Effects of Hydroxyurea on Crithidia fasciculata

SYNOPSIS Hydroxyurea (HU) inhibits increase in cell number in cultures of Crithidia fasciculata. Complete inhibition is produced by 8 mM and higher concentrations. If HU is not removed, population growth resumes in 45–50 h: if HU is removed, partially synchronous growth occurs through 2 cycles. During HU inhibition, the rate of DNA synthesis is reduced to 1% of that in exponentially growing cultures; protein and RNA syntheses continue at slightly reduced rates. Mean cell size and protein and RNA contents per cell increase; rate of oxygen consumption per mg cell protein remains constant. The behavior of a culture upon addition of HU and upon its removal agrees with predictions based on the hypothesis that the only direct effect of HU is to block DNA synthesis. The synchrony produced by HU is judged satisfactory for investigations of kinetoplast and nuclear replication but not for biochemical characterization of other aspects of the cell cycle.     

Trophic relationships in the soil microfood-web: predicting the responses to a changing global environment

In this article, we evaluate how global environmental change may affect microfood-webs and trophic interactions in the soil, and the implications of this at the ecosystem level. First we outline how bottom-up (resource control) and top-down (predation-control) forces regulate food-web components. Food-web components can respond either positively or negatively to shifts in NPP resulting from global change, thus creating difficulties in developing general principles about the response of soil biota to global change phenomena. We also demonstrate that top-down effects can be important in soil food-webs, creating negative feed-backs which may partially counter bottom-up effects. Secondly, we determine how soil food-webs and the processes they regulate respond to various global change phenomena. Enhanced atmospheric CO₂ levels can have two main effects on plants which are relevant for the soil food-web, i.e. enhanced NPP (often positive) and diminished organic matter quality (with negative effects, at least in the short term). Climate change effects resulting from elevated CO₂ levels may be mainly secondary through alteration of vegetation, as shown by examples. Intensification of land management is usually associated with greater disturbance, which alters soil food-web composition and key processes; this is particularly apparent in comparisons of conventionally tilled and nontilled agroecosystems. Global change involves shifts in plant species composition and diversity, possibly affecting soil food-webs; we interpret this in terms of theories relating biodiversity to ecosystem function. We conclude that a more detailed understanding of interactions between NPP, soil organic matter and components of the soil food-web, as well as their regulation of biogeochemical processes and ultimately ecosystem-level properties, is essential in better understanding long-term aspects of global change phenomena.     

Abscisic Acid Stimulation of the Formation of an Ageing-specific Nuclease in Avena Leaves

In excised Avena leaves, depending on the duration of treatment,abscisic acid (10^–5 M) had two distinctly different effectson the level of individual nucleases. In short-term experiments(3-h treatment, abscisic acid increased the level of a relativelypurine (guanine)-specific ribonuclease, in comparison with thewater control. Accumulation of the abscisie acid-induced ribonuclease,however, levelled off rapidly during incubation and the amountof the enzyme approached a plateau in about 6 h. As the accumulationof this ribonuclease became retarded, abscisic acid induceda striking increase in the level of another nuclease, an enzymenon-specific in relation to the sugar moiety but exhibitinga relative adenine specificity. This latter nuclease also wasshown to accumulate slowly in intact Avena leaves during ‘natural’senescence. The Avena leaves contain, in small concentrations,a chromatographic variant of the sugar non-specific nuclease.This minor variant, despite its identical enzymological properties,was found to be physiologically different from the main componentin that its concentration did not depend on the age of the tissuesand was not affected by abscisic acid.     

Traumatic myiasis in dogs caused by Wohlfahrtia magnifica and its importance in the epidemiology of wohlfahrtiosis of livestock

Abstract.  In the province of Al Hoceima, northern Morocco, and on two farms in Hungary, dogs were inspected for the presence of traumatic myiasis. Nine and four infested dogs were found in Morocco and Hungary, respectively. All the larvae and adults reared from them in the laboratory were identified as Wohlfahrtia magnifica (Schiner) (Diptera: Sarcophagidae). To our knowledge, these are the first cases of wohlfahrtiosis in dogs to be reported in these countries. All infested animals lived close to livestock, where wohlfahrtiosis was endemic. Infested body sites included limbs (six cases), external genitalia (two), ears (three), nose (one) and neck (one). Developing larvae caused severe welfare problems and tissue destruction in most cases. Although the number of cases reported here is small, wohlfahrtiosis in dogs may be very important from an epidemiological perspective because farm and stray dogs can act as both reservoirs and carriers of this parasitic fly species. Therefore, education of dog owners concerning the risk factors in endemic regions is recommended in order to reduce the prevalence of wohlfahrtiosis in dogs and thereby in livestock. Both owners and veterinarians should pay regular attention to any wounds and to the natural orifices of dogs, especially during the fly seasons.     

Hormonal Control of Nuclease Level in Excised Avena Leaf Tissues1

In excised Avena leaves, kinetin and benzyladenine decreased,while abscisic acid and benzimidazole increased the over-allnuclease level. Significant effects were observed as early as2 h after treatment. Not all the nucleases of the Avena leafwere affected by the growth regulators. Changes in over-allnuclease activity were accounted for almost entirely by changesin the amount of a relatively purine-specific endo-ribonuclease,which produces 2',3'-cyclic phosphates as breakdown products.Slight changes induced by the growth regulators were also detectedin the amount of a sugar non-specific endo-nuclease which produces5'-nucleotides and has a relative specificity for adenylic acid.The level of an alkaline phosphodiesterase, an exo-nucleasewhich produces 5'-nucleotides, was not affected by any of thegrowth regulators tested. Gibberellic acid and indol-3yl-aceticacid did not influence the level of Avena nucleases.     

Prevalence of flea infestation in dogs and cats in Hungary combined with a survey of owner awareness

A survey was conducted in order to gain current information on flea species (Siphonaptera: Pulicidae) infesting dogs and cats living in urban and rural areas of Hungary, along with data on the factors that affect the presence, distribution and seasonality of infestation. In addition, owner awareness of flea infestation was evaluated. Practitioners in 13 veterinary clinics were asked to examine all dogs and cats attending the clinic and to collect fleas, when present, on 2 days in each month from December 2005 to November 2006. They also completed a questionnaire for each animal examined. A total of 319 dogs (14.1%) were found to be infested; the highest prevalence (27.1%) of infestation on dogs occurred in August and the lowest (5.4%) in May. Prevalence of fleas on cats was higher (22.9%); the highest (35.0%) and lowest (8.1%) prevalences occurred in July and April, respectively. Fleas were more prevalent in rural (387/1924 animals, 20.2%) than in urban (161/1343 animals, 12.0%) areas. Three species, Ctenocephalides felis (Bouché), Ctenocephalides canis (Curtis) and Pulex irritans L., were found. On dogs, the prevalence of C. canis alone was 53.0%, whereas that of C. felis alone was 36.0%. Only 19 specimens of P. irritans were found on 14 dogs from rural habitats only. Prevalence of C. felis only on cats was 94.3%; the remaining cats were infested with either C. canis or with mixed infestations of C. felis and C. canis. More than half (51.4%) of the owners of infested dogs and cats had not used flea control products in the past year or more, and five times as many owners in rural than urban areas had not used flea control products in the same period. Very few owners reported having attempted to kill fleas in their animals' environment; instead, they believed that fleas were acquired from other cats or dogs.