RESUMO
Attempts to find and quantify the supposed low entropy of organisms and its preservation are revised. The absolute entropy of the mixed components of non-living biomass (approximately -1.6 × 103 J K-1 L-1) is the reference to which other entropy decreases would be ascribed to life. The compartmentation of metabolites and the departure from the equilibrium of metabolic reactions account for reductions in entropy of 1 and 40-50 J K-1 L-1, respectively, and, though small, are distinctive features of living tissues. DNA and proteins do not supply significant decreases in thermodynamic entropy, but their low informational entropy is relevant for life and its evolution. No other living feature contributes significantly to the low entropy associated with life. The photosynthetic conversion of radiant energy to biomass energy accounts for most entropy (2.8 × 105 J K-1 carbon kg-1) produced by living beings. The comparatively very low entropy produced in other processes (approximately 4.8 × 102 J K-1 L-1 day-1 in the human body) must be rapidly exported outside as heat to preserve low entropy decreases due to compartmentation and non-equilibrium metabolism. Enzymes and genes are described, whose control minimizes the rate of production of entropy and could explain selective pressures in biological evolution and the rapid proliferation of cancer cells.
Assuntos
Fenômenos Bioquímicos , Biologia , Biomassa , Entropia , Humanos , TermodinâmicaRESUMO
The polypeptides encoded by the chloroplast ndh genes and some nuclear genes form the thylakoid NADH dehydrogenase (Ndh) complex, homologous to the mitochondrial complex I. Except for Charophyceae (algae related to higher plants) and a few Prasinophyceae, all eukaryotic algae lack ndh genes. Among vascular plants, the ndh genes are absent in epiphytic and in some species scattered among different genera, families, and orders. The recent identification of many plants lacking plastid ndh genes allows comparison on phylogenetic trees and functional investigations of the ndh genes. The ndh genes protect Angiosperms under various terrestrial stresses, maintaining efficient photosynthesis. On the edge of dispensability, ndh genes provide a test for the natural selection of photosynthesis-related genes in evolution. Variable evolutionary environments place Angiosperms without ndh genes at risk of extinction and, probably, most extant ones may have lost ndh genes recently. Therefore, they are evolutionary endpoints in phylogenetic trees. The low number of sequenced plastid DNA and the long lifespan of some Gymnosperms lacking ndh genes challenge models about the role of ndh genes protecting against stress and promoting leaf senescence. Additional DNA sequencing in Gymnosperms and investigations into the molecular mechanisms of their response to stress will provide a unified model of the evolutionary and functional consequences of the lack of ndh genes.
Assuntos
Cloroplastos/genética , NADH Desidrogenase/genética , Fotossíntese/genética , Plastídeos/genética , Carofíceas/genética , Genes de Cloroplastos/genética , Senescência Vegetal/genética , Plastídeos/metabolismo , Tilacoides/enzimologia , Tilacoides/genéticaRESUMO
The minimum rate principle is applied to the chemical reaction in a steady-state open cell system where, under constant supply of the glucose precursor, reference to time or to glucose consumption does not affect the conclusions.
Assuntos
Entropia , Neoplasias , Glucose , HumanosRESUMO
Chloroplasts are the place for the major conversion of the sun's radiation energy to chemical energythat is usable by organisms[ ].
Assuntos
Evolução Biológica , Cloroplastos/fisiologiaRESUMO
Cancer cells consume more glucose by glycolytic fermentation to lactate than by respiration, a characteristic known as the Warburg effect. In contrast with the 36 moles of ATP produced by respiration, fermentation produces two moles of ATP per mole of glucose consumed, which poses a puzzle with regard to the function of the Warburg effect. The production of free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) per mole linearly varies with the fraction (x) of glucose consumed by fermentation that is frequently estimated around 0.9. Hence, calculation shows that, in respect to pure respiration, the predominant fermentative metabolism decreases around 10% the production of entropy per mole of glucose consumed in cancer cells. We hypothesize that increased fermentation could allow cancer cells to accomplish the Prigogine theorem of the trend to minimize the rate of production of entropy. According to the theorem, open cellular systems near the steady state could evolve to minimize the rates of entropy production that may be reached by modified replicating cells producing entropy at a low rate. Remarkably, at CO2 concentrations above 930 ppm, glucose respiration produces less entropy than fermentation, which suggests experimental tests to validate the hypothesis of minimization of the rate of entropy production through the Warburg effect.
Assuntos
Respiração Celular , Evolução Molecular , Fermentação , Neoplasias/metabolismo , EntropiaRESUMO
Three evergreen (Laurus nobilis, Viburnum tinus and Thuja plicata) and two autumnal abscission deciduous trees (Cydonia oblonga and Prunus domestica) have been investigated for the presence (zymogram and immunodetection) and functionality (post-illumination chlorophyll fluorescence) of the thylakoid Ndh complex. The presence of encoding ndh genes has also been investigated in T. plicata. Western assays allowed tentative identification of zymogram NADH dehydrogenase bands corresponding to the Ndh complex after native electrophoresis of solubilized fractions from L. nobilis, V. tinus, C. oblonga and P. domestica leaves, but not in those of T. plicata. However, Ndh subunits were detected after SDS-PAGE of thylakoid solubilized proteins of T. plicata. The leaves of the five plants showed the post-illumination chlorophyll fluorescence increase dependent on the presence of active Ndh complex. The fluorescence increase was higher in autumn in deciduous, but not in evergreen trees, which suggests that the thylakoid Ndh complex could be involved in autumnal leaf senescence. Two ndhB genes were sequenced from T. plicata that differ at the 350 bp 3' end sequence. Comparison with the mRNA revealed that ndhB genes have a 707-bp type II intron between exons 1 (723 bp) and 2 (729 bp) and that the UCA 259th codon is edited to UUA in mRNA. Phylogenetically, the ndhB genes of T. plicata group close to those of Metasequoia, Cryptomeria, Taxodium, Juniperus and Widdringtonia in the cupresaceae branch and are 5' end shortened by 18 codons with respect to that of angiosperms.
Assuntos
Eletroforese em Gel de Poliacrilamida/métodos , NADH Desidrogenase/metabolismo , Folhas de Planta/química , Tilacoides/genética , Tilacoides/metabolismo , Árvores/genética , Árvores/metabolismo , Envelhecimento/fisiologia , Fluorescência , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Laurus/genética , Laurus/metabolismo , Dados de Sequência Molecular , NADH Desidrogenase/genética , Prunus/genética , Prunus/metabolismo , Rosaceae/genética , Rosaceae/metabolismo , Estações do Ano , Thuja/genética , Thuja/metabolismo , Viburnum/genética , Viburnum/metabolismoRESUMO
Acetylated polymannan polysaccharide (ApmP) isolated from Aloe barbadensis Miller contains a stable peroxidase that was solubilized to investigate its biochemical, electrophoretic, immunological, and proteomic properties. In the electrophoretic band corresponding to the solubilized peroxidase, proteomic analysis detected seven tryptic peptides that matched homologous peptides covering one third of the ATP22a peroxidase of Arabidopsis thaliana. All the characteristics tested indicated that the activity stabilized within the ApmP pertains to the basic secretory peroxidase family, which includes members that have several biotechnological uses. Hence ApmP might yield a widely used peroxidase in stabilized form.
Assuntos
Aloe/enzimologia , Mananas/química , Peroxidases/isolamento & purificação , Extratos Vegetais/química , Proteínas de Plantas/isolamento & purificação , Acetilação , Aloe/química , Sequência de Aminoácidos , Arabidopsis/enzimologia , Arabidopsis/genética , Benzidinas/química , Eletroforese em Gel de Poliacrilamida , Peróxido de Hidrogênio/química , Cinética , Espectrometria de Massas , Dados de Sequência Molecular , Peptídeos/análise , Peroxidases/genética , Peroxidases/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Proteômica , Solubilidade , TripsinaRESUMO
To investigate the phosphorylation of the NDH-F subunit of the thylakoid Ndh complex, we constructed three site-directed mutant transgenic tobaccos (Nicotiana tabacum) (T181A, T181S and T181D) in which the (541)ACT(543) triplet encoding the Thr-181 has been substituted by GCT, TCT or GAT encoding alanine, serine and aspartic acid, respectively. Western blots with phospho-threonine antibody detected the 73 kD NDH-F phosphorylated polypeptide in control but not in mutant tobaccos. Differences in Ndh activity, chlorophyll fluorescence and photosynthesis among mutants and control plant demonstrate the key role of the phosphorylation of conserved Thr-181 in the activity and function of the Ndh complex. The substitution of aspartic acid for threonine in T181D mimics the presumable activation effects of the threonine phosphorylation in Ndh activity, post-illumination increase of chlorophyll fluorescence and photosynthesis rapid responses to changing light intensities. A tentative role of the phosphorylation-activated Ndh complex is suggested to poise the redox level and, consequently, optimizing the rate of cyclic electron transport under field conditions.
Assuntos
Genes de Plantas , Mutagênese Sítio-Dirigida , Nicotiana/genética , Tilacoides/genética , Alanina/metabolismo , Sequência de Aminoácidos , Substituição de Aminoácidos , Ácido Aspártico/metabolismo , Clorofila/metabolismo , Vetores Genéticos , Dados de Sequência Molecular , Fosforilação , Fotossíntese/fisiologia , Plantas Geneticamente Modificadas , Análise de Sequência de DNA , Serina/metabolismo , Tilacoides/metabolismo , Nicotiana/metabolismoRESUMO
The monocistronic mRNAs of ndhH and ndhA genes of the plastid ndhH-D operon accumulate during senescence. In a step forward to discover the mechanisms involved in the production of mature transcripts of the ndhH-D operon, we determined the 5 - and 3 -ends of low-molecular-weight ndhH, ndhA and ndhI transcripts of barley. The 3'-end of the only ndhH mRNA detected (1622 b) extends 421 b into exon1 of ndhA. Several monocistronic ndhA mRNAs were identified and most of them extend their 3'-ends through the adjacent intergenic 101 b region to around 105 b into ndhI, the neighboring gene in the operon. Unspliced ndhA transcripts (around 2.4 kb and intron-containing) were also identified with different 3'-ends extending almost 200 b into ndhI. In contrast, all ndhA transcripts showed the same 5'-end 65 b upstream of the ndhH stop codon. 5'-ends of all ndhA and ndhH transcripts seem produced by nuclease cleavages between the last AA of the consensus sequence AAUGAA present 66 and 16 b upstream of the respective start codon. Secondary structure predictions suggest that 3'-end extensions provide 3'-UTR stabilizing elements to ndhH-D transcripts. Therefore, the processing of the 7.8 kb primary transcript frequently involves intra-genic cleavages sacrificing downstream gene messages and decreasing the efficiency of the conversion to mature ndh mRNAs. Significantly, the maturation of ndhE mRNA would not sacrifice the downstream psaC message, contributing to higher levels of psaC mRNA than of ndh mRNAs.
Assuntos
Regiões 3' não Traduzidas/química , Genes de Plantas , Óperon , Plastídeos/genética , RNA Mensageiro/química , Regiões 5' não Traduzidas/química , Sequência de Bases , Cloroplastos/metabolismo , Regulação da Expressão Gênica , Hordeum/genética , Hordeum/metabolismo , Modelos Genéticos , Dados de Sequência Molecular , NADH Desidrogenase/genética , NADH Desidrogenase/metabolismo , Conformação de Ácido Nucleico , Fases de Leitura Aberta , Folhas de Planta/citologia , Folhas de Planta/metabolismo , Plastídeos/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
The physiology at limiting and stress conditions challenges the current view that the overall reaction of metabolic processes is always far from equilibrium and, therefore, that organisms are not committed to lower their rates of entropy production. Plausibly, critical steps of natural selection takes place at limiting conditions, near equilibrium, in the linear range response of entropy production, and consequently the trend to lower the rate of entropy production could be the fitness arrow of biological evolution. The evolutionary relevance of the Prigogine theorem is discussed in connection with the ergodic hypothesis of Boltzmann. The emergence of metabolic strategies to economise carbon/energy resources, of resource-waste systems like active transport and the irreversible increase in the complexity of organisms during evolution may be consequences of a more general trend of metabolic systems to lower the rates of entropy production.
Assuntos
Evolução Biológica , Entropia , Modelos Biológicos , Seleção GenéticaRESUMO
We have investigated the topologies of Ndh (a plastid complex with NADH dehydrogenase activity) and its NDH-F subunit in thylakoids by trypsin and proteinase V8 digestion of both intact and Triton X-100-permeabilized barley thylakoids and identification of the products with antibodies against specific sequences of the NDH-A, NDH-K and NDH-F subunits. Antibody binding and protection against proteinases were also assayed. The analysis of the digestion products of NDH-F by immunodetection and matrix-assisted laser-desorption ionization-time-of-flight allowed us to propose its membrane topology and to compare it with bioinformatic predictions and with that of the homologous subunit (ND5/NuoL/NQO12) of the respiratory complex I. Results indicate that the thylakoid Ndh complex may have an L-shaped structure, similar to that of respiratory complex I, with the hydrophilic arm orientated towards the stroma and the hydrophobic arm inserted into the thylakoid. NDH-A and NDH-K may be located at the bridge between the two arms. Similar to ND5/NuoL/NQO12 of complex I, NDH-F must be distally located in the hydrophobic arm. NDH-F would include up to 15 transmembrane helices and 14 hydrophilic regions. A conserved His-349 in the X transmembrane helix could be involved in H+ pumping. The conserved Thr-181 NDH-F, whose probable phosphorylation increases the activity of the Ndh complex, is located within the hydrophilic region between the V and VI transmembrane helices.
Assuntos
Hordeum/química , Membranas Intracelulares/química , NADH Desidrogenase/química , Proteínas de Plantas/química , Plastídeos/química , Subunidades Proteicas/química , Tilacoides/química , Sequência de Aminoácidos , Anticorpos/metabolismo , Proteínas de Escherichia coli/química , Modelos Moleculares , Dados de Sequência Molecular , NADH Desidrogenase/imunologia , NADH Desidrogenase/metabolismo , Mapeamento de Peptídeos/métodos , Peptídeos/metabolismo , Complexo de Proteínas do Centro de Reação Fotossintética/química , Proteínas de Plantas/imunologia , Proteínas de Plantas/metabolismo , Valor Preditivo dos Testes , Estrutura Quaternária de Proteína , Estrutura Terciária de Proteína , Subunidades Proteicas/metabolismo , Proteínas Ribossômicas/química , Alinhamento de Sequência/métodos , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz/métodos , Tilacoides/metabolismo , Tripsina/metabolismoRESUMO
The 11 plastid ndh genes have hovered frequently on the edge of dispensability, being absent in the plastid DNA of many algae and certain higher plants. We have compared the photosynthetic activity of tobacco (Nicotiana tabacum, cv. Petit Havana) with five transgenic lines (ΔndhF, pr-ΔndhF, T181D, T181A, and ndhF FC) and found that photosynthetic performance is impaired in transgenic ndhF-defective tobacco plants at rapidly fluctuating light intensities and higher than ambient CO2 concentrations. In contrast to wild type and ndhF FC, which reach the maximum photosynthetic rate in less than 1 min when light intensity suddenly increases, ndh defective plants (ΔndhF and T181A) show up to a 5 min delay in reaching the maximum photosynthetic rate at CO2 concentrations higher than the ambient 360 ppm. Net photosynthesis was determined at different CO2 concentrations when sequences of 130, 870, 61, 870, and 130 µmol m(-2) s(-1) PAR sudden light changes were applied to leaves and photosynthetic efficiency and entropy production (Sg) were determined as indicators of photosynthesis performance. The two ndh-defective plants, ΔndhF and T181A, had lower photosynthetic efficiency and higher Sg than wt, ndhF FC and T181D tobacco plants, containing full functional ndh genes, at CO2 concentrations above 400 ppm. We propose that the Ndh complex improves cyclic electron transport by adjusting the redox level of transporters during the low light intensity stage. In ndhF-defective strains, the supply of electrons through the Ndh complex fails, transporters remain over-oxidized (specially at high CO2 concentrations) and the rate of cyclic electron transport is low, impairing the ATP level required to rapidly reach high CO2 fixation rates in the following high light phase. Hence, ndh genes could be dispensable at low but not at high atmospheric concentrations of CO2.
RESUMO
Responses to low temperature, mechanical wounding and salicylic acid (SA) treatments were studied in 3-week-old (young) and 6-week-old (senescent) Arabidopsis thaliana (L.) Heynh. plants by analyzing increases in Pal1 and Pr1 expression and superoxide dismutase (SOD; EC 1.15.1.1) and peroxidase (POX; EC 1.11.1.7) activities. Young plants showed higher Pal1 transcript accumulation after low temperature and wounding. In contrast, senescent plants presented higher accumulation of Pr1 transcripts after SA treatments. Similar results were obtained with the ethylene-insensitive etr1 mutant, suggesting that these differences are not related to increased ethylene content in senescent tissues. SOD activity and inducibility were lower, whereas POX activity and inducibility were higher in senescent plants. A possible relationship between senescence-associated changes in responses to stress and in the metabolism of active oxygen species is discussed.
RESUMO
We describe here an experimental system to study the age-related decline of adventitious root formation in Arabidopsis thaliana L. (Heynh), ecotype Landsberg erecta (Ler). The system is based on the different rooting capacity of hypocotyls from de-rooted juvenile (12-day-old) and adult (26-day-old) plants. Hypocotyls from de-rooted juvenile plants rooted readily within a week of culture, and the rooting process was not dependent on exogenous auxin. In contrast, hypocotyls from de-rooted adult plants rooted poorly and only after longer periods of time. Exogenously applied auxin had no effect on rooting of hypocotyls from de-rooted adult plants. Rooting capacity, although correlated with the transition to flowering, did not depend on this transition. Root induction declined in a similar manner when the transition to flowering was delayed, either genetically with the fve mutant or physiologically with short days. The results showed that rooting of hypocotyls from de-rooted adult plants depended on the effect of peptides containing the RGD motif. Both the percentage of rooting and the number of roots were largely increased when the hypocotyls were treated transiently with the RGD peptide. The effect of the RGD peptide was a necessary, but not sufficient, condition for rooting of hypocotyls from de-rooted adult plants.
RESUMO
Experimental and theoretical flux models have been developed to reveal the influence of sun flecks and increasing CO2 concentrations on the energy and entropy balances of the leaf. The rapid and wide range of fluctuations in light intensity under field conditions were simulated in a climatic gas exchange chamber and we determined the energy and entropy balance of the leaf based on radiation and gas exchange measurements. It was estimated that the energy of photosynthetic active radiation (PAR) accounts for half of transpiration, which is the main factor responsible for the exportation of the entropy generated in photosynthesis (Sg) out of the leaf in order to maintain functional the photosynthetic machinery. Although the response of net photosynthetic production to increasing concentrations of CO2 under fluctuating light is similar to that under continuous light, rates of transpiration respond slowly to changes of light intensity and are barely affected by the concentration of CO2 in the range of 260-495 ppm, in which net photosynthesis increases by more than 100%. The analysis of the results confirms that future increases of CO2 will improve the efficiency of the conversion of radiant energy into biomass, but will not reduce the contribution of plant transpiration to the leaf thermal balance.
Assuntos
Dióxido de Carbono/análise , Luz , Fotossíntese , Transpiração Vegetal , Termodinâmica , Modelos TeóricosRESUMO
The level of reactive oxygen species (ROS) increases under different stresses and, by destroying cellular components, may cause cell death. In addition, ROS are part of the complex network of transduction signals that induce defense reactions against stress or, alternatively, trigger programmed cell death, and key questions are the levels of each ROS that, respectively determine defense and death responses of the cell. The answer to those questions is difficult because there are several patterns of cell death that frequently appear mixed and are hardly distinguishable. Moreover, although considerable progresses have been achieved in the determination of the levels of specific ROS, critical questions remain on the ROS level in specific cell compartments. By considering chloroplasts as the main source of ROS in photosynthetic tissues at light, a comparison of the levels in stress and senescence of the chloroplastic activities involved in the generation and scavenging of ROS suggests plausible differences in the levels of specific ROS between stress defense and death. In effect, the three activities of the chlororespiratory chain increase similarly in stress defense response. However, in senescence, superoxide dismutase (SOD), that converts superoxide anion radical ([Formula: see text]) to hydrogen peroxide (H2O2,) decreases, while the thylakoid Ndh complex, that favors the generation of singlet oxygen ((1)O2) and [Formula: see text], and peroxidase (PX), that consumes H2O2, increase. The obvious inference is that, in respect to defense response, the ratio ((1)O2 plus [Formula: see text])/H2O2 is increased in the senescence previous to cell death. We hypothesize that the different ROS ratios, probably through changes in the jasmonic acid/H2O2 ratio, could determine the activation of the defense network or the death network response of the cell.
RESUMO
The plastid ndh genes encode components of the thylakoid Ndh complex which purportedly acts as an electron feeding valve to adjust the redox level of the cyclic photosynthetic electron transporters. During the process of evolution from endosymbiosis to modern chloroplast, most cyanobacterial genes were lost or transferred to nucleus. Eleven ndh genes are among the 150-200 genes remaining in higher plant chloroplast DNA, out of some 3000 genes in the original prokaryotic Cyanobacteria in which homologues to ndh genes encode components of the respiratory Complex I and probably other complexes. The ndh genes are absent in all sequenced plastid DNAs of algae except for the Charophyceae and some Prasinophyceae. With the possible exclusion of some Conifers and Gnetales, the plastid DNA of all photosynthetic land plants contains the ndh genes, whereas they are absent in epiphytic plants that have also lost genes for the photosynthetic machinery. Therefore, the functional role of the ndh genes seems closely related to the land adaptation of photosynthesis. Transcripts of several plastid genes require C to U editing. The ndh genes concentrate about 50% of the editing sites of angiosperm plastid transcripts. Editing sites may be remnants from an ancestor in which a number of T to C inactivating mutations took place in the ndh genes which, during evolution, are being corrected back to T. The comparison of homologous editing sites in the mRNAs of angiosperm ndh genes provides a tool to investigate selective and permissive environmental conditions of past evolutionary events.
Assuntos
Evolução Molecular , NADPH Desidrogenase/genética , Plantas/genética , Plastídeos/genética , Cloroplastos/enzimologia , Cloroplastos/genética , Cianobactérias/enzimologia , Cianobactérias/genética , Eucariotos/enzimologia , Eucariotos/genética , NADPH Desidrogenase/metabolismo , Plantas/enzimologia , Plastídeos/enzimologia , Edição de RNA/genéticaRESUMO
We have deduced equations to quantify the entropy associated to the compartmentalization of components in eukaryotic cells as a function of cell and compartment volumes, and of the concentration of solutes. On the basis of known and plausible values of volume and solute concentrations and the deduced equations, we estimate that the contribution of compartmentalization to the decrease of entropy is approximately -14.4 x 10(-14)JK(-1)cell(-1) (-0.7 J K(-1)L(-1)) in the case of Saccharomyces cerevisiae, a typical eukaryotic cell, and approximately -49.6 x 10(-14)JK(-1)cell(-1) (-1.0 J K(-1)L(-1)) in the more complex Chlamydomonas reinhardtii. When compared with other potential contributing factors, such as the informational entropy of DNA and the conformational entropy of proteins, compartmentalization appears as an essential development that significantly decreased the entropy of living cells during biological evolution.
Assuntos
Biopolímeros/química , Transferência de Energia/fisiologia , Modelos Biológicos , Saccharomyces cerevisiae/fisiologia , Equilíbrio Hidroeletrolítico/fisiologia , Simulação por Computador , Entropia , SolubilidadeRESUMO
Proteomic analyses of the beta subunit of the plastid ATP synthase of barley (Hordeum vulgare L.) revealed that mature protein was not carboxy terminus processed and suggested the correction of the 274 codon (GAT to AAT) in the data bank that was confirmed by DNA sequencing. Six isoforms of the ATP synthase beta subunit with pI ranging from 4.95 to 5.14 were resolved by two-dimensional electrophoresis (2-DE). Mass spectrometry analyses indicated that the six isoforms differ in their phosphorylation degree, which was confirmed by the disappearance of more acidic forms after incubation with the protein phosphatase calcineurin. Six Ser and/or Thr were detected as phosphorylated, among them the conserved Thr-179 that is also phosphorylated in the beta subunit of human mitochondria. The results are discussed in relation with the proposed regulation of the ATP synthase by phosphorylation and 14-3-3 proteins.