Photosynthetic Energy Production Research Articles

Quantifying the roles of algal photosynthetic electron pathways: a milestone towards photosynthetic robustness.

During photosynthesis, electron transport reactions generate and shuttle reductant to allow CO2 reduction by the Calvin-Benson-Bassham cycle and the formation of biomass building block in the so-called linear electron flow (LEF). However, in nature, environmental parameters like light intensity or CO2 availability can vary and quickly change photosynthesis rates, creating an imbalance between photosynthetic energy production and metabolic needs. In addition to LEF, alternative photosynthetic electron flows are central to allow photosynthetic energy to match metabolic demand in response to environmental variations. Microalgae arguably harbour one of the most diverse set of alternative electron flows (AEFs), including cyclic (CEF), pseudocyclic (PCEF) and chloroplast-to-mitochondria (CMEF) electron flow. While CEF, PCEF and CMEF have large functional overlaps, they differ in the conditions they are active and in their role for photosynthetic energy balance. Here, I review the molecular mechanisms of CEF, PCEF and CMEF in microalgae. I further propose a quantitative framework to compare their key physiological roles and quantify how the photosynthetic energy is partitioned to maintain a balanced energetic status of the cell. Key differences in AEF within the green lineage and the potential of rewiring photosynthetic electrons to enhance plant robustness will be discussed.

Biotoxicity of NH4+ on Nostoc Sphaeroides (diazotrophic cyanobacteria) in paddy floodwater

In order to elucidate the toxicity of NH4+ on Nostoc Sphaeroides (commonly named GE-XIAN-MI in China, GXM), a diazotrophic cyanobacterium in paddy fields, this study investigated the growth, photosynthesis, N2-fixation, and oxidative-antioxidative characteristics of GXM under NH4+ stress in paddy floodwater. The results showed that the photosynthesis and the N2-fixing ability of GXM were inhibited by NH4+ at a concentration of 13.46 mg L-1 in paddy floodwater. The main target of NH4+ on photosystem II (PS II) of GXM was the electron donor side of react center. Oxygen evolution complex (OEC) was the secondary target of toxicity of NH4+ on PS II. The damage of PS II led to accumulation of ROS and resulted in oxidative damage on plasma membrane of GXM. Feedback inhibition and decrease of photosynthetic energy production may be the reasons for the decrease of N2-fixing ability of GXM under NH4+ stress. The results presented in this study suggest that high level of NH4+ loading may be a reason for the recession of GXM resource in paddy fields.

Resource allocation in Chlamydomonas reinhardtii exposed to sulphur starvation and anaerobiosis

ABSTRACT When environmental conditions change, microalgae can modulate the size of their macromolecular pools and their elemental composition in order to accommodate their nutritional and energetic demands. In this context, we evaluated how O2 levels and S starvation alter the resource partitioning in terms of organic and elemental composition in Chlamydomonas reinhardtii. The analysis of gene transcription, photosynthetic energy production and organic pool allocation allowed us to identify a two-phase cellular response related to external O2 concentration: (1) a short-term response where S starvation induced the expression of S starvation genes immediately after the start of the perturbation; (2) a long-term response that consisted of a drastic reduction of photosynthetic energy production and changes in C allocation following S deprivation, which was related to oxygen conditions. In anaerobic conditions, S starvation did not affect the pools of carbohydrates and lipids, whereas the protein pool decreased slightly over time. On the other hand, in aerobic conditions, S starvation modulated all organic pools: carbohydrates, lipids and proteins. We conclude that the energy levels produced by fermentation metabolism are not sufficient to sustain the acclimation process in C. reinhardtii; moreover, S availability affects C. reinhardtii more than do oxygen levels.

Diclofenac and atrazine restrict the growth of a synchronous Chlamydomonas reinhardtii population via various mechanisms

Non-steroidal anti-inflammatory drug diclofenac (DCF) is commonly found in freshwater bodies and can have adverse effects on non-target organisms. Among the studies on DCF toxicity, several ones have reported its harmful effects on plants and algae. To gain a better understanding of the mechanisms of DCF toxicity towards green algae, we used a synchronous Chlamydomonas reinhardtii cc-1690 culture and compared DCF (135 mg/L) effects with effects caused by atrazine (ATR; 77.6 μg/L), an herbicide with a well-known mechanism of toxic action. To achieve our goal, cell number and size, photosynthetic oxygen consumption/evolution, chlorophyll a fluorescence in vivo, H2O2 production by the cells, antioxidative enzymes encoding genes expression were analyzed during light phase of the cell cycle.We have found, that DCF and ATR affect C. reinhardtii through different mechanisms. ATR inhibited the photosynthetic electron transport chain and induced oxidative stress in chloroplast. Such chloroplastic energetics disruption indirectly influenced respiration, the intensification of which could partially mitigate low efficiency of photosynthetic energy production. As a result, ATR inhibited the growth of single cell leading to limitation in C. reinhardtii population development. In contrast to ATR-treated algae, in DCF-treated cells the fraction of active PSII reaction centers was diminished without drastic changes in electron transport or oxidative stress symptoms in chloroplast. However, significant increase in transcript level of gene encoding for mitochondria-located catalase indicates respiratory processes as a source of H2O2 overproduced in the DCF-treated cells. Because the single cell growth was not strongly affected by DCF, its adverse effect on progeny cell number seemed to be related rather to arresting of cell divisions. Concluding, although the DCF phytotoxic action appeared to be different from the action of the typical herbicide ATR, it can act as algal growth-inhibiting factor in the environment.

Antarctic root endophytes improve physiological performance and yield in crops under salt stress by enhanced energy production and Na+ sequestration

Climatic change is pointed as one of the major challenges for global food security. Based on current models of climate change, reduction in precipitations and in turn, increase in the soil salinity will be a sharp constraint for crops productivity worldwide. In this context, root fungi appear as a new strategy to improve plant ecophysiological performance and crop yield under abiotic stress. In this study, we evaluated the impact of the two fungal endophytes Penicillium brevicompactum and P. chrysogenum isolated from Antarctic plants on nutrients and Na+ contents, net photosynthesis, water use efficiency, yield and survival in tomato and lettuce, facing salinity stress conditions. Inoculation of plant roots with fungal endophytes resulted in greater fresh and dry biomass production, and an enhanced survival rate under salt conditions. Inoculation of plants with the fungal endophytes was related with a higher up/down-regulation of ion homeostasis by enhanced expression of the NHX1 gene. The two endophytes diminished the effects of salt stress in tomato and lettuce, provoked a higher efficiency in photosynthetic energy production and an improved sequestration of Na+ in vacuoles is suggested by the upregulating of the expression of vacuolar NHX1 Na+/H+ antiporters. Promoting plant-beneficial interactions with root symbionts appears to be an environmentally friendly strategy to mitigate the impact of climate change variables on crop production.

Roles of the Clock in Controlling Starch Metabolism.

Plants are photoautotrophs that grow via photosynthetic energy production. Under irradiation, chloroplasts in the plant’s green tissues convert light energy to chemical energy and assimilate atmospheric CO2 into sugars to support growth. Plants do not stop growing during the night, though: they

An additional role for chloroplast proteins—an amino acid reservoir for energy production during sugar starvation

ABSTRACTAutophagy is an evolutionarily conserved system that degrades intracellular components including proteins and organelles, and is important in the adaptive response to starvation in various eukaryotic organisms. Plant chloroplasts convert light energy into chemical energy and assimilate atmospheric carbon dioxide (CO2) for carbohydrate production through photosynthesis reactions. We previously described an autophagy process for chloroplast degradation, during which a portion of chloroplasts are mobilized into the vacuole via autophagic vesicles termed Rubisco-containing bodies. Our recent study demonstrated that the activation of autophagy in photoassimilate-limited leaves is required for the production of free amino acids (AAs) as an alternative energy source. The catabolism of free branched-chain amino acids (BCAAs) is particularly important for survival under starvation conditions. These recent findings suggest an additional role for chloroplasts as a reservoir of AA when photosynthetic energy production is limited.

Regulation of Chlorophagy during Photoinhibition and Senescence: Lessons from Mitophagy.

Light energy is essential for photosynthetic energy production and plant growth. Chloroplasts in green tissues convert energy from sunlight into chemical energy via the electron transport chain. When the level of light energy exceeds the capacity of the photosynthetic apparatus, chloroplasts undergo a process known as photoinhibition. Since photoinhibition leads to the overaccumulation of reactive oxygen species (ROS) and the spreading of cell death, plants have developed multiple systems to protect chloroplasts from strong light. Recent studies have shown that autophagy, a system that functions in eukaryotes for the intracellular degradation of cytoplasmic components, participates in the removal of damaged chloroplasts. Previous findings also demonstrated an important role for autophagy in chloroplast turnover during leaf senescence. In this review, we describe the turnover of whole chloroplasts, which occurs via a type of autophagy termed chlorophagy. We discuss a possible regulatory mechanism for the induction of chlorophagy based on current knowledge of photoinhibition, leaf senescence and mitophagy-the autophagic turnover of mitochondria in yeast and mammals.

Trade-Off between Growth and Carbohydrate Accumulation in Nutrient-Limited Arthrospira sp. PCC 8005 Studied by Integrating Transcriptomic and Proteomic Approaches.

Cyanobacteria have a strong potential for biofuel production due to their ability to accumulate large amounts of carbohydrates. Nitrogen (N) stress can be used to increase the content of carbohydrates in the biomass, but it is expected to reduce biomass productivity. To study this trade-off between carbohydrate accumulation and biomass productivity, we characterized the biomass productivity, biomass composition as well as the transcriptome and proteome of the cyanobacterium Arthrospira sp. PCC 8005 cultured under N-limiting and N-replete conditions. N limitation resulted in a large increase in the carbohydrate content of the biomass (from 14 to 74%) and a decrease in the protein content (from 37 to 10%). Analyses of fatty acids indicated that no lipids were accumulated under N-limited conditions. Nevertheless, it did not affect the biomass productivity of the culture up to five days after N was depleted from the culture medium. Transcriptomic and proteomic analysis indicated that de novo protein synthesis was down-regulated in the N-limited culture. Proteins were degraded and partly converted into carbohydrates through gluconeogenesis. Cellular N derived from protein degradation was recycled through the TCA and GS-GOGAT cycles. In addition, photosynthetic energy production and carbon fixation were both down-regulated, while glycogen synthesis was up-regulated. Our results suggested that N limitation resulted in a redirection of photosynthetic energy from protein synthesis to glycogen synthesis. The fact that glycogen synthesis has a lower energy demand than protein synthesis might explain why Arthrospira is able to achieve a similar biomass productivity under N-limited as under N-replete conditions despite the fact that photosynthetic energy production was impaired by N limitation.

Directed Evolution of Bacteriorhodopsin for Device Applications

Publisher Summary This chapter discusses the use of directed evolution of bacteriorhodopsin (BR) for device applications. This protein is synthesized by the salt marsh archaeon Halobacterium salinarum when oxygen availability drops below a level sufficient to sustain respiration. The organism then switches spontaneously to photosynthetic energy production by generating a purple membrane containing BR. It is found that when BR absorbs light it pumps a proton, and the pH gradient is utilized to convert ADP to ATP. Site-directed mutants are constructed using the Stratagene Quik-Change mutagenesis system. Construction of BR variants for expression in T. thermophilus is achieved using a combination of mutagenesis methods. Inserting mutant bop fragments into the multiple cloning site of pMKE1 is the final step in the construction of a BR thermoselection vector. A combination of mutagenesis techniques are used to create randomly mutated regions in the bop gene. It is found that the thermal stability of BR is achieved by expressing randomly mutated proteins in an extremely thermophilic background.

An energy budget for Porites porites (Scleractinia), growing in a stressed environment

An energy budget was determined for the coral Porites porites living in a stressed environment for comparison of the energy inputs and expenditure with those of the same species living in an adjacent clear water fore reef environment. The stressed site was characterised by higher sedimentation and lower irradiances than at the fore reef site. Zooplankton ingestion was found to be an insignificant component of the energy intake: the coral is fully autotrophic under stress conditions. The integrated 24 h rate of photosynthetic energy production on a clear sunny day was 20% higher for stressed corals compared to fore reef corals. This was largely the result of photoadaptation which resulted in increased values for α and decreased values for Ik in the hyperbolic tangent function equation for the photosynthesis versus irradiance curve. The energy investment in growth of animal tissue was lower in stressed corals. The percentage translocation of photosynthase to the animal tissue remained at about 78%, but the respiration rate of the animal tissue was reduced by 3 fold. These data combined with the high rate of photosynthetic production predict a net daily energy surplus of 67% in stressed corals compared with the 45% surplus in unstressed corals. Scope for growth is reduced under stress conditions.

Protein processing as a regulatory mechanism in the synthesis of the photosynthetic antenna in Chloroflexus

Chloroflexus aurantiacus can be induced to shift from respiratory to photosynthetic energy production by introducing light and/or lowering the oxygen concentration of a culture. After induction, cells synthesize bacteriochlorophyll and proteins for the formation of a functional photosynthetic apparatus. Bacteriochlorophyll is detectable within 2 h after induction. Chlorosome polypeptides are detected after 8–12 h. Two proteins, Mr 60,000 and Mr 47,000, are present in both induced and noninduced cells and react specifically with antibodies against chlorosome polypeptides. Immunological data suggest that these proteins (Mr 60,000 and 47,000) are polyproteins which are transcribed and translated in the dark. When cells are exposed to light or low oxygen tension these proteins are processed into functional polypeptides required in the assembly of the chlorosome. The reaction center polypeptide (Mr 26,000) appears to be part of a separate genetic control system.

The roots of bioenergetics.

Understanding metabolic energy transformation began with the realization of an 'intrusion' of phosphate into the mechanism of alcoholic fermentation. The discovery of an analogous participation of phosphate in muscle glycolysis connected the metabolic generation of energy-rich phosphate bonds fed into a common transmitter, adenosine triphosphate (ATP), with the production of mechanical energy through the finding that the phosphoryl group of creatine phosphate transferred to ATP could supply the energy for muscle contraction. In this way, a functional applicability of the energy of the phosphate bond was first shown. This observation was soon followed by the recognition that the phosphoanhydride bond of ATP provided the driving force in biosynthetic reactions; in this type of bond, metabolic energy apparently collects before it is transmitted for functional and biosynthetic use. The storage of energy in ATP was first detected in anaerobic energy-yielding reactions but soon was also found in respiratory and photosynthetic energy production. However, the mechanism by which energy derived from metabolites was converted into phosphate-bond energy in the latter processes appeared to differ from that of anaerobic energy transmission. Whereas phosphorylated compounds mediate the latter in homogeneous solutions, aerobic phosphorylation and photophosphorylation in prokaryotes seem to require special submembranous structures; and in eukaryotes, energy conversion is a function of special organelles, the mitochondria and chloroplasts. The evolutionary aspects of the transition from prokaryotes to eukaryotes are of considerable interest. In conclusion, the relevance of an apparent prokaryotic origin of the energy-transforming organelles in the eukaryotes will be commented on.