Weak Red Light Research Articles

Solid-state reaction synthesis of LuPO4:Yb3+, Tb3+ phosphors and the ultraviolet/near-infrared responsive spectra performances

Yb3+/Tb3+ co-doped LuPO4 phosphors were prepared by solid-state reaction method. The effects of Yb3+/Tb3+ doping concentrations on the downshifting and upconversion spectral performances of the synthesized phosphors were investigated. Upon the ultraviolet light excitation, the phosphors show obvious visible light emission, which can be assigned to the 5D4→7FJ (J=6, 5, 4, and 3) transitions of Tb3+ ions respectively, the green light emission at 543 nm is dominant. Upon 980 nm excitation, the phosphors display intense green and blue light emission, and weak yellow and red light emission, which originates from the cooperative energy transfer process between Yb3+ and Tb3+ ions. The synthesized LuPO4:Yb3+, Tb3+ phosphors show good ultraviolet/near-infrared responsive spectra, color-tunable and thermal-stability performances and may have potential applications in the related fields.

Luminescence Enhancement of K2LiAlF6:Mn4+ Phosphors by Zn2+-Mediated Charge Compensation for Fast-Response Backlighting Applications.

Wide-spectrum displays require narrow-band red phosphors activated by Mn4+, but most of them, such as K2SiF6:Mn4+, have long fluorescence decay lifetimes (>7 ms) that hinder their use in fast-response backlights. Interestingly, K2LiAlF6:0.05Mn4+ has a shorter fluorescence lifetime (3.43 ms), but its disadvantage is that its luminescence intensity is relatively weak. So, in this study, the luminescence intensity of K2LiAlF6:0.05Mn4+ is improved by doping with Zn2+. The experimental results show that enhancement of the luminous intensity is as high as 39%, the fluorescence lifetime is only increased by 13% (3.89 ms), and it is still less than 4 ms. Through experiments and differential charge density calculations, it has been revealed that the luminescence intensity improvement is due to an increased crystalline quality during the synthesis process. Specifically, the co-doping of Zn2+ reduces the formation of impurity ions Mn2+ and Mn3+ and the generation of K+ vacancies caused by nonequivalent doping. We demonstrate the advantage of this phosphor over K2SiF6:Mn4+ in terms of response speed by using a camera. It emits only weak red light after the blue chip stops working for 5 ms, indicating its potential application in next-generation fast-response displays.

Effects of Na+-doping on the structure and luminescence properties of Li1-xNaxBi(MoO4)2: Yb3+/Ho3+ phosphors

In this study, a series of Li1-xNaxBi (MoO4)2: 0.3 Yb3+, 0.01Ho3+ (x = 0–1) phosphors were prepared using a high-temperature solid-state reaction method. The as-prepared sample produced high-intensity green light (542 nm) and weak red light (646 nm) under the excitation of a 980 nm laser, which was generated by the radiative relaxation of 5S2/5F4→5I8 and 5F5→5I8 energy levels in Ho3+. We performed X-ray diffraction (XRD) tests on our samples, the XRD test data show that the incorporation of Yb3+ and Ho3+ shrank the lattice, and the luminescence intensity improved after doping with Na+. With an increase in Na+ concentration, two inflection points were observed in the luminescence intensity. The luminescence intensity was strongest when the Na+ concentration was 30% and 80%; moreover, it was also the inflection point of the 2θ value of the strongest diffraction peak (112) of the sample. By fitting the pump power and the up-converted luminescence intensity, it was inferred that the emission of one photon at 542 and 646 nm requires the absorption of three photons. Using the fluorescence decay time test, it was observed that the 2θ value corresponding to the strongest diffraction peak of the sample had a corresponding relationship with the fluorescence lifetime. Therefore, this study provides a reference for the further exploration of ion substituted upconversion luminescent materials.

Blue afterglow in Eu2+ doped CaAl2O4 by electron irradiation

1 mol% Eu2O3 – 99 mol% CaAl2O4 disc-shaped pellet sample was irradiated with a 5 keV electron beam on one of its surfaces to study the effects of electron bombardment on its structural, vibrational and photo-luminescence properties. X-ray diffraction studies found monoclinic phases of CaAl2O4 (major) and CaAl4O7 (minor) and the Raman spectra showed AlO bond vibrational bands in both the electron-irradiated and virgin (non-irradiated) sample surfaces. Electron irradiated surface has higher concentration of Eu2+ (strong blue light emission at 442 nm) than that of Eu3+ (weak red light emission at 616 nm) as compared to that in the virgin sample. Eu3+ reduce to Eu2+ with electron irradiation and this produces intense blue afterglow with a persistence time of ∼3 s, while the virgin surface exhibits orange-red light emission without afterglow effects.

Luminescence properties, crystal structure and high thermal stable of (Gd0.85-Lu )2MgTiO6: Eu3+ red phosphors

A series of double perovskite (Gd 0.85- x Lu x ) 2 MgTiO 6 : 0.3Eu 3+ red phosphors were prepared via a typical high temperature solid-state reaction. XRD and HRTEM exhibits that the phosphors well crystallized as a double perovskite with the space group of P21/n symmetry. The luminescent properties of samples were investigated via excitation and emission spectra. The phosphors emit strong red light and weak orange red light under ultraviolet (UV) and near-UV excitation suggesting that Eu 3+ ions situated in the sites without inversion symmetry. The UV–vis spectra included a broad host absorption band assigned to O 2- -Eu 3+ and some peaks at 395 nm, 465 nm and 533 nm attributed to the typical f-f transition of Eu 3+ . The CIE chromaticity coordinates of all samples were near to the standard red light, indicating that the (Gd 0.85- x Lu x ) 2 MgTiO 6 : 0.3Eu 3+ was a potential candidate material for red emitting phosphors. The decay curves matched with the lines fitted by a one exponential decay formula and the decay time increased with increasing Lu 3+ -dopant concentration within x < 0.8. The temperature-dependent emission spectra from 298 K to 473 K were used to evaluate the thermal stability of Gd 0.9 Lu 0.8 Eu 0.3 MgTiO 6 phosphors and the activation energy of Gd 0.9 Lu 0.8 Eu 0.3 MgTiO 6 for 5 D 0 - 7 F 2 transition was calculated to be 0.158eV. The results revealed that the phosphors have the excellent thermal stability and were promising material for applications in LEDs. • Enhance emission intensity by introducing Lu 3+ ions. • Monoclinic double perovskite with space group of P2 1 /n symmetry. • Keep thermally stability at temperature of 400 K.

Effects of removing temperature of reduction gas on the luminescence characteristics of Li2BaSiO4:0.003EU2+ green phosphor

We had successfully synthesized green-emitting phosphors based on Li2BaSiO4 material activated by bivalent europium ions (Eu[Formula: see text]) using a solid-state reaction method in a reducing gas environment and investigated their luminescence properties. The Li2BaSiO4:0.003Eu[Formula: see text] (LSB-Eu) phosphors were synthesized at 850[Formula: see text]C for 1 h, and the reduction gas was removed at 500[Formula: see text]C, 600[Formula: see text]C, 700[Formula: see text]C and 800[Formula: see text]C, respectively. XRD pattern showed that the Li2BaSiO4, Ba2SiO4 and Li4SiO4 phases were observed in the synthesized Li2BaSiO4 composition. As the reduction gas was removed at 800[Formula: see text]C, the LSB-Eu phosphor emitted a weak red light rather than a green light. Two weak emission peaks were found at about 588 nm and 613 nm corresponding to [Formula: see text] and [Formula: see text] transitions. As temperature to remove the reduction gas was lower than 800[Formula: see text]C, the emission spectra of LSB-Eu phosphors reveled a broad peak centered at 501 nm, which emitted a green color. The intensity of photoluminescence excitation (PLE) photoluminescence emission (PL) spectra increased as the removing temperature was decreased from 700[Formula: see text]C to 500[Formula: see text]C and saturated at 500[Formula: see text]C. These results show that LSB-Eu can be a noteworthy candidate of green-emitting phosphor for the investigation of white light-emitting diodes (WLEDs).

Impact of light quality (white, red, blue light and UV-C irradiation) on changes in anthocyanin content and dynamics of PAL and POD activities in apical and basal spear sections of white asparagus after harvest

Abstract Postharvest quality decay of white asparagus spears is often due to red discoloration of spear tips, caused by enhanced epidermal anthocyanin synthesis and accumulation. Exposure to light of different wavelengths triggers distinct physiological processes in plants leading to changes in pigments (e.g. phenolic compounds) and their associated enzymes, among them e.g. phenylalanine ammonia-lyase [PAL, EC 4.3.1.5] and guaiacol peroxidase [POD, EC 1.11.1.7]). The presented work evaluated the impact of light quality (white, red, blue light and UV-C irradiation) on changes in anthocyanin contents and the dynamics of PAL and POD activities in different morphological spears sections (apical and basal) of harvested white ‘Gijnlim’ asparagus. After harvest, spears were exposed to weak white, red and blue light (30 μmol m-2 s-1) for 3 h and to UV-C irradiation (254 nm, 1 kJ m-2) for 8 min; untreated spears were used as controls. Untreated and light-treated spears were stored in darkness at 20 °C in water vapour saturated atmosphere for up to 4 d. On days 0, 2 and 4, six spears per treatment were selected, severed into basal and apical segments, and respiration rate, anthocyanin content, and PAL and POD activity determined. Light quality did not influence respiration, but section-specifically mediated changes of anthocyanin contents, and PAL and POD activities. White light triggered anthocyanin synthesis via an associated PAL increase, whereas red light and UV-C irradiation tendentiously resulted in an anthocyanin inhibition or even degradation, coinciding with changes in PAL activity, respectively. Blue light increased anthocyanin content in spear tips to the same extent as for controls. However, also other enzymes might play an important role in the light induced anthocyanin synthesis. In basal segments, PAL and POD activities were higher than in apical segments; however, light treatments affected both enzyme activities differently. In the apical, PAL activity was enhanced by white light and UV-C. In contrast, in the basal segments the different wavelength ranges did not affect PAL except for UV-C also increasing PAL activity. The activity of POD increased in tip sections throughout storage and remained high irrespective of light treatments, except for UV-C, strongly stimulating POD activity. POD was also UV-C stimulated in basal segments, whereas white, blue and red light inhibited its activity for a limited time during storage. Differentiated responses in apical and basal segments indicated distinct physiological activity, signalling chains and availability of resources from primary metabolism. PAL may be a major factor controlling lignification in the basal segments of spears, irrespective of light quality, while POD activity is significantly triggered by mainly UV-C indicating its role as an antioxidant enzyme in the physiological active spear tips.

Intraoperative Fluorescence Cerebral Angiography by Laser Surgical Microscopy: Comparison With Xenon Microscopy and Simultaneous Observation of Cerebral Blood Flow and Surrounding Structures

Laser surgical microscopes should enable uniform illumination of the operative field, and require less luminous energy compared with existing xenon surgical microscopes. To examine the utility of laser illumination in fluorescence cerebral angiography. Fluorescein sodium (fluorescein) was used as a fluorescent dye. We first compared the clarity of cerebral blood flow images collected by fluorescence angiography between the laser illumination and xenon illumination methods. We then assessed use of the laser illuminator for simultaneous observation of blood flow and surrounding structures during fluorescence angiography. Furthermore, the study was designed to evaluate usefulness of the thus determined excitation light in clinical cases. Fluorescence angiography using blue light laser for excitation provided higher clarity and contrast blood flow images compared with using blue light generated from a xenon lamp. Further, illumination with excitation light consisting of a combination of 3 types of laser (higher level of blue light, no green light, and lower level of red light) enabled both blood flow and surrounding structures to be observed through the microscope directly by the surgeon. Laser-illuminated fluorescence angiography provides high clarity and contrast images of cerebral blood flow. Further, a laser providing strong blue light and weak red light for excitation light enables simultaneous visual observation of fluorescent blood flow and surrounding structures by the surgeon using a surgical microscope. Overall, these data suggest that laser surgical microscopes are useful for both ordinary operative manipulations and fluorescence angiography.

Weak red light plays an important role in awakening the photosynthetic machinery following desiccation in the subaerial cyanobacterium Nostoc flagelliforme.

The subaerial cyanobacterium Nostoc flagelliforme can survive for years in the desiccated state and light exposure may stimulate photosynthetic recovery during rehydration. However, the influence of light quality on photosynthetic recovery and the underlying mechanism remain unresolved. Exposure of field collected N. flagelliforme to light intensity ≥2 μmol photons m-2 s-1 showed that the speed of photosystem II (PSII) recovery was in the following order: red > green > blue ≈ violet light. Decreasing the light intensity showed that weak red light stimulated PSII recovery during rehydration. The chlorophyll fluorescence transient and oxygen evolution activity indicated that the oxygen evolution complex (OEC) was the activated site triggered by weak red light. The damaged D1 protein accumulated in the thylakoid membrane during dehydration and is degraded and resynthesized during dark rehydration. PsbO interaction with the thylakoid membrane was induced by weak red light. Thus, weak red light plays an important role in triggering OEC photoactivation and the formation of functional PSII during rehydration. In its arid habitats, weak red light could stimulate the awakening of dormant N. flagelliforme after absorbing water from nighttime dew or rain to maximize growth during the early daylight hours of the dry season.

Photo-carrier control of exchange bias in BiFeO3/La2/3Sr1/3MnO3 thin films

We report the facile control of exchange bias in BiFeO3/La2/3Sr1/3MnO3 (BFO/LSMO) thin films on an SrTiO3 (STO) substrate using light irradiation. Illumination with weak red light (λ: 630 nm, intensity: ∼1 mW/cm2) reduced the exchange bias field (HE) of BFO/LSMO from +30 Oe in the dark to −2 Oe with red light. In accompanying the decrease of HE, the resistance of BFO/LSMO significantly increased. These results were attributed to the reduction in the hole-doping ratio of LSMO and the weakened exchange coupling between Fe and Mn spins at the interface, resulting from photo-injected electrons from the STO substrate. Successive turning on/off of red light gives rise to cyclical change of corresponding HE, which should be useful for applications like photo-controlled tunneling magnetoresistance devices.

Growth Recovery of Barley Cultivated in Low-Nutrient Soil Conditions by Irradiation with Blinking Weak Red Light Emitted at 20 Hz Accompanied by Automatic Detection of Barley Bioelectric Signals

Growth Recovery of Barley Cultivated in Low-Nutrient Soil Conditions by Irradiation with Blinking Weak Red Light Emitted at 20 Hz Accompanied by Automatic Detection of Barley Bioelectric Signals

Self-induced transparency in diblock copolymer dispersions

We report on the versatile effect of weak red laser light impinging on diblock copolymer [poly(isoprene-b-styrene)] dispersions in two selective solvents for each block. In the strongly scattering but transparent micellar solutions in hexane (a good solvent for polyisoprene), higher refractive index copolymer-rich fibers were formed. In the turbid dispersions of the same copolymer in ethyl acetate (a good solvent for polystyrene), the effect of self-induced transparency was observed. A two-step patterning mechanism caused the generation of a transparent microchannel, increasing light transmission. The analogy between the current effect and that observed in homopolymer polyisoprene solutions in different solvents is discussed toward an understanding of the unanticipated light-soft-matter interaction.

Far-red Light Supplemented with Weak Red Light Promotes Flowering of Gypsophila paniculata

A low red (R): far-red (FR) ratio is known to promote flowering of Arabidopsis and several long-day cut flowers, whereas not much information is available on the effects of single light qualities and their combinations on flowering. Therefore, the effects of light quality on the flowering of Gypsophila paniculata were investigated using light-emitting diodes (LEDs) emitting the following lights: FR, R, and blue (B). Flowering and flower budding were observed under long-day conditions with FR, while no flowering was observed under short-day conditions. Promotion of flowering and flower budding was increased under FR supplemented with R compared to FR alone. Although generally R inhibits flowering in long-day plants, a certain intensity of R, for example, the R:FR ratio between 0.23 and 0.71, may be necessary for effective promotion of flowering. In contrast, B supplementation of FR was not effective at the ratio in this study in inducing flowering and flower budding. The quality of cut flowers produced under long-day conditions with LEDs that promoted flowering was not lower than that under incandescent lamps. These results will provide basic knowledge for the development of LED bulbs as a replacement for incandescent bulbs.

Strong up-conversion emissions in ZnO:Er 3+, ZnO:Er 3+–Yb 3+ nanoparticles and their surface modified counterparts

ZnO:Er 3+ and ZnO:Er 3+–Yb 3+ nanoparticles (NPs) are fabricated by a sol–gel method, afterwards parts of which are separated and surface modified in Mo(NO 3) 3 solution. Analyses on phase and structure based on X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) techniques indicate that Er 3+ and Yb 3+ are incorporated into the ZnO lattice successfully and after Mo treatment, a thin layer of MoO 3 forms on the NPs surface, forming core/shell structures. Raman scattering spectra reveal the existence of ZnMoO 4 in the shell part. Visible up-conversion (UC) is observed in all the samples, with Mo treated and untreated ZnO:Er 3+ emitting dominant but relatively weak red light, corresponding to 4F 9/2– 4I 15/2 transition of Er 3+. In Yb 3+-codoping systems, the integral UC intensity is enhanced obviously though red emission still dominates the UC spectra before surface modification. In the Mo treated system, ZnO:Er 3+–Yb 3+/MoO 3, green emission is increased while the red is suppressed in comparison to ZnO:Er 3+–Yb 3+, with the intensity of green to red ratio (GRR) changing from 0.25 to 8. A novel phenomenon is discovered that the green emissions in our samples involve three-photon processes.

Actin cytoskeleton in Arabidopsis thaliana under blue and red light

Actin cytoskeleton is the basis of chloroplast-orientation movements. These movements are activated by blue light in the leaves of terrestrial angiosperms. Red light has been shown to affect the spatial reorganization of F-actin in water plants, where chloroplast movements are closely connected with cytoplasmic streaming. The aim of the present study was to determine whether blue light, which triggers characteristic responses of chloroplasts, i.e. avoidance and accumulation, also influences F-actin organization in the mesophyll cells of Arabidopsis thaliana. Actin filaments in fixed mesophyll tissue were labelled with Alexa Fluor 488-conjugated phalloidin. The configuration of actin filaments, expressed as a form factor (4 pi x area/perimeter(2)), was determined for all actin formations which were measured in fluorescence confocal images. In the present study, we compare form-factor distributions and the median form factors for strong and weak, blue- and red-irradiated tissues. Spatial organization of the F-actin network did not undergo any changes which could be attributed specifically to blue light. Actin patterns were similar in blue-irradiated wild-type plants and phot2 (phototropin 2) mutants which lack the avoidance response of chloroplasts. However, significant differences in the shape and distribution of F-actin formations were observed between mesophyll cells of phot2 mutants irradiated with strong and weak red light. These differences were absent in wild-type leaves. Actin does not appear to be the main target for the blue-light chloroplast-orientation signal. The modes of actin involvement in chloroplast translocations are different in water and terrestrial angiosperms. The results suggest that co-operation occurs between blue- and red-light photoreceptors in the control of the actin cytoskeleton architecture in Arabidopsis.

OPSINS IN THE DEEP

James Bowmaker is fascinated by pineal glands. These photosensitive glands,which regulate circadian rhythms in response to light levels by releasing melatonin, are usually located on top of the brain just beneath the skull. Which is an ideal position for deep-sea fish exposed to weak downwelling light in the ocean's depths. But Bowmaker and his colleague Hans-Joachim Wagner were curious whether deep-sea fish's pineal glands were even sensitive to light when so little reaches those depths. Wagner already knew that some deep-sea species' pineal glands produced melatonin, but would they have retained the photopigments and the ability to respond to fluctuating light levels? Bowmaker and Wagner set off on the RRS Discovery to gather several deep-sea species from the tropical Atlantic Ocean to discover whether species from the ocean's depths produce pineal photopigments(p. 2379).But having successfully trawled fish from depths between 800 and 1000 m,the team faced the tricky problem of preserving the delicate pineal gland tissue ready for return to land. Bowmaker remembers that the tissue needed to be collected and stored in the dark, which required delicate surgery under weak red light while the boat bobbed about. Once Wagner had successfully extracted the glands, the team gently fixed the samples, hoping the procedure wouldn't ruin any delicate membrane bound photopigments that the tissue may contain.After five weeks at sea. the team had collected samples from eight species of deep-sea fish, but would the pineal gland tissue contain photopigment? Back in London, Bowmaker gently mounted a sample in his spectrophotometer, and measured an absorbance spectrum. The results were clear; the tissue contained opsins similar to the pineal gland opsins found in surface dwelling species. Taking a close look at the pineal glands in his lab in Germany, Wagner also realised that the gland's photoreceptors contained large amounts of the specialised opsins in dome-shaped membranes, for maximum sensitivity in the dim environment. And when they compared the pineal gland's photosensitive pigment with opsins found in the fish's retina, Bowmaker and Wagner found that the pineal gland opsins were tuned to wavelengths that were a few nanometers longer than the fish's retinal opsins, but shorter than the pineal gland opsins of surface dwelling species.But what about the pineal glands of creatures that never see the light of day, such as the deep demersal eels, Synaphobranchus kaupi, which live at 2000 m? Wagner was lucky enough to catch several of the creatures and return their pineal glands to land for investigation. Amazingly, the eel had an enormous pineal gland, packed with photopigment, even though the animals never see solar photons. Bowmaker and Wagner are puzzled why the eel produces such large amounts of photopigment. Also, the opsin's spectral sensitivity is tuned to an exceptionally long wavelength, 515 nm, similar to the wavelengths detected by surface species pineal gland opsins. Bowmaker suggests that the eels could have retained pigment in their pineal glands as they spend their juvenile life stages near the ocean surface. But until the team has evidence that components of the essential signalling cascades that propagate the receptors signal are present, they have no idea whether the mesopelagic species, or Synaphobranchus, even detect light with their pineal glands.

On the 710 nm fluorescence emitted by the diatom Phaeodactylum tricornutum at room temperature.

The fluorescence emitted at 710 nm by Phaeodactylum tricornutum (F(710)) was characterized. Development of F(710) was found to be regulated by the quality of light needed for algal growth: weak red light absorbed mainly by Chl a induced its development, and weak blue-green light absorbed mainly by fucoxanthin and Chl c suppressed it. The difference spectra between cells grown under the two light conditions revealed two Chl a forms, absorption peaks of which were located at 692 nm (Chl a(692)) and at 703 nm (Chl a(703)), respectively, in red-light-grown cells. During cell growth under red light, the appearance and intensification of the emission correlated well with development of Chl a(692) and Chl a(703) suggesting that the two forms of Chl a are involved in the energy flow to F(710). A clear induction phenomenon characteristic of the PSII fluorescence was observed not only with the emission at 680 nm but also with F(710), indicating that F(710) is emitted by PSII Chl a. Development of F(710) under red light was sensitive to cycloheximide, indicating that the development of the energy flow to F(710) requires protein synthesis and that the emitter is installed in a protein encoded in the nuclear genome like the light-harvesting complex (LHC). Centrifugal fractionation of pigment-protein complexes revealed F(710) to be located at fractions slightly heavier than the major LHC. Development of F(710) was also found in red-light-grown cells of the diatom Nitzschia closterium.

Mutant analyses define multiple roles for phytochrome C in Arabidopsis photomorphogenesis.

The analysis of Arabidopsis mutants deficient in the A, B, D, and E phytochromes has revealed that each of these phytochrome isoforms has both distinct and overlapping roles throughout plant photomorphogenesis. Although overexpression studies of phytochrome C (phyC) have suggested photomorphogenic roles for this receptor, conclusive evidence of function has been lacking as a result of the absence of mutants in the PHYC locus. Here, we describe the isolation of a T-DNA insertion mutant of phyC (phyC-1), the subsequent creation of mutant lines deficient in multiple phytochrome combinations, and the physiological characterization of these lines. In addition to operating as a weak red light sensor, phyC may perform a significant role in the modulation of other photoreceptors. phyA and phyC appear to act redundantly to modulate the phyB-mediated inhibition of hypocotyl elongation in red light and to function together to regulate rosette leaf morphology. In addition, phyC performs a significant role in the modulation of blue light sensing. Several of these phenotypes are supported by the parallel analysis of a quadruple mutant deficient in phytochromes A, B, D, and E, which thus contains only active phyC. Together, these data suggest that phyC has multiple functions throughout plant development that may include working as a coactivator with other phytochromes and the cryptochrome blue light receptors.

Reversible inactivation of PS II reaction centers and the dissociation of LHC II from PS II complex in soybean leaves

Both PS II photochemical efficiency ( F v/ F m) and the low-temperature fluorescence parameter F 685/ F 735 declined in soybean leaves after 3 h of strong light treatment. These two parameters returned to the fully dark-adapted level within 3 h in the dark, and NaF markedly inhibited these recovery processes. After sucrose gradient centrifugation of thylakoid membranes, the amount of LHC II from the strong light-treated leaves decreased in lower green layers and increased in upper green ones, but the distribution of LHC II in both stacked and unstacked thylakoid membranes did not change when compared with that of the fully dark-adapted leaves. When soybean leaves were illuminated with weak red light, F 685/ F 735 decreased while F 735 kept at almost the same level as control leaves in the dark. Based on the above results, it is concluded that: (1) partial reversible inactivation of PS II in soybean leaves is closely related to the dissociation of LHC II from the PS II complex; and (2) the detached LHC II does not migrate from the stacked membranes to the unstacked membrane regions.

An Evidence Indicating That a Weak Orange Light Absorbed by Phycobilisomes Causes Inactivation of PSII in Cells of the Red Alga Porphyridium cruentum Grown under a Weak Red Light Preferentially Exciting Chl a

Changes in the PSII fluorescence upon shift of light quality were studied with the red alga Porphyridium cruentum IAM R-l and supplementary with P. cruentum ATCC 50161, the cyanophytes Synechocystis spp. PCC6714 and PCC6803 and Synechococcus sp. NIBB1071. When Porphyridium cruentum grown under a weak red light (PSI light) preferentially absorbed by Chi a was illuminated with a weak orange light (PSII light) mainly absorbed by phycobilisomes (PBS), a change of PSII fluorescence at room temperature was induced. The ratio of Fvm (Fm — Fo) to Fm was reduced rapidly accompanying the increase in Fo (Ti/2, ca. 3 min). The effects of DCMU and 2,5dibromo-3-methyl-6-isopropyl-/7-benzoquinone indicated that the fluorescence change is induced when plastoquinone pool is highly reduced. The fluorescence change after a short PSII light illumination was reversible; it rapidly recovered in the dark (T1/2, ca. 3 min). The reversibility was gradually reduced and disappeared after 40 h under PSII light accompanying decrease in PSII activity per PBS down to almost 50%. Since the pattern of the fluorescence change resembles that observable when PSII is photoinactiva ted, PSII light probably induces the photoinactivation of PSII, possibly reversibly at first and irreversibly after prolonged illumination. Such a rapid fluorescence change was insignificant in Synechocystis sp. either PCC6714 or PCC6803. Only a slow and small decrease in Fvm/Fm level appeared after prolonged PSII light illumination (the reduction of PSII activity per PBS was around 20%). In Porphyridium, shift from PSII light to PSI light caused a rapid and chloramphenicol-sensitive Fvm/Fm elevation during the first 10 h while the increase in PSII activity per PBS was only 10% of that before the light shift. Then, a gradual elevation followed up to the level at the steady state under PSI light. A similar rapid increase in Fvm/Fm was observed with Synechocystis PCC6714, in which the synthesis of PSII is not regulated, suggesting that a rapid increase in Fvm/Fm