Cation control of fluorescence emission,light scatter,and membrane stacking in pigment mutants of Chlamydomonas reinhardi

The effect of monovalent and divalent cations on thylakoid membrane stacking, light scatter, and fluorescence yield were examined in broken-cell preparations of the wild type of Chlamydomonas reinhardi and mutants lacking various pigment-protein complexes. Membrane stacking as determined by electron microscopy and light scatter at 540 nm shows an approximate linear proportionality. In a mutant lacking photosystem II reaction centers, stimulation of light scatter and of fluorescence yield show different kinetics at a given cation concentration and show different titration curves as a function of cation concentration. Control of membrane stacking and fluorescence yield is attributed, respectively, to two locations differing in their anionic charge density. In a mutant lacking chlorophyll-protein complex I, the cation effect on the fluorescence yield is reversed giving rise to a decrease in fluorescence intensity upon cation addition instead of the usual increase. We conclude that the site of energy spillover between the two photosystems is located exterior to chlorophyll-protein complex I but not at the junction of chlorophyll-protein complex I and the rest of the light-harvesting antenna.     

Ultrastructure-function relationship in Chlamydomonas reinhartii thylakoids,by means of a comparison between the wild type and the F3 4 mutant which lacks the photosystem II reaction center

The F_{3 4} mutant strain ofChlamydomonas reinhartii is deficient in photosystem II reaction centers. The E fracture faces of the thylakoid membranes of this mutant show a considerable reduction in the number of particles present and in their size compared with the wild type. We conclude that the polypeptides associated with the photosystem II reaction centers, which are missing in SDS polyacrylamide gel electrophoresis patterns of proteins from this mutant strain, are part of the EF particles and are required for assembly of these particles.     

Developmental nicotine exposure enhances inhibitory synaptic transmission in motor neurons and interneurons critical for normal breathing

Nicotine exposure in utero negatively affects neuronal growth, differentiation, and synaptogenesis. We used rhythmic brainstems slices and immunohistochemistry to determine how developmental nicotine exposure (DNE) alters inhibitory neurotransmission in two regions essential to normal breathing, the hypoglossal motor nucleus (XIIn), and preBötzinger complex (preBötC). We microinjected glycine or muscimol (GABA_A agonist) into the XIIn or preBötC of rhythmic brainstem slices from neonatal rats while recording from XII nerve roots to obtain XII motoneuron population activity. Injection of glycine or muscimol into the XIIn reduced XII nerve burst amplitude, while injection into the preBötC altered nerve burst frequency. These responses were exaggerated in preparations from DNE animals. Quantitative immunohistochemistry revealed a significantly higher GABA_A receptor density on XII motoneurons from DNE pups. There were no differences in GABA_A receptor density in the preBötC, and there were no differences in glycine receptor expression in either region. Nicotine, in the absence of other chemicals in tobacco smoke, alters normal development of brainstem circuits that are critical for normal breathing. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 337–354, 2016     

Ultrastructure and some other properties of inverted thyroid follicles in suspension culture

Separated thyroid follicles in suspension culture invert in 5% serum. In some, the inversion is not complete in that a small normal follicle persists completely in the interior of an inverted follicle. In inverted follicles the lumens are distended and electron lucent. The bounding epithelial cells are stretched, have relatively few microvilli on the surface toward the medium but they have bundles of oriented microfilaments usually located near the lumen. The cells are connected together by tight junctions. When inverted follicles are punctured, the lumen shrinks, the cells retract and become cuboidal and microvilli reappear. Microfilaments persist at the luminal surface but no longer in oriented bundles. No appreciable extracellular matrix is present at the basal cell surface in contact with the lumen, but matrix is occasionally observed between cells. Since bundles of microfilaments like stress fibers are observed in the cells in suspension culture, the presence of stress fibers in cells in monolayer culture is probably not dependent on attachment but might be a reflection of the spreading of the attached cells.