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.
Rock cress (Arabidopsis)
Cryo-fixed rock cress (Arabidopsis) leaf: trichome with virus. 3kV, secondary electron image. Second picture is higher power: 2.5kV, secondary electron image. Uncoated.
Images courtesy of FEI and the Max Planck Institute, Cologne, Germany.
Organelles in cells from the apical meristem
Cells of the apical meristem are non-vacuolated with a cytoplasm rich in organelles. There are no intercellular spaces between them. In many meristematic cells the fracture has passed through nuclei (marked by arrows), and in places larger organelles (plastids and large vesicles) are obvious.