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SUMMARY Tomato leaf sections were freeze substituted with either ethanol, n-propanol, 20·0% acrolein: diethyl ether or acetone and then examined with an ion microscope to determine Na, K and Ca distributions. Thin sections were also examined for ultrastructural preservation using a transmission electron microscope. Generally, the 20·0% acrolein: diethyl ether and to a lesser degree the n-propanol substituted materials demonstrated better ultrastructural preservation than the ethanol or acetone substitued materials. Ion micrographs for Na, K and Ca2+ of the 20·0% acrolein:diethyl ether and n-propanol substituted leaves revealed a low contrast, well-graded response with more informational content while tissue substitued with ethanol gave a high contrast response with little or no gradation. Ion losses from the leaf sections after substitution were monitored with neutron activation analysis (NAA) and initial experiments revealed significant contamination by molecular sieve desiccants. Empirically derived correction factors compensated for these contaminants; however, further experimentation utilizing silica gel as a solvent desiccant demonstrated ion retention values in excess of 80%. |
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