Photophobic stop-response in a dinoflagellate: Modulation by preirradiation

Gyrodinium dorsum Kofoid responds photophobically to flashes of blue light. The photophobic response consists of a cessation of movement (stop-response). Without background light and after a flash fluence above 10 J m⁻², 75–85% of the cells show a stop-response, while only 50% of the cells show this response at 5 J m⁻². With a flash fluence of 5 J m⁻², background light of different wavelengths either increases (614 nm. 5.5–18.2 μmol m⁻² s⁻¹) or decreases (700 nm, 18.4–36.0 μmol m⁻² s⁻¹) the stop-response. Two hypotheses for the mechanism of the modulation by background light of the photophobic response are discussed: an effect of light on the balance of the photosynthetic system (PS I/PS II) or an effect on a phytochrome-like pigment (P_r/P_fr). This study supports the idea that a phytochrome-like pigment works in combination with a blue light-absorbing pigment. It was also found that cells of Gyrodinium dorsum cultured in red light (39.8 μmol m⁻²) had a higher absorption in the red region of the absorption spectra than those cultured in white light (92.7 μmol m⁻²).     

Spatial-specific regulation of root development by phytochromes in Arabidopsis thaliana

Distinct tissues and organs of plants exhibit dissimilar responses to light exposure – cotyledon growth is promoted by light, whereas hypocotyl growth is inhibited by light. Light can have different impacts on root development, including impacting root elongation, morphology, lateral root proliferation and root tropisms. In many cases, light inhibits root elongation. There has been much attention given to whether roots themselves are the sites of photoperception for light that impacts light-dependent growth and development of roots. A number of approaches including photoreceptor localization in planta, localized irradiation and exposure of dissected roots to light have been used to explore the site(s) of light perception for the photoregulation of root development. Such approaches have led to the observation that photoreceptors are localized to roots in many plant species, and that roots are capable of light absorption that can alter morphology and/or gene expression. Our recent results show that localized depletion of phytochrome photoreceptors in Arabidopsis thaliana disrupts root development and root responsiveness to the plant hormone jasmonic acid. Thus, root-localized light perception appears central to organ-specific, photoregulation of growth and development in roots.     

Factors affecting the inactivation of micro-organisms by intense light pulses

AIM: To determine the influence of several factors on the inactivation of micro-organisms by intense light pulses (ILP). METHODS AND RESULTS: Micro-organisms on agar media were flashed 50 times under different conditions and their inactivation measured. Micro-organisms differed in sensitivity to ILP but no pattern was observed among different groups. Several enumeration methods to quantify the effect of ILP were investigated and showed relevant differences, shading effect and photoreactivation accounted for them, the strike method yielded the most reliable results. Higher decontamination efficiencies were obtained for Petri dishes located close to the strobe and inside the illumination cone. Decontamination efficacy decreased significantly at contamination levels >6.85 log(10). After 13 successive treatments, no resistance to ILP could be demonstrated. Media warming up depended on the distance from the strobe and the number of flashes. CONCLUSIONS: For an industrial implementation: the position and orientation of strobes in an unit will determine the lethality, products should be flashed as soon as possible after contamination occurs, a cooling system should be used for heat-sensitive products and flashed products should be light protected. No resistant flora is expected to develop. SIGNIFICANCE AND IMPACT OF THE STUDY: Conclusions derived from this work will allow a better implementation of this decontamination technique at industrial level.     

The importance of PS I chlorophyll red forms in light-harvesting by leaves

We have investigated the importance of the long wavelength absorbing spectral forms (red forms) of Photosystem I in photosynthetic light harvesting by leaves. To this end leaf spectra were simulated by using a linear combination of absorption (OD) spectra of purified Photosystem I, Photosystem II and LHC II, multiplied by an empirical multiple scattering chloroplast/leaf conversion function. In this way it is demonstrated that while the PS I red forms account for only about 4–5% of light absorption in a normal daylight environment, in different shadelight environments these long wavelength pigments may be responsible for up to 40% of total photon capture. In the context of maximising the photosynthetic quantum efficiency under the low light conditions of shadelight, this relative increase in the absorption cross section of PS I can be understood by considering the increased synthesis of the major PS II antenna complex, LHC II, known to occur in plants growing under these light conditions. It is demonstrated that for plants in a moderate to deep shadelight regime the PS II cross section needs to increase by 50% to 100% via LHC II synthesis to balance the increased PS I absorption by the red forms. The possibility that under shade light conditions the increased PS I cross section may serve in cyclic phosphorylation is also discussed.     

Changes in alkaline phosphatase activity and phosphate uptake in P-limited phytoplankton,induced by light intensity and spectral quality

Alkaline phosphatase activity and P uptake were determined in P-limited Dunaliella tertiolecta, Thalassiosira pseudonana, Phaeodactylum tricornumtum, and Prymnesium parvum grown under different light intensities and colors. Both intracellular and extracellular enzyme activities varied with the intensity and quality of light in a species-specific manner. The spectral composition of the light also affected P uptake kinetics. No correlation was found between enzyme activity and V_max both within a species and for pooled data for all four species, indicating that the change in uptake kinetics and enzyme activity was not related to P limitation, but induced by the light conditions. Changes in the optimum N:P ratio induced by light were also not related to P uptake kinetics or enzyme activity. These data suggest that light conditions may in themselves have profound effects on species competition for limiting nutrients. Furthermore, since both alkaline phosphatase activity and P uptake were influenced by the prevailing light conditions we suggest that these parameters be used cautiously when determining the P nutritional status of phytoplankton in nature.Address for reprint requests     

Assessment of lighting needs by W-36 laying hens via preference test

Light intensity, spectrum and pattern may affect laying hen behaviors and production performance. However, requirements of these lighting parameters from the hens’ standpoint are not fully understood. This study was conducted to investigate hens’ needs for light intensity and circadian rhythm using a light tunnel with five identical compartments each at a different fluorescent light intensity of <1, 5, 15, 30 or 100 lux. The hens were able to move freely among the respective compartments. A group of four W-36 laying hens (23 to 30 weeks of age) were tested each time, and six groups or replicates were conducted. Behaviors of the hens were continuously recorded, yielding data on daily time spent, daily feed intake, daily feeding time, and eggs laid under each light intensity and daily inter-compartment movement. The results show that the hens generally spent more time in lower light intensities. Specifically, the hens spent 6.4 h (45.4%) at 5 lux, 3.0 h (22.1%) at 15 lux, 3.1 h (22.2%) at 30 lux and 1.5 h (10.3%) at 100 lux under light condition; and an accumulation of 10.0 h in darkness (<1 lux) per day. The 10-h dark period was distributed intermittently throughout the day, averaging 25.0±0.4 min per hour. This hourly light-dark rhythm differs from the typical commercial practice of providing continuous dark period for certain part of the day (e.g. 8 h at night). Distributions of daily feed intake (87.3 g/hen) among the different light conditions mirrored the trend of time spent in the respective light intensity, that is, highest at 5 lux (28.4 g/hen, 32.5% daily total) and lowest at 100 lux (5.8 g/hen, 6.7%). Hen-day egg production rate was 96.0%. Most of the eggs were laid in <1 lux (61.9% of total) which was significantly higher than under other light intensities (P<0.05). Findings from this study offer insights into preference of fluorescent light intensity by the laying hens. Further studies to assess or verify welfare and performance responses of the hens to the preferred lighting conditions and rhythm over extended periods are recommended.     

Removal and transformation of high molecular weight polycyclic aromatic hydrocarbons in water by live and dead microalgae

The removal and transformation of seven high molecular weight polycyclic aromatic hydrocarbons (PAHs), namely benz[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, indeno[1,2,3-c,d]pyrene and benzo[g,h,i]perylene, by a freshwater microalga Selenastrum capricornutum under gold and white light irradiation was studied. The two light sources did not result in significant differences in the biodegradation of the selected PAHs in live algal cells, but white light was more effective in promoting photodegradation than was gold light in dead cells. The removal efficiency of seven PAHs, as well as the difference between live and dead microalgal cells, was PAH compound-dependent. Benz[a]anthracene and benzo[a]pyrene were highly transformed in live and dead algal cells, and dead cells displayed greater transformation levels than live cells. Further investigation comparing the transformation of single PAH compound, benzo[a]pyrene, by S. capricornutum and another green microalgal species, Chlorella sp., demonstrated that the transformation in dead cells was similar, indicating the process was algal-species independent. Dead algal cells most likely acted as a photosensitizer and accelerated the photodegradation of PAHs.     

Light-dependent inhibition of photosynthetic electron transport by zinc

The effects of zinc concentrations up to 400 μ M were examined on three photosynthetic electron transport reactions of thylakoids isolated from Pisum sativum L. cv. Meteor. Zinc (400 μ M ) had no effect on photosystem I mediated electron transport from reduced N,N,N',N'-tetramethyl- p -phenylenediamine to methyl viologen, but inhibited uncoupled electron flow from water to methyl viologen by ca 50% and to 2,6-dichlorophenol-indophenol (DCPIP) by ca 30% at saturating light levels. Zinc inhibition of DCPIP photoreduction was independent of the light intensity to which thylakoids were exposed. Decreasing the photon flux density below 400 μmol m⁻² s⁻¹ produced a logarithmic reduction in the zinc-induced inhibition of methyl viologen photoceduction; a stimulation of this reaction was observed below 80 μmol photons m⁻² s⁻¹. Increasing light intensity decreased the amount of zinc tightly bound to the thylakoid membranes, but increased the weakly associated zinc which could be removed by washing the membranes with buffer containing Mg². The results suggest that zinc acts on the photosynthetic electron transport system at two sites. Site 1 is on the oxidizing side of photosystem 2 and the inhibition by zinc is independent of the light intensity. Site 2 is between photosystems 1 and 2 and the electron flow can be positively or negatively affected by zinc depending on the light intensity.     

Blue light emission spectra of popular mobile devices: The extent of user protection against melatonin suppression by built-in screen technology and light filtering software systems

ABSTRACT

Blue light, with wavelengths shorter than 440–450 nm, is the most energetic radiation of the visible spectrum for the human eye, and its possible multiple effects on the human nervous and other systems have become a line of research by many investigators. The use of mobile devices whose screens emit various amounts of blue light is common nowadays. This study evaluated the efficiency of the blue light screen and control software technologies of eight different mobile devices. Emitted screen spectra of the different mobile devices according to different conditions of blue light emission software control were obtained using a spectrograph, and the derived spectra were compared with the melatonin suppression action spectrum. The amount of blue light emission and predicted melatonin suppression varied according to the unique software control and screen technology of each device. AMOLED screen technology, compared with other screen technologies, achieved better control of blue light emission. The effect of blue light filters depends on the screen technology; however, the melatonin suppression index of mobile devices is not reduced sufficiently by the use of blue light-attenuating software.     

Rapid diagnosis of phenylketonuria and other aminoacidemias by quantitative analysis of amino acids in neonatal blood spots by gas chromatography-mass spectrometry

A reversed-phase HPLC method compatible with evaporative light scattering (ELS) and electrospray mass spectrometric (ES-MS) detection was developed for separation of phosphatidylserine (PS) molecular species. The method was optimised for separation of three disaturated synthetic species: dipalmitoyl glycerophosphoserine, palmitoyl-stearoyl glycerophosphoserine and distearoyl glycerophosphoserine using isocratic elution with a mixture of 2-propanol, tetrahydrofuran and ammonium formate. Baseline separation was obtained on three different columns: one polystyrene/divinylbenzene (PS/DVB) column and two silica based C(18) and C(30) columns. The best chromatographic resolution was achieved with the C(30) column. The limit of detection for DPPS was 5 microg/ml (S/N=3) with ELS detection and 0.1 microg/ml (S/N=3) with negative ion ES-MS in the single ion monitoring mode. Baseline separation of the five main species in a biological PS sample, bovine brain PS, was obtained with the PS/DVB column. Species identification was done by using the retention times of the intact PS species and their corresponding carboxylate anion fragments obtained by in-source fragmentation. Data have shown that individual PS species can be identified by their retention times using direct ELS detection in a mixture of disaturated PS species. However, for the bovine brain PS electrospray-MS detection was necessary for species identification due to the many possible fatty acid combinations in biological PS.     

Regulation by molluscan myosins

Molluscan myosins are regulated molecules that control muscle contraction by the selective binding of calcium. The essential and the regulatory light chains are regulatory subunits. Scallop myosin is the favorite material for studying the interactions of the light chains with the myosin heavy chain since the regulatory light chains can be reversibly removed from it and its essential light chains can be exchanged. Mutational and structural studies show that the essential light chain binds calcium provided that the Ca-binding loop is stabilized by specific interactions with the regulatory light chain and the heavy chain. The regulatory light chains are inhibitory subunits. Regulation requires the presence of both myosin heads and an intact headrod junction. Heavy meromyosin is regulated and shows cooperative features of activation while subfragment-1 is non-cooperative. The myosin heavy chains of the functionally different phasic striated and the smooth catch muscle myosins are products of a single gene, the isoforms arise from alternative splicing. The differences between residues of the isoforms are clustered at surface loop-1 of the heavy chain and account for the different ATPase activity of the two muscle types. Catch muscles contain two regulatory light chain isoforms, one phosphorylatable by gizzard myosin light chain kinase. Phosphorylation of the light chain does not alter ATPase activity. We could not find evidence that light chain phosphorylation is responsible for the catch state.     

The early time course of the inhibition of stem growth of etiolated pea seedlings by fluorescent light

The stem elongation responses of etiolated peas (Pisum sativum L.) to fluorescent light (35–45 mol.m^t-2.s^-1) were recorded using high resolution position transducers. Continuous fluorescent light decreased growth by 70% within 9 min. The growth rate declined to 5% of the control over the next 2 h and remained at this level for 7 h. Pulses of fluorescent light ranging from 8 s to 34 min led to partial suppression of growth and resulted in a complex kinetic response. The distinctive kinetics of blue and red light inhibition were apparent as components of the responses to non-saturating levels of fluorescent light. The rapid suppression of growth by blue light was not affected by concomitant red light. The lag time for the onset of red light inhibition was not affected by concomitant blue, but the rate of inhibition appeared accelerated.     

Entrainment of Arabidopsis roots to the light:dark cycle by light piping

Correct operation of the plant circadian clock is crucial for optimal growth and development. Recent evidence has shown that the plant clock is tissue specific and potentially hierarchical, implying that there are signalling mechanisms that can synchronise the clock in different tissues. Here, I have addressed the mechanism that allows the shoot and root clocks to be synchronised in light:dark cycles but not in continuous light. Luciferase imaging data from 2 different Arabidopsis accessions with 2 different markers show that the period of the root clock is much less sensitive to blue light than to red light. Decapitated roots were imaged either in darkness or with the top section of root tissue exposed to light. Exposure to red light reduced the period of the root tissue maintained in darkness, whereas exposure to blue light did not. The data indicate that light can be piped through root tissue to affect the circadian period of tissue in darkness. I propose that the synchronisation of shoots and roots in light:dark cycles is achieved by light piping from shoots to roots.     

Sporulatim in the fungus Verticillium agaricinum: Reversal of blue light inhibition by Ultraviolet radiation

In colonies ranging from 3- to 5-days-old, light in general stimulates conidiation in Verticillium , including V. agaricinum and several strains of V. albo-atrum . However, when growth was started by inoculating with conidial suspension spread evenly over the plate, it was found that blue light inhibited conidiation in our strain of V. egaticinum . We most light-sensitive phase was around 9 h after inoculation. A broad band blue light pulse of 10 J m⁻² saturated the response. The inhibitory effect of blue light could be reversed by a subsequent ultraviolet (UV) radiation, but a further effect of blue light was lost after the UV pulse. Blue light inhibition was also prevented by IJV radiation administered before the blue light.     

Motility of bovine spermatozoa studied by laser light scattering

Laser light scattering has been employed to determine the swimming speed distribution and the fraction of motile cells in samples of bovine spermatozoa. As predicted from theory, average trajectory velocities determined by laser light scattering were approximately four times the average translational speed estimated using light microscopy. The proportion of motile spermatozoa decreased with time at the same rate when samples were prepared in either HEPES or phosphate buffers. However, whereas the mean swimming velocity declined slowly in HEPES buffer, it dropped rapidly when phosphate buffer was used. Dilution (in the range 40–0.4×10⁶ spermatozoa·ml^-1) in either of these two buffers reduced the fraction of motile spermatozoa in the sample, but the mean swimming velocity of the remaining active spermatozoa was unchanged. Lowering the temperature from 37° C to 15° C reduced the mean swimming speed by a factor of 2–3 and the fraction of motile cells by a factor of 4–5.     

蓝光诱导促进黑曲霉产糖化酶的研究

考察了蓝光对黑曲霉产糖化酶的影响并采用扫描电镜观察蓝光下黑曲霉形态发育过程,结果表明,与黑暗对照组相比,蓝光处理使菌丝粗壮,孢囊增大,分生孢子发育提前,黑曲霉糖化酶活力增加,孢子发育和产糖化酶的进程有一定的对应性。黑曲霉在黑暗下生长至36h时,经蓝光诱导糖化酶产量提高更为明显,提示了黑曲霉存在一个对蓝光反应产生最适光感应的发育阶段,对于光调节黑曲霉产糖化酶来说,蓝光诱导的光强由弱到强,比持续蓝光培养或采用较高光强诱导效果更好,表明黑曲霉产糖化酶存在一种光适应机制,能够感应和适应光强度变化,调节其自身代谢。从抑制性扣除杂交实验和蓝光光强变化对差异基因表达的分析来看,糖化酶基因以及呼吸链中部分氧化还原酶基因在蓝光诱导下表达皆有增强,蓝光信号转导影响了核基因编码的线粒体呼吸链相关酶基因表达水平,交替氧化酶可能参与了蓝光信号途径,影响了黑曲霉产糖化酶和孢子发育。研究结果可为在现有水平上应用蓝光调节提高糖化酶产量找到新的技术突破口和提供新思路。     

Suppression by Red Light Irradiation of Corynespora Leaf Spot of Cucumber Caused by Corynespora cassiicola

The effect of red light irradiation on development of Corynespora leaf spot of cucumber plants (Cucumis sativus L. cv. Hokushin) caused by Corynespora cassiicola (Berk. & Court.) was investigated in greenhouses. In a greenhouse without red light (?Red), lesions enlarged, coalesced, and finally covered the entire leaves of cucumber. In a greenhouse with red light (+Red), however, lesion appearance was delayed relative to that under ?Red and its development was also significantly suppressed. Such difference in disease development was also observed in cucumbers grown under +Red and ?Red in the same greenhouse. Disease suppression under red light was also observed in glasshouse‐grown C. cassiicola‐inoculated cucumbers. Red light did not inhibit the infection behaviour of the pathogen. Our results indicated that the delay and suppression of Corynespora leaf spot of cucumber under +Red were due to induction of resistance in cucumber, and not to differences in environmental conditions or fungal population between the two greenhouses. Red light‐induced resistance might contribute to the development of new methods for controlling Corynespora leaf spot of greenhouse‐grown cucumber.     

Enhanced Light Harvesting in Perovskite Solar Cells by a Bioinspired Nanostructured Back Electrode

Light management holds great promise of realizing high‐performance perovskite solar cells by improving the sunlight absorption with lower recombination current and thus higher power conversion efficiency (PCE). Here, a convenient and scalable light trapping scheme is demonstrated by incorporating bioinspired moth‐eye nanostructures into the metal back electrode via soft imprinting technique to enhance the light harvesting in organic–inorganic lead halide perovskite solar cells. Compared to the flat reference cell with a methylammonium lead halide perovskite (CH₃NH₃PbI_3?x Cl_x ) absorber, 14.3% of short‐circuit current improvement is achieved for the patterned devices with moth‐eye nanostructures, yielding an increased PCE up to 16.31% without sacrificing the open‐circuit voltage and fill factor. The experimental and theoretical characterizations verify that the cell performance enhancement is mainly ascribed by the broadband polarization‐insensitive light scattering and surface plasmonic effects due to the patterned metal back electrode. It is noteworthy that this light trapping strategy is fully compatible with solution‐processed perovskite solar cells and opens up many opportunities toward the future photovoltaic applications.     

The effect of light intensity and spectrum on the incidence of first feeding by larval haddock

Under full–spectrum white light, feeding success of haddock Melanogrammus aeglefinus first feeding larvae, as measured both by proportion of larvae feeding and mean prey consumed, peaked at 1·7-18 μmol s^-1 m^-2. Feeding was significantly reduced at lower and higher intensities. A similar result was observed for larvae feeding under blue (470 nm) light, with significantly greater feeding success at intermediate light intensity (1·8 μmol s^-1 m^-2). When different light qualities were compared, larvae had significantly greater feeding success when exposed to blue (470 nm) light than either full-spectrum white or green (530 nm) light. Haddock larvae were capable of prey capture under all light treatments tested, indicating a necessary degree of adaptive flexibility in feeding response. The results are consistent with predisposition of haddock larvae to optimal feeding in a visual environment comparable with open ocean nursery grounds. Information on the impact of light on haddock first feeding can be incorporated into models of larval growth, survival, year-class strength and recruitment, and assist in developing husbandry protocols to maximize larval survival in aquaculture.