Characterization of cytoplasmic mutants of Nicotiana tabacum with altered photosynthetic function

Summary A series of cytoplasmic mutants of tobacco (Nicotiana tabacum) were generated and characterized. Compared to wild type tobacco, they were found to have diminished levels of photosynthetic pigments and a range of functional impairments including modified chlorophyll fluorescence properties, loss of Photosystem I and/or II electron transport activity, and aberrant ultrastructure. Although the loss of defined functional activities was correlated with the depletion of specific thylakoid membrane proteins, no simple rules governed the relationship between structural defects and photosynthetic deficiencies. All of these mutants exhibited pleiotropic losses of polypeptides, including those known to be nuclear-encoded; this is consistent with the concept that loss of one component of a multi-subunit membrane protein complex results in unstable complex assembly. The phenotype of two mutants was developmentally regulated, in one case with slow chloroplast developments and in the other by premature senescence of Photosystem II centers as a function of leaf development. These mutants should be especially useful in studying membrane protein assembly.Abbreviations CF₁ coupling factor (chloroplast ATPase) - Chl chlorophyll - CP chlorophyll protein - Diuron 3-(3,4-dichlorophenyl)-1,1-dimethyl urea - DPIP 2,6-dichlorophenolindolphenol - EDTA ethylenediaminetetraacetic acid - F₀ initial fluorescence - F_p peak fluorescence - F_t terminal fluorescence - F_v variable fluorescence - kDa kilodalton(s) - LDS lithium dodecyl sulfate - LHC light harvesting complex - MV methyl viologen - OEC oxygen evolving complex - PAGE polyacrylamide gel electrophoresis - PMSF phenylmethylsulfonylfluoride - PS photosystem - Q_A the primary quinone acceptor of Photosystem II - RC reaction center - TMPD N,N,N,N-tetramethyl-p-phenylenediamine - TMQH₂ tetramethyl-p-benzohydroquinone - TP tobacco plastome - Tricine N-tris (hydroxymethyl) methylglycine - WT wild type