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Photosynthesis Research

Current research articles..




The journal Photosynthesis Research is an international journal dealing with both basic and applied aspects of photosynthesis. The journal publishes research at all levels of plant organization: molecular, subcellular, cellular, whole plant, canopy, ecosystem and global.

The publisher is Springer. The copyright and publishing rights of specialized products listed below are in this publishing house. This is also responsible for the content shown.

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Additional research articles see Current Chemistry Research Articles. Magazines with similar content (photosynthesis):

 - Photosynthetica.



Photosynthesis Research - Abstracts



Characterization of mercury(II)-induced inhibition of photochemistry in the reaction center of photosynthetic bacteria

Abstract

Mercuric contamination of aqueous cultures results in impairment of viability of photosynthetic bacteria primarily by inhibition of the photochemistry of the reaction center (RC) protein. Isolated reaction centers (RCs) from Rhodobacter sphaeroides were exposed to Hg2+ ions up to saturation concentration (~ 103 [Hg2+]/[RC]) and the gradual time- and concentration-dependent loss of the photochemical activity was monitored. The vast majority of Hg2+ ions (about 500 [Hg2+]/[RC]) had low affinity for the RC [binding constant Kb ~ 5 mM−1] and only a few (~ 1 [Hg2+]/[RC]) exhibited strong binding (Kb ~ 50 μM−1). Neither type of binding site had specific and harmful effects on the photochemistry of the RC. The primary charge separation was preserved even at saturation mercury(II) concentration, but essential further steps of stabilization and utilization were blocked already in the 5 < [Hg2+]/[RC] < 50 range whose locations were revealed. (1) The proton gate at the cytoplasmic site had the highest affinity for Hg2+ binding (Kb ~ 0.2 μM−1) and blocked the proton uptake. (2) Reduced affinity (Kb ~ 0.05 μM−1) was measured for the mercury(II)-binding site close to the secondary quinone that resulted in inhibition of the interquinone electron transfer. (3) A similar affinity was observed close to the bacteriochlorophyll dimer causing slight energetic changes as evidenced by a ~ 30 nm blue shift of the red absorption band, a 47 meV increase in the redox midpoint potential, and a ~ 20 meV drop in free energy gap of the primary charge pair. The primary quinone was not perturbed upon mercury(II) treatment. Although the Hg2+ ions attack the RC in large number, the exertion of the harmful effect on photochemistry is not through mass action but rather a couple of well-defined targets. Bound to these sites, the Hg2+ ions can destroy H-bond structures, inhibit protein dynamics, block conformational gating mechanisms, and modify electrostatic profiles essential for electron and proton transfer.


Datum: 01.06.2018


Novel quantitative insights into carbon sources for synthesis of poly hydroxybutyrate in Synechocystis PCC 6803

Abstract

Many freshwater cyanobacteria accumulate polyhydroxybutyrate (PHB) under nitrogen or phosphorus deprivation. While prior literature has shed lights on transcriptomic and metabolomic changes in the model cyanobacterium Synechocystis PCC 6803 cells, the quantitative contributions of the newly fixed carbon following nitrogen deprivation or the externally added acetate to PHB synthesis are not clear. Similarly, it is not clear how photomixotrophy affects precursor contributions. In this study, we show that (i) the pre-growth mode (photoautotrophic or photomixotrophic), while significantly impacting glycogen levels, does not have any significant effect on PHB levels, (ii) the carbon fixed following nitrogen deprivation contributes 26% of C for PHB synthesis in photoautotrophically pre-grown cells and its contribution to the PHB synthesis goes down with the addition of acetate at the resuspension phase or with photomixotrophic pre-growth, (iii) the acetate added at the start of nitrogen deprivation, doubles the intracellular PHB levels and contributes 44–48% to PHB synthesis and this value is not greatly affected by how the cells were pre-grown. Indirectly, the labeling studies also show that the intracellular C recycling is the most important source of precursors for PHB synthesis, contributing about 74–87% of the C for PHB synthesis in the absence of acetate. The addition of acetate significantly reduces its contribution. In photoautotrophic pre-growth followed by acetate addition under nitrogen starvation, the contribution of intracellular C reduces to about 34%. Thus, our study provides several novel quantitative insights on how prior nutritional status affects the precursor contributions for PHB synthesis.


Datum: 01.06.2018


Effects of photosynthetic photon flux density, frequency, duty ratio, and their interactions on net photosynthetic rate of cos lettuce leaves under pulsed light: explanation based on photosynthetic-intermediate pool dynamics

Abstract

Square-wave pulsed light is characterized by three parameters, namely average photosynthetic photon flux density (PPFD), pulsed-light frequency, and duty ratio (the ratio of light-period duration to that of the light–dark cycle). In addition, the light-period PPFD is determined by the averaged PPFD and duty ratio. We investigated the effects of these parameters and their interactions on net photosynthetic rate (P n) of cos lettuce leaves for every combination of parameters. Averaged PPFD values were 0–500 µmol m−2 s−1. Frequency values were 0.1–1000 Hz. White LED arrays were used as the light source. Every parameter affected P n and interactions between parameters were observed for all combinations. The P n under pulsed light was lower than that measured under continuous light of the same averaged PPFD, and this difference was enhanced with decreasing frequency and increasing light-period PPFD. A mechanistic model was constructed to estimate the amount of stored photosynthetic intermediates over time under pulsed light. The results indicated that all effects of parameters and their interactions on P n were explainable by consideration of the dynamics of accumulation and consumption of photosynthetic intermediates.


Datum: 01.06.2018


C-terminal residues of ferredoxin-NAD(P) + reductase from Chlorobaculum tepidum are responsible for reaction dynamics in the hydride transfer and redox equilibria with NADP + /NADPH

Abstract

Ferredoxin-NAD(P)+ reductase ([EC 1.18.1.2], [EC 1.18.1.3]) from Chlorobaculum tepidum (CtFNR) is structurally homologous to the bacterial NADPH-thioredoxin reductase (TrxR), but possesses a unique C-terminal extension relative to TrxR that interacts with the isoalloxazine ring moiety of the flavin adenine dinucleotide prosthetic group. In this study, we introduce truncations to the C-terminal residues to examine their role in the reactions of CtFNR with NADP+ and NADPH by spectroscopic and kinetic analyses. The truncation of the residues from Tyr326 to Glu360 (the whole C-terminal extension region), from Phe337 to Glu360 (omitting Phe337 on the re-face of the isoalloxazine ring) and from Ser338 to Glu360 (leaving Phe337 intact) resulted in a blue-shift of the flavin absorption bands. The truncations caused a slight increase in the dissociation constant toward NADP+ and a slight decrease in the Michaelis constant toward NADPH in steady-state assays. Pre-steady-state studies of the redox reaction with NADPH demonstrated that deletions of Tyr326–Glu360 decreased the hydride transfer rate, and the amount of reduced enzyme increased at equilibrium relative to wild-type CtFNR. In contrast, the deletions of Phe337–Glu360 and Ser338–Glu360 resulted in only slight changes in the reaction kinetics and redox equilibrium. These results suggest that the C-terminal region of CtFNR is responsible for the formation and stability of charge-transfer complexes, leading to changes in redox properties and reactivity toward NADP+/NADPH.


Datum: 01.06.2018


On the source of non-linear light absorbance in photosynthetic samples

Abstract

This study presents a mathematical model, which expresses the absorbance of a photosynthetic sample as a non-linear polynomial of selected reference absorbance. The non-linearity is explained by inhomogeneities of a product of pigment concentration and light path length in the sample. The quadratic term of the polynomial reflects the extent of inhomogeneities, and the cubic term is related to deviation of the product distribution from a symmetric one. The model was tested by measurements of suspension of unstacked tobacco thylakoid membranes of different chlorophyll concentrations in cuvettes of different thicknesses. The absorbance was calculated from the diffuse transmittance and reflectance of sample, illuminated by perpendicular collimated light. The evaluated quantity was a sensitivity defined as the relative difference between the sample absorbance and the reference absorbance to the reference absorbance. The non-linearity of sample absorbance was demonstrated by a characteristic deviation of the sensitivity spectrum from a constant value. The absorbance non-linearity decreased on an increase of the product of pigment concentration and cuvette thickness. The model suggests that the sieve and detour effects influence the absorbance in a similar way. The model may be of interest in modeling of leaf or canopy optics including light absorption and scattering.


Datum: 01.06.2018


Gordon Research Conference on photosynthesis: photosynthetic plasticity from the environment to synthetic systems

Abstract

Here, we provide a summary of the 2017 Gordon Research Conference on Photosynthesis: “Photosynthetic plasticity: from the environment to synthetic systems”. This conference was held at the Grand Summit Resort Hotel at Sunday River, Newry, Maine, USA, from July 16 to 21, 2017. We have also included here a brief description of the Gordon Research Seminar (for students and post-docs) held during 2 days preceding this conference. Following the conclusion of the conference’s scientific program, four young scientists (Han Bao, Vivek Tiwari, Setsuko Wakao, and Usha Lingappa) were recognized for their research presentations, each of whom received a book as a gift from one of us (Govindjee). Having chaired the 2015 Gordon Research Conference on Photosynthesis in 2015, Fabrice Rappaport, who lost his fight against cancer in January 2016, was remembered for his profound impact on the field of photosynthesis research.


Datum: 01.06.2018


Anatomical and diffusional determinants inside leaves explain the difference in photosynthetic capacity between Cypripedium and Paphiopedilum , Orchidaceae

Abstract

Comparing with other angiosperms, most members within the family Orchidaceae have lower photosynthetic capacities. However, the underlying mechanisms remain unclear. Cypripedium and Paphiopedilum are closely related phylogenetically in Orchidaceae, but their photosynthetic performances are different. We explored the roles of internal anatomy and diffusional conductance in determining photosynthesis in three Cypripedium and three Paphiopedilum species, and quantitatively analyzed their diffusional and biochemical limitations to photosynthesis. Paphiopedilum species showed lower light-saturated photosynthetic rate (A N), stomatal conductance (g s), and mesophyll conductance (g m) than Cypripedium species. A N was positively correlated with g s and g m. And yet, in both species A N was more strongly limited by g m than by biochemical factors or g s. The greater g s of Cypripedium was mainly affected by larger stomatal apparatus area and smaller pore depth, while the less g m of Paphiopedilum was determined by the reduced surface area of mesophyll cells and chloroplasts exposed to intercellular airspace per unit of leaf area, and much thicker cell wall thickness. These results suggest that leaf anatomical structure is the key factor affecting g m, which is largely responsible for the difference in photosynthetic capacity between those two genera. Our findings provide new insight into the photosynthetic physiology and functional diversification of orchids.


Datum: 01.06.2018


Salt stress effects on the photosynthetic electron transport chain in two chickpea lines differing in their salt stress tolerance

Abstract

The main objective of this study was to evaluate the effects of salt stress on the photosynthetic electron transport chain using two chickpea lines (Cicer arietinum L.) differing in their salt stress tolerance at the germination stage (AKN 87 and AKN 290). Two weeks after sowing, seedlings were exposed to salt stress for 2 weeks and irrigated with 200 ml of 200 mM NaCl every 2 days. The polyphasic OJIP fluorescence transient and the 820-nm transmission kinetics (photosystem I) were used to evaluate the effects of salt stress on the functionality of the photosynthetic electron transport chain. It was observed that a signature for salt stress was a combination of a higher J step (VJ), a smaller IP amplitude, and little or no effect on the primary quantum yield of PSII (φPo). We observed for AKN 290 a shorter leaf life cycle, which may represent a mechanism to cope with salt stress. For severely salt-stressed leaves, an inhibition of electron flow between the PQ pool and P700 was found. The data also suggest that the properties of electron flow beyond PSI are affected by salt stress.


Datum: 01.06.2018


Comparative assessment of chloroplast transcriptional responses highlights conserved and unique patterns across Triticeae members under salt stress

Abstract

Chloroplast functional genomics, in particular understanding the chloroplast transcriptional response is of immense importance mainly due to its role in oxygenic photosynthesis. As a photosynthetic unit, its efficiency and transcriptional activity is directly regulated by reactive oxygen species during abiotic and biotic stress and subsequently affects carbon assimilation, and plant biomass. In crops, understanding photosynthesis is crucial for crop domestication by identifying the traits that could be exploited for crop improvement. Transcriptionally and translationally active chloroplast plays a key role by regulating the PSI and PSII photo-reaction centres, which ubiquitously affects the light harvesting. Using a comparative transcriptomics mapping approach, we identified differential regulation of key chloroplast genes during salt stress across Triticeae members with potential genes involved in photosynthesis and electron transport system such as CytB6f. Apart from differentially regulated genes involved in PSI and PSII, we found widespread evidence of intron splicing events, specifically uniquely spliced petB and petD in Triticum aestivum and high proportion of RNA editing in ndh genes across the Triticeae members during salt stress. We also highlight the role and differential regulation of ATP synthase as member of CF0CF1 and also revealed the effect of salt stress on the water-splitting complex under salt stress. It is worthwhile to mention that the observed conserved down-regulation of psbJ across the Triticeae is limiting the assembly of water-splitting complexes and thus making the BEP clade Triticeae members more vulnerable to high light during the salt stress. Comparative understanding of the chloroplast transcriptional dynamics and photosynthetic regulation will improve the approaches for improved crop domestication.


Datum: 01.06.2018


William E. Vidaver (1921–2017): an innovator, enthusiastic scientist, inspiring teacher and a wonderful friend

Abstract

William (Bill) E. Vidaver (February 2, 1921–August 31, 2017), who did his Ph.D. with Laurence (Larry) R. Blinks at Stanford (1964) and a postdoc with C. Stacy French (1965), taught and did research at Simon Fraser University (SFU) for almost 30 years. Here he published over 80 papers in photosynthesis-related areas co-authored by his graduate students, postdocs, visiting professors and SFU colleagues. He developed a unique high-pressure cuvette for the study of oxygen exchange and studied high-pressure effects in photosynthesis. Ulrich (Uli) Schreiber, as a postdoctoral fellow from Germany, introduced measurements on chlorophyll (Chl) a fluorescence to Bill’s lab, leading to the discovery of reversible inhibition of excitation energy transfer between photosynthetic pigments and of a pivotal role of O2 in the oxidation of the electron transport chain between Photosystem II (PS II) and PS I. Bill’s and Uli’s work led to a patent of a portable chlorophyll fluorometer, the first available commercially, which was later modified to measure whole plantlets. The latter was used in pioneering measurement of the health of forest and crop plants undergoing in vitro clonal micropropagation. With several other researchers (including Doug Bruce, the late Radovan Popovic, and Sarah Swenson), he localized the quenching site of O2 and showed a dampening effect on measurements of the four-step process of O2 production by endogenous oxygen uptake. Bill is remembered as a hard-working but fun-loving person with a keen mind and strong sense of social justice.


Datum: 01.06.2018


Chlorophyll fluorescence as a tool for nutrient status identification in rapeseed plants

Abstract

In natural conditions, plants growth and development depends on environmental conditions, including the availability of micro- and macroelements in the soil. Nutrient status should thus be examined not by establishing the effects of single nutrient deficiencies on the physiological state of the plant but by combinations of them. Differences in the nutrient content significantly affect the photochemical process of photosynthesis therefore playing a crucial role in plants growth and development. In this work, an attempt was made to find a connection between element content in (i) different soils, (ii) plant leaves, grown on these soils and (iii) changes in selected chlorophyll a fluorescence parameters, in order to find a method for early detection of plant stress resulting from the combination of nutrient status in natural conditions. To achieve this goal, a mathematical procedure was used which combines principal component analysis (a tool for the reduction of data complexity), hierarchical k-means (a classification method) and a machine-learning method—super-organising maps. Differences in the mineral content of soil and plant leaves resulted in functional changes in the photosynthetic machinery that can be measured by chlorophyll a fluorescent signals. Five groups of patterns in the chlorophyll fluorescent parameters were established: the ‘no deficiency’, Fe-specific deficiency, slight, moderate and strong deficiency. Unfavourable development in groups with nutrient deficiency of any kind was reflected by a strong increase in F o and ΔVt 0 and decline in φ Po, φ Eoδ Ro and φ Ro. The strong deficiency group showed the suboptimal development of the photosynthetic machinery, which affects both PSII and PSI. The nutrient-deficient groups also differed in antenna complex organisation. Thus, our work suggests that the chlorophyll fluorescent method combined with machine-learning methods can be highly informative and in some cases, it can replace much more expensive and time-consuming procedures such as chemometric analyses.


Datum: 01.06.2018


Antimycin A inhibits cytochrome b 559 -mediated cyclic electron flow within photosystem II

Abstract

The light reactions of photosynthesis are known to comprise both linear and cyclic electron flow in order to convert light energy into chemical energy in the form of NADPH and ATP. Antimycin A (AA) has been proposed as an inhibitor of ferredoxin-dependent cyclic electron flow around photosystem I (CEF-PSI) in photosynthesis research. However, its precise inhibitory mechanism and target site had not been elucidated yet. Here we show that AA inhibits the cyclic (alternative) electron flow via cytochrome b559 (Cyt b559) within photosystem II (CEF-PSII). When AA was applied to thylakoid membranes isolated from spinach leaves, the high potential form of Cyt b559, which was reduced in the dark, was transformed into the lower potential forms and readily oxidized by molecular oxygen. In the absence of AA, the reduced Cyt b559 was oxidized by P680+ upon light illumination and re-reduced in the dark, mainly by the electron from the QB site on the acceptor side of PSII. In contrast, AA suppressed the oxidation of Cyt b559 and induced its reduction under the illumination. This inhibition of Cyt b559 oxidation by AA enhanced photoinhibition of PSII. Based on the above results, we propose caution regarding the use of AA for evaluating CEF-PSI per se and concurrently propose that AA provides for new insights into, and interpretations of, the physiological importance of Cyt b559, rather than that of CEF-PSI in photosynthetic organisms.


Datum: 22.05.2018


Crystal structure of Arabidopsis thaliana glutamyl-tRNA Glu reductase in complex with NADPH and glutamyl-tRNA Glu reductase binding protein

Abstract

In higher plants, the tetrapyrrole biosynthesis pathway starts from the reaction catalyzed by the rate-limiting enzyme, glutamyl-tRNAGlu reductase (GTR). In Arabidopsis thaliana, GTR is controlled by post-transcriptional regulators such as GTR binding protein (GBP), which stimulates AtGTR activity. The NADPH-binding domain of AtGTR undergoes a substantial movement upon GBP binding. Here, we report the crystal structure of AtGTR-NADPH-GBP ternary complex. NADPH binding causes slight structural changes compared with the AtGTR-GBP binary complex, and possibly take a part of the space needed by the substrate glutamyl-tRNAGlu. The highly reactive sulfhydryl group of the active-site residue Cys144 shows an obvious rotation, which may facilitate the hydride transfer from NADPH to the thioester intermediate to form glutamate-1-semialdehyde. Furthermore, Lys271, Lys274, Ser275, Asn278, and Gln282 of GBP participate in the interaction between AtGTR and GBP, and the stimulating effect of GBP decreased when all of these residues were mutated to Ala. When the Cys144 of AtGTR was mutated to Ser, AtGTR activity could not be detected even in the presence of GBP.


Datum: 21.05.2018


Consequences of structural modifications in cytochrome b 559 on the electron acceptor side of Photosystem II

Abstract

Cytb559 in Photosystem II is a heterodimeric b-type cytochrome. The subunits, PsbE and PsbF, consist each in a membrane α-helix. Mutants were previously designed and studied in Thermosynechococcus elongatus (Sugiura et al., Biochim Biophys Acta 1847:276–285, 2015) either in which an axial histidine ligand of the haem-iron was substituted for a methionine, the PsbE/H23M mutant in which the haem was lacking, or in which the haem environment was modified, the PsbE/Y19F and PsbE/T26P mutants. All these mutants remained active showing that the haem has no structural role provided that PsbE and PsbF subunits are present. Here, we have carried on the characterization of these mutants. The following results were obtained: (i) the Y19F mutation hardly affect the Em of Cytb559, whereas the T26P mutation converts the haem into a form with a Em much below 0 mV (so low that it is likely not reducible by QB) even in an active enzyme; (ii) in the PsbE/H23M mutant, and to a less extent in PsbE/T26P mutant, the electron transfer efficiency from QA to QB is decreased; (iii) the lower Em of the QA/QA couple in the PsbE/H23M mutant correlates with a higher production of singlet oxygen; (iv) the superoxide and/or hydroperoxide formation was not increased in the PsbE/H23M mutant lacking the haem, whereas it was significantly larger in the PsbE/T26P. These data are discussed in view of the literature to discriminate between structural and redox roles for the haem of Cytb559 in the production of reactive oxygen species.


Datum: 19.05.2018


Impact of weak water deficit on growth, photosynthetic primary processes and storage processes in pine and spruce seedlings

Abstract

We investigated the influence of 40 days of drought on growth, storage processes and primary photosynthetic processes in 3-month-old Scots pine and Norway spruce seedlings growing in perlite culture. Water stress significantly affected seedling water status, whereas absolute dry biomass growth was not substantially influenced. Water stress induced an increase in non-structural carbohydrate content (sugars, sugar alcohols, starch) in the aboveground part of pine seedlings in contrast to spruce seedlings. Due to the relatively low content of sugars and sugar alcohols in seedling organs, their expected contribution to osmotic potential changes was quite low. In contrast to biomass accumulation and storage, photosynthetic primary processes were substantially influenced by water shortage. In spruce seedlings, PSII was more sensitive to water stress than PSI. In particular, electron transport in PSI was stable under water stress despite the substantial decrease of electron transport in PSII. The increase in thermal energy dissipation due to enhancement of non-photochemical quenching (NPQ) was evident in both species under water stress. Simultaneously, the yields of non-regulated energy dissipation in PSII were decreased in pine seedlings under drought. A relationship between growth, photosynthetic activities and storage processes is analysed under weak water deficit.


Datum: 19.05.2018


The artificial humic substance HS1500 does not inhibit photosynthesis of the green alga Desmodesmus armatus in vivo but interacts with the photosynthetic apparatus of isolated spinach thylakoids in vitro

Abstract

Humic substances (HSs) can influence the growth and composition of freshwater phytoplankton assemblage. Since HSs contain many phenolic and quinonic moieties and cause growth reductions in eco-physiological field experiments, HSs are considered photosystem II herbicides. To test this specific mode of action in vivo and in vitro, respectively, we used intact cells of the green alga Desmodesmus armatus, as well as thylakoids isolated from spinach (Spinacia oleracea) as a model system for the green algal chloroplast. Photosynthetic electron transport was measured as oxygen evolution and variable chlorophyll fluorescence. The in vivo effect of the artificial humic substance HS1500 on algae consisted of no impact on photosynthesis–irradiance curves of intact green algae compared to untreated controls. In contrast, addition of HS1500 to isolated thylakoids resulted in light-induced oxygen consumption (Mehler reaction) as an in vitro effect. Fluorescence induction kinetics of HS-treated thylakoids revealed a large static quenching effect of HS1500, but no inhibitory effect on electron transport. For the case of intact algal cells, we conclude that the highly hydrophilic and rather large molecules of HS1500 are not taken up in effective quantities and, therefore, cannot interfere with photosynthesis. The in vitro tests show that HS1500 has no inhibitory effect on photosystem II but operates as a weak, oxygen-consuming Hill acceptor at photosystem I. Hence, the results indicate that eco-physiological field experiments should focus more strongly on effects of HSs on extracellular features, such as reducing and red-shifting the underwater light field or influencing nutrient availability by cation exchange within the plankton network.


Datum: 18.05.2018


Effect of artificial redox mediators on the photoinduced oxygen reduction by photosystem I complexes

Abstract

The peculiarities of interaction of cyanobacterial photosystem I with redox mediators 2,6-dichlorophenolindophenol (DCPIP) and N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) were investigated. The higher donor efficiency of the reduced DCPIP form was demonstrated. The oxidized form of DCPIP was shown to be an efficient electron acceptor for terminal iron–sulfur cluster of photosystem I. Likewise methyl viologen, after one-electron reduction, DCPIP transfers an electron to the molecular oxygen. These results were discussed in terms of influence of these interactions on photosystem I reactions with the molecular oxygen and natural electron acceptors.


Datum: 16.05.2018


In memory of Achim Trebst (1929–2017): a pioneer of photosynthesis research

Abstract

The life and work of Achim Trebst (1929–2017) was dedicated to photosynthesis, involving a wide span of seminal contributions which cumulated in more than five decades of active research: Major topics include the separation of light and dark phases in photosynthesis, the elucidation of photosynthesis by the use of inhibitors, the identification of the three-dimensional structure of photosystem II and its degradation, and an explanation of singlet oxygen formation. For this tribute, which has been initiated by Govindjee, twenty-two personal tributes by former coworkers, scientific friends, and his family have been compiled and combined with an introduction tracing the different stages of Achim Trebst’s scientific life.


Datum: 16.05.2018


Effects of genetic manipulation of the activity of photorespiration on the redox state of photosystem I and its robustness against excess light stress under CO 2 -limited conditions in rice

Abstract

Under CO2-limited conditions such as during stomatal closure, photorespiration is suggested to act as a sink for excess light energy and protect photosystem I (PSI) by oxidizing its reaction center chlorophyll P700. In this study, this issue was directly examined with rice (Oryza sativa L.) plants via genetic manipulation of the amount of Rubisco, which can be a limiting factor for photorespiration. At low [CO2] of 5 Pa that mimicked stomatal closure condition, the activity of photorespiration in transgenic plants with decreased Rubisco content (RBCS-antisense plants) markedly decreased, whereas the activity in transgenic plants with overproduction of Rubisco (RBCS-sense plants) was similar to that in wild-type plants. Oxidation of P700 was enhanced at [CO2] of 5 Pa in wild-type and RBCS-sense plants. PSI was not damaged by excess light stress induced by repetitive saturated pulse-light (rSP) in the presence of strong steady-state light. On the other hand, P700 was strongly reduced in RBCS-antisense plants at [CO2] of 5 Pa. PSI was also damaged by rSP illumination. These results indicate that oxidation of P700 and the robustness of PSI against excess light stress are hampered by the decreased activity of photorespiration as a result of genetic manipulation of Rubisco content. It is also suggested that overproduction of Rubisco does not enhance photorespiration as well as CO2 assimilation probably due to partial deactivation of Rubisco.


Datum: 14.05.2018


Energy transfer in purple bacterial photosynthetic units from cells grown in various light intensities

Abstract

Three photosynthetic membranes, called intra-cytoplasmic membranes (ICMs), from wild-type and the ∆pucBAabce mutant of the purple phototrophic bacterium Rps. palustris were investigated using optical spectroscopy. The ICMs contain identical light-harvesting complex 1–reaction centers (LH1–RC) but have various spectral forms of light-harvesting complex 2 (LH2). Spectroscopic studies involving steady-state absorption, fluorescence, and femtosecond time-resolved absorption at room temperature and at 77 K focused on inter-protein excitation energy transfer. The studies investigated how energy transfer is affected by altered spectral features of the LH2 complexes as those develop under growth at different light conditions. The study shows that LH1 → LH2 excitation energy transfer is strongly affected if the LH2 complex alters its spectroscopic signature. The LH1 → LH2 excitation energy transfer rate modeled with the Förster mechanism and kinetic simulations of transient absorption of the ICMs demonstrated that the transfer rate will be 2–3 times larger for ICMs accumulating LH2 complexes with the classical B800–850 spectral signature (grown in high light) compared to the ICMs from the same strain grown in low light. For the ICMs from the ∆pucBAabce mutant, in which the B850 band of the LH2 complex is blue-shifted and almost degenerate with the B800 band, the LH1 → LH2 excitation energy transfer was not observed nor predicted by calculations.


Datum: 03.05.2018


 


Category: Current Chemistry Research

Last update: 28.03.2018.






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