| The pollution of heavy metal in soils has become the world's environmental problems and it must be solved as soon as possible. The way of preventing heavy metals in soils pollution, including phytoremediation also caused great concern and attention to environmental workers and government departments.It is the important foundation for achieving phytoremediation for heavy metal pollution in soils to research and try to find out physiology and hyperaccumulating characteristics of plants to metals interaction. Therefore, the present study investigated the effect of Fe and Mn interaction on the accumulation in Mn hyperaccumulator pokeweed (Phytolacca americana L.).The photosynthesis and antioxidant enzyme activities under Fe and Mn interaction were also investigated. The major results were summarized as follows:1. Hydroponic experiments were carried out to study the uptake kinetics of transport system for Mn2+ by root, and of their response to Fe2+.The results show that the time-dependent kinetics of Mn uptake in root of pokeweed consisted of two stages with an initial rapid stage(12h) followed by a longer but slower stage(>12h), reducing Mn2+ accumulation in root and equilibrium time shortens when added Fe+; Concentration-dependent kinetics of Mn uptake and the one effects by Fe2+ in roots yielded nonsaturating kinetic curves that could be divided into linear and saturable components. Both of the saturable component could be characterized by Michaelis-Menten equation, and there were no significant differences in the calculated Km, whereas Vmax values for added Fe2+ were much lower than that for only Mn2+, indicating that effects of Fe2+ on Mn2+ uptake were mainly attributed to its influence on the quantity of manganese carriers located at the cell membrane instead of on the affinity of the uptake sites for Mn2+.At the same time we added ions competitive experiments on the cell wall and further show that the main influence of Fe2+ on the Mn2+ absorption in root is plasma membrane rather than cell wall, cell wall may play a role in the process, but not the major factor.2. The Mn content of plant with 50,100,200μmol/L Fe2+ and 5,500,5000μmol/L Mn2+ interaction treatments decreased as Fe2+ concentration increased, especially in roots. The high Mn2+ concentration also reduced the Fe content of plant and the content of leaf dropped largely. Concerning cell levels, most Mn were stored in the soluble parts of pokeweed and the content of each component decrease due to Fe2+ effect. Fe2+ promoted the accumulation of Mn in the cell wall of the roots, the ratio of Mn in the cell walls were more than the soluble fraction when the Fe2+ concentration were 200μmol/L.Though Mn content of the shoot decreased as Fe2+ concentration increased, the dry weight increased and it cause that the accumulation of Mn in pokeweed increased.3. The chlorophyll a and total chlorophyll content in the pokeweed increased as Fe2+ concentration increased but the trends affected by Mn2+ concentration were complex:both of chlorophyll a and total chlorophyll increased as Mn2+ concentration increased at 50μmol/L Fe2+, and at the concentration 200μmol/L of Fe2+ they decrease as Mn2+ concentration increased; at the concentration (Fe2+ 200μmol/L) they increased in 14d and decrease in 28d as Mn2+ concentration increased. The photosynthetic rate,transpiration rate and stomatal conductance were increased as Mn2+ concentration increased and the gas exchange parameters improved after adding Fe2+. The fluorescence parameters did not show clear trend under Fe and Mn interaction, however, in a certain concentration(Fe2+ 200μmol/L Mn2+ 5μmol/L) FO reached the maximum, Fm and Fv/Fm to the minimum while at the concentrations (Fe2+ 100μmol/L Mn2+ 500μmol/L) FO to a minimum, Fm and Fv/Fm has a maximum. Soluble sugar content after 24d treatment was more than 14d, and at the concentration (Fe2+ 100μmol/L Mn2+ 500μmol/L) to the maximum.4. There were little increase of Pro and MAD content under Fe and Mn interaction treatments indicating that the cell membrane were still not be injured, the activity of SOD and POD with Mn concentration increased gradually increased, the improvement of enzyme activities would help to eliminate the active oxygen free radicals, the activity of CAT was not remarkablely changed in pokeweed when Fe and Mn interaction, however MAD content increased significantly as the Mn concentration increased after 28d, and the activity of SOD and POD decrease, but increased as the increase of Fe concentration in the treatments, indicating that the activity of antioxidant enzymes decreased with the treatment time, while Fe can improve the activity of antioxidant enzymes, alleviating the poisoning on pokeweed due to excess Mn. |
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