| Acknowledgements | 第7-8页 |
| Contents | 第8-10页 |
| Figures and Tables | 第10-11页 |
| Abstract | 第11-12页 |
| 摘要 | 第13-15页 |
| Abbreviations | 第15-16页 |
| Chapter 1:Literature review | 第16-28页 |
| 1.1 Historical background of tobacco and heavy metal stress | 第16页 |
| 1.2 Pb availability and uptake | 第16-18页 |
| 1.3 Effect of Pb stress on plants | 第18-21页 |
| 1.3.1 Effect on growth and photosynthetic activity | 第18-19页 |
| 1.3.2 Genotoxic effects of Pb stress | 第19-20页 |
| 1.3.3 Effect on plant water status | 第20页 |
| 1.3.4 Effect on germination | 第20-21页 |
| 1.3.5 Pb induced oxidative stress and lipid peroxidation | 第21页 |
| 1.4 Defense mechanisms against Pb stress | 第21-23页 |
| 1.5 Role of thiolic compounds in heavy metal stress alleviation | 第23-24页 |
| 1.6 Genotypic variations in heavy metal stress resistance | 第24-26页 |
| 1.7 Research objectives | 第26-28页 |
| Chapter 2:Genotypic differences in tolerance to Pb stress in different tobacco varieties(Nicotiana tabacum) and the underlying physiological mechanisms | 第28-50页 |
| 2.0 Materials and Methods | 第29页 |
| 2.1 Plant material and growth conditions | 第29-33页 |
| 2.1.1 Measurement of growth parameters | 第30-31页 |
| 2.1.2 Measurement of photosynthetic parameters | 第31页 |
| 2.1.3 Quantification of photosynthetic pigments | 第31页 |
| 2.1.4 Assay for antioxidant enzymes and lipid peroxidation | 第31-32页 |
| 2.1.5 Measurement of Pb content | 第32页 |
| 2.1.6 Calculation of tolerance indices (TI) | 第32-33页 |
| 2.1.7 Statistical analysis | 第33页 |
| 2.2 Results | 第33-45页 |
| 2.2.1 Growth response to Pb toxicity | 第33-38页 |
| 2.2.2 Photosynthetic response to Pb toxicity | 第38-41页 |
| 2.2.3 Photosynthetic pigments response to Pb toxicity | 第41页 |
| 2.2.4 Tissue Pb concentration | 第41-42页 |
| 2.2.5 Enzyme activity | 第42-45页 |
| 2.2.6 Lipid peroxidation | 第45页 |
| 2.3 Discussion | 第45-48页 |
| 2.4 Conclusion | 第48-50页 |
| Chapter 3:Alleviatory effect of N-acetyl cysteine (NAC)on Pb stressed tobaccoplants | 第50-75页 |
| 3.1 Materials and Methods | 第51-53页 |
| 3.1.1 Measurement of growth parameters | 第51-52页 |
| 3.1.2 Measurement of photosynthetic parameters | 第52页 |
| 3.1.3 Quantification of photosynthetic pigments | 第52页 |
| 3.1.4 Assay for antioxidant enzymes and lipid peroxidation | 第52页 |
| 3.1.5 Measurement of Pb content | 第52页 |
| 3.1.6 Statistical analysis | 第52-53页 |
| 3.1.7 Leaf ultra-structure analysis | 第53页 |
| 3.2 Results | 第53-69页 |
| 3.2.1 Growth response to Pb toxicity and NAC alleviation | 第53-58页 |
| 3.2.2 Photosynthetic response to Pb toxicity and NAC alleviation | 第58-60页 |
| 3.2.3 Photosynthetic pigments response to Pb toxicity and NAC alleviation | 第60-63页 |
| 3.2.4 Antioxidant enzymes response to Pb toxicity and NAC alleviation | 第63-66页 |
| 3.2.5 Lipid peroxidation response to Pb toxicity and NAC alleviation | 第66页 |
| 3.2.6 The effect of NAC application on Pb content | 第66-67页 |
| 3.2.7 Effects of Pb toxicity and NAC application on leaf ultrastructure | 第67-69页 |
| 3.3 Discussion | 第69-73页 |
| 3.4 Conclusion | 第73-75页 |
| References | 第75-83页 |
| Publications | 第83页 |
