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Light Sensitivity (light + sensitivity)
Selected AbstractsThe Heterotrimeric G-protein Complex Modulates Light Sensitivity in Arabidopsis thaliana Seed GerminationPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Javier F. Botto Release of dormancy and induction of seed germination are complex traits finely regulated by hormonal signals and environmental cues such as temperature and light. The Red (R):Far-Red (FR) phytochrome photoreceptors mediate light regulation of seed germination. We investigated the possible involvement of heterotrimeric G-protein complex in the phytochrome signaling pathways of Arabidopsis thaliana seed germination. Germination rates of null mutants of the alpha (G,) and beta (G,) subunits of the G-protein (Atgpa1-4 and agb1-2, respectively) and the double mutant (agb1-2/gpa1-4) are lower than the wildtype (WT) under continuous or pulsed light. The G, and G, subunits play a role in seed germination under hourly pulses of R lower than 0.1 ,mol m,2 s,1 whereas the G, subunit plays a role in higher R fluences. The germination of double mutants of G-protein subunits with phyA-211 and phyB-9 suggests that AtGPA1 seems to act as a positive regulator of phyA and probably phyB signaling pathways, while the role of AGB1 is ambiguous. The imbibition of seeds at 4°C and 35°C alters the R and FR light responsiveness of WT and G-protein mutants to a similar magnitude. Thus, G, and G, subunits of the heterotrimeric G-protein complex modulate light induction of seed germination by phytochromes and are dispensable for the control of dormancy by low and high temperatures prior to irradiation. We discuss the possible indirect role of the G-protein complex on the phytochrome-regulated germination through hormonal signaling pathways. [source] Bigger is better: implications of body size for flight ability under different light conditions and the evolution of alloethism in bumblebeesFUNCTIONAL ECOLOGY, Issue 6 2007A. KAPUSTJANSKIJ Summary 1In social insects, reproductive success and survival of the colony critically depend on the colony's ability to efficiently allocate workers to the various tasks which need to be performed. In bumblebees, workers show a large variation of body size within a colony. Large workers tend to leave the nest and forage for nectar and pollen, whereas small workers stay inside the nest and fulfill nest duties. It was speculated that size-related differences of the sensory system might contribute to alloethism found in bumblebee colonies. 2In the first part, we investigated how body size determines eye morphology. We measured several eye parameters of Bombus terrestris workers and drones. In both, workers and drones, larger individuals had larger eyes with larger facet diameters, more ommatidia and larger ocelli. At similar body size, drones exhibited larger eyes and ocelli compared to workers. Due to theoretical considerations, we predict that large individuals with large eyes should be better able to operate in illumination conditions of lower intensity than small individuals, since ommatidial sensitivity is proportional to the square of facet diameter. 3In the second part, we tested this prediction. In a behavioural experiment, we first caught bumblebees of various sizes in the field and then determined the lowest light intensity level at which they are just able to fly under controlled laboratory conditions. We tested workers of B. terrestris and B. pascuorum, and workers and drones of B. lapidarius. Large bumblebees were able to fly under lower light levels compared to small bees, with light intensity thresholds ranging from 1·1 to 5·5 lux. 4Our results indicate that the increased light sensitivity of the visual system of large bumblebees allows them to fly under poor light conditions, for example, very early in the morning or late at dusk. This is of potential benefit to the survival of a bumblebee colony since flowers that open early in the morning usually have accumulated a relatively high amount of nectar and pollen throughout the night, and large bumblebees can utilize these resources earlier than most other bees. Thus, our findings have important implications for the understanding of the functional significance and evolution of alloethism in bumblebee colonies. [source] Photoconductivity of a Single Small-Molecule Organic Nanowire,ADVANCED MATERIALS, Issue 12 2008Xiujuan Zhang The photoconductivity of a methyl squarylium (MeSq) single-nanowire device shows a high light sensitivity, wavelength-dependent photoresponse, good response speed, and excellent stability and reproducibility. Nanodevices fabricated on flexible substrates (see figure) exhibit good mechanical bendability and no obvious change in performance after bending to a curvature of 0.5,cm,1. [source] Diversity of algal endosymbionts (zooxanthellae) in octocorals: the roles of geography and host relationshipsMOLECULAR ECOLOGY, Issue 8 2005M. J. H. VAN OPPEN Abstract The presence, genetic identity and diversity of algal endosymbionts (Symbiodinium) in 114 species from 69 genera (20 families) of octocorals from the Great Barrier Reef (GBR), the far eastern Pacific (EP) and the Caribbean was examined, and patterns of the octocoral,algal symbiosis were compared with patterns in the host phylogeny. Genetic analyses of the zooxanthellae were based on ribosomal DNA internal transcribed spacer 1 (ITS1) region. In the GBR samples, Symbiodinium clades A and G were encountered with A and G being rare. Clade B zooxanthellae have been previously reported from a GBR octocoral, but are also rare in octocorals from this region. Symbiodinium G has so far only been found in Foraminifera, but is rare in these organisms. In the Caribbean samples, only Symbiodinium clades B and C are present. Hence, Symbiodinium diversity at the level of phylogenetic clades is lower in octocorals from the Caribbean compared to those from the GBR. However, an unprecedented level of ITS1 diversity was observed within individual colonies of some Caribbean gorgonians, implying either that these simultaneously harbour multiple strains of clade B zooxanthellae, or that ITS1 heterogeneity exists within the genomes of some zooxanthellae. Intracladal diversity based on ITS should therefore be interpreted with caution, especially in cases where no independent evidence exists to support distinctiveness, such as ecological distribution or physiological characteristics. All samples from EP are azooxanthellate. Three unrelated GBR taxa that are described in the literature as azooxanthellate (Junceella fragilis, Euplexaura nuttingi and Stereonephthya sp. 1) contain clade G zooxanthellae, and their symbiotic association with zooxanthellae was confirmed by histology. These corals are pale in colour, whereas related azooxanthellate species are brightly coloured. The evolutionary loss or gain of zooxanthellae may have altered the light sensitivity of the host tissues, requiring the animals to adopt or reduce pigmentation. Finally, we superimposed patterns of the octocoral,algal symbiosis onto a molecular phylogeny of the host. The data show that many losses/gains of endosymbiosis have occurred during the evolution of octocorals. The ancestral state (azooxanthellate or zooxanthellate) in octocorals remains unclear, but the data suggest that on an evolutionary timescale octocorals can switch more easily between mixotrophy and heterotrophy compared to scleractinian corals, which coincides with a low reliance on photosynthetic carbon gain in the former group of organisms. [source] Salamander Blue-sensitive Cones Lost During Metamorphosis,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2008Ying Chen The tiger salamander lives in shallow water with bright light in the aquatic phase, and in dim tunnels or caves in the terrestrial phase. In the aquatic phase, there are five types of photoreceptors,two types of rods and three types of cones. Our previous studies showed that the green rods and blue-sensitive cones contain the same visual pigment and have the same absorbance spectra; however, the green rods have a larger photon-catch area and thus have higher light sensitivity than the blue-sensitive cones. Here we show that after metamorphosis, the terrestrial salamander looses the blue-sensitive cones, while the density of the green rods increases. Moreover, the size of the green rod outer segments is increased in the terrestrial phase, compared to that in the aquatic phase. This switch from the blue-sensitive cones to the green rods may represent an adaptation to the dim light environment of the terrestrial phase. [source] UV-induced skin changes due to regular use of commercial sunbedsPHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 5 2002J. Ruegemer Background/aim: Increased pigmentation and thickening of the epidermis are the most important photoprotective skin reactions induced by ultraviolet (UV) radiation. The present study was designed to find out what changes are induced by regular use of commercial sunbeds twice weekly over a period of 6 weeks. Methods: The parameters analysed were skin pigmentation measured by chromametry, minimal erythema dose (MED) as a parameter of light sensitivity, epidermal thickening as determined by histology, induction of keratinocyte apoptosis as determined by TUNEL staining and antioxidant metabolism as measured by changes of cis - and trans -urocanic acid (UCA) content of the skin. Results: As expected, chromametry confirmed the clinically obvious increased skin pigmentation. However, no increase in MED was observed. In addition, neither epidermal thickening nor sunburn cells were seen. Significant detectable changes in proportion of the UCA isomer content of the UV-exposed skin were seen. The total UCA and cis -UCA content increased significantly between nearly all points of measurement. The amount of trans -UCA first decreased, then increased significantly between the different time points. Conclusion: Our data indicate that sunbed-induced tanning is non-protective, which has to be addressed for persons looking for this effect before planning a stay in a sunny climate. However, sunbed-induced tanning may influence immunological reactions. [source] 3164: Post-concussive syndromeACTA OPHTHALMOLOGICA, Issue 2010V PURVIN Purpose Over 85% of traumatic brain injuries (TBI) are considered "mild", also referred to as "concussion". Mild TBI is increasingly recognized as an important public health problem. Despite their designation as "mild", adverse outcomes from such injuries are significant, with 25% of patients still impaired at one year. Visual difficulties are common, reported by two-thirds of patients in a Veterans Administration study. Methods Visual symptoms of mild TBI typically include blurring, light sensitivity, eyestrain, difficulty with near focus, trouble tracking, seeing haloes around lights, and diplopia (monocular and binocular). Results Despite the high incidence of visual symptoms, results of standard eye examination and neuro-ophthalmic testing are typically normal. Conventional neuro-imaging also fails to demonstrate objective evidence of neurologic dysfunction in most cases. Recent developments in neuroimaging (particularly diffusion tensor imaging) and serologic testing (S-100B) have provided some correlates of such injury. Conclusion New information from neuroimaging and serologic testing has helped to provide some objective markers for post-concussive syndromes. The diagnosis of such post-traumatic syndromes remains largely clinical. [source] Gene therapy mediates cone rescue and rejuvenation in the R91W mutant form of Rpe65-deficiency miceACTA OPHTHALMOLOGICA, Issue 2009Y ARSENIJEVIC Purpose Given the advances of gene therapy studies to cure RPE65-derived Leber Congenital Amaurosis (LCA) (clinical trials phase I), it is of prime importance to examine how cones can be rescued in different mutant contexts. Consequently, we evaluated the effect on retinal activity and cone survival of lentivirus-mediated gene therapy in the R91W knock-in mouse model expressing the mutant Rpe65R91W gene. Methods An HIV-1-derived lentiviral vector (LV) expressing either the GFP or the mouse Rpe65 cDNA under the control of a 0.8 kb fragment of the human Rpe65 promoter (R0.8) was produced. LV-R0.8-RPE65 or GFP was injected into 5-days-old (P5) or 1 month-old R91W mice. Functional and morphological retinal rescues were investigated at 4 months of age. Results Increased light sensitivity was detected by ERG and pupillary light responses in animals injected with LV-R0.8-RPE65 at both P5 and 1 month compared to controls. Histological analysis showed improved expression of cone markers and cone outersegment morphology. Furthermore, the density of cones in the region of RPE65 delivery after treatment at P5 reached the wild type level. However, before injection at 1 month of age, only a fraction of the cones (40% of the number found in WT animals) in the Rpe65R91W/R91W mice expressed cone transducin, this fraction increased to 64% after treatment. Moreover, these cones appeared normal. Conclusion We show that lentivirus-mediated Rpe65 gene transfer is very efficacious in early treatments and still efficient during the course of cone degeneration. Moreover, the treatment at 1 month shows a rejuvenation process of the diseased cones. Thus patient suffering from R91W mutation might benefit from a prolonged therapeutic window. [source] | |||||||||||||