| Commelina communis L. was a new manganese hyperaccumulator found in China. However, the mechanisms of its Mn resistance are still not well clarified. 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 is13138mg·kg at500μmol·L-1Mn. At10000μmol·L-1, Mn content in stems and leaves reaches the maximum, that is16077and41404mg·kg-1, respectively. And Mn distribution sequence is:leaves> roots>stems, meanwhile the translocation factor>1.This implies that Commelina communis L. was a manganese-resistant plant, and was a potential Mn hyperaccumulator.FTIR analysis showed that using the roots, stems and leaves of Commelina communis L., absorption bands corresponding to carbohydrates, ester and proteins varied differently. The absorption band heights at3420and2926cm-1of 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 at2926cm-1(roots) and1640cm-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 at1060cm-1differed 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.Transmission electron microscopy results showed that, compared with the CK, under1000μmol·L-1Mn treatment, there is no obvious damage found in leaf and root cells structure and organelles of Commelina communis L., structure and function integrity. And when Mn supply level reached10000μmol·L-1, 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 Commelina communis L.to the excessive absorption of Mn. SEM and TEM shows that a kind of unknown acerose substance was an existence of manganese in plant cells. |
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