Physiological Responses To Nitrogen And Cadmium In Suspension Cells Of Populusx Canescens

Cadmium（Cd） is a major environmental pollutant with high toxicity to animals andplants. Phytoremediation as an emerging and promising technology is a cost-effective,environment-friendly and sustainable method. Populus species have been regarded aspotentially promising candidates in phytoextraction and phytoremediation of Cd due to theirfast growth, high biomass, extensive root mass and low impact on food chains. Nitrogenfertilizer have significant effects on Cd absorption, desorption, chemical transformation andtransportation. Cultured plant cells have a higher rate of growth and metabolism thanfield-grown plants and can be grown under conditions of high oxidative stress. Plant cellcultures are not limited by environmental, ecological and climatic conditions.The effects of different levels of nitrogen in alleviating cadmium toxicity to Populus×canescens were investigated using suspension culture. The aim of this work was to study theeffect of Cd and nitrogen on Populus cell metabolism through physiological parametersrelated to cell growth, Cd accumulation, lipid peroxidation, antioxidant system and Nmetabolism. The application of appropriate nitrogen levels may be useful approach toenhancing the phytoremediation efficiency of Cd-contaminated soils by Populus. This papercan provide theoretical basis for the cultivation of Populus suspension culture under Cdstress and the appropriate of nitrogen application.The study reached conclusions as follows:（1） The optimum callus induction medium is WPM+0.5mg L^-12,4-D+0.05mg L^-1KTand the callus inductivity is90%. The optimum suspension culture medium is WPM+0.1mgL^-12,4-D+0.08mg L^-1KT, the optimum subculture days is7d.（2） Appropriate supply of N （5.5mM） increased growth of cell dry matter and uptake ofCd and Zn when the concentration of Cd increased at3d. Growth rate increased with theincrease of Cd stress concentration and reached the max at Cd （100μM） treatment, thendeclined at high Cd concentration （200μM）. When nitrogen level increased （12.5mM）,growth of suspension cells of Populus×canescens was restrained.（3） Under the same N concentration, the contents of superoxide radical （O2.-）, hydrogenperoxide （H₂O₂） and malondialdehyde （MDA） showed an increase when the Cd concentration increased, but the trend was not marked and consistent in statistical analysis. Under the sameCd concentration, the5.5mM N treatment lead slight decrease in the levels of O2.-, H₂O₂andMDA. Suspension cells of Populus×canescens supplied with5.5mM N had less oxidativedamage by Cd stress in comparison with the cells supplied with12.5mM N.（4） Cd stress showed less pronounced effects than the N culture alone. Soluble proteinand Total soluble sugars of cultured cells under Cd stress had no markedly influence. Butincreasing nitrogen supply （12.5mM） led to increase in soluble protein and decrease insoluble sugar significantly.（5） The contents of reduced glutathione （GSH） and oxidized glutathione （GSSG）declined while contents of GSH/GSSG and ascorbate （ASC） enhanced with the increase of Cdstress concentration.（6） The activities of SOD, POD and GR significantly increased when cells were exposedto Cd excess and the increases were more pronounced under5.5mM N supply, CAT activityunder Cd stress had no significantly influence, the activities of AAO and APX enhancedfirstly and then decreased with increasing Cd concentration.（7） After3days stress, Cd treatments increased the activities of nitrate reductase（NR）,glutamine synthetase （GS）, glutamate synthase （GOGAT） and glutamate dehydrogenase（GDH） at appropriate supply of N （5.5mM） and decreased the activities of N metabolismenzymes under12.5mM nitrogen supply.The application of appropriate nitrogen could be useful to the cell growth and cadmiumabsorption and enhance the phytoremediation efficiency. This paper showed that theappropriate nitrogen concentration was5.5mM.