Virus Recovery in Chicken Cells Tested with Rous Sarcoma Cell DNA

DNA from non-virus-producing RSV transformed mammalian cells converts chicken fibroblasts into Rous sarcoma cells producing infectious RSV particles. The recovered virus is the same biologically and antigenically as the virus which originally transformed the mammalian cells.     

Sugar in moderation: sugar diets affect short‐term parasitoid behaviour

The biological control potential of parasitic wasps in the field is expected to increase with the provisioning of sugar sources, which increase longevity and replenish carbohydrate reserves. Apanteles aristoteliae is an important parasitoid of Argyrotaenia franciscana, the orange tortrix, an economic pest in fruit crops. In the present study, the effect of sugar diet on the physiological status of A. aristoteliae is investigated in the laboratory, as well as the effects of nutritional status on short‐term olfactory orientation and parasitism behaviour, and the association between olfactory orientation and immediate parasitism activity. Levels of glycogen, fructose, total sugars, proportional weight gain and volume consumed are higher among females fed 25% sucrose solution than 10% sucrose solution, and lowest for those fed water. Sugar feeding also affects behaviour: wasps with higher levels of fructose or weight gain have a lower probability of making a choice in the olfactometer. Wasps with intermediate fructose levels or weight gain have a higher probability of orienting towards hosts than wasps with low or high levels. Among wasps that make a choice in the olfactometer, wasps fed 10% or 25% sucrose significantly prefer host versus food cues, whereas starved wasps are just as likely to select food cues as host cues.     

Foraging Shorebird Response to Trail Use Around San Francisco Bay

Abstract: We studied how human use of trails affected foraging shorebirds over 24 months at 3 locations around San Francisco Bay, California, USA. By observing sites with trails and nearby sites without trails, we assessed whether numbers of trail users had an effect on the number of birds, species richness, or proportion of shorebirds foraging on tidal mudflats. Human use at non-trail sites averaged <1 person/hour, whereas use at trail sites averaged 68 people/hour. Despite these differences, we found no negative effects of trail use on the number of birds, species richness, or proportion of birds foraging, either overall or by season, when comparing trail to non-trail sites. Human use of trail sites on higher use days (typically weekends) averaged about 2.5 times the level on lower use days (typically weekdays). When comparing bird response on paired lower and higher use days at the trail sites, we found the number of shorebirds decreased with increasing trail use (F_1,119 = 4.20, P = 0.043), with higher trail-use days averaging 25% fewer birds than on lower use days. Although managers may allow human use of trails adjacent to shorebird foraging areas under some conditions, high levels of trail use may negatively affect birds, making it essential to offer birds alternative, trail-free foraging opportunities.     

Does plant height determine the freezing resistance in the páramo plants?

Neotropical ecosystems between treeline and snowline, called páramos, stretch along Andean ranges from Costa Rica to northern Peru. The páramo climate is characterized by regular night frosts occurring throughout the year. Páramo plants use two strategies to deal with freezing temperatures. They either avoid ice formation in the tissues or tolerate extracellular ice formation. We tested the microclimate hypothesis, which suggests that the freezing resistance of the páramo plants is determined by plant height, that is, that taller plants experience a milder microclimate and avoid freezing, whereas smaller plants are exposed to the more extreme thermal conditions near the ground and tolerate them. We measured the temperature at which ice formed inside the plants (the ‘exotherm’), and compared it with the temperature at which 50% damage to the tissue occurred (Lt50); a significant difference between the exotherm and Lt50 would indicate freezing tolerance whereas the absence of a difference would indicate avoidance by supercooling. We analysed the freezing resistance of 38 common Ecuadorian páramo species. We found no correlation between plant height and freezing resistance mechanism or injury temperature and reject the microclimate hypothesis. Tolerant plants reach higher altitudes than avoidant plants, but their altitudinal ranges largely overlap and the Lt50 does not differ between them. These results suggest that there is no qualitative difference between the two strategies to survive the páramo frosts. Shrub leaves were injured at significantly lower temperatures than other life forms, such as herbs, which may reflect leaf anatomical differences among the plants.     

Local and systemic production of nitric oxide in tomato responses to powdery mildew infection

Various genetic and physiological aspects of resistance of Lycopersicon spp. to Oidium neolycopersici have been reported, but limited information is available on the molecular background of the plant–pathogen interaction. This article reports the changes in nitric oxide (NO) production in three Lycopersicon spp. genotypes which show different levels of resistance to tomato powdery mildew. NO production was determined in plant leaf extracts of L. esculentum cv. Amateur (susceptible), L. chmielewskii (moderately resistant) and L. hirsutum f. glabratum (highly resistant) by the oxyhaemoglobin method during 216 h post-inoculation. A specific, two-phase increase in NO production was observed in the extracts of infected leaves of moderately and highly resistant genotypes. Moreover, transmission of a systemic response throughout the plant was observed as an increase in NO production within tissues of uninoculated leaves. The results suggest that arginine-dependent enzyme activity was probably the main source of NO in tomato tissues, which was inhibited by competitive reversible and irreversible inhibitors of animal NO synthase, but not by a plant nitrate reductase inhibitor. In resistant tomato genotypes, increased NO production was localized in infected tissues by confocal laser scanning microscopy using the fluorescent probe 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate. NO production observed in the extracts from pathogen conidia, together with elevated NO production localized in developing pathogen hyphae, demonstrates a complex role of NO in plant–pathogen interactions. Our results are discussed with regard to a possible role of increased NO production in pathogens during pathogenesis, as well as local and systemic plant defence mechanisms.     

Recombinational Events between Exogenous Mouse DNA and Newly Synthesized DNA Strands of Chicken Cells in Culture

When chicken cells are cultivated with mouse ³-DNA and BUdR, ³-labelled light segments are found in replicated strands of cellular DNA and heavy segments occur in DNA strands of mouse origin. This suggests that nascent strands of cellular DNA are partly replaced by pieces of mouse DNA and vice versa.     

Contingent productivity responses to more extreme rainfall regimes across a grassland biome

Climate models predict, and empirical evidence confirms, that more extreme precipitation regimes are occurring in tandem with warmer atmospheric temperatures. These more extreme rainfall patterns are characterized by increased event size separated by longer within season drought periods and represent novel climatic conditions whose consequences for different ecosystem types are largely unknown. Here, we present results from an experiment in which more extreme rainfall patterns were imposed in three native grassland sites in the Central Plains Region of North America, USA. Along this 600 km precipitation–productivity gradient, there was strong sensitivity of temperate grasslands to more extreme growing season rainfall regimes, with responses of aboveground net primary productivity (ANPP) contingent on mean soil water levels for different grassland types. At the mesic end of the gradient (tallgrass prairie), longer dry intervals between events led to extended periods of below-average soil water content, increased plant water stress and reduced ANPP by 18%. The opposite response occurred at the dry end (semiarid steppe), where a shift to fewer, but larger, events increased periods of above-average soil water content, reduced seasonal plant water stress and resulted in a 30% increase in ANPP. At an intermediate mixed grass prairie site with high plant species richness, ANPP was most sensitive to more extreme rainfall regimes (70% increase). These results highlight the inherent complexity in predicting how terrestrial ecosystems will respond to forecast novel climate conditions as well as the difficulties in extending inferences from single site experiments across biomes. Even with no change in annual precipitation amount, ANPP responses in a relatively uniform physiographic region differed in both magnitude and direction in response to within season changes in rainfall event size/frequency.