Relative Fluorescence Yield Research Articles

Zinc regulation of chlorophyll fluorescence and carbohydrate metabolism in saline-sodic stressed rice seedlings

Saline-sodic stress can limit the absorption of available zinc in rice, subsequently impacting the normal photosynthesis and carbohydrate metabolism of rice plants. To investigate the impact of exogenous zinc application on photosynthesis and carbohydrate metabolism in rice grown in saline-sodic soil, this study simulated saline-sodic stress conditions using two rice varieties, 'Changbai 9' and 'Tonghe 899', as experimental materials. Rice seedlings at 4 weeks of age underwent various treatments including control (CT), 2 μmol·L−1 zinc treatment alone (Z), 50 mmol·L−1 saline-sodic treatment (S), and 50 mmol·L−1 saline-sodic treatment with 2 μmol·L−1 zinc (Z + S). We utilized JIP-test to analyze the variations in excitation fluorescence and MR820 signal in rice leaves resulting from zinc supplementation under saline-sodic stress, and examined the impact of zinc supplementation on carbohydrate metabolism in both rice leaves and roots under saline-sodic stress. Research shows that zinc increased the chloroplast pigment content, specific energy flow, quantum yield, and performance of active PSII reaction centers (PIABS), as well as the oxidation (VOX) and reduction rate (Vred) of PSI in rice leaves under saline-sodic stress. Additionally, it decreased the relative variable fluorescence (WK and VJ) and quantum energy dissipation yield (φDO) of the rice. Meanwhile, zinc application can reduce the content of soluble sugars and starch in rice leaves and increasing the starch content in the roots. Therefore, the addition of zinc promotes electron and energy transfer in the rice photosystem under saline-sodic stress. It enhances rice carbohydrate metabolism, improving the rice plants’ ability to withstand saline-sodic stress and ultimately promoting rice growth and development.

An Improved Approach to Monitoring Wheat Stripe Rust with Sun-Induced Chlorophyll Fluorescence

Sun-induced chlorophyll fluorescence (SIF) has shown potential in quantifying plant responses to environmental changes by which abiotic drivers are dominated. However, SIF is a mixed signal influenced by factors such as leaf physiology, canopy structure, and sun-sensor geometry. Whether the physiological information contained in SIF can better quantify crop disease stresses dominated by biological drivers, and clearly explain the physiological variability of stressed crops, has not yet been sufficiently explored. On this basis, we took winter wheat naturally infected with stripe rust as the research object and conducted a study on the responses of physiological signals and reflectivity spectrum signals to crop disease stress dominated by biological drivers, based on in situ canopy-scale and leaf-scale data. Physiological signals include SIF, SIFyield (normalized by absorbed photosynthetically active radiation), fluorescence yield (ΦF) retrieved by NIRvP (non-physiological components of canopy SIF) and relative fluorescence yield (ΦF-r) retrieved by near-infrared radiance of vegetation (NIRvR). Reflectance spectrum signals include normalized difference vegetation index (NDVI) and near-infrared reflectance of vegetation (NIRv). At the canopy scale, six signals reached extremely significant correlations (P < 0.001) with disease severity levels (SL) under comprehensive experimental conditions (SL without dividing the experimental samples) and light disease conditions (SL < 20%). The strongest correlation between NDVI and SL (R = 0.69) was observed under the comprehensive experimental conditions, followed by NIRv (R = 0.56), ΦF-r (R = 0.53) and SIF (R = 0.51), and the response of ΦF (R = 0.45) and SIFyield (R = 0.34) to SL was weak. Under lightly diseased conditions, ΦF-r (R = 0.62) showed the strongest response to disease, followed by SIFyield (R = 0.60), SIF (R = 0.56) and NIRv (R = 0.54). The weakest correlation was observed between ΦF and SL (R = 0.51), which also showed a result approximating NDVI (R = 0.52). In the case of a high level of crop disease severity, NDVI showed advantages in disease monitoring. In the early stage of crop diseases, which we pay more attention to, compared with SIF and reflectivity spectrum signals, ΦF-r estimated by the newly proposed ‘NIRvR approach’ (which uses SIF together with NIRvR (i.e., SIF/ NIRvR) as a substitute for ΦF) showed superior ability to monitor crop physiological stress, and was more sensitive to plant physiological variation. At the leaf scale, the response of SIF to SL was stronger than that of NDVI. These results validate the potential of ΦF-r estimated by the NIRvR approach to monitoring disease stress dominated by biological drivers, thus providing a new research avenue for quantifying crop responses to disease stress.

Fluorescence Sensing of Nucleic Acid by Curcumin Encapsulated Poly(Ethylene Oxide)-Block-Poly(Propylene Oxide)-Block-Poly(Ethylene Oxide) Based Nanocapsules.

In a novel approach, curcumin has been encapsulated inside Poly(Ethylene Oxide)-Block-Poly(Propylene Oxide)-Block-Poly(Ethylene Oxide) (F108) nanocapsules. FTIR spectra have indicated a type of hydrogen bonding and dipole interaction between curcumin and F108. Fluorescence and UV-visible absorption profiles of curcumin in nanocapsules have indicated location of curcumin in more hydrophobic microenvironment. The relative fluorescence yield has increased by 6 times in the nanocapsules, which renders them as more sensitive probes to be used later on in sensing study. Therefore, based on the functionality of curcumin as a fluorescent transducer, encapsulated curcumin is used in biomedical application as DNA and RNA sensing. Detection limits are detected as 50μM and 60μM for DNA and RNA respectively. Linear dynamic concentration range obtained in this proposed method is much higher than reported in literature. The interaction between the nanocapsules and targeted DNA/RNA molecules is further approved by zeta potential studies. Furthermore, the real interaction of DNA with the encapsulated curcumin is confirmed by the interaction of the adenine and cytosine nucleotides. This has been verified through zeta potential measurements. Moreover, our prepared nanocapsules has presented a high percentage recovery of DNA and RNA (96-101%). Finally, stability results have illustrated a high photostability of encapsulated curcumin, indicating that proposed nanocapsules can be considered as a stable sensor during measurement time.

External quantum efficiency artifacts in partial‐irradiated GaInP/GaAs/Ge solar cells by protons and electrons

AbstractArtifact is a special kind of phenomenon related to fluorescence coupling and shunt resistance in external quantum efficiency (EQE) measurements in multijunction (MJ) solar cells, and it is sensitive to the defects and damages. In this paper, the changes of artifacts were studied in partial irradiated MJ solar cells by common or two‐dimension mapping Quantum Efficiency (QE) measurements. Simplified mathematical models and graphic analysis were applied to explain the mechanisms of changes of artifacts. Irradiation weakens the artifacts effects due to the decrease in relative fluorescence yield. Artifacts analysis results indicate that after 1 MeV electron irradiation, the open circuit voltage Voc of GaInP subcell decays from 1.40 V to 1.35 V, and the reverse saturation non‐radiative recombination current I02 increases 3.7 times. Correspondingly, after 70 keV protons irradiation, the open circuit voltage Voc decays to 0.90 V and I02 increases 7550 times by EQE artifacts analysis. Lateral scanning of the partial damaged samples shows a smooth artifacts transition region that appears near the boundary of damaged region in MJ solar cells. This is found correlated with the difference in the lighted areas of bias light and EQE pulse spot. 2D artifacts analysis could properly explain the smoothness and shift of damage interface.

A return to the genetic heritage of durum wheat to cope with drought heightened by climate change.

The objective of this work was to perform a comparative analysis of the physiological, biochemical and agronomical parameters of recent and heritage durum wheat cultivars (Triticum durum Desf.) under water-deficit conditions. Five cultivars were grown under irrigated (control) and rainfall (stressed) conditions. Different agro-physiological and biochemical parameters were studied: electrolyte leakage, relative water content, chlorophyll fluorescence, proline, soluble sugars, specific peroxidase activity, yield and drought stress indices. It was revealed that a water deficit increased proline content, electrolyte leakage, soluble sugars and specific peroxidase activity and decreased relative water content, fluorescence and grain yield. According to these parameters and drought stress indices, our investigation indicated that old cultivars are the best-adapted to local conditions and showed characteristics of drought tolerance, while recent cultivars showed more drought susceptibility. Therefore, local cultivars of each country should be kept by farmers and plant breeders to preserve their genetic heritage.

Gross Primary Production of a Wheat Canopy Relates Stronger to Far Red Than to Red Solar-Induced Chlorophyll Fluorescence

Sun-induced chlorophyll fluorescence (SIF) is a radiation flux emitted by chlorophyll molecules in the red (RSIF) and far red region (FRSIF), and is considered as a potential indicator of the functional state of photosynthesis in remote sensing applications. Recently, ground studies and space observations have demonstrated a strong empirical linear relationship between FRSIF and carbon uptake through photosynthesis (GPP, gross primary production). In this study, we investigated the potential of RSIF and FRSIF to represent the functional status of photosynthesis at canopy level on a wheat crop. RSIF and FRSIF were continuously measured in the O2-B (SIF687) and O2-A bands (SIF760) at a high frequency rate from a nadir view at a height of 21 m, simultaneously with carbon uptake using eddy covariance (EC) techniques. The relative fluorescence yield (Fyield) and the photochemical yield were acquired at leaf level using active fluorescence measurements. SIF was normalized with photosynthetically active radiation (PAR) to derive apparent spectral fluorescence yields (ASFY687, ASFY760). At the diurnal scale, we found limited variations of ASFY687 and ASFY760 during sunny days. We also did not find any link between Fyield and light use efficiency (LUE) derived from EC, which would prevent SIF from indicating LUE changes. The coefficient of determination ( r 2 ) of the linear regression between SIF and GPP is found to be highly variable, depending on the emission wavelength, the time scale of observation, sky conditions, and the phenological stage. Despite its photosystem II (PSII) origin, SIF687 correlates less than SIF760 with GPP in any cases. The strongest SIF–GPP relationship was found for SIF760 during canopy growth. When canopy is in a steady state, SIF687 and SIF760 are almost as effective as PAR in predicting GPP. Our results imply some constraints in the use of simple linear relationships to infer GPP from SIF, as they are expected to be better predictive with far red SIF for canopies with a high dynamic range of green biomass and a low LUE variation range.

Beyond just being foot soldiers – osmotin like protein (OLP) and chitinase (Chi11) genes act as sentinels to confront salt, drought, and fungal stress tolerance in tomato

Osmotin like protein (OLP) and chitinase (Chi11) belong to pathogenesis-related (PR) class of proteins and are induced during both biotic and abiotic stresses. Transgenic tomato was developed with OLP and Chi11 via in vitro and in planta transformation methods. Transgenes integration and transcript levels were confirmed by multiplex PCR, DNA blot, and multiplex reverse transcriptase PCR. Homozygous T2 transgenics when evaluated for salt, drought, and fungal stresses showed enhanced tolerance compared to untransformed controls (UC). Transgenics showed enhanced endochitinase activity and root biomass under normal conditions. Transformants also displayed higher proline content, K+, relative water content, chlorophyll fluorescence, total biomass, vascular conductivity, and fruit yield than the UC under stress conditions. Co-immunoprecipitation revealed that Chi11 co-expresses with phosphofructokinase2 (PFK2), which may play a role in enhanced root biomass. qPCR analysis resulted in higher transcript levels of OLP, Chi11, and PFK2 in transgenics as compared to the untransformed controls. Our findings suggest the use of multiples genes to confer multiple stress tolerance for enhanced crop productivity. This work unveils a new molecular player PFK2, which may play a role in enhanced root biomass.

Aerial extent, composition, bio-optics and biogeochemistry of a massive under-ice algal bloom in the Arctic

It has been long thought that coccolithophores are a minor component of the phytoplankton assemblage in Arctic waters, with diatoms typically being more dominant. Little is known about how the phytoplankton communities will change, however, as the Arctic warms. We participated in the 2011 Impacts of Climate on EcoSystems and Chemistry of the Arctic Pacific Environment (ICESCAPE) cruise to the western Arctic, performing a combination of discrete measurements (microscopy, calcification, particulate inorganic carbon (PIC), particulate organic carbon (POC), biogenic silica (BSi)) plus continuous surface bio-optical measurements (absorption, scattering, backscattering and acid-labile backscattering; the latter specific for coccolithophores). Here, we report bio-optical and coccolithophore observations from the massive under-ice algal bloom originally described in Arrigo et al. (2012). The most intense portions of the bloom were centered in cold Winter Water and there was evidence for nitrate drawdown in the top 10–20m with strong penetration of silicate rich water into the surface waters. Surface chlorophyll a and particulate absorption at 440nm approached 30μgL−1 and 1.0m−1, respectively. Particulate absorption of detritus (ap at 412nm) was highly correlated to ap at 440nm associated with chlorophyll a and slopes of the absorption spectrum showed that both dissolved and particulate absorption at 412nm exceeded that at 440nm, with slopes, Sg, of 0.01 nm–1. Colored dissolved organic matter fluorescence (FDOM) was high in the bloom but the relative fluorescence yields were low, characteristic of phytoplankton-produced FDOM (as opposed to terrestrially-produced FDOM). Coccolithophore backscattering was elevated in the under-ice bloom, but it only accounted for 10% of the total particle backscattering, relatively low compared to typical subpolar waters further to the south. Total particle scattering was significantly elevated in the under-ice bloom (values of almost 2m−1), likely due to the high abundance of large diatoms. Backscattering probabilities in the bloom were ~1%, again characteristic of diatom-dominated populations with few calcifiers. PIC standing stock in the under-ice bloom was low but measurable while biogenic silica molar concentrations were 150 times greater. POC:PON molar ratios were 6–10, characteristic of healthy, rapidly growing phytoplankton, observations further buttressed by carbon:chlorophyll mass ratios of 50–100. Coccolithophore calcification was low but measurable, reaching 1.75mgCm−3d−1 in the under-ice bloom, only 0.4% of the photosynthesis. However, the intrinsic carbon-specific growth rate was 0.4 per day for bulk POC and ~1 per day for bulk PIC, close to maximal growth rates expected at these temperatures. SEM and light microscopy results showed mostly diatoms in the bloom. The coccolithophore, Emiliania huxleyi, was observed, providing unequivocal evidence of the presence of coccolithophores in the under-ice algal bloom.

Regulation of guard cell photosynthetic electron transport by nitric oxide

Nitric oxide (NO) is one of the key elements in the complex signalling pathway leading to stomatal closure by inducing reversible protein phosphorylation and Ca(2+) release from intracellular stores. As photosynthesis in guard cells also contributes to stomatal function, the aim of this study was to explore the potential role of NO as a photosynthetic regulator. This work provides the first description of the reversible inhibition of the effect of NO on guard cell photosynthetic electron transport. Pulse amplitude modulation (PAM) chlorophyll fluorescence measurements on individual stomata of peeled abaxial epidermal strips indicated that exogenously applied 450nM NO rapidly increases the relative fluorescence yield, followed by a slow and constant decline. It was found that NO instantly decreases photochemical fluorescence quenching coefficients (qP and qL), the operating quantum efficiency of photosystem II (ΦPSII), and non-photochemical quenching (NPQ) to close to zero with different kinetics. NO caused a decrease in NPQ, which is followed by a slow and continuous rise. The removal of NO from the medium surrounding the epidermal strips using a rapid liquid perfusion system showed that the effect of NO on qP and ΦPSII, and thus on the linear electron transport rate through PSII (ETR), is reversible, and the constant rise in NPQ disappears, resulting in a near steady-state value. The reversible inhibition by NO of the ETR could be restored by bicarbonate, a compound known to compete with NO for one of the two coordination sites of the non-haem iron (II) in the QAFe(2+)QB complex.

Influence of rootstock on drought response in young ‘Gale Gala’ apple (Malus domestica Borkh.) trees

Drought is a major environmental stress limiting plant growth, productivity, and survival worldwide. Rootstocks are widely used to enhance plants resistance to drought stresses. This study determined influence of rootstock on drought responses in 1-year-old 'Gale Gala' apple trees grafted onto Malus sieversii or M. hupehensis. Choice of rootstock resulted in differential response to drought stress. Specifically, M. sieversii caused less drought-induced reduction in relative growth rate, biomass accumulation, leaf area, leaf chlorophyll content, relative water content, photosynthesis rate and maximum chlorophyll fluorescence yield but greater increase in whole-plant water use efficiency compared to M. hupehensis. Secondly, compared with M. hupehensis, M. sieversii caused less drought-induced accumulation of reactive oxygen species but more increase in activities of antioxidant enzymes. In addition, xylem sap abscisic acid concentration was greater in trees grafted onto M. hupehensis than in those grafted onto M. sieversii under drought stress. 'Gale Gala' trees' response to drought stress was associated with the rootstock's genotype onto which it was grafted. Trees with M. sieversii as rootstock are more drought resistant than trees with M. hupehensis as rootstock, which suggests that M. sieversii can be widely used as rootstock in arid and semi-arid regions.

Correlation of vibrational intensity with fluorescence lifetimes in π conjugated polymers

A series of novel pi (π) conjugated polymers, originating from the archetypical Polyphenylene vinylene, in which the phenyl units are successively replaced by the larger naphthyl and anthryl acene units, were previously found to have a well-defined relationship between their relative fluorescence yields and their vibrational characteristics, as determined by Raman spectroscopy. In this study the Strickler–Berg equation is used to probe the influence of continual substitution of higher order acene units into the conjugated backbone in terms of the variation of the radiative and non-radiative rates. The deconvolution of the radiative and non-radiative rates enables the correlation of the reduction of the Raman intensity and concomitant increase in the fluorescence yield with the reduction of the non-radiative rate. This confirms that the reduction of the non-radiative rate is the dominant process introduced by the vibrational confinement originating from systematic substitution of higher order acene units into the polymer backbone.

Photophysics of Aromatic Molecules with Low-Lying πσ* States: Excitation-Energy Dependence of Fluorescence in Jet-Cooled Aromatic Nitriles

Excitation-energy dependence of fluorescence intensity and fluorescence lifetime has been measured for 4-dimethylaminobenzonitrile (DMABN), 4-aminobenzonitrile (ABN), 4-diisopropylaminobenzonitrile (DIABN), and 1-naphthonitrile (NN) in a supersonic free jet. In all cases, the fluorescence yield decreases rather dramatically, whereas the fluorescence lifetime decreases only moderately for S1 (pi pi*, L(b)) excess vibrational energy exceeding about 1000 cm(-1). This is confirmed by comparison of the normalized fluorescence excitation spectrum with the absorption spectrum of the compound in the vapor phase. The result indicates that the strong decrease in the relative fluorescence yield at higher energies is due mostly to a decrease in the radiative decay rate of the emitting state. Comparison of the experimental results with the TDDFT potential energy curves for excited states strongly suggests that the decrease in the radiative decay rate of the aminobenzonitriles at higher energies is due to the crossing of the pi pi* singlet state by the lower-lying pi sigma*(C[triple bond]N) singlet state of very small radiative decay rate. The threshold energy for the fluorescence "break-off" is in good agreement with the computed energy barrier for the pi pi*/pi sigma* crossing. For NN, on the other hand, the observed decrease is in fluorescence yield at higher excitation energies can best be attributed to the crossing of the pi pi* singlet state by the pi sigma* triplet state.

P700 +- and 3P700-induced quenching of the fluorescence at 760 nm in trimeric Photosystem I complexes from the cyanobacterium Arthrospira platensis

The 5 K absorption spectrum of Photosystem I (PS I) trimers from Arthrospira platensis (old name: Spirulina platensis) exhibits long-wavelength antenna (exciton) states absorbing at 707 nm (called C707) and at 740 nm (called C740). The lowest energy state (C740) fluoresces around 760 nm (F760) at low temperature. The analysis of the spectral properties (peak position and line width) of the lowest energy transition (C740) as a function of temperature within the linear electron–phonon approximation indicates a large optical reorganization energy of ∼110 cm −1 and a broad inhomogeneous site distribution characterized by a line width of ∼115 cm −1. Linear dichroism (LD) measurements indicate that the transition dipole moment of the red-most state is virtually parallel to the membrane plane. The relative fluorescence yield at 760 nm of PS I with P700 oxidized increases only slightly when the temperature is lowered to 77 K, whereas in the presence of reduced P700 the fluorescence yield increases nearly 40-fold at 77 K as compared to that at room temperature (RT). A fluorescence induction effect could not be resolved at RT. At 77 K the fluorescence yield of PS I trimers frozen in the dark in the presence of sodium ascorbate decreases during illumination by about a factor of 5 due to the irreversible formation of P700 +F A/B − in about 60% of the centers and the reversible accumulation of the longer-lived state P700 +F X −. The quenching efficiency of different functionally relevant intermediate states of the photochemistry in PS I has been studied. The redox state of the acceptors beyond A 0 does not affect F760. Direct kinetic evidence is presented that the fluorescence at 760 nm is strongly quenched not only by P700 + but also by 3P700. Similar kinetics were observed for flash-induced absorbance changes attributed to the decay of 3P700 or P700 +, respectively, and flash-induced fluorescence changes at 760 nm measured under identical conditions. A nonlinear relationship between the variable fluorescence around 760 nm and the [P700 red]/[P700 total] ratio was derived from titration curves of the absorbance change at 826 nm and the variable fluorescence at 760 nm as a function of the redox potential imposed on the sample solution at room temperature before freezing. The result indicates that the energy exchange between the antennae of different monomers within a PS I trimer stimulates quenching of F760 by P700 +.

Singlet exciton interactions in solid films of Alq 3

The relative fluorescence yield of vacuum-evaporated films of tris-(8-hydroxyquinolinato) aluminum (III) (Alq 3) as a function of steady-state exciting light intensity has been measured. The yield decreases, due to singlet exciton–exciton interaction, with increasing intensities, to a half of the low-intensity yield at 5 × 10 21 ph/cm 2/s. The second order singlet–singlet annihilation rate constant is found to be γ SS = (1.1 ± 0.5) × 10 −10 cm 3/s. If the reaction is diffusion-limited, this rate implies an average singlet exciton diffusivity D S = (6 ± 2) × 10 −5 cm 2/s, and permits to rule out singlet–singlet interaction as the reason for the observed large-current density roll-off in the electroluminescence efficiency of Alq 3-based light emitting diodes.

Early reactions of light-induced protochlorophyllide and chlorophyllide transformations analyzed in vivo at room temperature with a diode array spectrofluorometer

The steps of protochlorophyllide (Pchlide) photoreduction and subsequent chlorophyllide (Chlide) transformations which occur in the seconds to minutes time-scale were studied using a diode array spectrofluorometer in dark-grown barley leaves. The intensity of the excitation light was varied between 3 and 2500 μmol m −2 s −1 and a series of fluorescence spectra were recorded at room temperature in the seconds and minutes time scales. In certain experiments, 77-K emission spectra were measured with the same equipment. The high quality of the spectra allowed us to run spectral resolution studies which proved the occurrence, at room temperature, of multiple Pchlide and Chlide forms found previously in 77-K spectra. The comparison of the 77-K and room-temperature spectra showed that the fluorescence yields of the nonphotoactive 633-nm Pchlide form and of the Chlide product emitting at 678 nm were temperature independent. The fluorescence intensity of aggregated NADPH–pigment–POR complexes (photoactive 656-nm Pchlide and 693-nm Chlide forms) were strongly increased at 77 K, while that of the NADP +–Chlide–POR (684–686-nm Chlide form) was much less affected by temperature. Information was obtained also about the dynamics of the transformation of pigment forms in the light at different photon densities. At low light intensities, the phototransformation of the 642–644-nm Pchlide form was faster than that of the 654–656-nm form. The relative amplitudes of Gaussian components related to different Chlide forms found after exposure to a constant amount of photons strongly depended on the light intensity used. Strong quenching of all Chlide components occurred upon prolonged exposure to high intensity light. These effects are discussed by considering the interconversion processes between different forms of the pigment–protein complexes, their relative fluorescence yields and energy migration processes.

Fluorescence of Cascade Blue™ inside nano-sized porous shells of silicate

Cascade Blue™ (CB) dye at a concentration as high as 0.227 M was encapsulated within nano-sized porous silicate shells, and its relative fluorescence yield determined over the pH range of 1.8–12.3, using 380 nm as the excitation wavelength. The results were compared with those obtained in aqueous solution using similar pH and total dye concentration. Near neutral pH, the relative fluorescence yields of CB inside the shells exhibited little fluorescence quenching, even though a high concentration of the dye was trapped inside the particles, while the peak wavelength of fluorescence was shifted from 420 nm in solution to 430 nm in shells. Both in shells and solution, the relative fluorescence intensity decreased as the solution pH was raised from 2 to 4, and in shells it nearly disappeared at about pH 3–4. As the pH was further increased, the red shift of fluorescence peak in the shell-trapped dyes was evident at pH 5 and its fluorescence intensity regained equal to that in acid. In the neutral pH range, the fluorescence intensity of CB in the shells was similar to that of the equivalent total concentration of the CB in solution. In solution, a similar red shift of the fluorescence maximum of CB to 430 nm was observed only above pH 9. These observations suggest that the fluorescence intensities of dyes trapped inside nano-sized porous silicate shells can be equal to or higher than that observed in solution under comparable conditions, leading to several hundreds times more fluorescent intensity when it is measured per single shell rather than per unit fluorophore.

Real-Time Measurement of Combustion Generated Particles with Photofragmentation-Fluorescence

Excimer laser fragmentation-fluorescence spectroscopy (ELFFS) is a viable technique for real-time monitoring of carbonaceous particles in combustion exhausts. The exhaust from a single-cylinder two-stroke engine is diluted and diverted into the laser interrogation region, resulting in a particle concentration of approximately 1 × 107/cm3. Light from a 193 nm ArF laser photofragments the particles and then produces fluorescence from the atomic carbon fragments at 248 nm, CH fragments at 431 nm, and C2 fragments at 468 nm. The atomic carbon fluorescence signal is proportional to the number concentration of particles in the laser interrogation region. The 100-shot (1 s) detection limit for particles in the exhaust is 1 mg/m3, expressed as a mass concentration of particulate matter. Interferences from carbon monoxide and carbon dioxide are negligible. The relative fluorescence yield at 248 nm is four times greater from particles than from the gas phase hydrocarbons present in the exhaust. This high yield suggests that the gas phase hydrocarbon interference would not be problematic for measurements of diesel exhaust, where the ratio of particulate carbon to gas phase hydrocarbon is high.

Regulation Mechanism of Excitation Energy Transfer in Phycobilisome-Thylakoid Membrane Complexes

Regulation mechanism of excitation energy transfer between phycobilisomes (PBS) and the photosynthetic reaction centres was studied by the state transition techniques in PBS-thylakoid membrane complexes. DCMU, betaine, and N-ethylmaleimide were applied to search for the details of energy transfer properties based on the steady fluorescence measurement and individual deconvolution spectra at state 2 or state 1. The closure of photosystem (PS) 2 did not influence on fluorescence yields of PS1, i.e., energy could not spill to PS1 from PS2. When the energy transfer pathway from PBS to PS1 was disturbed, the relative fluorescence yield of PS2 was almost the same as that of PS2 in complexes without treatment. If PBSs were fixed by betaine, the state transition process was restrained. Hence PBS may detach from PS2 and become associated to PS1 at state 2. Our results contradict the proposed "spill-over" or "PBS detachment" models and support the mobile "PBS model".

UV absorption by mycosporine-like amino acids in Phaeocystis antarctica Karsten induced by photosynthetically available radiation

Mycosporine-like amino acids (MAAs), which occur in diverse taxonomic groups, exhibit in vivo absorption maxima between 310 nm and 360 nm and may play a photoprotective role against ultraviolet (UV) exposure. Using cultures of colonial Phaeocystis antarctica, we examined the relationship between MAA concentration, in vivo UV absorption, photoprotective (carotenoid) and photosynthetic pigments, and photosynthetically available radiation (PAR, 350–700 nm). UV absorption was high; chlorophyll-specific absorption, a * ph, at 330 nm ranged from 0.06 to 0.41 m2/mg chlorophyll a. Values of a * ph (330) were 4–13 times greater than a * ph (676). Mycosporine-glycine, shinorine, and mycosporine-glycine valine are responsible for the strong in vivo UV absorption. The sum of all MAAs increased with irradiance when normalized to chlorophyll a or carbon concentrations, whereas individual MAAs varied independently from each other. Mycosporine-glycine concentrations showed no statistically significant change over the range of light intensities, whereas mycosporine-glycine and shinorine concentrations increased at higher irradiances. The relative fluorescence yield for chlorophyll a was low in the UV region compared to the visible region, implying that absorbed UV radiation (<375 nm) is transferred inefficiently to chlorophyll a in the reaction center. Quantitative estimates of UV screening by MAAs are attributed to elevated MAA concentrations and increased diameter at high light.

Time-resolved monitoring of flash-induced changes of fluorescence quantum yield and decay of delayed light emission in oxygen-evolving photosynthetic organisms.

The present contribution describes a new experimental setup that permits time-resolved monitoring of the rise kinetics of the relative fluorescence yield, Phi(rel)(t), and simultaneously of the decay of delayed light emission, L(t), induced by strong actinic laser flashes. The results obtained by excitation of dark-adapted samples with a train of eight flashes reveal (a) in suspensions of spinach thylakoids, Phi(rel)(t) exhibits a typical period four oscillation that is characteristic for a dependence on the redox states S(i)() of the water oxidizing complex (WOC), (b) the relative extent of the unresolved "instantaneous" rise to the level (100 ns) at 100 ns and the maximum values of Phi(rel)(t) attained at about 45 s after each actinic flash, (45 s) synchronously oscillate and exhibit the largest values at flash nos. 1 and 5 and minima after flash nos. 2 and 3, (c) opposite effects are observed for the normalized extent of the rise kinetics in the 100 ns to 5 s time domain of relative fluorescence yield, Phi(rel)(5 s) - Phi(rel)(100 ns), i.e., both parameters attain minimum and maximum values after the first/fifth and second/third flash, respectively, and (d) analogous features for the "fast" and "slow" ns-kinetics of the fluorescence rise were observed in suspensions of Chlamydomas reinhardtii cells. A slight phase shift by one flash is ascribed to physiological differences. The applicability of this noninvasive technique to study reactions of photosystem II, especially the reduction kinetics of P680(*)(+) and their dependence on the redox state S(i)() of the WOC, is discussed.