Study On Alleviation Of Lead Stress By Silicon And It's Mechanisms In Tobacco

Lead is the main pollution heavy metal in soil.Tobacco is an important economic crop in China.Tobacco had a strong ability to absorb and enrich lead.Lead pollution could harm the tobacco production,quality and the health of smokers.Therefore,the alleviation treatments of lead pollution were of great significance.In this paper,hydroponic experiment with five treatments:control(no silicon and lead,CK),100?mol·L-1Pb2+(Pb100),300?mol·L-1 Pb2+Pb300),100?mol·L-1Pb2++1.0mmol·L-1SiO2(Pb100+Si),300?mol·L-1Pb2++1.0mmol·L-1 SiO2(Pb300+Si)was carried out.Tobacco cultivar K326 was selected as experimental material.Pb as Pb(NO3)2 and Si as K2SiO3·4H2O were used.On the basis of eliminating the effects of pH and K+ of K2SiO3·4H2O,experiment was conducted to find out the influence of Si treatments on plant growth,photosynthesis,chlorophyll contents,oxidative stress,antioxidant enzymes,electrolyte leakage,lead uptake,morphology and subcellular distribution of lead under lead stress.The objective was to investigate that whether or not the exogenous application of Si activate the protective responses in tobacco plants exposed to lead stress.The main results of the study were as follows:1.Lead significantly inhibited the growth of tobacco.Compared with CK,the total biomass and root activity of Pb100 and Pb300 treatments were decreased by 51.43%,64.55%and 7.08%,33.60%respectively.Adding silicon could alleviate the harmfulness of lead on tobacco growth significantly.Compared with Pb100 and Pb300 treatments,the total biomass and root activity of Pb100+Si and Pb300+Si treatments increased by 75.24%,76.75%and 6.24%,18.60%respectively.2.Silicon increased the lead content of root,but decreased the lead content of stem,lower leaves and upper leaves of tobacco under lead stress.Compared with Pb300 treatment,the root lead content of Pb300+ Si treatment increased significantly by 64.61%.Compared with Pb100 and Pb300 treatment,the lead content of stem,1 lower leaves and upper leaves of Pb100+Si and Pb300+Si treatments were decreased significantly by 75.36%?36.06%,34.52%?14.82%and 61.37%?21.74%respectively.Adding silicon decreased the proportion of FE and FNaCl forms of lead,but increased the proportion of FHAC?FHCl?FR forms of lead in tobacco roots and leaves.Compared with Pb30 treatment,the lead content in chloroplasts and mitochondria of Pb300+Si treatment were decreased significantly by 18.14%,23.44%respectively.3.The CAT activity,GSH and AsA contents of tobacco leaves and root decreased,SOD and APX and GR activity increased under lead stress.Lead stress increased the POD activity of leaves,but decreased the POD activity of root.Adding silicon increased CAT activity,GSH and AsA content,but decreased the SOD and GR activity of tobacco leaves and root under lead stress.Silicon reduced POD activity of leaves,but increased the POD activity of root under lead stress.o2-·production rate,H2O2 content,MDA content,relative conductivity and the amount of K+,phosphorus and nitrate leakage of tobacco leaves and root increased significantly under lead stress.Adding silicon could significantly reduce O2-·production rate,H2O2 and MDA content,relative conductivity and the amount of K phosphorus and nitrate leakage of tobacco leaves and root under lead stress.4.Silicon increased the photosynthetic pigments content,the apparent quantum efficiency,the carboxylation efficiency and the net photosynthetic rate of tobacco under lead stress.Compared with Pb100 and Pb300 treatments,the Chla?Chib and Car content of Pb100+Si and Pb300+Si treatments increased significantly by 29.82%?40.73%?84.51%and 32.16%?76.77%?83.04%respectively.There were not significant differences of apparent quantum efficiency,carboxylation efficiency and net photosynthetic rate between Pb100+Si treatment and Pb,00 treatment.Compared with Pb300 treatments,the apparent quantum efficiency,carboxylation efficiency and net photosynthetic rate of Pb300+Si treatments increased significantly by 14.29%,87.50%and 76.62%respectively.Correlation analysis showed there were extreme significantly negative correlation between O2-· production rate,H2O2 eontent and the chlorophyll content,as well as the lead content of chloroplasts and the net photosynthetic rate,meaning silicon could alleviate chlorophyll degradation by active oxygen and the hurt of lead on chloroplasts.