Quantification of spatial metal accumulation patterns in Noccaea caerulescens by X-ray fluorescence image processing for genetic studies

Abstract

Background Hyperaccumulation of trace elements is a rare trait among plants which is being investigated to advance our understanding of the regulation of metal accumulation and applications in phytotechnologies. Noccaea caerulescens (Brassicaceae) is an intensively studied hyperaccumulator model plant capable of attaining extremely high tissue concentrations of zinc and nickel with substantial genetic variation at the population-level. Micro-X-ray Fluorescence spectroscopy (µXRF) mapping is a sensitive high-resolution technique to obtain information of the spatial distribution of the plant metallome in hydrated samples. We used laboratory-based µXRF to characterize a collection of 86 genetically diverse Noccaea caerulescens accessions from across Europe. We developed an image-processing method to segment different plant substructures in the µXRF images. We introduced the concentration quotient (CQ) to quantify spatial patterns of metal accumulation and linked that to genetic variation. Results Image processing resulted in automated segmentation of µXRF plant images into petiole, leaf margin, leaf interveinal and leaf vasculature substructures. The harmonic means of recall and precision (F1 score) were 0.79, 0.80, 0.67, and 0.68, respectively. Spatial metal accumulation as determined by CQ is highly heritable in Noccaea caerulescens for all substructures, with broad-sense heritability (H2) ranging from 76 to 92%, and correlates only weakly with other heritable traits. Insertion of noise into the image segmentation algorithm barely decreases heritability scores of CQ for the segmented substructures, illustrating the robustness of the trait and the quantification method. Very low heritability was found for CQ if randomly generated substructures were compared, validating the approach. Conclusions A strategy for segmenting µXRF images of Noccaea caerulescens is proposed and the concentration quotient is developed to provide a quantitative measure of metal accumulation pattern, which can be used to determine genetic variation for such pattern. The metric is robust to segmentation error and provides reliable H2 estimates. This strategy provides an avenue for quantifying XRF data for analysis of the genetics of metal distribution patterns in plants and the subsequent discovery of new genes that regulate metal homeostasis and sequestration in plants.

Mechanisms of Uptake and Translocation of Thallium in Brassica Vegetables: An X-ray Fluorescence Microspectroscopic Investigation

“…For experiment 1, on the 11th day, the nutrient solution was spiked with thallium(I)nitrate to make 7.5 μM Tl in a modified 1/2 strength Hoagland's solution. This 1/2 strength-modified Hoagland's formulation was prepared with K (3 mM as KNO 3 ), Ca (2 mM as Ca(NO 3 ) 2 35 After 11 days of exposure to Tl-spiked nutrient solution, leaves from each cultivar were imaged with laboratory-based μXRF analysis (Figure S1). Brassica oleracea cultivars with high Tl in their leaves (IDs 6, 9, 10, 11, 13, 15, and 16) were then selected for experiment 2 (Figure S2).…”

Thallium accumulation and distribution in Silene latifolia (Caryophyllaceae) grown in hydroponics

“…Hyperaccumulator plants can attain exceptionally high concentrations of potentially toxic metals and metalloids in their shoots without developing toxicity symptoms (Baker 1981;van der Ent et al 2013). These plants are models for fundamental research in ecophysiology and biogeochemistry, and applied research such as their use in 'green technologies ', e.g., phytoextraction to clean-up soils, and phytomining to extract valuable metal(loid)s from unconventional resources for economic purposes (Corzo Remigio et al 2020;Nkrumah et al 2019;van der Ent et al 2015). A notional threshold for Tl hyperaccumulation has been set at 100 μg Tl g −1 in above-ground tissues (dry weight) (Reeves et al 2018;van der Ent et al 2013).…”

“…These plants are models for fundamental research in ecophysiology and biogeochemistry, and applied research such as their use in 'green technologies ', e.g., phytoextraction to clean-up soils, and phytomining to extract valuable metal(loid)s from unconventional resources for economic purposes (Corzo Remigio et al 2020;Nkrumah et al 2019;van der Ent et al 2015). A notional threshold for Tl hyperaccumulation has been set at 100 μg Tl g −1 in above-ground tissues (dry weight) (Reeves et al 2018;van der Ent et al 2013). Thallium hyperaccumulators include two species from the Brassicaceae family: Biscutella laevigata with up to 32,700 μg Tl g −1 in its leaves (Fellet et al 2012), and Iberis linifolia (synonym: Iberis intermedia) with up to 4000 μg Tl g −1 in its leaves (LaCoste et al 1999).…”

Cadmium Content in Soil and Tomato (Lycopersicon Esculentum Miller) Around Industrial Areas of Bangladesh

“…One of the most essential aspects of food quality assurance is heavy metal contamination of the food items (Wang et al 2005). The presence of heavy metals in vegetables is influenced by many factors, principally by the crop species and its metabolism, and by others such as the soil's initial concentration of contaminants, pH, organic matter availability, and presence of other ions and molecules (Van der Zee et al 2021). Crops that are located close to vehicular traffic and factories also have an increased likelihood of heavy metals presence (Koptsik et al 2021).…”