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

Arsenic pollution reduced crop production and quality,and endangerd human health through the food chain.As an important economic crop in China,tobacco existed arsenic pollution.Therefore,it was of great significance to study the measures to alleviate arsenic toxicity.Hydroponic experiment was conducted on Yunyan87 with exogenous arsenic in the form of sodium arsenate?Na3AsO4·12H2O?and exogenous silicon in the form of sodium silicate?Na2SiO3·9H2O?.Five treatments were set as follow:control?CK?,0.25 mmol·L-1 As5+(As_0.25),0.35 mmol·L-1 As5+(As_0.35),1.0 mmol·L-1 SiO2+0.25 mmol·L-1 As5+(As_0.25+Si),1.0 mmol·L-1 SiO2+0.35 mmol·L-1 As5+(As_0.35+Si).Experiment was conducted to find out the effects of silicon on plant growth,nutrient uptake,photosynthesis and activate oxygen metabolism under arsenic stress and to clarify the mechanisms of silicon alleviated arsenic toxicity from the arsenic concentration,morphology and subcellular distribution.The main results of the study are as follows:1 The effects of silicon on tobacco growth under arsenic stressArsenic stress inhibited the growth of tobacco,reduced leaf area,plant height and the biomass of root,stem and leaf.Silicon could alleviate the inhibition of tobacco growth under arsenic stress.Compared with CK treatment,the plant height,maximum leaf area and total biomass of Aso.25 and As_0.35 treatments significantly decreased by 69.29%,77.54%,85.78%and 85.28%,85.58%,91.63%respectively,the total root length,average diameter,total root volume and the number of branches significantly decreased.Compared with As_0.25 and Aso.35 treatments,the plant height,maximum leaf area,total biomass of As_0.25+Si and As_0.35 +Si treatments increased by 53.41%,54.72%,146.79%and 120.22%,70.03%,141.03%,and the total root length,average diameter,total root volume,the number of branches of the tobacco increased significantly.2.The effects of silicon on nutrient absorption of tobacco under arsenic stressCompared with CK treatment,As_0.25,As_0.35 treatment decreased the contents of N,P,K,Mg in tobacco organs,the content of Fe,Mn,Cu,Zn,Si in the leaf,the content of Ca in both stem and leaf,but increased the content of Fe,Mn,Cu,Zn in root and stem,the content of Ca in root,the content of B in leaf and the content of S in the root and leaf.Compared with As_0.25 and As_0.35 treatments,As_0.25+Si and As_0.35+Si treatment significantly increased the content of Si,P,and N in tobacco organs,the content of S in root and leaf.3.The effects of silicon on the arsenic content,morphology and subcellular of arsenic in tobacco under arsenic stress.The contents of arsenic in tobacco increased with the increase of arsenic concentration in culture.Silicon could significantly reduce the arsenic content in stem and leaf of tobacco.Compared with As_0.25 and As_0.35,As_0.25+Si and As_0.35+Si treatments significantly decreased the contents of arsenic in stem and leaf by 43.98%,62.72%and 46.39%,52.41%respectively.Compared with As_0.25,As_0.25+Si treatment decreased the arsenic content in root by 20.63%,while As_0.35+Si treatment increased the arsenic content in root by 54.50%as compared with As_0.35 treatments.Silicon inhibited arsenic migration from root to stem and leaf.Compared with As_0.25,As_0.35,the stem/root transfer coefficients of As_0.25+Si,As_0.35+Si decreased by 29.48%and 76.17%,the leaf/root transfer coefficient decreased by 32.25%and 69.44%respectively.Compared with CK,As_0.25 and As_0.35 treatments significantly increased the morphology of arsenic in root and leaf of tobacco.Adding silicon decreased the arsenic content of FNaCl and FHAC in root and FE and FNaCl in leaf,but increased the arsenic content of FR in root.Addition of silicon could also reduce subcellular distribution of arsenic in tobacco.Adding silicon decreased the arsenic content of cell nucleus in root,the cell wall,chloroplast and cytoplasm in leave,but increased the arsenic content of cell wall in root.4.The effects of silicon on photosynthesis of tobacco under arsenic stressCompared with CK,As_0.25 and As_0.35 treatments reduced the net photosynthetic rate by 92.93%-96.46%,and decreased the content of photosynthetic pigment,TF,WUE,light use efficiency,the efficiency of RuBP carboxylation of tobacco.Compared with As_0.25 and As_0.35,As_0.25+Si and As_0.35+Si treatments increased net photosynthetic rate by 377.27%-563.64%,the content of chlorophyll by 47.00%-83.91%.Silicon could significantly increase the light use efficiency,the efficiency of RuBP carboxylation,and TF and WUE.There was a significant negative correlation between the arsenic content of chloroplast and the content of chlorophyll,which indicated that silicon could reduce the damage of chlorophyll under arsenic stress.Arsenic stress reduced the ?PS ?,Fv/Fm,Sm,?Eo,?o significantly,which indicated that arsenic could damage the reaction center of PSII,and lessen the PQ storage capacity of the receptor side,inhibited the electron transfer,decreased the electron transfer rate.Silicon could maintain the activity of light reaction center,reduce the invalid use of heat dissipation?DIo/RC?,increase the electron transfer ability?ETo/RC?and the structure parameters of photosynthetic organs?PIABS?under arsenic stress5.The effects of silicon on active oxygen metabolism of tobacco under arsenic stressArsenic stress did not affect the activity of SOD and CAT in root,but decreased the activity of POD and the content of GSH.As_0.35 treatment reduced the activity of APX and GR in root.Arsenic reduced the activity of CAT,but increased the activity of APX and the content of GSH,ASA in leaf.Silicon could increase the activity of CAT,POD,APX and the content of ASA in root and leaf under arsenic stress.Compared with CK,As_0.25 and As_0.35 treatments increased respectively the O2-contents in root and leave by 438.72%-610.68%and 99.08%-192.14%,and increased the content of H2O2 by 216.96%-586,08%and 235.92%-357.37%.Adding silicon significantly reduced the content of O2-,H2O2,the content of MDA and relative conductivity under arsenic stress.Compared with As_0.25 and As_0.35 treatments,the As_0.25+Si and As_0.35+Si treatments decreased the content of MDA in leaf and root by 16.69%-32.76%and 40.43%-62.37%respectively,and the relative conductivity by 15.93%-53.58%and 19.75%-21.28% respectively.