The characterization of plant species using first‐derivative fluorescence spectra

Plants are one of the most important parts of the ecological system and demand a reliable method for accurate classification. In this study, the first‐derivative fluorescence spectral curves (FDFSCs) based on laser‐induced fluorescence technology were proposed for the characterization of plant species. The measurement system is mainly composed of a spectrometer, an excitation light source (the two excitation wavelengths are 460 and 556 nm, respectively), and an intensified charge‐coupled device camera. FDFSCs were calculated from the deviation between the fluorescence values at each wavelength, plus and minus one band, divided by the wavelength range. Principal component analysis was utilized to analyze the FDFSCs by extracting the main attributes and reducing the dimensionality of variables. A support vector machine was used to evaluate FDFSC performance for the identification of plant species. Plant species that are difficult to distinguished by the naked eye, can be identified effectively using the proposed FDFSCs. For the 556 nm and 460 nm excitation wavelengths, the overall identification rates of the six plant species evaluated were 93.3% and 91.7%, respectively. Experimental results demonstrated that the combination of the FDFSCs with multivariate analysis could provide a simple and reliable method for the characterization of plant species.     

Sun‐induced fluorescence – a new probe of photosynthesis: First maps from the imaging spectrometer HyPlant

Variations in photosynthesis still cause substantial uncertainties in predicting photosynthetic CO₂ uptake rates and monitoring plant stress. Changes in actual photosynthesis that are not related to greenness of vegetation are difficult to measure by reflectance based optical remote sensing techniques. Several activities are underway to evaluate the sun‐induced fluorescence signal on the ground and on a coarse spatial scale using space‐borne imaging spectrometers. Intermediate‐scale observations using airborne‐based imaging spectroscopy, which are critical to bridge the existing gap between small‐scale field studies and global observations, are still insufficient. Here we present the first validated maps of sun‐induced fluorescence in that critical, intermediate spatial resolution, employing the novel airborne imaging spectrometer HyPlant. HyPlant has an unprecedented spectral resolution, which allows for the first time quantifying sun‐induced fluorescence fluxes in physical units according to the Fraunhofer Line Depth Principle that exploits solar and atmospheric absorption bands. Maps of sun‐induced fluorescence show a large spatial variability between different vegetation types, which complement classical remote sensing approaches. Different crop types largely differ in emitting fluorescence that additionally changes within the seasonal cycle and thus may be related to the seasonal activation and deactivation of the photosynthetic machinery. We argue that sun‐induced fluorescence emission is related to two processes: (i) the total absorbed radiation by photosynthetically active chlorophyll; and (ii) the functional status of actual photosynthesis and vegetation stress.     

Synthesis and photoluminescence study of di‐dendron dendrimers derived from mono‐Boc‐protected ethylenediamine cores

This work is focused on the synthesis and optical properties of cone‐shaped structural feature di‐dendron polyamidoamine dendrimers up to the third generation with mono‐Boc‐protected ethylenediamine (EDA) as a core. Strong UV absorbance spectra and fluorescence spectra from di‐dendron dendrimers with different terminal groups (‐NH₂, ‐COOCH₃) were studied under different conditions by varying experimental parameters such as concentration and pH. The optical density and fluorescence intensities increased when di‐dendron dendrimers generation number increased from 0.5 to 3.0. It was confirmed that the concentration of di‐dendron dendrimers plays an important role in fluorescence intensity. The increase in fluorescence intensity was linear in low concentration regions, but the intensity increased slowly in high concentration regions. The results also showed a rapid increase in fluorescence intensity at low pH. The formation of a fluorescence‐emitting moiety had a close relationship to protonated tertiary amine groups in di‐dendron dendrimers derived from mono‐Boc‐protected EDA cores. Furthermore, the formation of fluorescent chemical species was irreversible. Copyright © 2010 John Wiley & Sons, Ltd.     

Studies of the effect of halide ions on the fluorescence of quinine sulfate

The effect of halide ions (Cl^?, Br^? and I^?) on the fluorescence of quinine sulfate in dilute sulfuric acid solution was studied by fluorescence spectra, ultraviolet‐visible (UV‐visible) absorption spectra and fluorescence decay technique. The results exhibited that halide ions with heavier atomic mass could significantly reduce the fluorescence intensity of quinine sulfate, as a result, the order of fluorescence quenching caused by halide ions is Cl^? < Br^? < I^?. Therefore, halide ions with high concentration could seriously quench the fluorescence of quinine sulfate. The UV‐visible absorption spectra and fluorescence decay technique revealed that the fluorescence quenching of quinine sulfate caused by halide ions was attributed to dynamic quenching, static quenching process, self‐quenching fluorescence effect and electronic transfer.     

Effects of fire intensity on plant species composition of sandstone communities in the Sydney region

Abstract Fire intensity measures the heat output of a fire, and variation in fire intensity has been shown to have many effects on the demography of plant species, although the consequent effects on the floristic composition of communities have rarely been quantified. The effects of variation in fire intensity on the floristic composition of dry sclerophyll vegetation with different fire histories near Sydney was estimated. In particular, differences in species abundance of woodland and shrubland communities subjected to four fire‐intensity classes: unburnt, low intensity (<500 kW m^?1), medium intensity (500–2500 kW m^?1) and high intensity (>2500 kW m^?1) were examined. The samples had a standardized previous fire frequency and season, thus minimizing the effects of other aspects of the fire regime. There was a clear effect of fire intensity on the relative abundances of the vascular plant species, with increasing intensity of the fire producing vegetation that was increasingly different from the unburnt vegetation. This pattern was repeated in both the woodland and shrubland vegetation types, suggesting that it was not an artefact of the experimental conditions. However, the effects of fire intensity on floristic composition were no greater than were the differences between these two similar vegetation types, with variation in fire intensity accounting for only approximately 10% of the floristic variation. Nevertheless, the effects of fire intensity on the abundance of individual species were consistent across taxonomic groups, with the monocotyledon and Fabaceae species being more abundant at higher than lower intensities, the Proteaceae and Rutaceae more abundant at intermediate intensities, and the Epacridaceae more abundant at lower rather than higher intensities. The number of fire‐tolerant species increased with increasing fire intensity, and those fire‐tolerant species present were most abundant in the areas burnt with medium intensity. The number of fire‐sensitive species did not respond to fire intensity, and those species present were most abundant in the areas burnt with low intensity. This suggests that either fire‐sensitive species respond poorly to higher fire intensities or fire‐tolerant species respond poorly to lower fire intensities, perhaps because of differences in seed germination, seedling survival or competition among adults.     

A novel amphiphilic thiosemicarbazone derivative for binding and selective sensing of human serum albumin

The interaction of ligands and drug molecules with protein is of major interest in drug pharmacokinetics and pharmacodynamics. In this study, we synthesized a novel thiosemicarbazone‐based amphiphilic molecule for selective binding and detection of human serum albumin (HSA) with significant increase in fluorescence intensity. The compound 5‐(octyloxy) naphthalene substituted salicylaldehyde thiosemicarbazone was designed to interact with site I of HSA. The weak fluorescence of the probes in aqueous solution showed a dramatic increase in fluorescence intensity upon binding with HSA, while the responses to various other proteins and enzymes were negligible under similar experimental conditions. Changes in fluorescence intensity and formation of a new emission maximum of the compound in the presence of HSA as well as an increase in steady‐state anisotropy values reflected well the nature of binding and location of the probe inside the protein environment. Copyright © 2012 John Wiley & Sons, Ltd.     

Global transition of human serum albumin to prefibrillar aggregates induced by temsirolimus: Insight into implications of anti‐renal cancer drug

In our study, we have characterized the prefibrillar aggregates of human serum albumin (HSA) induced by temsirolimus, anti‐renal cancer drug. Molecular docking was retorted to confirm binding of HSA and temsirolimus. Temsirolimus caused the structural transition of native HSA to non‐native species after prolonged incubation of 20 days. These non‐native species were characterized as prefibrillar aggregates as evident by decreased intrinsic fluorescence and enhanced 8‐anilino‐1‐naphthalene‐sulphonic acid (ANS) fluorescence. Further, enhanced thioflavin T fluorescence and shift in congo red (CR) spectra of temsirolimus‐incubated HSA as compared to native HSA are suggestive of global transition of HSA in presence of temsirolimus towards prefibrillar aggregates. Circular dichroism spectroscopy revealed α to β transition upon prolonged incubation with temsirolimus suggesting the formation of prefibrillar aggregates as aggregates are known to possess high β content. Scanning electron microscopy confirmed these non‐native species to be prefibrillar aggregates evident by observed sheath‐like structures. Comet assay was retorted to confirm genotoxic nature of these prefibrillar aggregates; DNA damage was observed for temsirolimus‐incubated HSA confirming the genotoxic nature of prefibrillar aggregates. These prefibrillar aggregates are observed at heart of many pathological conditions, thus making our study clinically significant.     

Remote sensing of sun-induced fluorescence to improve modeling of diurnal courses of gross primary production (GPP)

Terrestrial gross primary production (GPP) is an important parameter to explore and quantify carbon fixation by plant ecosystems at various scales. Remote sensing (RS) offers a unique possibility to investigate GPP in a spatially explicit fashion; however, budgeting of terrestrial carbon cycles based on this approach still remains uncertain. To improve calculations, spatio-temporal variability of GPP must be investigated in more detail on local and regional scales. The overarching goal of this study is to enhance our knowledge on how environmentally induced changes of photosynthetic light-use efficiency (LUE) are linked with optical RS parameters. Diurnal courses of sun-induced fluorescence yield ( F _Syield) and the photochemical reflectance index of corn were derived from high-resolution spectrometric measurements and their potential as proxies for LUE was investigated. GPP was modeled using Monteith's LUE-concept and optical-based GPP and LUE values were compared with synoptically acquired eddy covariance data. It is shown that the diurnal response of complex physiological regulation of photosynthesis can be tracked reliably with the sun-induced fluorescence. Considering structural and physiological effects, this research shows for the first time that including sun-induced fluorescence into modeling approaches improves their results in predicting diurnal courses of GPP. Our results support the hypothesis that air- or spaceborne quantification of sun-induced fluorescence yield may become a powerful tool to better understand spatio-temporal variations of fluorescence yield, photosynthetic efficiency and plant stress on a global scale.     

Lipid‐polymorphism of plant thylakoid membranes. Enhanced non‐bilayer lipid phases associated with increased membrane permeability

Earlier experiments, using ³¹P‐NMR and time‐resolved merocyanine fluorescence spectroscopy, have shown that isolated intact, fully functional plant thylakoid membranes, in addition to the bilayer phase, contain three non‐bilayer (or non‐lamellar) lipid phases. It has also been shown that the lipid polymorphism of thylakoid membranes can be characterized by remarkable plasticity, i.e. by significant variations in ³¹P‐NMR signatures. However, changes in the lipid‐phase behaviour of thylakoids could not be assigned to changes in the overall membrane organization and the photosynthetic activity, as tested by circular dichroism and 77 K fluorescence emission spectroscopy and the magnitude of the variable fluorescence of photosystem II, which all showed only marginal variations. In this work, we investigated in more detail the temporal stability of the different lipid phases by recording ³¹P‐NMR spectra on isolated thylakoid membranes that were suspended in sorbitol‐ or NaCl‐based media. We observed, at 5°C during 8 h in the dark, substantial gradual enhancement of the isotropic lipid phases and diminishment of the bilayer phase in the sorbitol‐based medium. These changes compared well with the gradually increasing membrane permeability, as testified by the gradual acceleration of the decay of flash‐induced electrochromic absorption changes and characteristic changes in the kinetics of fast chlorophyll a‐fluorescence transients; all variations were much less pronounced in the NaCl‐based medium. These observations suggest that non‐bilayer lipids and non‐lamellar lipid phases play significant roles in the structural dynamics and functional plasticity of thylakoid membranes.     

Measuring photosynthetic parameters at a distance: laser induced fluorescence transient (LIFT) method for remote measurements of photosynthesis in terrestrial vegetation

We have developed a laser induced fluorescence transient (LIFT) technique and instrumentation to remotely measure photosynthetic properties in terrestrial vegetation at a distance of up to 50 m. The LIFT method uses a 665 nm laser to project a collimated, 100 mm diameter excitation beam onto leaves of the targeted plant. Fluorescence emission at 690 nm is collected by a 250 mm reflective telescope and processed in real time to calculate the efficiency of photosynthetic light utilization, quantum efficiency of PS II, and the kinetics of photosynthetic electron transport. Operating with peak excitation power of 125 W m⁻², and duty cycle of 10–50%, the instrument conforms to laser safety regulations. The LIFT instrument is controlled via an Internet connection, allowing it to operate from remote locations or platforms. Here we describe the theoretical basis of the LIFT methodology, and demonstrate its applications in remote measurements of photosynthetic properties in the canopy of cottonwood and oak trees, and in the rosette of Arabidopsis mutants.     

紫外激光消融主动脉斑块和感生荧光光谱观测

利用XeCI准分子激光辐照主动脉血管正常组织和斑块组织,观察到组织被激光消融。消融所产生的凹坑与辐射时间呈对数直线关系。308nm激光感生的血管壁荧光光谱在可见波段出现二个荧光极大值,用二极值的相对强度之比可以判断正常或斑块组织。     

Copper nanocluster‐based fluorescence enhanced determination of d‐penicillamine

Taking advantage of the compelling properties of d ‐penicillamine (d ‐PA) combined with copper, a method for the sensitive and selective determination of d ‐PA was established using copper nanocluster (Cu NC)‐based fluorescence enhancement. d ‐PA molecules containing a thiol compound showed a strong tendency to combine with the surface of Cu NCs, causing the re‐dispersion of nanoclusters and therefore fluorescence intensity was enhanced. Fluorescence enhancement efficiency of Cu NCs induced by d ‐PA was linear, with the d ‐PA concentration varying from 0.6–30 μg ml^?1 (R² = 0.9952) and with a detection limit of 0.54 μg ml^?1. d ‐PA content in human urine samples was detected with recoveries of 104.8–112.99%. Fluorescence‐enhanced determination of d ‐PA using Cu NCs was established for the first time and this rapid, easy and sensitive method should attract much attention for this application.     

Vegetation and soil recovery following Eucalyptus grandis removal in Limpopo Province,South Africa

South African terrestrial ecosystems are invaded by hundreds of alien plant species, and large‐scale clearing based on the passive restoration assumption that cleared areas will recover unaided is underway. This study assessed the recovery of vegetation and soil properties, three years following Eucalyptus grandis clearing using fell‐and‐removal and fell‐and‐stackburn methods at Zvakanaka Farm in Limpopo Province, South Africa. The main aim was to ascertain the extent of vegetation and soil recovery, as well as determining which clearing methods facilitate passive vegetation and soil restoration. Results indicate significantly (p < 0.001) lower native species diversity, cover and composition in cleared than in uninvaded sites. However, the recorded low species diversity and composition in cleared sites were more pronounced in the fell‐and‐stackburn than in the fell‐and‐removal sites. Measured soil physical properties varied, with compaction being higher in fell‐and‐removal, whereas soils were more repellent in fell‐and‐stackburn sites. The study concludes that vegetation and soil recovery, following E. grandis clearing, is complex and involves several interacting factors, which are linked to invasion history and intensity. Therefore, for vegetation and soil properties to recover, following E. grandis removal, the clearing programme should consider active restoration techniques, for example soil manipulation and native plant seeding.     

Combining time‐resolved fluorescence with synchronous fluorescence spectroscopy to study bovine serum albumin‐curcumin complex during unfolding and refolding processes

We investigated the complex interaction between bovine serum albumin (BSA) and curcumin by combining time‐resolved fluorescence and synchronous fluorescence spectroscopy. The interaction was significant and sensitive to fluorescence lifetime and synchronous fluorescence characteristics. Binding of curcumin significantly shortened the fluorescence lifetime of BSA with a bi‐molecular quenching rate constant of k_q = 3.17 × 10¹² M^‐1s^‐1. Denaturation by urea unfolded the protein molecule by quenching the fluorescence lifetime of BSA. The tyrosine synchronous fluorescence spectra were blue shifted whereas the position of tryptophan synchronous fluorescence spectra was red shifted during the unfolding process. However, denaturation of urea had little effect on the synchronous fluorescence peak of tyrosine in curcumin‐BSA complex except in the low concentration range; however, it shifted the peak to the red, indicating that curcumin shifted tryptophan moiety to a more polar environment in the unfolded state. Decreases in the time‐resolved fluorescence lifetime and curcumin‐BSA complex during unfolding were recovered during refolding of BSA by a dilution process, suggesting partial reversibility of the unfolding process for both BSA and curcumin‐BSA complex. Copyright © 2012 John Wiley & Sons, Ltd.     

紫外激光消融主动脉斑块和感生荧光光谱观测

利用XeCI准分子激光辐照主动脉血管正常组织和斑块组织,观察到组织被激光消融。消融所产生的凹坑与辐射时间呈对数直线关系。308nm激光感生的血管壁荧光光谱在可见波段出现二个荧光极大值,用二极值的相对强度之比可以判断正常或斑块组织。     

Increasing fluorescence lifetime for resolution improvement in stimulated emission depletion nanoscopy

Super‐resolution microscopy (SRM) has had a substantial impact on the biological sciences due to its ability to observe tiny objects less than 200 nm in size. Stimulated emission depletion (STED) microscopy represents a major category of these SRM techniques that can achieve diffraction‐unlimited resolution based on a purely optical modulation of fluorescence behaviors. Here, we investigated how the laser beams affect fluorescence lifetime in both confocal and STED imaging modes. The results showed that with increasing illumination time, the fluorescence lifetime in two kinds of fluorescent microspheres had an obvious change in STED imaging mode, compared with that in confocal imaging mode. As a result, the reduction of saturation intensity induced by the increase of fluorescence lifetime can improve the STED imaging resolution at the same depletion power. The phenomenon was also observed in Star635P‐labeled human Nup153 in fixed HeLa cells, which can be treated as a reference for the synthesis of fluorescent labels with the sensitivity to the surrounding environment for resolution improvement in STED nanoscopy.      

In vivo measurements of diffuse reflectance and time‐resolved autofluorescence emission spectra of basal cell carcinomas

We present a clinical investigation of diffuse reflectance and time‐resolved autofluorescence spectra of skin cancer with an emphasis on basal cell carcinoma. A total of 25 patients were measured using a compact steady‐state diffuse reflectance/fluorescence spectrometer and a fibre‐optic‐coupled multispectral time‐resolved spectrofluorometer. Measurements were performed in vivo prior to surgical excision of the investigated region. Singular value decomposition was used to reduce the dimensionality of steady state diffuse reflectance and fluorescence spectra. Linear discriminant analysis was then applied to the measurements of basal cell carcinomas (BCCs) and used to predict the tissue disease state with a leave‐one‐out methodology. This approach was able to correctly diagnose 87% of the BCCs. With 445 nm excitation a decrease in the spectrally averaged fluorescence lifetime was observed between normal tissue and BCC lesions with a mean value of 886 ps. Furthermore, the fluorescence lifetime for BCCs was lower than that of the surrounding healthy tissue in all cases and statistical analysis of the data revealed that this decrease was significant (p = 0.002). (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Variability of sun‐induced chlorophyll fluorescence according to stand age‐related processes in a managed loblolly pine forest

Leaf fluorescence can be used to track plant development and stress, and is considered the most direct measurement of photosynthetic activity available from remote sensing techniques. Red and far‐red sun‐induced chlorophyll fluorescence (SIF) maps were generated from high spatial resolution images collected with the HyPlant airborne spectrometer over even‐aged loblolly pine plantations in North Carolina (United States). Canopy fluorescence yield (i.e., the fluorescence flux normalized by the light absorbed) in the red and far‐red peaks was computed. This quantifies the fluorescence emission efficiencies that are more directly linked to canopy function compared to SIF radiances. Fluorescence fluxes and yields were investigated in relation to tree age to infer new insights on the potential of those measurements in better describing ecosystem processes. The results showed that red fluorescence yield varies with stand age. Young stands exhibited a nearly twofold higher red fluorescence yield than mature forest plantations, while the far‐red fluorescence yield remained constant. We interpreted this finding in a context of photosynthetic stomatal limitation in aging loblolly pine stands. Current and future satellite missions provide global datasets of SIF at coarse spatial resolution, resulting in intrapixel mixture effects, which could be a confounding factor for fluorescence signal interpretation. To mitigate this effect, we propose a surrogate of the fluorescence yield, namely the Canopy Cover Fluorescence Index (CCFI) that accounts for the spatial variability in canopy structure by exploiting the vegetation fractional cover. It was found that spatial aggregation tended to mask the effective relationships, while the CCFI was still able to maintain this link. This study is a first attempt in interpreting the fluorescence variability in aging forest stands and it may open new perspectives in understanding long‐term forest dynamics in response to future climatic conditions from remote sensing of SIF.     

Herbaceous vegetation change in variable rangeland environments: The relative contribution of grazing and climatic variability

Abstract. A 44‐yr record of herbaceous vegetation change was analysed for three contrasting grazing regimes within a semi‐arid savanna to evaluate the relative contribution of confined livestock grazing and climatic variability as agents of vegetation change. Grazing intensity had a significant, directional effect on the relative composition of short‐ and mid‐grass response groups; their composition was significantly correlated with time since the grazing regimes were established. Interannual precipitation was not significantly correlated with response group composition. However, interannual precipitation was significantly correlated with total plant basal area while time since imposition of grazing regimes was not, but both interannual precipitation and time since the grazing regimes were established were significantly correlated with total plant density. Vegetation change was reversible even though the herbaceous community had been maintained in an altered state for ca. 60 yr by intensive livestock grazing. However, ca. 25 yr were required for the mid‐grass response group to recover following the elimination of grazing and recovery occurred intermittently. The increase in mid‐grass composition was associated with a significant decrease in total plant density and an increase in mean individual plant basal area. Therefore, we failed to reject the hypotheses based on the proportional change in relative response group composition with grazing intensity and the distinct effects of grazing and climatic variability on response group composition, total basal area and plant density. Long‐term vegetation change indicates that grazing intensity established the long‐term directional change in response group composition, but that episodic climate events defined the short‐term rate and trajectory of this change and determines the upper limit on total basal area. The occurrence of both directional and non‐directional vegetation responses were largely a function of (1) the unique responses of the various community attributes monitored and (2) the distinct temporal responses of these community attributes to grazing and climatic variation. This interpretation supports previous conclusions that individual ecosystems may exist in equilibrial and non‐equilibrial states at various temporal and spatial scales.     

Assay of ceftazidime and cefepime based on fluorescence quenching of carbon quantum dots

A novel and sensitive method for the determination of ceftazidime and cefepime in an active pharmaceutical ingredient (API) has been developed based on the fluorescence quenching of poly(ethylene glycol) (PEG)2000‐capped carbon quantum dots (CQDs) prepared using a chemical oxidation method. The quenching of fluorescence intensity is proportional to the concentration of ceftazidime and cefepime over the range of 0.33–3.30 and 0.24–2.40 µg/mL, respectively. The mode of interaction between PEG2000‐capped CQDs and ceftazidime/cefepime in aqueous solutions was investigated using a fluorescence, UV/Vis and Fourier transform infrared spectrometry (FTIR) at physiological pH. UV/Vis and FTIR spectra demonstrated that ground state compounds were formed through hydrophobic interaction the fluorescence quenching of CQDs caused by ceftazidime and cefepime. The quenching constants decreased with increases in temperature, which was consistent with static quenching. Copyright © 2015 John Wiley & Sons, Ltd.