Toxic And Resistance Mechanisms Of Pb Pollution In Pisum Sativum L. And Robinia Pseudoacacia L.

Heavy metal pollution is one of today's most serious problems.Nowadays,there is a growing concern over the issues of use of plants in phytoremediation and mechanisms of their resistance and inside damages under heavy metal stress.Choosing Pisum sativum L.and Robinia pseudoacacia L.as the main experimental material,we analyzed the distribution and accumulation of heavy metal Pb in the leaves and roots of Pisum sativum L.and Robinia pseudoacacia L.using transmission electron microscopy(TEM) and TEM X-ray microanalysis.We detected Pb contents in organelles of leaf and root ofPisum sativum L.and Robinia pseudoacacia L.by semi-quantitative measuring methods,and K⁺ contents by Pb²⁺ treatments were also measured,and effective factors of Pb distribution and corresponding K⁺ contents were analyzed.The aim of this study is to answer questions concerning the mechanisms of Pb tolerance and hyperaccumulation in Pisum sativum L.and Robinia pseudoacacia L..The potted seedlings were watered with Pb²⁺ with concerntrations of 100mg/L and 400mg/L every day as modest and serious stress. We analyzed the changes of cell and ultrastructural toxic effects and the changes of heavy metal contents and distribution of Pb in the cellular and subcelluar level.With comparison to the control,some possible mechanisms of the damages and tolerance traits within the cells of polluted seedlings of Pisum sativum L.and Robinia pseudoacacia L.were suggested and discussed.As the results of transmission electron microscopy(TEM) and TEM X-ray microanalysis,it was indicated that Pb²⁺ might injure all the membranous structures of cells,nucleus,cell walls and organelles though there existed different degrees of endurance of cell structures to the poison.The mechanisms of heavy metal resistance to some extent of Pisum sativum L.and Robinia pseudoacacia L. involved the different degrees of endurance of organelles,accumulating in roots,binding to cell wall, accumulating in vacuole and other possible mechanisms.When it comes to the distribution of Pb within the seedlings of Pisum sativum L.and Robinia pseudoacacia L.,we found that Pb mostly distributed in the roots,especially in the epidermis and cortex, while little amount of Pb were allocated in the leaves,and were mainly concentrated in leaf vascular bundle cells.In the different organelles within one cell,Pb tend to be distributed on cell walls and vacuoles..Furthermore,as far as the issue of spatial distribution pattern and injury mechanisms concerned in Pisum sativum L.and Robinia pseudoacacia L.seedlings,Pb displayed a negative correlation with the variation of K⁺.