Comparison of Soft X-Ray Contact Microscopy with Other Microscopical Techniques for the Study of the Fine Structure of Plant Cells

Abstract

The maximum resolution of light microscopy is about 250 nm, so for most biological ultrastructural work the electron microscope with its higher resolution of approximately 5 nm is used. However, since electrons are readily absorbed by biological material, thin sections (usually 50–100 nm) are essential, with subsequent heavy metal deposition to enhance contrast. The preparative procedures necessary for electron microscopy (fixation, embedding, sectioning and post-staining all have the potential for introducing artefacts into the final image obtained. During the development of electron microscopy such problems have been reduced and this technique is now widespread and accepted as the only practical method for examining the fine structure of cells. The technique of soft x-ray contact microscopy offers the potential for examining wet (living) cells with a higher resolution (< 100 nm) than light microscopy though its resolution is unlikely to approach that of transmission electron microscopy (TEM). Initial work at Daresbury using the lower energy synchrotron-generated soft x-rays, required relatively long exposure times (10–20 secs.). The possibility of cell damage before imaging necessitated the use of critical point dried (CPD) rather than wet cells. The higher energy of laser-produced plasmas at the Rutherford-Appleton Laboratory (RAL) permitted very short exposure times (1–50ns) so enabling wet cell imaging to be attempted. We report here preliminary results on the imaging of whole algal cells which were selected because their dimensions (1–10μm) were within the theoretical penetration limit of soft x-rays. The images obtained are compared with those produced by light microscopy (Nomarski interference) and TEM.