| Manganese, an essential trace element that is found in varying amounts in all tissues, is one of the most widely used metals in industry. However, exposure to excess manganese results in manganese toxicity, including Parkinson-like symptoms, and abnormalities of the reproductive system and the immune system. Manganese -contaminated soils and waters originating from industrial and agricultural activities and mining are becoming an environmental concern following increased awareness of the need for environmental protection.Phytoremediation is attracting interest and attention from governments and enterprises as a potentially cost-effective, engineering-economical and green technique to clean up heavy metal-polluted soil using hyperaccumulators. Unfortunately, some of the strongest hyperaccumulators are relatively small in size and grow very slowly, making it difficult to harvest them mechanically, and limiting the metal extraction that can be achieved. Only a limited selection of the known hyperaccumulators may be suitable for large-scale phytoremediation. Accordingly, exploring the mechanism of manganese tolerance and hyperaccumulation is important to found or create new manganese hyperaccumulator plant which grows rapidly, has substantial biomass, wide distribution and a broad ecological amplitude. The perennial herb Phytolacca acinosa Roxb. (Phytolaccaceae), which occurs in Southern China, has been found to be a new manganese hyperaccumulator by means of field surveys at Xiangtan manganese tailings wastelands, Hunan Province.In the present study, field surveys and glasshouse experiments were conducted to characterize manganese uptake and accumulation of P. acinosa, and to elucidate the possible mechanisms employed by P. acinosa in the tolerance and hyperaccumulation of manganese by means of a series of instrumentations, such asScan electronic microscopy (SEM), Transmission electronic microscopy (TEM), Energy dispersive analysis of X-rays (EDAX), Extended x-ray adsorption fine structure (EXAFS), Inductively-coupled plasma optical emission spectroscopy (ICP-OES), High-speed centrifuger, and so on. In addition, the capacity of P. acinosa to remove heavy metals (Mn, Cd, Zn) from waste water was investigated in the hope of phytoremediation of manganese -contaminated waters. The major results obtained are as follows:P. acinosa not only has remarkable tolerance to Mn, but also has extraordinary uptake and accumulation capacity for this element. The maximum Mn concentration in the leaf dry matter was 19300 mg/kg on Xiangtan Mn tailings wastelands, with a mean of 14480mg/kg. Under nutrient solution culture conditions, the Mn concentration in the leaves reached its highest value (36380 mg/kg) with the bioaccumulation coefficient of 55 at a Mn supply level of 12000 umol/l. P. acinosa could grow normally with Mn supplied at a concentration of 8000 mol/l, although with less biomass than that in control samples supplied with Mn at 5 mol/l. Manganese concentration in the shoots increased with increasing external Mn levels, but the total mass of Mn accumulated in the shoots first increased and then decreased. At a Mn concentration of 5000 umol/l in the culture solution, the Mn accumulation in the shoot dry matter was the highest (258 mg/plant). Partitioning of Mn between the aerial parts and the roots showed that 87% ~ 95% of Mn was transported into the former in all the treatments of the experiment, demonstrating the great capacity of the plant transporting Mn from the roots to the aerial parts. These results confirm that P. acinosa is a Mn hyperaccumulator which grows rapidly, has substantial biomass, wide distribution and a broad ecological amplitude.Both high tolerance and hyperaccumulating ability of Mn in P. acinosa are constitutive properties. Manganese uptake and accumulation by two contrasting populations of P. acinosa were investigated. One population (MP) was from Xiangtan manganese tailings and the other (NMP) was from a Magnolia grandiflora plantation with lower Mn status. In addition to these field investigations, s...
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