No description available.

No description available.

University, Diss., 2000--München.

Universiẗat, Diss., 2000--Dortmund. / Dateiformat: PDF.

Hatchling marine turtles use visual cues to orient from their nest to the sea at night. However, the wavelengths of light that carry this information have not been properly documented, nor do we understand why they are favored. I measured wavelength irradiance at 20 nm intervals between 340 – 600 nm at a dark nesting beach and then, in the laboratory, determined the thresholds of the hatchlings for each λ that evoked a positive phototaxis. In this study, I show that green turtle hatchlings are (i) most sensitive to the shorter (360 – 480 nm) light wavelengths. Those light energies (ii) dominated the available natural lighting at the nesting beach. They also (iii) presented a steep gradient in irradiance between a landward and seaward view, an important cue for orientation. I attribute the phototactic responses to “stimulus filtering”, the outcome of natural selection that optimizes behavioral responses (seafinding) according to their function, as well as when and where they occur. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

No description available.

The circadian clock is an endogenous timer that allows an organism to anticipate and properly prepare for the daily changes in the environment. This preparation occurs in the form of daily rhythms in metabolism, physiology, and behavior. These approximately 24-hour rhythms are reset upon environmental time cues such as the daily light/dark and temperature cycles. The unicellular green alga Chlamydomonas reinhardtii is a useful model organism for circadian clock research. It shows several well-characterized circadian rhythms of behavior, and the monitoring of its rhythm of phototaxis, or swimming towards light, has been automated. The receptors involved in entraining the clock to the daily light/dark cycle have not yet been identified in this organism. Previous research has shown that blue, green, and red light are effective in resetting the clock in C. reinhardtii. This study focused on identifying the blue light sensor for resetting. One possibility was reception through photosynthesis. This was tested by looking for a defect in the ability to reset the clock upon blue light in cultures treated with the photosynthesis inhibitor DCMU. It was found that photosynthesis does not mediate this process. Instead, a photoreceptor must be involved, and plant-like cryptochrome was the most probable candidate, as it is known to perform this function in higher plants. To determine if plant-like cryptochrome serves this function, available transformants of C. reinhardtii with an RNA interference construct designed to knockdown plant-like cryptochrome expression were used. In this study, the transformants were screened for a reduction in cryptochrome amount using western blot analysis. The two strains with consistently the largest knockdown were tested for defects in resetting the circadian clock upon blue light pulses. Neither strain was found to be less sensitive than the parent strain to blue light induced entrainment. On the contrary, one strain was significantly more sensitive than the parent strain, which suggests a possible inhibitory role for plant-like cryptochrome in the photoentrainment of the clock to blue light in this organism.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 137-142).

Hatchling marine turtles exhibit a positive phototaxis by crawling toward the lowest and brightest horizon when they emerge from nests on the beach at night, which should lead them to the ocean (“seafinding”). Previous research with cheloniid (loggerhead and green turtle) hatchlings demonstrated that the perceptual spectral sensitivities are well below the light available on the beach regardless of lunar phase. The goal of this research was to determine the perceptual spectral sensitivities of leatherback hatchlings, the most distantly related of all extant sea turtle species. This study revealed that, like cheloniids, leatherbacks are most sensitive to shorter wavelengths (< 500 nm). However, leatherbacks were 10 – 100x less sensitive than cheloniids at all tested wavelengths. This difference in sensitivity corresponds with increased crawl duration and circling behavior under new moon conditions when light levels are lowest and the difference in radiance between the landward and seaward direction is small. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2021. / FAU Electronic Theses and Dissertations Collection

Einleitung: Fibroblasten bilden essentielle Komponenten des Bindegewebes und reagieren auf Bestrahlung mit langwelligem Licht. In der Zellkultur lässt sich durch Lichtsignale eine gerichtete Migration (= Phototaxis) induzieren. Da die Migration von Fibroblasten eine zentrale Rolle für die Wundheilung und Regeneration des Bindegewebes spielt, hat die Phototherapie mit langwelligem, nicht-thermischem Licht besondere klinische Bedeutung erlangt. Eindeutige Vorgaben für phototherapeutische Anwendungsparameter existieren bisher jedoch nicht. Fragestellung: Frühere Versuchsanordnungen zur vitalmikroskopischen Untersuchung der Phototaxis von 3T3-Fibroblasten arbeiteten in geschlossenen Kulturflaschen mit Latex- Kügelchen als Lichtquellen, die von externen Strahlungsquellen aktiviert wurden. Die vorliegende Arbeit beschreibt die Entwicklung einer faseroptischen Anordnung mit freier Positionierbarkeit in der offenen Kulturschale. Die primäre Fragestellung war die Eignung der Methode zur Erstellung eines Aktionsspektrums für Phototaxis photoresponsiver, adhärent wachsender Zellen. Material und Methoden: Die Versuche wurden mit NIH-3T3-Zellen der Schweizer Maus durchgeführt. Um die Ergebnisse nicht durch Fremd-Chromophore zu verfälschen, wurden native Zellen ohne Färbemethoden vitalmikroskopisch untersucht. Eine speziell entwickelte Faseroptik und LED-Lichtquellen mit verschiedenen Wellenlängen ermöglichten die direkte Einbringung und Positionierung der Lichtsignale auf dem Boden der Kulturschale. Ein wissenschaftliches Bildbearbeitungsprogramm wurde durch ein Plug-In so modifiziert, dass die Bewegungs- und Zeitparameter halbautomatisch erfasst werden konnten. Ergebnisse: Bei 18 von 44 Langzeitversuchen konnte eindeutiges phototaktisches Verhalten mit Zellkontakt zur Lichtquelle induziert werden. In 16 Fällen kam es zur migratorischen Annäherung und in 10 Fällen zu keiner Reaktion bzw. einer diskret negativen Phototaxis. Das positive phototaktische Verhalten der beiden reagierenden Gruppen war hochsignifikant, der zweiseitige p-Wert des Binomialtests beträgt 0,000388. Bei 77,3 % der Versuche konnte positive Phototaxis demonstriert werden. Schlussfolgerungen: Das neu entwickelte Verfahren eignet sich zur Untersuchung einer Phototaxis und kann damit prinzipiell zur Erstellung von phototaktischen Aktionsspektren eingesetzt werden. Im Vergleich zu bisherigen Methoden können die Bestrahlungsstärken direkt am Lichtwellenleiter gemessen und unerwünschte Fremdkörper-induzierte Wechselwirkungen eliminiert werden. Durch die freie Positionierbarkeit der Lichtquelle in der Kulturschale können die zu beobachtenden Zellen beliebig ausgewählt werden. / Background: Fibroblasts are essential constituents of connective tissue and react upon irradiation with long-wavelength light. In cell culture, directed migration (= phototaxis) can be induced by light stimuli. Fibroblast migration and activity play a central role for wound healing and connective tissue regeneration. In consequence, phototherapy with non-thermal, long wavelength light obtained increasing clinical importance. However, accepted guidelines for phototherapeutical treatment parameters are still lacking. Objective: Existing assays for microscopic observation of phototactic reaction of 3T3- fibroblasts in a live cell chamber use closed cell culture flasks with small light-scattering latex particles attached to the surface of the flask bottom prior to cell seeding, which can be illuminated by an external light source. The present work describes the development of a fiberoptic assembly providing free positioning of the light source in an open culture dish. The primary objective is the eligibility of this method for determination of a phototactic action spectrum for photoresponsive adherent cell species. Materials and Methods: Experiments were conducted using Swiss mouse NIH-3T3-cells. Native cells without staining were used for elimination of potential dye-induced cell-light interferences. A light microscope with field illumination shutter simulation and live cell chamber was used in combination with a specially devised LED-light-fed fiberoptic assembly providing different wavelengths, which could be directly positioned on the inner bottom of the culture dish. A scientific image processing application was modified by a special plug-in for semi-automatic acquisition of cellular locomotion parameters and temporal data token. Results: A total of 44 experiments were conducted. 18 essays resulted in full phototactic reaction characterized by pseudopodium contact with the fiberoptic aperture, another 16 essays showed migratory approximation without direct contact with the light source. 10 essays displayed no reaction or discrete negative phototaxis. The positive phototaxis of the two responding groups was highly significant in the two-sided binomial test (p = 0.000388). For 77.3 % of the experiments positive phototaxis could be demonstrated. Conclusions: The newly developed assay is appropriate for the induction of phototactic behaviour and can be utilized for the determination of phototactic action spectra. In contrast to existing methods the irradiances can be measured directly at the aperture of the optical fiber and biasing foreign object-induced effects can be eliminated. Due to arbitrary positioning of the light source the cells can be chosen freely for examination.