1,721,074 research outputs found
The functional organization of Plant Photosystems: biochemical and spectroscopic analysis of the role of antenna proteins in photoprotection and acclimation to environmental conditions
No full textnon disponibilePhotosynthesis is the process by which plants absorb solar energy and convert it to chemical energy to produce biomass.
During this process some key functions are carried out by Photosystems. Photosystems I and II are the multiproteic
complexes responsible for light harvesting, charge separation, and electron transport from water to NADPH. These
events leads to the formation of a transmembrane ΔpH that is used by ATP-ases enzymes to produce ATP. PSI and PSII
represent extraordinary machines for solar energy use, combining high quantum efficiency and the presence of
inducible mechanisms in order to avoid photoinhibition.
The peculiar organization of Photosystems is determinant for their functions. Both photosystems are composed by two
moieties: a core complex and an antenna system constituted by the conserved Lhc proteins. This thesis focused into
investigation of the functional organization of photosystems I (PSI) and II (PSII) using biochemical and spectroscopic
methods. The role of the different Lhc subunits and the role of the specific pigments bound to them have been
investigated through evaluation of basic functional properties of PSI and PSII, as the efficiency of light harvesting,
stabilility and/or dynamic of the supercomplexes, mode of adaptation to different environmental conditions and
activation of photoprotective mechanisms. We conclude that PSI and PSII strongly differs with respect to many
fundamental properties of their mode of long term acclimation and short term protection to harmful conditions.
However, at least one mechanism, namely chlorophyll triplet quenching, appears to be regulated in the same way in
both
Increased biomass productivity in green algae by tuning non-photochemical quenching
Full text linkPhotosynthetic microalgae have a high potential for the production of biofuels and highly valued metabolites. However, their current industrial exploitation is limited by a productivity in photobioreactors that is low compared to potential productivity. The high cell density and pigment content of the surface layers of photosynthetic microalgae result in absorption of excess photons and energy dissipation through non-photochemical quenching (NPQ). NPQ prevents photoinhibition, but its activation reduces the efficiency of photosynthetic energy conversion. In Chlamydomonas reinhardtii, NPQ is catalyzed by protein subunits encoded by three lhcsr (light harvesting complex stress related) genes. Here, we show that heat dissipation and biomass productivity depends on LHCSR protein accumulation. Indeed, algal strains lacking two lhcsr genes can grow in a wide range of light growth conditions without suffering from photoinhibition and are more productive than wild-type. Thus, the down-regulation of NPQ appears to be a suitable strategy for improving light use efficiency for biomass and biofuel production in microalgae
High Light-Dependent Phosphorylation of Photosystem II Inner Antenna CP29 in Monocots Is STN7 Independent and Enhances Nonphotochemical Quenching
No full textPhosphorylation of the photosystem II antenna protein CP29 has been reported to be induced by excess light and further enhanced by low temperature, increasing resistance to these stressing factors. Moreover, high light-induced CP29 phosphorylation was specifically found in monocots, both C3 and C4, which include the large majority of food crops. Recently, knockout collections have become available in rice (Oryza sativa), a model organism for monocots. In this work, we have used reverse genetics coupled to biochemical and physiological analysis to elucidate the molecular basis of high light-induced phosphorylation of CP29 and the mechanisms by which it exerts a photoprotective effect. We found that kinases and phosphatases involved in CP29 phosphorylation are distinct from those reported to act in State 1-State 2 transitions. In addition, we elucidated the photoprotective role of CP29 phosphorylation in reducing singlet oxygen production and enhancing excess energy dissipation. We thus established, in monocots, a mechanistic connection between phosphorylation of CP29 and nonphotochemical quenching, two processes so far considered independent from one another
Chlamydomonas reinhardtii LHCSR1 and LHCSR3 proteins involved in photoprotective non-photochemical quenching have different quenching efficiency and different carotenoid affinity
No full textMicroalgae are unicellular photosynthetic organisms considered as potential alternative sources for biomass, biofuels or high value products. However, their limited biomass productivity represents a bottleneck that needs to be overcome to meet the applicative potential of these organisms. One of the domestication targets for improving their productivity is the proper balance between photoprotection and light conversion for carbon fixation. In the model organism for green algae, Chlamydomonas reinhardtii, a photoprotective mechanism inducing thermal dissipation of absorbed light energy, called Non-photochemical quenching (NPQ), is activated even at relatively low irradiances, resulting in reduced photosynthetic efficiency. Two pigment binding proteins, LHCSR1 and LHCSR3, were previously reported as the main actors during NPQ induction in C. reinhardtii. While previous work characterized in detail the functional properties of LHCSR3, few information is available for the LHCSR1 subunit. Here, we investigated in vitro the functional properties of LHCSR1 and LHCSR3 subunits: despite high sequence identity, the latter resulted as a stronger quencher compared to the former, explaining its predominant role observed in vivo. Pigment analysis, deconvolution of absorption spectra and structural models of LHCSR1 and LHCR3 suggest that different quenching efficiency is related to a different occupancy of L2 carotenoid binding site
Valorization of wastewater from industrial hydroponic cultivations using the microalgal species Chlorella vulgaris
Full text linkThe continuous increase in the world population is associated with a greater demand for food. This need has driven the development of new cultivation systems capable of producing large quantities of vegetable biomass in a small space, with precise and regulated control of the use of resources. Among these, vertical farms are systems developed in height, and they produce continuously throughout the year.
The hydroponic system is commonly used in vertical farming and entails the growth of plants in a solution rich in nutrients, easily assimilated by plants. However, hydroponic solutions still contain nutrient salts at the end of the productive cycle. Consequently, spent hydroponic solutions cannot be directly released into the environment because they would cause water pollution. Thus, they need to be appropriately treated, increasing production costs.
Microalgae represent a cost-effective solution for treating and valorizing hydroponic wastewater. They can easily consume the residual nutrients, generating valuable biomass that can be exploited as a biofertilizer, a biostimulant, or even as a valuable food supplement.
The present work showed the ability of the model eukaryotic microalga Chlorella vulgaris to use valuable resources derived from industrial cultivations of basil and tobacco in a hydroponic deep-water culture system. Although the use of spent hydroponic solutions slightly affected the microalgal biomass accumulation of more than ~40 % compared to the fresh solution, possibly due to the presence of root exudates that have an antagonistic effect toward microalgae, the phytoremediation activity of microalgae was achieved. The reported results described the consumption of more than 80 % and 70 % of P and N residual nutrients in hydroponic formulations, respectively. Moreover, more than 2 g/L of microalgal biomass was generated after 7 days of growth in air-lifted photobioreactors. The outcomes of this research provide new insights toward greater sustainability of vertical farming, following circular economy principles
Dynamics of zeaxanthin binding to the photosystem II monomeric antenna protein Lhcb6 (CP24) and modulation of its photoprotection properties.
No full textLhcb6 (CP24) is a monomeric antenna protein of photosystem II, which has been shown to play special roles in photoprotective mechanisms, such as the Non-Photochemical Quenching and reorganization of grana membranes in excess light conditions. In this work we analyzed Lhcb6 in vivo and in vitro: we show this protein, upon activation of the xanthophyll cycle, accumulates zeaxanthin into inner binding sites faster and to a larger extent than any other pigment-protein complex. By comparative analysis of Lhcb6 complexes violaxanthin or zeaxanthin binding, we demonstrate that zeaxanthin not only down-regulates chlorophyll singlet excited states, but also increases the efficiency of chlorophyll triplet quenching, with consequent reduction of singlet oxygen production and significant enhancement of photo-stability. On these bases we propose that Lhcb6, the most recent addition to the Lhcb protein family which evolved concomitantly to the adaptation of photosynthesis to land environment, has a crucial role in zeaxanthin-dependent photoprotection
Regulation of plant light harvesting by thermal dissipation of excess energy
No full textElucidating the molecular details of qE induction in higher plants has proven to be a major challenge. Identification of qE mutants provided initial information on functional elements involved in the energy quenching mechanism; furthermore, investigations on isolated pigment-protein complexes and the analysis in vivo and in vitro by sophisticated spectroscopic methods, have been used for elucidation of mechanisms involved. The aim of this review is to summarize the current knowledge on the phenotype of npq knockout mutants, the role of gene products involved in the energy quenching process and compare the molecular models proposed for this process
Chlorophyll triplet quenching and photoprotection in the higher plant monomeric antenna protein Lhcb5.
No full textIn oxygenic photosynthetic organisms, chlorophyll triplets are harmful excited states readily reacting with molecular oxygen to yield the reactive oxygen species (ROS) singlet oxygen. Carotenoids have a photoprotective role in photosynthetic membranes by preventing photoxidative damage through quenching of chlorophyll singlets and triplets. In this work we used mutation analysis to investigate the architecture of chlorophyll triplet quenching sites within Lhcb5, a monomeric antenna protein of Photosystem II. The carotenoid and chlorophyll triplet formation as well as the production of ROS molecules were studied in a family of recombinant Lhcb5 proteins either with WT sequence, mutated into individual chlorophyll binding residues or refolded in vitro to bind different xanthophyll complements. We observed a site-specific effect in the efficiency of chlorophyll-carotenoid triplet-triplet energy transfer. Thus chlorophyll (Chl) 602 and 603 appear to be particularly important for triplet-triplet energy transfer to the xanthophyll bound into site L2. Surprisingly, mutation on Chl 612, the chlorophyll with the lower energy associated and in close contact with lutein in site L1, had no effect on quenching chlorophyll triplet excited states. Finally, we present evidence for an indirect role of neoxanthin in chlorophyll triplet quenching and show that quenching of both singlet and triplet states is necessary for minimizing singlet oxygen formation
Heterologous expression of cyanobacterial Orange Carotenoid Protein (OCP2) as a soluble carrier of ketocarotenoids in Chlamydomonas reinhardtii
Full text linkPhotosynthetic organisms evolved different mechanisms to protect themselves from high irradiances and photodamage. In cyanobacteria, the photoactive Orange Carotenoid-binding Protein (OCP) acts both as a light sensor and quencher of excitation energy. It binds keto-carotenoids and, when photoactivated, interacts with phycobilisomes, thermally dissipating the excitation energy absorbed by the latter, and acting as efficient singlet oxygen quencher. Here, we report the heterologous expression of an OCP2 protein from the thermophilic cyanobacterium Fischerella thermalis (FtOCP2) in the model organism for green algae, Chlamydomonas reinhardtii. Robust expression of FtOCP2 was obtained through a synthetic redesigning strategy for optimized expression of the transgene. FtOCP2 expression was achieved both in UV-mediated mutant 4 strain, previously selected for efficient transgene expression, and in a background strain previously engineered for constitutive expression of an endogenous β-carotene ketolase, normally poorly expressed in this species, resulting into astaxanthin and other ketocarotenoids accumulation. Recombinant FtOCP2 was successfully localized into the chloroplast. Upon purification it was possible to demonstrate the formation of holoproteins with different xanthophylls and ketocarotenoids bound, including astaxanthin. Moreover, isolated ketocarotenoid-binding FtOCP2 holoproteins conserved their photoconversion properties. Carotenoids bound to FtOCP2 were thus maintained in solution even in absence of organic solvent. The synthetic biology approach herein reported could thus be considered as a novel tool for improving the solubility of ketocarotenoids produced in green algae, by binding to water-soluble carotenoids binding proteins
The Living Concrete Experiment: Cultivation of Photosynthetically Active Microalgal on Concrete Finish Blocks
Full text linkClimate change is a global critical issue. High carbon dioxide emissions and concentrations
are important factors. In the construction field, concrete contributes significantly to greenhouse
gas emissions. Therefore, a pioneering team of researchers has developed a new “living concrete”
construction finish material capable of scrubbing carbon dioxide from the atmosphere. The material
consists of ASTM (ASTM is the acronym for American Society for TestingMaterials)-certified concrete
block(s) with Chlorella vulgaris cultivated on the surface. Chlorella vulgaris is a common micro-algae
with photosynthetic activity; these species require water, nutrients, light, and carbon dioxide to
live while releasing oxygen in return. The “living concrete” block was developed in dedicated
laboratories; its photosynthetic activity was quantified. Proposed as an external application assembly
to a new or an existing building envelope—up to 3 m high, i.e., anthropogenic street-level emissions,
or installed on roof(s) in horizontal mode—this concrete/biological composite material reverses
carbon dioxide emissions and may present itself as a valid solution for climate change issues in urban
moderate climates
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