Studies On The Tolerance And Detoxification Mechanism To Cadmium In Salix Matsudana Koidz Seedlings

With the rapid development of industrial and agricultural production,the heavy metal pollution in soil is becoming increasingly serious.Cadmium(Cd),with high toxicity,high mobility,and easy to enter the food chain,attracts much attention.Recently willow has been widely used in remediation of heavy metal polluted soils in European and American countries.Willow can also replace coal and oil as fuel,which can combine biomass production with phytoremediation.Cd was used as the stress factor and Salix matsudana Koidz seedlings as the research object in this study in order to deal with the comprehensive evaluation on the resistance mechanisms of S.matsudana to Cd,including the mechanisms on absorption,accumulation,toxicity and resistance in the seedlings of S.matsudana stressed by Cd.The main results were as follows:1.Cd inhibited the growth of S.matsudana,caused ROS accumulation in the roots and leaves,also activated the antioxidant enzyme system to protect plant from peroxidation damage at the same time,but this protection was limited under high concentration and long time of Cd stress.High concentrations of Cd stress inhibited the synthesis of chlorophyll,interfered with the photosynthesis process.2.Root was the main organ of absorbing and accumulating Cd.The root had not yet reached the absorbed saturation concentration when the treated Cd concentration was 100 μmol/L.In addition,Cd inhibited the accumulation of Fe,Zn,Mn and Cu.3.The S.matsudana root meristem and elongation zone were the primary sites of Cd accumulation.By EDXA analysis,Cd distributed mainly on the cell walls of the epidermis and vascular column cells in the mature region of root tips,and Cd could pass through the endodermis and transport through the vascular column to the shoot of S.matsudana.4.The strategy of Cd resistance in the root cells of S.matsudana was to make Cd deposited on the cell wall,and gradually transferred and isolated to the vacuole.Cd chelated mainly with proteins and organic acids,and gradually existed in the form of metal phosphate and oxalate sediments.That is to say,the compartmentalization of heavy metals by the cell walls and vacuoles of plants played a major role in detoxification and tolerance of heavy metals.5.The physiological activity of S.matsudana root cells was affected by the high concentration and long time of Cd stress.Cd inhibited the mitotic index of root meristem cells.Cd stress affected the microtubule cycle,leading that microtubules arranged disorderly,fractured slightly,even condensed into granules,appeared adhesion phenomenon between microtubules,finally resulting in C-mitosis and chromosome adhesion and even leading to the mother cell not spliting into two daughter cells.Therefore,the Cd stress destroyed the normal cell cycle.6.The differential gene expression induced by Cd stress was analyzed using high-throughput transcriptome sequencing and bioinformatic analysis methodology.The results showed that metal transporters,antioxidant related genes,amino acids and carbohydrate metabolism related genes,DNA replication and transcription related genes and some transcription factors were closely related to the mechanism of Cd detoxification in S.matsudana.In conclusion,this study explored the tolerance and detoxification mechanism of S.matsudana seedlings to Cd,which can provide scientific and objective data for using S.matsudana in remediation of Cd contaminated soil.