THE PREPARATION OF CRYOSECTIONS FROM PLANT-TISSUE - AN ALTERNATIVE METHOD APPROPRIATE FOR SECONDARY-ION MASS-SPECTROMETRY STUDIES OF NUTRIENT TRACERS AND TRACE-METALS

A method involving cryostat sectioning (10 mu m thickness) and freeze- drying is presented for the preparation of plant tissue for microanaly tical studies. The method is well suited for semi-quantitative imaging by secondary ion mass spectrometry (SIMS) and offers significant adva ntages oner bulk freeze-dried or freeze-substitution preparations. Seg ments of corn or soybean root (5 mm) are quench-frozen, embedded exter nally, sectioned in a cryostat (10 mu m), pressed onto ultrapure Si an d slowly freeze-dried. Images of these sections with secondary electro n microscopy and SIMS indicated good morphological preservation. It wa s possible to section tissues of a wide developmental range, as well a s roots varying sixfold in diameter. SIMS images are presented which d emonstrate the ability to detect and localize nutrient tracers, such a s Rb+, following brief exposures (10 min) to the intact plant. Likewis e, a toxic metal (Al) was localized in root tissue after brief exposur e (<1 day) of the intact plant root to micromolar external concentrati ons. Elemental redistribution during processing was minimal, as demons trated most explicitly by the lack of movement of loosely bound Ca fi om the outer cell walls into the adjacent embedding material. Preserva tion of compositional differences between cellular content and cell wa ll was supported by a semi-quantitative treatment of SIMS images.