Cryo-scanning electron microscopy (CSEM) in the advancement of functional plant biology: energy dispersive X-ray microanalysis (CEDX) applications

Abstract

The capacity to make measurements of elemental concentrations at the level of single cells by energy dispersive X-ray microanalysis of cryo-fixed, inherently-hydrated plant parts (CEDX) is changing or extending our understanding of many plant functions. We include in this review a wide-ranging catalogue of studies that have used CEDX which provides access to the literature on elements measured, plants and tissues studied, techniques used, level of quantitation and the significant findings. These findings include new perspectives on the following areas: salt tolerance; xylem maturation and solute content, root pressure and embolism refilling; the contents of intercellular spaces; sequestration of toxic elements; biomineralisation with silicon; movement of tracer homologues of native cations; indirect localisation of molecules with a distinctive element component; transfer of nutrients from vesicular-arbuscular (VA) mycorrhizas; the role of mucilages in protection and in generating mechanical force. In an Appendix we discuss the procedures involved in CEDX: cryo-fixation, specimen planing, etching, elemental quantitation and mapping. Limitations on sample numbers, elements measurable, spatial resolution, sensitivity and threshold concentrations quantifiable are outlined. A brief discussion of the potential of emerging technologies for cell-specific analysis of cryo-fixed, hydrated specimens is included. In the Accessory Publication we list our standard protocol for CEDX.