14 research outputs found
Dimeric and monomeric organization of photosystem II - Distribution of five distinct complexes in the different domains of the thylakoid membrane
The supramolecular organization of photosystem II (PSII) was characterized in distinct domains of the thylakoid membrane, the grana core, the grana margins, the stroma lamellae, and the so-called Y100 fraction. PSII supercomplexes, PSII core dimers, PSII core monomers, PSII core monomers lacking the CP43 subunit, and PSII reaction centers were resolved and quantified by blue native PAGE, SDS-PAGE for the second dimension, and immunoanalysis of the D1 protein. Dimeric PSII (PSII supercomplexes and PSII core dimers) dominate in the core part of the thylakoid granum, whereas the monomeric PSII prevails in the stroma lamellae. Considerable amounts of PSII monomers lacking the CP43 protein and PSII reaction centers (D1-D2-cytochrome b(559) complex) were found in the stroma lamellae. Our quantitative picture of the supramolecular composition of PSII, which is totally different between different domains of the thylakoid membrane, is discussed with respect to the function of PSII in each fraction. Steady state electron transfer, flash-induced fluorescence decay, and EPR analysis revealed that nearly all of the dimeric forms represent oxygen-evolving PSII centers. PSII core monomers were heterogeneous, and a large fraction did not evolve oxygen. PSII monomers without the CP43 protein and PSII reaction centers showed no oxygen-evolving activity
Rapid and highly specific monitoring of reversible thylakoid protein phosphorylation by polyclonal antibody to phosphothreonine-containing proteins
Reversible thylakoid protein phosphorylation in plant chloroplast probably plays an important role in acclimation of the photosynthetic apparatus to changes in environmental conditions. Studies of regulation and the significance of these reactions have in vivo greatly benefited from recent availability of phosphothreonine antibodies. To verify the specificity of these polyclonal antibodies, leaves were treated in conditions expected to induce either phosphorylation or dephosphorylation of thylakoid proteins D1, D2 and CP43 of the photosystem II core as well as light harvesting polypeptides of 27 and 25 kDa; subsequently, the proteins were isolated to homogeneity. Immunoreactions of these purified proteins with phosphothreonine antibodies were very similar to those observed with intact thylakoids. Moreover, their positive immunoresponse could be totally abolished by treating the thylakoid samples or purified photosystem II core preparations with acid phosphatase before immunoblotting. We conclude that the analytical method of using polyclonal phosphothreonine antibodies will turn out to be a highly specific and valuable tool in monitoring changes in the phosphorylation patterns of individual thylakoid phosphoproteins, both in vivo and in vitro
The Arabidopsis Thylakoid Chloride Channel ClCe Regulates ATP Availability for Light-harvesting Complex II Protein Phosphorylation
Coping with changes in light intensity is challenging for plants, but well-designed mechanisms allow them to acclimate to most unpredicted situations. The thylakoid K+/H+ antiporter KEA3 and the voltage-dependent Cl− channel VCCN1 play important roles in light acclimation by fine-tuning electron transport and photoprotection. Good evidence exists that the thylakoid Cl− channel ClCe is involved in the regulation of photosynthesis and state transitions in conditions of low light. However, a detailed mechanistic understanding of this effect is lacking. Here we report that the ClCe loss-of-function in Arabidopsis thaliana results in lower levels of phosphorylated light-harvesting complex II (LHCII) proteins as well as lower levels of the photosystem I-LHCII complexes relative to wild type (WT) in low light conditions. The phosphorylation of the photosystem II core D1/D2/CP43 proteins was less affected either in low or high light conditions. In low light conditions, the steady-state levels of ATP synthase conductivity and of the total proton flux available for ATP synthesis were lower in ClCe loss-of-function mutants, but comparable to WT at standard and high light intensity. As a long-term acclimation strategy, expression of the ClCe gene was upregulated in WT plants grown in light-limiting conditions, but not in WT plants grown in standard light even when exposed for up to 8 h to low light. Taken together, these results suggest a role of ClCe in the regulation of the ATP synthase activity which under low light conditions impacts LHCII protein phosphorylation and state transitions
A previously found thylakoid membrane protein of 14 kDa (TMP14) is a novel subunit of plant photosystem I and is designed PSI-P
AbstractWe show that the thylakoid membrane phosphoprotein TMP14 is a novel subunit of plant photosystem I (PSI). Blue native/SDS–PAGE and sucrose gradient fractionation demonstrated the association of the protein exclusively with PSI. We designate the protein PSI-P. The presence of PSI-P subunit in Arabidopsis mutants lacking other PSI subunits was analyzed and suggested a location in the proximity of PSI-L, -H and -O subunits. The PSI-P protein was not differentially phosphorylated in state 1 and state 2