Evidence for yellow light suppression of lettuce growth

Researchers studying plant growth under different lamp types often attribute differences in growth to a blue light response. Lettuce plants were grown in six blue light treatments comprising five blue light fractions (0, 2, 6% from high-pressure sodium [HPS] lamps and 6, 12, 26% from metal halide [MH] lamps). Lettuce chlorophyll concentration, dry mass, leaf area and specific leaf area under the HPS and MH 6% blue were significantly different, suggesting wavelengths other than blue and red affected plant growth. Results were reproducible in two replicate studies at each of two photosynthetic photon fluxes, 200 and 500 mumol m-2 s-1. We graphed the data against absolute blue light, phytochrome photoequilibrium, phototropic blue, UV, red:far red, blue:red, blue: far red and 'yellow' light fraction. Only the 'yellow' wavelength range (580-600 nm) explained the differences between the two lamp types.     

Application of very small force measurements in monitoring the response of sunflower to weak blue light

A diaheliotropic response of sunflower, Helianthus annuus, following a short pulse of low intensity blue light to a small area of leaf surface was examined with the application of the very low-force-measurements technique (the order of magnitude of 10(-5) N). One leaf from a pair was illuminated with a low intensity blue-light-pulse and the force was recorded, generated by the stem of the plant tending to bend. A very low phototropic effect in response to blue light alone was observed which could be considerably enhanced by the application of background illumination with red light. Microelectrode measurements of the membrane potential of the mesophyll cells of the sunflower leaf showed hyperpolarization in response to a blue light pulse, observed very clearly under application of the red light background illumination. The hyperpolarization of the membrane potential was accompanied by acidification of extracellular compartments as monitored with a miniature pH-sensitive electrode, placed in the epidermis of the stem. The relatively short lag period between the hyperpolarization of the membrane potential and the decrease in pH suggests that the hyperpolarization is a direct effect of the blue light-induced proton extrusion. The acidification correlates with the light response, which suggests that acidification-induced stem wall loosening is responsible for the blue light-induced bending. The examined mechanisms are discussed in terms of sun tracking by a sunflower.     

Monoolein cubic phase containing azobenzene and its UV/visible light irradiation-dependent release property

Monoolein (MO) cubic phase, whose MO/azobenzene mass ratios were 1:0, 1:0.0025, 1:0.005, and 1:0.025, was prepared by a melt-hydration method. According to the polarized optical micrographs and the differential thermograms, the phase transition temperature of the cubic phase was lower as the content of azobenzene was higher, and it decreased upon the subsequent irradiation of UV light for 1 hour and visible light for 1 hour. The photoirradiation significantly promoted the release of methylene blue (a water-soluble dye) loaded in the cubic phase only when the MO/azobenzene mass ratio was 1:0.025. The photoirradiation could promote the release of Nile red (an oil-soluble dye) even when the MO/azobenzene mass ratio was less than 1:0.025. The higher photo-susceptibility of Nile red release was possibly because the dye would be intercalated in the MO lipid matrix and the photoirradiation could affect the lipid matrix property.     

Optical control of excited-state vibrational coherences of a molecule in solution: The influence of the excitation pulse spectrum and phase in LD690

Spectral and phase shaping of femtosecond laser pulses is used to selectively excite vibrational wave packets on the ground (S0) and excited (S1) electronic states in the laser dye LD690. The transient absorption signals observed following excitation near the peak of the ground-state absorption spectrum are characterized by a dominant 586 cm(-1) vibrational mode. This vibration is assigned to a wave packet on the S0 potential energy surface. When the excitation pulse is tuned to the blue wing of the absorption spectrum, a lower frequency 568 cm(-1) vibration dominates the response. This lower frequency mode is assigned to a vibrational wave packet on the S1 electronic state. The spectrum and phase of the excitation pulse also influence both the dephasing of the vibrational wave packet and the amplitude profiles of the oscillations as a function of probe wavelength. Excitation by blue-tuned, positively chirped pulses slows the apparent dephasing of the vibrational coherences compared with a transform-limited pulse having the same spectrum. Blue-tuned negatively chirped excitation pulses suppress the observation of coherent oscillations in the ground state.     

Wave packet calculations on the effect of the femtosecond pulse width in the time-resolved photodissociation of CH3I in the A-band

The effect of changing the temporal width of the pump and probe pulses in the time-resolved photodissociation of CH(3)I in the A-band has been investigated using multisurface nonadiabatic wave packet calculations. The effect is analyzed by examining properties like the photodissociation reaction times and the CH(3) fragment vibrational and rotational distributions, by using four different widths of the pump and probe pulses, namely pulses with full-width-at-half-maximum of 100, 50, 20, and 10 fs. Simulations are carried out for two different excitation wavelengths, 295 and 230 nm, located to the red and to the blue of the maximum of the absorption spectrum, in order to explore possible effects of the excitation wavelength. The reaction times are found to decrease significantly with decreasing pulse temporal width. The times associated with the CH(3) + I*((2)P(1/2)) dissociation channels decrease more remarkably than those of the CH(3) + I((2)P(3/2)) channels. The results indicate that for excitation wavelengths located to the blue of the absorption spectrum maximum the effect of changing the pulse width is less pronounced than for wavelengths to the red of the spectrum maximum. On the contrary, the CH(3) vibrational and rotational distributions show little variation upon large changes in the pulse width. The trends found are explained in terms of the changes in the spectral bandwidth of the pulses and of the shape and slope of the absorption spectrum at the different excitation wavelengths.     

Nonlinear dynamics of intracellular methylene blue during light activation of cell cultures

Methylene blue (MB+) is a well-known dye in medicine and has been discussed as an easily applicable drug for topical treatment in photodynamic therapy (PDT). Methylene blue can potentially be used as a redox indicator to detect the important redox reactions that are induced during PDT. The kinetics of this process was analyzed on a subcellular level with confocal laser scanning microscopy. BKEz-7 endothelial cells were incubated 4 h with 1 microM MB+. The fluorescence dynamics of MB+ during irradiation with 633 nm light was observed with subcellular resolution. Images were acquired at 0.5 s intervals (frame rate 1 image/0.5 s). Fluorescence was observed in the red channel of the laser scanning microscope. Synchronously, the phase-contrast image was visualized with the green channel. Morphological changes could therefore be correlated with the dynamics of MB+. In addition, the light-dose-dependent phototoxicity at 633 nm irradiation was determined by viable cell counting. After an induction period (phase I), fast fluorescent spikes could be observed in the whole cytoplasm, which decayed with a time constant of about 20 s (phase II), followed by a period of nearly constant fluorescence intensity (phase III) and exponential photobleaching (phase IV). Phase II exhibits highly nonlinear kinetics, which is hypothesized to correlate probably with a nonlinear quantal production of reactive oxygen species (ROS). Morphological cell changes were not observed during phase II. During phase III, a pycnotic cell nucleus developed. From the determination of viable cells we can conclude that a light dose applied within phase II was only sublethal in correlation with morphological observations. Overproduction of ROS leading finally to cell killing during phases III and IV is discussed.     

Dual wavelength excitation fluorescence detector for capillary electrophoresis using a pulsed bi-colour light emitting diode

A simple and novel two-colour fluorescence detector for capillary electrophoresis was created using a single bi-colour light emitting diode (LED), multi-band pass excitation and emission filters and a single detector. Excitation light from a blue/red (470/635 nm) bi-colour LED was filtered through a 390/482/563/640 nm multi-band bandpass filter, with emitted light filtered through a 446/523/600/677 nm multi-band bandpass filter before being detected using a photon counting detector. Sequential pulsing of the blue/red LED and deconvolution of the collected fluorescence data allowed extracted electropherograms to be obtained corresponding to excitation with the blue and red LEDs. Optimisation of the pulsed LED conditions revealed an optimum LED on-time of 50 ms, off-time of 30 ms with a pulsed current of 40 mA, giving an effective data acquisition rate of 6.25 Hz. The characteristics of this system were validated by the simultaneous separation and determination of six fluorescent dyes: fluorescein, FITC, coumarin 334, dibromo(R)fluorescein (Ex/Em 470/525 nm), and Cy 5 and the Agilent Bioanalyser DNA dye (Ex/Em 635/670 nm). Under optimum conditions, the detection limits for FITC, fluorescein and Cy 5 were 69 nM, 42 nM and 289 nM (S/N = 3), respectively. These were lower than those obtained with continuous operation of the individual wavelengths at a constant current of 20 mA, but were slightly higher than those obtained using dedicated single wavelength filter combinations designed specifically for use with these fluorophores. The intraday repeatability (n = 6) of migration times was less than 1.0% and less than 3.4% for peak areas, while interday (n = 3) migration time and peak area reproducibility were less than 0.9% and 3.6%, respectively. This simple detector is capable of performing quantitative two-wavelength excitation without the need for complex optics and light source configurations.     

Influencing parameters in time resolved picosecond spectroscopy and a new light gate method

We show that the open period of a CS₂ light gate, triggered by a picosecond optical pulse, depends on the optical pathlength through the CS₂. An alternative to the light gate is suggested for time resolved spectroscopy. The working principle is based on scattering induced in CS₂. We have found that the broadband emission from H₂O or D₂O excited by a 5300 Å picosecond pulse is also of picosecond duration, but the blue part is delayed with respect to the red. From this delay time the lifetime of the ground state vibrational levels may be measured directly.     

Azobenzene photoswitching without ultraviolet light

Most azobenzene-based photoswitches use UV light for photoisomerization. This can limit their application in biological systems, where UV light can trigger unwanted responses, including cellular apoptosis. We have found that substitution of all four ortho positions with methoxy groups in an amidoazobenzene derivative leads to a substantial (~35 nm) red shift of the n-π* band of the trans isomer, separating it from the cis n-π* transition. This red shift makes trans-to-cis photoswitching possible using green light (530-560 nm). The cis state is thermally stable with a half-life of ~2.4 days in the dark in aqueous solution. Reverse (cis-to-trans) photoswitching can be accomplished with blue light (460 nm), so bidirectional photoswitching between thermally stable isomers is possible without using UV light at all.     

Effect of light quality on the accumulation of photosynthetic pigments, proteins and mycosporine-like amino acids in the red alga Porphyra leucosticta (Bangiales, Rhodophyta)

The effect of different light qualities (white, blue, green, yellow and red light) on photosynthesis, measured as chlorophyll fluorescence, and the accumulation of photosynthetic pigments, proteins and the UV-absorbing mycosporine-like amino acids (MAAs) was studied in the red alga Porphyra leucosticta. Blue light promoted the highest accumulation of nitrogen metabolism derived compounds i.e., MAAs, phycoerythrin and proteins in previously N-starved algae after seven days culture in ammonium enriched medium. Similar results were observed in the culture under white light. In contrast, the lowest photosynthetic capacity i.e., lowest electron transport rate and lowest photosynthetic efficiency as well as the growth rate were found under blue light, while higher values were found in red and white lights. Blue light favored the accumulation of the MAAs porphyra-334, palythine and asterina-330 in P. leucosticta. However, white, green, yellow and red lights favored the accumulation of shinorine. The increase of porphyra-334, palythine and asterina-330 occurred in blue light simultaneous to a decrease in shinorine. The accumulation of MAAs and other nitrogenous compounds in P. leucosticta under blue light could not be attributed to photosynthesis and the action of a non-photosynthetic blue light photoreceptor is suggested. A non-photosynthetic photoreceptor could be also involved in the MAAs interconversion pathways in P. leucosticta.     

Action of light on the relative activity of peroxidase in the aerobic oxidation of lignin

It has been established that the activity of peroxidase depends to a considerable degree on the radiation dose and the spectral composition of the light. A special sensitivity of the enzyme to the action of the blue and red regions of the spectrum has been shown. In the investigation it was found that light with a wavelength greater than 520 nm promotes the liberation, and short wave light the consumption, of oxygen during the aerobic oxidation of lignin in the presence of peroxidase.Siberian-Research Institute of Cellulose and Cardboard, Bratsk. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 375–378, May–June, 1984.     

THE BLUE LIGHT RESPONSE OF STOMATA: PULSE KINETICS AND SOME MECHANISTIC IMPLICATIONS*

Abstract— Intact leaves of Commelina communis irradiated with high fluence rates of red light, showed discrete increases in stomatal conductance in response to pulses (1-100 s) of blue light (250 μmol m^?2 s^?1). Red light pulses were ineffective, indicating that the conductance increases were not mediated by photosynthesis and that they constitute a specific stomatal response to blue light. The response peaked 15 min after the pulse and was completed within50–60 min. Conductance increases were proportional to pulse duration up to about 30 s and saturated at longer exposures. The relationship between stomatal responses and pulse duration approximately fitted an exponential function, with a t 9s. Pulse responses at two different fluences indicated that reciprocity held. Responses to two consecutive pulses varied with time between pulses. A saturating pulse applied immediately after a preceding one induced no additional response; two saturating pulses 50 min apart caused two identical, consecutive responses. Total increases in conductance induced by two pulses separated by intermediate time intervals increased with time between pulses with a = 9 min. These results point to a blue light-dependent photoconversion of a molecular form, with the activity of the photoconversion product decaying in a thermal reaction. Under continuous blue light, prevailing fluence rates and rates of the light and thermal reactions are postulated to determine steady-state activities of the photoconversion product and proportional increases in conductance levels. These findings have implications for the environmental and metabolic roles of the stomatal response to blue light.     

Bond lengths of diatomic molecules periodically driven by light: the p-LAMB scheme

A laser scheme using a periodically changing frequency is used to induce oscillations of the internuclear motion, which are quantum analogs of classical vibrations in diatomic molecules. This is what we call the periodic laser adiabatic manipulation of the bond, or p-LAMB scheme. In p-LAMB, the carrier frequency of the laser must vary periodically from the blue to the red of a photodissociation band and backwards, following for instance a cosine-dependent frequency of period τ(c). In the adiabatic regime the dynamics is fully time-reversible. The amplitude of the internuclear oscillation is controlled by the pulse frequency ω(t), while τ(c) determines the duration (or period) of the bond oscillation. In the presence of efficient dipole coupling, the bandwidth of the pulse is the main constraint to the maximum bond stretch that can be obtained. Before the onset of the adiabatic regime the dynamics are more complex, showing dispersion of the vibrational wave packet and anharmonic deformation of the bond. However, the nonadiabatic effects are mostly canceled and full revivals are observed at certain multiples of τ(c).     

Effect of light on soluble guanylyl cyclase activity in Pharbitis nil seedlings

Cyclic GMP acts as a chemical switch in plant cells to modulate cellular reactions. However, its metabolism has not been extensively explored and is still poorly understood. Previous experiments suggest that an endogenous cGMP system could participate in the mechanism of phytochrome controlled photoperiodic flower induction in Pharbitis nil. In order to gain further information on the role of cGMP, we have begun to study the enzyme of cGMP synthesis. In this article, the presence of the enzyme with guanylyl cyclase (GC) activity in soluble protein fractions of P. nil is reported. A large portion of the enzymatic activity is present in the cotyledons, where enzyme activity amounted to 0.45 pmol cGMP/min/mg protein. The enzyme exhibited a K(m) 0.5mM for GTP. A plot of 1/v versus 1/[GTP] was linear and V(max) was 0.74 pmol cGMP/min/mg protein. It was shown that the anti-sGC antibody recognise a 40 kDa protein. Moreover, the NO-donor, sodium nitroprusside (SNP) and YC-1, as a NO-independent stimulator, enhanced enzyme activity. The NS 2028 (a potent GC inhibitor) treatments provoked a 3-fold reduction of the enzyme activity in comparison to the untreated fractions. Furthermore, the influence of light on GC activity was analysed. It was noted that cGMP level increased in cool white light, and darkness inhibited enzyme activity. Exposure to blue light acts to stimulate cGMP formation, whereas in red light a rapid decrease in GC activity was observed that returned to the high level when far-red light was applied after the red light treatment. The results presented in this work strongly argue that an enzyme with guanylyl cyclase activity is present in P. nil organs and its activity is controlled by light via the photoreceptors-dependent pathways.     

Blue light irradiation inhibits the production of HGF by human retinal pigment epithelium cells in vitro

Blue visible light damage to retinal pigment epithelial cells occurs through a photooxidative mechanism and the resultant damage is hypothesized to induce or exacerbate age-related macular degeneration. The purpose of the present study was to identify changes in the cell growth and the expression of hepatocyte growth factor (HGF) in cultured human retinal pigment epithelium (RPE) cells as a result of both blue and red light irradiation. HGF is a growth factor and neurotrophic factor that stimulates growth of various ocular cells and promotes the survival of RPE and retinal neurons. Early passages of human RPE cells were exposed to blue light (460 nm) and red light (640 nm). Nonirradiated cells were used as controls. After 24 and 48 h, conditioned medium was collected and the amount of HGF was measured by ELISA. Cells were detached from the well and counted. Cell viability was evaluated by trypan-blue exclusion study. Blue light at dosage of 63 J/cm(2) significantly inhibited the growth of RPE cells without affecting of cell viability. Amounts of HGF in the culture medium were significantly inhibited by blue-light irradiation at the dosage from 32 to 63 J/cm(2). Red light at a dose of 174 J/cm(2) causes a nonsignificant inhibition of growth of RPE cells and a slight decrease of secretion of HGF. As HGF promotes survival of RPE cells and retinal neurons, the inhibition of production of HGF by visible light, especially by blue light, may enhance the phototoxic effects of visible light on the RPE and retinal neurons.     

PHYTOCHROME CONTROL OF EXTRACELLULAR PEROXIDASE ACTIVITY IN MUSTARD INTERNODES: CORRELATION WITH GROWTH, and COMPARISON WITH THE EFFECT OF WOUNDING

Abstract— The effects of phytochrome status on extracellular peroxidase activity were investigated in Sinapis alba L. seedlings grown for 12 days under continuous white light and transferred to darkness after a red light or a far-red light pulse. The rates of extension growth and dry matter accumulation in the first internode were increased by the far-red light pulse. Extracellular proteins, obtained by low speed centrifugation of intact internodes infiltrated with CaCl₂, were separated by isoelectrofocusing, and four extracellular acidic peroxidases were resolved, the most active being A3 and A4 (both ˜60 kD). The activity of A4 was reduced by the far-red light pulse perceived by phytochrome, while the activity of A3 was unaffected. The promotion of internode extension growth caused by far-red light is biphasic [Casal and Smith (1989) Plant, Cell Environ. 12 ,511–50]. Changes in peroxidase activity were detected prior to the second, but not to the first phase of the internode growth promotion. The effects on both growth and peroxidase activity were virtually restricted to the upper half of the internode and, once established, did not subsequently increase in magnitude.
In contrast to the effects mediated by phytochrome, blue light pretreatments affected growth but not extracellular peroxidase activity. Wounding the internode reduced extension growth, increased the activity of A3, but caused no significant effects on A4.
Other extracellular proteins, separated in sodium dodecyl sulphate polyacrylamide gels and stained with Coomassie blue, showed no significant differences. The concentration of extracellular proteins was higher in the upper than the lower half of the internode.
Results are discussed in terms of phytochrome effects in light grown plants, peroxidase activitv-arowth relationships, and extracellular peroxidase isoform functions.     

Electrical breakdown of human erythrocytes: a technique for the study of electro-haemolysis

This paper describes a technique suitable for investigating the electromechanical breakdown properties of erythrocyte cells. The cells were exposed to square wave electric pulses of precise duration and voltage. The erythrocytes were suspended in normal isotonic saline between two opposing platinum electrodes. A red LED light source and photodiode detector system were positioned orthogonally to the electrodes to record changes in the light transmission that occur immediately after applying an electric pulse. The light transmitted through the electrically treated erythrocyte suspension could be monitored continuously. Experiments were conducted to explore the inter-relationship between the critical voltage and pulse length for haemolysis. Human blood taken from "healthy" donors underwent haemolysis at a critical field strength of 304 kV/m for a 5 micros pulse and 292 kV/m for a 50 micros pulse. The relationship of critical pulse length and critical voltage for the blood samples was found to be inversely linear.     

A metal-free carbon dots for wastewater treatment by visible light active photo-Fenton-like reaction in the broad pH range

Carbon dots (Cdots) has been proved to possess the catalytic decomposition of H₂O₂ in the photocatalytic system. It is a potential photo-Fenton catalyst. Since multiple emissive Cdots have different light response range. There is rarely investigation on the performance of Cdots based photo-Fenton on the light wavelength. Herein, blue, green and red emissive carbon dots were synthesized from the different ratio of o-phenylenediamine and catechol by the solvothermal method. They exhibit different light adsorption range from UV to visible light. Furthermore, the photo-Fenton reactivity of Cdots was studied for catalyzing the decomposition of H₂O₂ to generate free hydroxyl radicals and consequently applying for the removal of methyl blue. The results exhibit that Cdots with the broader light adsorption rang possess the stronger catalytic activity for the photo-Fenton reaction. The H₂O₂ decomposition rate of red emissive Cdots is 0.074 min^?1, which is 2.64 and 1.46 times than the blue and green emissive Cdots, respectively. And the radical detection results confirm that the photo-Fenton happens in the reaction. In addition, the Cdots photo-Fenton can be carried out in the broad pH range from acidic to basic solution, which has a great potential to treat wastewater in the neutral system.     

LIGHT REQUIREMENTS FOR THE ENHANCED SYNTHESIS OF A PLASTID mRNA DURING SPIRODELA GREENING

A plastid mRNA (5 × 10⁵ mol wt) appears as a burst 3 h after white light greening of steady state dark grown plants of Spirodela oligorrhiza. In this species, chlorophyll synthesis begins after 12 h. The light requirement is different from the pulse of far-red reversible red light required to abolish the lag of chlorophyll synthesis in many species, including Spirodela. Continuous high energy far-red is not stimulatory. When the illumination is not continued throughout the time of incorporation, the stimulation is minimal. Low energy blue and red light are stimulatory, and green and far-red light are ineffectual. Blue light was > 5 times as effective as red light at many dose levels. Illumination with 3 × 10¹⁷ quanta/m²/s (50pEm/cm²/s) blue light at 476 nm gave about half maximum stimulation.