| Hyperaccumulator is an extreme metal accumulating plants as a potentially cost-effective, engineering-economical and green technique to clean up heavy metal-polluted soil using hyperaccumulators. Accordingly, exploring the mechanism of manganese tolerance and hyperaccumulation is important to found or create new manganese hyperaccnmulator plant which grows rapidly,has substantial biomass, wide distribution and a broad ecological amplitude.Polygonum perfoliatum L. has been found to be a new manganese hyperaccumulator by means of field surveys at Xiangtan manganese railings wastelands, Hunan Province. The present study carried out series of experiments, including hydroponic culture, scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM), inductively coupled Plasma optical emission spectrometer (ICP-OES), fourier transform infrared spectroscopy (FTIR), to investigate the responses of pokeweeds treated with different levels of Mn, detect Mn uptake, accumulation and subcellular distribution in pokeweed, analyze the correlation between the possible factors involved with Mn resistance and Mn accumulation and detoxification, and further explore the potential mechanisms of Mn resistance in the plant. This research could advance our understanding of Mn resistance in plant, and provide theoretical evidence and scientific directions for the correction of Mn toxicity to crops and phytoremediation of acid soils or relative heavy metal-contaminated soils. The major results obtained are as follows.The growth of the plant was not affected by low concentration of Mn, while differences were showed at high concentration of Mn like growth was slow, biomass reduced significantly and manganese toxicity symptoms revealed in the final phase, but life cycle was still finished completely at the end. As Mn treatment concentration increasing, Mn content in Perfoliate Knotweed tissues is higher. Mn content in leaves of Perfoliate Knotweed is 13138 mg·kg-1 at 500μmol·L-1 Mn. At 10000μmol·L-1, Mn content in stems and leaves reaches the maximum, that is 16077 and 41404 mg·kg-1, respectively. And Mn distribution sequence is:leaves> roots>stems, meanwhile the translocation factor>1.This implies that Polygonum perfoliatum L. was a manganese-resistant plant, and was a potential Mn hyperaccumulator.FTIR analysis showed that using the roots, stems and leaves of Polygonum perfoliatum L., absorption bands corresponding to carbohydrates, ester and proteins varied differently. The absorption band heights at 3420 and 2926 cm-1 of stem tissues rose firstly and then decreased, indicating the exudation and transporting situation of organic substances which served as organic osmotic contents to enhance manganese tolerance under low treatments; Meanwhile, the band heights at 2926 cm-1(roots) and 1640 cm-1(leaves) which have different tendency in accordance with Mn treatments showed that the capability to chelate Mn decreased under higher manganese concentration. In addition, the changes of the bands at 1060 cm-1 differed from each other, suggesting that under the conditions of severe Mn stress the ex-oxidation of membrane lipid increased. All the result implied that it is practical to apply FTIR to the research comparing the chemical differences of the tolerate plants under metal treatments.Scanning electronic microscopy and transmission electronic microscopy results showed that, compared with the CK, under 1000μmol·L-1 Mn treatment, there is no obvious damage found in leaf and root cells structure and organelles of Polygonum perfoliatum L., structure and function integrity. And when Mn supply level reached 10000μmol·L-the structure of part cells and organelles (mitochondria, chloroplasts, et al) have significant damage. At the same time, a kind of unknown acerose substance was found in the Mn treatment cells, this could be the low biological activity formation of Mn deposits or crystals which product by the detoxification mechanisms of Polygonum perfoliatum L. |
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