Distribution and mobility of manganese in the hyperaccumulator plant Phytolacca acinosa Roxb. (Phytolaccaceae)

Abstract

The distribution and mobility of manganese (Mn) in the hyperaccumulator plant species Phytolacca acinosa Roxb. (Phytolaccaceae) were investigated in a hydroponic system. The plants were exposed to 2 or 5 mM Mn for up to 28 days. For any given plant, the Mn content in the mature leaves (nos. 5-9) was always higher than that in the old (nos. 1-4) and young leaves (nos. 10-14). Within the different parts of a leaf, Mn was preferentially accumulated in the leaf marginal area, where the observed level was threefold higher than that in the midrib. Crosssectional analysis of the leaf revealed that the concentration of Mn was higher in the leaf epidermis than in the mesophyll. Cell fractionation analysis with P. acinosa leaves showed that most of the Mn (78.4%) was present in the final supernatant fraction (following centrifugation at 20,000 g for 45 min). The distribution of Mn in the leaves of P. acinosa was controlled mainly by the transpiration rate. Our investigation demonstrated that Mn was readily transported from the roots to shoots of P. acinosa but that it could not be remobilized readily after it reached leaves.

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

“…Our attempt to localise these substances by isolating protoplast and vacuole was unsuccessful. In our previous studies, we found that the highest Mn concentration occurred in the supernatant fraction (after centrifugation at 20,000g for 45 min) using a cell fractionation analysis method (Xu et al 2006). This fraction corresponded to the vacuolar and cytoplasm (excluding the organelles) fraction.…”

“…This fraction corresponded to the vacuolar and cytoplasm (excluding the organelles) fraction. Since the vacuole occupies~95% of the total volume of a mature plant cell (Memon and Yatazawa 1984), it could be inferred that most of the Mn found in the supernatant fraction might derive from the vacuoles (Xu et al 2006). Organic acids are also known to accumulate in plant vacuoles (Ryan et al 1983).…”

Manganese tolerance and accumulation in six Mn hyperaccumulators or accumulators

“…Well-known Mn hyperaccumulators, plants capable of acquiring more than 10,000 mg kg −1 of Mn (dry weight) in its aboveground biomass (Xu et al 2006), include the Gossia bidwillii and Austromyrtus bidwillii from Eastern Australia (Bidwell et al 2002;Fernando et al 2006a), nine species listed by Reeves and Baker, and an unidentified Eugenia species described by Sabah (Proctor et al 1989). In addition, Japan is well known for the accumulator Eleutherococcus sciadophylloides that can sequester up to 7,900 mg.g −1 Mn in the leaf dry matter (Memon et al 1980).…”

Microbeam methodologies as powerful tools in manganese hyperaccumulation research: present status and future directions

“…Between 2002 and 2008, additional Mn hyperaccumulators were discovered in eastern Australia (Bidwell et al, 2002), China (Xue et al, 2004) and Japan (Mizuno et al, 2008), that has now led to recognition of several new species and renewed interest in the phenomenon. To date, the woody species have only been investigated through a series of ecophysiological studies, whereas the two herbaceous Phytolacca (Phytolaccaceae) species have mainly been examined in controlled experiments (Xue et al, 2005; Fernando et al, 2006b; Mizuno et al, 2006; Xu et al, 2006a,b, 2009; Fernando et al, 2007a,b). Unlike their herbaceous metal-hyperaccumulating counterparts, Mn-hyperaccumulating trees and shrubs are extremely slow growing and often difficult to propagate.…”

“…This has led to: (a) the discovery of several new Mn hyperaccumulators, which has augmented the overall biogeographic knowledge base of hyperaccumulators by providing new perspective on Mn-accumulating taxa analogous to those with already well-established links to other metals (Baker and Brooks, 1989; Baker et al, 1992; Pollard et al, 2000, 2002; Fernando et al, 2009); (b) the discovery that foliar Mn detoxification varies specifically in a manner possibly unique to Mn hyperaccumulators (Fernando et al, 2008); (c) indication that the physiological mechanisms associated with excess Mn uptake and storage in herbaceous Mn hyperaccumulators are similar to those found in herbaceous hyperaccumulators of other metals (Küpper et al, 2000, 2001; Xu et al, 2006a,b); and (d) the pursuit to identify Mn-specific transporters, particularly in woody species where Mn is compartmentalized in highly localized vacuolar concentrations (T. Mizuno unpublished data).…”