An efficient protocol for extracting thylakoid membranes and total leaf proteins from Posidonia oceanica and other polyphenol-rich plants

BACKGROUND

The extraction of thylakoids is an essential step in studying the structure of photosynthetic complexes and several other aspects of the photosynthetic process in plants. Conventional protocols have been developed for selected land plants grown in controlled conditions. Plants accumulate defensive chemical compounds such as polyphenols to cope with environmental stresses. When the polyphenol levels are high, their oxidation and cross-linking properties prevent thylakoid extraction.

RESULTS

In this study, we developed a method to counteract the hindering effects of polyphenols by modifying the grinding buffer with the addition of both vitamin C (VitC) and polyethylene glycol (PEG4000). This protocol was first applied to the marine plant Posidonia oceanica and then extended to other plants synthesizing substantial amounts of polyphenols, such as Quercus pubescens (oak) and Vitis vinifera (grapevine). Native gel analysis showed that photosynthetic complexes (PSII, PSI, and LHCII) can be extracted from purified membranes and fractionated comparably to those extracted from the model plant Arabidopsis thaliana. Moreover, total protein extraction from frozen P. oceanica leaves was also efficiently carried out using a denaturing buffer containing PEG and VitC.

CONCLUSIONS

Our work shows that the use of PEG and VitC significantly improves the isolation of native thylakoids, native photosynthetic complexes, and total proteins from plants containing high amounts of polyphenols and thus enables studies on photosynthesis in various plant species grown in natural conditions.

BAG8 positively regulates cold stress tolerance by modulating photosystem, antioxidant system and protein protection in Solanum lycopersicum

The B-cell lymphoma 2 (Bcl-2)-associated athanogene (BAG) family is a relatively conserved and multifunctional co-chaperones in animals and plants, which can flexibly interact with a variety of proteins and regulate various processes from growth and development to stress response. However, compared with animals, the function of BAG family in plant remains largely unknown, especially in response to cold stress. In this study, we have found that the expression of BAG8 was significantly induced in tomato under cold stress. Results showed that bag8 mutants exhibit significantly reduced tolerance towards cold stress, while BAG8 overexpressing lines were relatively resistant as reflected by the phenotype and membrane peroxidation. Measuring of gas exchange parameters, photosystem I (PSI) and photosystem II (PSII) of tomato leaves under cold stress further revealed that BAG8 mitigated cold-induced damage in photosynthetic system. Additionally, bag8 mutants exhibited more cold-induced reactive oxygen species, which were substantially normalized in BAG8 overexpressing plants. Nevertheless, the activities of antioxidant enzymes which were compromised in bag8 mutants were improved in BAG8 overexpressing plants facing cold stress. Additionally, BAG8 interacted with heat shock protein Hsp70 and protein phosphatase PP2A both in vitro and in vivo. Our results demonstrate that BAG8 plays a positive role in cold tolerance in tomato probably by the improvement of photosystems and antioxidant systems, and by interacting with Hsp70 involved in photosynthesis and PP2A involved in stomatal development.

Ambiguous changes in photosynthetic parameters of Lemna minor L. after short-term exposure to naproxen and paracetamol: Can the risk be ignored?

Non-steroidal anti-inflammatory drugs (NSAID) are recently monitored in the aquatic environment. Naproxen (NPX), paracetamol (PCT) and their transformation products can influence the biochemical and physiological processes at the sub-cellular and cellular levels taking part in the growth and development of plants. This study aimed to compare the effects of NPX and PCT, drugs with different physico-chemical properties, on the growth and photosynthetic processes in Lemna minor during a short-term (7 days) exposure. Although duckweed took up more than five times higher amount of PCT as compared to NPX (275.88 µg/g dry weight to 43.22 µg/g when treated with 10 mg/L), only NPX limited the number of new plants by 9% and 26% under 1 and 10 mg/L, respectively, and increased their dry weight (by 18% under 10 mg/L) and leaf area per plant. A considerable (by 30%) drop in the content of photosynthetic pigments under 10 mg/L treatment by both drugs did not significantly affect the efficiency of the primary processes of photosynthesis. Values of induced chlorophyll fluorescence parameters (F₀, F_V/F_M, Φ_II, and NPQ) showed just a mild stimulation by PCT and a negative effect by NPX (by up to 10%), especially on the function of photosystem II and electron transport in both intact duckweed plants and isolated chloroplasts. Lowered efficiency of Hill reaction activity (by more than 10% under 0.1 - 10 mg/L treatments) in isolated chloroplasts suspension proved the only inhibition effect of PCT to primary photosynthetic processes. In intact plants, higher treatments (0.5 - 10 mg/L) by both NPX and PCT induced an increase in RuBisCO content. The results prove that the potential effect of various drugs on plants is hard to generalise.

Seed priming with NaCl helps to improve tissue tolerance, potassium retention ability of plants, and protects the photosynthetic ability in two different legumes, chickpea and lentil, under salt stress

MAIN CONCLUSION

Seed priming with NaCl mimicked the conditions of natural priming to improve the tissue tolerance nature of sensitive legumes, which helps to maintain survivability and yield in mildly saline areas. Seed priming with NaCl is a seed invigoration technique that helps to improve plant growth by altering Na⁺ and K⁺ content under salt stress. Legumes are overall sensitive to salt and salinity hampers their growth and yield. Therefore, a priming (50 mM NaCl) experiment was performed with two different legume members [Cicer arietinum cv. Anuradha and Lens culinaris cv. Ranjan] and different morpho-physiological, biochemical responses at 50 mM, 100 mM, and 150 mM NaCl and molecular responses at 150 mM NaCl were studied in hydroponically grown nonprimed and primed members. Similarly, a pot experiment was performed at 80 mM Na⁺, to check the yield. Tissue Na⁺ and K⁺ content suggested NaCl-priming did not significantly alter the accumulation of Na⁺ among nonprimed and primed members but retained more K⁺ in cells, thus maintaining a lower cellular Na⁺/K⁺ ratio. Low osmolyte content (e.g., proline) in primed members suggested priming could minimize their overall osmolytic requirement. Altogether, these implied tissue tolerance (TT) nature might have improved in case of NaCl-priming as was also reflected by a better TT score (LC₅₀ value). An improved TT nature enabled the primed plants to maintain a significantly higher photosynthetic rate through better stomatal conductance. Along with this, a higher level of chlorophyll content and competent functioning of the photosynthetic subunits improved photosynthetic performance that ensured yield under stress. Overall, this study explores the potential of NaCl-priming and creates possibilities for considerably sensitive members; those in their nonprimed forms have no prospect in mildly saline agriculture.

The photosynthetic apparatus of the CAM plant Tillandsia flabellate and its response to water deficit

CAM plants are superior to C₃ plants in drought resistance because of their peculiar photosynthesis pathway and morphological features. While those aspects have been studied for decades, little is known about the photosynthetic machinery of CAM plants. Here, we used a combination of biochemical and biophysical methods to study the photosynthetic apparatus of Tillandsia flabellate, an obligatory CAM plant. Most of the Photosystems super- and sub-complexes have properties very similar to those of Arabidopsis, with the main difference that in Tillandsia PSI-LHCI complexes bind extra LHCI. Functional measurements show that the PSI/PSII ratio is rather low compared to other plants and that the antenna size of both PSI and PSII is small. Upon 30-day water deficiency, the composition of the photosystems does not change significantly, PSII efficiency remains high and no Photosystem II photoinhibition was detected despite a reduction of non-photochemical quenching (NPQ).

High light-induced changes in thylakoid supercomplexes organization from cyclic electron transport mutants of Chlamydomonas reinhardtii

The localization of carotenoids and macromolecular organization of thylakoid supercomplexes have not been reported yet in Chlamydomonas reinhardtii WT and cyclic electron transport mutants (pgrl1 and pgr5) under high light. Here, the various pigments, protein composition, and pigment-protein interactions were analyzed from the cells, thylakoids, and sucrose density gradient (SDG) fractions. Also, the supercomplexes of thylakoids were separated from BN-PAGE and SDG. The abundance of light-harvesting complex (LHC) II trimer complexes and pigment-pigment interaction were changed slightly under high light, shown by circular dichroism. However, a drastic change was seen in photosystem (PS)I-LHCI complexes than PSII complexes, especially in pgrl1 and pgr5. The lutein and β-carotene increased under high light in LHCII trimers compared to other supercomplexes, indicating that these pigments protected the LHCII trimers against high light. However, the presence of xanthophylls, lutein, and β-carotene was less in PSI-LHCI, indicating that pigment-protein complexes altered in high light. Even the real-time PCR data shows that the pgr5 mutant does not accumulate zeaxanthin dependent genes under high light, which shows that violaxanthin is not converting into zeaxanthin under high light. Also, the protein data confirms that the LHCSR3 expression is absent in pgr5, however it is presented in LHCII trimer in WT and pgrl1. Interestingly, some of the core proteins were aggregated in pgr5, which led to change in photosynthesis efficiency in high light.

The effects of secondary bacterial metabolites on photosynthesis in microalgae cells

Secondary metabolites of bacteria are regulatory molecules that act as "info-chemicals" that control some metabolic processes in the cells of microorganisms. These molecules provide the function of bacteria communication in microbial communities. As primary producers of organic matter in the biosphere, microalgae play a central ecological role in various ecosystems. Photosynthesis is a central process in microalgae cells, and it is exposed to various biotic and abiotic factors. Various secondary metabolites of bacteria confer a noticeable regulatory effect on photosynthesis in microalgae cells. The main purpose of this review is to highlight recent experimental results that demonstrate the impact of several types of common bacterial metabolites (volatile organic compounds, non-protein amino acids, and peptides) on photosynthetic activity in cells of microalgae. The use of these molecules as herbicides can be of great importance both for practical applications and for basic research.

Draft genome analysis, poly-phasic study and lipid biosynthesis pathway of Scenedesmus sp. SVMIICT1

A comprehensive polyphasic evaluation of a microalgal isolate Scenedesmus sp. SVMIICT1 through morphological, biochemical, photosynthetic characterization, next-generation sequencing and lipid pathway analysis was reported. The strain was cultivated photo-autotrophically, where the maximum photosynthetic yield (F_V/F_M) of 0.75 was observed on the 4^th day with optimal PSII photochemical efficiency. Enhanced electron transport rate (ETR(I)) with inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) resulted in cyclic electron flow. A fair share of carbohydrate content (36 µg/mg) was ascribed to the presence of pyrenoid towards higher CO₂ sequestration pursuant to carbon concentrating mechanism (CCM). Denovo sequencing of the genome was assembled, annotated for the prediction of gene and protein. KEGG automatic annotation server (KAAS) analysis depicted the presence of genes accompanying the biosynthesis of the glycerophospholipid pathway. Fatty acid profile represented a higher fraction of palmitic acid (C16:0; 41.6%) followed by alpha-linolenic acid (C18:3; 44.5%).

My precarious career in photosynthesis: a roller-coaster journey into the fascinating world of chloroplast ultrastructure, composition, function and dysfunction

Despite my humble beginnings in rural China, I had the good fortune of advancing my career and joining an international community of photosynthesis researchers to work on the 'light reactions' that are a fundamental process in Nature. Along with supervisors, mentors, colleagues, students and lab assistants, I worked on ionic redistributions across the photosynthetic membrane in response to illumination, photophosphorylation, forces that regulate the stacking of photosynthetic membranes, the composition of components of the photosynthetic apparatus during acclimation to the light environment, and the failure of the photosynthetic machinery to acclimate to too much light or even to cope with moderate light due to inevitable photodamage. These fascinating underlying mechanisms were investigated in vitro and in vivo. My career path, with its ups and downs, was never secure, but the reward of knowing a little more of the secret of Nature offset the job uncertainty.

Role of cyclic electron transport mutations pgrl1 and pgr5 in acclimation process to high light in Chlamydomonas reinhardtii

Light is crucial for photosynthesis, but the amount of light that exceeds an organism's assimilation efficacy can lead to photo-oxidative damage and even cell death. In Chlamydomonas (C). reinhardtii cyclic electron flow (CEF) is very important for the elicitation of non-photochemical quenching (NPQ) by controlling the acidification of thylakoid lumen. This process requires the cooperation of proton gradient regulation (PGR) proteins, PGRL1 and PGR5. Here, we compared the growth pattern and photosynthetic activity between wild type (137c, t222+) and mutants impaired in CEF (pgrl1 and pgr5) under photoautotrophic and photoheterotrophic conditions. We have observed the discriminative expression of NPQ in the mutants impaired in CEF of pgrl1 and pgr5. The results obtained from the mutants showed reduced cell growth and density, Chl a/b ratio, fluorescence, electron transport rate, and yield of photosystem (PS)II. These mutants have reduced capability to develop a strong NPQ indicating that the role of CEF is very crucial for photoprotection. Moreover, the CEF mutant exhibits increased photosensitivity compared with the wild type. Therefore, we suggest that besides NPQ, the fraction of non-regulated non-photochemical energy loss (NO) also plays a crucial role during high light acclimation despite a low growth rate. This low NPQ rate may be due to less influx of protons coming from the CEF in cases of pgrl1 and pgr5 mutants. These results are discussed in terms of the relative photoprotective benefit, related to the thermal dissipation of excess light in photoautotrophic and photoheterotrophic conditions.

Purification of Protein-complexes from the Cyanobacterium Synechocystis sp. PCC 6803 Using FLAG-affinity Chromatography

Exploring the structure and function of protein complexes requires their isolation in the native state-a task that is made challenging when studying labile and/or low abundant complexes. The difficulties in preparing membrane-protein complexes are especially notorious. The cyanobacterium Synechocystis sp. PCC 6803 is a widely used model organism for the physiology of oxygenic phototrophs, and the biogenesis of membrane-bound photosynthetic complexes has traditionally been studied using this cyanobacterium. In a typical approach, the protein complexes are purified with a combination of His-affinity chromatography and a size-based fractionation method such as gradient ultracentrifugation and/or native electrophoresis. However, His-affinity purification harbors prominent contaminants and the levels of many proteins are too low for a feasible multi-step purification. Here, we have developed a purification method for the isolation of 3x FLAG-tagged proteins from the membrane and soluble fractions of Synechocystis. Soluble proteins or solubilized thylakoids are subjected to a single affinity purification step that utilizes the highly specific binding of FLAG-affinity resin. After an intensive wash, the captured proteins are released from the resin under native conditions using an excess of synthetic 3x FLAG peptide. The protocol allows fast isolation of low abundant protein complexes with a superb purity.

Pigment-protein complexes are organized into stable microdomains in cyanobacterial thylakoids

Thylakoids are the place of the light-photosynthetic reactions. To gain maximal efficiency, these reactions are conditional to proper pigment-pigment and protein-protein interactions. In higher plants thylakoids, the interactions lead to a lateral asymmetry in localization of protein complexes (i.e. granal/stromal thylakoids) that have been defined as a domain-like structures characteristic by different biochemical composition and function (Albertsson P-Å. 2001,Trends Plant Science 6: 349-354). We explored this complex organization of thylakoid pigment-proteins at single cell level in the cyanobacterium Synechocystis sp. PCC 6803. Our 3D confocal images captured heterogeneous distribution of all main photosynthetic pigment-protein complexes (PPCs), Photosystem I (fluorescently tagged by YFP), Photosystem II and Phycobilisomes. The acquired images depicted cyanobacterial thylakoid membrane as a stable, mosaic-like structure formed by microdomains (MDs). These microcompartments are of sub-micrometer in sizes (~0.5-1.5 μm), typical by particular PPCs ratios and importantly without full segregation of observed complexes. The most prevailing MD is represented by MD with high Photosystem I content which allows also partial separation of Photosystems like in higher plants thylakoids. We assume that MDs stability (in minutes) provides optimal conditions for efficient excitation/electron transfer. The cyanobacterial MDs thus define thylakoid membrane organization as a system controlled by co-localization of three main PPCs leading to formation of thylakoid membrane mosaic. This organization might represent evolutional and functional precursor for the granal/stromal spatial heterogeneity in photosystems that is typical for higher plant thylakoids.

High ammonium supply impairs photosynthetic efficiency in rice exposed to excess light

Mechanisms involving ammonium toxicity, excess light, and photosynthesis are scarcely known in plants. We tested the hypothesis that high NH₄⁺ supply in presence of high light decreases photosynthetic efficiency of rice plants, an allegedly tolerant species. Mature rice plants were previously supplied with 10 mM NH₄⁺ or 10 mM NO₃^- and subsequently exposed to 400 µmol m^-2 s^-1 (moderate light-ML) or 2000 µmol m^-2 s^-1 (high light-HL) for 8 h. HL greatly stimulated NH₄⁺ accumulation in roots and in a minor extent in leaves. These plants displayed significant delay in D1 protein recovery in the dark, compared to nitrate-supplied plants. These responses were related to reduction of both PSII and PSI quantum efficiencies and induction of non-photochemical quenching. These changes were also associated with higher limitation in the donor side and lower restriction in the acceptor side of PSI. This later response was closely related to prominent decrease in stomatal conductance and net CO₂ assimilation that could have strongly affected the energy balance in chloroplast, favoring ATP accumulation and NPQ induction. In parallel, NH₄⁺ induced a strong increase in the electron flux to photorespiration and, inversely, it decreased the flux to Rubisco carboxylation. Overall, ammonium supply negatively interacts with excess light, possibly by enhancing ammonium transport towards leaves, causing negative effects on some photosynthetic steps. We propose that high ammonium supply to rice combined with excess light is capable to induce strong delay in D1 protein turnover and restriction in stomatal conductance, which might have contributed to generalized disturbances on photosynthetic efficiency.

Changes in the photosynthetic apparatus and lipid droplet formation in Chlamydomonas reinhardtii under iron deficiency

The unicellular photosynthetic alga Chlamydomonas reinhardtii was propagated in iron deficiency medium and patterns of growth, photosynthetic efficiency, lipid accumulation, as well as the expression of lipid biosynthetic and photosynthesis-related proteins were analysed and compared with iron-sufficient growth conditions. As expected, the photosynthetic rate was reduced (maximally after 4 days of growth) as a result of increased non-photochemical quenching (NPQ). Surprisingly, the stress-response protein LHCSR3 was expressed in conditions of iron deficiency that cause NPQ induction. In addition, the protein contents of both the PSI and PSII reaction centres were gradually reduced during growth in iron deficiency medium. Interestingly, the two generations of Fe deficiency cells could be able to recover the photosynthesis but the second generation cells recovered much slower as these cells were severely in shock. Analysis by flow cytometry with fluorescence-activated cell sorting and thin layer chromatography showed that iron deficiency also induced the accumulation of triacylglycerides (TAG), which resulted in the formation of lipid droplets. This was most significant between 48 and 72 h of growth. Dramatic increases in DGAT2A and PDAT1 levels were caused by iron starvation, which indicated that the biosynthesis of TAG had been increased. Analysis using gas chromatography mass spectrometry showed that levels of 16:0, 18:0, 18:2 and 18:3^Δ9,12,15 fatty acids were significantly elevated. The results of this study highlight the genes/enzymes of Chlamydomonas that affect lipid synthesis through their influence on photosynthesis, and these represent potential targets of metabolic engineering to develop strains for biofuel production.

Non-photochemical quenching-dependent acclimation and thylakoid organization of Chlamydomonas reinhardtii to high light stress

Light is essential for all photosynthetic organisms while an excess of it can lead to damage mainly the photosystems of the thylakoid membrane. In this study, we have grown Chlamydomonas reinhardtii cells in different intensities of high light to understand the photosynthetic process with reference to thylakoid membrane organization during its acclimation process. We observed, the cells acclimatized to long-term response to high light intensities of 500 and 1000 µmol m^-2 s^-1 with faster growth and more biomass production when compared to cells at 50 µmol m^-2 s^-1 light intensity. The ratio of Chl a/b was marginally decreased from the mid-log phase of growth at the high light intensity. Increased level of zeaxanthin and LHCSR3 expression was also found which is known to play a key role in non-photochemical quenching (NPQ) mechanism for photoprotection. Changes in photosynthetic parameters were observed such as increased levels of NPQ, marginal change in electron transport rate, and many other changes which demonstrate that cells were acclimatized to high light which is an adaptive mechanism. Surprisingly, PSII core protein contents have marginally reduced when compared to peripherally arranged LHCII in high light-grown cells. Further, we also observed alterations in stromal subunits of PSI and low levels of PsaG, probably due to disruption of PSI assembly and also its association with LHCI. During the process of acclimation, changes in thylakoid organization occurred in high light intensities with reduction of PSII supercomplex formation. This change may be attributed to alteration of protein-pigment complexes which are in agreement with circular dichoism spectra of high light-acclimatized cells, where decrease in the magnitude of psi-type bands indicates changes in ordered arrays of PSII-LHCII supercomplexes. These results specify that acclimation to high light stress through NPQ mechanism by expression of LHCSR3 and also observed changes in thylakoid protein profile/supercomplex formation lead to low photochemical yield and more biomass production in high light condition.

Spectral microscopic imaging of heterocysts and vegetative cells in two filamentous cyanobacteria based on spontaneous Raman scattering and photoluminescence by 976 nm excitation

Photosynthetic pigment-protein complexes are highly concentrated in thylakoid membranes of chloroplasts and cyanobacteria that emit strong autofluorescence (mainly 600-800 nm). In Raman scattering microscopy that enables imaging of pigment concentrations of thylakoid membranes, near infrared laser excitation at 1064 nm or visible laser excitation at 488-532 nm has been often employed in order to avoid the autofluorescence. Here we explored a new approach to Raman imaging of thylakoid membranes by using excitation wavelength of 976 nm. Two types of differentiated cells, heterocysts and vegetative cells, in two diazotrophic filamentous cyanobacteria, Anabaena variabilis, and Rivularia M-261, were characterized. Relative Raman scattering intensities of phycobilisomes of the heterocyst in comparison with the nearest vegetative cells of Rivularia remained at a significantly higher level than those of A. variabilis. It was also found that the 976 nm excitation induces photoluminescence around 1017-1175 nm from the two cyanobacteria, green alga (Parachlorella kessleri) and plant (Arabidopsis thaliana). We propose that this photoluminescence can be used as an index of concentration of chlorophyll a that has relatively small Raman scattering cross-sections. The Rivularia heterocysts that we analyzed were clearly classified into at least two subgroups based on the Chla-associated photoluminescence and carotenoid Raman bands, indicating two physiologically distinct states in the development or aging of the terminal heterocyst.

Blue light reduces photosynthetic efficiency of cyanobacteria through an imbalance between photosystems I and II

Several studies have described that cyanobacteria use blue light less efficiently for photosynthesis than most eukaryotic phototrophs, but comprehensive studies of this phenomenon are lacking. Here, we study the effect of blue (450 nm), orange (625 nm), and red (660 nm) light on growth of the model cyanobacterium Synechocystis sp. PCC 6803, the green alga Chlorella sorokiniana and other cyanobacteria containing phycocyanin or phycoerythrin. Our results demonstrate that specific growth rates of the cyanobacteria were similar in orange and red light, but much lower in blue light. Conversely, specific growth rates of the green alga C. sorokiniana were similar in blue and red light, but lower in orange light. Oxygen production rates of Synechocystis sp. PCC 6803 were five-fold lower in blue than in orange and red light at low light intensities but approached the same saturation level in all three colors at high light intensities. Measurements of 77 K fluorescence emission demonstrated a lower ratio of photosystem I to photosystem II (PSI:PSII ratio) and relatively more phycobilisomes associated with PSII (state 1) in blue light than in orange and red light. These results support the hypothesis that blue light, which is not absorbed by phycobilisomes, creates an imbalance between the two photosystems of cyanobacteria with an energy excess at PSI and a deficiency at the PSII-side of the photosynthetic electron transfer chain. Our results help to explain why phycobilisome-containing cyanobacteria use blue light less efficiently than species with chlorophyll-based light-harvesting antennae such as Prochlorococcus, green algae and terrestrial plants.

Metallic nanoparticles influence the structure and function of the photosynthetic apparatus in plants

The applications of nanoparticles continue to expand into areas as diverse as medicine, bioremediation, cosmetics, pharmacology and various industries, including agri-food production. The widespread use of nanoparticles has generated concerns given the impact these nanoparticles - mostly metal-based such as CuO, Ag, Au, CeO₂, TiO₂, ZnO, Co, and Pt - could be having on plants. Some of the most studied variables are plant growth, development, production of biomass, and ultimately oxidative stress and photosynthesis. A systematic appraisal of information about the impact of nanoparticles on these processes is needed to enhance our understanding of the effects of metallic nanoparticles and oxides on the structure and function on the plant photosynthetic apparatus. Most nanoparticles studied, especially CuO and Ag, had a detrimental impact on the structure and function of the photosynthetic apparatus. Nanoparticles led to a decrease in concentration of photosynthetic pigments, especially chlorophyll, and disruption of grana and other malformations in chloroplasts. Regarding the functions of the photosynthetic apparatus, nanoparticles were associated with a decrease in the photosynthetic efficiency of photosystem II and decreased net photosynthesis. However, CeO₂ and TiO₂ nanoparticles may have a positive effect on photosynthetic efficiency, mainly due to an increase in electron flow between the photosystems II and I in the Hill reaction, as well as an increase in Rubisco activity in the Calvin and Benson cycle. Nevertheless, the underlying mechanisms are poorly understood. The future mechanistic work needs to be aimed at characterizing the enhancing effect of nanoparticles on the active generation of ATP and NADPH, carbon fixation and its incorporation into primary molecules such as photo-assimilates.

Changes in activities of both photosystems and the regulatory effect of cyclic electron flow in field-grown cotton (Gossypium hirsutum L) under water deficit

To clarify the influence of water deficit on the functionality of the photosynthetic apparatus of cotton plants, leaf gas exchange, chlorophyll a fluorescence, and P700 redox state were examined in field-grown cotton Gossypium hirsutum L. cv. Xinluzao 45. In addition, we measured changes in the P515 signal and analyzed the activity of ATP synthase and the trans-thylakoid proton gradient (ΔpH). With increasing water deficit, the net CO₂ assimilation rate (A_N) and stomatal conductance (g_s) significantly decreased, but the maximum quantum efficiency of PSII photochemistry (F_v/F_m) did not change. The photochemical activity of photosystem II (PSII) was reflected by the photochemical quenching coefficient (qP), quantum efficiency of photosystem II [Y(II)], and electron transport rate through PSII [ETR(II)], while the activity of photosystem I (PSI) was reflected by the quantum efficiency of photosystem I [Y(I)] and the electron transport rate through PSI [ETR(I)]. Both activities were maintained under mild water deficit, but were slightly decreased under moderate water deficit. Under moderate water deficit, cyclic electron flow (CEF), the fraction of absorbed light dissipated thermally via the ΔpH- and xanthophyll-regulated process [Y(NPQ)], and the fraction of P700 oxidized under a given set of conditions [Y(ND)] increased. Our results suggest that the activities of both photosystems are stable under mild water deficit and decrease only slightly under moderate water deficit. Moderate water deficit stimulates CEF, and the stimulation of CEF is essential for protecting PSI and PSII against photoinhibition.

Culture density influence on the photosynthetic efficiency of microalgae growing under different spectral compositions of light

A density in algal suspension causes a significant change in the intensity and spectral composition of light reaching individual cells. Measurements of chlorophyll fluorescence allow us to observe any general changes in the bioenergetic status of photosynthesis. The aim of the study was to determine the effect of cultivation density on the PSII photochemical efficiency of three species of algae (Chlorella vulgaris, Botryococcus braunii and Chlorella emersonii), each with a different rate of growth - high, medium and low - respectively. The cell density of algae in suspension differentiated through the cultivation time (2, 4, and 8days) and the spectral composition of light. The results showed that the density of cultivation led to change in the photosynthetic apparatus of algae. The differences described between each day of cultivation (2, 4, and 8) in the kinetics of chlorophyll a fluorescence intensity in cells of the algal strains under study probably resulted from the different phases of growth of these cultures. In addition the results showed the beneficial effect of far red light on the photosynthetic apparatus and the growth of biomass in investigated algal strains.

Salt-stress-responsive chloroplast proteins in Brassica juncea genotypes with contrasting salt tolerance and their quantitative PCR analysis

Brassica juncea is mainly cultivated in the arid and semi-arid regions of India where its production is significantly affected by soil salinity. Adequate knowledge of the mechanisms underlying the salt tolerance at sub-cellular levels must aid in developing the salt-tolerant plants. A proper functioning of chloroplasts under salinity conditions is highly desirable to maintain crop productivity. The adaptive molecular mechanisms offered by plants at the chloroplast level to cope with salinity stress must be a prime target in developing the salt-tolerant plants. In the present study, we have analyzed differential expression of chloroplast proteins in two Brassica juncea genotypes, Pusa Agrani (salt-sensitive) and CS-54 (salt-tolerant), under the effect of sodium chloride. The chloroplast proteins were isolated and resolved using 2DE, which facilitated identification and quantification of 12 proteins that differed in expression in the salt-tolerant and salt-sensitive genotypes. The identified proteins were related to a variety of chloroplast-associated molecular processes, including oxygen-evolving process, PS I and PS II functioning, Calvin cycle and redox homeostasis. Expression analysis of genes encoding differentially expressed proteins through real time PCR supported our findings with proteomic analysis. The study indicates that modulating the expression of chloroplast proteins associated with stabilization of photosystems and oxidative defence plays imperative roles in adaptation to salt stress.

Remembering Joan (Jan) Mary Anderson (1932-2015)

Joan Mary Anderson, known to most people as Jan, was born on May 12, 1932 in Dunedin, New Zealand. She died on August 28, 2015 in Canberra, Australia. To celebrate her life, we present here a brief biography, some comments on her discoveries in photosynthesis during a career spanning more than half a century, and reminiscences from family and friends. We remember this wonderful person who had an unflagging curiosity, creative ability to think laterally, enthusiasm, passion, generosity and love of color and culture.

Powered by light: Phototrophy and photosynthesis in prokaryotes and its evolution

Photosynthesis is a complex metabolic process enabling photosynthetic organisms to use solar energy for the reduction of carbon dioxide into biomass. This ancient pathway has revolutionized life on Earth. The most important event was the development of oxygenic photosynthesis. It had a tremendous impact on the Earth's geochemistry and the evolution of living beings, as the rise of atmospheric molecular oxygen enabled the development of a highly efficient aerobic metabolism, which later led to the evolution of complex multicellular organisms. The mechanism of photosynthesis has been the subject of intensive research and a great body of data has been accumulated. However, the evolution of this process is not fully understood, and the development of photosynthesis in prokaryota in particular remains an unresolved question. This review is devoted to the occurrence and main features of phototrophy and photosynthesis in prokaryotes. Hypotheses concerning the origin and spread of photosynthetic traits in bacteria are also discussed.

The specific localizations of phosphorylated Lhcb1 and Lhcb2 isoforms reveal the role of Lhcb2 in the formation of the PSI-LHCII supercomplex in Arabidopsis during state transitions

State transitions are an important photosynthetic short-term response that maintains the excitation balance between photosystems I (PSI) and II (PSII). In plants, when PSII is preferentially excited, LHCII, the main heterotrimeric light harvesting complex of PSII, is phosphorylated by the STN7 kinase, detaches from PSII and moves to PSI to equilibrate the relative absorption of the two photosystems (State II). When PSI is preferentially excited LHCII is dephosphorylated by the PPH1 (TAP38) phosphatase, and returns to PSII (State I). Phosphorylation of LHCII that remain bound to PSII has also been observed. Although the kinetics of LHCII phosphorylation are well known from a qualitative standpoint, the absolute phosphorylation levels of LHCII (and its isoforms) bound to PSI and PSII have been little studied. In this work we thoroughly investigated the phosphorylation level of the Lhcb1 and Lhcb2 isoforms that compose LHCII in PSI-LHCII and PSII-LHCII supercomplexes purified from WT and state transition mutants of Arabidopsis thaliana. We found that, at most, 40% of the monomers that make up PSI-bound LHCII trimers are phosphorylated. Phosphorylation was much lower in PSII-bound LHCII trimers reaching only 15-20%. Dephosphorylation assays using a recombinant PPH1 phosphatase allowed us to investigate the role of the two isoforms during state transitions. Our results strongly suggest that a single phosphorylated Lhcb2 is sufficient for the formation of the PSI-LHCII supercomplex. These results are a step towards a refined model of the state transition phenomenon and a better understanding of the short-term response to changes in light conditions in plants.

Supramolecular nanostructures based on bacterial reaction center proteins and quantum dots

Design of the nanostructures based on membrane proteins (the key functional elements of biomembranes) and colloid nanoparticles is a fascinating field at the interface of biochemistry and colloids, nanotechnology and biomedicine. The review discusses the main achievements in the field of ultrathin films prepared from bacterial reaction center proteins and light-harvesting complexes, as well as these complexes tagged with quantum dots. The principles of preparation of these thin films and their structure and properties at different interfaces are described; as well as their characteristics estimated using a combination of the modern interfacial techniques (absorption and fluorescence spectroscopy, atomic force and Brewster angle microscopy, etc.) are discussed. Further approaches to develop the nanostructures based on the membrane proteins and quantum dots are suggested. These supramolecular nanostructures are promising prototypes of the materials for photovoltaic, optoelectronic and biosensing applications.

Assessment of photosystem II thermoluminescence as a tool to investigate the effects of dehydration and rehydration on the cyclic/chlororespiratory electron pathways in wheat and barley leaves

Thermoluminescence emission from wheat leaves was recorded under various controlled drought stress conditions: (i) fast dehydration (few hours) of excised leaves in the dark (ii) slow dehydration (several days) obtained by withholding watering of plants under a day/night cycle (iii) overnight rehydration of the slowly dehydrated plants at a stage of severe dessication. In fast dehydrated leaves, the AG band intensity was unchanged but its position was shifted to lower temperatures, indicating an activation of cyclic and chlororespiratory pathways in darkness, without any increase of their overall electron transfer capacity. By contrast, after a slow dehydration the AG intensity was strongly increased whereas its position was almost unchanged, indicating respectively that the capacity of cyclic pathways was enhanced but that they remained inactivated in darkness. Under more severe dehydration, the AG band almost disappeared. Rewatering caused its rapid bounce significantly above the control level. No significant differences in AG emission could be found between the two drought-sensitive and drought-tolerant wheat cultivars. The afterglow thermoluminescence emission in leaves provides an additional tool to follow the increased capacity and activation of cyclic electron flow around PSI in leaves during mild, severe dehydration and after rehydration.

Action spectra of photosystems II and I and quantum yield of photosynthesis in leaves in State 1

The spectral global quantum yield (YII, electrons/photons absorbed) of photosystem II (PSII) was measured in sunflower leaves in State 1 using monochromatic light. The global quantum yield of PSI (YI) was measured using low-intensity monochromatic light flashes and the associated transmittance change at 810nm. The 810-nm signal change was calibrated based on the number of electrons generated by PSII during the flash (4·O2 evolution) which arrived at the PSI donor side after a delay of 2ms. The intrinsic quantum yield of PSI (yI, electrons per photon absorbed by PSI) was measured at 712nm, where photon absorption by PSII was small. The results were used to resolve the individual spectra of the excitation partitioning coefficients between PSI (aI) and PSII (aII) in leaves. For comparison, pigment-protein complexes for PSII and PSI were isolated, separated by sucrose density ultracentrifugation, and their optical density was measured. A good correlation was obtained for the spectral excitation partitioning coefficients measured by these different methods. The intrinsic yield of PSI was high (yI=0.88), but it absorbed only about 1/3 of quanta; consequently, about 2/3 of quanta were absorbed by PSII, but processed with the low intrinsic yield yII=0.63. In PSII, the quantum yield of charge separation was 0.89 as detected by variable fluorescence Fv/Fm, but 29% of separated charges recombined (Laisk A, Eichelmann H and Oja V, Photosynth. Res. 113, 145-155). At wavelengths less than 580nm about 30% of excitation is absorbed by pigments poorly connected to either photosystem, most likely carotenoids bound in pigment-protein complexes.