Regulation der Zeaxanthin- und der Diatoxanthin-Epoxidase in Chlorophyll a/b- und Fucoxanthin-Chlorophyll a/c-haltigen Pflanzen

In der vorliegenden Arbeit wird der Vx-Zyklus und der Ddx-Zyklus unterschiedlicher Pflanzen hinsichtlich ihrer Regulation untersucht. Es konnte an Hand von in vivo Messungen gezeigt werden, dass bei zwei Kieselalgen unterschiedlicher Ordnung (Pennales bzw. Centrales) und einer Haptophyte mit Ddx-Zyklus die Dtx-Epoxidase delta-pH-reguliert ist. Im Gegensatz dazu steht die nicht-regulierte Zx-Epoxidase des Vx-Zyklus einer Raphidophyceae, einer Grünalge und einer aquatischen Höheren Pflanze. Es konnte gezeigt werden, dass der Grund für diese unterschiedliche Regulation der beiden Epoxidasen die verschiedenen Quench-Eigenschaften der Pigmente Dtx bzw. Zx ist. Durch parallele Messungen des NPQ und des De-Epoxidierungsgrads wurde deutlich, dass Zx zum Aufbau eines Quenching direkt den im Licht aufgebauten delta-pH benötigt, während Dtx alleine ausreichend ist, um ein Quenching zu verursachen. Bei diesen in vivo Messungen wurde außerdem deutlich, dass die Aktivitäten der untersuchten Epoxidasen große Unterschiede aufweisen. Diese sind abhängig von der entsprechenden Pigmentierung des jeweiligen Lichtsammelsystems, stehen also in Zusammenhang mit den Carotinoidbiosynthesen. Es konnte gezeigt werden, dass bei allen untersuchten Organismen, die eine Xanthophyll-dominierte Antenne mit Fx als Massenpigment enthielten, die Umsatzraten der Epoxidase sehr hoch waren, im Gegensatz zu Chl-dominierten Antennen. Nach diesen Erkenntnissen wurde die Dtx-Epoxidase weiter untersucht und so erstmalig durch Western-Blotting identifiziert. Es ergaben sich, allerdings erst nach zusätzlicher Proteinstabilisierung, zwei Signale, eins bei 60 kDa, das andere bei 57 kDa. Hierbei ist nach wie vor unklar, warum das Antiserum zwei Signale lieferte und ob es sich dabei um Isoformen, um anderweitige Modifizierungen, oder um eine Kreuzreaktion handelt. Auch der Mechanismus der delta-pH-Regulation der Dtx-Epoxidase konnte trotz in vivo und in vitro durchgeführter Studien nicht endgültig geklärt werden. Allerdings konnten verschiedene Mechanismen, wie z.B. eine direkte pH-Abhängigkeit des Enzyms, eine Regulation durch Reduktion und Oxidation oder durch Phosphorylierung und Dephosphorylierung, auf Grund der Daten falsifiziert werden. Es konnte schließlich die Regulation mit Hilfe eines transmembranen Rezeptors als das einzige, mit allen Daten konsistente Regulationsmodell vorgeschlagen werden.

Co-stressors chilling and high light increase photooxidative stress in diuron-treated red alga Kappaphycus alvarezii but with lower involvement of H(2)O(2)

Diuron is one of the most commonly found N-phenylurea herbicides in marine/estuarine waters that promotes toxic effects by inhibiting photosynthesis and affecting the production of reactive oxygen species (ROS) in autotrophs. Since photo- and thermoacclimation are also ROS-mediated processes, this work evaluates a hypothetical additive effect of high light (HL) and chilling (12 degrees C) on 50 nM diuron toxicity to the highly-photosynthetically active apices of the red alga Kappaphycus alvarezii. Additive inhibition of photosynthesis was mainly evidenced by significant decreases of quantum yield of photosystem II and electron transfer rates upon co-stressors exposure to diuron-treated algae. Under extreme 12 degrees C/HL/diuron conditions, unexpected lower correlations between H(2)O(2) concentrations in seawater and radical-sensitive protein thiols were concomitantly measured with the highest indexes of photoinhibition (parameter beta). Altogether, these data support the hypothesis that co-stressors chilling/HL additively inhibit photosynthesis in diuron-exposed K. alvarezii but with less involvement of H(2)O(2) in injury effects than with only chilling or HL. (C) 2010 Elsevier Inc. All rights reserved.

Co-stressors chilling and high light increase photooxidative stress in diuron-treated red alga Kappaphycus alvarezii but with lower involvement of H2O2

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Tomato response to a high light transmission greenhouse film

Increasing greenhouse light transmission has a positive effect not only in Northern latitudes but in Mediterranean countries as well. A greenhouse, H2, with a tetrafluoroethylene copolymer 60 microns film, (Asahi Glass company, Aflex) characterised by its high light transmission and durability was compared to another greenhouse with a co-extruded film considered as a control, H1. Tomato crop response to the increase in light during winter and summer with high temperature and light was evaluated. Light transmission in H2 remained very high in spite of the observed dust accumulation and the low angle of incidence of the winter solar radiation. Transmissivity was clearly higher for H2 (81 to 83 % throughout the season) than in the control (around 63 %). The rest of the climatic parameters were similar in both greenhouses, either in the winter or in the summer evaluations. In spite of the high solar radiation in H2, the summer temperature could be maintained at the desired levels by using evaporative cooling. Accumulated tomato yield and quality was better in the H2 greenhouse (15 % more for the winter crop and 27% more for the summer crop). Fruit size was bigger in the winter crop. As an overall conclusion, the use of high light transmissive films in Mediterranean areas is very convenient for many vegetable crops. This is valid not only in winter but in summer, provided the greenhouse has good ventilation or evaporative cooling to overcome the increase in sensible heat caused by this increase in light..

Kinetic study of the plastoquinone pool availability correlated with H2O2 release in seawater and antioxidant responses in the red alga Kappaphycus alvarezii exposed to single or combined high light, chilling and chemical stresses

Under biotic/abiotic stresses, the red alga Kappaphycus alvarezii reportedly releases massive amounts of H2O2 into the surrounding seawater. As an essential redox signal, the role of chloroplast-originated H2O2 in the orchestration of overall antioxidant responses in algal species has thus been questioned. This work purported to study the kinetic decay profiles of the redox-sensitive plastoquinone pool correlated to H2O2 release in seawater, parameters of oxidative lesions and antioxidant enzyme activities in the red alga Kappaphycus alvarezii under the single or combined effects of high light, low temperature, and sub-lethal doses of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), which are inhibitors of the thylakoid electron transport system. Within 24 h, high light and chilling stresses distinctly affected the availability of the PQ pool for photosynthesis, following Gaussian and exponential kinetic profiles, respectively, whereas combined stimuli were mostly reflected in exponential decays. No significant correlation was found in a comparison of the PQ pool levels after 24 h with either catalase (CAT) or ascorbate peroxidase (APX) activities, although the H2O2 concentration in seawater (R = 0.673), total superoxide dismutase activity (R = 0.689), and particularly indexes of protein (R = 0.869) and lipid oxidation (R = 0.864), were moderately correlated. These data suggest that the release of H2O2 from plastids into seawater possibly impaired efficient and immediate responses of pivotal H2O2-scavenging activities of CAT and APX in the red alga K. alvarezii, culminating in short-term exacerbated levels of protein and lipid oxidation. These facts provided a molecular basis for the recognized limited resistance of the red alga K. alvarezii under unfavorable conditions, especially under chilling stress. © 2006 Elsevier B.V. All rights reserved.

High-resolution dynamic computer simulation analysis of the behavior of sample components with pI values outside the pH gradient established by carrier ampholyte CIEF

The behavior of sample components whose pI values are outside the pH gradient established by 101 hypothetical biprotic carrier ampholytes covering a pH 6-8 range was investigated by computer simulation under constant current conditions with concomitant constant electroosmosis toward the cathode. Data obtained with the sample being applied between zones of carrier ampholytes and on the anodic side of the carrier ampholytes were studied and found to evolve into zone structures comprising three regions between anolyte and catholyte. The focusing region with the pH gradient is bracketed by two isotachopheretic zone structures comprising selected sample and carrier components as isotachophoretic zones. The isotachophoretic structures electrophoretically migrate in opposite direction and their lengths increase with time due to the gradual isotachophoretic decay at the pH gradient edges. Due to electroosmosis, however, the overall pattern is being transported toward the cathode. Sample components whose pI values are outside the established pH gradient are demonstrated to form isotachophoretic zones behind the leading cation of the catholyte (components with pI values larger than 8) and the leading anion of the anolyte (components with pI values smaller than 6). Amphoteric compounds with appropriate pI values or nonamphoteric components can act as isotachophoretic spacer compounds between sample compounds or between the leader and the sample with the highest mobility. The simulation data obtained provide for the first time insight into the dynamics of amphoteric sample components that do not focus within the established pH gradient.

Relationship between photosynthetic electron transport and pH gradient across the thylakoid membrane in intact leaves.

Under conditions (0.2% CO2; 1% O2) that allow high rates of photosynthesis, chlorophyll fluorescence was measured simultaneously with carbon assimilation at various light intensities in spinach (Spinacia oleracea) leaves. Using a stoichiometry of 3 ATP/CO2 and the known relationship between ATP synthesis rate and driving force (Delta pH), we calculated the light-dependent pH gradient (Delta pH) across the thylakoid membrane in intact leaves. These Delta pH values were correlated with the photochemical (qP) and nonphotochemical (qN) quenching of chlorophyll fluorescence and with the quantum yield of photosystem II (phiPSII). At Delta pH > 2.1 all three parameters (qP, qN, and phiPSII) changed very steeply with increasing DeltapH (decreasing pH in the thylakoid). The observed pH dependences followed hexacooperative titration curves with slightly different pKa values. The significance of the steep pH dependences with slightly different pKa values is discussed in relation to the regulation of photosynthetic electron transport in intact leaves.

Different colors of light lead to different adaptation and activation as determined by high-density EEG.

Light adaptation is crucial for coping with the varying levels of ambient light. Using high-density electroencephalography (EEG), we investigated how adaptation to light of different colors affects brain responsiveness. In a within-subject design, sixteen young participants were adapted first to dim white light and then to blue, green, red, or white bright light (one color per session in a randomized order). Immediately after both dim and bright light adaptation, we presented brief light pulses and recorded event-related potentials (ERPs). We analyzed ERP response strengths and brain topographies and determined the underlying sources using electrical source imaging. Between 150 and 261ms after stimulus onset, the global field power (GFP) was higher after dim than bright light adaptation. This effect was most pronounced with red light and localized in the frontal lobe, the fusiform gyrus, the occipital lobe and the cerebellum. After bright light adaptation, within the first 100ms after light onset, stronger responses were found than after dim light adaptation for all colors except for red light. Differences between conditions were localized in the frontal lobe, the cingulate gyrus, and the cerebellum. These results indicate that very short-term EEG brain responses are influenced by prior light adaptation and the spectral quality of the light stimulus. We show that the early EEG responses are differently affected by adaptation to different colors of light which may contribute to known differences in performance and reaction times in cognitive tests.

The O2, pH and Ca2+ Microenvironment of Benthic Foraminifera in a High CO2 World

Ocean acidification (OA) can have adverse effects on marine calcifiers. Yet, phototrophic marine calcifiers elevate their external oxygen and pH microenvironment in daylight, through the uptake of dissolved inorganic carbon (DIC) by photosynthesis. We studied to which extent pH elevation within their microenvironments in daylight can counteract ambient seawater pH reductions, i.e. OA conditions. We measured the O2 and pH microenvironment of four photosymbiotic and two symbiont-free benthic tropical foraminiferal species at three different OA treatments (~432, 1141 and 2151 µatm pCO2). The O2 concentration difference between the seawater and the test surface (delta O2) was taken as a measure for the photosynthetic rate. Our results showed that O2 and pH levels were significantly higher on photosymbiotic foraminiferal surfaces in light than in dark conditions, and than on surfaces of symbiont-free foraminifera. Rates of photosynthesis at saturated light conditions did not change significantly between OA treatments (except in individuals that exhibited symbiont loss, i.e. bleaching, at elevated pCO2). The pH at the cell surface decreased during incubations at elevated pCO2, also during light incubations. Photosynthesis increased the surface pH but this increase was insufficient to compensate for ambient seawater pH decreases. We thus conclude that photosynthesis does only partly protect symbiont bearing foraminifera against OA.

Seawater carbonate chemistry and combined mechanistic effects of CO2 and light on the N2-fixing cyanobacterium Trichodesmium IMS101, 2010

The marine diazotrophic cyanobacterium Trichodesmium responds to elevated atmospheric CO2 partial pressure (pCO2) with higher N2 fixation and growth rates. To unveil the underlying mechanisms, we examined the combined influence of pCO2(150 and 900 µatm) and light (50 and 200 µmol photons m-2 s-1) on TrichodesmiumIMS101. We expand on a complementary study that demonstrated that while elevated pCO2 enhanced N2 fixation and growth, oxygen evolution and carbon fixation increased mainly as a response to high light. Here, we investigated changes in the photosynthetic fluorescence parameters of photosystem II, in ratios of the photosynthetic units (photosystem I:photosystem II), and in the pool sizes of key proteins involved in the fixation of carbon and nitrogen as well as their subsequent assimilation. We show that the combined elevation in pCO2 and light controlled the operation of the CO2-concentrating mechanism and enhanced protein activity without increasing their pool size. Moreover, elevated pCO2 and high light decreased the amounts of several key proteins (NifH, PsbA, and PsaC), while amounts of AtpB and RbcL did not significantly change. Reduced investment in protein biosynthesis, without notably changing photosynthetic fluxes, could free up energy that can be reallocated to increase N2 fixation and growth at elevated pCO2 and light. We suggest that changes in the redox state of the photosynthetic electron transportchain and posttranslational regulation of key proteins mediate the high flexibility in resources and energy allocation in Trichodesmium. This strategy should enableTrichodesmium to flourish in future surface oceans characterized by elevated pCO2, higher temperatures, and high light.