Energy-transducing Organelles Research Articles

Multi-scale analysis of heat stress acclimation in Arabidopsis seedlings highlights the primordial contribution of energy-transducing organelles.

Much progress has been made in understanding the molecular mechanisms of plant adaptation to heat stress. However, the great diversity of models and stress conditions, and the fact that analyses are often limited to a small number of approaches, complicate the picture. We took advantage of a liquid culture system in which Arabidopsis seedlings are arrested in their development, thus avoiding interference with development and drought stress responses, to investigate through an integrative approach seedlings' global response to heat stress and acclimation. Seedlings perfectly tolerate a noxious heat shock (43°C) when subjected to a heat priming treatment at a lower temperature (38°C) the day before, displaying a thermotolerance comparable to that previously observed for Arabidopsis. A major effect of the pre-treatment was to partially protect energy metabolism under heat shock and favor its subsequent rapid recovery, which was correlated with the survival of seedlings. Rapid recovery of actin cytoskeleton and mitochondrial dynamics were another landmark of heat shock tolerance. The omics confirmed the role of the ubiquitous heat shock response actors but also revealed specific or overlapping responses to priming, heat shock, and their combination. Since only a few components or functions of chloroplast and mitochondria were highlighted in these analyses, the preservation and rapid recovery of their bioenergetic roles upon acute heat stress do not require extensive remodeling of the organelles. Protection of these organelles is rather integrated into the overall heat shock response, thus allowing them to provide the energy required to elaborate other cellular responses toward acclimation.

Electrometric and Electron Paramagnetic Resonance Measurements of a Difference in the Transmembrane Electrochemical Potential: Photosynthetic Subcellular Structures and Isolated Pigment-Protein Complexes.

A transmembrane difference in the electrochemical potentials of protons (ΔμH+) serves as a free energy intermediate in energy-transducing organelles of the living cell. The contributions of two components of the ΔμH+ (electrical, Δψ, and concentrational, ΔpH) to the overall ΔμH+ value depend on the nature and lipid composition of the energy-coupling membrane. In this review, we briefly consider several of the most common instrumental (electrometric and EPR) methods for numerical estimations of Δψ and ΔpH. In particular, the kinetics of the flash-induced electrometrical measurements of Δψ in bacterial chromatophores, isolated bacterial reaction centers, and Photosystems I and II of the oxygenic photosynthesis, as well as the use of pH-sensitive molecular indicators and kinetic data regarding pH-dependent electron transport in chloroplasts, have been reviewed. Further perspectives on the application of these methods to solve some fundamental and practical problems of membrane bioenergetics are discussed.

Computer modeling of electron and proton transport in chloroplasts.

Photosynthesis is one of the most important biological processes in biosphere, which provides production of organic substances from atmospheric CO2 and water at expense of solar energy. In this review, we contemplate computer models of oxygenic photosynthesis in the context of feedback regulation of photosynthetic electron transport in chloroplasts, the energy-transducing organelles of the plant cell. We start with a brief overview of electron and proton transport processes in chloroplasts coupled to ATP synthesis and consider basic regulatory mechanisms of oxygenic photosynthesis. General approaches to computer simulation of photosynthetic processes are considered, including the random walk models of plastoquinone diffusion in thylakoid membranes and deterministic approach to modeling electron transport in chloroplasts based on the mass action law. Then we focus on a kinetic model of oxygenic photosynthesis that includes key stages of the linear electron transport, alternative pathways of electron transfer around photosystem I (PSI), transmembrane proton transport and ATP synthesis in chloroplasts. This model includes different regulatory processes: pH-dependent control of the intersystem electron transport, down-regulation of photosystem II (PSII) activity (non-photochemical quenching), the light-induced activation of the Bassham-Benson-Calvin (BBC) cycle. The model correctly describes pH-dependent feedback control of electron transport in chloroplasts and adequately reproduces a variety of experimental data on induction events observed under different experimental conditions in intact chloroplasts (variations of CO2 and O2 concentrations in atmosphere), including a complex kinetics of P700 (primary electron donor in PSI) photooxidation, CO2 consumption in the BBC cycle, and photorespiration. Finally, we describe diffusion-controlled photosynthetic processes in chloroplasts within the framework of the model that takes into account complex architecture of chloroplasts and lateral heterogeneity of lamellar system of thylakoids. The lateral profiles of pH in the thylakoid lumen and in the narrow gap between grana thylakoids have been calculated under different metabolic conditions. Analyzing topological aspects of diffusion-controlled stages of electron and proton transport in chloroplasts, we conclude that along with the NPQ mechanism of attenuation of PSII activity and deceleration of PQH2 oxidation by the cytochrome b6f complex caused by the lumen acidification, the intersystem electron transport may be down-regulated due to the light-induced alkalization of the narrow partition between adjacent thylakoids of grana. The computer models of electron and proton transport described in this article may be integrated as appropriate modules into a comprehensive model of oxygenic photosynthesis.

Interference Microscopy in Cell Biophysics. 2. Visualization of Individual Cells and Energy-Transducing Organelles

The coherent phase microscopy (CPM) provides a convenient and non-invasive tool for imaging cells and intracellular organelles. In this article, we consider the applications of the CPM method to imaging different cells and energy-transducing intracellular organelles (mitochondria and chloroplasts). Experimental data presented below demonstrate that the optical path length difference of the object, which is the basic optical parameter measured by the CPM method, can serve as an indicator of metabolic states of different biological objects at cellular and subcellular levels of structural organization.

Interference Microscopy in Cell Biophysics. 1. Principles and Methodological Aspects of Coherent Phase Microscopy

The purpose of our tandem publications is to review the applications of the coherent phase microscopy to cell biophysics. In this article, we briefly consider the fundamentals and methodological aspects of the coherent phase microscopy (CPM). One of important advantages of this method is a high sensitivity of CPM images to changes in physical-chemical properties of biological samples. The optical path length difference (OPLD), measured with CPM instruments in different domains of an object, serves as the informative optical parameter used for visualization of individual cells or intracellular organelles. Metabolically dependent variations of CPM images reflect changes in the functional state of biological objects. In the next article, we review results of CPM studies of different cells and intracellular energy-transducing organelles.

Photosynthesis and respiration in the needles of Pinus sibirica and Pinus pumila and their putative hybrids

A putative interspecific hybridization in Pinaceae family was investigated. Very rarely the physiological methods were involved in hybridization processes that occurs in the hybrid zones. It is well known that in most gymnosperms, the plastid genome is inherited from the paternal component while the mitochondrion is inherited from the maternal one. Therefore functioning pattern of organelles in the hybrid plant can suggest parent, from which they were inherited. The aim of this study was to indirectly establish the inheritance energy-transducing organelles (mitochondria, chloroplast) according to their functioning. Current year needles from Siberian Stone Pine (Pinus sibirica Du Tour) and Japanese Stone Pine (Pinus pumila (Pall.) Regel) as parent species and their putative hybrids were collected from Baikal Region. The photosynthesis rate was determined by using the spectrophotometer. The study of emission CO2 under dark respiration of needle was conducted with laser optical-acoustic gasanalyzer. The quantity was measured at 1, 2 and 3 hour after experiment start. The rate of the photoreduction ferricyanide potassium was characterized by the primary photochemical processes activity at the level of photosystem II. Comparison of pure species was shown that Japanese Stone Pine had higher functional activity of chloroplast as compared with Siberian Stone Pine in spite of the fact that they are growing in similar environment conditions. Two of three analyzed hybrids had decreased activity of their chloroplasts. Unfortunately, in this case we can't conclude if the chloroplasts were inherited from Siberian Stone Pine or from Japanese Stone Pine. Chloroplast activity of the third hybrid was approximately similar to that of Japanese Stone Pine suggesting that its chloroplasts were inherited from this parent. Consequently, the Siberian Stone Pine and the Japanese Stone Pine were maternal and paternal, respectively parents of the hybrid. Compared to the Siberian Stone Pine, the Japanese Stone Pine had higher dark respiration rate. The hybrid respiration rate was similar to that of the Japanese Stone Pine suggesting that the hybrid inherited mitochondria from this species. Our findings indicated that the P. pumila exhibited particular ecological plasticity and this phenomenon is attributable to its high potential activity of photosynthetic and respiratory processes. These physiological features explained the large transcontinental natural habitat of Japanese Stone Pine.

The function of genomes in bioenergetic organelles.

Mitochondria and chloroplasts are energy-transducing organelles of the cytoplasm of eukaryotic cells. They originated as bacterial symbionts whose host cells acquired respiration from the precursor of the mitochondrion, and oxygenic photosynthesis from the precursor of the chloroplast. The host cells also acquired genetic information from their symbionts, eventually incorporating much of it into their own genomes. Genes of the eukaryotic cell nucleus now encode most mitochondrial and chloroplast proteins. Genes are copied and moved between cellular compartments with relative ease, and there is no obvious obstacle to successful import of any protein precursor from the cytosol. So why are any genes at all retained in cytoplasmic organelles? One proposal is that these small but functional genomes provide a location for genes that is close to, and in the same compartment as, their gene products. This co-location facilitates rapid and direct regulatory coupling. Redox control of synthesis de novo is put forward as the common property of those proteins that must be encoded and synthesized within mitochondria and chloroplasts. This testable hypothesis is termed CORR, for co-location for redox regulation. Principles, predictions and consequences of CORR are examined in the context of competing hypotheses and current evidence.

Biogenesis and evolution of photosynthetic (thylakoid) membranes.

Work in molecular phylogeny during the past few years has documented that the biogenesis, maintenance, adaptation, and controlled resorption of thylakoid (photosynthetic) membranes are by far more complex than the requirements for maintaining their function, especially in plants (eukaryotic photoautotrophs). Plants, due to their genome compartmentation that originated in a cohabitation of cells (endosymbiotic events), have evolved an exquisite set of regulatory mechanisms for their energy-transducing organelles. These operate in concert with basically ancient regulatory circuits originating in the organelle ancestors. It appears that the biogenesis of thylakoid membranes, as that of chloroplasts in general, cannot be understood without knowledge of the history of the cells.

Shift from localized to delocalized protonic energy coupling in thylakoids by permeant amines

We have suggested that in energy-transducing organelles structural constraints may hinder H + transport from their sites of active, redox translocation to their sites of passive or phosphorylating escape (microchemiosmosis). We could modulate these constraints first by affecting the physico-chemical properties of the medium, and now by adding permeant amine buffers to a suspension of thylakoids. The following results are obtained. (1) Whether driven by Photosystem I or by Photosystem II, phosphorylation is stimulated by amines (imidazole, hexylamine, NH 4CI) at concentrations low enough hardly to modify the proton gradient: ΔpH is stable if not reduced, Δψ is slightly increased but still negligible; this extends the observations made by Giersch. (2) The concentration curves of phosphorylation stimulation by amines exhibit a minor peak before the main one previously reported. (3) ATP synthesis and ΔpH are decreased by amines at higher concentrations, but the dependence of the phosphorylation rate (flow) versus ΔpH (force) is then shifted towards lower ΔpH values. (4) The normally less efficient Photosystem II-driven phosphorylation is comparable to Photosystem I with amines. (5) The flow-force curves, which are distinct when traced by limiting ΔpH by an H + influx decrease (light) or efflux increase (nigericin), are much closer with either photosystem when amines are added. The Photosystem I curve produced by increasing nigericin beyond approx. 200 nM becomes insensitive to amines. (6) In general, Photosystem II requires significantly less nigericin or amines than Photosystem I to obtain similar effects. It is proposed that amines have a double effect. By efficiently carrying protons along the membrane, amines lower the protonic resistances and thereby delocalize the proton gradient. At higher amine concentrations, uncoupling occurs, probably by an indirect backflow of protons more than by a buffering effect, as generally admitted. In conclusion, the multiple-resistances microchemiosmotic scheme which we have proposed earlier is strengthened; it predicts that intermediate states may link delocalized (canonical chemiosmosis) and localized coupling modes, which is established here.

Intracellular protein catabolism: state of the art

There are several reasons why intracellular protein catabolism is incompletely understood. The most quoted are the facts that protein catabolism involves multiple mechanisms and does not easily occur in the test tube, at least, to a readily manipulatable degree (cf. protein synthesis). However, a much more fundamental reason is that the multiple systems are intimately connected with all aspects of the life process. Degradation is the alternative for proteins during or immediately after synthesis, during secretion and after reaching their cytomorphological functional sites: in short, protein catabolism (including degradation after protein endocytosis) is primarily a cell biological phenomenon. Extracting the molecular detail of the multiple processes requires multiple biological approaches, providing a literature rich in a mixture of experimental models, designs and interpretations. In this review we want to consider critically the biological questions, the literature which addresses the questions and the current conundrums: the state of the art. We have taken the excellent 1982 review of Hershko and Ciechanover [l] as representative of knowledge and understanding in 1981 and have predominantly reviewed the literature from 1981 to 85. We have not considered degradative events after endocytosis since they are adequately addressed elsewhere [2]. Those people interested in the views of many workers in the field would do well to read the summaries of presentations at the Vth International Symposium on Protein Catabolism [3]. Hershko’s analyses [l] saw intracellular protein catabolism as an extensive, selective set of energy(ATP)-requiring processes which have several functions including elimination of abnormal proteins and provision of amino acids in times of need. Non-lysosomal and lysosomal systems were identified which may act on ‘short’ and ‘long’ lived proteins respectively: the latter system being activated in a variety of cellular deprivation states. Finally and importantly, much of the earlier experimentation was seen as phenomenological rather than molecular in nature. The analyses did not consider: (i) the question of cellular architecture, i.e. proteins function in defined sites and yet must interact with the catabolic systems; (ii) that proteins are really degraded with the rate of heterogeneity previously supposed; (iii) the existence of ‘special’ systems, e.g. in heat shock or regulatory proteases responsive to calcium; (iv) degradation of proteins during secretion; (v) mitochondrial and chloroplast systems. We will consider intracellular protein catabolism from the point of view of (section 2) the systems: (section 2.1) the lysosomal system, (2.2) the secretory degradative system (defined as secretioncoupled degradation), (2.3) non-lysosomal systems, (2.4) ATP-dependent systems in prokaryotes, eukaryotes and energy-transducing organelles, (2.5) calcium-dependent systems; and (section 3) the substrates: (3.1) how are the systems organised topographically with respect to

Structural gene coding for the dicyclohexylcarbodiimide-binding protein of the proton-translocating ATPase from escherichia coli: Locus of the gene in the F 1F 0 gene cluster

The proton-translocating ATPase (F,-F,) is an apparatus for the synthesis of ATP common to different energy-transducing organelles, such as mitochondria, chloroplasts and bacterial cytoplasmic membranes (reviews [l-4] ). The ATPase consists of two portions, F, and F,. F, is a peripheral membrane component with 5 different subunits (cw,P.rJ ,E), and it is bound to the integral membrane component, Fo, which functions as a proton pathway. Two or more subunits have been found in F, from different sources. The proteolipid subunits, dicyclohexylcarbodiimide (DCCD)-binding proteins, have been purified from several organisms [2,5,6] and their primary sequences have been determined [7]. Two types of E. coli mutant of this subunit, which both result in inability to bind DCCD, have been reported; the F, of mutant strain DG7/1 is defective in proton translocation [8,9], whereas that of the other type of mutant RF7 [lo] is normal. Thus DG7/1 cannot grow with succinate as the sole carbon source because of defective oxidative phosphorylation, whereas RF7 can grown normally. Both mutant strains have functional F,, although their membrane ATPase activities are not sensitive to DCCD because the mutant protein cannot bind this compound. DCCD binds to an aspartyl residue at position 61 of the polypeptide, and this residue is replaced by a glytine residue in the protein of DG7/1 [8,9]. It has not been shown directly whether these mutations are in

Membrane structure in relation to function of energy-transducing organelles.

Membrane structure in relation to function of energy-transducing organelles.