Physiological Response By Hyperaccumulator Of Phytolacca Americana To Manganese Toxicity

Phytoremediation is defined as the use of plants to decontaminate and removepollutants from the environment. It has emerged as an alternative technique forremoving toxic metals from soil.In this study, a survey of nine plants growing on the soil polluted by manganese mine inDaxin County was firstly conducted.In addition, Four herbaceous plants, ConyzaCanadensis, Polygonum hydropiper, Polygonum perfoliatum and Phytolacca americanawere tested for their tolerance to manganese toxicity. At last, soil culture experimentswere carried out to characterize the mechanism of Mn tolerance in Phytolaccaamericana by means of a series of chemical, biochemical methods. The major resultswere summarized as follows:1. A survey of nine plants growing on the soil polluted by manganese mine in DaxinCounty was conducted. The result indicated that the exceptional-high concentrations ofMn were found to be the most important limiting factor for plant growth among threemetals (Mn, Zn and Ni). Pteris vittata Linn, which roots showed good metal-enrichmentof Mn and Ni, turned out to have good tolerant ability of Mn, Zn and Ni according to theanalysis in the paper. In addition, Miscanthus floridulus (Labiil.) Warb, Erigeronbonariensis L, Polygonum lapathifolium L and Erigeron canadensis L were proved tohave good Mn-tolerant ability; Microstegium gratum (Hack.) A. Camus, Digitariasanguinalis (L.)Scop and Alocasia macrorrhiza (L.) Schott & Endl were Zn-tolerantplants while Miscanthus floridulus (Labill.) Warb and Erigeron canadensis L wereNi-tolerant plants. Further researches which are of some significance to these plants willbe still in process though no hyperaccummulators of these three heavy metals werefound in the survey. 2. Four herbaceous plants, Conyza Canadensis, Polygonum hydropiper, Polygonumperfoliatum and Phytolacca americana response differently to a wide range of Mn²⁺treatments. According to the hydroponic culture experiments, 16000μmol.L^-1Mn²⁺significantly (P＜0.05) promoted the contents of MDA (Phytolacca americana L wasexceptive), MP and the overground Mn content when compared to the controlrespectively and these indexes in Polygonum hydropiper increased most whilePhytolacca americana rose less. Meanwhile, the soluble sugar (SS), as well as thecontents of chlorophyll nearly maintained the same level as each control inConyza Canadensis, Polygonum perfoliatum and Phytolacca americana in comparisonwith Polygonum hydropiper, whereas, the content of soluble protein didn't show theobvious tendency.The results also implied that Conyza Canadensis, Polygonum perfoliatum andPhytolacca americana could enhance the tolerance to Mn stress under hightreatments by maintaining lower contents of MDA and MP, higher root activity (RA),steady contents of SS and chlorophyll and the three herbaceous plants, which weresatisfied with the standard of Mn phytoaccumulators can be expected during thephytoremediation application.3. The total Mn in plants' tissues was positively correlated with Mn²⁺ treatment. Thetotal Mn in leaves(7d) was satisfied with the standard of Mn phytoaccumulators whenthe Mn treatments reached 0.25g/kg. Accordingly, the ratio of soluble Mn in tissuesincreased and accounted for 45.78ï¼…of total Mn while soluble Mn reached19283.21mg/kg with highest Mn treatments.. Meanwhile, there were positive correlationbetween Mn concentrations in plants' tissues and Mn activation due to increasing Mn²⁺supply. As a result, The soluble sugar (SS), as well as the contents of weakly-absorbedMn in soil significantly rose.4. The activity of POD, ASA—POD and PPO increased as the concentration ofManganese were enhanced while SOD activity changed slightly. Among four enzymes,ASA—POD had a widest variety range. The order of variety range wasASA—POD＞POD＞PPO＞SOD. There was a positive correlation between POD,ASA-POD, PPO and manganese resistance under Mn stress, but there was no significant correlation between SOD activity and manganese resistance.5. There wasn't obvious toxic effect of Manganese on the chlorophyll fluorescencekinetic parameters of Phytolacca americana leaves, but F₀,Fm and qN were significantlyinhibited,Meanwhile, we can see that plants photosynthesis of the first stage was betterthan the seceond one.6. Using the roots, stems and leaves of Phytolacca Americana, absorption bandscorresponding to carbohydrates, ester and proteins varied differently. The absorptionband heights at 3000 cm^-1 and 2916 cm^-1 of stem tissues rose firstly then decreased,indicating the exudation and transporting situation of organic substances which servedas organic osmotic contents to enhance manganese tolerance under low treatments;Meanwhile, the band heights at 2922 cm^-1(roots) and 1606 cm^-1(leaves) which havedifferent tendency in accordance with Mn treatments showing that the capability tochelate Mn decreased under higher manganese concentration.In addition, the changes ofthe bands at 1732 cm^-1 and 1026 cm^-1(roots), 1028 cm^-1(stems), 1052 cm^-1 and 967cm^-1(leaves) differed from each other, suggesting that under the conditions of severe Mnstress the ex-oxidation of membrane lipid increased; Otherwise, the band heights at 1375cm^-1 increased firstly and then decreased, representing that the cell wall in, proved Mnresistance by increasing cation-exchange capacity(CEC). The result also implied that itis practical to apply FIIR to the research comparing the chemical differences ofphytoaccumulators under metal treatments.