Factors affecting male-production in Hydatina

Ohne Zusammenfassung

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Factors affecting male-production in Hydatina

     

Legionella pneumophila in Cooling Towers: Fluctuations in Counts, Determination of Genetic Variability by Pulsed-Field Gel Electrophoresis (PFGE), and Persistence of PFGE Patterns

The concentrations of Legionella pneumophila in cooling towers may vary considerably over short periods of time, producing significant fluctuations throughout the year. Despite genetic variability, in small geographical areas the same indistinguishable pulsed-field gel electrophoresis patterns may be shared among different cooling towers and persist over time.     

Purified viral neuraminidase vaccine to control influenza.

The control of influenza by immunoprophylaxis is difficult because of the antigenic mutability of the influenza virus and the unpredictability of its epidemiologic behaviour. The inactivated whole-virus vaccine currently used is not ideal. Vaccination with pure neuraminidase is suggested. The induced antineuraminidase antibody will restrict viral invasion. Mild illness may or may not occur. On subsequent exposure to influenza virus the individual will produce antihemagglutinin and antineuraminidase antibodies and will be resistant to both infection and illness. Since antigenic changes are less frequent in the viral neuraminidase than in the viral hemagglutinin, the vaccine would be usable for longer periods than the presently used inactivated whole-virus vaccine.     

Chloride cell responses to long-term exposure to distilled and hard water in the gill of the armored catfish, Hypostomus tietensis (Loricariidae)

The morphological changes in the gill chloride cells of the armored catfish, Hypostomus tietensis , were investigated after 15 days' exposure to either distilled or hard water. The thickness of the water–blood barrier in the lamellae increased significantly in fish kept in distilled water due to the high proliferation of chloride cells. The apical surface of about 68% of chloride cells was sharply reduced by the development of an apical crypt with a sponge-like surface, although no change in the chloride cell fractional area was found. In contrast, H. tietensis kept in Na⁺, Cl⁻ and Ca²⁺ rich water displayed no significant changes in the number of chloride cells or in their apical surface morphology compared with the control fish. Chloride cell response to ion challenge in H. tietensis suggested the involvement of different strategies to maintain homeostasis in ion-poor water, which may be related to the life history of species.     

Relative sensitivity of photosynthesis and respiration to freeze-thaw stress in herbaceous species : importance of realistic freeze-thaw protocols

The relative effect of a freeze-thaw cycle on photosynthesis, respiration, and ion leakage of potato leaf tissue was examined in two potato species, Solanum acaule Bitt. and Solanum commersonii Dun. Photosynthesis was found to be much more sensitive to freezing stress than was respiration, and demonstrated more than a 60% inhibition before any impairment of respiratory function was observed. Photosynthesis showed a slight to moderate inhibition when only 5 to 10% of the total electrolytes had leaked from the tissue (reversible injury). This was in contrast to respiration which showed no impairment until temperatures at which about 50% ion leakage (irreversible injury) had occurred. The influence of freeze-thaw protocol was further examined in S. acaule and S. commersonii, in order to explore discrepancies in the literature as to the relative sensitivities of photosynthesis and respiration. As bath cooling rates increased from 1°C/hour to about 3 or 6°C/hour, there was a dramatic increase in the level of damage to all measured cellular functions. The initiation of ice formation in deeply supercooled tissue caused even greater damage. As the cooling rates used in stress treatments increased, the differential sensitivity between photosynthesis and respiration nearly disappeared. Examination of agriculturally relevant, climatological data from an 11 year period confirmed that air cooling rates in the freezing range do not exceed 2°C/hour. It was demonstrated, in the studies presented here, that simply increasing the actual cooling rate from 1.0 to 2.9°C/hour, in frozen tissue from paired leaflet halves, meant the difference between cell survival and cell death.