Advanced Micronutrient Imaging in Plants: The POLYX Beamline at the NSRC SOLARIS JU

Abstract

Micronutrients such as Zn, Cu, Fe, and Mn play essential roles in plant physiology, yet their low concentrations and tissue-specific distributions pose significant analytical challenges. While various imaging techniques exist, most either sacrifice resolution for throughput or lack the ability to quantify elemental co-localization across scales. In this study, using the POLYX beamline at the National Synchrotron Radiation Centre SOLARIS, we applied micro X-ray fluorescence (µXRF) mapping to investigate the spatial distribution and co-localization of Zn, Cu, Fe, Mn, and Ca in the root system. Whole-root scans at 100 µm resolution provided an overview of elemental architecture, while selected regions imaged at 5 µm resolution revealed tissue-level heterogeneity. To interpret elemental relationships, we generated overlap matrices using both loose (92%) and strict (97%) intensity thresholds and calculated Pearson and Spearman correlation coefficients alongside Manders' overlap metrics. Our  results  show  that  coarse  resolution  inflates apparent co-localization, particularly for Zn, which appears broadly distributed at  100 µm  but  is  confined  to  outer  tissues  at 5 µm.  In contrast, Ca-based overlaps remained stable across scales, while Fe–Mn pairs showed intermediate resolution sensitivity. This study demonstrates that the whole plant root may be analysed using the POLYX beamline setup with a multiresolution range (from 5 µm). We show a methodological framework for micronutrient localization in roots of relatively large (beyond seedling) plants and offer first insights into potential differences in element heterogeneity that may result from the spatial regulation of nutrient uptake and transport, giving a preliminary framework for future studies.