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Nitric oxide (NO) is a non-traditional regulator of the growth of plants and phytoplankton. Here, the growth of five marine phytoplankton species, Platymonas helgolandica var. tsingtaoensis, Platymonas subcordiformis, Skeletonema costatum, Gymnodinium sp., and Prorocentrum donghaiense, was monitored, and carbonate system parameters in the culture media were determined after adding different concentrations of NO and sodium nitroprusside (SNP, NO donor) solutions. The two dietary algae (P. helgolandica var. tsingtaoensis and P. subcordiformis) and three red tide algae (S. costatum, Gymnodinium sp., and P. donghaiense) showed different responses to the same NO concentration. The red tide algae were more sensitive to exogenous NO than the dietary algae. NO with a concentration of 1.4 x 10.sup.-6 mol L.sup.-1 had the optimal stimulatory effect on the growth of the microalgae and increased the cell density by 9.8-38.3%. SNP solution with a concentration of 100 [mu]mol L.sup.-1 inhibited the growth of the two dietary algae, and the cell density decreased by 38.8-84.3%. The addition of 10 [mu]mol L.sup.-1 SNP solution to the three red tide algae decreased the cell density by 95.3-99.9%. Low concentrations of SNP (0.1 [mu]mol L.sup.-1 for the two dietary algae and 0.01 [mu]mol L.sup.-1 for the red tide algae) slightly promoted the growth of microalgae. High concentrations of NO (100 [mu]mol L.sup.-1 SNP) inhibited CO.sub.2 assimilation, whereas low concentrations of NO (0.01-1.0 [mu]mol L.sup.-1 SNP) promoted CO.sub.2 assimilation, indicating that NO participates in the regulation of photosynthesis., Author(s): Pei-Feng Li [sup.1] , Min Zhao [sup.1] , Chun-Ying Liu [sup.1] [sup.2] , Gui-Peng Yang [sup.1] [sup.2] Author Affiliations: (1) grid.4422.0, 0000 0001 2152 3263, Frontiers Science Center for [...]

Cloud cover regulates the gross primary productivity (GPP) of forest ecosystems by changing the radiation component and other environmental factors. In this study, we used an open-path eddy covariance system and microclimate sensors installed over a poplar plantation in northern China to measure the carbon exchange and climate variables during the mid-growing seasons (June to August) in 2014 and 2015. The results indicated that the GPP of the plantation peaked when the clearness index (CI) was between 0.45 and 0.65, at which point diffuse photosynthetically active radiation ([PAR.sub.dif]) had reached its maximum. Cloudy skies increased the maximum ecosystem photosynthetic capacity ([P.sub.max]) by 28% compared with clear skies. [PAR.sub.dif] and soil moisture were the most and the least crucial drivers for photosynthetic productivity of the plantation under cloudy skies, respectively. The ecosystem photosynthetic potential was higher under lower vapor pressure deficit (VPD < 1.5 kPa), lower air temperature ([T.sub.a] < 30 [degrees]C), and nonstressed conditions (REW > 0.4) for cloudy skies due to effects of [T.sub.a] and VPD on stoma. Overall, our research highlighted the importance of cloud-induced radiation component change and environmental variation in quantifying the GPP of forest ecosystems. Key words: cloudiness, gross primary productivity, poplar plantation, environmental conditions, path analysis. Couverture nuageuse regularise la productivite primaire brute (PPB) des ecosystemes forestiers en modifiant les composantes de la radiation et d'autres facteurs environnementaux. Dans cette etude, nous avons utilise un systeme de mesure de la covariance des turbulences a champ ouvert et des capteurs microclimatiques au-dessus d'une plantation de peuplier dans le nord de la Chine pour mesurer les echanges de carbone et les variables climatiques durant le milieu de la saison de croissance (juin a aout) en 2014 et 2015. Les resultats indiquent que la PPB de la plantation a culmine lorsque l'indice de clarte (IC) etait entre 0,4 et 0,65, au point ou le rayonnement photosynthetiquement actif diffus ([RPA.sub.dif]) avait atteint son maximum. Un ciel couvert a augmente la capacite photosynthetique maximale de l'ecosysteme ([P.sub.max]) de 28 % comparativement a un ciel degage. Le [RPA.sub.dif] et l'humidite du sol etaient les facteurs respectivement le plus et le moins determinants pour la productivite photosynthetique de la plantation sous un ciel couvert. Le potentiel photosynthetique de l'ecosysteme etait plus eleve lorsque que le deficit de pression de vapeur (DPV) etait plus faible (DPV < 1,5 kPa), la temperature de l'air etait plus basse ([T.sub.a] < 30 [degrees]C) et en l'absence de stress (proportion d'eau du sol extractible > 0,4) sous un ciel couvert a cause des effets de la [T.sub.a] et du DPV sur les stomates. Globalement, nos travaux de recherche mettent en evidence l'importance du changement dans les composantes du rayonnement cause par les nuages et des variations environnementales pour quantifier la PPB des ecosystemes forestiers. [Traduit par la Redaction] Mots-cles: couverture nuageuse, productivite primaire brute, plantation de peuplier, conditions environnementales, analyse des pistes causales., 1. Introduction The global-dimming phenomenon, caused by the drastic increase in clouds and atmospheric particulates produced by fossil fuel combustion and other human activities, has continuously decreased the amount of [...]

Chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a light-regulated, NAD(P)H-dependent enzyme involved in plant photosynthetic carbon reduction. Unlike lower photosynthetic organisms, which only contain [A.sub.4]-GAPDH, the major GAPDH isoform of land plants is made up of A and B subunits, the latter containing a C-terminal extension (CTE) with fundamental regulatory functions. Light-activation of AB-GAPDH depends on the redox state of a pair of cysteines of the CTE, which can form a disulfide bond under control of thioredoxin f, leading to specific inhibition of the NADPH-dependent activity. The tridimensional structure of [A.sub.2][B.sub.2]-GAPDH from spinach chloroplasts, crystallized in the oxidized state, shows that each disulfide-containing CTE is docked into a deep cleft between a pair of A and B subunits. The structure of the CTE was derived from crystallographic data and computational modeling and confirmed by site-specific mutagenesis. Structural analysis of oxidized [A.sub.2][B.sub.2]-GAPDH and chimeric mutant [[A+CTE].sub.4]-GAPDH revealed that Arg-77, which is essential for coenzyme specificity and high NADPH-dependent activity, fails to interact with NADP in these kinetically inhibited GAPDH tetramers and is attracted instead by negative residues of oxidized CTE. Other subtle changes in catalytic domains and overall conformation of the tetramers were noticed in oxidized [A.sub.2][B.sub.2]-GAPDH and [[A+CTE]].sub.4]-GAPDH, compared with fully active [A.sub.4]-GAPDH. The CTE is envisioned as a redox-sensitive regulatory domain that can force AB-GAPDH into a kinetically inhibited conformation under oxidizing conditions, which also occur during dark inactivation of the enzyme in vivo. Calvin cycle | disulfide | light/dark | protein structure | redox

The analysis of cell signaling requires the rapid and selective manipulation of protein function. We have synthesized photoswitches that covalently modify target proteins and reversibly present and withdraw a ligand from its binding site due to photoisomerization of an azobenzene linker. We describe here the properties of a glutamate photoswitch that controls an ion channel in cells. Affinity labeling and geometric constraints ensure that the photoswitch controls only the targeted channel, and enables spatial patterns of light to favor labeling in one location over another. Photoswitching to the activating state places a tethered glutamate at a high (millimolar) effective local concentration near the binding site. The fraction of active channels can be set in an analog manner by altering the photostationary state with different wavelengths. The bistable photoswitch can be turned on with millisecond-long pulses at one wavelength, remain on in the dark for minutes, and turned off with millisecond long pulses at the other wavelength, yielding sustained activation with minimal irradiation. The system provides rapid, reversible remote control of protein function that is selective without orthogonal chemistry. azobenzene | ion channel | photoisomerization | optical switch | remote control

An attempt is made to examine whether it is possible to trap an [S.sub.2] to [S.sub.3] state intermediate in oxygen-evolving photosystem II preparations. These experiments show that an intermediate of the [S.sub.2] to [S.sub.3] transition is formed at temperatures much lower than the threshold for the [S.sub.2] to [S.sub.3] transition.

Photosynthetic oxygen production by photosystem II (PSII) is responsible for the maintenance of aerobic life on earth. The production of oxygen occurs at the PSII oxygen-evolving complex (OEC), which contains a tetranuclear manganese (Mn) cluster. Photo-induced electron transfer events in the reaction center lead to the accumulation of oxidizing equivalents on the OEC. Four sequential photooxidation reactions are required for oxygen production. The oxidizing complex cycles among five oxidation states, called the [S.sub.n] states, where n refers to the number of oxidizing equivalents stored. Oxygen release occurs during the [S.sub.3]-to-[S.sub.0] transition from an unstable intermediate, known as the [S.sub.4] state. In this report, we present data providing evidence for the production of an intermediate during each S state transition. These protein-derived intermediates are produced on the microsecond to millisecond time scale and are detected by time-resolved vibrational spectroscopy on the microsecond time scale. Our results suggest that a protein-derived conformational change or proton transfer reaction precedes Mn redox reactions during the [S.sub.2]-t0-[S.sub.3] and [S.sub.3]-to-[S.sub.0] transitions. manganese cluster | photosynthesis | photosystem II | time-resolved IR | water oxidation

Special rapid-mixing isotopic experiments using (super 18)O/(super 13)C-labeled bicarbonate are employed to quantify the inherent carbonic anhydrase activity in photosystem II (PS II) samples and the potential flux of oxygen from bicarbonate into the photosynthetically produced O2. The results show that bicarbonate is not the substrate for O2 production in these contemporary oxygenic photoautotrophs when assayed under single turnover conditions.

The pathway and its possible role for water oxidation in photosystem II (PSII) is elucidated by calculating the pKa for the residues along the proposed proton exit pathway by solving the linearized Poisson-Boltzmann equation for the whole PSII complex, taking into account the atomic coordinates of all amino acid residues and bound cofactors. The pKa of these residues are dramatically affected when the atomic coordinates of PsbO are removed, indicating a significant role of PsbO in tuning the pKa of those residues in the proton pathway.

The effect of adding azide to photosystem II (PS II) membrane samples (BBY preparation), with or without chloride is investigated using continuous wave (CW) and pulsed EPR spectroscopy. The results demonstrate an azide-binding site in the immediate vicinity of the Mn cluster, and provide further evidence that chloride is bound proximal to the Mn cluster as well.

Photosynthesis uses light energy to drive the oxidation of water at an oxygen-evolving catalytic site within photosystem II (PSII). We report the structure of PSII of the cyanobacterium Thermosynechococcus elongatus at 3.5 angstrom resolution. We have assigned most of the amino acid residues of this 650-kilodalton dimeric multisubunit complex and refined the structure to reveal its molecular architecture. Consequently, we are able to describe details of the binding sites for cofactors and propose a structure of the oxygen-evolving center (OEC). The data strongly suggest that the OEC contains a cubane-like [Mn.sub.3]Ca[O.sub.4] cluster linked to a fourth Mn by a mono-μ-oxo bridge. The details of the surrounding coordination sphere of the metal cluster and the implications for a possible oxygen-evolving mechanism are discussed., Photosynthesis uses light energy to couple the formation of molecular dioxygen to the fixation of C[O.sub.2]. This process simultaneously generates an aerobic atmosphere and produces a readily usable carbon source, [...]

A study on triplet quenching, the major photoprotection mechanism in antenna proteins, is studied in the light-harvesting complex of photosystem I. The process was investigated at low temperature by means of optically detected magnetic resonance that is well suited for investigation of triplet states in photosynthetic systems.