Autofluorescence of the fungus <Emphasis Type="Italic">Morchella conica</Emphasis> var. <Emphasis Type="Italic">rigida</Emphasis>

Autofluorescence (primary fluorescence (AF)) of fruiting bodies and stems of the fungus Morchella conica var. rigida was studied by fluorescence microscopy including sporangia and ascospores. The ascospores were characterized by a weak green–yellow AF at blue excitation. Using a green excitation, no AF was observed. The hyphae located under the layer of asci with ascospores exhibited a higher primary fluorescence, namely their walls that had green-yellow color at blue excitation. Also, their red AF observed when a green excitation was used was significant. Similarly, the hyphae located in the fungal stem exhibited a significant AF, especially their walls when the blue light was used for excitation. In addition, large, yellow-to-yellow/green, oval-to-round bodies with strong fluorescence were detected whose morphological equivalents were not clearly visible in the white halogen light. The AF of the fungus M. conica var. rigida was lower compared with the other higher fungi studied so far.     

Autofluorescence of the fruiting body of the fungus <Emphasis Type="Italic">Macrolepiota rhacodes</Emphasis>

The autofluorescence (primary fluorescence, AF) of the freshly collected fruiting bodies of the fungus Macrolepiota rhacodes was studied in a Zeiss Jenalumar fluorescence microscope at a blue and a green excitation. The strongest yellow AF at blue excitation was displayed by irregular granules on the surface of the fungal pileus. A weaker yellow-green AF was exhibited by spherical cells and hyphae in the central part of the pileus while basidiospores emitted somewhat stronger AF. At green excitation, a considerable red AF was emitted only by basidiospores, other parts of the pileus showing a very weak red AF. M. rhacodes AF is much weaker than the AF of wood-rotting fungi, such as Fomes fomentarius, Daedalea quercina, Piptoporus betulinus, Fomitopsis pinicola and others.     

Evaluating UV-B effects and EDU protection in cucumber leaves using fluorescence images and fluorescence emission spectra

A newly developed laboratory fluorescence imaging system was used to obtain fluorescence images (FImage) of freshly excised cucumber (Cucumis sativus L.) leaves in spectral bands centered in the blue (F450), green (F550), red (F680), and far-red (F730) spectral regions that resulted from a broad-band (300-400 nm) excitation source centered at 360 nm. Means of relative fluorescence intensities (RFI) from these spectral fluorescence images were compared with spectral fluorescence emission data obtained from excitation wavelengths at 280 nm (280EX, 300-550 nm) and 380 nm (380EX, 400-800 nm) of dimethyl sulfoxide (DMSO) extracts from these leaves. All three fluorescence data types (FImage, 280EX, 380EX) were used to assess ultraviolet-B (UV-B, 280-320 nm) induced physiological changes and the possible use of N-[2-(2-oxo-1-imidazolidinyl) ethyl]-N′-phenylurea (EDU or ethylenediurea) as a chemical protectant against UV-B damage. Plants exhibited well known foliar growth and pigment responses to UV-B exposure (e.g., increased UV-B absorbing compounds and decreased leaf area, chlorophyll a content; and and lower chlorophyll a/b and chlorophyll/carotenoid pigment ratios). Since EDU alone had no effect on foliar variables, there was no evidence that EDU afforded protection against UV-B. Instead, EDU augmented some UV-B effects when provided in conjunction with UV-B irradiation (e.g., reductions in the chlorophyll/carotenoid ratio, total photosynthetic pigments, and chlorophyll b content).Relative fluorescence intensities (RFI) in the longer visible wavelengths (green, red, and far-red) were uncorrelated for comparisons between the FImage and 380EX data sets. However, blue and green RFI were significantly correlated (0.8r0.6; P ≤0.002) for comparisons between FImage and 280EX data sets. UV-B treatment caused an increase in blue RFI (e.g., F450) in both images and 280EX measurements. One explanation is that the UV-B excitation of both 280EX and FImage stimulates processes that produce excess blue fluorescence. The molecules that produce the excess blue fluorescence in both the 280EX and the Fimage data are different electron transfer agents that operate in parallel. For FImage, the UV excitation penetrates leaf surface layers to stimulate fluorescence from compounds in mesophyll and epidermal tissues (as occurs for the extracts of leaf discs), whereas emissions captured at longer, less energetic wavelengths, were primarily from the epidermal layer. UV-B irradiated leaves showed much greater heteorgeneity of RFI in both the green (F550_FImag) and the red (F680_FImag) bands than unirradiated leaves; this was true irrespective of EDU treatment.Although qualitative responses in individual bands differed between FImage and 380EX data, similar results were obtained in the detection of UV-B induced effects when the red/green and blue/far-red fluorescence ratios of these data were compared. The red/green ratio (either F680/F550_FImage or F675/F525_380EX) was lower for UV-B exposed plants in both images and 380EX data. UV-B exposure also significantly enhanced the blue/far-red ratio of images (F450/F740_FImage) and the comparable 380EX ratio (F450/F730_380EX) for the combined UV-B/EDU group. The far-red/red ratios were not useful in separating treatment effects in images or 380EX. Although comparable ratios were not available in 280EX data, the UV/blue ratio (F315/F420_280EX) was substantially reduced by UV-B exposure and was inversely related to total photosynthetic pigment content. These findings suggest that the red/green ratio (FImage, 380EX) and the UV/blue ratio (280EX) may be as useful as the blue/far-red ratio (380EX) reported previously in detection of UV-B stress. Furthermore, the results support the validity of the imaging technique as a non-destructive diagnostic tool for assessing UV-B stress damage in plants.     

Investigations of the Blue-green Fluorescence Emission of Plant Leaves

The UV light (337 nm) induced blue-green fluorescence emission of green leaves is characterized at room temperature (298 K) by a maximum near 450 nm (blue region) and a shoulder near 525 nm (green region) and was here also studied at 77 K. At liquid nitrogen temperature (77 K) the blue (F450) and green fluorescence (F525) are much enhanced as is the red chlorophyll fluorescence near 735 nm. During development of green tobacco leaves the blue fluorescence F450 (77 K) is shifted towards longer wavelengths from about 410 nm to 450 nm. The isolated leaf epidermis of tobacco showed only slight fluorescence emission with a maximum near 410 nm. The green fluorescence F525 was found to mainly originate from the mesophyll of the leaf, its intensity increased when the epidermis was removed. The red chlorophyll fluorescence emission was also enhanced when the epidermis was stripped off; this considerably changed the blue/red fluorescence ratios F450/F690 and F450/F735. The epidermis, with its cell wall and UV-light-absorbing substances in its vacuole, plays the role of a barrier for the exciting UV-light. In contrast to intact and homogenized leaves, isolated intact chloroplasts and thylakoid membranes did not exhibit a blue-green fluorescence emission.     

Studies on the Localization and Spectral Characteristics of the Fluorescence Emission of Differently Pigmented Wheat Leaves

Intensity, spectral characteristics and localization of the UV-laser (337 nm) induced blue-green and red fluorescence emission of green, etiolated and white primary leaves of wheat seedlings were studied in a combined fluorospectral and fluoromicroscopic investigation. The blue-green fluorescence of the green leaf was characterized by a maximum near 450 nm (blue region) and a shoulder near 530 nm (green region), whereas the red chlorophyll fluorescence exhibited maxima in the near-red (F690) and far-red (F735). The etiolated leaf with some carotenoids and traces of chlorophyll a, in turn, showed a higher intensity of the blue-green fluorescence with a shoulder in the green region and a strong red fluorescence peak near 684 to 690 nm, the far-red chlorophyll fluorescence maximum (F735) was, however, absent. The norfluorazone-treated white leaf, free of chlorophylls and carotenoids, only exhibited blue-green fluorescence of a very high intensity. In green and etiolated leaves the blue-green fluorescence primarily derived from the cell walls of the epidermis and the red fluorescence from the chlorophyll a of the mesophyll cells. In white leaves the blue-green fluorescence emanated from all cell walls of epidermis, mesophyll and leaf vein bundles. The shape and intensity of the blue-green and red fluorescence emission is determined by the reabsorption properties of chlorophylls and carotenoids in the mesophyll, thus giving rise to quite different values of the various fluorescence ratios F450/F690, F450/F530, F450/F735 and F690/F735 in green and etiolated leaves.     

Dual‐color‐emitting green fluorescent protein from the sea cactus Cavernularia obesa and its use as a pH indicator for fluorescence microscopy

We isolated and characterized a green fluorescent protein (GFP) from the sea cactus Cavernularia obesa. This GFP exists as a dimer and has absorption maxima at 388 and 498 nm. Excitation at 388 nm leads to blue fluorescence (456 nm maximum) at pH 5 and below, and green fluorescence (507 nm maximum) at pH 7 and above, and the GFP is remarkably stable at pH 4. Excitation at 498 nm leads to green fluorescence (507 nm maximum) from pH 5 to pH 9. We introduced five amino acid substitutions so that this GFP formed monomers rather than dimers and then used this monomeric form to visualize intracellular pH change during the phagocytosis of living cells by use of fluorescence microscopy. The intracellular pH change is visualized by use of a simple long‐pass emission filter with single‐wavelength excitation, which is technically easier to use than dual‐emission fluorescent proteins that require dual‐wavelength excitation. Copyright © 2013 John Wiley & Sons, Ltd.     

Extracellular Streptomyces lividans vesicles: composition,biogenesis and antimicrobial activity

We selected Streptomyces lividans to elucidate firstly the biogenesis and antimicrobial activities of extracellular vesicles that a filamentous and highly differentiated Gram‐positive bacterium produces. Vesicle types range in diameter from 110 to 230 nm and 20 to 60 nm, respectively; they assemble to clusters, and contain lipids and phospholipids allowing their in situ imaging by specific fluorescent dyes. The presence of the identified secondary metabolite undecylprodigiosin provokes red fluorescence of a portion of the heterogeneous vesicle populations facilitating in vivo monitoring. Protuberances containing vesicles generate at tips, and alongside of substrate hyphae, and enumerate during late vegetative growth to droplet‐like exudates. Owing to in situ imaging in the presence and absence of a green fluorescent vancomycin derivative, we conclude that protuberances comprising vesicles arise at sites with enhanced levels of peptidoglycan subunits [pentapeptide of lipid II (C55)‐linked disaccharides], and reduced levels of polymerized and cross‐linked peptidoglycan within hyphae. These sites correlate with enhanced levels of anionic phospholipids and lipids. Vesicles provoke pronounced damages of Aspergillus proliferans, Verticillium dahliae and induced clumping and distortion of Escherichia coli. These harmful effects are likely attributable to the action of the identified vesicular compounds including different enzyme types, components of signal transduction cascades and undecylprodigiosin. Based on our pioneering findings, we highlight novel clues with environmental implications and application potential.     

Alteration of Components of Chlorophyll-Protein Complexes and Distribution of Excitation Energy Between the Two Photosystems in Two New Rice Chlorophyll b-less mutants

Two new yellow rice chlorophyll (Chl) b-less (lack) mutants VG28-1 and VG30-5 differ from the other known Chl b-less mutants with larger amounts of soluble protein and ribulose-1,5-bisphosphate carboxylase/oxygenase small sub-unit and smaller amounts of Chl a. We investigated the altered features of Chl-protein complexes and excitation energy distribution in these two mutants, as compared with wild type (WT) rice cv. Zhonghua 11 by using native mild green gel electrophoresis and SDS-PAGE, and 77 K Chl fluorescence in the presence of Mg²⁺. WT rice revealed five pigment-protein bands and fourteen polypeptides in thylakoid membranes. Two Chl b-less mutants showed only CPI and CPa pigment bands, and contained no 25 and 26 kDa polypeptides, reduced amounts of the 21 kDa polypeptide, but increased quantities of 32, 33, 56, 66, and 19 kDa polypeptides. The enhanced absorption of CPI and CPa and the higher Chl fluorescence emission ratio of F685/F720 were also observed in these mutants. This suggested that the reduction or loss of the antenna LHC1 and LHC2 was compensated by an increment in core component and the capacity to harvest photon energy of photosystem (PS) 1 and PS2, as well as in the fraction of excitation energy distributed to PS2 in the two mutants. 77 K Chl fluorescence spectra of thylakoid membranes showed that the PS1 fluorescence emission was shifted from 730 nm in WT rice to 720 nm in the mutants. The regulation of Mg²⁺ to excitation energy distribution between the two photosystems was complicated. 10 mM Mg²⁺ did not affect noticeably the F685/F730 emission ratio of WT thylakoid membranes, but increased the ratio of F685/F720 in the two mutants due to a reduced emission at 685 nm as compared to that at 720 nm.     

Effects of different excitation and detection spectral regions on room temperature chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence parameters

The effects of different spectral region of excitation and detection of chlorophyll (Chl) a fluorescence at room temperature on the estimation of excitation energy utilization within photosystem (PS) 2 were studied in wild-type barley (Hordeum vulgare L. cv. Bonus) and its Chl b-less mutant chlorina f2 grown under low and high irradiances [100 and 1 000 μmol(photon) m⁻² s⁻¹]. Three measuring spectral regimes were applied using a PAM 101 fluorometer: (1) excitation in the red region (maximum at the wavelength of 649 nm) and detection in the far-red region beyond 710 nm, (2) excitation in the blue region (maximum at the wavelength of 461 nm) and detection beyond 710 nm, and (3) excitation in the blue region and detection in the red region (660– 710 nm). Non-photochemical quenching of maximal (NPQ) and minimal fluorescence (SV₀), determined by detecting Chl a fluorescence beyond 710 nm, were significantly higher for blue excitation as compared to red excitation. We suggest that this results from higher non-radiative dissipation of absorbed excitation energy within light-harvesting complexes of PS2 (LHC2) due to preferential excitation of LHC2 by blue radiation and from the lower contribution of PS1 emission to the detected fluorescence in the case of blue excitation. Detection of Chl a fluorescence originating preferentially from PS2 (i.e. in the range of 660–710 nm) led to pronounced increase of NPQ, SV₀, and the PS2 photochemical efficiencies (F_V/F_M and F_V′/F_M′), indicating considerable underestimation of these parameters using the standard set-up of PAM 101. Hence PS1 contribution to the minimal fluorescence level in the irradiance-adapted state may reach up to about 80 %.     

Fluorescence kinetic parameters and cyclic electron transport in guard cell chloroplasts of chlorophyll-deficient leaf tissues from variegated weeping fig (<Emphasis Type="Italic">Ficus benjamina</Emphasis> L.)

Residual chlorophyll in chlorophyll-deficient (albino) areas of variegated leaves of Ficus benjamina originates from guard cell chloroplasts. Photosynthetic features of green and albino sectors of F. benjamina were studied by imaging the distribution of the fluorescence decrease ratio Rfd within a leaf calculated from maximum (Fm) and steady-state leaf chlorophyll fluorescence (Fs) at 690 and 740 nm. Local areas of albino sectors demonstrated an abnormally high Rfd₇₄₀/Rfd₆₉₀ ratio. Fluorescence transients excited in albino sectors at red (640 and 690 nm) wavelengths showed an abrupt decrease of the Rfd values (0.4 and 0.1, correspondingly) as compared with those excited at blue wavelengths (1.7–2.4). This “Red Drop” was not observed for green sectors. Normal and chlorophyll-deficient leaf sectors of F. benjamina were also tested for linear and cyclic electron transport in thylakoids. The tests have been performed studying fluorescence at a steady-state phase with CO₂-excess impulse feeding, photoacoustic signal generated by pulse light source at wavelengths selectively exciting PSI, fluorescence kinetics under anaerobiosis and fluorescence changes observed by dual-wavelength excitation method. The data obtained for albino sectors strongly suggest the possibility of a cyclic electron transport simultaneously occurring in guard cell thylakoids around photosystems I and II under blue light, whereas linear electron transport is absent or insufficient.     

Highly luminescent and biocompatible,l‐citrulline‐capped ZnS:Mn nanocrystals for rapid screening of metal accumulating Lysinibacillus fusiformis bacteria

Biocompatible and highly luminescent manganese doped zinc sulfide (ZnS:Mn) nanocrystals of average particle size 10 nm have been synthesized by capping with a novel amino acid ligand, l ‐citrulline. Though there are many reports on the bioimaging applications of nanostructured semiconductors, the present study focused on the detection of a special type of metal accumulating bacteria, Lysinibacillus fusiformis. This bacterium has significant applications in the disposal of metal components from industrial effluents. In this context, the detection of this bacterium is quite important and the present work demonstrates a novel technique for this bacterial detection. The synthesized nanocrystals were attached to Lysinibacillus fusiformis and characteristics of the bioconjugated system were studied. The blue shift observed in the ultraviolet‐visible absorption and photoluminescence spectra of the bioconjugated system, confirms conjugation of the Lysinibacillus fusiformis with l ‐citrulline‐capped ZnS:Mn. When the bioconjugated system (capped ZnS:Mn + bacteria) was observed using a fluorescent microscope under excitation wavelengths 365.4 nm (ultraviolet), 435.8 nm (blue) and 546.1 nm (green), fluorescence emissions were obtained in yellow, green and red regions respectively. The study of relative growth of Lysinibacillus fusiformis in the presence of l ‐citrulline‐capped ZnS:Mn proves biocompatible property of these nanocrystals and their tunable color properties under different excitation wavelengths make them ideal for biolabeling applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Fluorescence changes accompanying short-term light adaptations in photosystem I and photosystem II of the cyanobacterium <Emphasis Type="Italic">Synechocystis</Emphasis> sp. PCC 6803 and phycobiliprotein-impaired mutants: State 1/State 2 transitions and carotenoid-induced quenching of phycobilisomes

The features of the two types of short-term light-adaptations of photosynthetic apparatus, State 1/State 2 transitions, and non-photochemical fluorescence quenching of phycobilisomes (PBS) by orange carotene-protein (OCP) were compared in the cyanobacterium Synechocystis sp. PCC 6803 wild type, CK pigment mutant lacking phycocyanin, and PAL mutant totally devoid of phycobiliproteins. The permanent presence of PBS-specific peaks in the in situ action spectra of photosystem I (PSI) and photosystem II (PSII), as well as in the 77 K fluorescence excitation spectra for chlorophyll emission at 690 nm (PSII) and 725 nm (PSI) showed that PBS are constitutive antenna complexes of both photosystems. The mutant strains compensated the lack of phycobiliproteins by higher PSII content and by intensification of photosynthetic linear electron transfer. The detectable changes of energy migration from PBS to the PSI and PSII in the Synechocystis wild type and the CK mutant in State 1 and State 2 according to the fluorescence excitation spectra measurements were not registered. The constant level of fluorescence emission of PSI during State 1/State 2 transitions and simultaneous increase of chlorophyll fluorescence emission of PSII in State 1 in Synechocystis PAL mutant allowed to propose that spillover is an unlikely mechanism of state transitions. Blue–green light absorbed by OCP diminished the rout of energy from PBS to PSI while energy migration from PBS to PSII was less influenced. Therefore, the main role of OCP-induced quenching of PBS is the limitation of PSI activity and cyclic electron transport under relatively high light conditions.     

Fluorescence of plant microspores as biosensors

Possibilities of fluorescent microscopic single-cell analysis on plant microspores as biosensors for study of chemosignaling involving neurotransmitters and mechanisms of action of fluorescent medicinal compounds—antagonists of neurotransmitters were studied on some examples. By methods of luminescence microscopy, microspectrofluorimetry and laser scanning confocal microscopy using as an example field horsetail Equisetum arvense microspores, the penetration of these compounds into the cell and associate it with individual compartments (estimated as the changes in their autofluorescence) has been analyzed. Fluorescent in blue antagonists of neurotransmitters d-tubocurarine, yohimbine and azulene (blockers of cholinoreceptor, adrenoreceptor, and histamine receptor, respectively) decreased the number of the E. arvense cells with red fluorescence. Tubocurarine and yohimbine bound to the cellular surface and did not penetrate into the cells. Azulene was found both on the cell surface and inside cells, demonstrating blue (excitation 360–380 nm) or green (excitation 420 nm) fluorescence of DNA-containing organelles. The effects of lipophilic (lecithin and amphotericin B) and proteinous (albumin, enzyme cholinesterase, cytoskeleton proteins actin, myosin, and titin) compounds on the manifestation of the effects of the neurotransmitters and antagonist d-tubocurarine have been shown. The intensity of the red light at 680 nm, has evolved in many variants. Most notable was the decline of the emission in the presence of albumin and cholinesterase as compared with the action of dopamine itself. After the addition of the cytoskeleton proteins and cholinesterase to the medium, the decrease of red fluorescence intensity, usually induced by d-tubocurarine, was not observed.     

Far‐red dependent changes in the chemical composition of Spirulina platensis

The influence of far‐red light (FRL) was studied on the chemical composition of Spirulina platensis biomass. The following light compositions were used during the culture white light, blue‐red LED light (BRL) and BRL supplemented with FRL (BRFRL). Chlorophyll and phenol contents were measured by spectrophotometric methods, whereas presence of carotenoids, lipids, and phycobiliproteins were estimated by Fourier‐transform Raman spectrometry. Additionally, phenol content was investigated by fluorescence intensity of algae culture in the range of 430–650 nm. The content of chlorophyll and phenols in algae cells depended on the spectral composition of light and was the highest under BRL (16.7 ± 0.5 and 9.1 ± 0.6, respectively). It was shown that there is a positive linear correlation (R = 0.902 at p < 0.0000001) between the ratio of relative fluorescence intensity of S. platensis suspensions at 450 nm to the suspensions at 540 nm (F450/F540) and the content of phenolic compounds in the biomass. Changes in the F450/F540 ratio can explain approximately 80% changes of phenol contents in algae cells. Spirulina platensis Raman spectra demonstrated that the biomass of algae growing under white light and BRL had a significantly higher intensity of phycobiliprotein bands than the algae growing under BRFRL.     

Two equilibration pools of chlorophylls in the Photosystem I core antenna of <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis>

Summary Femtosecond transient absorption spectroscopy was applied for a comparative study of excitation decay in several different Photosystem I (PSI) core preparations from the green alga Chlamydomonas reinhardtii. For PSI cores with a fully interconnected network of chlorophylls, the excitation energy was equilibrated over a pool of chlorophylls absorbing at ∼683 nm, independent of excitation wavelength [Gibasiewicz et al. J Phys Chem B 105:11498–11506, 2001; J Phys Chem B 106:6322–6330, 2002]. In preparations with impaired connectivity between chlorophylls, we have found that the spectrum of chlorophylls connected to the reaction center (i.e., with ∼20 ps decay time) over which the excitation is equilibrated becomes excitation-wavelength-dependent. Excitation at 670 nm is finally equilibrated over chlorophylls absorbing at ∼675 nm, whereas excitation at 695 nm or 700 nm is equilibrated over chlorophylls absorbing at ∼683 nm. This indicates that in the vicinity of the reaction center there are two spectrally different and spatially separated pools of chlorophylls that are equally capable of effective excitation energy transfer to the reaction center. We propose that they are related to the two groups of central PSI core chlorophylls lying on the opposite sides of reaction center.     

Fluorescence change of <Emphasis Type="Italic">Fusobacterium nucleatum</Emphasis> due to <Emphasis Type="Italic">Porphyromonas gingivalis</Emphasis>

The aim of this study was to measure changes in the fluorescence of Fusobacterium nucleatum interacting with Porphyromonas gingivalis for excitation with blue light at 405-nm. P. gingivalis was mono- and co-cultivated in close proximity with F. nucleatum. The fluorescence of the bacterial colonies was photographed using a QLF-D (Quantitative Light-induced Fluorescence-Digital) Biluminator camera system with a 405 nm light source and a specific filter. The red, green and blue intensities of fluorescence images were analyzed using the image analysis software. A fluorescence spectrometer was used to detect porphyrin synthesized by each bacterium. F. nucleatum, which emitted green fluorescence in single cultures, showed intense red fluorescence when it was grown in close proximity with P. gingivalis. F. nucleatum co-cultivated with P. gingivalis showed the same pattern of fluorescence peaks as for protoporphyrin IX in the red part of the spectrum. We conclude that the green fluorescence of F. nucleatum can change to red fluorescence in the presence of adjacent co-cultured with P. gingivalis, indicating that the fluorescence character of each bacterium might depend on the presence of other bacteria.     

Temperature dependence and polarization of fluorescence from Photosystem I in the cyanobacterium Synechocystis sp. PCC 6803

To determine the fluorescence properties of cyanobacterial Photosystem I (PS I) in relatively intact systems, fluorescence emission from 20 to 295 K and polarization at 77 K have been measured from phycobilisomes-less thylakoids of Synechocystis sp. PCC 6803 and a mutant strain lacking Photosystem II (PS II). At 295 K, the fluorescence maxima are 686 nm in the wild type from PS I and PS II and at 688 nm from PS I in the mutant. This emission is characteristic of bulk antenna chlorophylls (Chls). The 690-nm fluorescence component of PS I is temperature independent. For wild-type and mutant, 725-nm fluorescence increases by a factor of at least 40 from 295 to 20 K. We model this temperature dependence assuming a small number of Chls within PS I, emitting at 725 nm, with an energy level below that of the reaction center, P700. Their excitation transfer rate to P700 decreases with decreasing temperature increasing the yield of 725-nm fluorescence.Fluorescence excitation spectra of polarized emission from low-energy Chls were measured at 77 and 295 K on the mutant lacking PS II. At excitation wavelengths longer than 715 nm, 760-nm emission is highly polarized indicating either direct excitation of the emitting Chls with no participation in excitation transfer or total alignment of the chromophores. Fluorescence at 760 nm is unpolarized for excitation wavelengths shorter than 690 nm, inferring excitation transfer between Chls before 760-nm fluorescence occurs.Our measurements illustrate that: 1) a single group of low-energy Chls (F725) of the core-like PS I complex in cyanobacteria shows a strongly temperature-dependent fluorescence and, when directly excited, nearly complete fluorescence polarization, 2) these properties are not the result of detergent-induced artifacts as we are examining intact PS I within the thylakoid membrane of S. 6803, and 3) the activation energy for excitation transfer from F725 Chls to P700 is less than that of F735 Chls in green plants; F725 Chls may act as a sink to locate excitations near P700 in PS I.Abbreviations Chl chlorophyll - BChl bacteriochlorophyll - PS Photosystem - S. 6803 Synechocystis sp. PCC 6803 - PGP potassium glycerol phosphate     

Photosynthetic characteristics of marine aerobic anoxygenic phototrophic bacteria <Emphasis Type="Italic">Roseobacter</Emphasis> and <Emphasis Type="Italic">Erythrobacter</Emphasis> strains

A coastal Roseobacter strain of marine aerobic anoxygenic phototrophic bacteria (AAnPB) was isolated and phylogenetically determined. The strain OBYS 0001 was characterized by its physiological and biochemical properties with reference to the Erythrobacter longus type strain NBRC 14126. When grown in batch cultures, the growth curves of the both strains were similar. Cellular bacteriochlorophyll a concentrations of the strains reached the maxima in the stationary growth conditions. In vivo fluorescence excitation/optical density spectra between 470 and 600 nm for OBYS 0001 represented higher values than NBRC 14126. Variable fluorescence measurements revealed that the functional absorption cross section (σ) of the bacterial photosynthetic complexes for OBYS 0001 was significantly higher than that for NBRC 14126 under green excitation. These results suggest that Roseobacter can capture green light more efficiently than Erythrobacter for photosynthesis. The photochemical quantum efficiencies (F _v/F _m) of the bacterial photosynthetic complexes for OBYS 0001 were consistently lower than those for NBRC 14126. A relationship between the growth rate and F _v/F _m was significant for OBYS 0001, but that was not found for NBRC 14126. These results suggested that F _v/F _m for AAnPB could not be used as a proxy of the growth rate which is consistent with their mostly heterotrophic characters.     

Optimization of variable fluorescence measurements of phytoplankton communities with cyanobacteria

Excitation–emission fluorescence matrices of phytoplankton communities were simulated from laboratory-grown algae and cyanobacteria cultures, to define the optical configurations of theoretical fluorometers that either minimize or maximize the representation of these phytoplankton groups in community variable fluorescence measurements. Excitation sources that match the photosystem II (PSII) action spectrum of cyanobacteria do not necessarily lead to equal representation of cyanobacteria in community fluorescence. In communities with an equal share of algae and cyanobacteria, inducible PSII fluorescence in algae can be retrieved from community fluorescence under blue excitation (450–470 nm) with high accuracy (R ² = 1.00). The highest correlation between community and cyanobacterial variable fluorescence is obtained under orange-red excitation in the 590–650 nm range (R ² = 0.54). Gaussian band decomposition reveals that in the presence of cyanobacteria, the emission detection slit must be narrow (up to 10 nm) and centred on PSII chlorophyll-a emission (~683 nm) to avoid severe dampening of the signal by weakly variable phycobilisomal fluorescence and non-variable photosystem I fluorescence. When these optimizations of the optical configuration of the fluorometer are followed, both cyanobacterial and algal cultures in nutrient replete exponential growth exhibit values of the maximum quantum yield of charge separation in PSII in the range of 0.65–0.7.     

Spectral analysis on origination of the bands at 437 nm and 475.5 nm of chlorophyll fluorescence excitation spectrum in Arabidopsis chloroplasts

Chlorophyll fluorescence has been often used as an intrinsic optical molecular probe to study photosynthesis. In this study, the origin of bands at 437 and 475.5 nm in the chlorophyll fluorescence excitation spectrum for emission at 685 nm in Arabidopsis chloroplasts was investigated using various optical analysis methods. The results revealed that this fluorescence excitation spectrum was related to the absorption characteristics of pigment molecules in PSII complexes. Moreover, the excitation band centred at 475.5 nm had a blue shift, but the excitation band at 437 nm changed relatively less due to induction of non‐photochemical quenching (NPQ). Furthermore, fluorescence emission spectra showed that this blue shift occurred when excitation energy transfer from both chlorophyll b (Chl b) and carotenoids (Cars) to chlorophyll a (Chl a) was blocked. These results demonstrate that the excitation band at 437 nm was mainly contributed by Chl a, while the excitation band at 475.5 nm was mainly contributed by Chl b and Cars. The chlorophyll fluorescence excitation spectrum, therefore, could serve as a useful tool to describe specific characteristics of light absorption and energy transfer between light‐harvesting pigments. Copyright © 2015 John Wiley & Sons, Ltd.