Light inhibition

Action spectrum for the light-inhibited circadian rhythm of conidiation in the timex-mutant of Neurospora149(... 

Buchholz, G., Ehmann, B., and Wellmann, E., Ultraviolet light inhibition of phytochrome-induced flavonoid biosynthesis and DNA photolyase formation in mustard cotyledons Sinapis alba L.), Plant Physiol, 108, 227, 1995. 

The production of melatonin varies over the course of a day. Darkness stimulates the pineal gland to produce melatonin, while the presence of light inhibits the release of this hormone. Melatonin levels are so low during the day lime that they are almost immeasurable. The amount of melatonin starts to increase around 9 p.m. or 10 p.m. 

Vibrio fischeri (Microtox light inhibition test) Escherichia coli (SOS... 

Decomposer Bacterial testa,h Vibrio fischeri Microtox toxicity Acute sublethal light inhibition (after a 15-min exposure) Environment Canada, 1992a... 

Vibrio fischeri, Microtox light inhibition test Pseudokirchneriella subcapitata, micro-algal growth inhibition assay Daphnia magna, acute immobilization test Ceriodaphnia dubia, chronic reproduction and survival test Thamnocephalus platyurus, Thamnotoxkit lethality assay. 

The following example explains how a pT-value is determined. Within a dilution series, light inhibition percentages in the luminescent bacteria test at a dilution of 1 16 are below the threshold of 20 % (see Sections 5.2 and 5.4). In exponential form, 1 16 is written as 1 24 = 2A. The negative logarithm on a base of 2 of the 1 16 dilution factor is 4, or explained differently, 2 raised to the negative 4th power corresponds to 1 16. Thus, the pT-value of 4 can be attributed to the tested material. 

Microtox V. fischeri BA Light inhibition PW 15 min IC50 4 Microbics, 1992... 

Microtox SPTa V. fischeri ERA Light inhibition WT 20 min IC50 2 Blaise et al., 1994... 

In principle, any battery of bioassays can be employed, but small-scale toxicity tests are preferred because of their performance output (Wells et al., 1998). It is highly desirable that bioassays used were part of the initial bioassay battery (prerequisite step) that proved to be sufficiently sensitive in the WASTOXHAS approach. Examples include the Microtox light inhibition test (Vibrio fischeri) and the microalgal growth inhibition assay (Selenastrum capricornutum ) that were found suitable for two tested wastes (see Section 7). 

The Microtox assay which measures light inhibition with the bacterium Vibrio fisheri is a well known and useful aquatic toxicity test (see Chapter 1, volume 1 of this book). As previously reported (Blaise et al., 1994) and based on our own experience, it appears more appropriate to determine 60 min IC50 for waste leachates, as opposed to 15 min or 30 min endpoints. IC50s measured after 60 min on MIOM leachates were clearly more sensitive and reproducible than those measured at 30 min and 15 min (Ferrari et ah, 1999). Since WASTOXHAS was applied on (poly)metallic matrices in this study, we also found it more suitable to use zinc sulphate as a reference toxicant to periodically verify the sensitivity of the Microtox bacterial light reagent. 

Meanwhile literature has been found (e.g., B.L. Epel in Photophysiology j5, 209, 1973) according to which visible light inhibits various biological processes in E coli. Also experimentation with flow instrumentation has begun and appears to yield interesting results which will be published in due course by F. Drissler. 

Incubating in the dark may release the nitrifiers from light inhibition such that the measured rate exceeds the in situ rate. 

Incubations typicaUy last 48 h, which is sufficient to overcome the lag induced by light inhibition, but is also long enough to create quite unnatural conditions. 

Nitrification rates are often low in the well lit surface waters of the ocean, probably due to light inhibition and competition for NH4 with phytoplankton and heterotrophic bacteria. 

Lipschultz et al. (1985) documented the light inhibition of NH3 oxidation in the Delaware River and concluded that this effect influenced the spatial distribution of nitrification in the estuary. Depending on their depth, light is not usually a problem for nitrification in sediments. In shallow sediments, light may have an indirect positive effect on nitrification rates by increasing photosynthesis, and thus increasing oxygen supply to the sediments (Lorenzen et al., 1998). 

Horrigan, S. G., Carlucci, A. F., and Williams, P. M. (1981). Light inhibition of nitrification in sea-surface films. Journal of Marine Research 39, 557-565. 

Characteristics of free radical reactions include acceleration by free radical initiators or light, inhibition by compounds such as phenols, kinetics including half-powers of concentrations, and the production of small quantities of by-products resulting from radical combination. 

High levels of stress combined with lack of sleep or distorted wake/sleep cycles (e.g., shift work) leads to elevated levels of circulating cortisol. Cortisol depresses the synthesis and release of thymic hormones resulting in compromised development of T lymphocytes and a depressed immune response. Light inhibits the production of melatonin so its level falls when individuals have inadequate sleep. This reduces the melatonin-dependent inhibition of CRH release which amplifies the increase in circulating cortisol. The stress induced immunosuppression is therefore enhanced and prolonged. 

CO can be oxidized to carbon dioxide by selected microbial groups including ammonia oxidizers and methylotrophs that have a broad substrate specificity and high affinity for CO. However, only the carbox-idotrophs obtain energy from this reaction, and these may be unable to assimilate CO efficiently at in situ concentrations. CO turnover times of 4 hours are typical for coastal waters, whereas this varies between 1 and 17 days in the open ocean. The lower oxidation rate in the open ocean may be due to light inhibition of CO oxidation. Extrapolation from laboratory... 

In contrast to the paucity of biochemical data on the photosensory functions of cryptochromes, there are extensive genetic and cell biology data on the roles of cryptochromes in blue light, photoreception in plants and animals, and circadian clock regulation in animals (Gashmore, 2003 Lin and Shalitin, 2003 Sancar, 2003). In Arabidopsis, blue light inhibits elongation of hypocotyls in a cryptochrome-dependent manner. In animals. 

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