Blue light regeneration of bacteriorhodopsin bleached by continuous light

Photobleaching of bacteriorhodopsin (BR) by continuous light has recently been demonstrated. This bleaching consists of at least two subsequent product states. One of them is absorbing maximally in the blue spectral region. Our present study shows that upon illumination of the bleached sample with blue light a back photoprocess appears, resulting in regeneration of the original BR state. From a technical point of view, the observed phenomenon is similar to the reverting effect of blue light on the photocycle. An important difference is that the photobleached state of BR is much more stable than any of the photocycle intermediates, and may provide an advantage for several technical applications.     

Marine cyanophages and light

In contrast to the phages of heterotrophic hosts, light can play a key role in all aspects of the life cycle of phages infecting ecologically important marine unicellular cyanobacteria of the genera Synechococcus and Prochlorococcus. Phage adsorption, replication, modulation of the host cell metabolism, and survival in the environment following lysis, all exhibit light-dependent components. The analysis of cyanophage genomes has revealed the acquisition of key photosynthetic genes during the course of evolution, such as those encoding central components of the light harvesting apparatus. These discoveries are beginning to reveal novel features of the interactions between parasite and host that shape the biology of both.     

Ultraviolet light and pterygium

The purpose of this study was to evaluate the contribution of ultraviolet light (UV) as a causal factor of primary and pterygium recurrence. A conjuctival autograft transplantation was a surgical method of pterygium treatment. In the first group (38 eyes) were patients with primary and recurrent pterygium exposed to sun (worked outdoors), evaluating geodemographic status, and in the second group (20 eyes) were patients who were not. During 6-12 months of follow up recurrence rate after surgical removal was 27% in the first group and 10% in the second one. UV light seems to have an important role in cause of primary and recurrent pterygium.     

Ultraviolet light provides a major input to non-image-forming light detection in mice

The change in irradiance at dawn and dusk provides the primary cue for the entrainment of the mammalian circadian pacemaker. Irradiance detection has been ascribed largely to melanopsin-based phototransduction [1-5]. Here we examine the role of ultraviolet-sensitive (UVS) cones in the modulation of circadian behavior, sleep, and suprachiasmatic nucleus (SCN) electrical activity. UV light exposure leads to phase-shifting responses comparable to those of white light. Moreover, UV light exposure induces sleep in wild-type and melanopsin-deficient (Opn4(-/-)) mice with equal efficacy. Electrical recordings from the SCN of wild-type mice show that UV light elicits irradiance-dependent sustained responses that are similar to those induced by white light, with characteristic fast transient components occurring at the light transitions. These responses are retained in Opn4(-/-) mice and preserved under saturating photopic conditions. The sensitivity of phase-shifting responses to UV light is unaffected by the loss of rods but is severely attenuated by the additional loss of cones. Our data show that UVS cones play an important role in circadian and sleep regulation in mice.     

Green light for galactolipid trafficking

Galactolipids not only play a crucial role in photosynthesis but are also important for the adaptation of membrane-lipid composition in plants to phosphate-limiting conditions. The enzymes of galactolipid assembly have been localised to the envelope membranes of chloroplasts. Lipid trafficking is essential for galactolipid synthesis and redistribution because lipid precursors originate from two compartments, the endoplasmic reticulum (ER) and the plastid, and because galactolipids have to be transported to extraplastidial membranes during phosphate deprivation. Analysis of Arabidopsis mutants that are impaired in galactolipid synthesis (i.e. dgd1 and dgd2) or in ER-to-plastid lipid transport (i.e. tgd1) has resulted in the identification of a processive galactosyltransferase whose function is still enigmatic.     

Gravity, light and plant form

Plants have evolved highly sensitive and selective mechanisms that detect and respond to various aspects of their environment. As a plant develops, it integrates the environmental information perceived by all of its sensory systems and adapts its growth to the prevailing environmental conditions. Light is of critical importance because plants depend on it for energy and, thus, survival. The quantity, quality and direction of light are perceived by several different photosensory systems that together regulate nearly all stages of plant development, presumably in order to maintain photosynthetic efficiency. Gravity provides an almost constant stimulus that is the source of critical spatial information about its surroundings and provides important cues for orientating plant growth. Gravity plays a particularly important role during the early stages of seedling growth by stimulating a negative gravitropic response in the primary shoot that orientates it towards the source of light, and a positive gravitropic response in the primary root that causes it to grow down into the soil, providing support and nutrient acquisition. Gravity also influences plant form during later stages of development through its effect on lateral organs and supporting structures. Thus, the final form of a plant depends on the cumulative effects of light, gravity and other environmental sensory inputs on endogenous developmental programs. This article is focused on developmental interactions modulated by light and gravity.     

Prokaryotic evolution in light of gene transfer

Accumulating prokaryotic gene and genome sequences reveal that the exchange of genetic information through both homology-dependent recombination and horizontal (lateral) gene transfer (HGT) is far more important, in quantity and quality, than hitherto imagined. The traditional view, that prokaryotic evolution can be understood primarily in terms of clonal divergence and periodic selection, must be augmented to embrace gene exchange as a creative force, itself responsible for much of the pattern of similarities and differences we see between prokaryotic microbes. Rather than replacing periodic selection on genetic diversity, gene loss, and other chromosomal alterations as important players in adaptive evolution, gene exchange acts in concert with these processes to provide a rich explanatory paradigm-some of whose implications we explore here. In particular, we discuss (1) the role of recombination and HGT in giving phenotypic "coherence" to prokaryotic taxa at all levels of inclusiveness, (2) the implications of these processes for the reconstruction and meaning of "phylogeny," and (3) new views of prokaryotic adaptation and diversification based on gene acquisition and exchange.     

Influence of constant light and darkness, light intensity, and light spectrum on plasma melatonin rhythms in senegal sole

Light is the most important synchronizer of melatonin rhythms in fish. This paper studies the influence of the characteristics of light on plasma melatonin rhythms in sole. The results revealed that under long-term exposure to constant light conditions (LL or DD), the total 24 h melatonin production was significantly higher than under LD, but LL and DD conditions influenced the rhythms differently. Under LL, melatonin remained at around 224 pg/ml throughout the 24 h, while under DD a significant elevation (363.6 pg/ml) was observed around the subjective evening. Exposure to 1 h light pulses at MD (mid-dark) inhibited melatonin production depending on light intensity (3.3, 5.3, 10.3, and 51.9 microW/cm(2)). The light threshold required to reduce nocturnal plasma melatonin to ML (mid-light) values was 5.3 microW/cm(2). Melatonin inhibition by light also depended on the wavelength of the light pulses: while a deep red light (lambda>600 nm) failed to reduce plasma melatonin significantly, far violet light (lambda(max)=368 nm) decreased indoleamine's concentration to ML values. These results suggest that dim light at night (e.g., moonlight) may be perceived and hence affect melatonin rhythms, encouraging synchronization to the lunar cycle. On the other hand, deep red light does not seem to inhibit nocturnal melatonin production, and so it may be used safely during sampling at night.     

Coralline photosynthetic physiology across a steep light gradient

Photosynthesis Research - Coralline algae (CA) are globally distributed and fulfil many important roles within coastal ecosystems. In this study, photosynthetically active radiation (PAR) measured...     

On photoprotective mechanisms of carotenoids in light harvesting complex

Carotenoids in light harvesting complex (LHC) play an important role in preventing plants photodamage caused by excess light. Non-photochemical quenching (NPQ) is an important mechanism adopted by plants to deal with high light intensity and the major component is referred to as energy dependent quenching (qE). Despite numerous studies have been devoted to investigating the site and mechanism of qE, there are still much debate on these topics. In this article, we discussed the possible site and underlying mechanism of qE based on the structural similarity of carotenoids. Moreover, being as good antioxidants, carotenoids’ potential protective effects against LHC photo-oxidation by quenching active oxygen species or triplet excited state chlorophyll are also discussed.     

Long-term variation in light intensity on a coral reef

Coral Reefs - An important goal of coral reef science is to understand the roles played by environmental conditions in determining benthic community structure. Pursuit of this goal typically...     

A fly rhodopsin sheds light on thermal taste

In their recent paper, Li and colleagues discover that cold food tastes less sweet to flies, in part by activating bitter sensory neurons through a rhodopsin-dependent mechanism [1]. This work establishes temperature as an important variable in understanding fly taste processing and adds diversity to the sensory roles for rhodopsin receptors.     

Characterization of light gluten and light steep water from a corn wet milling plant

The primary commodity of corn wet milling is starch, but two coproducts (corn gluten feed, CGF and corn gluten meal, CGM) also are produced. CGM and CGF are marketed as animal foodstuffs and are important economically; however, variation in composition reduces quality. There are few data on the effect of composition of the parent process streams, light steep water (LSW) and light gluten (LG), respectively, on composition of CGF and CGM. The objective was to characterize LG and LSW. Samples of LG and LSW were collected: (1) hourly for one day, (2) every 3 h for 3 days, and (3) daily for 3 weeks. Dry matter, N and ash were determined. Variation in composition of LG and LSW was greatest during longer periods of time (days and weeks) rather than shorter (hourly or every 3 h). There was significant variation in DM (solids) content, which directly affected the concentration of other components. Variation in N (protein) of LG and LSW accounted for much of the variation in CGF and CG. Processes that modify processing and reduce variation could increase the quality of CGF and CGM.     

Molecular mechanisms of vertebrate photoreceptor light adaptation.

An important recent advance in the understanding of vertebrate photoreceptor light adaptation has come from the discovery that as many as eight distinct molecular mechanisms may be involved, and the realization that one of the principal mechanisms is not dependent on calcium. Quantitative analysis of these mechanisms is providing new insights into the nature of rod photoreceptor light adaptation.     

Blue light and the regeneration of human rhodopsin in situ

Hubbard has found that the photoisomerization of retinene was important for the regeneration of rhodopsin in vitro, and the object of the present investigation was to find whether this was also true for regeneration in the living human eye. In the Appendix is described a device which permits the rhodopsin density to be measured by analysing the light reflected from the fundus oculi in an ophthalmoscopic arrangement, the measurement taking about 5 seconds. Now if a blue and a yellow light viewed scotopically are adjusted in intensity so as to appear identical, they must bleach rhodopsin equally, but the blue will be more than 10 times as effective in isomerizing retinene. Therefore if retinene isomerization is important for rhodopsin regeneration, blue light should cause a more rapid regeneration after bleaching, and during bleaching the equilibrium level attained should be less profound. But, as the figures show, the course of bleaching and regeneration is identical for the matched yellow or blue bleaching lights, therefore isomerization of retinene is not important for rhodopsin regeneration in the living human eye.     

Phytochrome phosphorylation in plant light signaling.

Reversible protein phosphorylation is a switching mechanism used in eukaryotes to regulate various cellular signalings. In plant light signaling, sophisticated photosensory receptor systems operate to modulate growth and development. The photoreceptors include phytochromes, cryptochromes and phototropins. Despite considerable progresses in defining the photosensory roles of these photoreceptors, the primary biochemical mechanisms by which the photoreceptor molecules transduce the perceived light signals into cellular responses remain to be elucidated. The signal-transducing photoreceptors in plants are all phosphoproteins and/or protein kinases, suggesting that light-dependent protein phosphorylation and dephosphorylation play important roles in the function of the photoreceptors. This review focuses on the role of phytochromes' reversible phosphorylation involved in the light signal transduction in plants.     

Bioluminescence imaging: looking beyond the light

Bioluminescence imaging (BLI) enables in vivo imaging of molecular and cellular processes. It has gained in popularity over the past decade because of its easy translation from in vitro to in vivo experiments, its sensitivity, and its ease of use. However, experience in applying BLI in living subjects is still limited, and many researchers have encountered unexpected or biased BLI readout and reported important influencing factors. In this review, we summarize both the biological and physical effects that occur at the enzyme level or during light propagation towards the camera. The knowledge and detection of such factors, together with the development of new strategies and better BLI compounds, will improve the accuracy of the technique in the future.     

Flowering responses to light and temperature

Light and temperature signals are the most important environmental cues regulating plant growth and development. Plants have evolved various strategies to prepare for, and adapt to environmental changes. Plants integrate environmental cues with endogenous signals to regulate various physiological processes, including flowering time. There are at least five distinct pathways controlling flowering in the model plant Arabidopsis thaliana: the photoperiod pathway, the vernalization/thermosensory pathway, the autonomous floral initiation, the gibberellins pathway, and the age pathway. The photoperiod and temperature/vernalization pathways mainly perceive external signals from the environment, while the autonomous and age pathways transmit endogenous cues within plants. In many plant species, floral transition is precisely controlled by light signals(photoperiod) and temperature to optimize seed production in specific environments. The molecular mechanisms by which light and temperature control flowering responses have been revealed using forward and reverse genetic approaches. Here we focus on the recent advances in research on flowering responses to light and temperature.     

Phytochrome ancestry: sensors of bilins and light

Phytochromes were long thought to have evolved in non-motile photosynthetic eukaryotes for adaptation to unfavorable light environments, but recent studies suggest that phytochromes evolved billions of years earlier from a tetrapyrrole sensor protein progenitor. These investigations have identified phytochromes and phytochrome-related proteins in photosynthetic bacteria (cyanobacteria and purple bacteria), nonphotosynthetic eubacteria and fungi - an observation that has opened new avenues for investigating the origins, molecular evolution and biochemical functions of this ecologically important family of plant photoreceptors.