The Ability of Cyanobacterial Cells to Restore UV-B Radiation Induced Damage to Photosystem II is Influenced by Photolyase Dependent DNA Repair

Damage of DNA and Photosystem-II are among the most significant effects of UV-B irradiation in photosynthetic organisms. Both damaged DNA and Photosystem-II can be repaired, which represent important defense mechanisms against detrimental UV-B effects. Correlation of Photosystem-II damage and repair with the concurrent DNA damage and repair was investigated in the cyanobacterium Synechocystis PCC6803 using its wild type and a photolyase deficient mutant, which is unable to repair UV-B induced DNA damages. A significant amount of damaged DNA accumulated during UV-B exposure in the photolyase mutant concomitant with decreased Photosystem-II activity and D1 protein amount. The transcript level of psbA3, which is a UV-responsive copy of the psbA gene family encoding the D1 subunit of the Photosystem-II reaction center, is also decreased in the photolyase mutant. The wild-type cells, however, did not accumulate damaged DNA during UV-B exposure, suffered smaller losses of Photosystem-II activity and D1 protein, and maintained higher level of psbA3 transcripts than the photolyase mutant. It is concluded that the repair capacity of Photosystem-II depends on the ability of cells to repair UV-B-damaged DNA through maintaining the transcription of genes, which are essential for protein synthesis-dependent repair of the Photosystem-II reaction center

Effect of UV-A radiation on photosynthetic electron transport

We have studied the inhibition of photosynthetic electron transport by UV-A (320-400nm) radiation in isolated spinach thylakoids by flash-induced oxygen and thermoluminescence (TL) measurements. The flash pattern of oxygen evolution showed an increased amount of the S0 state in the dark, which indicate a direct effect of UV-A radiation in the water-oxidizing complex. TL measurements revealed the UV-A induced loss of PSII centers. Flash-induced oscillation of the B TL band, originating from the S2Q8 recombination, indicated a UV-A induced decrease in the amount of Q8 relative to Q8. In conclusion, our data show that UV-A radiation is highly damaging for PSII, whose electron transport is affected both at the water oxidizing complex, and the binding site of the Q8 quinone electron acceptor

Photoinactivation of Photosystem II at low light intensity. Mathematical models

We studied the effect of low light intensity on Photosystem II (PSII) of thylakoid membranes isolated form spinach. The application of low frequency single turnover flashes results in the decreased oxygen evolving activity of PSII. This effect was explained in the framework of a model, which assumes that saturating visible light flashes at low frequency can result in the degradation of the D1 protein, since S23/Q8 and S2/Qa recombinations generate singlet oxygen through the intermediate triplet chlorophyll formation. We propose a pathway for the light-induced transitions and dark period processes of the S-states, which results the best fit of our experimental data

Monitoring drought responses of barley genotypes with semi-robotic phenotyping platform and association analysis between recorded traits and allelic variants of some stress genes

Genetic improvement of complex traits such as drought adaptation can be advanced by the combination of genomic and phenomic approaches. Semi-robotic phenotyping platform was used for computer-controlled watering, digital and thermal imaging of barley plants grown in greenhouse. The tested barley variants showed 0–76% reduction in green pixel-based shoot surface area in soil with 20% water content, compared to well-watered plants grown in soil with 60% water content. The barley HvA1 gene encoding the group 3 LEA (Late Embryogenesis Abundant) protein exhibited four (A–D) haplotypes as identified by the EcoTILLING and subsequent DNA sequencing. The green pixel mean value of genotypes with haplotype D was higher than the mean value of the remaining haplotypes, indicating a pivotal role of haplotype D in optimizing the green biomass production under drought condition. In water limitation, the canopy temperature of a highly sensitive genotype was 18.0°C, as opposed to 16.9°C of leaves from a tolerant genotype as measured by thermal imaging. Drought-induced changes in leaf temperature showed moderate correlation with the water use efficiency (r2 = 0.431). The haplotype/trait association analysis based on the t-test has revealed a positive effect of a haplotype B (SNPs:GCCCCTGC) in a gene encoding the barley fungal pathogen induced mRNA for pathogen-related protein (HvPPRPX), on harvest index, thousand grain weight, water use efficiency and grain yield. The presented pilot study established a basic methodology for the integrated use of phenotyping and haplotyping data in characterization of genotype-dependent drought responses in barley

Interaction of nanoparticles with biological systems

Nanoparticles (NPs) are literally and figuratively infiltrating all fields of biological research. They are sophisticated tools that can be customized, either by smart engineering or by the attachment of specific ligands, to match the requirements of a particular task. Through their inherent and functionalized properties they are the basis for new developments while enhancing the efficiency of already existing techniques or rendering methods to be more specific. They provide new approaches for therapeutic applications and brand new platforms for diagnostic processes. In this review we provide an insight into the practical applications of NPs, emphasizing their use in biosensing, bioimaging, biomolecule delivery systems and enzyme immobilization. Since the interest in the interactions of NPs and biological systems is fairly new, we also elaborate on the drawbacks of their practical applications by reporting their potential toxicity in in vitro and in vivo systems

A stresszfehérjék és lipidek membrán kapcsolt homeosztázisa = Coupled homeostasis of membrane lipids and stress proteins

1. Megállapítottuk, hogy az IbpA/B fehérje in vivo különböző mértékben asszociálódik az E. coli membrán(ok)hoz. Langmuir-Blodget monolayer kísérletekben igazoltuk az IbpAB membránlipid kötését. Jellemeztük az E. coli IbpAB- mutánst mind molekuláris, mind fiziológiás szinten. Megállapítottuk, hogy az IbpAB- mutáns törzsek rendelkeznek „membrán-fenotípussal”, a vad típustól markánsan eltérő lipid zsírsavösszetétellel, valamint megváltozott fluiditással és permeabilitással. A lipidomikai kísérletek rávilágítottak a fluiditásváltozás kompenzációs jellegére, a homeosztatikus membrán adaptáció elvének megfelelően. A membránlipidek és hősokkfehérjék kapcsolatának egy másik dimenziójára kívántunk rávilágítani a vad típusú és mutáns törzsek globális „transcriptome” analízisével. A wt és az IbpAB mutánsok mRNS profilja hatalmas eltérést mutat, a változások gének egész sorát érintik, amelyek megértése további kísérleteket kíván. 2. Munkánk során elsőként igazoltuk Synechocystisben a DnaK2 fehérje szubfrakciójának tilakoid asszociációját. A DnaK2 részleges hiánya megváltoztatta a tilakoid membrán lipid- és zsírsavösszetételét, valamint a membrán fizikai állapotát. A membránváltozások befolyásolják a tilakoid membrán működését, ami eltérő hő- illetve UV-B stresszérzékenységben is megnyilvánul. A DnaK2 protein részleges hiánya UV károsodás után a PSII “repair” részleges inhibícióját eredményezte. Ily módon kimutattuk egy új, membránasszociált DnaK-függő stresszvédő mechanizmus létezését. | 1. In E. Coli the small heat shock protein IbpAB interacts with membranes in vivo and in vitro and rigidifides it which counterbalances heat-induced fluidization, indicating a protective role of this Hsp in the heat-shocked membrane. IbpAB- cells have an increased membrane permeability but higher outer membrane transition temperature and better survival at heat challenge. The improved survival is linked to the altered membrane phenotype. These include unique fatty acid changes and fluidization in the hydrophobic core of the membranes, which are associated with better survival upon heat challenge. 2. We have shown that in Synechocystis PCC6803 DnaK2 chaperon interacts with the thylakoid membrane, especially with the phosphatidyl glycerol (PG) lipid of the thylakoid. In DnaK2- cells the fatty acid composition of the thylakoid membrane differed from that of the wild type resulting in altered physico-chemical properties. We exposed cells to UV-B damage and concluded, that lack of the DnaK2 leads to partial inhibition of PSII repair and the rate of forward electron transport between QA and QB quinone electron acceptors is slowed down. PG plays an important role in binding extrinsic proteins required for a functional Mn cluster on the donor side of PSII. The binding of DnaK2 may take place trough binding specifically to PG and/or with the PSII complex. This interaction leads directly or indirectly to change in membrane fluidity which influences PSII electron transport