Analysis of photoprotection and apparent non-photochemical quenching of chlorophyll fluorescence in <Emphasis Type="Italic">Tradescantia</Emphasis> leaves based on the rate of irradiance-induced changes in optical transparence

The kinetics of irradiation-induced changes in leaf optical transparence (ΔT) and non-photochemical quenching (NPQ) of chlorophyll fluorescence in Tradescantia fluminensis and T. sillamontana leaves adapted to different irradiance in nature was analyzed. Characteristic times of a photoinduced increase and a dark decline of ΔT in these species were 12 and 20 min, respectively. The ΔT was not confirmed to be the main contributor to the observed middle phase of NPQ relaxation kinetics (τ = 10-28 min). Comparison of rate of photoinduced increase in ΔT and photosystem II quantum yield recovery showed that the former did not affect the tolerance of the photosynthetic apparatus (PSA) to irradiances up to 150 μmol PAR·m^–2·s^–1. Irradiance tolerance correlated with the rate of “apparent NPQ” induction. Considering that the induction of apparent NPQ involves processes significantly faster than ΔT, we suggest that the photoprotective mechanism induction rate is crucial for tolerance of the PSA to moderate irradiance during the initial stage of light acclimation (first several minutes upon the onset of illumination).     

Estimation of biophysical characteristics for <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis> pigment mutants with an M-PEA-2 fluorometer

Light green pigment mutants with a reduced chlorophyll b content were constructed in the microalga Chlamydomonas reinhardtii Dangeard. A simultaneous recording of the induction curves for prompt and delayed fluorescence and the redox state of P700 in the microsecond range with a M-PEA-2 fluorometer revealed decreases in the quantum yield of electron transport in PS2 (φE₀) and the performance index (PI_ABS) and increases in the quantum efficiency of energy dissipation (φD₀) and ΔpH-dependent nonphotochemical quenching (qE and NPQ). The light-dependence curves of the fluorescence parameters confirmed a decrease in the coefficient of maximum utilization of light energy (α) for the mutants. However, the mutants showed an adequate rate of electron transport at a medium light intensity under steady-state conditions. The mutations did not directly affect the oxidation reactions of the PS1 pigment (P700) and the decrease in delayed fluorescence. Experience in using the mutants to test polluted waters of Kazakhstan confirmed that the mutants are promising for use in biomonitoring for mutagens.     

Evaluation of microbial globin promoters for oxygen-limited processes using <Emphasis Type="Italic">Escherichia coli</Emphasis>

Oxygen-responsive promoters can be useful for synthetic biology applications, however, information on their characteristics is still limited. Here, we characterized a group of heterologous microaerobic globin promoters in Escherichia coli. Globin promoters from Bacillus subtilis, Campylobacter jejuni, Deinococcus radiodurans, Streptomyces coelicolor, Salmonella typhi and Vitreoscilla stercoraria were used to express the FMN-binding fluorescent protein (FbFP), which is a non-oxygen dependent marker. FbFP fluorescence was monitored online in cultures at maximum oxygen transfer capacities (OTR_max) of 7 and 11 mmol L^?1 h^?1. Different FbFP fluorescence intensities were observed and the OTR_max affected the induction level and specific fluorescence emission rate (the product of the specific fluorescence intensity multiplied by the specific growth rate) of all promoters. The promoter from S. typhi displayed the highest fluorescence emission yields (the quotient of the fluorescence intensity divided by the scattered light intensity at every time-point) and rate, and together with the promoters from D. radiodurans and S. coelicolor, the highest induction ratios. These results show the potential of diverse heterologous globin promoters for oxygen-limited processes using E. coli.     

Influence of electrochemical proton gradient on electron flow in photosystem I of pea leaves

Photoinduced changes in the redox state of photosystem I (PSI) primary donor, chlorophyll P700 were studied by measuring differential absorbance changes of pea leaves at 810 nm minus 870 nm (ΔA ₈₁₀). The kinetics of ΔA ₈₁₀ induced by 5-s pulses of white light were strongly affected by preillumination. In dark-adapted leaves, the light pulse caused a transient oxidation of P700 and its subsequent reduction. An identical pulse, applied after 30-s preillumination with white light, induced sequential appearance of two peaks of P700 oxidation. These kinetic differences of ΔA ₈₁₀ reflect regulatory changes of electron flow on the donor and acceptor sides of PSI induced by illumination of leaf for 20–40 s. The amplitude of ΔA ₈₁₀ second peak depended nonmonotonically on the dark interval preceding illumination: it increased with the length of dark period in the range 3–10 s and decreased upon longer dark intervals. The second wave of ΔA ₈₁₀ disappeared after the treatment with combination of ionophores preventing ΔpH and electric potential formation at the thylakoid membrane. In leaves treated with monensin eliminating ΔpH only, the ΔA ₈₁₀ signals become incompletely reversible and were characterized by slow relaxation in darkness. The results indicate an important role of electrochemical proton gradient in generation of the second wave of light-induced P700 oxidation.     

Putrescine biosynthesis and export genes are essential for normal growth of avian pathogenic <Emphasis Type="Italic">Escherichia coli</Emphasis>

Background

Avian pathogenic Escherichia coli (APEC) is the infectious agent of a wide variety of avian diseases, which causes substantial economic losses to the poultry industry worldwide. Polyamines contribute to the optimal synthesis of nucleic acids and proteins in bacteria. The objectives of this study were to investigate; i) whether APEC E. coli encodes the same systems for biosynthesis and uptake as described for E. coli K12 and ii) the role of polyamines during in vitro growth of an avian pathogenic E. coli strain (WT-ST117- O83:H4T).

Results

Following whole genome sequencing, polyamine biosynthesis and export genes present in E. coli MG1655 (K-12) were found to be identical in WT-ST117. Defined mutants were constructed in putrescine and spermidine biosynthesis pathways (ΔspeB, ΔspeC, ΔspeF, ΔspeB/C and ΔspeD/E), and in polyamines transport systems (ΔpotE, ΔyeeF, ΔpotABCD and ΔpotFGHI). Contrary to what was observed for MG1655, the ΔpotE-ST117 mutant was growth attenuated, regardless of putrescine supplementation. The addition of spermidine or orthinine restored the growth to the level of WT-ST117. Growth attenuation after induction of membrane stress by SDS suggested that PotE is involved in protection against this stress. The ΔspeB/C-ST117 mutant was also growth attenuated in minimal medium. The addition of putrescine or spermidine to the media restored growth rate to the wild type level. The remaining biosynthesis and transport mutants showed a growth similar to that of WT-ST117. Analysis by Ultra-High Performance Liquid Chromatography revealed that the ΔspeB/C mutant was putrescine-deficient, despite that the gene speF, which is also involved in the synthesis of putrescine, was expressed.

Conclusions

Deletion of the putrescine transport system, PotE, or the putrescine biosynthesis pathway genes speB/C affected in vitro growth of APEC (ST117- O83:H4) strain, but not E. coli MG1655, despite the high similarity of the genetic make-up of biosynthesis and transport genes. Therefore, blocking these metabolic reactions may be a suitable way to prevent APEC growth in the host without disturbing the commensal E. coli population.

     

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.     

Acclimation of shade-tolerant and light-resistant <Emphasis Type="Italic">Tradescantia</Emphasis> species to growth light: chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence,electron transport,and xanthophyll content

In this study, we have compared the photosynthetic characteristics of two contrasting species of Tradescantia plants, T. fluminensis (shade-tolerant species), and T. sillamontana (light-resistant species), grown under the low light (LL, 50–125 µmol photons m^?2 s^?1) or high light (HL, 875–1000 µmol photons m^?2 s^?1) conditions during their entire growth period. For monitoring the functional state of photosynthetic apparatus (PSA), we measured chlorophyll (Chl) a emission fluorescence spectra and kinetics of light-induced changes in the heights of fluorescence peaks at 685 and 740 nm (F ₆₈₅ and F ₇₄₀). We also compared the light-induced oxidation of P₇₀₀ and assayed the composition of carotenoids in Tradescantia leaves grown under the LL and HL conditions. The analyses of slow induction of Chl a fluorescence (SIF) uncovered different traits in the LL- and HL-grown plants of ecologically contrasting Tradescantia species, which may have potential ecophysiological significance with respect to their tolerance to HL stress. The fluorometry and EPR studies of induction events in chloroplasts in situ demonstrated that acclimation of both Tradescantia species to HL conditions promoted faster responses of their PSA as compared to LL-grown plants. Acclimation of both species to HL also caused marked changes in the leaf anatomy and carotenoid composition (an increase in Violaxanthin?+?Antheraxantin?+?Zeaxanthin and Lutein pools), suggesting enhanced photoprotective capacity of the carotenoids in the plants grown in nature under high irradiance. Collectively, the results of the present work suggest that the mechanisms of long-term PSA photoprotection in Tradescantia are based predominantly on the light-induced remodeling of pigment-protein complexes in chloroplasts.     

Effect of chromate ions on marine microalgae <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis>

Effect of chromate ions on the culture of a marine diatom Phaeodactylum tricornutum was studied using an M-PEA-2 fluorimeter, which carries out simultaneous measurement of fluorescence induction and redox transformations of the P₇₀₀ pigment within a millisecond range. Chromate ions were shown to inhibit electron transport in PS II and decrease the rate of Q_А reduction. This results in decreased values of the quantum yield of electron transport in PS II (?_Eo) and performance index (PI _ABS), lower rates of P700 reduction, and increased energy (DI0/RC) and ΔpH-dependent nonphotochemical quenching (q _E ). Emergence of the slow component of P₇₀₀ reduction was observed, indicating the activation of cyclic transport in the presence of chromate. Performance index (PI _ABS), which was the most sensitive parameter, may be recommended for detection of chromate ions at early stages of their toxic action. The fluorescence parameter F _O is promising application in biotesting to assess the algal growth rates.     

Adaptive loss of color polymorphism and character displacements in sympatric <Emphasis Type="Italic">Mnais</Emphasis> damselflies

A geographical survey of two Mnais damselfly species in the Kinki area of Japan showed evidence for character displacements when the two species were found in sympatry. Mnais costalis, a species that has polymorphic male mating types of orange-winged territorial and clear-winged non-territorial morphs (hereafter abbreviated to orange and clear morphs respectively) in allopatry often shifted to having monomorphic orange morphs in sympatry. The mean body size of orange morphs was consistently larger than that of clear morph in allopatry. The mean body size of the sympatric orange morphs was even larger than that of allopatric orange morphs. By contrast, Mnais pruinosa, a species that also has two morphs of large orange and small clear morphs in allopatry, shifted to having monomorphic clear morphs in sympatry. The mean body size of the sympatric clear morphs was smaller than that of allopatric clear morphs. Divergence was also detected in the preference for habitat insolation conditions between sympatric Mnais damselflies. Both species in allopatric regions prefer half-light forest habitats, while in sympatric regions they showed diversified habitat preference: M. costalis preferred sunny habitats while M. pruinosa preferred shady habitats. Multiple character displacements in signal traits and habitat preference emerged in heterogeneous forest light environments are likely to have synergistic effects on the reproductive isolation of the two species.     

Somatic embryogenesis of a seedless sweet orange (<Emphasis Type="Italic">Citrus sinensis</Emphasis> (L.) Osbeck)

Somatic embryogenesis is an important in vitro technique used to obtain Citrus sinensis (L.) Osbeck (sweet orange) plantlets for conservation, sanitation, propagation, and breeding. The induction of somatic embryogenesis from adult tissues of sweet orange could be an alternative to in vitro organogenesis from epicotyl segments, especially in seedless cultivars, where the latter is not feasible. The aim of this study was to obtain plantlets from ovary-derived somatic embryos of sweet orange cv. ‘Washington Navel’, an important seedless cultivar for citrus fresh fruit production. The explants used were pistils from flower buds, pre-anthesis, from 20-y-old plants cultivated in the field. Forty plantlets from 47 somatic embryos were obtained, in vitro-grafted, and acclimatized in greenhouse conditions. Ploidy evaluation through flow cytometric analysis, as well as the results of target region amplification polymorphism (TRAP) molecular markers confirmed the somatic origin of embryos as genetically similar to donor plants. This technique could be used for obtaining embryogenic cell suspension cultures or regenerated plants from mature tissues other than seed-derived tissues, especially for seedless genotypes.     

The relationship between leaf and ecosystem CO<Subscript>2</Subscript> exchanges in a maize field

The relationship between leaf photosynthetic rate (A) in a vegetation canopy and the net ecosystem CO₂ exchange (NEE) over an entire ecosystem is not well understood. The aim of the present study is to assess the coordinated changes in NEE derived with eddy covariance, A measured in leaf cuvette, and their associations in a rainfed maize field. The light response-curves were estimated for the carbon assimilation rate at both the leaf and ecosystem scales. NEE and A synchronically changed throughout the day and were greater around noon and persisted longer during rapid growth periods. The leaf A had a similar pattern of daytime changes in the top, middle, and bottom leaves. Only severe leaf ageing led to a significant decline in the maximum efficiency of photosystem II (PSII) photochemistry. The greater maximum NEE was associated with a higher ecosystem quantum yield. NEE was positively and significantly correlated with the leaf A averaged based on the vertical distribution of leaf area. The finding highlights the feasibility of assessing NEE by leaf CO₂ exchange because of most of experimental data obtained with leaf cuvette methods; and also implies that simultaneously enhancing leaf photosynthetic rate, electron transport rate, net carbon assimilation at whole ecosystem might play a critical role for the enhancement of crop productivity.     

Cloning and Functional Analysis of <Emphasis Type="Italic">SaCLCc1</Emphasis>, a Gene Belonging to the Chloride Channel Family (<Emphasis Type="Italic">CLC</Emphasis>), from the Halophyte <Emphasis Type="Italic">Suaeda altissima</Emphasis> (L.) Pall.

One of the genes of the CLC (Chloride Channel) family, SaCLCc1, from the halophyte Suaeda altissima (L.) Pall. was cloned. To investigate the function of SaCLCc1, it was expressed in the S. cerevisiae deletion mutant Δgef1::LEU2 for the only gene of the CLC family in this organism. The growth of the transformed SaCLCc1-expressing mutant Δgef1 was restored when cells were grown in Fe²⁺-deficient YPEG medium, in minimal synthetic media SD and SR (pH 7.0), and in rich YPD medium containing Mn²⁺. The complementation of the Δgef1 mutant phenotype with the SaClCc1 gene indicates the involvement of the SaClCc1 protein in the transport of Cl^– ions.     

Cytochrome P<Subscript>450</Subscript>, CYP93A1, as defense marker in soybean

Cytochrome P₄₅₀, CYP93A1, is involved in the synthesis of the phytoalexin glyceollin in soybean (Glycine max L. Merr). The gene encoding CYP93A1 has been used as defense marker in soybean cell cultures, however, little is known regarding how this gene is expressed in the intact plant. To further understand the tissue-specific role of CYP93A1 in soybean defense, we analyzed the expression of this gene in mechanically damaged leaves and stems. In leaves, CYP93A1 was constitutively expressed; its expression did not change in response to mechanical damage. In stems, however, expression of CYP93A1 was induced as quickly as 4 h after mechanical damage and remained upregulated for at least 48 h. The induction of CYP93A1 was associated with the synthesis of glyceollins. In comparison to several other defense-related genes encoding cysteine protease inhibitors L1 and R1 and storage proteins vspA and vspB, CYP93A1 was the most strongly induced by stem wounding. The induction of CYP93A1 was observed only locally, not systemically. Similar stem expression patterns were consistently observed among three different soybean genotypes. The strong induction of CYP93A1 in mechanically damaged stems suggests an important role in the soybean stem defense response; therefore, this study expands the use of CYP93A1 as a defense response marker to stems, not just soybean cell cultures.     

VeA of <Emphasis Type="Italic">Aspergillus niger</Emphasis> increases spore dispersing capacity by impacting conidiophore architecture

Aspergillus species are highly abundant fungi worldwide. Their conidia are among the most dominant fungal spores in the air. Conidia are formed in chains on the vesicle of the asexual reproductive structure called the conidiophore. Here, it is shown that the velvet protein VeA of Aspergillus niger maximizes the diameter of the vesicle and the spore chain length. The length and width of the conidiophore stalk and vesicle were reduced nearly twofold in a ΔveA strain. The latter implies a fourfold reduced surface area to develop chains of spores. Over and above this, the conidial chain length was approximately fivefold reduced. The calculated 20-fold reduction in formation of conidia by ΔveA fits the 8- to 17-fold decrease in counted spore numbers. Notably, morphology of the ΔveA conidiophores of A. niger was very similar to that of wild-type Aspergillus sydowii. This suggests that VeA is key in conidiophore architecture diversity in the fungal kingdom. The finding that biomass formation of the A. niger ΔveA strain was reduced twofold shows that VeA not only impacts dispersion capacity but also colonization capacity of A. niger.     

Blue light reduces photosynthetic efficiency of cyanobacteria through an imbalance between photosystems I and II

Several studies have described that cyanobacteria use blue light less efficiently for photosynthesis than most eukaryotic phototrophs, but comprehensive studies of this phenomenon are lacking. Here, we study the effect of blue (450 nm), orange (625 nm), and red (660 nm) light on growth of the model cyanobacterium Synechocystis sp. PCC 6803, the green alga Chlorella sorokiniana and other cyanobacteria containing phycocyanin or phycoerythrin. Our results demonstrate that specific growth rates of the cyanobacteria were similar in orange and red light, but much lower in blue light. Conversely, specific growth rates of the green alga C. sorokiniana were similar in blue and red light, but lower in orange light. Oxygen production rates of Synechocystis sp. PCC 6803 were five-fold lower in blue than in orange and red light at low light intensities but approached the same saturation level in all three colors at high light intensities. Measurements of 77 K fluorescence emission demonstrated a lower ratio of photosystem I to photosystem II (PSI:PSII ratio) and relatively more phycobilisomes associated with PSII (state 1) in blue light than in orange and red light. These results support the hypothesis that blue light, which is not absorbed by phycobilisomes, creates an imbalance between the two photosystems of cyanobacteria with an energy excess at PSI and a deficiency at the PSII-side of the photosynthetic electron transfer chain. Our results help to explain why phycobilisome-containing cyanobacteria use blue light less efficiently than species with chlorophyll-based light-harvesting antennae such as Prochlorococcus, green algae and terrestrial plants.