| With the development of industry and society,the contamination of cadmium in farmland of China was a growing problem,Excess cadmium inhibited the growth,yield and quality for crop.Tobacco was an important economic crop in China.Tobacco had a strong enrichment capability of cadmium.Cadmium pollution could harm tobacco production,the quality and the health of smokers.So,it was important to study the alleviation and treatments of cadmium toxicity.In this paper,hydroponic experiment five treatments:control(CK),0.05mmol·L-1 Cd2+(Cd0.05),0.1mmol·L-1 Cd2+(Cd0.1),0.055mmol·L-1 Cd2++1.0 mmol·L-1 SiO2(Cd0.05+Si)and O.1mmol·L-1 Cd2+1.0mmol·L-1 SiO2(Cd0.1+Si)was carried out.Tobacco cultivar Yunyan 87 was selected as experimental material.Cd as CdCl2·2.5H2O 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 silicon on plant growth,photosynthesis,chlorophyll contents,oxidative stress,antioxidant enzymes,electrolyte leakage,cadmium uptake,morphology and subcellular distribution of cadmium under cadmium stress.The objective was to investigate that whether or not the exogenous application of silicon activate the protective responses in tobacco plants exposed to cadmium stress.The main results were presented as follows:1.Silicon alleviated the inhibition of tobacco growth under cadmium stressThe growth of tobacco in term of plant height,leaf area and biomass was decreased significantly in the presence of cadmium in the nutrient medium at both cadmium levels.Compared with CK treatment,plant height and leaf area of tobacco at resetting stage decreased by 11.74%-24.85%and 12.82%-28.28%respectively,and the dry weight of root,stem and leaf decreased by 48.27%?49.88%,33.75%?43.72%,41.12%-50.97%,respectively under cadmium treatments,which were significant difference.Silicon could alleviate the inhibition of growth for tobacco under cadmium stress.As compared with Cd0.05 and Cd0.1 treatments,Cd0.05+Si and Cdo.i+Si treatments significantly or very significantly increased the plant height and leaf area of tobacco at resetting stage by 5.39%-15.73%and 6.72%-34.64%,respectively,and the dry weight of root,stem and leaf by 30.80%-42.86%,43.14%-44.92%and 21.76%-49.70%respectively.And the growth trend of tobacco in toping stage was same to resetting stage.2.Silicon reduced the content,the form and the subcellular distribution of cadmium under cadmium stress of tobaccoThe silicon contents of root,stem and leaf decreased with increasing cadmium concentration in the nutrient medium.Adding silicon could increase the silicon content of root,stem and leaf under cadmium stress.As compared to Cd0.05 and Cd0.1 treatments,Cd0.05+Si and Cd0.1+Si treatments significantly decreased cadmium content of root,stem and leaf by 20.77%,37.08%,23.65%and 12.14%,27.07%,12.59%,respectively.Silicon inhibited the migration of cadmium in root to shoot.Compared with Cd0.05 and Cd0.1 treatments,Cd0.05+Si and Cd1.1+Si treatments decreased cadmium migration coefficient from root to stem and from root to leaf by 21.75%-24.37%and 5.28%-12.54%,respectively.The contents of all chemical forms of cadmium increased with the increasing of cadmium concentration in the nutrient medium.Silicon could reduce the contents of cadmium in the forms of ethanol-extractable,water-extractable,sodium chloride-extractable and acetic acid-extractable in root and leaf under cadmium stress,while increase the forms of hydrochloric acid-extractable and residual.With the increased of cadmium concentration in the nutrient medium,the cadmium contents of organelles increased.Silicon could reduce the cadmium contents of organelles,especially in chloroplasts and mitochondria under cadmium stress.3.Silicon affected nutrient content of tobacco under cadmium stressCadmium stress decreased significantly the contents of Mg,Mn,Zn,B,Fe,while increased the contents of P,K,Ca and Cu in tobacco leaf.Silicon increased significantly the contents of Mg,Mn,Zn,B,Fe,while increased the contents of K,Ca and Cu in tobacco leaf under cadmium stress.But it was no indiscipline change of P in tobacco leaf.Cadmium stress reduced significantly the contents of Mg,Mn and Zn,but increased the contents of P,K,Ca,B,Fe and Cu in tobacco root.Silicon decreased significantly the contents of Mg,Mn and Zn,but increased the content of P,K,Ca,B,Fe and Cu in tobacco root of under cadmium treatment.4.Silicon mitigated the membrane injury of tobacco root and leaf under Cd stressCadmium stress decreased significantly the activities of SOD and CAT,but increased significantly the activities of APX,GR.By the exogenous application of silicon,the activities of SOD,CAT,APX and GR of tobacco root and leaf increased significantly under cadmium stress.Compared with Cd0.05 and Cdo.i treatments,Cd0.05+Si and Cdo.i+Si treatments improved the activities of SOD,CAT of tobacco root and leaf by 44.40%-56.76%,54.71%-61.53%and 48.58%-58.37%,24.90%-43.55%,respectively,improved the activities of APX and GR by 55.16%-83.40%,31.00%-31.12%and 31.61%-39.20%,38.53%-40.50%,respectively.Cadmium stress increased the content of GSH and AsA,further improvement was found by the exogenous application of silicon.Compared with Cd0.05 and Gd0.1 treatments,Cd0.05+Si and Cd0.1+Si treatments increased the content of GSH of root and leaf at by 10.67%,52.77%and 9.21%,20.00%,respectively,the content of AsA increased by 65.00%,25.37%and 27.2 7%,21.62%,respectively.The adverse effects of cadmium were alleviated by the exogenous application of silicon.Compared with Cd0.05 and Cd0.1 treatments,Cd0.05+Si and Cd0.1+Si treatments reduced O2-production rate by 27.71%,5 1.85%and 1 5.10%,57.29%,respectively,and the content of MDA by8.81%,21.10%and 14.47%,30.97%,respectively.5.Silicon improved the photosynthesis of tobacco under cadmium stressCadmium stress decreased significantly the stomatal conductance,photosynthetic pigments,apparent quantum yield,carboxylation efficiency and Fv'/Fm',?pPS ?,Fv/Fm,qP,while CO2 compensation point and qN increased significantly.As compared to CK treatment,Cd0.05 and Cd0.1 treatments reduced the net photosynthesis rate by 52.02%and 73.75%,respectively.Compared with Cd0.05 and Cd0.1 treatments,Cd0.05+Si and Cd0.1+Si treatments increased the stomatal conductance,total photosynthetic pigment by 259.90%,99.90%and 43.37%,92.33%,respectively.Silicon improved the apparent quantum yield,carboxylation efficiency and Fv\/Fm',?pPS ?,Fv/Fm,qP,reduced qN under cadmium stress.compare with Cd0.05 and Cd0.1 treatments,Cd0.05+Si and Cd0.1+Si treatments increased net photosynthesis by 13.29%,72.78,respectively.The correlation analysis showed that the rate of O2-production had a significantly negative correlation with the content of chlorophyll a,chlorophyll b and carotenoids,and the content of cadmium in chloroplasts had a significantly negative correlation with the net photosynthesis.And these results showed that silicon could relieve the deterioration of photosynthetic pigment caused by active oxygen,and reduced the harm of cadmium to chloroplast.These were the important reasons for silicon on improving photosynthesis of tobacco under Cd stress. |
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