Mirabilis Lead Stress Response And Tolerance Study

Environmental management and rehabilitation of mine wasteland is one of the pressing needs to be addressed for social and economic development to be healthy and sustainable in China. Tailing wasteland from metalliferous mines often poses the extreme stressful conditions and is tougher for ecological restoration. As a newly emerged environment -friendly technology, phytostabilization is defined as the use of metal -tolerant plant species to reduce the mobility and bioavailability of heavy metals in the substrates either by immobilization or by prevention of migration. Compared with traditional methods, phytostabilization is a cost-effective and environment-friendly technology. Mirabilis jalapa Linn is a plant found in Xiangtan and Jishou tailing wasteland. There are less researches on the toxicity and the tolerance machanisms of M. jalapa to lead up to now. And this would restrain its application on phytostabilization.To elucidate systematically the changing of biomass and organs tissue structure, the uptake and accumulation of mineral elements and the alteration of chemistry components in M. jalapa organs to different lead stress, hydroponic experiment were applied in this study based on a lot of field survey by means of a series of instrumentations, such as Inductively -coupled plasma optical emission spectroscopy (ICP-OES), Transmission Electron Microscope (TEM), paraffin- embedded tissue slice and Fourier transform infrared(FTIR). The major results obtained are as follows:1. The distribution of lead among roots, stems and leaves in M. jalapa is different. The ICP-OES analysis revealed that the levels of Pb in roots,stems and leaves of the plants increased while the concentration of Pb²⁺ increasing in the culture solution. The results showed that Pb distribution sequence is: roots > leaves > stems.And most of Pb was accumulated in roots, few Pb was transferred in shoots, meanwhile the translocation factor<0.04. This could be one of Pb defense mechanisms employed by M. jalapa. The results indicated that M. jalapa could alleviate toxic effect on vegetative organs and reproductive organs by low transportation ability of Pb from roots to shoots and also reduce the bioavailability of Pb by the Pb immobilization in roots.2. In the present work, there existed no significant effects of Pb stress on the concentration of Macronutrients such as Ca,Mg,Fe in different organs of M.jalapa. These elements were not decreasing evidently while the concentration of Pb²⁺ increasing in the culture solution,but increasing in some treatment. The uptake and accumulation of trace elements Cu,Mn,Zn in M. jalapa was researched. All the result showed that the concentrations of Cu,Mn,Zn was rising under the low Pb stress and decreasing under high Pb stress. Macronutrients such as Ca,Mg,Fe was enough in M. jalapa during the whole growth cycle. The homeostasis of macronutrients maintained may revealed that M. jalapa had the strong resistance to Pb stress.3. In our study, the biomass of M. jalapa had no significant differences between all rates. The results showed that plant grew normally and did not show any symptoms of lead toxicity during the period of treatment even at 1000μmol·L^-1 Pb in the growth medium. There were no significant differences between 200μmol·L^-1 Pb treatment and control plants in M. jalapa roots anatomize tissue structure. Meanwhile, the trachea of root was significant decreasing under 1000μmol·L^-1 Pb stress, but the structure of epidermis cells, cortical cells and fibrovascular tissue maintained complete. And the tissue structure of leaf was not effected even the Pb treatment reached 1000μmol·L^-1 basically. Therefore, there is great potential for using M.jalapa in the application of phytostabilization for lead contaminated mining wasteland because of its strong Pb tolerance.4. The FTIR of M. jalapa showed the chemical composition such as organic acids, carbohydrate, protein and amino acids was effected by the Pb stress in roots. The absorbance of the dominating bands near 3420, 2920, 1610, 1060 cm^-1 which correspond to organic acids, carbohydrate, protein and amino acids rose firstly and then decreased in root tissues. These material could reduce the availability and toxicity of heavy metal by chelation and strengthen the tolerance to heavy metal. But M. jalapa did not show obvious changes in leaves and stems because less Pb was transported into shoot tissues in all treatments. This could be a kind of feedback mechanism of Mirabilis jalapa Linn under Pb stress.