High-resolution imaging of the ultrastructure of living algal cells using soft x-ray contact microscopy

摘要

Soft x-ray contact microscopy provides the biologist with a technique for examining the ultrastructure of living cells at a much higher resolution than that possible by various forms of light microscopy. Readout of the developed photoresist using atomic force microscopy (AFM) produces a detailed map of the carbon densitites generated in the resist following exposure of the specimen to water-window soft x-rays (2-4nm) produced by impact of a high enrgy laser onto a suitable target. The established high resolution imaging method of transmission electron microscopy (TEM) has inherent problems in the chemical pretreatment required for producing the ultrathin sections necessary for this technique. Using the unicellular green alga Chlamydomonas the ultrastructural appearance of the cells following SXCM and TEM has been compared. While SXCM confirms the basic structural organization of the cell as seen by TEM (e.g. the organization of the thylakoid membranes within the chloroplast; flagellar insertion into the cytoplasm), there are important difference. These are in the appearance of the cell covering and the presence of carbon-dense spherical cellular inclusions.