Characterization of foliar manganese (Mn) in Mn (hyper)accumulators using X‐ray absorption spectroscopy

Abstract

Summary Plant hyperaccumulation of the essential nutrient manganese (Mn) is a rare phenomenon most evident in the Western Pacific region, and differs from hyperaccumulation of other elements. Mn hyperaccumulators employ a variety of species‐dependent spatial distribution patterns in sequestering excess foliar Mn, including primary sequestration in both nonphotosynthetic and photosynthetic tissues. This investigation employed synchrotron X‐ray absorption spectroscopy (XAS) in a comparative study of Mn (hyper)accumulators, to elucidate in situ the chemical form(s) of foliar Mn in seven woody species from Australia, New Caledonia and Japan. Foliar Mn was found to predominate as Mn(II) in all samples, with strong evidence of the role of carboxylic acids, such as malate or citrate, as complexing ligands. Overall, the X‐ray absorption near‐edge spectroscopy (XANES) and extended X‐ray absorption fine‐structure spectroscopy (EXAFS) data appeared weighted against previous observations that oxalate binds excess Mn in Mn‐(hyper)accumulating species.

Synchrotron-based Techniques Shed Light on Mechanisms of Plant Sensitivity and Tolerance to High Manganese in the Root Environment

“…The Mn in roots of the four species was mostly Mn(II) complexed by malate or citrate. This finding and that of LC-MS analysis is in keeping with that of Fernando et al (2010), who concluded that malate or citrate is the most likely carboxylate to complex Mn in hyperaccumulators. Dou et al (2009), however, determined oxalate to be important, a finding not supported by data for the species examined in this study.…”

“…A similar mechanism would occur in white lupin also (data not shown). Using XANES, Fernando et al (2010) concluded that Mn(II) predominates in Mn hyperaccumulators, with Fernando et al (2008) being the first to show that Mn is evenly distributed in leaf photosynthetic and nonphotosynthetic tissues. White lupin would be classified as a Mn accumulator (van der Ent et al, 2013) by growing well at 100 mM Mn, with leaves containing 17.1 and 25.0 mmol Mn kg -1 FM (14,100 and 20,700 mg Mn kg -1 DM; Fig.…”

“…For example, Fernando et al (2010) used x-ray absorption near-edge spectroscopy (XANES) to confirm the widely accepted view that Mn(II) predominates in seven Mn hyperaccumulators. Synchrotron-based x-ray fluorescence microspectroscopy (m-XRF) was used by McNear and Küpper (2014) to show that the basal region of trichomes of A. murale plants grown at no more than 10 mM Mn contained Mn(II) complexed with phosphate.…”

“…Celosia argentia, a species adapted to growth on Mn-contaminated mine tailings, accumulated more than 20,000 mg kg -1 Mn in leaves (Liu et al, 2014). Tolerance of high Mn in shoots of some Mn hyperaccumulators has been found to occur through binding to ligands (such as malate or citrate) or sequestration in the vacuole (Fernando et al, 2010).…”

Malate Synthesis and Secretion Mediated by a Manganese-Enhanced Malate Dehydrogenase Confers Superior Manganese Tolerance in Stylosanthes guianensis

“…detoxification are suggested through analysis of foliar Mn species in Mn hyperaccumulator plants (Xu et al, 2009;Fernando et al, 2010). Furthermore, increased organic acid exudation from roots was observed in ryegrass (Lolium perenne) and white clover (Trifolium repens) subjected to different Mn levels (Rosas et al, 2007;de la Luz Mora et al, 2009), suggesting that secreted organic acids might be responsive to Mn toxicity.…”