Chemical forms of manganese in the leaves of manganese hyperaccumulator Phytolacca acinosa Roxb. (Phytolaccaceae)

Abstract

Phytolacca acinosa Roxb. is a Mn hyperaccumulating plant. In the present study, the chemical forms of Mn in the leaves of P. acinosa were investigated using chemical analyses and X-ray absorption spectroscopy (XAS). P. acinosa plants were grown hydroponically with 2 mM Mn for 28 days. About 80% of the Mn in the leaves of P. acinosa was found in the supernatant fraction after centrifugation at 20,000g for 45 min. The supernatant fraction was then used to identify the chemical forms of Mn. Gel filtration analysis (Sephadex G-10) showed that oxalate and Mn appeared in the same fraction of the supernatant and the molar ratio of oxalic acid to Mn was 1.12, indicating that there was sufficient oxalic acid in P. acinosa leaves to complex Mn. XAS was employed to investigate the chemical species of Mn in leaves of P. acinosa. Results showed that Mn in leaves was bivalent and almost 90% of the total Mn was Mn-oxalate. The oxalate concentration in the leaves of P. acinosa was not affected by increasing Mn concentration in the solution, suggesting that oxalate biosynthesis was not induced by Mn.

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

“…For example, with the help of x-ray absorption near-edge spectroscopy and extended x-ray absorption fine-structure spectroscopy techniques, malate has been demonstrated to chelate internal Mn within the leaf tissues in Gossia bidwillii (Fernando et al, 2010). Furthermore, in the roots of cowpea and leaves of Phytolacca acinosa, it has been estimated that 80% and 90% of internal Mn can be bound in complexes with citrate and oxalate, respectively (Xu et al, 2009;Kopittke et al, 2013). Therefore, in this study, changes in the internal concentrations of malate, oxalate, and citrate in response to Mn toxicity were examined in both S. guianensis genotypes.…”

“…These results suggest that malate synthesis could be partially controlled by excess Mn, and may thus be related to Mn tolerance. Furthermore, it has been documented that Mn could be complexed with oxalate, citrate, or malate at a ratio of approximately 1:1 in plants (Dou et al, 2009;Xu et al, 2009;Fernando et al, 2010). However, to further clarify the functions of malate in internal Mn detoxification, it will be valuable and necessary to investigate whether Mn-malate complexes are present in S. guianensis leaves and roots using x-ray absorption near-edge spectroscopy or extended x-ray absorption fine-structure spectroscopy techniques.…”

“…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.…”

Manganese tolerance and accumulation in six Mn hyperaccumulators or accumulators

“…Each Mn treatment was independently replicated three times. In order to maintain a high Mn 2+ availability in nutrient solution (Xu et al 2009), the nutrient solution was renewed every 3 days and the pH of the solution was checked and adjusted daily to 4.5 using either 0.1 mM NaOH or 0.1 mM HCl. To balance water loss due to evaporation and transpiration, distilled water was added to maintain the solution volume.…”

“…XAS analysis found that Mn in the leaves of the hyperaccumulator Phytolacca acinosa Roxb. was bivalent and that almost 90% of the total Mn was in the form of Mn-oxalate (Xu et al 2009). It was presumed that Mn tolerance of P. perfoliatum might be related to comolexation of Mn with oxalate for detoxification.…”