Emerson Enhancement Effect Research Articles

Enhancing the luminescence of Mn4+-doped double perovskite oxide Ca2LuNbO6 phosphor by utilizing A-site cationic fluoride as a flux

Supplement illumination is indispensable in the indoor plant cultivation domain. In this research work, double perovskite Ca2LuNbO6:Mn4+ phosphors were produced. A strategy of enhancing luminescence performance by utilizing A-site cationic fluoride as a flux was proposed. The structure and morphology of Ca2LuNbO6:Mn4+ phosphor was characterized. Under the excitation of 360 nm, the emission spectra of Ca2LuNbO6:Mn4+ phosphor cover from 600 nm to 750 nm peaking at 683 nm. It benefits the red section of chlorophyll absorption band and possesses the wavelengths of 680 nm and 700 nm demanded by photosystem I (PS I) and photosystem II (PS II) to realize Emerson enhancement effect. After adding CaF2 as flux, the emission intensity increases by 2.5 times. Due to its compatibility with the A-site cation of host, CaF2 agent not only lower the sintering temperature but also increase the crystallite size, which result in the enhancement of luminescence. The Dq/B and optical band gap of Ca2LuNbO6 host is 2.32 and 3.79 eV, respectively, which show that Mn4+ ions locate in the [NbO6] octahedra of strong crystal field and host has the suitable optical band gap for Mn4+ ions. With the help of CaF2, the thermal stability, activation energy ΔEa, internal quantum efficiency of Ca2LuNbO6:Mn4+ phosphors are promoted at 373 K from 64.8% to 70.7% of that at 273 K, from 0.33 to 0.36 eV, and from 9.1% to 23.5%. The luminescence lifetime of Ca2LuNbO6:Mn4+ is the order of a fraction of a millisecond. Finally, the as-prepared Ca2LuNb0.996O6:0.004Mn4+ phosphor was successfully fabricated through a 365 nm near ultraviolet (NUV) chip, which has the peak wavelengths of 683 nm and possesses 680 nm and 700 nm demanded by PS I and PS II. It is implied that Ca2LuNbO6:Mn4+ phosphor-converted light emitting diode has prospective market in the domain of supplement illumination of plant cultivation.

Leaf morphology, optical characteristics and phytochemical traits of butterhead lettuce affected by increasing the far-red photon flux.

Light and its spectral characteristics are crucial for plant growth and development. The far-red photon flux mediates many plant processes through the action of phytochrome and also accelerates the photosynthetic electron transfer rate. In this study, we assessed the effects of far-red addition on butterhead lettuce morphology, light use efficiency, optical properties, and phytochemical characteristics. Three-week-old lettuce plants (Lactuca sativa L. cv. Alyssa) were grown for up to 28 days under a 10% blue and 90% red light spectrum (200 µmol m-2 s-1, 16h photoperiod) to which five different intensities of far-red light (peak at 735 nm) were added (0-9-18-36-72 µmol m-2 s-1). White light-emitting diodes were included as a proxy for sunlight. Increasing supplemental far-red photon flux from zero to 21% increased the light use efficiency (g per mol) by 37% on day 14; 43% on day 21; and 39% on day 28. Measurements of projected head area suggest that this was associated with an increase in leaf expansion and photon capture and not necessarily a direct effect on photosynthesis. Moreover, vegetation indices based on leaf reflectance showed a decrease in chlorophyll-related indices under a high far-red photon flux. This decrease in pigment content was confirmed by chemical analyses, suggesting that the plants may not reach their full potential in terms of photon capture, limiting the overall photosynthetic performance. Furthermore, the stress-related Carter 1 index increased in plants grown under a high far-red photon flux, indicating early plant stress. Far-red tended to decrease the content of total phenolics and increase soluble sugars. The higher sugar levels can be attributed to an improved photochemical efficiency due to photosystem I excitation by far-red wavelengths, also known as the Emerson Enhancement effect. Despite these higher sugar levels, no effect on foliar nitrate content was observed. Our results show that far-red supplementation has the potential to enhance light interception at the early growth stages, although higher intensities of far-red may cause plant stress.

Carl Nelson Cederstrand (1927–2022): A Biophysicist, an Innovator and a Wonderful Person

We provide a glimpse of the personal and professional life of Carl Nelson Cederstrand, most of the personal part is contributed by the daughter Laura Cederstrand (LC), and his research part in the Life Sciences is provided by Govindjee, his early collaborator and friend. Carl is remembered for his critical contributions to the discovery, in 1957, of the Emerson Enhancement Effect that led to the current Z-Scheme of photosynthesis, and later to the absorption and fluorescence spectroscopy of algae through his design and construction of a unique spectrophotometer, at the University of Illinois at Urbana Champaign (UIUC). After receiving his PhD at UIUC, he worked at Beckman Instrument’s research division in California, where he designed an oxygen analyser that went to the Moon as part of one of the Apollo missions. Carl is best known for designing many infrared and ultraviolet detectors and creatively applying these in various ways in the life sciences, for which he is listed as inventor in nearly a dozen patents. Above all, Carl is remembered for his inventions that have significantly impacted many areas of the life sciences. We have included here his great insight into and fascination with MG cars. We end this Tribute to Carl with a reminiscence by his wife Darlene Kelly, and our summary of his personal family life.

Red phosphors A2GdNbO6: Mn4+ (A = Ca, Sr, Ba) for plant growth LEDs with Emerson enhancement effect

Mn4+-doped A2GdNbO6 (A = Ca, Sr, Ba) oxide-based red emitting phosphors were prepared via high-temperature solid-state reaction method. Under the irradiation of 365 nm light, all samples emit a broad red light in the range of 650–700 nm which matches well with the absorption band of photosynthetic pigments. Their emission spectra composed of zero-phonon line emissions at about 665 nm and a broad phonon sideband beyond 680 nm, which can induce plant Emerson Enhancement Effect to accelerate plant growth extremely. Furthermore, composition-dependent the quantum yield, thermal stability and zero-phonon line emissions intensity have been significantly enhanced and zero-phonon line shifted from 682 to ~665 nm with substituting Ca by Sr or Ba. The dependence of zero-phonon lines of Mn4+ on structural symmetry have also been investigated though density functional theory (DFT) calculation and structural symmetry analysis. LED devices have also been fabricated by combining 365 nm n-UV chip with 0.5%Mn4+-doped A2GdNbO6 (A = Ca, Sr, Ba).

Far-red light is needed for efficient photochemistry and photosynthesis

The efficiency of monochromatic light to drive photosynthesis drops rapidly at wavelengths longer than 685nm. The photosynthetic efficiency of these longer wavelengths can be improved by adding shorter wavelength light, a phenomenon known as the Emerson enhancement effect. The reverse effect, the enhancement of photosynthesis under shorter wavelength light by longer wavelengths, however, has not been well studied and is often thought to be insignificant. We quantified the effect of adding far-red light (peak at 735nm) to red/blue or warm-white light on the photosynthetic efficiency of lettuce (Lactuca sativa). Adding far-red light immediately increased quantum yield of photosystem II (ΦPSII) of lettuce by an average of 6.5 and 3.6% under red/blue and warm-white light, respectively. Similar or greater increases in ΦPSII were observed after 20min of exposure to far-red light. This longer-term effect of far-red light on ΦPSII was accompanied by a reduction in non-photochemical quenching of fluorescence (NPQ), indicating that far-red light reduced the dissipation of absorbed light as heat. The increase in ΦPSII and complementary decrease in NPQ is presumably due to preferential excitation of photosystem I (PSI) by far-red light, which leads to faster re-oxidization of the plastoquinone pool. This facilitates reopening of PSII reaction centers, enabling them to use absorbed photons more efficiently. The increase in ΦPSII by far-red light was associated with an increase in net photosynthesis (Pn). The stimulatory effect of far-red light increased asymptotically with increasing amounts of far-red. Overall, our results show that far-red light can increase the photosynthetic efficiency of shorter wavelength light that over-excites PSII.

ALGAL MODEL SYSTEMS AND THE ELUCIDATION OF PHOTOSYNTHETIC METABOLISM

The main impact of algal investigations on a wider understanding of photosynthesis in O2 evolvers has come about through studies on microalgae. Experiments with flashing light led to the concepts of photo‐ synthetic units and reaction centers. Work on photon yields and the Emerson enhancement effect with fluorescence and spectroscopy, as well as investigations with mutants, were crucial in elaborating and then testing the validity of the Z scheme for light reactions. The carbon reduction (or Calvin) cycle was discovered using 14C, chromatography, and Chlorella (plus Scenedesmus). The availability of complete gene sequences for several cyanobacteria and the flowering plant Arabidopsis and very soon for the eukaryotic alga Chlamydomonas permit important advances in our understanding of photosynthesis in all these organisms. Eukaryotic microalgae and cyanobacteria remain advantageous in fundamental photosynthetic studies.

Lighting the path:a tribute to Robert Emerson (1903-1959)

Today, we shall re-live the discoveries of the basic concepts of the light reactions of oxygenic photosynthesis. The concept of the Photosynthetic Unit, and the quantum efficiency emerged as early topics of quantitative studies. Determination of the minimum number of quanta needed for the release of one O2 molecule had a long and bitter controversy. According to Otto Warburg (1883-1970), the minimum quantum requirement per O2 was between 2.8 and 4. The experiments of Robert Emerson (1901-1959), on the other hand, gave values of 8 to 12. The latter range was finally accepted. A number of important basic discoveries led to support the two-light reaction/two photosystem scheme of photosynthesis that we now use as the basis of design of further research. These discoveries will be considered, and include: the Emerson Enhancement Effect, the Hill Reaction, and the existence of different spectral forms of Chl a. Several kinds of experimental evidence reinforced the two-light/two-photosystem concept; the researches of Bessel Kok, Lou Duysens, Jan Amesz and Horst Witt were particularly significant. The theoretical ideas of Hans Gaffron, James Franck and Eugene Rabinowitch, the experiments of William Arnold, Larry Blinks, and C. Stacy French, and the challenges of Daniel Arnon added much spice to the evolution of our current understanding. It was, however, the biochemical insights of Robin Hill (1899-1991) that rationalized the diverse kinds of evidence that accounted for the experimental facts in terms of the two-light/two-photosystem mechanism, popularly known as the Z? scheme.

Iron stress restricts photosynthetic intersystem electron transport in Synechococcus sp. PCC 7942

Although exposure of Synechococcus sp. PCC 7942 to iron stress induced the accumulation of the isiA gene product (CP43′) compared with non-stressed controls, immunodetection of the N-terminus of cytochrome (Cyt) f indicated that iron stress not only reduced the content of the 40 kDa, heme-binding, Cyt f polypeptide by 32% but it also specifically induced the accumulation of a new, 23 kDa, non-heme-binding, putative Cyt f polypeptide. Concomitantly, iron stress restricted intersystem electron transport based on the in vivo reduction of P700 +, monitored as Δ A 820/ A 820 in the presence and absence of electron transport inhibitors, as well as the inhibition of the Emerson enhancement effect on O 2 evolution. However, iron stress appeared to be associated with enhanced rates of PS I cyclic electron transport, low rates of PS I-driven photoreduction of NADP + but comparable rates for PS II+PS I photoreduction of NADP + relative to controls. We hypothesize that Synechococcus sp. PCC 7942 exhibits a dynamic capacity to uncouple PS II and PS I electron transport, which may allow for the higher than expected growth rates observed during iron stress.

Emerson enhancement effect and quantum yield of photosynthesis for marine macroalgae in simulated underwater light fields

The contribution of enhancement to the total photosynthesis of marine macroalgae in their natural habitats was estimated by comparing the photosynthesis measured by O2-electrode in five broad-band light fields with that predicted (on the assumption that no enhancement was occurring) from the photosynthetic action spectrum of each plant and the spectral distribution of the light fields. The excess of measured values divided by calculated values provided a measure of enhancement. Although 37% enhancement was observed for red algae in unfiltered quartz-iodine light, and 18% for green and brown algae, substantially lower values were obtained for all species in more natural light fields. In those typical of shallow coastal waters, phycoerythrin-rich red algae exhibited 15 to 20% enhancement, but little enhancement (<5%) was detected in other algae. In a green light field, representing deep coastal water, there was no significant enhancement in any species, and only green and brown algae showed any enhancement (ca 8%) in broad-band blue light, similar to that in deep oceanic waters. Quantum yields of 0.09 to 0.10 O2 molecules per absorbed photon were recorded in most light fields for green and brown algae with thin thalli, but yields decreased in the blue light field and in species with thicker thalli. All red algae had quantum yields of about 0.08 O2 molecules per absorbed photon, except in the blue light field, in which quantum yields were reduced by 70%.

Far-Red Light-Induced Changes in Intracellular Potentials of Spinach Mesophyll Cells

In green plants, the large bioelectric changes that photosynthetically active light stimulates make it difficult to observe electrical potential changes related to phytochrome photoconversion. As a first step towards distinguishing between photosynthetic and phytochrome effects, we showed that red light enhances far-red stimulated intracellular potential changes in spinach (Spinacia oleracea) leaf mesophyll cells.For a dark-adapted leaf, the response to far-red light increased during the first 10 to 30 exposures of 2.5 minutes, after which it was constant. The intracellular potential depolarized by an average of 0.3 millivolts during each 2.5-minute far-red light period, and returned to the resting value during each subsequent dark period. Continuous supplementary red light (at 1-5% of the fluence rate of the far-red light that stimulated the depolarizations) increased the response to far-red 2- to 3-fold. Supplementary red light did not amplify the response to alternating 702 nanometers light and dark periods. The Emerson enhancement effect thus does not seem to explain amplification of the response to 730 nanometers light by supplementary red light. This does not prove that photosynthetic pigments are not involved in some other way.

The effect of adenosine-5'-triphosphate on oxygen evolution, fluorescence emission and the Emerson enhancement effect

The effect of adenosine-5'-triphosphate on oxygen evolution, fluorescence emission and the Emerson enhancement effect

The Effect of Photosynthetic Enhancement on Photorespiration in Sinapis alba

AbstractIn Sinapis alba, the Emerson enhancement effect, measured as CO2 uptake, was significantly lower in an O2‐free atmosphere than in normal air. Photorespiration, when measured as 14CO2 release after a period of 14C‐photosynthetic labeling in white or monochromatic light, was reduced during photosynthetic enhancement. The 14C‐glycolate pool and the 14C‐labeled amino acids associated with the glycolale pathway (glutamate, glycine and serine) decreased during photosynthetic enhancement when Pholosyslem I was ‘overexcited’. This demonstrates that photosynthesis and photorespiration are oxygen dependent and that photorespiration is wavelength dependent in Sinapis alba. The effect of oxygen on pholosynthetic enhancement and photorespiraion, as well as the effect of wavelength on these processes suggest that light is involved not only in the production of glycolate, but also in its further metabolism. It seems that Photosystem I is a key factor in the regulation of glycolate metabolism. Furthermore, the product from the consumption of glycolate in a reaction associated with Pholosystem 1 does not seem to be metabolized via the glycolate pathway.

Photosynthetic Enhancement Studied in Intact Spinach Chloroplasts

The Emerson enhancement effect was evaluated in the intact spinach (Spinacia oleracea var. Long Standing Bloomsdale) chloroplast by monitoring the uptake of (14)CO(2) during illumination by 640 nm and 720 nm lights. Low levels (about 10 mum) of fructose 1,6-diphosphate, ribose 5-phosphate, and glycerate 3-phosphate stimulated the rate of photosynthesis and abolished enhancement values observed in their absence. Concentrations of the two sugar phosphates at levels of 1 mm responded similarly. In contrast, 1 mm glycerate 3-phosphate inhibited the rate of photosynthesis and increased enhancement. The exchange of glycerate 3-phosphate for glyceraldehyde 3-phosphate was speculated to be a factor underlying the decrease in photosynthesis and the increase in enhancement. Glucose 6-phosphate, NADPH, and l-malate did not influence photosynthesis or enhancement.The uncoupler, p-trifluoromethoxyphenylhydrazone, decreased the rate of photosynthesis but did not change the enhancement values. ATP (0.2 to 1 mm) had an occasional stimulating effect on CO(2) fixation but no effect on enhancement. Magnesium ions inhibited photosynthesis and decreased the enhancement values. It was concluded that the enhancement phenomenon reflects events of the photosynthetic carbon reduction cycle as well as the photochemical act.

Pigment systems and electron transport in chloroplasts. II. Emerson enhancement in broken spinach chloroplasts

The Emerson enhancement effect using red illumination supplemented by far-red light is a characteristic phenomenon of photosynthetic oxygen evolution by plants and algae. It has been cited as an important evidence in support of the mechanism of photosynthetic electron transport involving two light reactions operating in series. The present study confirms the occurrence of enhancement in isolated, broken spinach chloroplasts for the photoreduction of NADP + by water: [H 2O → NADP +] reaction. Far-red light at 700 nm is supplemented optimally with wavelengths of 650 or 670 nm. Divalent cations such as magnesium or manganese are shown to be required for enhancement to occur. The optimum concentrations of added MgCl 2 or MnCl 2 are about 7.5 mM; at concentrations below 3 mM enhancement is not obtained. The critical dependence on divalent ion concentration is felt to be the reason why the enhancement phenomenon has not been observed in some previous studies using broken chloroplasts. A role for Mg 2+ is proposed in which it alters the structure of the active chloroplast membranes in a manner which controls the transfer of electronic excitation between the two photosynthetic pigment systems. These findings favor the series two-light reaction mechanism over the alternative parallel scheme.

Cyclic and Non-cyclic Photophosphorylation as Energy Sources for Active K Influx in Hydrodictyon africanum

Under anaerobic conditions in the light, active K influx in Hydrodictyon africanum is supported by cyclic photophosphorylation. The use of selective inhibitors shows that, in the presence of CO2, a considerable portion of the ATP used by the K pump is supplied by noncyclic photophosphorylation. The rest of the ATP in these conditions comes from cyclic photophosphorylation. This is true under light-limiting as well as light-saturated conditions. If non-cyclic photophosphorylation is inhibited (by removal of carbon dioxide, by the addition of cyanide which interferes with the carboxylation reaction, or by inhibition of photosystem two with DCMU or supplying only far-red light), the K influx at low light intensities is stimulated, and its characteristics become those of a process powered by cyclic photophosphorylation alone. These results are interpreted in terms of a competition for ATP between K influx and CO2 fixation. Implicit in this explanation is a requirement for a switch of excitation energy absorbed by photosystem one from cyclic photophosphorylation to non-cyclic photophosphorylation whenever conditions (presence of CO2and photosystem two activity) allow CO2 fixation to occur. Further evidence for such a switch of excitation energy absorbed by photosystem one was obtained in experiments in which red and far-red light were applied separately and together. It was found that CO2 fixation showed the Emerson enhancement effect, while K influx (in the presence of CO2) shows a ‘de-enhancement’. This suggests that far-red light alone powers cyclic photophosphorylation; if red light is also present, some of the far-red quanta are diverted to non-cyclic photophosphorylation. The nature of the interaction between cyclic and non-cyclic photophosphorylation is discussed in relation to these and other published results.

Photosynthesis: A Simple Demonstration of the Emerson Enhancement Effect

Photosynthesis is perhaps the single most important living process. However, the rapid advances within the last 25 years have resulted in a dearth of simple experiments that can demonstrate the basis of our present understanding. The experiment described here illustrates the operation of two separate light reactions in photosynthesis by showing the Emerson enhancement effect. The efficiency of photosynthesis has been found to vary as plants are illuminated with monochromatic light of different wavelengths. One common finding has been that the efficiency of photosynthesis decreases with the use of longer wavelengths of light. The decline in photosynthetic rate occurs in spite of strong light-absorption by chlorophyll. Robert Emerson (1957) and his colleagues discovered that the low rate of photosynthesis in long-wavelength light could be overcome, or even surpassed, by simultaneously illuminating the plants with a second beam of shorter-wavelength light. The rate of photosynthesis in the combined light beams was greater than could be expected by adding the rates found when either beam was provided alone. This relative excess of photosynthesis is known as the Emerson enhancement effect. One conclusion that Emerson reached on the basis of his discovery was that photosynthesis involves two photochemical processes. The exact, detailed explanations of how these two processes are achieved by the chlorophyll and accessory pigments have been modified considerably since Emerson published his work. Howevrer,

The Role of Cyclic and Pseudocyclic Photophosphorylation in Photosynthetic14CO2Fixation inHydrodictyon africanum

Experiments are reported in which the effects on photosynthesis of various inhibitors of cyclic photophosphorylation were investigated. These inhibitors, generally had only a small inhibitory effect on photosynthesis, and the inhibition was not increased by conditions which inhibit pseudocyclic photophosphorylation. These inhibitors do not inhibit the Emerson enhancement effect. From these results it was concluded that photosynthesis does not need any ATP other than that produced in non-cyclic photophosphorylation. The effects of these inhibitors on active K influx in light-anaerobic conditions in the presence or absence of C02 suggest that some of the ATP produced by non-cyclic photophosphorylation can be used to support active K influx. The results are discussed in relation to the mechanism of the Emerson effect, the stoichiometry of non-cyclic photophosphorylation, and the ATP requirements for autotrophic growth.

ACTION SPECTRA FOR PHOTOSYNTHESIS AND LIGHT‐STIMULATED ION TRANSPORT PROCESSES IN HYDRODICTYON AFRICANUM

SummaryThe action spectra in the wavelength range 436–759 nm of photosynthesis and light‐dependent ion transport processes in Hydrodictyon africanum were determined. The action spectra for active Cl influx and the associated components of K and Na influx, and the passive K efflux and the passive component of K influx, all had action spectra very similar to that of photosynthesis. These processes are stimulated by light absorbed by the photosynthetic system, and require photosystem 2. Active K influx and the coupled Na efflux, on the other hand, do not show such a pronounced drop in the action spectrum above 680 nm as does photosynthesis; below 680 nm the action spectrum is very similar to that of photosynthesis. This cation regulation mechanism thus only needs photosystem I. The results obtained above 680 nm confirm and extend those previously obtained with cut‐off filters (Raven, 1967b).The Emerson enhancement effect was exhibited by photosynthesis but not by Cl influx. The absence of enhancement of Cl influx could not be explained by a de‐enhancing action of photochrome at the wavelengths used. This absence of enhancement, if genuine, implies that only photosystem 2 is needed for light‐stimulation of Cl influx.No evidence was found for participation of the blue pigment or of phytochrome in any of the processes studied.

Transformation of Light Energy Chemical Energy: Photochemical Aspects of Photosynthesis 1

The physical and chemical events leading from the absorption of light by chlorophyll a in vivo to the production of the “reducing power” (reduced nicotinamide adenine dinucleotide phosphate) and the “high energy phosphate” (adenosine triphosphate) are reviewed here for the benefit of those students who have little understanding of the biophysical processes associated with photosynthesis and who are interested in appreciating the current status of the knowledge in this field. The capture of light energy, the fate of excitation, energy transfer, the trapping of energy, the Emerson enhancement effect, the two light reactions and the electron pathways in photosynthesis are discussed in this review; it cites detractors as well as supporters of the current dogma on photosynthesis.

Quantum Yield of Oxygen Evolution and the Emerson Enhancement Effect in Deuterated Chlorella

The maximum quantum yield of oxygen evolution in deuterated chlorella is found to be 0.075, while normal chlorella showed, in parallel experiments, a value of 0.10. Deuterated Chlorella vulgaris showed a decline in the quantum yield of oxygen evolution ("red drop") beginning at 680 millimicrons and a clear Emerson enhancement effect qualitatively similar to that obtained in normal chlorella cells. However, the ratio of quantumn yield at 680 to that at 710 millimicrons was about 1.5 times higher in normal than in deuterated chlorella cells. Action spectra of the Emerson enhancement effect in deuterated chlorella also are qualitatively similar to those of normal cells.