensitive to dehydration and this preparation displays almost universal collapse.
Critical point dried root hair
Root hair, cryo-SEM preserved.
Starch granules in maize
Starch granules in maize.
Image courtesy of Tongji University, Shanghai.