The kinetic relationship between the C-550 absorbance change,the reduction of Q(ΔA320) and the variable fluorescence yield change in chloroplasts at room temperature

The light minus dark difference spectrum and the kinetics of the indicator pigment C-550 have been measured at room temperature in isolated, envelopefree chloroplasts in the presence of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU). The C-550 spectrum indicates a band shift with peaks at 540 and 550 nm and has an isosbestic point at 545 nm. On the assumption of 400 chlorophyll molecules per electron transfer chain the differential extinction coefficient Δ?(540–550) is calculated to be approximately 5 mM^?1 · cm^?1. The kinetics of the C-550 absorbance change, occurring upon the onset of continuous illumination, are shown to be biphasic and strictly correlated with the kinetics of the complementary area measured from the fluorescence induction curve under identical conditions and with those of the absorbance increase at 320 nm due to photoreduction of Q. The light-induced change in these three parameters can be described as a function of the variable fluorescence yield change occurring under the same conditions. Such functions are non-linear and reveal a heterogeneous dependence of the variable fluorescence yield on the fraction of closed System II reaction centers.It is concluded that for every molecule of the primary electron acceptor Q of Photosystem II that is photochemically reduced there corresponds an equivalent change in the absorbance of the indicator pigment C-550 and in the size of the complementary area. Thus, C-550 and area are two valid parameters for monitoring the primary photochemical activity of System II at room temperature.     

Rapid, Blue-Light Induced Transpiration in Avena

The transpiration responses of primary Avena leaves to blue-light pulses were investigated. Only light with wave length shorter than 524 nm can produce the rapid transpiration response. The action spectrum has a maximum around 450 nm. The rapid transpiration response induced by blue-light pulses successively disappeared in long-term experiments if the plant was kept in darkness between the pulses. However, if visible light was given to the plant between the pulses, the rapid response was restored. The magnitude of the rapid transpiration response was investigated under different conditions of background illumination and blue-light exposure. Saturation of the response was obtained with an irradiation level of 1.5–2 mW.cm^?2 (5 min pulses) and with a pulse duration of 4 min (pulse irradiance 2 mW.cm^?2). A pulse duration of 3 s was sufficient to produce a significant rapid response at an irradiation level of 2 mW.cm^?2.     

Characterization of the Xanthophyll Cycle and Other Photosynthetic Pigment Changes Induced by Iron Deficiency in Sugar Beet (Beta vulgaris L.)

In this work we characterize the changes induced by iron deficiency in the pigment composition of sugar beet (Beta vulgaris L.) leaves. When sugar beet plants were grown hydroponically under limited iron supply, neoxanthin and β-carotene decreased concomitantly with chlorophyll a, whereas lutein and the carotenoids within the xanthophyll cycle were less affected. Iron deficiency caused major increases in the lutein/chlorophyll a and xanthophyll cycle pigments/chlorophyll a molar ratios. Xanthophyll cycle carotenoids in Fe-deficient plants underwent epoxidations and de-epoxidations in response to ambient light conditions. In dark adapted Fe-deficient plants most of the xanthophyll cycle pigment pool was in the epoxidated form violaxanthin. We show, both by HPLC and by in vivo 505 nanometers absorbance changes, that in Fe deficient plants and in response to light, the de-epoxidated forms antheraxanthin and zeaxanthin were rapidly formed at the expense of violaxanthin. Several hours after returning to dark, the xanthophyll cycle was shifted again toward violaxanthin. The ratio of variable to maximum chlorophyll fluorescence from intact leaves was decreased by iron deficiency. However, in iron deficient leaves this ratio was little affected by light conditions which displace the xanthophyll cycle toward epoxidation or de-epoxidation. This suggests that the functioning of the xanthophyll cycle is not necessarily linked to protection against excess light input.     

The Effect of Leaf Water Potential, Leaf Temperature and Light Intensity on Leaf Diffusion Resistance and the Transpiration of Leaves of Malus sylvestris

The relationship between leaf resistance to water vapour diffusion and each of the factors leaf water potential, light intensity and leaf temperature was determined for leaves on seedling apple trees (Malus sylvestris Mill. cv. Granny Smith) in the laboratory. Leaf cuticular resistance was also determined and transpiration was measured on attached leaves for a range of conditions. Leaf resistance was shown to be independent of water potential until potential fell below — 19 bars after which leaf resistance increased rapidly. Exposure of leaves to CO₂-free air extended the range for which resistance was independent of water potential to — 30 bars. The light requirement for minimum leaf resistance was 10 to 20 W m^?2 and at light intensities exceeding these, leaf resistance was unaffected by light intensity. Optimum leaf temperature for minimum diffusion resistance was 23 ± 2°C. The rate of change measured in leaf resistance in leaves given a sudden change in leaf temperature increased as the magnitude of the temperature change increased. For a sudden change of 1°C in leaf temperature, diffusion resistance changed at a rate of 0.01 s cm^?1 min^?1 whilst for a 9°C leaf temperature change, diffusion resistance changed at a rate of 0.1 s cm^?1 min^?1. Cuticular resistance of these leaves was 125 s cm^?1 which is very high compared with resistances for open stomata of 1.5 to 4 s cm^?1 and 30 to 35 s cm^?1 for stomata closed in the dark. Transpiration was measured in attached apple leaves enclosed in a leaf chamber and exposed to a range of conditions of leaf temperature and ambient water vapour density. Peak transpiration of approximately 5 × 10^?6 g cm^?2 s^?1 occurred at a vapour density gradient from the leaf to the air of 12 to 14 g m^?3 after which transpiration declined due presumably to increased stomatal resistance. Leaves in CO₂-free air attained a peak transpiration of 11 × 10^?6 g cm^?2 s^?1 due to lower values of leaf resistance in CO₂ free air. Transpiration then declined in these leaves due to development of an internal leaf resistance (of up to 2 s cm^?1). The internal resistance was masked in leaves at normal CO₂ concentrations by the increase in stomatal resistance.     

CRITICAL LEVELS OF LIGHT AND TEMPERATURE REGULATING THE GAMETOGENESIS OF THREE LAMINARIA SPECIES (PHAEOPHYCEAE)1

Gametophytes of three Laminaria species occurring near Helgoland, North Sea, were cultivated 4 wk in a 12:12 LD regime at different temperatures in artificial light fields, and in the sea at different water depths. In the artificial light fields underwater spectral distribution was simulated according to Jerlov water Types 5, 7, 9. Blue light in the simulated light fields amounted to 17, 12 or 4% of total quanta. The rate of vegetative growth did not depend on spectral distribution, was light-saturated at 4–6 W · m^?2, and increased with temperature up to 15 C. L. saccharina (L.) Lamour. exhibited the highest tolerance towards temperature, light and UV. Gametophytes survived 1 wk at 21 C ± 0.1, but not 22 C ± 0.1. Gametophytes of L. hyperborea (Gunn.) Fosl. and L. digitata (Huds.) Lamour. survived 1 wk at 20 C ± 0.1, but not at 21 C ± 0.1. In sunlight, and in the light field of a xenon lamp, 50% of L. saccharina gametophytes were killed by a quantum dose of 50 μEin · cm^?2, and 100% of the plants by 90 μEin · cm^?2. Approximately half of these quantum doses killed the corresponding percent of the other species gametophytes. Appreciably higher quantum doses were survived in visible light, with red being the most detrimental. Fertility depended on a critical quantum dose of blue light which decreased almost exponentially with decreasing temperature. The quantum dose (400–512 nm) required for induction of fertilization of 50% of the female gametophytes (males react similarly) was 90 μEin · cm^?2 at 5 C, 110 μEin · cm^?2 at 10 C, 230 (560 in L. digitata)μEin · cm^?2 at 15 C, and 560 (L. hyperborea) or about 850 (other 2 species) μEin · cm^?2 at 18 C. In the sea the gametophytes survived the dark winter months in the unicellular stage, with almost no vegetative growth of the primary cell, due to lack of light. In early spring the female gametophytes matured in the unicellular, and the males in a few-celled stage at the depth of 2 m, as did the laboratory cultures under conditions inducing maximal fertility.     

Factors affecting photosynthesis and its seasonal variation in the seagrasses Cymodocea nodosa (Ucria) Aschers,and Posidonia oceanica (L.) Delile in the mediterranean

Measurements of photosynthesis, dark respiration, and leaf chlorophyll content were made in the laboratory on both shallow (1 to 5 m) and deep (25 to 33 m) leaves of Cymooceu nodosa (Ucria) Aschers, and Posidonia oceanica (L.) Delile in Malta in April and August. Light saturated photosynthetic rates in Cymodocea were similar in spring (18 μg C cm^?2h^?1) and summer (25μg Ccm^?2h^?1) if the 9 C increase in water temperature in summer is taken into account: however, photosynthetic rates in Posidonia were higher in spring than in summer, especially in shallow leaves which fixed ≈ 10 μg C cm^?2h^?1 in spring but less than half that in summer when rates of carbon accretion were close to compensation point. Levels of irradiance at which photosynthesis was light saturated (Iλ were ≈ 3 mW cm^?2 PAR for Cymodocea and 2 mW cm^?2 PAR for Posidonia: underwater irradiance at the lower depth limit for these plants (≈33 m) was ≈3 mW cm^?2 PAR. corresponding closely to the saturation irradiances. Compensation irradiance for both species was between 0.3 and 0.5 mW cm^?2 PAR.Photosynthesis in both species had a temperature optimum at about 30 C (slightly higher in Cymodocea in summer). Dark respiration rates were generally similar in spring and summer, in the region of 3 μg C cm^?2 h^?1 in Cymodocea and 1.5 to 2 μg C cm^?2 h^?1 in Posidonia. Increase in dark respiration rates with increased temperature was considerably greater in spring than in summer in both species. Photosynthesis was directly proportional to chlorophyll content in Posidonia in the range encountered (up to 58 μg Chl cm^?2) and the summer reduction in photosynthesis was closely correlated with reduction in chlorophyll content. It seems unlikely that environmental factors such as seasonal changes in light intensity, nutrient availability or water temperature were directly responsible for this loss of chlorophyll and it is suggested that this is a manifestation of general leaf senescence, probably induced by daylength changes but possibly enhanced by increased water temperature. Cymodocea showed a similar reduction in chlorophyll content in summer but this was not reflected in reduced photosynthesis. Thus, although Cymodocea may grow rapidly throughout the spring and summer with an overall productivity of 3.6 g C m^?2 day^?1 in shallow water, the luxuriant growths of Posidonia must develop in the first half of the year when a dense meadow may produce up to 2.1 g C m^?2 day^?1 in shallow water, declining to ?0.6 g C m^?2 day^?1 in summer.     

Click‐Functionalized Ru(II) Complexes for Dye‐Sensitized Solar Cells

Three heteroleptic ruthenium complexes incorporating new ancillary ligands synthesized by sequential connection of different alkyl functionalities with triazole as a linker are prepared using click chemistry. These sensitizers exhibit low‐energy metal‐to‐ligand charge transfer bands centered at 540 nm with molar extinction coefficients of up to 1.54 × 10⁴ L mol^?1 cm^?1. The devices using these sensitizers in conjunction with a volatile electrolyte show high photovoltaic conversion efficiencies of 8.7 to 9.9% under standard AM 1.5G sunlight (100 mW cm^?2) conditions. Using an ionic liquid electrolyte, the cells show not only a good power‐conversion efficiency of up to 7.1%, but also promising long‐term stability under full sunlight intensity at 60 °C. The difference in the photovoltaic parameters during the ageing process is investigated by employing transient photoelectrical measurements.     

The Effects of Illumination on the Xanthophyll Composition of the Photosystem II Light-Harvesting Complexes of Spinach Thylakoid Membranes

The xanthophyll composition of the light-harvesting chlorophyll a/b proteins of photosystem II (LHCII) has been determined for spinach (Spinacia oleracea L.) leaves after dark adaptation and following illumination under conditions optimized for conversion of violaxanthin into zeaxanthin. Each of the four LHCII components was found to have a unique xanthophyll composition. The major carotenoid was lutein, comprising 60% of carotenoid in the bulk LHCIIb and 35 to 50% in the minor LHCII components LHCIIa, LHCIIc, and LHCIId. The percent of carotenoid found in the xanthophyll cycle pigments was approximately 10 to 15% in LHCIIb and 30 to 40% in LHCIIa, LHCIIc, and LHCIId. The xanthophyll cycle was active for the pigments bound to all of the LHCII components. The extent of deepoxidation for complexes prepared from light-treated leaves was 27, 65, 69, and 43% for LHCIIa, -b, -c, and -d, respectively. These levels of conversion of violaxanthin to zeaxanthin were found in LHCII prepared by three different isolation procedures. It was estimated that approximately 50% of the zeaxanthin associated with photosystem II is in LHCIIb and 30% is associated with the minor LHCII components.     

Solar Rechargeable Batteries Based on Lead–Organohalide Electrolyte

A dye‐sensitized solar cell (DSC) with in situ energy storage capacity is demonstrated using a lead–organohalide electrolyte CH₃NH₃I·PbCl₂ (LOC) to replace the conventional I^?/I₃^? electrolyte. The coupling of lead and iodine in one electrolyte creates a dual‐function rechargeable solar battery that combines the working processes of photoelectrochemical cells with electrochemical batteries. Optimization of the H⁺ concentration in the electrolyte leads to increased photocharging efficiency and storage. The power conversion efficiency of the LOC–DSC is 8.6% under one sun illumination (AM 1.5, 100 mW cm^?2) as a DSC. When operating as a battery, Faraday efficiency can be achieved as high as 81.5% using a bromide‐based CH₃NH₃Br·PbBr₂ (LOB) electrolyte in a DSC configuration. This new cell design suggests a means of combining photovoltaic energy conversion and electrical energy storage.     

Photochemical efficiency of Photosystem II and xanthophyll cycle components in Zea mays leaves exposed to water stress and high light

The effects of two light treatments (photosynthetically active photon flux density of either 650 or 1950 µmol m^–2 s^–1) on the photochemical efficiency of Photosystem II (PS II) (measured as variable to maximum fluorescence ratio) and on the xanthophyll cycle components was studied in wilted Zea mays leaves. For comparison, these parameters were followed under the same light conditions in well-hydrated leaves maintained either in normal or CO₂-free air. The net CO₂ assimilation of dehydrated leaves declined rapidly as their relative water content (RWC) decreased from 100 to 60% while the PS II efficiency measured after a prolonged dark period of 16 h declined only when RWC leaves was lower than 60%. Furthermore, drought caused an increase in the pool size of the xanthophyll cycle pigments and the presence of a sustained elevated level of zeaxanthin and antheraxanthin at the end of the long dark period. The leaf water deficit enhanced the sensitivity of PS II efficiency to light exposure. During illumination, strong inhibition of PS II efficiency and large violaxanthin deepoxidation was observed in wilted leaves even under moderate photon flux density compared to control leaves in the same conditions. After 2 h of darkness following the light treatment, the PS II efficiency that is dependent on the previous PPFD, decreased with leaf water deficit. Moreover, zeaxanthin epoxidation led to an accumulation of antheraxanthin in dehydrated leaves. All these drought effects on PS II efficiency and xanthophyll cycle components were also obtained in well-hydrated leaves by short-term CO₂ deprivation during illumination. We conclude that the increased susceptibility of PS II efficiency to light in wilted maize leaves is mainly explained by the decrease of CO₂ availability and the resulting low net CO₂ assimilation.     

Simple oscillations in photosynthesis of higher plants

Illumination of leaves of Vicia faba L. provoked oscillations in the rates of CO₂ uptake and O₂ evolution. The oscillations were marked under anaerobic conditions, but were absent at 20% O₂. The minimum CO₂ concentration required for the appearance of oscillations was 600 μl · l^?1. The higher the CO₂ concentration, the stronger the oscillations. The effect of CO₂ concentration was saturated at 1000 μl CO₂ · l^?1. The period of the oscillations was 5–6 min at a light intensity of 80 nE · cm^?2 · s^?1 and became longer on lowering of the intensity. No oscillations appeared at intensities below 12 nE · cm^?2 · s^?1. Oscillations could also be generated by increasing the CO₂ concentration in the atmosphere during strong illumination under anaerobic conditions. The chlorophyl a fluorescence yield showed oscillations, similar in shape and frequency to those of photosynthesis, after such an environmental change. Oscillations were also observed in photosynthesis of other C₃ plants, Lycopersicon esulentum Mill and Glycine max Merrill, under the same conditions as those required for V. faba, but were absent for the C₄ plants, Zea mays and Amaranthus retroflexus L.     

Ferredoxin circular dichroism at 3600 cm−1

A very broad circular dichroism band is observed in reduced spinach ferredoxin at 3600 cm^?1. The maximum Δε is +1.1 M^?1 · cm^?1. The rotational strength is if+1.0 · 10^?39 merg · cm³ (+0.11 Debye-Bohr magneton); the minimum magnetic transition dipole moment is 0.14 Bohr magneton. These values are roughly consistent with expectations for a d → d transition of tetrahedrally coordinated Fe²⁺.No CD is detected in the oxidized protein between 5000 and 2800 cm^?1.     

Light-Induced Absorption Changes in Etiolated Coleoptiles

Blue (or green) light induced reversible and irreversible absorption changes in etiolated wheat (Triticum aestivum) coleoptiles. Immediately after a 10 s pulse of blue light there was an absorbance increase at 440 nm and a decrease at 420 nm. The absorbance at 440 nm returned to the original level in a biphasic way, with first-order rate constants of 0.05 s^?1 and 0.006 s^?1 at 25°C. The change at 440 nm was partly, but not completely, inhibited by iodide. In the 500–600 nm region complex changes occurred, indicating the participation of at least two different cytochromes, one of which was oxidized during a 10 s light pulse and the other oxidized more slowly during the following dark period.     

Metarhizium robertsii illuminated during mycelial growth produces conidia with increased germination speed and virulence

Light conditions during fungal growth are well known to cause several physiological adaptations in the conidia produced. In this study, conidia of the entomopathogenic fungi Metarhizium robertsii were produced on: 1) potato dextrose agar (PDA) medium in the dark; 2) PDA medium under white light (4.98 W m^?2); 3) PDA medium under blue light (4.8 W m^?2); 4) PDA medium under red light (2.8 W m^?2); and 5) minimum medium (Czapek medium without sucrose) supplemented with 3 % lactose (MML) in the dark. The conidial production, the speed of conidial germination, and the virulence to the insect Tenebrio molitor (Coleoptera: Tenebrionidae) were evaluated. Conidia produced on MML or PDA medium under white or blue light germinated faster than conidia produced on PDA medium in the dark. Conidia produced under red light germinated slower than conidia produced on PDA medium in the dark. Conidia produced on MML were the most virulent, followed by conidia produced on PDA medium under white light. The fungus grown under blue light produced more conidia than the fungus grown in the dark. The quantity of conidia produced for the fungus grown in the dark, under white, and red light was similar. The MML afforded the least conidial production. In conclusion, white light produced conidia that germinated faster and killed the insects faster; in addition, blue light afforded the highest conidial production.     

DOES LIGHT QUALITY AFFECT THE SINKING RATES OF MARINE DIATOMS?1

Although the spectral quality of light in the ocean varies considerably with depth, the effect of light quality on different physiological processes in marine phytoplankton remains largely unknown. In cases where experiments are performed under full spectral irradiance, the meaning of these experiments in situ is thus unclear. In this study, we determined whether variations in spectral quality affected the sinking rates of marine diatoms. Semicontinuous batch cultures of Thalassiosira weissflogii (Gru.) Fryxell et Hasle and Ditylum brightwellii (t. West) Grunow in Van Huerk were grown under continuous red, white, or blue light. For T. weissflogii, sinking rates (SETCOL method) were twice as high (～0.2 m·d^?1)for cells grown under red light as for cells grown under white or blue light (～0.08 m·d^?1), but there were no significant differences in carbohydrate content (～105 fg·μm^?3) or silica content (～ 17 fg·μ^?3) to account for the difference in sinking rates. Thalassiosira weissflogii grown under blue light was significantly smaller (495 μm³) than cells grown under red light (661 μm³), which could contribute to its reduced sinking rate. However, cells grown under white light were similar in size to those grown under red light but had sinking rates not different from those of cells grown under blue light, indicating the involvement of factors other than size. There were no significant differences in sinking rate (～0.054 m·d^?1) or silica content (～20 fg·μm^?3) in D. brightwellii grown under red, white, or blue light, but cells grown under red light were significantly (20%) larger and contained significantly (20%) more carbohydrate per μm³ than cells grown under white or blue light. Spectral quality had no consistent effect on sinking rate, biochemical composition (carbohydrate or silica content), or cell volume in the two diatoms studied. The similarity in sinking rate of cells grown under white light compared to those grown under blue light supports the ecological validity of sinking rate studies done under white light.     

Effects of anaerobiosis as probed by the polyphasic chlorophyll a fluorescence rise kinetic in pea (Pisum sativum L.)

We analysed the changes of the chlorophyll (Chl)a fluorescence rise kinetic (from 50 s to 1 s) that occur when leaves or chloroplasts of pea ( Pisum sativum L.) are incubated under anaerobic conditions in the dark. In control leaves, Chl a fluorescence followed a typical O-J-I-P polyphasic rise [Strasser et al. (1995) Photochem Photobiol 61: 32–42]. Anaerobiosis modified the shape of the transient with the main effect being a time-dependent increase in the fluorescence yield at the J-step (2 ms). Upon prolongation of the anaerobic treatment (> 60 min), the O-J-I-P fluorescence rise was eventually transformed to an O-J (J = P) rise. A similar transformation was observed when pea leaves were treated with DCMU or sodium dithionite. Anaerobiosis resulted in a 10–20% reduction in the maximum quantum yield of the primary photochemistry of Photosystem II, as measured by the ratio of the maximal values of variable and total fluorescence (F_V/F_M). When the leaves were returned to the air in the dark, the shape of the fluorescence transient showed a time-dependent recovery from the anaerobiosis-induced change. The original O-J-I-P shape could also be restored by illuminating the anaerobically treated samples with far-red light but not with blue or white light. Osmotically broken chloroplasts displayed under anaerobic conditions fluorescence transients similar to those observed in anaerobically treated leaves, but only when they were incubated in a medium comprising reduced pyridine nucleotides (NADPH or NADH). As in intact leaves, illumination of the anaerobically treated chloroplasts by far-red light restored the original O-J-I-P transient, although only in the presence of methyl viologen. The results provide additional evidence for the existence of a chlororespiratory pathway in higher plant cells. Furthermore, they suggest that the J-level of the fluorescence transient is strongly determined by the redox state of the electron carriers at the PS II acceptor side.     

Quantum Dot Based Heterostructures for Unassisted Photoelectrochemical Hydrogen Generation

TiO₂ hollow nanowires (HNWs) and nanoparticles (NPs) constitute promising architectures for QDs sensitized photoanodes for H₂ generation. We sensitize these structures with CdS/CdSe quantum dots by two different methods (chemical bath deposition, CBD and succesive ionic layer adsorption and reaction, SILAR) and evaluate the performance of these photoelectrodes. Remarkable photocurrents of 4 mA·cm and 8 mA·cm^?2 and hydrogen generation rates of 40 ml·cm^?2·day^?1 and 80 ml·cm^?2·day^?1 have been obtained in a three electrode configuration with sacrificial hole scavengers (Na₂S and Na₂SO₃), for HNWs and NPs respectively, which is confirmed through gas analysis. More importantly, autonomous generation of H₂ (20 ml·cm^?2·day^?1 corresponding to 2 mA·cm^?2 photocurrent) is obtained in a two electrode configuration at short circuit under 100 mW·cm^?2 illumination, clearly showing that these photoanodes can produce hydrogen without the assistance of any external bias. To the best of the authors' knowledge, this is the highest unbiased solar H₂ generation rate reported for these of QDs based heterostructures. Impedance spectroscopy measurements show similar electron density of trap states below the TiO₂ conduction band while the recombination resistance was higher for HNWs, consistently with the much lower surface area compared to NPs. However, the conductivity of both structures is similar, in spite of the one dimensional character of HNWs, which leaves some room for improvement of these nanowired structures. The effect of the QDs deposition method is also evaluated. Both structures show remarkable stability without any appreciable photocurrent loss after 0.5 hour of operation. The findings of this study constitute a relevant step towards the feasibility of hydrogen generation with wide bandgap semiconductors/quantum dots based heterostructures.     

Xanthophyll cycle induction by anaerobic conditions under low light in Chlamydomonas reinhardtii

The effect of anaerobiosis on the induction of the xanthophyll cycle was investigated in Chlamydomonas reinhardtii. The results showed that, anaerobiosis obtained by either sulfur starvation or by bubbling nitrogen in the culture grown in complete medium induced the xanthophyll cycle even when cultures were exposed to low light conditions. The zeaxanthin content reached 35 mmol mol^?1 Chl a, after 110 h in anaerobic sulfur-starved cultures, and 30 mmol mol^?1 Chl a within 24 h in sulfur replete cultures bubbled with nitrogen. Both starved and non-starved cultures grown under aerobic conditions, did not exhibit any sizeable increase in the zeaxanthin content. Chlorophyll fluorescence measurements revealed a decrease in the maximum photochemical quantum yield of PSII (F_v/F_m) by more than 50 %. The chlorophyll fluorescence kinetics (OJIP) analysis showed a strong rise at the J-step indicating a strong reduction of Q_A. Our findings demonstrated that anaerobiosis in low light exposed cultures induced the xanthophyll cycle through a strong increase of the level of plastoquinone pool reduction, which was associated to the formation of a trans-thylakoid membranes proton gradient, while in dark anaerobic cultures, no appreciable induction of xanthophyll cycle could be observed, despite the sizeable increase in non–photochemical quenching.     

High‐Performance Thermomagnetic Generators Based on Heusler Alloy Films

Recent developments on Heusler alloys including Ni–Mn–X and Ni–Co–Mn–X (X = Ga, In, Sn,…) demonstrate multiferroic phase transformations with large abrupt changes in lattice parameters of several percent and corresponding abrupt changes in ferromagnetic ordering near the transition temperatures. These materials enable a new generation of thermomagnetic generators that convert heat to electricity within a small temperature difference below 5 K. While thermodynamic calculations on this energy conversion method predict a power density normalized to material volume of up to 300 mW cm^?3, experimental results have been in the range of µW cm^?3. Challenges are related to the development of materials with bulk‐like single‐crystal properties as well as geometries with large surface‐to‐volume ratio for rapid heat exchange. This study demonstrates efficient thermomagnetic generation via resonant actuation of freely movable thin‐film devices of the Heusler alloy Ni–Mn–Ga with unprecedented power density of 118 mW cm^?3 that compares favorably with the best thermoelectric generators. Due to the large temperature‐dependent change of magnetization of the films, a periodic temperature change of only 3 K is required for operation. The duration of thermomagnetic duty cycle is only about 12 ms, which matches with the period of oscillatory motion.     

Efficient Solar Cells Based on Light‐Harvesting Antimony Sulfoiodide

Although antimony sulfoiodide (SbSI) exhibits very interesting properties including high photoconductivity, ferroelectricity, and piezoelectricity, it is not applied to solar cells. Meanwhile, SbSI is predominantly prepared as a powder using a high‐temperature, high‐pressure system. Herein, the fabrication of solar cells utilizing SbSI as light harvesters is reported for the first time to the best of knowledge. SbSI is prepared by solution processing, followed by annealing under mild temperature conditions by a reaction between antimony trisulfide, which is deposited by chemical bath deposition on a mesoporous TiO₂ electrode and antimony triiodide, under air at a low temperature (90 °C) without any external pressure. The solar cells fabricated using SbSI exhibit a power conversion efficiency of 3.05% under standard illumination conditions of 100 mW cm^?2.