Effects of salt concentration, pH, and their interaction on plant growth, nutrient uptake, and photochemistry of alfalfa (Medicago sativa) leaves

In order to explore the main limiting factors affecting the growth and physiological function of alfalfa under salt and alkali stress, the effect of the salt and alkali stress on the growth and physiological function of alfalfa was studied. The results showed that effects of the excessive salt concentration (100 and 200 mM) on the growth and physiological characteristics were significantly greater than that of pH (7.0 and 9.0). Under 100 mM salt stress, there was no significant difference in the growth and photosynthetic function between pH 9.0 and pH 7.0. Under the 200 mM salt concentration the absorption of Na⁺ by alfalfa treated at the pH 9.0 did not increase significantly compared with absorption at the pH 7.0. However, the higher pH directly reduced the root activity, leaf's water content, and N-P-K content also decreased significantly. The PSII and PSI activities decreased with increasing the salt concentration, especially the damage degree of PSI. Although the photoinhibition of PSII was not significant, PSII donor and electron transfer from the Q_A to Q_B of the PSII receptor sides was inhibited. In a word, alfalfa showed relatively strong salt tolerance capacity, at the 100 mM salt concentration, even when the pH reached 9.0. Thus, the effect on the growth and photosynthetic function was not significant. However, at 200 mM salt concentration, pH 9.0 treatment caused damage to root system and the photosynthetic function in leaves of alfalfa was seriously injured.

Photo-degradation dynamics of five neonicotinoids: Bamboo vinegar as a synergistic agent for improved functional duration

The effects of photo-degradation on the utilization of pesticides in agricultural production has been investigated. Various influencing factors were compared, with results showing that the initial pesticide concentration, light source, water quality and pH possessed different effects on neonicotinoids photo-degradation. The initial concentration and pH were found to be most critical effects. The photo-degradation rate decreased by a factor of 2-4 when the initial concentration increased from 5 mg L-1 to 20 mg L-1, particularly for acetamiprid and imidacloprid. The photo-degradation pathways and products of the five neonicotinoids were also investigated, with similar pathways found for each pesticide, except for acetamiprid. Degradation pathways mainly involved photo-oxidation processes, with products identified using liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS) found to be consistent with literature reported results. Bamboo vinegar exerted a photo-quenching effect on the neonicotinoids, with an improved efficiency at higher vinegar concentrations. The photo-quenching rates of thiamethoxam and dinotefuran were 381.58% and 310.62%, respectively, when a 30-fold dilution of vinegar was employed. The photo-degradation products in bamboo vinegar were identical to those observed in methanol, with acetic acid being the main factor influencing the observed quenching effects.

Simultaneous photoreduction and Raman spectroscopy of red blood cells to investigate the effects of organophosphate exposure

Simultaneous photoreduction and Raman spectroscopy with 532 nm laser has been used to study the effects of organophosphate (chlorpyrifos [CPF]) exposure on human red blood cells (RBCs). Since in RBCs, auto-oxidation causes oxidative stress, which, in turn, is balanced by the cellular detoxicants, any possible negative effect of CPF on this balance should results in an increased level of damaged (permanently oxygenated) hemoglobin. Therefore, when 532 nm laser, at a suitable power, was applied to photoreduce the cells, only common oxygenated form of hemoglobin got photoreduced leaving the permanently oxygenated hemoglobin detectable in the Raman spectra simultaneously excited by the same laser. Using the technique effects of CPF to build up oxidative stress on RBCs could be detected at concentrations as low as 10 ppb from a comparison of relative strengths of different Raman bands. Experiments performed using simultaneously exposing the cells, along with CPF, to H₂ O₂ (oxidative agent) and/or 3-Aminotriazole (inhibitor of anti-oxidant catalase), suggested role of CPF to suppress the cellular anti-oxidant mechanism. Since the high level of damaged hemoglobin produced by the action of CPF (at concentrations >100 ppm) is expected to cause membrane damage, atomic force microscopy (AFM) was used to identify such damages.Upper panel: Raman spectra of normal, photoreduced CPF exposed and unexposed RBCs. Lower panel: The weak Fe-O₂ Raman band for CPF exposed cells shown on the left. The AFM images of unexposed and exposed cells are shown on the right. Scale bar, 2.5 μm.

Photochemical and Structural Studies on Cyclic Peptide Models

Ultra-violet (UV) irradiation has a significant impact on the structure and function of proteins that is supposed to be in relationship with the tryptophan-mediated photolysis of disulfide bonds. To investigate the correlation between the photoexcitation of Trp residues in polypeptides and the associated reduction of disulfide bridges, a series of small, cyclic oligopeptide models were analyzed in this work. Average distances between the aromatic side chains and the disulfide bridge were determined following molecular mechanics (MM) geometry optimizations. In this way, the possibility of cation–π interactions was also investigated. Molecular mechanics calculations revealed that the shortest distance between the side chain of the Trp residues and the disulfide bridge is approximately 5 Å in the cyclic pentapeptide models. Based on this, three tryptophan-containing cyclopeptide models were synthesized and analyzed by nuclear magnetic resonance (NMR) spectroscopy. Experimental data and detailed molecular dynamics (MD) simulations were in good agreement with MM geometry calculations. Selected model peptides were subjected to photolytic degradation to study the correlation of structural features and the photolytic cleavage of disulfide bonds in solution. Formation of free sulfhydryl groups upon illumination with near UV light was monitored by fluorescence spectroscopy after chemical derivatization with 7-diethylamino-3-(4-maleimidophenyl)-4-methylcoumarin (CPM) and mass spectrometry. Liquid cromatography-mass spectrometry (LC-MS) measurements indicated the presence of multiple photooxidation products (e.g., dimers, multimers and other oxidated products), suggesting that besides the photolysis of disulfide bonds secondary photolytic processes take place.

[Optically dissecting brain nicotinic receptor function with photo-controllable designer receptors]

Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels widely expressed in the central nervous system and the periphery. They play an important modulatory role in learning, memory and attention, and have been implicated in various diseases such as Alzheimer's disease, Parkinson's disease, epilepsy, schizophrenia and addiction. These receptors are activated by the endogenous neurotransmitter acetylcholine, or by nicotine, the alkaloid found in tobacco leaves. Both molecules open the ion channel and cause the movement of cations across the membrane, which directly affects neuronal excitability and synaptic plasticity. nAChRs are very heterogeneous in their subunit composition (α2-10 et β2-4), in their brain distribution (cortex, midbrain, striatum…) and in their sub-cellular localization (pre- vs post-synaptic, axonal, dendritic…). This heterogeneity highly contributes to the very diverse roles these receptors have in health and disease. The ability to activate or block a specific nAChR subtype, at a defined time and space within the brain, would greatly help obtaining a clearer picture of these various functions. To this aim, we are developing novel optogenetic pharmacology strategies for optically controlling endogenous nAChR isoforms within the mouse brain. The idea is to tether a chemical photoswitch on the surface of a cysteine-modified nAChR, and use light for rapidly and reversibly turning that receptor mutant on and off. Here we will discuss the history of optogenetic pharmacology, and the recent advances for the optical control of brain nicotinic receptors in vivo.

Diversity of strategies for escaping reactive oxygen species production within photosystem I among land plants: P700 oxidation system is prerequisite for alleviating photoinhibition in photosystem I

In land plants, photosystem I (PSI) photoinhibition limits carbon fixation and causes growth defects. In addition, recovery from PSI photoinhibition takes much longer than PSII photoinhibition when the PSI core-complex is degraded by oxidative damage. Accordingly, PSI photoinhibition should be avoided in land plants, and land plants should have evolved mechanisms to prevent PSI photoinhibition. However, such protection mechanisms have not yet been identified, and it remains unclear whether all land plants suffer from PSI photoinhibition in the same way. In the present study, we focused on the susceptibility of PSI to photoinhibition and investigated whether mechanisms of preventing PSI photoinhibition varied among land plant species. To assess the susceptibility of PSI to photoinhibition, we used repetitive short-pulse (rSP) illumination, which specifically induces PSI photoinhibition. Subsequently, we found that land plants possess a wide variety of tolerance mechanisms against PSI photoinhibition. In particular, gymnosperms, ferns and mosses/liverworts exhibited higher tolerance to rSP illumination-induced PSI photoinhibition than angiosperms, and detailed analyses indicated that the tolerance of these groups could be partly attributed to flavodiiron proteins, which protected PSI from photoinhibition by oxidizing the PSI reaction center chlorophyll (P700) as an electron acceptor. Furthermore, we demonstrate, for the first time, that gymnosperms, ferns and mosses/liverworts possess a protection mechanism against photoinhibition of PSI that differs from that of angiosperms.

Effects of acetylacetone on the photoconversion of pharmaceuticals in natural and pure waters

Acetylacetone (AcAc) has proven to be a potent photo-activator in the degradation of color compounds. The effects of AcAc on the photochemical conversion of five colorless pharmaceuticals were for the first time investigated in both pure and natural waters with the UV/H₂O₂ process as a reference. In most cases, AcAc played a similar role to H₂O₂. For example, AcAc accelerated the photodecomposition of carbamazepine, oxytetracycline, and tetracycline in pure water. Meanwhile, the toxicity of tetracyclines and carbamazepine were reduced to a similar extent to that in the UV/H₂O₂ process. However, AcAc worked in a way different from that of H₂O₂. Based on the degradation kinetics, solvent kinetic isotope effect, and the inhibiting effect of O₂, the underlying mechanisms for the degradation of pharmaceuticals in the UV/AcAc process were believed mainly to be direct energy transfer from excited AcAc to pharmaceuticals rather than reactive oxygen species-mediated reactions. In natural waters, dissolved organic matter (DOM) played a crucial role in the photoconversion of pharmaceuticals. The role of H₂O₂ became negligible due to the scavenging effects of DOM and inorganic ions. Interestingly, in natural waters, AcAc first accelerated the photodecomposition of pharmaceuticals and then led to a dramatic reduction with the depletion of dissolved oxygen. Considering the natural occurrence of diketones, the results here point out a possible pathway in the fate and transport of pharmaceuticals in aquatic ecosystems.

Mitochondrial Alternative Pathway-Associated Photoprotection of Photosystem II is Related to the Photorespiratory Pathway

Respiratory electron transport has two ubiquinol-oxidizing pathways, the cytochrome pathway (CP) and the alternative pathway (AP). The AP, which is catalyzed by the alternative oxidase (AOX), is energetically wasteful but may alleviate PSII photoinhibition under light conditions excessive for photosynthesis. However, its mechanism remains unknown. We used Arabidopsis aox1a mutants lacking AOX activity and studied the mutation's effects on photoinhibition by measuring the decrease in the maximum quantum yield of PSII (F_v/F_m) after high light exposure. Since the CP compensates for the lack of AOX, we monitored the extent of photoinhibition under conditions where CP activity is partially inhibited by antimycin A. When leaves were exposed to high light at 350 µmol m^-2 s^-1, the decline in F_v/F_m was significantly faster in the aox1a mutants than in the wild type. However, under conditions where photorespiration was suppressed by high CO₂ or low O₂ levels, the decline in F_v/F_m was suppressed in the aox1a mutants, but not in the wild type, making the difference between the wild type and mutants small. Our results demonstrate that the lack of the AP causes an acceleration of PSII photoinhibition in relation to the photorespiratory pathway, suggesting that the AP can support the activity of the photorespiratory pathway under high light conditions.

Production of biomass and lipids by the oleaginous microalgae Monoraphidium sp. QLY-1 through heterotrophic cultivation and photo-chemical modulator induction

A two-step strategy comprising heterotrophic cultivation and photo-chemical modulator induction was developed to enhance biomass and lipid accumulation in the oleaginous Monoraphidium sp. QLY-1, which was isolated from Qilu Lake in Yunnan Plateau. The algae were first cultivated heterotrophically to achieve high biomass concentration (5.54gL(-1)) with a lipid content of 22.47%. The cultivated algae were diluted, transferred to light environment, and treated with different chemical elicitors. Results showed that the lipid content increased to 36.68% after 3-day of photoinduction. The lipid content was further enhanced by 1.21, 1.32, and 1.29 folds in algal cells treated with nitrogen deficiency, 20gL(-1) NaCl, and 5mM glycine betaine, respectively. The maximum lipid content (48.54%) and lipid productivity (121.27mgL(-1)d(-1)) were obtained in treatments with 20gL(-1) NaCl and 5mM GB, respectively. This study proposes a strategy to efficiently produce lipids by using microalgae.

The Type II NADPH Dehydrogenase Facilitates Cyclic Electron Flow, Energy-Dependent Quenching, and Chlororespiratory Metabolism during Acclimation of Chlamydomonas reinhardtii to Nitrogen Deprivation

When photosynthetic organisms are deprived of nitrogen (N), the capacity to grow and assimilate carbon becomes limited, causing a decrease in the productive use of absorbed light energy and likely a rise in the cellular reduction state. Although there is a scarcity of N in many terrestrial and aquatic environments, a mechanistic understanding of how photosynthesis adjusts to low-N conditions and the enzymes/activities integral to these adjustments have not been described. In this work, we use biochemical and biophysical analyses of photoautotrophically grown wild-type and mutant strains of Chlamydomonas reinhardtii to determine the integration of electron transport pathways critical for maintaining active photosynthetic complexes even after exposure of cells to N deprivation for 3 d. Key to acclimation is the type II NADPH dehydrogenase, NDA2, which drives cyclic electron flow (CEF), chlororespiration, and the generation of an H(+) gradient across the thylakoid membranes. N deprivation elicited a doubling of the rate of NDA2-dependent CEF, with little contribution from PGR5/PGRL1-dependent CEF The H(+) gradient generated by CEF is essential to sustain nonphotochemical quenching, while an increase in the level of reduced plastoquinone would promote a state transition; both are necessary to down-regulate photosystem II activity. Moreover, stimulation of NDA2-dependent chlororespiration affords additional relief from the elevated reduction state associated with N deprivation through plastid terminal oxidase-dependent water synthesis. Overall, rerouting electrons through the NDA2 catalytic hub in response to photoautotrophic N deprivation sustains cell viability while promoting the dissipation of excess excitation energy through quenching and chlororespiratory processes.

Energy dissipation pathways in Photosystem 2 of the diatom, Phaeodactylum tricornutum, under high-light conditions

To prevent photooxidative damage under supraoptimal light, photosynthetic organisms evolved mechanisms to thermally dissipate excess absorbed energy, known as non-photochemical quenching (NPQ). Here we quantify NPQ-induced alterations in light-harvesting processes and photochemical reactions in Photosystem 2 (PS2) in the pennate diatom Phaeodactylum tricornutum. Using a combination of picosecond lifetime analysis and variable fluorescence technique, we examined the dynamics of NPQ activation upon transition from dark to high light. Our analysis revealed that NPQ activation starts with a 2-3-fold increase in the rate constant of non-radiative charge recombination in the reaction center (RC); however, this increase is compensated with a proportional increase in the rate constant of back reactions. The resulting alterations in photochemical processes in PS2 RC do not contribute directly to quenching of antenna excitons by the RC, but favor non-radiative dissipation pathways within the RC, reducing the yields of spin conversion of the RC chlorophyll to the triplet state. The NPQ-induced changes in the RC are followed by a gradual ~ 2.5-fold increase in the yields of thermal dissipation in light-harvesting complexes. Our data suggest that thermal dissipation in light-harvesting complexes is the major sink for NPQ; RCs are not directly involved in the NPQ process, but could contribute to photoprotection via reduction in the probability of (3)Chl formation.

Self-decontaminating photocatalytic zinc oxide nanorod coatings for prevention of marine microfouling: a mesocosm study

The antifouling (AF) properties of zinc oxide (ZnO) nanorod coated glass substrata were investigated in an out-door mesocosm experiment under natural sunlight (14:10 light: dark photoperiod) over a period of five days. The total bacterial density (a six-fold reduction) and viability (a three-fold reduction) was significantly reduced by nanocoatings in the presence of sunlight. In the absence of sunlight, coated and control substrata were colonized equally by bacteria. MiSeq Illumina sequencing of 16S rRNA genes revealed distinct bacterial communities on the nanocoated and control substrata in the presence and absence of light. Diatom communities also varied on nanocoated substrata in the presence and the absence of light. The observed AF activity of the ZnO nanocoatings is attributed to the formation of reactive oxygen species (ROS) through photocatalysis in the presence of sunlight. These nanocoatings are a significant step towards the production of an environmentally friendly AF coating that utilizes a sustainable supply of sunlight.

Light-Harvesting Complex Stress-Related Proteins Catalyze Excess Energy Dissipation in Both Photosystems of Physcomitrella patens

Two LHC-like proteins, Photosystem II Subunit S (PSBS) and Light-Harvesting Complex Stress-Related (LHCSR), are essential for triggering excess energy dissipation in chloroplasts of vascular plants and green algae, respectively. The mechanism of quenching was studied in Physcomitrella patens, an early divergent streptophyta (including green algae and land plants) in which both proteins are active. PSBS was localized in grana together with photosystem II (PSII), but LHCSR was located mainly in stroma-exposed membranes together with photosystem I (PSI), and its distribution did not change upon high-light treatment. The quenched conformation can be preserved by rapidly freezing the high-light-treated tissues in liquid nitrogen. When using green fluorescent protein as an internal standard, 77K fluorescence emission spectra on isolated chloroplasts allowed for independent assessment of PSI and PSII fluorescence yield. Results showed that both photosystems underwent quenching upon high-light treatment in the wild type in contrast to mutants depleted of LHCSR, which lacked PSI quenching. Due to the contribution of LHCII, P. patens had a PSI antenna size twice as large with respect to higher plants. Thus, LHCII, which is highly abundant in stroma membranes, appears to be the target of quenching by LHCSR.

Betalain induction by l-DOPA application confers photoprotection to saline-exposed leaves of Disphyma australe

The capacity to synthesize betalains has arisen in diverse phylogenetic lineages across the Caryophyllales, and because betalainic plants often grow in deserts, sand dunes, or salt marshes, it is likely that these pigments confer adaptive advantages. However, possible functional roles of foliar betalains remain largely unexplored and are difficult to test experimentally. We adopted a novel approach to examine putative photoprotective roles of betalains in leaves for which chloroplast function has been compromised by salinity. Responses of l-DOPA-treated red shoots of Disphyma australe to high light and salinity were compared with those of naturally red- and green-leafed morphs. Betalain content and tyrosinase activity were measured, and Chl fluorescence profiles and H2 O2 production were compared under white, red or green light. Green leaves lacked tyrosinase activity, but when supplied with exogenous l-DOPA they produced five betacyanins. Both the naturally red and l-DOPA-induced red leaves generated less H2 O2 and showed smaller declines in photosystem II quantum efficiency than did green leaves when exposed to white or green light, although not when exposed to red light. Light screening by epidermal betalains effectively reduces the propensity for photoinhibition and photo-oxidative stress in subjacent chlorenchyma. This may assist plant survival in exposed and saline environments.

NPR1-dependent salicylic acid signaling is not involved in elevated CO2-induced heat stress tolerance in Arabidopsis thaliana

Elevated CO2 can protect plants from heat stress (HS); however, the underlying mechanisms are largely unknown. Here, we used a set of Arabidopsis mutants such as salicylic acid (SA) signaling mutants nonexpressor of pathogenesis-related gene 1 (npr1-1 and npr1-5) and heat-shock proteins (HSPs) mutants (hsp21 and hsp70-1) to understand the requirement of SA signaling and HSPs in elevated CO2-induced HS tolerance. Under ambient CO2 (380 µmol mol(-1)) conditions, HS (42°C, 24 h) drastically decreased maximum photochemical efficiency of PSII (Fv/Fm) in all studied plant groups. Enrichment of CO2 (800 µmol mol(-1)) with HS remarkably increased the Fv/Fm value in all plant groups except hsp70-1, indicating that NPR1-dependent SA signaling is not involved in the elevated CO2-induced HS tolerance. These results also suggest an essentiality of HSP70-1, but not HSP21 in elevated CO2-induced HS mitigation.

Effect of naphthalene on photosystem 2 photochemical activity of pea plants

The effect of a typical polyaromatic hydrocarbon, naphthalene (Naph), on photosystem 2 (PS-2) photochemical activity in thylakoid membrane preparations and 20-day-old pea leaves was studied. Samples were incubated in water in the presence of Naph (0.078, 0.21, and 0.78 mM) for 0.5-24 h under white light illumination (15 μmol photons·m(-2)·s(-1)). The PS-2 activity was determined by studying fast and delayed chlorophyll (Chl) a fluorescence. Incubation of samples in water solutions at Naph concentrations of 0.21 and 0.78 mM led to a decrease in the maximum PS-2 quantum efficiency (Fv/Fm), noticeable changes in the polyphasic induction kinetics of fluorescence (OJIP), and a decrease in the amplitudes of the fast and slow components of delayed fluorescence of Chl a. The rate of release of electrolytes from leaves that were preliminarily incubated with Naph (0.21 mM) was also increased. Significant decrease in the fluorescence parameters in thylakoid membrane preparations was observed at Naph concentration of 0.03 mM and 12-min exposure of the samples. Chlorophyll (a and b) and carotenoid content (mg per gram wet mass) was insignificantly changed. The quantum yields of electron transfer from QA to QB (φET2o) and also to the PS-1 acceptors (φRE1o) were reduced. These results are explained by the increase in the number of QB-non-reducing centers of PS-2, which increased with increasing Naph concentration and exposure time of leaves in Naph solution. The suppression of PS-2 activity was partly abolished in the presence of the electron donor sodium ascorbate. Based on these results, it is suggested that Naph distorts cell membrane intactness and acts mainly on the PS-2 acceptor and to a lesser degree on the PS-2 donor side.

Photosystem I shows a higher tolerance to sorbitol-induced osmotic stress than photosystem II in the intertidal macro-algae Ulva prolifera (Chlorophyta)

The photosynthetic performance of the desiccation-tolerant, intertidal macro-algae Ulva prolifera was significantly affected by sorbitol-induced osmotic stress. Our results showed that photosynthetic activity decreased significantly with increases in sorbitol concentration. Although the partial activity of both photosystem I (PS I) and photosystem II (PS II) was able to recover after 30 min of rehydration, the activity of PS II decreased more rapidly than PS I. At 4 M sorbitol concentration, the activity of PS II was almost 0 while that of PS I was still at about one third of normal levels. Following prolonged treatment with 1 and 2 M sorbitol, the activity of PS I and PS II decreased slowly, suggesting that the effects of moderate concentrations of sorbitol on PS I and PS II were gradual. Interestingly, an increase in non-photochemical quenching occurred under these conditions in response to moderate osmotic stress, whereas it declined significantly under severe osmotic stress. These results suggest that photoprotection in U. prolifera could also be induced by moderate osmotic stress. In addition, the oxidation of PS I was significantly affected by osmotic stress. P700(+) in the thalli treated with high concentrations of sorbitol could still be reduced, as PS II was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), but it could not be fully oxidized. This observation may be caused by the higher quantum yield of non-photochemical energy dissipation in PS I due to acceptor-side limitation (Y(NA)) during rehydration in seawater containing DCMU.

Uptake of CeO2 nanoparticles and its effect on growth of Medicago arborea In vitro plantlets

The present study analyzes some effects of nano-CeO2 particles on the growth of in vitro plantlets of Medicago arborea when the nanoceria was added to the culture medium. Various concentrations of nano-CeO2 and bulk ceric oxide particles in suspension form were introduced to the agar culture medium to compare the effects of nanoceria versus ceric oxide bulk material. Germination rate and shoot dry weight were not affected by the addition of ceric oxide to the culture media. Furthermore, no effects were observed on chlorophyll content (single-photon avalanche diode (SPAD) measurements) due to the presence of either nano- or micro-CeO2 in the culture medium. When low concentrations of nanoceria were added to the medium, the number of trifoliate leaves and the root length increased but the root dry weight decreased. Also the values of maximum photochemical efficiency of PSII (F(v)/F m) showed a significant decrease. Dark-adapted minimum fluorescence (F 0) significantly increased in the presence of 200 mg L(-1) nanoceria and 400 mg L(-1) bulk material. Root tissues were more sensitive to nanoceria than were the shoots at lower concentrations of nanoceria. A stress effect was observed on M. arborea plantlets due to cerium uptake.

Combined effects of lead and acid rain on photosynthesis in soybean seedlings

To explore how lead (Pb) and acid rain simultaneously affect plants, the combined effects of Pb and acid rain on the chlorophyll content, chlorophyll fluorescence reaction, Hill reaction rate, and Mg(2+)-ATPase activity in soybean seedlings were investigated. The results indicated that, when soybean seedlings were treated with Pb or acid rain alone, the chlorophyll content, Hill reaction rate, Mg(2+)-ATPase activity, and maximal photochemical efficiency (F(v)/F(m)) were decreased, while the initial fluorescence (F 0) and maximum quantum yield (Y) were increased, compared with those of the control. The combined treatment with Pb and acid rain decreased the chlorophyll content, Hill reaction rate, Mg(2+)-ATPase activity, F(v)/F(m), and Y and increased F 0 in soybean seedlings. Under the combined treatment with Pb and acid rain, the two factors showed additive effects on the chlorophyll content in soybean seedlings and exhibited antagonistic effects on the Hill reaction rate. Under the combined treatment with high-concentration Pb and acid rain, the two factors exhibited synergistic effects on the Mg(2+)-ATPase activity, F 0, F v/F m, as well as Y. In summary, the inhibition of the photosynthetic process is an important physiological basis for the simultaneous actions of Pb and acid rain in soybean seedlings.

Low induction of non-photochemical quenching and high photochemical efficiency in the annual desert plant Anastatica hierochuntica

Non-photochemical quenching (NPQ) plays a major role in photoprotection. Anastatica hierochuntica is an annual desert plant found in hot deserts. We compared A. hierochuntica to three other different species: Arabidopsis thaliana, Eutrema salsugineum and Helianthus annuus, which have different NPQ and photosynthetic capacities. Anastatica hierochuntica plants had very different induction kinetics of NPQ and, to a lesser extent, of photosystem II electron transport rate (PSII ETR), in comparison to all other plants species in the experiments. The major components of the unusual photosynthetic and photoprotective response in A. hierochuntica were: (1) Low NPQ at the beginning of the light period, at various light intensities and CO2 concentrations. The described low NPQ cannot be explained by low leaf absorbance or by low energy distribution to PSII, but was related to the de-epoxidation state of xanthophylls. (2) Relatively high PSII ETR at various CO2 concentrations in correlation with low NPQ. PSII ETR responded positively to the increase of CO2 concentrations. At low CO2 concentrations PSII ETR was mostly O2 dependent. At moderate and high CO2 concentrations the high PSII ETR in A. hierochuntica was accompanied by relatively high CO2 assimilation rates. We suggest that A. hierochuntica have an uncommon NPQ and PSII ETR response. These responses in A. hierochuntica might represent an adaptation to the short growing season of an annual desert plant.

Identification of phototransformation products of thalidomide and mixture toxicity assessment: an experimental and quantitative structural activity relationships (QSAR) approach

The fate of thalidomide (TD) was investigated after irradiation with a medium-pressure Hg-lamp. The primary elimination of TD was monitored and structures of phototransformation products (PTPs) were assessed by LC-UV-FL-MS/MS. Environmentally relevant properties of TD and its PTPs as well as hydrolysis products (HTPs) were predicted using in silico QSAR models. Mutagenicity of TD and its PTPs was investigated in the Ames microplate format (MPF) aqua assay (Xenometrix, AG). Furthermore, a modified luminescent bacteria test (kinetic luminescent bacteria test (kinetic LBT)), using the luminescent bacteria species Vibrio fischeri, was applied for the initial screening of environmental toxicity. Additionally, toxicity of phthalimide, one of the identified PTPs, was investigated separately in the kinetic LBT. The UV irradiation eliminated TD itself without complete mineralization and led to the formation of several PTPs. TD and its PTPs did not exhibit mutagenic response in the Salmonella typhimurium strains TA 98, and TA 100 with and without metabolic activation. In contrast, QSAR analysis of PTPs and HTPs provided evidence for mutagenicity, genotoxicity and carcinogenicity using additional endpoints in silico software. QSAR analysis of different ecotoxicological endpoints, such as acute toxicity towards V. fischeri, provided positive alerts for several identified PTPs and HTPs. This was partially confirmed by the results of the kinetic LBT, in which a steady increase of acute and chronic toxicity during the UV-treatment procedure was observed for the photolytic mixtures at the highest tested concentration. Moreover, the number of PTPs within the reaction mixture that might be responsible for the toxification of TD during UV-treatment was successfully narrowed down by correlating the formation kinetics of PTPs with QSAR predictions and experimental toxicity data. Beyond that, further analysis of the commercially available PTP phthalimide indicated that transformation of TD into phthalimide was not the cause for the toxification of TD during UV-treatment. These results provide a path for toxicological assessment of complex chemical mixtures and in detail show the toxic potential of TD and its PTPs as well as its HTPs. This deserves further attention as UV irradiation might not always be a green technology, because it might pose a toxicological risk for the environment in general and specifically for water compartments.

Photorespiration and carbon concentrating mechanisms: two adaptations to high O2, low CO2 conditions

This review presents an overview of the two ways that cyanobacteria, algae, and plants have adapted to high O2 and low CO2 concentrations in the environment. First, the process of photorespiration enables photosynthetic organisms to recycle phosphoglycolate formed by the oxygenase reaction catalyzed by ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Second, there are a number of carbon concentrating mechanisms that increase the CO2 concentration around Rubisco which increases the carboxylase reaction enhancing CO2 fixation. This review also presents possibilities for the beneficial modification of these processes with the goal of improving future crop yields.

Expression of a highly active catalase VktA in the cyanobacterium Synechococcus elongatus PCC 7942 alleviates the photoinhibition of photosystem II

The repair of photosystem II (PSII) after photodamage is particularly sensitive to reactive oxygen species-such as H2O2, which is abundantly produced during the photoinhibition of PSII. In the present study, we generated a transformant of the cyanobacterium Synechococcus elongatus PCC 7942 that expressed a highly active catalase, VktA, which is derived from a facultatively psychrophilic bacterium Vibrio rumoiensis, and examined the effect of expression of VktA on the photoinhibition of PSII. The activity of PSII in transformed cells declined much more slowly than in wild-type cells when cells were exposed to strong light in the presence of H2O2. However, the rate of photodamage to PSII, as monitored in the presence of chloramphenicol, was the same in the two lines of cells, suggesting that the repair of PSII was protected by the expression of VktA. The de novo synthesis of the D1 protein, which is required for the repair of PSII, was activated in transformed cells under the same stress conditions. Similar protection of the repair of PSII in transformed cells was also observed under strong light at a relatively low temperature. Thus, the expression of the highly active catalase mitigates photoinhibition of PSII by protecting protein synthesis against damage by H2O2 with subsequent enhancement of the repair of PSII.

Improvement of cerium on photosynthesis of maize seedlings under a combination of potassium deficiency and salt stress

Added Ce(3+) can partly substitute for Ca(2+) or Mg(2+) and improve photosynthesis under the deficiency of these elements, but very few studies focused on photosynthetic improvement in maize seedlings caused by K(+) deficiency, salt stress, especially a combination of K(+) deficiency and salt stress. In the present study, the effects of Ce(3+) on the photosynthesis of maize seedlings under the three different stresses were investigated. The results showed that added Ce(3+) under various stresses increased the ratios of free water/bound water and of K(+)/Na(+), the pigment contents, the values of Fv/Fm, Y(II), ETR(II), Y(NPQ), Qp, qL, NPQ, and qN of photosystem II (PSII), the values of Y(I) and ETR(I) of photosystem I (PSI) and the expression levels of LhcII cab1 and rbcL, and decreased the values of Y(NO) and Y(NA). This implied that added Ce(3+) depressed ion toxicity, photodamage of PSII, and acceptor side constraints of PSI, and enhanced adjustable energy dissipation, the responses of photochemistry, and carbon assimilation caused by K(+) deficiency, salt stress, and the combination of K(+) deficiency and salt stress. However, Ce(3+) mitigation of photosynthetic inhibition in maize seedlings caused by the combined stresses was greater than that of salt stress, and Ce(3+) mitigation under salt stress was greater than that under K(+) deficiency. In addition, the results also showed that Ce(3+) cannot improve photosynthesis and growth of maize seedlings under K(+) deficiency by substituting for K(+).

Microalgae mediated bio-electrocatalytic fuel cell facilitates bioelectricity generation through oxygenic photomixotrophic mechanism

Electrogenic activity of oxygenic photo-bioelectrocatalytic fuel cell (PhFCOX) under mixotrophic mode was evaluated using atmospheric CO2 and domestic wastewater as carbon sources for harnessing bioelectricity with mixed microalgae as anodic biocatalyst. PhFCOX operation showed good electrogenic activity (3.55 μW/m(2)) associated with higher biomass growth (2.87 g/l) and chlorophyll content (5.12 mg/l). Electrogenic activity was relatively higher during the day time (46 mV; 0.6 mA) compared to the night (6 mV; 0.01 mA). Performance of PhFCOX undergoing oxygenic photosynthesis (DO; 3.5 mg/l) was compared with the mixotrophic fuel cell (PhFCAX) with photosynthetic bacteria as biocatalyst under anoxygenic conditions (DO; 0.45 mg/l). The dissolved oxygen produced during photolysis of water in oxygenic photosynthesis is a major limiting factor affecting the electrogenic activity. Voltammetric and amperometric analysis along with electron transfer kinetics (Tafel analysis) supported the bio-electrochemical behavior of PhFCOX and PhFCAX.

Oxidative and photochemical processes for the removal of galaxolide and tonalide from wastewater

Synthetic musks have been reported in wastewaters at concentrations as high as tens of micrograms per litre. The two most significant polycyclic musk fragrance compounds are 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta(g)-2-benzopyran (HHCB, trade name galaxolide®) and 7-acetyl-1,1,3,4,4,6-hexamethyltetrahydronaphthalene (AHTN, trade name tonalide®). We report the result of several irradiation and advanced oxidation processes carried out on samples of the effluent of a wastewater treatment plant located in Alcalá de Henares, Madrid. Wastewater samples were pre-ozonated and spiked with 500 ng/L of tonalide or galaxolide in order to obtain final concentrations in the same order as the raw effluent. The treatments assayed were ozonation with and without the addition of hydrogen peroxide (O₃, O₃/H₂O₂), ultraviolet (254 nm low pressure mercury lamp) and xenon-arc visible light irradiation alone and in combination with ozone (UV, O₃/UV, Xe, O₃/Xe) and visible light photocatalytic oxidation using a Ce-doped titanium dioxide photocatalyst performed under continuous oxygen or ozone gas bubbling (O₂/Xe/Ce-TiO₂, O₃/Xe/Ce-TiO₂). In all cases, samples taken at different contact times up to 15 min were analyzed. An analytical method based on stir bar sorptive extraction (SBSE), followed by comprehensive two-dimensional gas chromatography (SBSE-GC × GC-TOF-MS), was used for the automatic searching and evaluation of the synthetic musks and other nonpolar or semipolar contaminants in the wastewater samples. In all cases tonalide was more easily removed than galaxolide. The best results for the latter (more than 75% removal after 5 min on stream) were obtained from ozonation (O₃) and visible light photocatalytic ozonation (O₃/Xe/Ce-TiO₂). A significant removal of both pollutants (∼60% after 15 min) was also obtained during visible light photocatalysis (O₂/Xe/Ce-TiO₂). UV radiation was able to deplete tonalide (+90%) after 15 min but only reduced the concentration of galaxolide to about half of its initial concentration. The toxicity of treated samples decreased for O₃/UV and O₃/Ce-TiO₂, but increased during irradiation processes UV, Xe and Xe/Ce-TiO₂. Ozone treatments tend to decrease toxicity up to a certain dosage, from which point the presence of toxic transformation products has adverse effects on aquatic microorganisms.

Effects of humic acid and electrolytes on photocatalytic reactivity and transport of carbon nanoparticle aggregates in water

The effects of naturally occurring macromolecules such as humic acid (HA) and electrolytes on four fullerene nanoparticle suspensions (i.e., C(60), C(60)(OH)(24), single- and multiwall carbon nanotubes) were explored with respect to: (1) characteristics of nanoparticle aggregates, (2) transport of the aggregates through a silica porous media, and (3) production of reactive oxygen species (ROS) from the photosensitized fullerene aggregates. The presence of HA and salts increased the size of aggregates and relative hydrophobicity associated with transport through silica beads, while decreasing ROS production. These data illustrate the importance that transformation of engineered nanomaterials (ENMs) through interactions with aquatic solutes may have in altering the environmental behavior of nanomaterials.

High-to-low CO2 acclimation reveals plasticity of the photorespiratory pathway and indicates regulatory links to cellular metabolism of Arabidopsis

BACKGROUND

Photorespiratory carbon metabolism was long considered as an essentially closed and nonregulated pathway with little interaction to other metabolic routes except nitrogen metabolism and respiration. Most mutants of this pathway cannot survive in ambient air and require CO(2)-enriched air for normal growth. Several studies indicate that this CO(2) requirement is very different for individual mutants, suggesting a higher plasticity and more interaction of photorespiratory metabolism as generally thought. To understand this better, we examined a variety of high- and low-level parameters at 1% CO(2) and their alteration during acclimation of wild-type plants and selected photorespiratory mutants to ambient air.

METHODOLOGY AND PRINCIPAL FINDINGS

The wild type and four photorespiratory mutants of Arabidopsis thaliana (Arabidopsis) were grown to a defined stadium at 1% CO(2) and then transferred to normal air (0.038% CO(2)). All other conditions remained unchanged. This approach allowed unbiased side-by-side monitoring of acclimation processes on several levels. For all lines, diel (24 h) leaf growth, photosynthetic gas exchange, and PSII fluorescence were monitored. Metabolite profiling was performed for the wild type and two mutants. During acclimation, considerable variation between the individual genotypes was detected in many of the examined parameters, which correlated with the position of the impaired reaction in the photorespiratory pathway.

CONCLUSIONS

Photorespiratory carbon metabolism does not operate as a fully closed pathway. Acclimation from high to low CO(2) was typically steady and consistent for a number of features over several days, but we also found unexpected short-term events, such as an intermittent very massive rise of glycine levels after transition of one particular mutant to ambient air. We conclude that photorespiration is possibly exposed to redox regulation beyond known substrate-level effects. Additionally, our data support the view that 2-phosphoglycolate could be a key regulator of photosynthetic-photorespiratory metabolism as a whole.

Photocatalytic oxidation of monuron in the suspension of WO3 under the irradiation of UV-visible light

A comprehensive study of the degradation of monuron, one of the phenylurea herbicides, was conducted by UV-Vis/WO(3) process. It was found that hydroxyl radicals played a major role in the decay of monuron while other radicals (e.g. superoxide) and hole might also contribute to the decomposition of monuron. The oxidation path likely plays a major role in the generation of hydroxyl radicals. The effects of initial pH level, initial concentration of monuron, and inorganic oxidants on the performance of UV-Vis/WO(3) process were also investigated and optimized. Comparison between monuron decay pathways by UV-Vis/WO(3) and UV/TiO(2) was conducted. The decay mechanisms, including N-terminus demethylation, dechlorination and direct hydroxylation on benzene ring, were observed to be involved in the oxidation of monuron in these two processes. Sixteen intermediates were identified during the photodegradation of monuron and degradation pathways were proposed accordingly.

Unique properties vs. common themes: the atypical cyanobacterium Gloeobacter violaceus PCC 7421 is capable of state transitions and blue-light-induced fluorescence quenching

The atypical unicellular cyanobacterium Gloeobacter violaceus PCC 7421, which diverged very early during the evolution of cyanobacteria, can be regarded as a key organism for understanding many structural, functional, regulatory and evolutionary aspects of oxygenic photosynthesis. In the present work, the performance of two basic photosynthetic adaptation/protection mechanisms, common to all other oxygenic photoautrophs, had been challenged in this ancient cyanobacterium which lacks thylakoid membranes: state transitions and non-photochemical fluorescence quenching. Both low temperature fluorescence spectra and room temperature fluorescence transients show that G. violaceus is capable of performing state transitions similar to evolutionarily more recent cyanobacteria, being in state 2 in darkness and in state 1 upon illumination by weak blue or far-red light. Compared with state 2, variable fluorescence yield in state 1 is strongly enhanced (almost 80%), while the functional absorption cross-section of PSII is only increased by 8%. In contrast to weak blue light, which enhances fluorescence yield via state 1 formation, strong blue light reversibly quenches Chl fluorescence in G. violaceus. This strongly suggests regulated heat dissipation which is triggered by the orange carotenoid protein whose presence was directly proven by immunoblotting and mass spectrometry in this primordial cyanobacterium. The results are discussed in the framework of cyanobacterial evolution.

Investigating photoexcitation-induced mitochondrial damage by chemotherapeutic corroles using multimode optical imaging

We recently reported that a targeted, brightly fluorescent gallium corrole (HerGa) is highly effective for breast tumor detection and treatment. Unlike structurally similar porphryins, HerGa exhibits tumor-targeted toxicity without the need for photoexcitation. We have now examined whether photoexcitation further modulates HerGa toxicity, using multimode optical imaging of live cells, including two-photon excited fluorescence, differential interference contrast (DIC), spectral, and lifetime imaging. Using two-photon excited fluorescence imaging, we observed that light at specific wavelengths augments the HerGa-mediated mitochondrial membrane potential disruption of breast cancer cells in situ. In addition, DIC, spectral, and fluorescence lifetime imaging enabled us to both validate cell damage by HerGa photoexcitation and investigate HerGa internalization, thus allowing optimization of light dose and timing. Our demonstration of HerGa phototoxicity opens the way for development of new methods of cancer intervention using tumor-targeted corroles.

Effects of the measuring light on the photochemistry of the bacterial photosynthetic reaction center from Rhodobacter sphaeroides

The bacterial reaction center (RC) has become a reference model in the study of the diverse interactions of quinones with electron transfer complexes. In these studies, the RC functionality was probed through flash-induced absorption changes where the state of the primary donor is probed by means of a continuous measuring beam and the electron transfer is triggered by a short intense light pulse. The single-beam set-up implies the use as reference of the transmittance measured before the light pulse. Implicit in the analysis of these data is the assumption that the measuring beam does not elicit the protein photochemistry. At variance, measuring beam is actinic in nature at almost all the suitable wavelengths. In this contribution, the analytical modelling of the time evolution of neutral and charge-separated RCs has been performed. The ability of measuring light to elicit RC photochemistry induces a first order growth of the charge-separated state up to a steady state that depends on the light intensity and on the occupation of the secondary quinone (Q(B)) site. Then the laser pulse pumps all the RCs in the charge-separated state. The following charge recombination is still affected by the measuring beam. Actually, the kinetics of charge recombination measured in RC preparation with the Q(B) site partially occupied are two-exponential. The rate constant of both fast and slow phases depends linearly on the intensity of the measuring beam while their relative weights depend not only on the fractions of RC with the Q(B) site occupied but also on the measuring light intensity itself.

Concentration and photochemistry of PAHs, NPAHs, and OPAHs and toxicity of PM2.5 during the Beijing Olympic Games

Atmospheric particulate matter with diameter <2.5 um (PM(2.5)) was collected at Peking University (PKU) in Beijing, China before, during, and after the 2008 Olympics and analyzed for black carbon (BC), organic carbon (OC), lower molecular weight (MW < 300) and MW302 Polycyclic Aromatic Hydrocarbons (PAHs), nitrated PAHs (NPAHs) and oxygenated PAHs (OPAHs). In addition, the direct and indirect acting mutagenicity of the PM(2.5) and the potential for DNA damage to human lung cells were also measured. Significant reductions in BC (45%), OC (31%), MW< 300 PAH (26-73%), MW 302 PAH (22-77%), NPAH (15-68%), and OPAH (25-53%) concentrations were measured during the source control and Olympic periods. However, the mutagenicity of the PM(2.5) was significantly reduced only during the Olympic period. The PAH, NPAH, and OPAH composition of the PM(2.5) was similar throughout the study, suggesting similar sources during the different periods. During the source control period, the parent PAH concentrations were correlated with NO, CO, and SO(2) concentrations, indicating that these PAHs were associated with both local and regional emissions. However, the NPAH and OPAH concentrations were only correlated with the NO concentrations, indicating that the NPAH and OPAH were primarily associated with local emissions. The relatively high 2-nitrofluoranthene/1-nitropyrene ratio (25-46) and 2-nitrofluoranthene/2-nitropyrene ratio (3.4-4.8), suggested a predominance of photochemical formation of NPAHs through OH-radical-initiated reactions in the atmosphere. On average, the ∑NPAH and ∑OPAH concentrations were 8% of the parent PAH concentrations, while the direct-acting mutagenicity (due to the NPAH and OPAH) was 200% higher than the indirect-acting mutagenicity (due to the PAH). This suggests that NPAH and OPAH make up a significant portion of the overall mutagenicity of PM(2.5) in Beijing.

Allelochemical stress inhibits growth, leaf water relations, PSII photochemistry, non-photochemical fluorescence quenching, and heat energy dissipation in three C3 perennial species

In this study, the effect of two allelochemicals, benzoxazolin-2(3H)-one (BOA) and cinnamic acid (CA), on different physiological and morphological characteristics of 1-month-old C(3) plant species (Dactylis glomerata, Lolium perenne, and Rumex acetosa) was analysed. BOA inhibited the shoot length of D. glomerata, L. perenne, and R. acetosa by 49%, 19%, and 19% of the control. The root length of D. glomerata, L. perenne, and R. acetosa growing in the presence of 1.5 mM BOA and CA was decreased compared with the control. Both allelochemicals (BOA, CA) inhibited leaf osmotic potential (LOP) in L. perenne and D. glomerata. In L. perenne, F(v)/F(m) decreased after treatment with BOA (1.5 mM) while CA (1.5 mM) also significantly reduced F(v)/F(m) in L. perenne. Both allelochemicals decreased ΦPSII in D. glomerata and L. perenne within 24 h of treatment, while in R. acetosa, ΦPSII levels decreased by 72 h following treatment with BOA and CA. There was a decrease in qP and NPQ on the first, fourth, fifth, and sixth days after treatment with BOA in D. glomerata, while both allelochemicals reduced the qP level in R. acetosa. There was a gradual decrease in the fraction of light absorbed by PSII allocated to PSII photochemistry (P) in R. acetosa treated with BOA and CA. The P values in D. glomerata were reduced by both allelochemicals and the portion of absorbed photon energy that was thermally dissipated (D) in D. glomerata and L. perenne was decreased by BOA and CA. Photon energy absorbed by PSII antennae and trapped by 'closed' PSII reaction centres (E) was decreased after CA exposure in D. glomerata. BOA and CA (1.5 mM concentration) decreased the leaf protein contents in all three perennial species. This study provides new understanding of the physiological and biochemical mechanisms of action of BOA and CA in one perennial dicotyledon and two perennial grasses. The acquisition of such knowledge may ultimately provide a rational and scientific basis for the design of safe and effective herbicides.

Roles of xanthophylls and exogenous ABA in protection against NaCl-induced photodamage in rice (Oryza sativa L) and cabbage (Brassica campestris)

Changes in actual efficiency of PS II photochemistry, non-photochemical quenching (NPQ), content of xanthophylls and kinetics of de-epoxidation were studied in ABA-fed and non-ABA-fed leaves of rice and cabbage under NaCl stress. Salt stress induced more progressive decrease in actual efficiency of PS II photochemistry (ФPS II), higher reduction state of PS II, and a small significant increase in NPQ in NaCl-sensitive rice plants as compared with NaCl-tolerant cabbage plants, whereas exogenously supplied ABA alleviated the decrease in actual efficiency of PS II photochemistry (ФPS II), induced a lower reduction state of PS II, and caused higher capacity of NPQ in ABA-fed plants than in non-ABA-fed plants. As a result, there were higher activities of photosynthetic electron transport, higher capacity of energy dissipation, and lower cumulation of excess light in cabbage than in rice plants, and in ABA-fed leaves than in non-ABA-fed leaves. The effect of ABA was more efficient in cabbage than in rice plants. Addition of exogenous ABA resulted in enhancement of the size of the xanthophyll cycle pool, promotion of de-epoxidation of the xanthophyll cycle components, and a rise in the level of NPQ by altering the kinetics of de-epoxidation of the xanthophyll cycle. Protection from photodamage appears to be achieved by coordinated contributions by exogenous ABA and xanthophyll cycle-mediated NPQ. This variety of photoprotective mechanisms may be essential for conferring photodamage tolerance under NaCl stress.

Adsorption and degradation of model volatile organic compounds by a combined titania-montmorillonite-silica photocatalyst

A series of adsorptive photocatalysts, combined titania-montmorillonite-silica were synthesized. The resultant photocatalysts consisted of more and more spherically agglomerated TiO(2) particles with increasing of TiO(2) content, and anatase was the only crystalline phase with nano-scale TiO(2) particles. With increasing of the cation exchange capacity to TiO(2) molar ratio, specific surface area and pore volume increased very slightly. In a fluidized bed photocatalytic reactor by choosing toluene, ethyl acetate and ethanethiol as model pollutants, all catalysts had relatively high adsorption capacities and preferred to adsorb higher polarity pollutants. Langmuir isotherm model better described equilibrium data compared to Freundlich model. Competitive adsorptions were observed for the mixed pollutants on the catalysts, leading to decrease adsorption capacity for each pollutant. The combined titania-montmorillonite-silica photocatalyst exhibited excellent photocatalytic removal ability to model pollutants of various components. Almost 100% of degradation efficiency was achieved within 120 min for each pollutant with about 500 ppb initial concentration, though the efficiencies of multi-component compounds slightly decreased. All photocatalytic reactions followed the Langmuir-Hinshelwood model. Degradation rate constants of multi-component systems were lower than those for single systems, following the order of toluene<ethyl acetate<ethanethiol, and increased with the increase of adsorption capacities for different pollutants of various components.

Suspended C60 nanoparticles protect against short-term UV and fluoranthene photo-induced toxicity, but cause long-term cellular damage in Daphnia magna

The increased production of nanotechnology materials is a potential source of nano-sized particles (NSPs) in aquatic ecosystems. Meanwhile, polycyclic aromatic hydrocarbons (PAHs), in the presence of ecologically relevant levels of ultraviolet radiation (UV), can be acutely toxic to aquatic species including fish and invertebrates. Considering that suspended carbon-based NSPs (e.g., C60 fullerenes) may act in similar ways as dissolved organic matter (DOM) by altering the bioavailability of PAHs, the objective of this research was to determine the effect of suspended C60 on the photo-induced toxicity of fluoranthene. Transmission electron microscopy indicated that the presence of C60 protected cellular components (e.g., mitochondria, microvilli, and basal infoldings) in organisms exposed to UV and fluoranthene phototoxicity in short-term exposures. However, we found that long-term exposure (21d) of low-level C60 caused significant cellular damage in the Daphnia magna alimentary canal. This paper highlights the importance of examining the interactions between existing stressors and nanoparticles in the aquatic environment.

Short flashes and continuous light have similar photoinhibitory efficiency in intact leaves

Lincomycin-treated pumpkin leaves were illuminated with either continuous light or saturating single-turnover xenon flashes to study the dependence of photoinactivation of photosystem II (PSII) on the mode of delivery of light. The flash energy and the time interval between the flashes were varied between the experiments, and photoinactivation was measured with oxygen evolution and the ratio of variable to maximum fluorescence (F(v)/F(m)). The photoinhibitory efficiency of saturating xenon flashes was found to be directly proportional to flash energy and independent of the time interval between the flashes. These findings indicate that a low-light-specific mechanism, based on charge recombination between PSII electron acceptors and the oxygen-evolving complex, is not the main cause of photoinactivation caused by short flashes in vivo. Furthermore, the relationship between the rate constant of photoinactivation and photon flux density was similar for flashes and continuous light when F(v)/F(m) was used to quantify photoinactivation, suggesting that continuous-light photoinactivation has a mechanism in which the quantum yield does not depend on the mode of delivery of light. A similar quantum yield of photoinhibition for flashes and continuous light is compatible with the manganese-based photoinhibition mechanism and with mechanisms in which singlet oxygen, produced via a direct photosensitization reaction, is the agent of damage. However, the classical acceptor-side and donor-side mechanisms do not predict a similar quantum yield for flashes and continuous light.

Spectral reflectance from a soybean canopy exposed to elevated CO2 and O3

By affecting the physiology and structure of plant canopies, increasing atmospheric CO(2) and O(3) influence the capacity of agroecosystems to capture light and convert that light energy into biomass, ultimately affecting productivity and yield. The objective of this study was to determine if established remote sensing indices could detect the direct and interactive effects of elevated CO(2) and elevated O(3) on the leaf area, chlorophyll content, and photosynthetic capacity of a soybean canopy growing under field conditions. Large plots of soybean (Glycine max) were exposed to ambient air (∼380 μmol CO(2) mol(-1)), elevated CO(2) (∼550 μmol mol(-1)), elevated O(3) (1.2× ambient), and combined elevated CO(2) plus elevated O(3) at the soybean free air gas concentration enrichment (SoyFACE) experiment. Canopy reflectance was measured weekly and the following indices were calculated from reflectance data: near infrared/red (NIR/red), normalized difference vegetation index (NDVI), canopy chlorophyll content index (chl. index), and photochemical reflectance index (PRI). Leaf area index (LAI) also was measured weekly. NIR/red and LAI were linearly correlated throughout the growing season; however, NDVI and LAI were correlated only up to LAI values of ∼3. Season-wide analysis demonstrated that elevated CO(2) significantly increased NIR/red, PRI, and chl. index, indicating a stimulation of LAI and photosynthetic carbon assimilation, as well as delayed senescence; however, analysis of individual dates resolved fewer statistically significant effects of elevated CO(2). Exposure to elevated O(3) decreased LAI throughout the growing season. Although NIR/red showed the same trend, the effect of O(3) on NIR/red was not statistically significant. Season-wide analysis showed significant effects of O(3) on PRI; however, analysis of individual dates revealed that this effect was only statistically significant on two dates. Elevated O(3) had minimal effects on the total canopy chlorophyll index. PRI appeared to be more sensitive to decreased photosynthetic capacity of the canopy as a whole compared with previously published single leaf gas exchange measurements at SoyFACE, possibly because PRI integrates the reflectance signal of older leaves with accumulated O(3) damage and healthy young, upper canopy leaves, enabling detection of significant decreases in photosynthetic carbon assimilation which have not been detected in previous studies which measured gas exchange of upper canopy leaves. When the canopy was exposed to elevated CO(2) and O(3) simultaneously, the deleterious effects of elevated O(3) were diminished. Reflectance data, while less sensitive than direct measurements of physiological/structural parameters, corroborate direct measurements of LAI and photosynthetic gas exchange made during the same season, as well as results from previous years at SoyFACE, demonstrating that these indices accurately represent structural and physiological effects of changing tropospheric chemistry on soybean growing in a field setting.

Aquatic photochemistry of fluoroquinolone antibiotics: kinetics, pathways, and multivariate effects of main water constituents

The ubiquity of fluoroquinolone antibiotics (FQs) in surface waters urges insights into their fate in the aqueous euphotic zone. In this study, eight FQs (ciprofloxacin, danofloxacin, levofloxacin, sarafloxacin, difloxacin, enrofloxacin, gatifloxacin, and balofloxacin) were exposed to simulated sunlight, and their photodegradation was observed to follow apparent first-order kinetics. Based on the determined photolytic quantum yields, solar photodegradation half-lives for the FQs in pure water and at 45 degrees N latitude were calculated to range from 1.25 min for enrofloxacin to 58.0 min for balofloxacin, suggesting that FQs would intrinsically photodegrade fast in sunlit surface waters. However, we found freshwater and seawater constituents inhibited their photodegradation. The inhibition was further explored by a central composite design using sarafloxacin and gatifloxacin as representatives. Humic acids (HA), Fe(III), NO(3)(-), and HA-Cl(-) interaction inhibited the photodegradation, as they mainly acted as radiation filters and/or scavengers for reactive oxygen species. The photodegradation product identification and ROS scavenging experiments indicated that the FQs underwent both direct photolysis and self-sensitized photo-oxidation via *OH and (1)O(2). Piperazinyl N(4)-dealkylation was primary for N(4)-alkylated FQs, whereas decarboxylation and defluorination were comparatively important for the other FQs. These results are of importance toward the goal of assessing the persistence of FQs in surface waters.

Effect of temperature on the formation of macroporous ZnO bundles and its application in photocatalysis

In this article, the effects of temperature on the formation of macroporous zinc oxide bundles and its photocatalytic activity under a variety of experimental conditions were reported. Thermal decomposition of zinc oxalate dihydrate yields hexagonal wurtzite-type ZnO bundles. Increased the decomposition temperatures resulted in decreased time required for bundle formation, with a corresponding increase in nanoparticles agglomeration. ZnO bundle formation was facilitated up to 200 degrees C after complete decomposition of zinc oxalate into ZnO at 400 degrees C in 15 min. However, low temperature (such as 100 degrees C) was not facilitated nanobundle formation, suggesting the importance of temperature on ZnO bundles formation. In addition, nitrogen adsorption experiments confirmed the presence of macroporous structure in the bundles. The photocatalytic decolorization and adsorption of methylene blue dye (MB) on ZnO bundles were investigated under UV light irradiation. The adsorption and decolorization efficiency of macroporous bundles were higher than the fused bundles. In conclusion, ZnO bundles are efficient and easily recyclable photocatalyst.

Inhibition vs. enhancement of the nitrate-induced phototransformation of organic substrates by the *OH scavengers bicarbonate and carbonate

Contrary to common expectations, the hydroxyl scavengers, carbonate and bicarbonate, are able to enhance the phototransformation by nitrate of a number of substituted phenols. Carbonate and bicarbonate, in addition to modifying the solution pH, are also able to induce a considerable formation of the carbonate radicals upon nitrate photolysis. The higher availability of less-reactive species than the hydroxyl radical would contribute to substantially enhance the photodegradation of the phenols/phenolates that are sufficiently reactive toward the carbonate radical. This phenomenon has a potentially important impact on the fate of the relevant compounds in surface waters. In contrast, the degradation of compounds that are not sufficiently reactive toward CO(3)(-*) is inhibited by carbonate and bicarbonate because of the scavenging of *OH.

Acclimation to future atmospheric CO2 levels increases photochemical efficiency and mitigates photochemistry inhibition by warm temperatures in wheat under field chambers

A study was conducted over 2 years to determine whether growth under elevated CO(2) (700 μmol mol(-1) ) and temperature (ambient + 4 °C) conditions modifies photochemical efficiency or only the use of electron transport products in spring wheat grown in field chambers. Elevated atmospheric CO(2) concentrations increased crop dry matter at maturity by 12-17%, while above-ambient temperatures did not significantly affect dry matter yield. In measurements with ambient CO(2) at ear emergence and after anthesis, growth at elevated CO(2) concentrations decreased flag leaf light-saturated carbon assimilation. The quantum yield of electron transport (Φ(PSII) ) measured at ambient CO(2) and higher irradiances increased at ear emergence and decreased after anthesis in plants grown at elevated CO(2) . At higher light intensities, but not in low light, photochemical quenching (qP) decreased after growth in elevated CO(2) conditions. Growth under CO(2) enrichment increased dark- (Fv:Fm) and light-adapted (Fv':Fm') photochemical efficiencies, and decreased the chlorophyll a:b ratio, suggesting an increase in light-harvesting complexes relative to PSII reaction centres. A relatively higher decrease in carbon assimilation than the decrease in Φ(PSII) pointed to a sink other than CO(2) assimilation for electron transport products at defined growth stages. With higher light intensities, warmer temperatures increased Φ(PSII) and Fv':Fm' at ear emergence and decreased Φ(PSII) after anthesis; in ambient-but not elevated-CO(2) , warmer temperatures also decreased qP after anthesis. CO(2) fixation increased or did not change with temperature, depending on the growth stage and year. We conclude that elevated CO(2) decreases the carbon assimilation capacity, but increases photochemistry and resource allocation to light harvesting, and that elevated levels of CO(2) can mitigate photochemistry inhibition as a result of warm temperatures.

Acclimation to future atmospheric CO2 levels increases photochemical efficiency and mitigates photochemistry inhibition by warm temperatures in wheat under field chambers

A study was conducted over 2 years to determine whether growth under elevated CO(2) (700 μmol mol(-1) ) and temperature (ambient + 4 °C) conditions modifies photochemical efficiency or only the use of electron transport products in spring wheat grown in field chambers. Elevated atmospheric CO(2) concentrations increased crop dry matter at maturity by 12-17%, while above-ambient temperatures did not significantly affect dry matter yield. In measurements with ambient CO(2) at ear emergence and after anthesis, growth at elevated CO(2) concentrations decreased flag leaf light-saturated carbon assimilation. The quantum yield of electron transport (Φ(PSII) ) measured at ambient CO(2) and higher irradiances increased at ear emergence and decreased after anthesis in plants grown at elevated CO(2) . At higher light intensities, but not in low light, photochemical quenching (qP) decreased after growth in elevated CO(2) conditions. Growth under CO(2) enrichment increased dark- (Fv:Fm) and light-adapted (Fv':Fm') photochemical efficiencies, and decreased the chlorophyll a:b ratio, suggesting an increase in light-harvesting complexes relative to PSII reaction centres. A relatively higher decrease in carbon assimilation than the decrease in Φ(PSII) pointed to a sink other than CO(2) assimilation for electron transport products at defined growth stages. With higher light intensities, warmer temperatures increased Φ(PSII) and Fv':Fm' at ear emergence and decreased Φ(PSII) after anthesis; in ambient-but not elevated-CO(2) , warmer temperatures also decreased qP after anthesis. CO(2) fixation increased or did not change with temperature, depending on the growth stage and year. We conclude that elevated CO(2) decreases the carbon assimilation capacity, but increases photochemistry and resource allocation to light harvesting, and that elevated levels of CO(2) can mitigate photochemistry inhibition as a result of warm temperatures.

Effect of photoinitiators on the in vitro performance of a dentin adhesive exposed to simulated oral environment

OBJECTIVES

Our previous study showed poor mechanical durability and nano-sized heterogeneities in cross-linked dentin adhesives cured in the presence of water. To further explore the relationship between nano-scale heterogeneities and the long-term mechanical properties of dentin adhesives, the properties of model dentin adhesives polymerized using hydrophilic photoinitiators were compared with those of adhesives polymerized using hydrophobic camphorquinone-based photoinitiators.

METHODS

The model adhesives consisted of HEMA and bisGMA with a mass ratio of 45/55 and were photopolymerized in the presence of 8.3 mass% water. The photo-polymerization of the model adhesives during irradiation was monitored in situ using a Perkin-Elmer Spectrum One FTIR in the ATR sampling mode. The tensile properties were determined for all samples after dry storage at room temperature, or after aqueous storage in distilled deionized water.

RESULTS

There was a continuous decline of mechanical properties for the specimens cured in the presence of water during 3 months aqueous storage, especially for the specimens that contained hydrophobic photoinitiators. The multi-component systems containing hydrophilic photoinitiators were shown to produce superior model dental adhesives when these materials are cured in the presence of water.

SIGNIFICANCE

Designing initiator systems to perform in this heterogeneous environment may improve the mechanical performance of dentin adhesives, as the results presented here indicate.

Correlation of photocatalytic bactericidal effect and organic matter degradation of TiO2. Part I: observation of phenomena

This study aims to investigate the correlation of the photocatalytic oxidation effect of decomposing organic matter and inactivating bacteria using two different TiO2 materials: a Degussa P25 powder film and a commercial TiO2 thin film. The destructed organic matter was formaldehyde and the test bacterium was E. coli (JM 109 strain). The decomposition tests and the bactericidal tests were carried out in a plate reactor and on the TiO2 surface, respectively. Observations indicate that there exists an apparent correlation between the two photocatalytic processes of decomposing formaldehyde and inactivating E. coli. However, it is essential to distinguish the exact driver for microbe inactivation, in which both UV light irradiation and reactive oxygen species reaction are directfactors of disinfection, and for organic matter, in which only reactive oxygen species reaction contributes to degradation. Observations from this study would make it possible to use analogy as a potential method to evaluate the antimicrobial effect based on the organic compound degradation effect, whereby the latter is much easier to measure quantitatively.

Effects of cadmium on antioxidant enzyme and photosynthetic activities in leaves of two maize cultivars

Effects of cadmium (Cd(2+)) on photosynthetic and antioxidant activities of maize (Zea mays L.) cultivars (3223 and 32D99) were investigated. Fourteen-day-old cultivar seedlings were exposed to different Cd concentrations [0, 0.3, 0.6 and 0.9mM Cd(NO(3))(2) x 4H(2)O] for 8 days. The results of chlorophyll fluorescence indicated that different levels of Cd affected photochemical efficiency in 3223 much more than that in 32D99. In parallel, the level of Cd at 0.9mM caused oxidative damage but did not indicate cessation of PSII activity of the cultivars; plant death was not observed at highly toxic Cd levels. Additionally, the increase in Cd concentration caused loss of chlorophylls and carotenoid and membrane damage in both cultivars, but greater membrane damage was observed in 3223 than in 32D99. Depending on Cd accumulation, a significant reduction in dry biomass was observed in both cultivars at all Cd concentrations. The accumulation of Cd was higher in roots than in leaves for both cultivars. Nevertheless, cultivar 3223 transferred more Cd from roots to leaves than did 32D99. On the other hand, our results suggest that there were similar responses in SOD, APX and GR activities with increasing Cd concentrations for both cultivars. However, POD activity significantly increased at highly toxic Cd levels in 32D99. This result may be regarded as an indication of better tolerance of the Z. mays L. cultivar 32D99 to Cd contamination.