@phdthesis{oai:sucra.repo.nii.ac.jp:00010423,
 author = {PENPORN, SAE-TANG},
 month = {},
 note = {108 p., Effects of overexpression of superoxide dismutase and catalase on the tolerance of photosystem II (PSII) to photo-oxidative stress were studies in the cyanobacterium Synechococcus elongatus PCC 7942.
Chapter 1 describes the photosynthetic process, photo-oxidative stress, and the antioxidative systems in photosynthetic organisms that include plants and cyanobacteria. Effects of photo-oxidative stress on cyanobacteria, as well as other photosynthetic organisms, and on their photosynthetic machinery under environmental stresses are reviewed. Reactive oxygen species (ROS) that are generated as by-products during photosynthetic reactions are reviewed. Each type of ROS is described in details in term of their properties and detoxifying processes. In addition, the defense mechanisms in cyanobacteria against ROS are described. The aim of the present study is to enhance the tolerance of photosystem II to photo-oxidative stress by improving the antioxidative systems with a special focus on ROS-scavenging enzymes.
Chapter 2 describes the effects of overexpression of superoxide dismutase (SOD) and catalase on photosystem II (PSII) under photo-oxidative stress in the cyanobacterium Synechococcus elongatus PCC 7942. In the present study, an iron superoxide dismutase (Fe-SOD) from Synechocystis sp. PCC6803; a highly active catalase (VktA) from Vibrio rumoiensis; and both enzymes together were overexpressed. Then I examined the sensitivity of PSII to photoinhibition in the three strains. In cells that overexpressed either Fe-SOD or VktA, PSII was more tolerant to strong light than it was in wild-type cells. Moreover, in cells that overexpressed both Fe-SOD and VktA, PSII was even more tolerant to strong light. However, the rate of photodamage to PSII, as monitored in the presence of chloramphenicol, was similar in all three transformant stains and in wild-type cells, suggesting that the overexpression of these ROS-scavenging enzymes might not protect PSII from photodamage but might protect the repair of PSII. Under strong light, intracellular levels of ROS fell significantly, and the synthesis de novo of proteins that are required for the repair of PSII, such as the D1 protein, was enhanced. These observations suggest that overexpressed Fe-SOD and VktA might act synergistically to alleviate the photoinhibition of PSII by reducing intracellular levels of ROS, with resultant protection of the repair of PSII from oxidative inhibition.
Chapter 3 describes the conclusions from the present study and the perspectives of future study. Future study should be directed towards fuller understanding of the mechanisms by which the overexpression of Fe-SOD and VktA enhances the synthesis of the D1 protein. Effects of the overexpression of Fe-SOD and VktA on other antioxidative systems also remain to be elucidated. The established strategy with Fe-SOD and VktA to protect photosynthesis from photo-oxidative stress should also be applied to improvements in the tolerance of photosynthetic organisms to various types of environmental stress., Contents 2-5
Acknowledgement 6
Abstract 7-8
Abbreviations 9
Chapter 1 General Introduction 10
1.1 Photosynthesis 11
1.1.1 Photosynthesis in Cyanobacteria 11
1.2 Photo-oxidative stress 15
1.2.1 Photoinhibition of PSII 17
1.2.1.1 Photodamage to PSII 19
1.2.1.2 The repair of PSII 22
1.3 Reactive oxygen species(ROS) 26
1.3.1 Singlet oxygen (1O2) 30
1.3.2 Superoxide (O2-) 30
1.3.3 Hydrogen peroxide (H2O2) 31
1.3.4 Hydroxyl radical (OH●) 32
1.4 Antioxidative systems against ROS in cyanobacteria 33
1.4.1 Non-enzymatic antioxidants 36
1.4.1.1 Carotenoids 36
1.4.1.2 α-Tocopherol 37
1.4.1.3 Glutathione 38
1.4.1.4 Flavonoids 39
1.4.1.5 Ascorbate 40
1.4.1.6 Proline 40
1.4.2 ROS-scavenging enzymes 41
1.4.2.1 Superoxide dismutase 41
1.4.2.1.1 Fe-SOD 43
1.4.2.1.2 Mn-SOD 44
1.4.2.1.3 Cu/Zn-SOD 44
1.4.2.1.4 Ni-SOD 45
1.4.2.2 Catalase 46
1.4.2.3 Glutathione peroxidase 47
1.5 Aim of the present study 48
Chapter 2 Overexpression of SOD and catalase in Synechococcus elongatus PCC 7942 50
2.1 Summary 51
2.2 Introduction 52
2.3 Materials and methods 55
2.3.1 Cells and culture conditions 55
2.3.2 Generation of transformants 55
2.3.3 Confirmation of expression of sodA, sodB and vktA 58
2.3.4 Assay of the photoinhibition of PSII 58
2.3.5 Determination of intracellular levels of ROS 58
2.3.6 Labeling of proteins in vivo 59
2.4 Results 60
2.4.1 Overexpression of Mn-SOD and Fe-SOD 60
2.4.2 Overexpression of Mn-SOD and Fe-SOD alleviates the photoinhibition of PSII 63
2.4.3 Overexpression of Fe-SOD and VktA 66
2.4.4 Overexpression of Fe-SOD and VktA alleviates the photoinhibition of PSII 69
2.4.5 Overexpression of Fe-SOD and VktA protects the repair of PSII in the presence of methyl viologen 71
2.4.6 Overexpression of Fe-SOD and VktA depresses intracellular levels of H2O2 and related ROS 73
2.4.7 Overexpression of Fe-SOD and VktA enhances the synthesis of the D1 protein under strong light 75
2.4.8 Effects of overexpression of Fe-SOD and VktA in growth of cells under photo-oxidative stress 79
2.5 Discussion 84
2.5.1 Roles of SOD and catalase in the protection of PSII from photoinhibition 84
2.5.2 Actions of ROS in the photoinhibition of PSII 85
2.5.3 Role of SOD and catalase in the protection of protein synthesis from ROS 86
2.5.4 Conclusions and perspectives 87
Chapter 3 Conclusions and perspectives 88
References 95
Publications 108, 主指導教員 :　西山佳孝, text, application/pdf},
 school = {埼玉大学},
 title = {Improvements in the Tolerance of Photosystem II to Photo-Oxidative Stress in Cyanobacteria},
 year = {2016},
 yomi = {ペンポーン, サエ タン}
}