Imaging techniques for elements and element species in plant science

Abstract

Revealing the uptake, transport, localization and speciation of both essential and toxic elements in plants is important for understanding plant homeostasis and metabolism, subsequently, providing information for food and nutrient studies, agriculture activities, as well as environmental research. In the last decade, emerging techniques for elemental imaging and speciation analysis allowed us to obtain increasing knowledge of elemental distribution and availabilities in plants. Chemical imaging techniques include mass spectrometric methods such as secondary ionization mass spectrometry (SIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and synchrotron-based techniques such as X-ray fluorescence spectroscopy (SRXRF), and so forth. On the other hand, X-ray absorption spectroscopy (XAS) based on synchrotron radiation is capable of in situ investigation of local atomic structure around the central element of interest. This technique can also be operated in tandem with SRXRF to image each element species of interest within plant tissue. In this review, the principles and stateof-the-art of these techniques regarding sample preparation, advantages and limitations, and improvement of sensitivity and spatial resolution are discussed. New results with respect to elemental distribution and speciation in plants revealed by these techniques are presented.

Imaging element distribution and speciation in plant cells

“…The charged ions are detected by their mass-to-charge ratio, m/z, in the mass spectrometer. The spatial resolution of the common laser ablation systems generally ranges from 50 to 300 mm [25]. A high resolution can be achieved using a laser beam with a smaller spot size, although this may lead to insufficient energy focused on the sample and, hence, limited ablation of the material.…”

Influence of Soil Chemistry and Plant Physiology in the Phytoremediation of Cu, Mn, and Zn

“…The distribution of trace metals in leaf tissues is generally asymmetric (Wu and Becker, 2012). Trace metal accumulation in leaf vacuoles makes sense because vacuoles do not contain a photosynthetic apparatus that would be sensitive to metal toxicity (Leitenmaier and Kupper, 2011).…”

Analytical approaches to support current understanding of exposure, uptake and distributions of engineered nanoparticles by aquatic and terrestrial organisms

“…LA-ICP-MS can be used to simultaneously analyse a range of elements, including isotopes (Becker et al 2010;Durrant and Ward 2005) with a spatial resolution of 5-200 lm and detection limits in the lower ppb range (Qin et al 2011). Technical improvements are currently being developed, such as near field LA-ICP-MS (Zoriy and Becker 2009) that may take spatial resolution to\200 nm, although this comes with the potential for some trade-offs in analytical sensitivity (Wu and Becker 2012).…”

“…Specimen preparation for LA-ICP-MS is relatively easy, partly because imaging is performed at atmospheric pressure. Whole tissue or 20-30 lm thick cryosections are ideal (Becker et al 2010;Wu and Becker 2012), as these dispense with the need for elaborate fixation, dehydration and resin or wax embedding which might alter the distribution, concentration, or chemical form of analytes. Overall quantification using LA-ICP-MS is generally easier to achieve than with other mass spectrometry techniques such as SIMS and Matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) (Santos et al 2009), hence the method can act as a good first tier spatial distribution analysis tool.…”