Doctor of Philosophy (PhD)


Biological Sciences

Document Type



The function of the PsbO and the PsbR protein in Arabidopsis thaliana were studied. The Arabidopsis mutant psbo1 contains a point mutation in the psbO-1 gene leading to defective expression of the PsbO-1 protein. Functional studies demonstrated both the reducing-side and oxidizing-side of Photosystem II are significantly altered. Using the psbo1 mutant plant as a transgenic host, two plant lines were produced, which contained an N-terminally His6-tagged PsbO-1 protein. Photosystem II closure kinetics demonstrated that the defective double reduction of QB and the delayed exchange of QBH2 with the plastoquinone pool in the psbo1 mutant were effectively restored to the wild type levels by the His6-tagged PsbO-1 protein. Flash fluorescence induction analysis indicated that a higher level of the modified PsbO-1 protein was required to increase the ratio of PS IIα to PS IIβ reaction centers to wild type levels. Fluorescence decay kinetics in the absence of DCMU indicated that the His6-tagged PsbO-1 protein restored deficient reducing-side electron transfer, while in the presence of DCMU, charge recombination between QA- and the S2 state of OEC occurred at near wild type rates. Our results indicated that high expression of the His6-tagged PsbO-1 protein efficiently complemented all of the photochemical defects observed in the psbo1 mutant. Additionally, this study established a new method to isolate PS II core complex in higher plants which can be used for biochemical and biophysical analysis. The psbR mutant was screened and characterized. The D2 protein of the Photosystem II complex is reduced in this mutant. Immunological analysis indicated that less than 50% of the PsbP protein is bound to the PS II when compared to wild type. A similar pattern is observed for the PsbQ protein. Impaired electron transport on the reducing side of the photosystem may result from the reduced level of the D2, PsbP and PsbQ components. The transgenic studies demonstrated that most of the defective phenotype of the can be complemented with a C-terminally His6-tagged PsbR protein in the PsbRICH transgenic plant. This is the first report that C-terminus of the PsbR protein is not involved in most photochemical processes in higher plants.



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Committee Chair

Terry M. Bricker