scholarly journals Acclimation of leaves to low light produces large grana: the origin of the predominant attractive force at work

2012 ◽  
Vol 367 (1608) ◽  
pp. 3494-3502 ◽  
Author(s):  
Husen Jia ◽  
John R. Liggins ◽  
Wah Soon Chow
Keyword(s):  
Thylakoid Membranes ◽  
Enthalpy Change ◽  
Attractive Force ◽  
Gibbs Free Energy Change ◽  
Photosynthetic Membrane ◽  
Low Light ◽  
Cyclic Photophosphorylation ◽  
Thylakoid Stacking ◽  
Endothermic Process ◽  
Fine Tune

Photosynthetic membrane sacs (thylakoids) of plants form granal stacks interconnected by non-stacked thylakoids, thereby being able to fine-tune (i) photosynthesis, (ii) photoprotection and (iii) acclimation to the environment. Growth in low light leads to the formation of large grana, which sometimes contain as many as 160 thylakoids. The net surface charge of thylakoid membranes is negative, even in low-light-grown plants; so an attractive force is required to overcome the electrostatic repulsion. The theoretical van der Waals attraction is, however, at least 20-fold too small to play the role. We determined the enthalpy change, in the spontaneous stacking of previously unstacked thylakoids in the dark on addition of Mg 2+ , to be zero or marginally positive (endothermic). The Gibbs free-energy change for the spontaneous process is necessarily negative, a requirement that can be met only by an increase in entropy for an endothermic process. We conclude that the dominant attractive force in thylakoid stacking is entropy-driven. Several mechanisms for increasing entropy upon stacking of thylakoid membranes in the dark, particularly in low-light plants, are discussed. In the light, which drives the chloroplast far away from equilibrium, granal stacking accelerates non-cyclic photophosphorylation, possibly enhancing the rate at which entropy is produced.

The thylakoid membranes of cyanobacteria: structure, dynamics and function

1999 ◽  
Vol 26 (7) ◽  
pp. 671 ◽  
Author(s):  
Conrad W. Mullineaux
Keyword(s):  
Genetic Manipulation ◽  
Three Dimensional ◽  
Thylakoid Membranes ◽  
Model Systems ◽  
Photosynthetic Membrane ◽  
Membrane Function ◽  
Intact Membrane ◽  
Photosynthetic Organism ◽  
Dynamics And Function ◽  
And Function

In recent years there has been remarkable progress in determining the three-dimensional structures of photosynthetic complexes. A new challenge is emerging: can we understand the organisation and interaction of those complexes in the intact photosynthetic membrane? Intact membranes are complex, dynamic systems. If we are to understand the function of the intact membrane, we will need to understand the organisation of the complexes, how they can diffuse and interact in the membrane, how they are assembled, repaired and broken down, and how their function is regulated. Cyanobacteria have some crucial advantages as model systems. The complete sequencing of the Synechocystis 6803 genome, coupled with the ease of genetic manipulation of Synechocystis (and certain other cyanobacteria) have given us a unique tool for studying a photosynthetic organism. Furthermore, some cyanobacteria have a very simple, regular thylakoid membrane structure. The unique geometry of photosynthetic membranes of these cyanobacteria will greatly facilitate biophysical studies of membrane function. This review summarises recent progress in understanding the structure, function and dynamics of cyanobacterial thylakoid membranes, highlights the questions that remain to be answered and suggests some possible approaches towards solving those questions.

scholarly journals Equilibrium and thermodynamic studies of stearic acid adsorption on Celtek clay

2007 ◽  
Vol 72 (5) ◽  
pp. 485-494 ◽  
Author(s):  
Ahmet Sari ◽  
Mustafa Soylak
Keyword(s):  
Free Energy ◽  
Stearic Acid ◽  
Thermodynamic Parameters ◽  
Enthalpy Change ◽  
Isotherm Models ◽  
Gibbs Free Energy Change ◽  
Linear Forms ◽  
Considerable Potential ◽  
Olive Oils ◽  
Increasing Temperature

This paper presents the equilibrium and thermodynamic parameters of the adsorption of stearic acid on Celtek clay as a function of temperature. It was found that the adsorption of stearic acid on Celtek clay decreased with increasing temperature from 293 to 313 K. The equilibrium modelled data fitted well with the linear forms of both the Langmuir and the Freundlich models (R2 = 0.99 in both cases). The R L and 1/n values determined from the isotherm models proved that Celtek clay is a suitable adsorbent for stearic acid. The Dubinin-Radushkevich (D-R) isotherm was applied to describe the nature of the adsorption of stearic acid on Celtek clay and it was found that the adsorption occurred physically. Thermodynamic parameters of adsorption, such as Gibbs free energy change (?G0), enthalpy change (?H0) and enthropy change (?S0) were also calculated. These parameters showed that the adsorption of stearic acid on Celtek clay was feasible, spontaneous, and exothermic in nature. On the basis of the results, it can be concluded that Celtek clay has considerable potential for the removal of stearic acid from the main sources, such as raw and edible soybean, sunflower and olive oils.

scholarly journals High-Light versus Low-Light: Effects on Paired Photosystem II Supercomplex Structural Rearrangement in Pea Plants

2020 ◽  
Vol 21 (22) ◽  
pp. 8643
Author(s):  
Alessandro Grinzato ◽  
Pascal Albanese ◽  
Roberto Marotta ◽  
Paolo Swuec ◽  
Guido Saracco ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Photosystem Ii ◽  
Structural Rearrangement ◽  
Structural Features ◽  
Thylakoid Membranes ◽  
Variable Number ◽  
High Light ◽  
Low Light ◽  
Cryo Electron Microscopy ◽  
Light Effects

In plant grana thylakoid membranes Photosystem II (PSII) associates with a variable number of antenna proteins (LHCII) to form different types of supercomplexes (PSII-LHCII), whose organization is dynamically adjusted in response to light cues, with the C2S2 more abundant in high-light and the C2S2M2 in low-light. Paired PSII-LHCII supercomplexes interacting at their stromal surface from adjacent thylakoid membranes were previously suggested to mediate grana stacking. Here, we present the cryo-electron microscopy maps of paired C2S2 and C2S2M2 supercomplexes isolated from pea plants grown in high-light and low-light, respectively. These maps show a different rotational offset between the two supercomplexes in the pair, responsible for modifying their reciprocal interaction and energetic connectivity. This evidence reveals a different way by which paired PSII-LHCII supercomplexes can mediate grana stacking at diverse irradiances. Electrostatic stromal interactions between LHCII trimers almost completely overlapping in the paired C2S2 can be the main determinant by which PSII-LHCII supercomplexes mediate grana stacking in plants grown in high-light, whereas the mutual interaction of stromal N-terminal loops of two facing Lhcb4 subunits in the paired C2S2M2 can fulfil this task in plants grown in low-light. The high-light induced accumulation of the Lhcb4.3 protein in PSII-LHCII supercomplexes has been previously reported. Our cryo-electron microscopy map at 3.8 Å resolution of the C2S2 supercomplex isolated from plants grown in high-light suggests the presence of the Lhcb4.3 protein revealing peculiar structural features of this high-light-specific antenna important for photoprotection.

scholarly journals Adsorption of U(VI) from Aqueous Solution onto Hydrotalcite-Like Compounds

2012 ◽  
Vol 9 (2) ◽  
pp. 669-679 ◽  
Author(s):  
Nguyen Van Suc
Keyword(s):  
Adsorption Capacity ◽  
Enthalpy Change ◽  
Time Dependent ◽  
Freundlich Isotherms ◽  
Langmuir And Freundlich Isotherms ◽  
Equilibrium Data ◽  
Endothermic Process ◽  
Ph Range ◽  
Initial Adsorption ◽  
Hydroxide Hydrate

Uranium adsorption by the synthesized compound of magnesium aluminum hydroxide hydrate – layered double hydrotalcite (STH)-like compounds was studied. The calcinated STH was proven to be a highly effective in U(VI) adsorption in pH range from 6.5 to 7. The time dependent experimental data were found to be fit to the pseudo-second-oder model. The equilibrium data have been modeled using Langmuir and Freundlich isotherms. The results showed that both model provide the best correlation with equilibrium data. The highest adsorption capacity, approximated 62.5 mg/g, was observed in the calcinated STH at 500 °C. The positive value of enthalpy change indicated that adsorption reaction of U(VI) on STH was endothermic process. The regeneration experiments of STH using 0.1M Na2CO3solution was successfully demonstrated multiple times without any significant effect on the initial adsorption capacity.

Removal of 4-nitrophenol from aqueous solution by adsorption onto activated carbon prepared from Acacia glauca sawdust

2015 ◽  
Vol 73 (4) ◽  
pp. 955-966 ◽  
Author(s):  
Prashant T. Dhorabe ◽  
Dilip H. Lataye ◽  
Ramakant S. Ingole
Keyword(s):  
Aqueous Solution ◽  
Activated Carbon ◽  
Adsorption Process ◽  
Enthalpy Change ◽  
Optimum Dose ◽  
Batch Adsorption ◽  
Gibbs Free Energy Change ◽  
Pseudo Second Order ◽  
Percentage Removal ◽  
Maximum Removal

The present paper deals with a complete batch adsorption study of 4-nitrophenol (4NP) from aqueous solution onto activated carbon prepared from Acacia glauca sawdust (AGAC). The surface area of the adsorbent determined by methylene blue method is found to be 311.20 m2/g. The optimum dose of adsorbent was found to be 2 g/l with 4NP uptake of 25.93 mg/g. The equilibrium time was found to be 30 minutes with the percentage removal of 96.40 at the initial concentration of 50 ppm. The maximum removal of 98.94% was found to be at pH of 6. The equilibrium and kinetic study revealed that the Radke–Prausnitz isotherm and pseudo second order kinetics model fitted the respective data well. In the thermodynamic study, the negative value of Gibbs free energy change (−26.38 kJ/mol at 30°C) and enthalpy change (−6.12 kJ/mol) showed the spontaneous and exothermic nature of the adsorption process.

Interaction of Quaternary Ammonium and Phosphonium Salts with Photosynthetic Membranes

2001 ◽  
Vol 56 (11-12) ◽  
pp. 1057-1066 ◽  
Author(s):  
Susanne Spiegel ◽  
Klaus P. Bader
Keyword(s):  
Quaternary Ammonium ◽  
Alkyl Chain ◽  
Chemical Reduction ◽  
Effective Interaction ◽  
Direct Interaction ◽  
Thylakoid Membranes ◽  
Fluorescence Induction ◽  
Strong Increase ◽  
Phosphonium Salts ◽  
Photosynthetic Membrane

Abstract Distinct concentration ranges of selected quaternary ammonium and phosphonium salts were elaborated to induce stimulatory or inhibitory effects, respectively, on photosynthetic reactions. By means of fluorescence induction measurements 3 different effects of alkylbenzyldimethylammonium chloride (ABDAC; zephirol) in chloroplast preparations from Pisum sativum were observed. 60 μᴍ ABDAC produced a strong increase in Fmax with concurrently improved Kautsky kinetics. Increased ABDAC concentration (500 μᴍ) led to a strong fluorescence quenching - virtually indistinguishable from the conditions following the addition of photosystem II electron acceptors like K3Fe[CN]6. Further increase of ABDAC to 5 mᴍ provoked a drastic increase in the fluorescence yield together with the complete loss of any detectable kinetics. We suggest a 3-step interaction of ABDAC with the thylakoid membranes of photosynthetic organisms similar to our earlier discussion (Bader and Höper (1993), Z. Naturforsch. 49 c, 87 -94 ). We examined a series of derivatives with selectively modified side chains, central atoms and counter ions, respectively. Both an alkyl chain of the type ([-CH2-]n; n ~ > 10) and effective polar components are indispensable for the adsorption and intercalation of the molecule onto and into the thylakoid membranes. The benzyl group could be replaced by a methyl residue without any loss of effectiveness; replacement of the central nitrogen (N) by phosphorus (P) and the counter ion Cl by Br did not modify the effects and the results were indistinguishable from the ABDAC effect proper. Shortening of the alkyl chain to (-CH2-)6 resulted in a less effective interaction of e.g. tetraoctylammonium bromide with the photosynthetic membrane. Flash-induced oxygen evolution measurements with selected derivatives (15 μᴍ) substantiated our interpretation of an improved OEC functioning by a substantial lowering of the miss parameter a and the exclusion of a chemical reduction as the standard S-state distribution was not affected. As evidenced by both SDS-PAGE and Western blot analyses the investigated molecules showed a direct interaction. The polypeptide patterns were characterized by a severe shift of the molecular weight components from high (20 -67 kDa) to low (< 20 kDa) values.

scholarly journals Charting the native architecture of Chlamydomonas thylakoid membranes with single-molecule precision

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Wojciech Wietrzynski ◽  
Miroslava Schaffer ◽  
Dimitry Tegunov ◽  
Sahradha Albert ◽  
Atsuko Kanazawa ◽  
...  
Keyword(s):  
Single Molecule ◽  
Electron Tomography ◽  
Protein Complexes ◽  
Membrane Surface ◽  
Thylakoid Membranes ◽  
Surface Topology ◽  
Thylakoid Stacking ◽  
Molecular Forces ◽  
Photosynthetic Regulation ◽  
The Individual

Thylakoid membranes scaffold an assortment of large protein complexes that work together to harness the energy of light. It has been a longstanding challenge to visualize how the intricate thylakoid network organizes these protein complexes to finely tune the photosynthetic reactions. Previously, we used in situ cryo-electron tomography to reveal the native architecture of thylakoid membranes (Engel et al., 2015). Here, we leverage technical advances to resolve the individual protein complexes within these membranes. Combined with a new method to visualize membrane surface topology, we map the molecular landscapes of thylakoid membranes inside green algae cells. Our tomograms provide insights into the molecular forces that drive thylakoid stacking and reveal that photosystems I and II are strictly segregated at the borders between appressed and non-appressed membrane domains. This new approach to charting thylakoid topology lays the foundation for dissecting photosynthetic regulation at the level of single protein complexes within the cell.

Grana formation: entropy-assisted local order in chloroplasts?

1999 ◽  
Vol 26 (7) ◽  
pp. 641 ◽  
Author(s):  
W. S. Chow
Keyword(s):  
Free Energy ◽  
Short Range ◽  
Protein Complexes ◽  
Minimum Free Energy ◽  
Thylakoid Membranes ◽  
Local Order ◽  
Chlorophyll B ◽  
Van Der Waals Attraction ◽  
Physical Forces ◽  
Fine Tune

Grana formation is a prominent feature of the ultrastructure of chlorophyll b-containing chloroplasts, serving to fine-tune photosynthetic efficiency. This paper examines the physical forces that determine the state of minimum free energy of the chloroplast as manifested by grana formation. In particular, it considers the interplay of van der Waals attraction, electrostatic repulsion and short-range hydration repulsion between thylakoid membranes. In addition to these interactions as determinants of the free energy of the system, it is also proposed that ordering of thylakoid membranes and of intramembrane protein complexes is driven by an increase in the overall entropy of the system. This local order may partly come about by an increase in entropy associated with a greater free volume for diffusion of membrane and stromal components.

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