The Effects Of Pb And Cd Stress On Growth,Physiological And Biochemical Indexes Of Flue Cured Tobacco

In order to study effects of heavy metals stress on tobacco growth and physiological and biochemical parameters,the soils in which cultivated tobacco variety of Jiyan No.9 in potted plant were irrigated Pb,Cd and complex solution,influence of differentconcentration of Pb,Cd and their combined stress on tobacco growth and physiological and biochemical parameters in simulated soil,as well as Pb,Cd distribution of tobacco in vivo,which providea theoretical basisfor prediction,evaluation,prevention and control of heavy metal stress for tobacco.The results are as follows:The leaf length,leaf width,plant height,stem perimeter were decreasingalong withincreasedPbconcentration gradually under Pb Stress and combined stress,tobacco agronomic traits were not influenced under Cd concentration<3 mg l kg treatment.tobacco agronomic traits were not better than control except the shoot ratio under3 mg l kg Cd treatment.Under Pb,Cd and their combined stress,chlorophyll contents were decreasing along with increased stress concentration;the trends in CAT and SOD activities were consistent that as stress concentration increased first and then decreased;POD activitieswere increasing with the increased stress concentration;the contents of MDA were increasing with the increased stress concentration;soluble sugar contentswere the highest in 150 mg/kg of Pb concentration and(100+3)mg/kg of the combined treatment;Pro contentswere decreasingalong with increased Pbconcentrations,and increasing first and then decreasing along with increased Cd and combined stress concentration.With increased Pb,Cd and their combined stress concentration,total nitrogen,protein,total sugar,reducing sugar content were increasing first and then decreasing consistently;nicotine content were decreasing and the starch and chlorine content were decreasing first and then increasing with increased stress concentration.As a whole,the distribution discipline of heavy metal in the root,stems and leaves were as follows:root>leaf>stem;Pb,Cd contents of flue-cured tobacco were less than before;the baseleaves were the least accumulated Pb,Cd among middle leaves,baseleaves and tip leaves.In general,when Pb>150 mg/kg,Cd>3 mg/kg and Pb+Cd>(100+3)mg/kg,tobacco growth were limited and chemical component ratio were imbalance which was not beneficial to tobacco quality formation.It is noted that soil heavy metal pollution thresholds of achieving safe production of flue-cured tobacco are:Pb150 mg/kg,Cd3 mg/kg,Pb+Cd(100+3)mg/kg.