Manganese distribution and speciation help to explain the effects of silicate and phosphate on manganese toxicity in four crop species

Abstract

Soil acidity and waterlogging increase manganese (Mn) in leaf tissues to potentially toxic concentrations, an effect reportedly alleviated by increased silicon (Si) and phosphorus (P) supply. Effects of Si and P on Mn toxicity were studied in four plant species using synchrotron-based micro X-ray fluorescence (μ-XRF) and nanoscale secondary ion mass spectrometry (NanoSIMS) to determine Mn distribution in leaf tissues and using synchrotron-based X-ray absorption spectroscopy (XAS) to measure Mn speciation in leaves, stems and roots. A concentration of 30 μM Mn in solution was toxic to cowpea and soybean, with 400 μM Mn toxic to sunflower but not white lupin. Unexpectedly, μ-XRF analysis revealed that 1.4 mM Si in solution decreased Mn toxicity symptoms through increased Mn localization in leaf tissues. NanoSIMS showed Mn and Si co-localized in the apoplast of soybean epidermal cells and basal cells of sunflower trichomes. Concomitantly, added Si decreased oxidation of Mn(II) to Mn(III) and Mn(IV). An increase from 5 to 50 μM P in solution changed some Mn toxicity symptoms but had little effect on Mn distribution or speciation. We conclude that Si increases localized apoplastic sorption of Mn in cowpea, soybean and sunflower leaves thereby decreasing free Mn accumulation in the apoplast or cytoplasm.

Chemical Heterogeneity of Mg, Mn, Na, S, and Sr in Benthic Foraminiferal Calcite

“…In Figures 10C,D, the averaged spectra of the samples are presented with the associated references for each location. Internal coating spectra exhibit very similar patterns to several references such as MnSO 4 , MnPO 4 ( Figure 10C), and Mn-organic compounds published in Blamey et al (2018), for example, Mn-oxalate, Mn-phytate, and Mn-cystine. The spectra for calcite locations show similar features as kutnohorite (CaMn(CO 3 ) 2 ) and manganoan calcite ((Ca,Mn)CO 3 ) published in Johnson et al (2016) with a smaller pre-edge peak and two distinct peaks in the near-edge region of the spectra.…”

“…Some of the references were acquired during the same session at ID21, that is, references Mn metal and MnO 2 , MnO(OH), Mn 3 O 4 , MnCl 2 , and MnSO 4 , prepared as powder spread in a tape (spectra simultaneously acquired in transmission and XRF modes). Other reference spectra were kindly provided by Dr. Samuel M. Webb (SLAC) [manganoan calcite ((Ca,Mn)CO 3 ), kutnohorite (CaMn(CO 3 ) 2 ), rhodochrosite (MnCO 3 ), and KMnO 4 ], calibration tuned using a MnCO 3 reference) previously published in Johnson et al (2016) and by Peter Kopittke (MnSO 4 , MnPO 4 , MnCO 3 , Mn(II) oxide (MnO), Mn(III) oxide (Mn 2 O 3 ), Mn(IV) oxide (MnO 2 ), pyrolusite (MnO 2 ), hausmannite (Mn 3 O 4 ), Mn-oxalate, Mncitrate, Mn-cystine, Mn-malate, and Mn-phytate, calibration tuned using the Mn reference) previously published in Blamey et al (2018). The ATHENA software (Ravel and Newville, 2005) was used for interpolation and energy shifting on the external references.…”

“…The first observations of the combined spectra from the different locations, that is, internal coating ( Figure 10C) and calcite locations ( Figure 10D) with reference spectra, suggests that Mn is systematically under a Mn(II) speciation. The results of the PCA performed on normalized (second derivative) spectra of all samples (in total 169 spectra) plus the set of references (measured during the ID21 synchrotron session and from other authors; Johnson et al, 2016;Blamey et al, 2018) are presented in Figure 10A. The first two axes of the PCA explain 77% of the variability of the data.…”

The controversies of silicon's role in plant biology

“…Na, As, Mn and Cd), and thus their cellular accumulation in leaf tissues (Yeo et al, 1999;Gong et al, 2006;Sanglard et al, 2014;Che et al, 2016;Shao et al, 2017;Flam-Shepherd et al, 2018;cf. Rogalla & R€ omheld, 2002;Blamey et al, 2018). A reduction in toxicant accumulation will obviously reduce the strains imposed on shoot tissues, and thus be reflected in reduced oxidative stress.…”

Time-resolved X-ray fluorescence analysis of element distribution and concentration in living plants: An example using manganese toxicity in cowpea leaves

“…The present study investigated the potential of synchrotron-based µ-XRF analysis to quantify timeresolved changes in elemental distribution in leaves of living plants. To develop this method, we have utilized a well-characterized plant system, with cowpea grown in complete nutrient solution with 0.2 and 30 µM Mn, levels that are adequate and toxic (Blamey et al, 2018). Worldwide, Mn toxicity is a potential limitation to plant growth in approximately 30 % of soils that are acid and in soils that become waterlogged through increased solubility of Mn minerals.…”