Abstract
Excitation imbalances between photosystem I and II generate redox signals in the thylakoid membrane of higher plants which induce acclimatory changes in the structure of the photosynthetic apparatus. They affect the accumulation of reaction center and light-harvesting proteins as well as chlorophylls a and b. In Arabidopsis thaliana the re-adjustment of photosystem stoichiometry is mainly mediated by changes in the number of photosystem I complexes, which are accompanied by corresponding changes in transcripts for plastid reaction center genes. Because chloroplast protein complexes contain also many nuclear encoded components we analyzed the impact of such photosynthetic redox signals on nuclear genes. Light shift experiments combined with application of the electron transport inhibitor 3-(3',4'-dichlorophenyl)-1,1'-dimethyl urea have been performed to induce defined redox signals in the thylakoid membrane. Using DNA macroarrays we assessed the impact of such redox signals on the expression of nuclear genes for chloroplast proteins. In addition, studies on mutants with lesions in cytosolic photoreceptors or in chloroplast-to-nucleus communication indicate that the defective components in the mutants are not essential for the perception and/or transduction of light-induced redox signals. A stable redox state of glutathione suggest that neither glutathione itself nor reactive oxygen species are involved in the observed regulation events pointing to the thylakoid membrane as the main origin of the regulatory pathways. Our data indicate a distinct role of photosynthetic redox signals in the cellular network regulating plant gene expression. These redox signals appear to act independently and/or above of cytosolic photoreceptor or known chloroplast-to-nucleus communication avenues.
Highlights
The light environment of plants is highly variable
Responses of such plants were compared with responses of plants acclimated to PSI or PSII light followed by an additional acclimation to the respective other light source (PSI–II plants or PSII–I plants)
In Western analyses with antisera raised against the D1 protein and the P700 apoproteins (Fig. 1A) the D1 protein exhibited more or less constant amounts under all conditions, whereas the amounts of P700 apoproteins increased in PSI–II plants in comparison to PSI plants and decreased in PSII–I plants in comparison to PSII plants
Summary
Plant Growth—Plants were grown in temperature-controlled growth chambers at 22 °C under continuous light. After 2 days at 4 °C plants were grown for 10 days under white light provided by 30-watt white stripe lamps (OSRAM, Munchen, Germany) with a photosynthetic-active radiation of ϳ35 E. Western Analyses of Chloroplast Proteins—20 g of leaf material of plants grown on soil were harvested under the respective light source and directly homogenized in ice-cold buffer containing 0.05 M Hepes/ KOH, pH 8.0, 0.33 M sorbitol, 0.001 M MgCl2, and 0.002 M EDTA. Determination of Thiol Group Content and Redox State of Glutathione—For isolation of total glutathione and cysteine 25 mg of leaf material was ground in liquid N2 and extracted with 0.5 ml of buffer E (100 mM phosphate, pH 7.1, 50% methanol, 5 mM dithiothreitol) for 10 min at 60 °C while shaking. Differential expression values fulfilling the criteria of this statistical procedure were used for the expression profiling
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