Study On Accumulation Mechanisms Of Manganese In Hyperaccumulator Polygonum Hydropiper L.(Water Smartweed)

Growth response and accumulated profile of individual Polygonum hydropiper L.,distributions and chemical fractions of Mn in its cells and its physiological and biochemical responses under Mn press were researched by aquicultural simulated experiments in order that our results could be used for reference to plant genetic improvements on Mn-contaminated soil or mechanisms of research of other potential hyperaccumulators. The main conclusions of our study as followings:1. The tolerance and hyperaccumulation of Polygonum hydropiper L. to Mn were very higher. Their growth were natural when the concentration of Mn was 2000 mg·kg-1 in soil of contaminated-site and Mn concentration of their leaves was as high as 3675.89 mg·kg-1. Their Mn accumulated-concentration of shoots were as high as 26.84 mg·plant-1 and Mn concentration of their leaves were 24447.1 mg·kg-1 when Mn concentration was 15000μmol·L-1 in solutions under the condition of their grow 48d in aquicultural experiments. Their biomass decreased with increasing of Mn concentration levels, the differences of their biomass of shoots were remarkably differrent (P=0.05), comparing control.2. The absorption and transport of Polygonum hydropiper L. to Mn correlated with Mn concentrations and the time of their growth intimately. The Mn concentration of their roots, stems, and leaves increased with increasing Mn concentration levels and time whether Mn concentration was lower (500μmol·L-1) or was higher (5000μmol·L-1) in solutions.3. Distribution characteristics of Mn in Polygonum hydropiper L.: Their laminaes were the main organs hyperaccumulated Mn. Under different Mn concentration levels, Mn concentrations of their cell wall of roots were 25.36～61.22% of total Mn, Mn concentration of soluble cytosol (vacuole were about 95%)of their stems were 19.34～58.59% of total Mn, there were about 58.18～65.64% of Mn in vacuole of their leaves and Mn concentrations of their cell wall of leaves were 31.73～36.34% of total Mn, whereas Mn concentrations, only 2.60～5.48% of total Mn, were very low in their organelle of leaves. High Mn concentration of soluble cytosol of their stems benefited for transport and accumulation of Mn. In one word, accumulation of Mn in cell wall and vacuole of leaves may be one of the mechanisms of tolerance and hyperaccumulation of Polygonum hydropiper L. to Mn. 4. The roots, stems and leaves of Polygonum hydropiper L. were extracted by different extracting solvents in lab, the results indicated that with the increasing of Mn concentration levels, the speciation of Mn in their roots transform from H2O-extractable species to HCl-extractable species and NaCl-extractable species, showed increases of Mn of oxalate binding and pectate binding or prontein binding in cell wall of roots; Mn of H2O-extractable species were 34.55～50.26% of total Mn in stems and increased with the increasing of Mn concentration levels, which benefited upward transport of Mn; Percentage of Mn of H2O-extractable species were 38.55～44.19% and Mn of HCl-extractable species were 20.66～28.74% to total Mn in leaves, suggesting that most Mn in leaves were the speciation of H2O-solubility organic salts or manganese oxalates.5. Chlorophyll in leaves of Polygonum hydropiper L. were analyzed in lab, the results illustrated that the content of chlorophyll A did not change under different Mn concentration levels except that its concentrations decreased remarkably when Mn concentration was 8000μmol·L-1 in solutions, whereas the concentrations of chlorophyll b are relative unchanged, which accord with the biomass of shoots.6. Under different Mn concentration levels, the permeability of plasma membrane of leaves of Polygonum hydropiper L. there were the tendency of increases, but their differences were not evident (P=0.05), illustrated that the membrane of leaves of Polygonum hydropiper L.did not harm by Mn even its concentration up to 8000μmol·L-1. While the concentration of their soluble protein of leaves appeared to some degree change, suggesting the plant adjust its metabolism and structure to Mn.7. Antioxidant enzymes in laminaes of Polygonum hydropiper L. were analyzed in lab, the results showed that the activity of SOD and POD were gradually improvement with the increasing of Mn concentration treatments, whereas active improvement of these two protective enzymes could eliminate activated oxygen free radical, this may be another evidence for physiological response mechanism of tolerance and hyperaccumulation of Polygonum hydropiper L. to Mn.