Electron probe analysis of freeze-substituted, epoxy resin embedded tissue for ion transport studies in plants

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Abstract
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.