The Role of Phosphorylation in Redox Regulation of Photosynthesis Genes psaA and psbA during Photosynthetic Acclimation of Mustard

The long-term response （LTR） to light-quality gradients improves performance and survival of plants in dense stands. It involves redox-controlled transcriptional regulation of the plastome-encoded genes psaAB （encoding the P700 apoproteins of photosystem I） and psbA （encoding the D1 protein of photosystem II） and requires the action of plastidlocalized kinases. To study the potential impact of phosphorylation events on plastid gene expression during the LTR, we analyzed mustard seedlings acclimated to light sources favoring either photosystem I or photosystem II. Primer extension analyses of psaA transcripts indicate that the redox regulation occurs at the principal bacterial promoters, suggesting that the plastid encoded RNA polymerase （PEP） is the target for redox signals. Chloroplast protein fractions containing PEP and other DNA-binding proteins were purified from mustard via heparin-Sepharose chromatography. The biochemical properties of these fractions were analyzed with special emphasis on promoter recognition and specificity, phosphorylation state, and kinase activity. The results demonstrate that the LTR involves the action of small DNA-binding proteins; three of them exhibit specific changes in the phosphorylation state. Auto-phosphorylation assays, in addition, exhibit large differences in the activity of endogenous kinase activities. Chloroplast run-on transcription experiments with the kinase inhibitor H7 and the reductant DTT indicate that phosphorylation events are essential for the mediation of redox signals toward psaA and psbA transcription initiation, but require the synergistic action of a thiol redox signal. The data support the idea that redox signals from the thylakoid membrane are linked to gene expression via phosphorylation events; however, this mediation appears to require a complex network of interacting proteins rather than a simple phosphorelay.

Modulus spectroscopy for the detection of parallel electric responses in electroceramics

Impedance spectroscopy has become one of the most versatile and essential investigation methods concerning electrical properties of materials for electronic and energy applications.Deriving knowledge about physical mechanisms,however,often demands excellent expertise in evaluating the spectra.Investigating different representations of the same data set can help elucidate the underlying physics,but this is rarely applied.In this work,the importance of using the modulus representation to identify parallel electric responses is rationalized.Those responses result from parallel conducting pathways,e.g.,at grain boundaries,or from regions with differing permittivity,e.g.,in composites.Qualitative and quantitative data can be obtained,as it is illustrated based on experimental data from electroceramics and respective physical simulation results using the finite element method.The findings should help to study intricate electric responses of materials with chemical or structural heterogeneity.