Search results for "Synthetic"
showing 10 items of 723 documents
Boronic Acids of Pharmaceutical Importance Affect the Growth and Photosynthetic Apparatus of Cyanobacteria in a Dose-Dependent Manner
2020
The dynamic increase in the commercial application of antimicrobial derivatives of boronic acids, and potential impact of their presence in aquatic systems, supports the necessity to study the toxicity of these substances towards microorganisms of crucial meaning in the environment. One example of the mentioned derivatives is tavaborole (5-fluoro-substituted benzoxaborole), a pharmaceutical agent with antifungal activity. Cyanobacteria were used as model organisms, which are photoautotrophic prokaryotes, as representative aquatic bacteria and photoautotrophs associated with the plant kingdom. To the best of our knowledge, we investigated this issue for the first time. In order to recognize …
Cadmium accumulation and buffering of cadmium-induced stress by arbuscular mycorrhiza in three Pisum sativum L. genotypes
2002
The role of arbuscular mycorrhiza in reducing Cd stress was investigated in three genotypes of Pisum sativum L. (cv. Frisson, VIR4788, VIR7128), grown in soil/sand pot cultures in the presence and absence of 2-3 mg kg(-1) bioavailable Cd, and inoculated or not with the arbuscular mycorrhizal fungus Glomus intraradices. Shoot, root and pod biomass were decreased by Cd in non-mycorrhizal plants. The presence of mycorrhiza attenuated the negative effect of Cd so that shoot biomass and activity of photosystem II, based on chlorophyll a fluorescence, were not significantly different between mycorrhizal plants growing in the presence or absence of the heavy metal (HM). Total P concentrations were…
Carotenoid binding sites in LHCIIb
2000
The major light-harvesting complex of photosystem II can be reconstituted in vitro from its bacterially expressed apoprotein with chlorophylls a and b and neoxanthin, violaxanthin, lutein, or zeaxanthin as the only xanthophyll. Reconstitution of these one-carotenoid complexes requires low-stringency conditions during complex formation and isolation. Neoxanthin complexes (containing 30–50% of the all-trans isomer) disintegrate during electrophoresis, exhibit a largely reduced resistance against proteolytic attack; in addition, energy transfer from Chl b to Chl a is easily disrupted at elevated temperature. Complexes reconstituted in the presence of either zeaxanthin or lutein contain nearly …
De-epoxidation of Violaxanthin in Light-harvesting Complex I Proteins
2004
The conversion of violaxanthin (Vx) to zeaxanthin (Zx) in the de-epoxidation reaction of the xanthophyll cycle plays an important role in the protection of chloroplasts against photooxidative damage. Vx is bound to the antenna proteins of both photosystems. In photosystem II, the formation of Zx is essential for the pH-dependent dissipation of excess light energy as heat. The function of Zx in photosystem I is still unclear. In this work we investigated the de-epoxidation characteristics of light-harvesting complex proteins of photosystem I (LHCI) under in vivo and in vitro conditions. Recombinant LHCI (Lhcal-4) proteins were reconstituted with Vx and lutein, and the convertibility of Vx wa…
Localization of the N-terminal Domain in Light-harvesting Chlorophyll a/b Protein by EPR Measurements
2005
The conformational distribution of the N-terminal domain of the major light-harvesting chlorophyll a/b protein (LHCIIb) has been characterized by electron-electron double resonance yielding distances between spin labels placed in various domains of the protein. Distance distributions involving residue 3 near the N terminus turned out to be bimodal, revealing that this domain, which is involved in regulatory functions such as balancing the energy flow through photosystems (PS) I and II, exists in at least two conformational states. Models of the conformational sub-ensembles were generated on the basis of experimental distance restraints from measurements on LHCIIb monomers and then checked f…
Evidence for two spectroscopically different dimers of light-harvesting complex I from green plants
2000
A preparation consisting of isolated dimeric peripheral antenna complexes from green plant photosystem I (light-harvesting complex I or LHCI) has been characterized by means of (polarized) steady-state absorption and fluorescence spectroscopy at low temperatures. We show that this preparation can be described reasonably well by a mixture of two types of dimers. In the first dimer about 10% of all Q(y)() absorption of the chlorophylls arises from two chlorophylls with absorption and emission maxima at about 711 and 733 nm, respectively, whereas in the second about 10% of the absorption arises from two chlorophylls with absorption and emission maxima at about 693 and 702 nm, respectively. The…
Light-harvesting chlorophyll protein (LHCII) drives electron transfer in semiconductor nanocrystals
2017
Type-II quantum dots (QDs) are capable of light-driven charge separation between their core and the shell structures; however, their light absorption is limited in the longer-wavelength range. Biological light-harvesting complex II (LHCII) efficiently absorbs in the blue and red spectral domains. Therefore, hybrid complexes of these two structures may be promising candidates for photovoltaic applications. Previous measurements had shown that LHCII bound to QD can transfer its excitation energy to the latter, as indicated by the fluorescence emissions of LHCII and QD being quenched and sensitized, respectively. In the presence of methyl viologen (MV), both fluorescence emissions are quenched…
Characterization of the Fast and Slow Reversible Components of Non-Photochemical Quenching in Isolated Pea Thylakoids by Picosecond Time-Resolved Chl…
1999
The fast and slow reversible components of non-photochemical chlorophyll fluorescence quenching commonly assigned to the qE and the qI mechanism have been studied in isolated pea thylakoids which were prepared from leaves after a moderate photoinhibitory treatment. Chlorophyll fluorescence decays were measured at picosecond resolution and analyzed on the basis of the heterogeneous exciton/radical pair equilibrium model. Our results show that the fast reversible non-photochemical quenching is completely assigned to the PS II antenna and is related to zeaxanthin. The slow reversible qI type quenching is located at the PS II reaction center and involves enhanced nonradiative decay of the prima…
Assessing and modeling nitrite inhibition in microalgae-bacteria consortia for wastewater treatment by means of photo-respirometric and chlorophyll f…
2022
Abstract Total nitrite (TNO2 = HNO2 + NO−2) accumulation due to the activity of ammonia-oxidizing bacteria (AOB) was monitored in microalgae-bacteria consortia, and the inhibitory effect of nitrite/free nitrous acid (NO2-N/FNA) on microalgae photosynthesis and inhibition mechanism was studied. A culture of Scenedesmus was used to run two sets of batch reactors at different pH and TNO2 concentrations to evaluate the toxic potential of NO2-N and FNA. Photo-respirometric tests showed that NO2-N accumulation has a negative impact on net oxygen production rate (OPRNET). Chlorophyll a fluorescence analysis was used to examine the biochemical effects of NO2-N stress and the mechanism of NO2-N inhi…
Expression of a higher plant light-harvesting chlorophyll a/b-binding protein in Synechocystis sp. PCC 6803
1999
A chimeric lhcb gene, coding for Lhcb, a higher plant chlorophyll a/b-binding light-harvesting complex of photosystem II (LHCII), was constructed using the Synechocystis sp. PCC 6803 psbA3 promoter and a modified lhcb gene from pea. This construct drives synthesis of full-length, mature Lhcb under the control of the strong psbA3 promoter that usually drives expression of the D1 protein of photosystem II. This chimeric gene was transformed into a photosystem I-less/chlL(-) Synechocystis sp. PCC 6803 strain that is unable to synthesize chlorophyll in darkness. In the resulting strain, a high level of lhcb transcript was detected and transcript accumulation was enhanced by addition of exogenou…