A new technique is described to prepare plant material for electron probe analysis. Root segments 1 mm in length were frozen at-170°, freeze-substituted with anhydrous ether at-30° and infiltrated with Spurr's low-viscosity epoxy resin embedding medium at low temperatures. Sections 1 and 2μ thick were cut anhydrously using hexylene glycol in the ultramicrotome trough, mounted on the polished surface of a Be disc and vacuum coated with 150-200 Å aluminum.The new technique allows retention of water-soluble ions at the original sites in the tissue and is superior to cryostat sectioning in spatial resolution of electron probe analysis and in the preservation of cellular structures.The lateral transport of K(+) into the xylem of corn roots has been successfully studied by electron probe analysis of freeze-substituted, epoxy resin embedded material.
In the use of diamond knives for sectioning materials to be observed by electron microscopy, new knives occasionally do not have the expected durability or do not yield satisfactory sections from the outset. The problem seems to be inherent in specific diamond knives with no apparent tearing on the manufacturing source. Among the causes or combination of factors that may account for this, we are confining our attention to one, namely, variations in composition of the diamond itself. Impurities such as silicon, magnesium, aluminum, calcium, iron, and copper in quantities of 0-79 ppm are reported in diamond (Raal, 1957; Bunting and Van Valkenburg, 1958) and some are believed to be related to lattice defects.
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