Mitochondria. II. The nuclear-mitochondrial relationship in Pelomyxa carolinensis Wilson (Chaos chaos L.)

This study has demonstrated that in the ameba, Pelomyxa carolinensis Wilson (Chaos chaos L.) the limiting membranes of mitochondria and postdivision nuclei are often continuous. The morphological relationship may be functional in that it permits an exchange of material resulting directly or indirectly in an increased enzyme content of the mitochondria. It is suggested that through a series of progressive foldings of its envelope, the nucleus may be a site of formation of mitochondria.     

The effect of nutritional state on photoreversal of ultraviolet injuries in Didinium nasutum

1. The effect of the nutritional state of Didinium nasutum on its resistance to short ultraviolet (UV) radiation (2654 A) and its recovery from the injury following illumination with visible light (4350 A, blue) was studied. 2. The resistance of a didinium to UV is considerably increased by feeding it a paramecium 15 to 60 minutes before exposure to UV. If fed just before exposure to UV, the resistance is less than that of an unfed control. 3. Photoreversal is only slightly greater in didinia fed after irradiation with UV but before exposure to visible light as compared to those fed after exposure to visible light. 4. Irradiated paramecia are eaten by didinia, provided they have not started to cytolyze. Didinia fed on irradiated paramecia divide at about the same rate as controls or slightly faster. 5. The available stock of Didinium declines in vigor with lapse of time after excystment, as measured by the time required for division. The sensitivity of Didinium to UV did not change essentially during the 5 month period over which tests were made. 6. The theoretical implications of the results are considered.     

Effect of Chilling Temperatures on the Protoplasmic Streaming of Plants from Different Climates

A microscope mount was designed so that specimen temperaturescould be monitored and controlled without impairing phase contrastoptics and used to measure rates of protoplasmic streaming between0 and 25 ?C in trichome cells of Lycopersicon esculentum, Lycopersiconhirsutum, Citrullus vulgaris, Tradescantia albiflora, Digitalispurpurea, and Veronica persica. Between 10 and 20 ?C the rates of streaming varied from 2–6µm s^–1 depending on the temperature, and differencesbetween the species were small. The temperature coefficientof streaming rates was found to increase as the temperaturewas lowered so that the plot of log rate against temperaturehad a steeper slope at the lower temperatures. The largest temperature cofficients were for the warmth-requiringL. esculentum (tomato) and C. vulgaris (water melon), and thesmallest for the temperate-zone plants V. persica (speedwell)and D. purpurea (foxglove). The changes in rate always occurredover a range of temperature; no ‘critical temperature’wasobserved below which streaming abruptly stopped and above whichit was active, although the amount of streaming as well as therate decreased as the lowest temperatures were approached. The temperatures experienced by the specimens during the experimentdid not affect the recovery of normal streaming rates betweenabout 10 and 20 ?C. In a population of a wild tomato, Lycopersicon hirsutum Humb.and Bonpl., collected from different altitudes in Peru and Ecuador,i.e. from locations of different environmental temperature,the rate of protoplasmic streaming at 5 ?C was greatest in thevarieties collected from the highest altitudes. The resultssuggest that streaming rates correlate with genetic adaptationto low temperature in the species examined.     

Ribulose 1, 5-Bisphosphate Carboxylase/Oxygenase Activity and Photorespiration during the Ageing of Flag Leaves of Wheat

Photosynthesis, photorespiration, and ribulose bisphosphatecarboxylase/oxygenase activities were measured in intact flagleaves of wheat during ageing. Photorespiration declined verylittle as the leaves aged, and much less than photosynthesis.These changes could not be explained by changes in the ribulosebisphosphate carboxylase to oxygenase ratio of fraction 1 protein.As the leaves grew older the enzyme activities in extracts ofleaves declined in parallel so the ratio remained constant.     

Fine-structural Alterations in Leishmania tropica within Human Macrophages Exposed to Antileishmanial Drugs in Vitro1

The mechanism of action of antileishmanial compounds is poorly understood. Ultrastructural changes in Leishmania tropica within human macrophages exposed in vitro to Pentostam, pentamidine, amphotericin B, WR 6026, ketoconazole, and Formycin B were examined in these experiments. In Pentostam-treated cultures, some organisms exhibited diminished definition of mitochondrial and other membranes, while other organisms had completely disintegrated. Pentostam-exposed macrophages demonstrated loss of membrane definition in the absence of further alterations; it is therefore hypothesized that impaired macrophage membrane function may contribute towards the effect of this drug against macrophage-contained organisms. Leishmania parasites in pentamidine-treated cultures initially demonstrated swollen kinetoplasts and fragmentation of the kinetoplast DNA core. The initial observed effect of the other four drugs on the parasites was cytoplasmic condensation. These ultrastructural studies suggest that all five non-antimonial drugs may have different mechanisms of action than antimony (Pentostam) against Leishmania.     

The effect of introducing the aphid-pathogenic fungus Erynia neoaphidis into populations of cereal aphids

The aphid-pathogenic fungus Erynia neoaphidis, as dried fungus-infected aphids, was applied to caged plots of winter wheat infested with cereal aphids at two sites, one in Hertfordshire and the other in Hampshire, in 1983. In each trial, the fungus became established in the aphid populations in the treated plots even though conditions were drier than average and therefore sub-optimal for fungus spread. Treatment applied in the third week of June increased the proportion of infected aphids more than that applied two weeks later at one site, and the early application was the only treatment to have an obvious effect at the other. In spite of the observed effect of treatments on the proportion of infected aphids, the fungus failed to reduce the numbers of aphids relative to those in untreated plots, chiefly because in these plots many aphids were killed by fungi of the same species as that introduced and other related species from natural sources. Artificial introduction of E. neoaphidis acts too slowly and unpredictably to be likely to form a practical alternative to conventional insecticides for cereal aphid control.