Iron Status Affects the Zinc Accumulation in the Biomass Plant Szarvasi-1.

Thinopyrum obtusiflorum (syn. Elymus elongatus subsp. ponticus) cv. Szarvasi-1 (Poaceae, Triticeae) is a biomass plant with significant tolerance to certain metals. To reveal its accumulation capacity, we investigated its Zn uptake and tolerance in a wide range: 0.2 to 1000 µM Zn concentration. The root and shoot weight, shoot length, shoot water content and stomatal conductance proved to be only sensitive to the highest applied Zn concentrations, whereas the concentration of malondialdehyde increased only at the application of 1 mM Zn in the leaves. Although physiological status proved to be hardy against Zn exposure, shoot Zn content significantly increased in parallel with the applied Zn treatment, reaching the highest Zn concentration at 1.9 mg g-1 dry weight. The concentration of K, Mg and P considerably decreased in the shoot at the highest Zn exposures, where that of K and P also correlated with a decrease in water content. Although the majority of microelements remained unaffected, Mn decreased in the root and Fe content had a negative correlation with Zn both in the shoot and root. In turn, the application of excessive EDTA maintained a proper Fe supply for the plants but lowered Zn accumulation both in roots and shoots. Thus, the Fe-Zn competition for Fe chelating phytosiderophores and/or for root uptake transporters fundamentally affects the Zn accumulation properties of Szarvasi-1. Indeed, the considerable Zn tolerance of Szarvasi-1 has a high potential in Zn accumulation.

Improved Micro-X-ray Fluorescence Confocal Imaging of Two-Dimensional Distribution of Arsenic Concentration in Cucumber Hypocotyls Using Synchrotron Radiation.

An optimized micro-X-ray fluorescence confocal imaging (µXRF-CI) analytical method has been developed to determine the 2D distribution of elemental composition in small (1-3 mm) biological objects at a 10-20 µm spatial resolution. Plants take up chemical elements from soil, and the vascular system transports them toward shoots. In order to obtain biochemical information related to this biological process, 2D distributions of chemical elements in roots and in hypocotyls of cucumber plants were analyzed by synchrotron radiation based on micro-X-ray fluorescence computer tomography and µXRF-CI techniques. The experiments were carried out at HASYLAB Beamline L of the DORIS-III storage ring in Hamburg, a facility that provided optimal physical conditions for developing and performing these unique analyses: high flux monochromatic synchrotron beam, X-ray optical elements, precision moving stages, and silicon drift detectors. New methodological improvements and experimental studies were carried out for applicability of lyophilized samples and cryo-cooling. Experimental parameters were optimized to maximize the excitation yield of arsenic Kα radiation and improvement of the spatial resolution of the µXRF-CI analytical method.

Polycapillary-optics-based micro-XANES and micro-EXAFS at a third-generation bending-magnet beamline.

A focusing system based on a polycapillary half-lens optic has been successfully tested for transmission and fluorescence micro-X-ray absorption spectroscopy at a third-generation bending-magnet beamline equipped with a non-fixed-exit Si(111) monochromator. The vertical positional variations of the X-ray beam owing to the use of a non-fixed-exit monochromator were shown to pose only a limited problem by using the polycapillary optic. The expected height variation for an EXAFS scan around the Fe K-edge is approximately 200 microm on the lens input side and this was reduced to approximately 1 microm for the focused beam. Beam sizes (FWHM) of 12-16 microm, transmission efficiencies of 25-45% and intensity gain factors, compared with the non-focused beam, of about 2000 were obtained in the 7-14 keV energy range for an incoming beam of 0.5 x 2 mm (vertical x horizontal). As a practical application, an As K-edge micro-XANES study of cucumber root and hypocotyl was performed to determine the As oxidation state in the different plant parts and to identify a possible metabolic conversion by the plant.

A Monte Carlo program for quantitative electron-induced X-ray analysis of individual particles.

A versatile Monte Carlo program for quantitative particle analysis in electron probe X-ray microanalysis is presented. The program includes routines for simulating electron-solid interactions in microparticles lying on a flat surface and calculating the generated X-ray signal. Simulation of the whole X-ray spectrum as well as phi(z) curves is possible. The most important facility of the program is the reverse Monte Carlo quantification of the chemical composition of microparticles, including low-Z elements, such as C, N, O, and F. This quantification method is based on the combination of a single scattering Monte Carlo simulation and a robust successive approximation. An iteration procedure is employed; in each iteration step, the Monte Carlo simulation program calculates characteristic X-ray intensities, and a new set of concentration values for chemical elements in the particle is determined. When the simulated X-ray intensities converge to the measured ones, the input values of elemental concentrations used for the simulation are determined as chemical compositions of the particle. This quantification procedure was evaluated by investigating various types of standard particles, and good accuracy of the methodology was demonstrated. A methodology for heterogeneity assessment of single particles is also described.