Higher Electron Transport Rate Research Articles

Fabrication of Electrochemical Sensor Modified with Porous Graphene for Determination of Trace Calycosin

Abstract In this study, the porous graphene (PG) with excellent structure was successfully prepared by a simple pyrolysis process, and applied to construct electrochemical sensor (PG@GCE) for detection of calycosin (CYS). PG was characterized by Raman spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. Also, the electrochemical properties of the proposed sensors were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and the results indicated that sensors had relatively large specific surface area and higher electron transport rate. Based on all those characteristics, CYS, a traditional Chinese medicine (TCM) active ingredient, displayed a great response on the surface of PC@GCE. Under the optimized conditions, the sensors displayed a good linear relationship between the peak current and the CYS concentration in the range of 1.8 × 10–7–4.4 × 10–5 M with the detection limit of 5.8 × 10–8 M (S/N = 3). This study provided a novel analytical method for detection of CYS, rapid identification of Radix Hedysari and Radix Astragali, and gave another way for the trace analysis of CYS in biological samples. Furthermore, it would also deepen the application of PG in the field of pharmaceutical analysis.

Size scaling of photophysiology and growth in four freshly isolated diatom species from Ryder Bay, western Antarctic peninsula.

Diatoms are one of the dominant groups in phytoplankton communities of the western Antarctic Peninsula (WAP). Although generally well‐studied, little is known about size dependent photophysiological responses in diatom bloom formation and succession. To increase this understanding, four Antarctic diatom species covering two orders of magnitude in cell size were isolated in northern Marguerite Bay (WAP). Fragilariopsis sp., Pseudo‐nitzschia cf. subcurvata, Thalassiosira cf. antarctica, and Proboscia cf. alata were acclimated to three different irradiances after which photophysiology, electron transport, carbon fixation, and growth were assessed. The small species Fragilariopsis sp., Pseudo‐nitzschia cf. subcurvata, and large species Proboscia cf. alata showed similar photoacclimation to higher irradiances with a decrease in cellular chlorophyll a and an increase in chlorophyll a specific absorption and xanthophyll cycle pigments and activity. In contrast, pigment concentrations and absorption remained unaffected by higher irradiances in the large species Thalassiosira cf. antarctica. Overall, the small species showed significantly higher growth rates compared to the large species, which was related to relatively high light harvesting capacity and electron transport rates in the smaller species. However, photophysiological responses related to photoinhibition and photoprotection and carbon fixation showed no relationship with cell size. This study supports the dominance of small diatoms at low irradiances during winter and early spring, but does not provide photophysiological evidence for the dominance of large diatoms during the phytoplankton bloom in the WAP. This suggests that other factors such as grazing and nutrient availability are likely to play a major role in diatom bloom formation.

Photophysiology of nitrate limited phytoplankton communities in Kongsfjorden, Spitsbergen

AbstractIn Arctic coastal regions, the phytoplankton bloom is often initiated by meltwater induced stratification in spring, while subsequent nutrient depletion is believed to drive phytoplankton succession in summer. The associated changes in photophysiology are difficult to identify, because these can be governed by acclimation to light and nutrient availability as well as variations in phytoplankton biomass and taxonomic composition. In the present study, the consequences of nutrient limitation for photophysiology and growth were assessed in natural phytoplankton communities from Kongsfjorden, Spitsbergen. A series of nutrient addition experiments demonstrated N‐limitation from mid‐June onwards and possible co‐limitation with P later in summer. The onset of N‐limitation was associated with a pronounced change in taxonomic composition from a dictyochophytes to a haptophytes dominated community. Fast Repetition Rate fluorometry measurements of photosystem II (PSII) photophysiology showed that the dictyochophytes dominated community was characterized by high PSII efficiency and electron transport rates which were efficiently used for growth. Marked changes in PSII photophysiology were observed later in summer, with decreasing efficiencies, lower connectivity between reaction centers, and slower turnover rates. Simultaneously, alternative electron requirements downstream of PSII became more important and energy was likely allocated to the uptake of nutrients rather than carbon fixation and growth. Relief of nutrient limitation during the nutrient addition experiments did not lead to pronounced changes in PSII photophysiology. It is, therefore, concluded that PSII photophysiology of the phytoplankton community in Kongsfjorden is associated with changes in species composition rather than a direct effect of nutrient availability or nutrient limitation.

Altitude of origin influences the responses of PSII photochemistry to heat waves in European beech (Fagus sylvatica L.)

The photosynthetic responses to the combined effect of drought and heat stress were studied in leaves of 19-years-old European beech (Fagus sylvatica L.) trees originating from five provenances in Central Europe differing by altitude (55–1250 m), and grown in the same experimental plot. The measurements were conducted at the beginning of heat waves, under two different conditions: during a dry period (middle of July) and after recovery in wetter period, at the beginning of August. The decreases of stomatal conductance (gs) and net photosynthesis rate (ACO2) during drought and heat wave stress were very similar in all provenances. However, we observed distinct response of PSII photochemistry on combined drought and high temperature stress, well associated with altitude of origin of the beech provenances. Measurements of pulse amplitude modulated (PAM) fluorescence identified maintenance of a high electron transport rate in beech provenances from high altitudes under drought and heat wave conditions, associated with some decrease of excitation pressure on PSII. This can be explained by enhanced capacity of alternative electron sinks to utilize the excess of electrons as a photoprotective mechanism. The analyses of fast chlorophyll fluorescence kinetics confirmed the differences in responses of PSII photochemistry between provenances originating from different altitudes. Compared with provenances at higher altitudes, we found more sensitive response (i.e. more limited electron transport at the PSII acceptor side and changes in the size of light harvesting complexes) to drought and heat stress, in those growing at low altitudes. Our results support the hypothesis that the provenances originating from higher altitudes possess enhanced phenotypic plasticity related to photoprotective responses, resulting from the long-term adaptation to marginal mountain conditions.

An optimized protocol for the preparation of oxygen-evolving thylakoid membranes from Cyclotella meneghiniana provides a tool for the investigation of diatom plastidic electron transport

BackgroundThe preparation of functional thylakoid membranes from diatoms with a silica cell wall is still a largely unsolved challenge. Therefore, an optimized protocol for the isolation of oxygen evolving thylakoid membranes of the centric diatom Cyclotella meneghiniana has been developed. The buffer used for the disruption of the cells was supplemented with polyethylene glycol based on its stabilizing effect on plastidic membranes. Disruption of the silica cell walls was performed in a French Pressure cell and subsequent linear sorbitol density gradient centrifugation was used to isolate the thylakoid membrane fraction.ResultsSpectroscopic characterization of the thylakoids by absorption and 77 K fluorescence spectroscopy showed that the photosynthetic pigment protein complexes in the isolated thylakoid membranes were intact. This was supported by oxygen evolution measurements which demonstrated high electron transport rates in the presence of the artificial electron acceptor DCQB. High photosynthetic activity of photosystem II was corroborated by the results of fast fluorescence induction measurements. In addition to PSII and linear electron transport, indications for a chlororespiratory electron transport were observed in the isolated thylakoid membranes. Photosynthetic electron transport also resulted in the establishment of a proton gradient as evidenced by the quenching of 9-amino-acridine fluorescence. Because of their ability to build-up a light-driven proton gradient, de-epoxidation of diadinoxanthin to diatoxanthin and diatoxanthin-dependent non-photochemical quenching of chlorophyll fluorescence could be observed for the first time in isolated thylakoid membranes of diatoms. However, the ∆pH, diadinoxanthin de-epoxidation and diatoxanthin-dependent NPQ were weak compared to intact diatom cells or isolated thylakoids of higher plants.ConclusionsThe present protocol resulted in thylakoids with a high electron transport capacity. These thylakoids can thus be used for experiments addressing various aspects of the photosynthetic electron transport by, e.g., employing artificial electron donors and acceptors which do not penetrate the diatom cell wall. In addition, the present isolation protocol yields diatom thylakoids with the potential for xanthophyll cycle and non-photochemical quenching measurements. However, the preparation has to be further refined before these important topics can be addressed systematically.

Self-Assembly of ZnO-Nanorods and Its Performance in Quasi Solid Dye Sensitized Solar Cells

Zinc oxide (ZnO) nanorods (NRs) were successfully prepared by self-assembly methods using zinc nitrate hexahydrate and hexamethylenetetramine as raw materials. ZnO-NRs were grown on FTO/ZnO seed layer and to enhance dye adsorption it was continued by deposition of titania (TiO2) paste by screen printing method. Deposition time of ZnO-NRs were varied, for 120, 150 and 180 minutes and subsequently stacked with one layer of TiO2 mesoporous. The resulting heterojunction layers of FTO/ZnO-Nrs/TiO2 was then applied as a photoanode in quasi-solid dye sensitized solar cell (QS- DSSC) with polymer gel electrolyte (PGE) as a hole conductor. UV-Vis spectrometer was used to investigate the changes of dye adsorption in photoanode with/without inserting titania mesoporous. Characterizations of scanning electron microscopy (SEM) and X-ray diffraction was carried out and the results shows that increasing the deposition time produces a smaller average grain size, diameter and denser layer of ZnO-nanorods. From current-voltage measurement, higher efficiency (η = 2.53%) was obtained for 120 min ZnO nanorods with short circuit current density (Jsc ) of 2.84 mA/cm2 and open circuit voltage (Voc) of 0.7 V. The combination of TiO2 and ZnO-NRs shows a better performance in solar cells characteristics due to increases of dye adsorption on photoanode and high photogenerated electron transport rate. This work emphasizes an optimum condition of ZnO-NRs in combination with TiO2 mesoporous as an alternative photoanode in QS-DSSC.

The absence of chlorophyll b affects lateral mobility of photosynthetic complexes and lipids in grana membranes of Arabidopsis and barley chlorina mutants.

The lateral mobility of integral components of thylakoid membranes, such as plastoquinone, xanthophylls, and pigment-protein complexes, is critical for the maintenance of efficient light harvesting, high rates of linear electron transport, and successful repair of damaged photosystem II (PSII). The packaging of the photosynthetic pigment-protein complexes in the membrane depends on their size and stereometric parameters which in turn depend on the composition of the complexes. Chlorophyll b (Chlb) is an important regulator of antenna size and composition. In this study, the lateral mobility (the mobile fraction size) of pigment-protein complexes and lipids in grana membranes was analyzed in chlorina mutants of Arabidopsis and barley lacking Chlb. In the Arabidopsis ch1-3 mutant, diffusion of membrane lipids decreased as compared to wild-type plants, but the diffusion of photosynthetic complexes was not affected. In the barley chlorina f2 3613 mutant, the diffusion of pigment-protein complexes significantly decreased, while the diffusion of lipids increased, as compared to wild-type plants. We propose that the size of the mobile fractions of pigment-protein complexes in grana membranes in vivo is higher than reported previously. The data are discussed in the context of the protein composition of antennae, characteristics of the plastoquinone pool, and production of reactive oxygen species in leaves of chlorina mutants.

Photosynthetic acclimation to warming in tropical forest tree seedlings.

Tropical forests have a mitigating effect on man-made climate change by acting as a carbon sink. For that effect to continue, tropical trees will have to acclimate to rising temperatures, but it is currently unknown whether they have this capacity. We grew seedlings of three tropical tree species over a range of temperature regimes (TGrowth = 25, 30, 35 °C) and measured the temperature response of photosynthetic CO2 uptake. All species showed signs of acclimation: the temperature-response curves shifted, such that the temperature at which photosynthesis peaked (TOpt) increased with increasing TGrowth. However, although TOpt shifted, it did not reach TGrowth at high temperature, and this difference between TOpt and TGrowth increased with increasing TGrowth, indicating that plants were operating at supra-optimal temperatures for photosynthesis when grown at high temperatures. The high-temperature CO2 compensation point did not increase with TGrowth. Hence, temperature-response curves narrowed with increasing TGrowth. TOpt correlated with the ratio of the RuBP regeneration capacity over the RuBP carboxylation capacity, suggesting that at high TGrowth photosynthetic electron transport rate associated with RuBP regeneration had greater control over net photosynthesis. The results show that although photosynthesis of tropical trees can acclimate to moderate warming, carbon gain decreases with more severe warming.

Distinct ecophysiological strategies of widespread and endemic species from the megadiverse campo rupestre

The Espinhaço Mountain Range in eastern Brazil hosts a megadiverse and endemic tropical flora. The main vegetation is the campo rupestre, which harbors several endemic plant species. In this study, we sought to compare photosynthetic and leaf nutrient-use strategies in widespread and endemic species that allow its adjustments to high light and impoverished soils in campo rupestre. Three species with contrasting levels of endemism were selected: Coccoloba cereifera, an endangered micro-endemic species from Serra do Cipó; Lavoisiera cordata, vulnerable and endemic to Espinhaço range; and Vochysia thyrsoidea, a common widespread species from the Cerrado domain. During the dry season, we performed field measurements of chlorophyll a fluorescence and pigment content to evaluate the photosynthetic efficiency of these species. We also assessed soil fertility, nutrient status and leaf anatomy. Widespread and endemic species in campo rupestre showed distinct strategies to cope with high light levels and nutrient-impoverished soils. The micro-endemic species C. cereifera showed high nutrient use efficiency, which enables it to colonize impoverished sandy soils. This species and L. cordata minimize excessive light absorption at midday through shoot architecture as well as present efficient non-photochemical energy dissipation during high light level exposures. The high effective quantum yield and electron transport rate of the widespread species V. thyrsoidea may account in part for its wide distribution under extreme environmental conditions in Neotropical sites. The occurrence of widespread and endemic species in this megadiverse mountain environment might be attributed to distinct physiological strategies of species to cope with high light levels and impoverished soils.

Rice (Oryza sativa L.) with reduced chlorophyll content exhibit higher photosynthetic rate and efficiency, improved canopy light distribution, and greater yields than normally pigmented plants

The net photosynthesis and photosynthetic N use efficiency (PNUE) of a rice mutant with reduced chlorophyll synthesis were much higher than those of its wild type (WT). To understand the physiological mechanism, we conducted a model analysis and pot and field experiments under different N rates. Both the model analysis and the experiments showed that low chlorophyll content did not impede the development of chloroplast in the mutant; the reduced chlorophyll content and high expression levels of chlorophyll binding protein genes suggested the smaller light-harvesting chlorophyll antenna size, and higher expression levels of thylakoid membrane protein genes indicated high potential for chloroplast electron transport in the mutant; the small antenna size avoided excessive light absorption, and increased PSII efficiency, resulting in high electron transport rate in the mutant. The higher Rubisco content in the mutant ensured a higher Rubisco capacity for carboxylation. The high CO2 conductivity of stomata and mesophyll ensured availability of CO2 at the site of carboxylation. All these contributed to the increased photosynthetic rate in the mutant. Leaf N content was found higher in the mutant than in the WT, however, the extent to which the photosynthetic rate was increased was much larger than that of leaf N content, leading to improved PNUE in mutant. Furthermore vertical light distribution was improved in the canopy of the mutant, as greater transmittance of sunlight within the canopy was observed in the density experiment in the field. The mutant showed yield advantages considering its shorter growth duration, indicating the higher photosynthetic capacity and improved canopy light distribution with reduced chlorophyll synthesis. The mutant plant could potentially be used to improve photosynthetic efficiency.

Important roles for membrane lipids in haloarchaeal bioenergetics

Recent advances in lipidomic analysis in combination with various physiological experiments set the stage for deciphering the structure-function of haloarchaeal membrane lipids. Here we focused primarily on changes in lipid composition of Haloferax volcanii, but also performed a comparative analysis with four other haloarchaeal species (Halobacterium salinarum, Halorubrum lacusprofundi, Halorubrum sodomense and Haloplanus natans) all representing distinctive cell morphologies and behaviors (i.e., rod shape vs. pleomorphic behavior). Common to all five haloarchaea, our data reveal an extraordinary high level of menaquinone, reaching up to 72% of the total lipids. This ubiquity suggests that menaquinones may function beyond their ordinary role as electron and proton transporter, acting simultaneously as ion permeability barriers and as powerful shield against oxidative stress. In addition, we aimed at understanding the role of cations interacting with the characteristic negatively charged surface of haloarchaeal membranes. We propose for instance that by bridging the negative charges of adjacent anionic phospholipids, Mg2+ acts as surrogate for cardiolipin, a molecule that is known to control curvature stress of membranes. This study further provides a bioenergetic perspective as to how haloarchaea evolved following oxygenation of Earth's atmosphere. The success of the aerobic lifestyle of haloarchaea includes multiple membrane-based strategies that successfully balance the need for a robust bilayer structure with the need for high rates of electron transport – collectively representing the molecular basis to inhabit hypersaline water bodies around the planet.

Photochemical changes and oxidative damage in the aquatic macrophyte Cymodocea nodosa exposed to paraquat-induced oxidative stress

The non-selective herbicide paraquat (Pq) is being extensively used for broad-spectrum weed control. Through water runoff and due to its high water solubility it contaminates aquatic environments. Thus, the present study was carried out to investigate the photochemical changes and oxidative damage in the aquatic macrophyte Cymodocea nodosa to short- (2h) and long-term (24h) exposure to 2, 20, 200 and 1000μM paraquat (Pq) toxicity by using chlorophyll fluorescence imaging and H2O2 real-time imaging. The effective quantum yield of PSII (ΦPSII) show a tendency to increase at 2μM Pq after 2h exposure, and increased significantly at 20 and 200μM Pq. Τhe maximum oxidative effect on C. nodosa leaves was observed 2h after exposure to 200μM Pq concentration when the highest increases of ΦPSII due to high electron transport rate (ETR) resulted in a significant increase of H2O2 production due to the lowest non-photochemical quenching (NPQ) that was not efficient to serve as a protective mechanism, resulting in photooxidation. Prolonged exposure (24h) to 200μM Pq resulted in a decreased ΦPSII not due to an increase of the photoprotective mechanism NPQ, but due to high quantum yield of non-regulated energy loss in PSII (ΦNO), resulting to the lowest fraction of open PSII reaction centers (qp). This decreased ΦPSII has resulted to less Pq radicals to be formed, with a consequence of a small increase of H2O2 production compared to control C. nodosa leaves, but substantial lower than that of 2h exposure to 200μM Pq. Exposure of C. nodosa leaves to 1000μM Pq toxicity had lower effects on the efficiency of photochemical reactions of photosynthesis under both short- (2h) and long-term (24h) exposure than 200μM Pq. This was evident by an almost unchanged ΦPSII and qp, that remained unchanged even at a longer exposure time (48h), compared to control C. nodosa leaves. Thus, the response of C. nodosa leaves to Pq toxicity fits the “Threshold for Tolerance Model”, with a threshold concentration of 200μM Pq required for initiation of a tolerance mechanism, by increasing H2O2 production for the induction of genes encoding protective processes in response to Pq-induced oxidative stress. Overall, it is concluded that chlorophyll fluorescence imaging constitutes a promising basis for investigating herbicide mode of action in aquatic plants and for detecting their protective mechanisms.

Photosynthesis and photoprotection under drought in the annual desert plant Anastatica hierochuntica

Anastatica hierochuntica is an annual desert plant, which was recently shown to have unusually low nonphotochemical quenching (NPQ) and a high PSII electron transport rate (ETR). In the current study, we examined how these unusual characteristics are related to a lack of CO2 and inhibition of net photosynthetic rate (P N). We compared the photosynthetic and photoprotective response of A. hierochuntica and sunflower (Helianthus annuus), under conditions of photosynthetic inhibition, with either low CO2 or drought. We found that under nonsteady state conditions of low CO2 availability, A. hierochuntica exhibited about half of the NPQ values and almost twice of the ETR values of H. annuus. However, the long-term inhibition of P N under drought caused a similar increase in NPQ and a decrease in ETR in both A. hierochuntica and H. annuus. These results suggest that the unusually low NPQ and high ETR in A. hierochuntica are not directly related to a response to drought conditions.

Photosynthetic activity and productivity of intertidal macroalgae: In situ measurements, from thallus to community scale

The photosynthetic activity and productivity of four dominant canopy intertidal macroalgae were measured under emersion and immersion, at saturating light levels (PAR>300μmolphotonsm−2s−1), and compared at two sites (eastern and western English Channel) in spring and summer. The photosynthetic activity of thalli was measured by the electron transport rate (ETR) using pulse-amplitude modulated (PAM) fluorescence and the productivity of individuals and of communities was measured by carbon fluxes in closed chambers. Under emersion, when thalli were still hydrated, the uppermost species Pelvetia canaliculata had higher photosynthetic activity (mean ETR between 327 and 460μmole−m−2s−1) and individual gross productivity (between 60 and 212μmolCgDW−1h−1) than the lowermost species Laminaria digitata (mean ETR between 24 and 53μmole−m−2s−1 and gross productivity between 2 and 38μmolCgDW−1h−1), whatever the site and season. P. canaliculata had higher ETR in air than underwater (averaged 146μmole−m−2s−1) and L. digitata had lower ETR in air than underwater (averaged 112μmole−m−2s−1), while they exhibited, respectively, 3 and 5 times higher gross productivity underwater. At the community scale, the low mid-shore zone of Fucus serratus had the highest mean gross productivity under emersion (47mmolCm−2h−1) while rates were higher for the uppermost than lowermost zone at the eastern site (average 20 and 6mmolCm−2h−1, respectively) and of the same order of magnitude for both zones at the western site (about 30mmolCm−2h−1). Finally, the variability of under emersion primary productivity among sites and seasons was reduced when the measurements were performed on entire communities compared to isolated individuals of the dominant species.

Photosynthetic Capacities and Productivity of Indoor Hydroponically Grown <i>Brassica alboglabra</i> Bailey under Different Light Sources

A major challenge for growing vegetables in an indoor vertical farming system will be supplying not only sufficient quantity but also quality of light. It has been reported that yield of crops is enhanced under appropriate combination of red and blue light compared with red light alone. This project aims to investigate the effects of different combinations of red and blue. Plants were cultured for a 12-h photoperiod at 210 μmol·m–2·s–1 photosynthetic photon flux density (PPFD) under different combinations of red (R) and blue (B) light-emitting diodes (LED). The R:B-LED ratios are: 1) 100:0 (0B); 2) 92:8 (8B); 3) 84:16 (16B) and; 4) 76:24 (24B). All combined RB-LEDs significantly increased light-saturated photosynthetic CO2 assimilation rate (Asat), stomatal conductance (gs sat) and productivity compared with those under 0B. Results suggested that 16B was the most suitable combination of LEDs to achieve the highest productivity for B. alboglabra. To further substantiate these results, comparative studies were conducted under equal photoperiod and PPFD among 16B (RB-LED), white LED (RBW-LED) and high-pressure sodium (HPS) lamps. Shoot, root biomass, leaf number, leaf mass per area and Asat were higher in plants under HPS lamps and RB-LED, than under RBW-LED. However, gs sat was lower under RB-LED and RBW-LED, than under HPS lamps. Plants under RB-LED had higher electron transport rate and photochemical quenching but lower non-photochemical quenching than those under RBW-LED and HPS lamps. Thus, these results more conclusively affirmed that 16B was the most suitable light source to achieve the highest photosynthetic capacities. The findings of this study could also be used in vertical farming to achieve the highest productivity of vegetable crops such as B. alboglabra within the shortest growth cycle with reduced energy consumption.

Ocean acidification modulates the response of two Arctic kelps to ultraviolet radiation

The combined effects of ocean acidification and ultraviolet radiation (UVR) have been studied in the kelps Alaria esculenta and Saccharina latissima from Kongsfjorden (Svalbard), two major components of the Arctic macroalgal community, in order to assess their potential to thrive in a changing environment. Overall results revealed synergistic effects, however with a different amplitude in the respective species. Changes in growth, internal N, C:N ratio, pigments, optimum quantum yield (Fv/Fm) and electron transport rates (ETR) following CO2 enrichment and/or UVR were generally more pronounced in S. latissima than in A. esculenta. The highest growth rates were recorded under simultaneous CO2 enrichment and UVR in both species. UVR-mediated changes in pigment content were partially prevented under elevated CO2 in both species. Similarly, UVR led to increased photosynthetic efficiency (α) and ETR only if CO2 was not elevated in A. esculenta and even under high CO2 in S. latissima. Increased CO2 did not inhibit external carbonic anhydrase (eCA) activity in the short-term but in the mid-term, indicating a control through acclimation of photosynthesis rather than a direct inhibition of eCA by CO2. The higher benefit of simultaneous CO2 enrichment and UVR for S. latissima respect to A. esculenta seems to involve higher C and N assimilation efficiency, as well as higher ETR, despite a more sensitive Fv/Fm. The differential responses shown by these two species indicate that ongoing ocean acidification and UVR could potentially change the dominance at lower depths (4–6m), which will eventually drive changes at the community level in the Arctic coastal ecosystem. These results support an existing consideration of S. latissima as a winner species in the global change scenario.

Development in Photoanode Materıals for Highly Efficient Dye Sensitized Solar Cells

Dye-sensitized solar cells (DSSC) have been extensively studied due to their promising potential for high efficiency, low production cost and eco-friendly production. The photoanode is one of the main components in DSSCs which determines its performance. The main issues facing in DSSCs are the charge recombinations and low light harvesting capacity. Conventional TiO 2 nanoparticles with large surface area has low light scattering ability and low electron transport rate while one dimensional nanostructures have high electron transport rate and good light scattering ability but has a low surface area. Different approaches such as nanocomposite, light scattering layer and hierarchical structures to improve performance of 1D DSSCs are discussed. Besides that, works done on the optimization of TiO 2 photoanode in cobalt based DSSC is also discussed. Additionally, doping of TiO 2 to improve the properties of TiO 2 and studies on alternative photoanode materials which involved the application of band gap engineering are discussed to further improve the performance of DSSCs.

Leaf chloroplast ultrastructure and photosynthetic properties of a chlorophyll-deficient mutant of rice

Leaf chloroplast ultrastructure and photosynthetic properties of a natural, yellow-green leaf mutant (ygl1) of rice were characterized. Our results showed that chloroplast development was significantly delayed in the mutant leaves compared with the wild-type rice (WT). As leaves matured, more grana stacks formed concurrently with increasing leaf chlorophyll (Chl) content. Except for the lower intercellular CO2 concentration, the ygl1 plants had a higher leaf net photosynthetic rate, stomatal conductance, and transpiration rate than those of the WT plants. Under equal amounts of Chl, the excitation energy of PSI and PSII was much stronger in the mutant than that in the WT. The ygl1 plants showed higher nonphotochemical quenching and lower photochemical quenching. They also exhibited higher actual photochemical efficiency of PSII with a higher electron transport rate. Under the light of 200 μmol(photon) m-2 s-1, the ygl1 mutant showed lesser deepoxidation of violaxanthin in the xanthophyll cycle than WT, but it increased substantially under strong light conditions. In conclusion, the photosynthetic machinery of the ygl1 remained stable during leaf development. The plants were less sensitive to photoinhibition compared with WT due to the active xanthophyll cycle. The ygl1 plants were efficient in both light harvesting and conversion of solar energy.

Light induction of nonphotochemical quenching, CO<sub>2</sub> fixation, and photoinhibition in woody and fern species adapted to different light regimes

We aimed to find out relations among nonphotochemical quenching (NPQ), gross photosynthetic rate (PG), and photoinhibition during photosynthetic light induction in three woody species (one pioneer tree and two understory shrubs) and four ferns adapted to different light regimes. Pot-grown plants received 100% and/or 10% sunlight according to their light-adaptation capabilities. After at least four months of light acclimation, CO2 exchange and chlorophyll fluorescence were measured simultaneously in the laboratory. We found that during light induction the formation and relaxation of the transient NPQ was closely related to light intensity, light-adaption capability of species, and PG. NPQ with all treatments increased rapidly within the first 1–2 min of the light induction. Thereafter, only species with high PG and electron transport rate (ETR), i.e., one pioneer tree and one mild shade-adapted fern, showed NPQ relaxing rapidly to a low steady-state level within 6–8 min under PPFD of 100 μmol(photon) m−2 s−1 and ambient CO2 concentration. Leaves with low PGand ETR, regardless of species characteristics or inhibition by low CO2 concentration, showed slow or none NPQ relaxation up to 20 min after the start of low light induction. In contrast, NPQ increased slowly to a steady state (one pioneer tree) or it did not reach the steady state (the others) from 2 to 30 min under PPFD of 2,000 μmol m−2 s−1. Under high excess of light energy, species adapted to or plants acclimated to high light exhibited high NPQ at the initial 1 or 2 min, and showed low photoinhibition after 30 min of light induction. The value of fastest-developing NPQ can be quickly and easily obtained and might be useful for physiological studies.

Plant mitochondria: Source and target for nitric oxide

Plant mitochondria generate nitric oxide (NO) under anoxia through the action of cytochrome c oxidase and other electron transport chain components on nitrite. This reductive mechanism operates under aerobic conditions at high electron transport rates. Indirect evidence also indicates that the oxidative pathway of NO production may be associated with mitochondria. We review the consequences of mitochondrial NO production, including the inhibition of oxygen uptake by cytochrome c oxidase, the inhibition of aconitase and succinate dehydrogenase, the induction of alternative oxidase, and the nitrosylation of several proteins, including glycine decarboxylase. The importance of these events in adaptation to abiotic and biotic stresses is discussed.