RESUMEN
Confocal microscopy in combination with real-space particle tracking has proven to be a powerful tool in scientific fields such as soft matter physics, materials science and cell biology. However, 3D tracking of anisotropic particles in concentrated phases remains not as optimized compared to algorithms for spherical particles. To address this problem, we developed a new particle-fitting algorithm that can extract the positions and orientations of fluorescent rod-like particles from three dimensional confocal microscopy data stacks. The algorithm is tailored to work even when the fluorescent signals of the particles overlap considerably and a threshold method and subsequent clusters analysis alone do not suffice. We demonstrate that our algorithm correctly identifies all five coordinates of uniaxial particles in both a concentrated disordered phase and a liquid-crystalline smectic-B phase. Apart from confocal microscopy images, we also demonstrate that the algorithm can be used to identify nanorods in 3D electron tomography reconstructions. Lastly, we determined the accuracy of the algorithm using both simulated and experimental confocal microscopy data-stacks of diffusing silica rods in a dilute suspension. This novel particle-fitting algorithm allows for the study of structure and dynamics in both dilute and dense liquid-crystalline phases (such as nematic, smectic and crystalline phases) as well as the study of the glass transition of rod-like particles in three dimensions on the single particle level.
Asunto(s)
Coloides/química , Interpretación de Imagen Asistida por Computador/métodos , Microscopía Confocal/métodos , Modelos Químicos , Nanotubos/química , Nanotubos/ultraestructura , Algoritmos , Simulación por Computador , Modelos Moleculares , Conformación Molecular , Imagen Molecular/métodosRESUMEN
The gymnotid electric fish, Eigenmannia virescens, exhibits electric discharge rhythmicity both in alternate light-dark (LD; 12 h light, 12 h dark [LD 12:12]) and in constant dark (DD) conditions. It suggests that the electric discharge rhythm is under control of the circadian clock. The free-running periods (FRPs) of electric discharge rhythms at 21 degrees C in DD are greater than, but close to, 24 h. The maximum of the electric discharge in the Eigenmannia system peaks approximately at circadian time 6 (CT6) in the middle of the subjective day. The circadian oscillator in the system is temperature compensated. This original report reveals the relationship between electric discharge activity and the circadian pacemaker in Eigenmannia and provides an alternative system to investigate circadian rhythms in vertebrates.
Asunto(s)
Ritmo Circadiano/fisiología , Pez Eléctrico/fisiología , Animales , Electrofisiología , Ambiente Controlado , Fotoperiodo , TemperaturaRESUMEN
Twenty-nine Fusarium species isolated from various sources in different districts of Taiwan were tested for their ability to produce fumonisins in corn cultures. Only Fusarium moniliforme produced fumonisin B1 (FB1) and fumonisin B2 (FB2). The finding that the other 28 Fusarium species produced neither FB1 nor FB2 is preliminary because only one strain per species was studied. The detection of FB1 and FB2 in cultures of F. moniliforme was demonstrated by TLC and HPLC, and FB1 was further confirmed by mass spectrometry. In a separate experiment, in which 38 strains of F. moniliforme were tested for fumonisins, approximately 66% (25/38) produced FB1 and/or FB2. Of the 25 strains, 14 produced only FB1 and 11 produced both FB1 and FB2, and the amounts of FB1 and FB2 produced by different strains varied greatly. This is the first report that fumonisins are found in corn cultures experimentally infected with F. moniliforme strains from Taiwan. It is safe to assume that fumonisin producing strains of F. moniliforme are widely distributed among the economic crops such as corn, rice, sugarcane, and sorghum throughout the Island.
Asunto(s)
Fumonisinas , Fusarium/metabolismo , Micotoxinas/biosíntesis , Microbiología de Alimentos , Fusarium/aislamiento & purificación , Especificidad de la Especie , TaiwánRESUMEN
The mechanisms of the biological clock are today being investigated in single neurons in cell culture or in unicellular and in other microorganisms. The results show that all components of this "endogenous clock" can be found at the cellular level. The cellular circadian program is controlled by a complex system of biochemical reactions, which can contain more than one circadian pacemaker and which comprises several feed-back loops at the input and the output side. This complex temporal program is a prerequisite for specialization and survival within the chrono-ecological niches of the "temporal space" day. It enables organisms on the one hand to adaptively react to environmental changes and thereby reaching transient independence of the external, physical time course; on the other side, it ensures that the endogenous day never runs out of synchrony with the solar day of the environment.