The Physiological And Molecular Mechanisms Of Grafted Poplar Species In Response To Cadmium Stress

Over accumulation of cadmium(Cd)in soils,not only causes enormous damage to plants,but also posed a serious threat to human health.Phytoremediation technology is one of efficient way to repair Cd contaminated soils.Because of the deep-rooting system,rapid growth,and so on,poplars have became good candidates for repairing Cd contaminated soils.Previous studies indicated that different genotypes of poplar varied in the ability of accumulating Cd.Populus cathayana accumulated the largest Cd amount in aerial parts,but large amounts of Cd were sequestered in roots of Populus × euramericana.However,the effects of roots and aerial parts in poplars on Cd distribution in different tissues and Cd enrichment abilities are still unknown.To determine the relative importance of roots and shoots in Cd accumulation of poplars,and further clarify the mechanisms of Cd accumulation in poplar,we used reciprocal grafting between P.cathayana and P.× euramericana,and all the plants were treatment with 0 and 75 ?M Cd Cl2 for 39 days,and analyzed the differences in the related physiological and molecular aspects of poplars in both roots and leaves.The main results were as follow:(1)Under Cd exposure,compared to P.cathayana,the rootstock of P.× euramericana had higher Cd accumulation in the roots.Meanwhile,transcriptional expression analysis of genes involved in Cd uptake and transport processes(such as ZIP2,NRAMP1.3,PCS,ABCC1,ATM3,MTP1,NRAMP3,HMA4,PDR8),showed that P.× euramericana had advantages in the expression of these genes in comparison with P.cathayana.This may indicate that,compared to the P.cathayana,the roots of P.× euramericana have strong capacity of Cd absorption,accumulation and transportion.(2)Under Cd exposure,compared to P.× euramericana,the aerial parts of P.cathayana showed greater accumulation of Cd,but lower H2O2 and MDA contents,while higher starch and thiol contents in leaves.These results may indicate that the shoot scion of the P.cathayana has optimum mechanism of accumulations and detoxification of Cd.(3)Under Cd exposure,plants with P.× euramericana rootstock and P.cathayana shoot scion had the highest Cd accumulation in the aerial parts,and the ROS and non-enzyme antioxidants concentrations were relatively low.These results indicate that,accumulation of Cd in aerial parts of poplars not only primarily drived by root processes,but also depended on the shoot processes.And,since the plants with P.× euramericana rootstock and P.cathayana shoot scion can accumulate more Cd,and maintain lower oxidative stress,so grafting P.cathayana shoot scion onto P.× euramericana rootstock may be an effective mean for phytoremediation.