THE MODE OF INTERACTION BETWEEN BLUE (UV) LIGHT PHOTORECEPTOR AND PHYTOCHROME IN ANTHOCYANIN FORMATION OF THE SORGHUM SEEDLING

Two non-photosynthetic photoreceptors (phytochrome and a blue light photoreceptor) are involved in light-mediated anthocyanin synthesis in the mesocotyl of Sorghum seedlings. The present study was undertaken to investigate the kind of interaction between phytochrome and the blue light photoreceptor. The data show that phytochrome (P_fr) can only act once a blue light effect has occurred. On the other hand, the blue light effect cannot express itself without P_fr. It is concluded that there is an obligatory dependency (or sequential interaction) between the blue light effect and the light effect occurring through phytochrome, although the blue light photoreaction per se is not affected by the presence or absence of phytochrome. The latter statement is based on the results of dichromatic experiments, i.e. simultaneous, high fluence rate irradiation with two kinds of light. Blue light can be replaced by UV light. It is not clarified yet whether the effect of blue and UV light is due to the same photoreceptor.     

Light-induced absorbance changes in cell-free extracts of Neurospora crassa.

Abstract— The mycelium of Neurospora crassa was ground and extracted with buffer and separated into a soluble supernatant fraction and a particulate fraction by centrifugation. Both fractions were examined for light-induced absorbance changes. Irradiation of the supernatant fraction caused a reversible photooxidation of cytochrome c which was inhibited by sodium azide or by dialysis. The action spectrum for the photooxidation showed that the response was mediated by an endogenous flavin. The photooxidation of cytochrome c, lost by dialysis, could be restored by adding flavin mononucleotide. Irradiation of the particulate fraction with blue light caused a reversible photoreduction of cytochrome c and cytochrome oxidase and, in some samples, of cytochrome b as well. The supernatant fraction showed photooxidation of cytochrome c rather than the more usual photoreductive changes because of the presence of super-oxide dismutase activity.     

INTERACTION BETWEEN PHYTOCHROME AND THE BLUE LIGHT PHOTORECEPTOR SYSTEM IN Mougeotia*

Abstract— Face-to-profile chloroplast movement in Mougeotia was induced by sequences of strong blue and red short irradiations. This type of response occured only when blue light was applied prior to or simultaneously with red light, and far-red irradiation was necessary after the sequence to cancel the remaining gradient of the far-red absorbing form of phytochrome P_fr. The dependence of the response magnitude on blue and red light sequences was studied for a wide range of light durations and dark intervals. The relationship between the response and the dark interval points to the lack of direct coupling between phytochrome and blue-absorbing “cryptochrome”. It was postulated that a photoproduct having a life-time of2–3 min is formed by the blue-light-mediated reaction. This photoproduct interacts with phytochrome during its transformation or with its final P_fr form.     

Evaluation of Photocatalytic Activity by Dye Decomposition

A novel rapid evaluation method for the photocatalytic activity of TiO₂ thin films was developed. An organic dye with a polyvinyl alcohol (PVA) binder was spin coated on the TiO₂ thin film, and the decrease in the absorbance of the dye's absorption peak during UV light irradiation was measured. Acid Blue 9 (Brilliant Blue FCF; CI-42090) could be used as the probe, while Methylene Blue (CI-52015) was not applicable to this method because of the reversible color change after the UV irradiation was stopped. PVA has virtually no interaction with oxidizing radicals, therefore, it is regarded as a simple binder holding dye molecules in the coated dye-PVA film. It was found that the ambient humidity during the UV irradiation strongly accelerates the discoloration rate of the dye, probably due to the increase in the photogenerated oxidizing radicals on the TiO₂ surface. This dye discoloration could be explainedby the one-dimensional diffusion model with a first order reaction.     

Biphasic fluence-response curves and derived action spectra for light-induced absorbance changes in Phycomyces mycelium

The photoresponses of Phycomyces, including phototropism and photocontrol of sporangiophore development, are mediated primarily by blue and UV light. Recent results on these two responses indicated a subsidiary role for green light. We have measured in vivo light-induced absorbance changes (LIAC) in mycelial samples of a caroteneless (carB) strain to compare the effectiveness of UV, blue, and green light. In the dual-wavelength kinetic mode of the spectrophotometer, measuring wavelengths of 445 and 470 nm were chosen, because green light produces substantial absorbance changes between these two wavelengths. Fluence-response curves were measured for 13 wavelengths between 365 and 530 nm, and for variable exposure times between 0.5 and 320 s. With one exception (365 nm), the curves were biphasic. The low fluence component was generally sigmoidal with an abrupt rise. The high fluence component failed to reach saturation for the fluences tested (less than 70 μmol m⁻² s⁻¹). Using the inferred threshold fluences of these two components as criterion effects, we obtained two action spectra. For the low fluence component, the action spectrum showed major peaks at 394, 450, and 530 nm and a minor peak at 416 nm. The high fluence component action spectrum showed very little sensitivity in the blue region. The major sensitivity was in the near UV, and a relatively small peak appeared in the green part of the spectrum at 507 nm. The biphasic character of the fluence-response curves suggests that two photosystems are responsible for the absorbance changes. The low fluence photosystem is sensitive mainly to blue and UV light and may thus represent a physiological blue-light photoreceptor. The high fluence photosystem is clearly not of this type. It (and perhaps the low fluence system as well) may mediate some of the subsidiary physiological effects of green light.     

Improving mechanical properties and chemical resistance of ink‐jet printer color filter by using diblock polymeric dispersants

The diblock copolymers of polystyrene and poly(tert‐butyl acrylate) (PSt‐b‐PtBA) with various molecular weights and hydrophobic/hydrophilic (styrene/acrylic acid) chain length were prepared by atom transfer radical polymerization (ATRP). Selective hydrolysis of the diblock copolymers (PSt‐b‐PtBA) resulted in amphiphilic block copolymers of polystyrene and poly(acrylic acid) (PSt‐b‐PAA). The amphiphilic block copolymers of PSt‐b‐PAA with average molecular weight (M_n) <7500 were proved to be critical in dispersing the pigments of UV curable ink‐jet inks for manufacturing the color filter. Incorporating DB2 diblock copolymer dispersants with styrene/acrylic acid ratio at 1.5 allowed more UV curable compositions in the red and blue inks without deteriorating pigment dispersing stability and jetting properties of the ink‐jet inks. The ink drops can be precisely ejected into the tiny color area. Better properties of the cured red stripe such as nanoindentation hardness and chemical resistance were found. The competing absorption of UV light by the blue pigment hindered the through cure of monomers near the interface between glass substrate and the blue stripe. This leads to lower hardness and poor chemical resistance of the UV cured blue stripe. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3337–3353, 2005     

BLUE AND WHITE LIGHT EFFECTS ON CHLOROPLAST DEVELOPMENT IN A SOYBEAN MUTANT

Phenotypic difference for chloroplast development between the normal green (CL1) and the Cy₉y₉ soybean mutant was observed when the plants were grown under 18W m^?2 white or blue light. Under these conditions the mutant soybean accumulated less Chi b, neoxanthin, carotene and less total pigment than the CL1 genotype. Chloroplasts of the Cy₉y₉ line were deficient in the LHP complex relative to that of chloroplasts from the normal soybean. Specific differences were noted between chloroplasts from plants grown under blue and white light. Accumulations of a 34 kD (PSII) and a 16–17 kD (PSI) membrane polypeptide were decreased by blue light in both soybean genotypes. Blue light induced a greater accumulation of a 32 kD (PSII) polypeptide than white light. Blue light reduced granal thylakoid stacking and increased the proportion of stroma thylakoids compared to those that developed under white light. PSI electron transport activity was stimulated by the blue light treatment more than that of PSII.     

Light‐Regulated Polymerization under Near‐Infrared/Far‐Red Irradiation Catalyzed by Bacteriochlorophyll a

Photoregulated polymerizations are typically conducted using high‐energy (UV and blue) light, which may lead to undesired side reactions. Furthermore, as the penetration of visible light is rather limited, the range of applications with such wavelengths is likewise limited. We herein report the first living radical polymerization that can be activated and deactivated by irradiation with near‐infrared (NIR) and far‐red light. Bacteriochlorophyll a (Bachl a) was employed as a photoredox catalyst for photoinduced electron transfer/reversible addition–fragmentation chain transfer (PET‐RAFT) polymerization. Well‐defined polymers were thus synthesized within a few hours under NIR (λ=850 nm) and far‐red (λ=780 nm) irradiation with excellent control over the molecular weight (M_n/M_w<1.25). Taking advantage of the good penetration of NIR light, we showed that the polymerization also proceeded smoothly when a translucent barrier was placed between light source and reaction vessel.     

Electric Field‐Assisted Photochemical Water Splitting Should Operate with 287 nm Light

The major photoreaction of water is the homolytic splitting of one O–H bond starting from the 1¹B₁ excited state (λ_max = 167 nm). This reaction produces H? and ?OH radicals. The combination of two H? atoms leads to the potential energy carrier dihydrogen. However, the energy required to obtain the photoreactive 1¹B₁ electronic state is about 7.4 eV, which cannot be effectively provided by solar radiation. The sun light spectrum on earth comprises the visible and ultraviolet region, but shows vanishing intensity near 7 eV (177.1 nm). This work provides theoretical evidence that the photoreactive 1¹B₁ state of water can be shifted into the ultraviolet (UV‐B) light region (≈287 nm) by including explicitly an electric field in the calculations of the water absorption spectrum. To accomplish such bathochromic shift, a large field strength of 3.08 VÅ^?1 is required. The field‐dependent excitation energies were calculated by applying the symmetry‐adapted cluster configuration interaction (SAC‐CI) procedure. Based on this theoretical analysis, we propose that photochemical water splitting can be accomplished by means of 287 nm light provided the water molecule is favorably oriented by an external electric field and is subsequently activated by a reversal of the field orientation.     

BLUE and NEAR ULTRAVIOLET REVERSIBLE PHOTOREACTION IN THE INDUCTION OF FUNGAL CONIDIATION

Abstract— The effects of blue light and near UV light on the induction of conidiation in the fungus, Aliernuriu tomato, were investigated. Induction of conidiation was repeatedly controlled by alternating doses of near UV light and blue light. When the final light was near UV, conidiation was induced and conidia developed in the following darkness; when it was blue, the induction of conidiation was suppressed. When conidiation was induced by irradiation with a light mixed with near UV and blue, not only the time lag for inducing conidiation but also the amount of conidia formed were regulated by the fluence rates of both those lights.
Thus, 'mycochrome' is considered to function as a photoreceptor system in the induction of conidiation of this fungus.     

Stabilization of phytochrome intermediates by low temperature

Abstract— The photocon versions between the red-absorbing form (P_r) and the far-red absorbing form (P_fr) of phytochrome were examined at low temperatures. Partially purified preparations of the chromoprotein were examined in phosphate buffer and in 25 per cent buffer plus 75 per cent glycerol. Actinic irradiation of P, below – 150°C produces an intermediate with maximum absorbance near 695 nm, R₆₉₅. Actinic irradiation of R₆₉₅ converts it back to P. Above – 150°C R₆₉₅ decays to a low extinction form of phytochrome, R, which in turn decays to P_fr upon further warming. Light absorption by P_fr below – 150°C results in the formation of an intermediate form of phytochrome with maximum absorbance near 660 nm, FR₆₆₀. FR₆₆₀ decays upon warming to a lower extinction form, FR'. which in turn decays to P_r on continued warming. No evidence was obtained to suggest that any of the observed intermediate states are involved in more than one direction of phytochrome photocon version.     

UV Sensitivity of Vegetative and Reproductive Tissues of Two Antarctic Brown Algae is Related to Differential Allocation of Phenolic Substances

UV sensitivity of the vegetative and reproductive tissues of two Antarctic brown macroalgae was compared. Photosynthesis as well as the content and localization of phenolic substances were determined. Responses to UV radiation were quantified as chlorophyll fluorescence (F_v/F_m). Ascoseira mirabilis showed high UV tolerance, while in Cystosphaera jacquinotii F_v/F_m decreased by 15–21%, the receptacles being more tolerant than the vegetative blades. The phlorotannin contents showed an opposite pattern: the soluble fraction dominated in C. jacquinotii while in A. mirabilis the insoluble fraction was more abundant. Soluble phlorotannins were higher in the reproductive than in vegetative tissues in both species. Images of tissue cross‐sections under violet‐blue light excitation confirmed a high allocation of phenolic compounds (as blue autofluorescence) in C. jacquinotii, both in reproductive and vegetative blades. The allocation and proportions of the soluble and insoluble phlorotannins could be related with the observed UV tolerance of the vegetative and reproductive tissues.     

Bistable Retinal Schiff Base Photodynamics of Histidine Kinase Rhodopsin HKR1 from Chlamydomonas reinhardtii

The photodynamics of the recombinant rhodopsin fragment of the histidine kinase rhodopsin HKR1 from Chlamydomonas reinhardtii was studied by absorption and fluorescence spectroscopy. The retinal cofactor of HKR1 exists in two Schiff base forms RetA and RetB. RetA is the deprotonated 13‐cis‐retinal Schiff base (RSB) absorbing in the UVA spectral region. RetB is the protonated all‐trans RSB absorbing in the blue spectral region. Blue light exposure converts RetB fully to RetA. UVA light exposure converts RetA to RetB and RetB to RetA giving a mixture determined by their absorption cross sections and their conversion efficiencies. The quantum efficiencies of conversion of RetA to RetB and RetB to RetA were determined to be 0.096 ± 0.005 and 0.405 ± 0.01 respectively. In the dark thermal equilibration between RetA and RetB with dominant RetA content occurred with a time constant of about 3 days at room temperature. The fluorescence emission behavior of RetA and RetB was studied, and fluorescence quantum yields of ?_F(RetA) = 0.00117 and ?_F(RetB) = 9.4 × 10^?5 were determined. Reaction coordinate schemes of the photodynamics are developed.     

Cyclic methacrylic acid oligomer as a novel pH‐sensitive carrier material

The pH effect of inclusion of methylene blue (MB) in cyclic methacrylic acid oligomer (CMAA) with degree of polymerization 14, which was a novel cationic host material with pK_a 4.83, was investigated in methanol. The self‐diffusion coefficients of MB in methanol at pH 7.0 and 4.0 with and without CMAA were measured by ¹H‐NMR spectrometry with pulsed‐field‐gradient stimulated‐echo pulse (PGSE) analysis. At both pH values, the addition of CMAA to MB solution resulted in the complex formation between CMAA and MB. MB was included in CMAA in methanol at a wide range of pH. The molar fraction of the slow diffusion component corresponding to the complex increased by varying the pH from 7.0 to 4.0. Then, SiO–CMAA was synthesized by immobilization of CMAA on silica gel beads. The time dependence of adsorption of MB to SiO–CMAA was investigated by UV–Vis spectrometry. At pH 7.0, the absorbance of MB–methanol solution gradually decreased by the addition of SiO–CMAA. The absorbance drastically decreased on varying the pH from 7.0 to 4.0, and the absorbance quickly increased on varying the pH from 4.0 to 7.0. The inclusion of MB in CMAA was fast and reversible on changing the pH of the solution. CMAA was the novel pH sensitive host material. Inclusion of MB in CMAA enhanced at pH 4.0 rather than at pH 7.0. Copyright © 2008 John Wiley & Sons, Ltd.     

Isomerism and Blue Electroluminescence of a Novel Organoboron Compound: BIII2(O)(7-azain)2Ph2

Bright blue light with a maximum at 450 nm is emitted by both structural isomers of the novel, stable B^III₂(O)(7-azain)₂Ph₂ (7-azain=7-azaindole anion) on irradiation with UV light. The isomer shown in the picture has approximate C₂ symmetry (the other isomer approximate C_s symmetry) and electroluminesces when used as the emitting layer in an electroluminescent device.     

A FLAVOPROTEIN MAY MEDIATE THE BLUE LIGHT-ACTIVATED BINDING OF GUANOSINE 5'-TRIPHOSPHATE TO ISOLATED PLASMA MEMBRANES OF Pisum sativum L.*

Abstract— A blue light photoreceptor has not been identified in higher plants. Most proposals for a blue light-absorbing chromophore lack evidence for a direct connection between the putative chromophdre and a biological effect. Fluorescence data for the plasma membrane from etiolated buds of Pisum sativum L. suggest that we are measuring fluorescence emission of flavin species, and probably not pterin species. Fluorescence data indicate that a putative flavin exists associated with a protein or protein complex in the plasma membrane. Excitation of plasma membranes that were boiled in the presence of 0.1% sodium dodecyl sulfate and treated with blue light yields a fluorescence band with a maximum of approximately 552 nm. This fluorescence emission can be rapidly quenched by the flavin antagonists phenylacetic acid (PAA) and KI. Blue light-enhanced binding of guanosine 5'-[Γ-thio]triphosphate (GTPγS) to a protein in the plasma membrane is strongly inhibited by PAA, KI, and NaN₃, all quenchers of flavin excited states, indicating that a chromophore for this photoreaction may be a flavin associated with a plasma membrane protein. The above evidence is consistent with the participation of a flavin as the chromophore for the light-induced GTP-binding reaction in pea plasma membrane.     

Comparison of irreversible and reversible cluster formation

Covalent and reversible cluster molecules were synthesized by an A₃B₂ type gelation. Crosslinking of three-arm hydroxyl-terminated star polymers with 2,4-toluenediisocyanate gave branched polymers, while the reversible analogue was made by crosslinking of tertiary amine-terminated star polymers with bis(4-hydroxy-3,5-dinitrophenyl) adipate. Gelation process was followed by static and dynamic light scattering. The extent of reacted groups was measured with UV spectroscopy. Growth of the covalent clusters could be described in terms of percolation scaling laws. The experimental gel point (P_{OH, cr} = 0.70) was shifted significantly from the theoretical predicted gel point (P_{OH, cr} = 0.50), indicating extensive ring formation during the gelation. The reversible endlinking reaction gave no macroscopic gelation, though increase of the cluster dimensions was observed. Ring formation proved to be an important side reaction in both cases; however, the ring formation ability seems to change in a different manner during the course of a gelation.     

Increased Antioxidant Activity and Changes in Phenolic Profile of Kalanchoe pinnata (Lamarck) Persoon (Crassulaceae) Specimens Grown Under Supplemental Blue Light

Antioxidant compounds protect plants against oxidative stress caused by environmental conditions. Different light qualities, such as UV‐A radiation and blue light, have shown positive effects on the production of phenols in plants. Kalanchoe pinnata (Lamarck) Persoon (Crassulaceae) is used for treating wounds and inflammations. Some of these beneficial effects are attributed to the antioxidant activity of plant components. We investigated the effects of blue light and UV‐A radiation supplementation on the total phenol content, antioxidant activity and chromatographic profile of aqueous extracts from leaves of K. pinnata. Monoclonal plants were grown under white light, white plus blue light and white plus UV‐A radiation. Supplemental blue light improved the antioxidant activity and changed the phenolic profile of the extracts. Analysis by HPLC of supplemental blue‐light plant extracts revealed a higher proportion of the major flavonoid quercetin 3‐O‐α‐l ‐arabinopyranosyl (1→2) α‐l ‐rhamnopyranoside, as well as the presence of a wide variety of other phenolic substances. These findings may explain the higher antioxidant activity observed for this extract. Blue light is proposed as a supplemental light source in the cultivation of K. pinnata, to improve its antioxidant activity.     

BLUE LIGHT PERCEPTION BY ENDOGENOUS REDOX COMPONENTS OF THE PLANT PLASMA MEMBRANE

b-Type cytochromes of the higher plant plasma membrane may be reduced by irradiation with actinic blue light (light-induced absorbance change). Although this reaction has been reported to depend on the presence of an exogenous oxygen-scavenging system, significant cytochrome reduction was obtained in bean hook (Phaseolus vulgaris L. cv. “Limburgse Vroege”) plasma membranes without any addition. An endogenous oxygen-consuming reaction is apparently sufficient to achieve a proper redox balance. A blue light-mediated absorbance change with absorbance minima at 450 and 475 nm precedes cytochrome b reduction and indicates the presence of a flavoprotein in the plasma membrane fraction. Cytochrome b reduction by blue light in the absence of an oxygen scavenger is highly sensitive to flavin photosensitizers. Glucose oxidase, which has previously been used to lower the oxygen concentration in membrane samples, was demonstrated to have a photosensitizing effect. Inhibitors of flavin photochemical reactions (KI and phenylacetic acid) were highly effective in preventing cytochrome b reduction. These results indicate that the blue light-mediated reaction probably involves an endogenous plasma membrane flavoprotein as the photoreceptor. As plasma membrane NADH-dependent oxidoreductases potentially are flavoproteins these experiments raise the question whether a plasma membrane cytochrome b and a flavin-enzyme may cooperate in blue light reactions. Evidence is also discussed, suggesting the possible involvement of oxygen radicals in the blue light-induced cytochrome b reduction.     

COOPERATIVITY OF THE DEHYDRATION BLUE-SHIFT OF BACTERIORHODOPSIN*

Abstract– Dehydration of purple membrane (PM) causes a hlue-shift of the absorbance maximum from 570 nm to about 530 nm [Lazarev and Terpugov (1980) Biochim. Biophys. Acta 590 .324–338; Hildebrandt and Stockburger (1984) Biochemistry 23 ,5539–5548]. The absorbance spectra of PM dried in films at pH 0, 7 and 11 were measured at controlled relative humidities (RH). At pH 7, a blue-shift was observed similar to that previously reported. At pH 0(1M H₂SO₄) a reversible transition was observed from the “acid blue membrane” (maximum near 600 nm at 100% RH) to a blue-shifted dehydrated pigment (maximum near 578 nm at 50% RH), with isosbestic points at 592 and 710 nm. At pH 11 (NaOH) the absorbance maximum shifted to 530 nm, similar to the dehydrated form at pH 7. The fraction of hydrated chromophore, X_h, was calculated (assuming only two chromophore states, hydrated and dehydrated) as a function of humidity and pH. The resulting curve at pH 7 showed a steep decline in X_h below 20% RH. Near this hydration level, water clusters on protein surfaces break up, causing side-chain pK reversals. The Hill coefficient for the transition was about 2, indicating the minimum number of water molecules involved in a cooperative transition. The results suggest that as few as two water molecules are coordinated to the protonated retinal Schiff base of bacteriorhodopsin. A mechanism for the pH 7 dehydration blue-shift is proposed, involving a pK reversal of the protonated Schiff base and a nearby carboxyl side chain. At pH 0, a sharp decline in X_h occurs between 100 and 70% RH. Near this hydration level, complete protein surface coverage by a water monolayer occurs. The Hill coefficient is about 20, suggesting involvement of a large region of the surface.