Characterization of cytoplasmic mutants of Nicotiana tabacum with altered photosynthetic function

Abstract

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.