相較于其他重金屬,鎘(Cd)具有高流動性、高水溶性和植物致毒性,是一種高致死性元素。Cd以離子形態(tài)通過根系進入植物后,經(jīng)主動運輸和被動運輸轉(zhuǎn)移至植物木質(zhì)部和韌皮部。植物體內(nèi)大量累積的Cd會通過抑制根部Fe(III)還原酶的活性而降低光合作用,還可影響固定CO₂的酶活性,影響礦物元素的吸收,進而引起植物營養(yǎng)失衡(如N和K+等)、氣孔關(guān)閉等癥狀。Cd脅迫下植物細胞產(chǎn)生的大量活性氧(ROS)可導(dǎo)致植物體內(nèi)抗氧化酶活性顯著降低。此外,Cd通過食物鏈在人體累積,易對腎臟、骨骼和肺造成損害。在影響植物生長發(fā)育的非生物脅迫因子中,土壤pH是最關(guān)鍵的因子之一,這是因為土壤pH在土壤發(fā)生過程和物化性質(zhì)中起核心作用,可影響植物生長、微生物多樣性以及營養(yǎng)物質(zhì)的溶解度和有效性,且酸性條件Cd的存在會使這些效應(yīng)進一步復(fù)雜化。植物對Cd的生物利用度不僅與Cd化學(xué)形態(tài)和土壤中Cd含量相關(guān),還受土壤pH值的影響。生態(tài)毒理學(xué)研究已表明土壤pH值對Cd生物利用度作用顯著,因此研究酸性土壤條件下Cd對植物的影響具有重要的意義。硅(Si)作為一種有益元素,在不同類型植物的生長發(fā)育中起著至關(guān)重要的作用。施...

【文章頁數(shù)】：127 頁

【學(xué)位級別】：博士

【文章目錄】：
摘要
Abstract
Chapter 1 Introduction
    1.1 Background
    1.2 Cadmium
        1.2.1 Cadmium in the Soil
        1.2.2 Cadmium Mobilization,Uptake,and Transport
        1.2.3 Plant Response to Cd Toxicity
        1.2.4 Factor Effecting Cd Uptake and Accumulation
    1.3 Silicon
        1.3.1 Silicon and Plants
        1.3.2 Silicon Role in Wheat Plants
        1.3.3 Silicon Role Against Abiotic Stress
    1.4 Need for the Project
    1.5 Significance of Research
    1.6 Research Aims
Chapter 2 Materials and Methods
    2.1 Plant Culture and Experimental Design
        2.1.1 Recipe of Hoagland’s Solution
        2.1.2 Recipe of Si Treatment
    2.2 Experimental Layout
        2.2.1 Experiment 01
        2.2.2 Experiment 02
        2.2.3 Experiment 03
        2.2.4 Experiment 04
        2.2.5 Experiment 05
    2.3 Determination of Plant Growth and Biomass
    2.4 Measurements of Photosynthetic Pigments
    2.5 Biochemical Analysis
    2.6 Electrolyte Leakage
    2.7 Determination of Nutrient Elements in Plant Tissues
Chapter 3 The Effect of Silicon Foliar and Root Application on Growth,Physiology,and Antioxidant Enzymes Activity of Wheat Plants under Cadmium Toxicity
    3.1 Introduction
    3.2 Results
        3.2.1 Growth Parameters
        3.2.2 Photosynthetic Pigments
        3.2.3 Reactive Oxygen Species(ROS)
        3.2.4 Enzymatic and Non-enzymatic Antioxidants in Wheat Seedlings
        3.2.5 Essential Nutrients in Wheat
    3.3 Discussion
    3.4 Conclusion
Chapter 4 Mechanisms of Silicon-Mediated Enhancement of Cadmium Tolerance in Wheat(Triticum Aestivum L.)Grown in Cadmium Contaminated Acidic Nutrient Solution
    4.1 Introduction
    4.2 Results
        4.2.1 Biomass Production
        4.2.2 Photosynthetic Pigments
        4.2.3 Enzymatic Antioxidants
        4.2.4 Non-enzymatic Antioxidants
        4.2.5 Osmoprotectants
        4.2.6 Protein Contents
        4.2.7 Relative Water Contents and Membrane Stability Index
        4.2.8 Reactive Oxygen Species(ROS)Production and Lipid Peroxidation
        4.2.9 Nutrient Concentrations
        4.2.10 Tissue-specific Cadmium Concentration
        4.2.11 Tissue-specific Silicon Concentration
    4.3 Discussions
    4.4 Conclusions
Chapter 5 Silicon Attenuates Acidic and Alkaline Stress in the Wheat Plant by Improving Nutrient Availability,Membrane Stability Index and Antioxidative Defense System
    5.1 Introduction
    5.2 Results
        5.2.1 Biomass Production
        5.2.2 Photosynthetic Pigments
        5.2.3 Antioxidative Enzymes
        5.2.4 Reactive Oxygen Species(ROS)Production and Lipid Peroxidation
        5.2.5 Nutrients Concentration
        5.2.6 Tissue-specific Silicon Concentration
    5.3 Discussion
    5.4 Conclusion
Chapter 6 Interactions of pH and Cadmium Toxicity in Their Effect on Growth,Membrane Stability,and Antioxidant Defense Systems of Triticum Aestivum(L.)
    6.1 Introduction
    6.2 Results
        6.2.1 Biomass Production
        6.2.2 Photosynthetic Pigments
        6.2.3 Enzymatic and Non-enzymatic Antioxidants
        6.2.4 Reactive Oxygen Species(H2O2,EL,and MDA)Production and Lipid Peroxidation
        6.2.5 Nutrient Concentration
        6.2.6 Tissue-specific Cadmium Concentration
    6.3 Discussion
    6.4 Conclusion
Chapter 7 Alleviatory Effects of Silicon on the Physiology,Morphology and Antioxidative Mechanisms of Wheat(Triticum Aestivum L.)Roots under Cadmium Stress in Acidic Nutrient Solution
    7.1 Introduction
    7.2 Results
        7.2.1 Effect of Silicon and Cadmium on Root Biomass
        7.2.2 Effect of Silicon and Cadmium on Root Volume and Average Diameter
        7.2.3 Effect of Silicon and Cadmium on Total Root Length and Root Tips
        7.2.4 Effect of Silicon and Cadmium on Enzymatic Antioxidant and Protein Contents
        7.2.5 Effect of Silicon and Cadmium on Non-enzymatic Antioxidants
        7.2.6 Effect of Silicon and Cadmium on Osmoprotectants
        7.2.7 Effect of Silicon and Cadmium on Reactive Oxygen Species
        7.2.8 Effect of Silicon and Cadmium on Nutrient Concentrations in Roots of Wheat Plants
        7.2.9 Tissue-specific Silicon Concentration in Roots
        7.2.10 Tissue-specific Cadmium Concentration in Roots
    7.3 Discussion
    7.4 Conclusion
Chapter 8 Conclusion
    8.1 Silicon Soil and Foliar Application Alleviates Cd Toxicity
    8.2 Silicon Alleviates Alone as well as Combines Effects of Cd and Acidic pH Toxicities in Wheat Plants
    8.3 Silicon Alleviates Acidic and Alkine pH Toxicities in Wheat Plants
    8.4 Silicon Improves Morphology and Physiology of Roots of Wheat Plants Grown under Cd-contaminated Acidic Nutrient Solution
    8.5 Cadmium Uptake and Accumulation in Different Levels of pHs
References
Acknowledgements
Curriculum Vitae Malik Shafeeq-ur-Rahman



本文編號：3773419