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  • 1
    Digitale Medien
    Digitale Medien
    Cell death in cranial neural crest development (1992)
    Springer
    Anatomy and embryology 185 (1992), S. 583-588 
    Details
    ISSN: 1432-0568
    Schlagwort(e): Avian embryo ; Hindbrain ; Neural crest ; Cell death ; Cell migration pathways
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The rhombencephalic neural crest, crucial to the patterning and development of many craniofacial structures, migrates laterally from the dorsal hindbrain, but not as a continuous sheet. We have used a vital dye to demonstrate a discontinuous pattern of cell death in the dorsal midline of the avian rhombencephalon associated with the migration of the neural crest. Whilst cell death commences in the dorsal midline of the presumptive mesencephalon at stage 8, two distinct domains of cell death are apparent in the rhombencephalon by stage 11. The rostral domain lies over primary rhombomere RhA1 and rhombomere rh3, while the caudal domain occurs on the neural midline between the otic vesicles, in the region of rh5. Using a marker for the neural crest, we show that the rostral and caudal domains of cell death correlate with the absence of neural crest migration from rh3 and rh5. Thus segment-specific cell death in the dorsal region of particular rhombomeres may account for their subsequent failure to contribute to the cranial neural crest.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00185617
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  • 2
    Digitale Medien
    Digitale Medien
    A segmented pattern of cell death during development of the chick embryo (1992)
    Springer
    Anatomy and embryology 185 (1992), S. 589-598 
    Details
    ISSN: 1432-0568
    Schlagwort(e): Chick embryo ; Development ; Segmentation ; Cell death ; Neural crest
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary During the early development of the chick embryo, specific groups of cells die in characteristic patterns. In this study, Nile Blue sulphate staining was used to reveal a novel pattern of segmentally repeated cell death in the paraxial mesoderm of the chick prior to stage 23. This pattern varies according to the developmental stage of the embryo and shifts rostrocaudally, corresponding to progressing somite differentiation. Initially, during early somite differentiation, cell death is restricted to the rostral half of the somite (the rostral pattern of cell death). After the somite has differentiated into dermomyotome and sclerotome, dead cells appear in superficial tissues in a pyramidal pattern which lies in register (rostrocaudally) with the central part of the sclerotome. Finally, small bands of dying cells are seen between the neural tube and the expanding sclerotome. This third pattern (the ventral path) lies in register with the rostral part of the caudal half of the sclerotome. We show by fluorescent labelling of the migrating neural crest that these patterns of cell death correspond to the routes of neural crest migration. In addition, serial sectioning of stage 23 chick embryos confirms that the position of dying cells correlates with the known routes of neural crest migration and with the sites of development of certain neural crest-derived tissues.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00185618
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  • 3
    Digitale Medien
    Digitale Medien
    O2-dependent inhibition of photosynthetic capacity in intact isolated chloroplasts and isolated cells from spinach leaves illuminated in the absence of CO2 (1978)
    Springer
    Planta 142 (1978), S. 229-233 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Chloroplasts ; Leaf cells ; Photoinhibition ; Photorespiration ; Photosynthesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract When isolated intact chloroplasts or cells from spinach (Spinacia oleracea L.) leaves are incubated in the light in the absence of CO2, their capacity for subsequent CO2-dependent photosynthetic oxygen evolution is drastically decreased. This inhibition is light and oxygen-dependent and can be prevented by addition of bicarbonate. It is concluded that the normal dissipation of photosynthetic energy by carbon assimilation and in processes related to photorespiration is an essential condition for the physiological stability of illuminated intact chloroplasts and cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00388218
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  • 4
    Digitale Medien
    Digitale Medien
    Changes of fluorescence and xanthophyll pigments during dehydration in the resurrection plantSelaginella lepidophylla in low and medium light intensities (1993)
    Springer
    Oecologia 94 (1993), S. 528-533 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Fluorescence ; Photoinhibition ; Photoprotection ; Selaginella lepidophylla ; Xanthophyll cycle
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The changes in photosynthetic efficiency and photosynthetic pigments during dehydration of the resurrection plantSelaginella lepidophylla (from the Chiuhahuan desert, S.W. Texas, USA) were examined under different light conditions. Changes in the photosynthetic efficiency were deduced from chlorophyll a fluorescence measurements (Fo, Fm, and Fv) and pigment changes were measured by HPLC analysis. A small decrease in Fv/Fm was seen in hydrated stems in high light (650 μmol photons·m−2·s−1) but not in low light (50 μmol photons·m−2·s−1). However, a pronounced decline in Fv/Fm was observed during dehydration in both light treatments, after one to two hours of dehydration. A rise in Fo was observed only after six to ten hours of dehydration. Concomitant with the decrease in photosynthetic efficiency during dehydration a rise in the xanthophyll zeaxanthin was observed, even in low-light treatments. The increase in zeaxanthin can be related to previously observed photoprotective non-photochemical quenching of fluorescence in dehydrating stems ofS. lepidophylla. We hypothesize that under dehydrating conditions even low light levels become excessive and zeaxanthin-related photoprotection is engaged. We speculate that these processes, as well as stem curling and self shading (Eickmeier et al. 1992), serve to minimize photoinhibitory damage toS. lepidophylla during the process of dehydration.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00566968
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  • 5
    Digitale Medien
    Digitale Medien
    Photosynthetic response of Ulva rotundata to light and temperature during emersion on an intertidal sand flat (1992)
    Springer
    Oecologia 89 (1992), S. 516-523 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Chlorophyll fluorescence ; Photoinhibition ; Photosynthesis ; Temperature stress ; Ulva
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary We have investigated the diurnal response of photosynthesis and variable photosystem II (PSII) chlorophyll fluorescence at 77 K for thalli of the chlorophyte macroalga, Ulva rotundata, grown in outdoor culture and transplanted to an intertidal sand flat in different seasons. The physiological response in summer indicated synergistic effects of high PFD and aerial exposure, the latter probably attributable to temperature, which usually increased by 8 to 10° C during midday emersion. Except at extreme emersed temperatures in summer (38° C), the light-saturated photosynthesis rate (Pm) did not decline at midday. In contrast, light-limited quantum yield of photosynthetic O2 exchange (τ) and the ratio of variable to maximum fluorescence yield (Fv/Fm) reversibly declined during midday low tides in all seasons. Shade-grown thalli exhibited a fluorescence response suggestive of greater photodamage to PSII, whereas sun-grown thalli had greater photoprotective capacity. The fluorescence decline was smaller when high tide occurred at midday, and was delayed during morning cloudiness. These results suggest that the diurnal response to PFD in this shallow water species is modified by tidal and meteorological factors. U. rotundata has a great capacity for photoprotection which allows it to tolerate and even thrive in the harsh intertidal environment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00317158
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  • 6
    Digitale Medien
    Digitale Medien
    Two components of onset and recovery during photoinhibition of Ulva rotundata (1992)
    Springer
    Planta 186 (1992), S. 399-408 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Chlorophyll fluorescence ; Chloroplast protein (32 kDa) ; Photoinhibition of photosynthesis ; Photosynthesis (photoinhibition) ; Ulva ; Xanthophyll cycle
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Short-term (up to 5 h) transfers of shade-adapted (100 μmol · m−2 · s−1) clonal tissue of the marine macroalga Ulva rotundata Blid. (Chlorophyta) to higher irradiances (1700, 850, and 350 μmol · m−2 · s−1) led to photoinhibition of room-temperature chlorophyll fluorescence and O2 evolution. The ratio of variable to maximum (Fv/Fm) and variable (Fv) fluorescence, and quantum yield (ϕ) declined with increasing irradiance and duration of exposure. This decline could be resolved into two components, consistent with the separation of photoinhibition into energy-dissipative processes (photoprotection) and damage to photosystem II (PSII) by excess excitation. The first component, a rapid decrease in Fv/Fm and in Fv, corresponds to an increase in initial (Fo) fluorescence and is highly sensitive to 1 mM chloramphenicol. This component is rapidly reversible under dim (40 μmol · m−2 · s−1) light, but is less reversible with increasing duration of exposure, and may reflect damage to PSII. The second (after 1 h exposure) component, a slower decline in Fv/Fm and Fv with declining Fo, appears to be associated with the photoprotective interconversion of violaxanthin to zeaxanthin and is sensitive to dithiothreitol. The accumulation of zeaxanthin in U. rotundata is very slow, and may account for the predominance of increases in Fo at high irradiances.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00195321
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