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Light Regulation (light + regulation)
Selected AbstractsLIGHT REGULATION OF PHYCOBILISOME BIOSYNTHESIS AND CONTROL BY A PHYTOCHROME-LIKE PHOTORECEPTORJOURNAL OF PHYCOLOGY, Issue 2000K. Terauchi Ambient light quality changes dramatically affect the composition of light harvesting structures, the phycobilisomes, in many cyanobacterial species. In the cyanobacterium Fremyella diplosiphon, shifts in the ratio of red to green light lead to transcriptional changes and altered synthesis of several phycobilisome components. This process is called complementary chromatic adaptation (CCA). These two colors have opposite effects: red light activates an operon encoding the biliprotein phycocyanin (PC) and inactivates the operon encoding phycoerythrin (PE), whereas green light activates PE synthesis and shuts down PC synthesis. The effects of red and green light on CCA are photoreversible. Thus, CCA is similar to transcriptional processes that are controlled by phytochromes, a family of eukaryotic red/far red photoreversible photoreceptors. We are using molecular genetics to determine the mechanisms by which F. diplosiphon senses changes in the color of light of its environment. Initial mutant generation and complementation lead to the discovery of three CCA regulatory components that are part of a complex two component system. The most interesting of these is RcaE (regulator of chromatic adaptation), a histidine kinase-class protein containing a region in its amino-terminal half with similarity to the chromophore binding domains of phytochromes. Within this region, RcaE contains a cysteine residue in a similar location as that used for covalent attachment of the open-chain tetrapyrrole chromophore in phytochromes. We will present recent data characterizing RcaE, including in vivo analysis of the chromophore that is attached to RcaE, as well as results from our recent isolation of a new CCA regulatory component. [source] Sporulation of Plasmopara viticola: Differentiation and Light RegulationPLANT BIOLOGY, Issue 3 2002J. Rumbolz Abstract: The development of grape downy mildew (Plasmopara viticola) was followed histologically during the entire latent period until the appearance of mature sporangia. Production of sporangiophores and sporangia was assessed using low-temperature scanning electron (LTSEM) and fluorescent light microscopy. Time-course studies using attached leaves of Vitis vinifera cv. Müller-Thurgau revealed that the production of sporangiophores and sporangia is a highly coordinated process and is completed within 7 h. As this differentiation is assumed to occur only in darkness, the influence of light was investigated. For this purpose, different light regimes were applied to infected leaf discs of V. viniferacv. Müller-Thurgau. White light irradiation prevented formation of sporangia, although the growth of the mycelium was not affected. Many sporangiophores were observed that were abnormally shaped, i.e., short hyphae in clusters or thin, extremely elongated hyphae. For the formation of mature sporangia, a prolonged dark period was necessary. Light experiments suggest photosensitivity at the end of the latent period. A terminal white light irradiation caused an inhibitory effect, whereas a final phase of darkness promoted sporangium development. Different light qualities were tested, revealing an inhibition of sporangium development by blue light whereas neither red nor far-red light were effective. [source] Light regulation of retinal dopamine that is independent of melanopsin phototransductionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2009M. A. Cameron Abstract Light-dependent release of dopamine (DA) in the retina is an important component of light-adaptation mechanisms. Melanopsin-containing inner retinal photoreceptors have been shown to make physical contacts with DA amacrine cells, and have been implicated in the regulation of the local retinal environment in both physiological and anatomical studies. Here we determined whether they contribute to photic regulation of DA in the retina as assayed by the ratio of DA with its primary metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), and by c-fos induction in tyrosine hydroxylase (TH)-labelled DA amacrine cells. Light treatment (,0.7 log W/m2 for 90 min) resulted in a substantial increase in DA release (as revealed by an increase in the DOPAC : DA ratio), as well as widespread induction of nuclear c-fos in DA amacrine cells in wild-type mice and in mice lacking melanopsin (Opn4,/,). Light-induced DA release was also retained in mice lacking rod phototransduction (Gnat1,/,), although the magnitude of this response was substantially reduced compared with wild-types, as was the incidence of light-dependent nuclear c-fos in DAergic amacrines. By contrast, the DAergic system of mice lacking both rods and cones (rd/rd cl) showed no detectable light response. Our data suggest that light regulation of DA, a pivotal retinal neuromodulator, originates primarily with rods and cones, and that melanopsin is neither necessary nor sufficient for this photoresponse. [source] The 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] Mutual, non-profit or public interest company?ANNALS OF PUBLIC AND COOPERATIVE ECONOMICS, Issue 2 2002An evaluation of options for the ownership, control of water utilities The purpose of this paper is to evaluate various organizational models for the ownership and control of natural monopolies , specifically the infrastructure of water and sewage provision in England and Wales. First, it summarizes recent discussion of who should own water assets in Britain. The paper notes the opportunity that has arisen for increased consumer involvement, and examines the relative merits of three models that have been suggested as alternatives: a non-profit trust or company, a public interest company, and a consumer mutual. Five criteria are suggested for evaluating the merits of each type: its ability to safeguard the interests of the most important stakeholder, the consumer; avoid the necessity for a heavy regulatory regime; incentivize management to manage efficiently but without ,producer capture'; raise capital relatively cheaply; and resist pressures to demutualize. The paper agrees with the recent paper in this Journal by Morse (2000) that, in theory, the consumer mutual has advantages. It draws on Hansmann's work that suggests consumer ownership of water would be less costly than investor-ownership, providing there are no large conflicts of interest between different types of consumer. Hansmann's thesis is expanded to consider the likely benefits from wider member participation, and the hidden costs of not taking members into account. It then tests out whether customers would be motivated in practice to be active members, introducing a theoretical model of what motivates members of co-operatives and mutuals to participate. The conclusions are that provided managers and board members are committed to encouraging member participation, the consumer mutual model would work well. It would need only light regulation, would avoid producer capture, and would be able to raise capital fairly easily, both from money markets and from members. It would need legislation to prevent it from being demutualized at some time in the future. However, if a participatory corporate culture cannot be guaranteed, or if there is a risk of decline of participation over time, other options such as a non-profit trust or a public interest company would be less risky. [source] Evaluating the British Model of Electricity DeregulationANNALS OF PUBLIC AND COOPERATIVE ECONOMICS, Issue 3 2004by Stephen Thomas It was expected that replacement of monopolies in some areas by markets and price-setting in monopoly areas using a simple incentive formula would mean that regulation of the industry would be ,light'. This article examines how regulation has turned out in practice. It concludes that the promise of ,light' regulation has not been fulfilled. Regulation of competitive markets is a major regulatory activity, incentive regulation has evolved into a complex and intrusive form of rate-of-return, while regulation of industry structure has allowed the industry to descend into a concentrated, vertically integrated structure, at odds with the aims of the reforms. [source] | ||||||||||