Performance of endophyte infected tall fescue in Europe and North America

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The effect of polar lipids on tear film dynamics

In this paper we present a mathematical model describing the effect of polar lipids on the evolution of a precorneal tear film, with the aim of explaining the interesting experimentally observed phenomenon that the tear film continues to move upwards even after the upper eyelid has become stationary. The polar lipid is an insoluble surface species that locally alters the surface tension of the tear film. In the lubrication limit, the model reduces to two coupled nonlinear partial differential equations for the film thickness and the concentration of lipid. We solve the system numerically and observe that the presence of the lipid causes an increase in flow of liquid up the eye. We further exploit the size of the parameters in the problem to explain the initial evolution of the system

Mutations in the TΨC Loop of E. coli tRNA(Lys,3 )Have Varied Effects on In Trans Complementation of HIV-1 Replication

BACKGROUND: Human immunodeficiency virus (HIV-1) exclusively selects and utilizes tRNA(Lys,3 )as the primer for initiation of reverse transcription. Several elements within the TΨC stem loop of tRNA(Lys,3 )are postulated to be important for selection and use in reverse transcription. The post-transcriptional modification at nucleotide 58 could play a role during plus-strand synthesis to stop reverse transcriptase from re-copying the tRNA primer. Nucleotides 53 and 54 within the TΨC stem loop of the tRNA have been shown to be important to form the complex between tRNA and the HIV-1 viral genome during initiation of reverse transcription. RESULTS: To further delineate the features of the TΨC stem loop of tRNA(Lys,3 )in reverse transcription, we have developed a complementation system in which E. coli tRNA(Lys,3 )is provided in trans to an HIV-1 genome in which the PBS is complementary to this tRNA. Successful selection and use of E. coli tRNA(Lys,3 )results in the production of infectious virus. We have used this single round infectious system to ascertain the effects that different mutants in the TΨC stem loop of tRNA(Lys,3 )have on complementation. Mutants were designed within the TΨC loop (nucleotide 58) and within the stem and loop of the TΨC loop (nucleotides 53 and 54). Analysis of the expression of E. coli tRNA(Lys,3 )mutants revealed differences in the capacity for aminoacylation, which is an indication of intracellular stability of the tRNA. Alteration of nucleotide 58 from A to U (A58U), T54G and TG5453CC all resulted in tRNA(Lys,3 )that was aminoacylated when expressed in cells, while a T54C mutation resulted in a tRNA(Lys,3 )that was not aminoacylated. Both the A58U and T54G mutated tRNA(Lys,3 )complemented HIV-1 replication similar to wild type E. coli tRNA(Lys,3). In contrast, the TG5453CC tRNA(Lys,3 )mutant did not complement replication. CONCLUSION: The results demonstrate that post-transcriptional modification of nucleotide 58 in tRNA(Lys,3 )is not essential for HIV-1 reverse transcription. In contrast, nucleotides 53 and 54 of tRNA(Lys,3 )are important for aminoacylation and selection and use of the tRNA(Lys,3 )in reverse transcription

Influence of the Neotyphodium--Tall Fescue Symbiosis on Belowground Processes

Much of the work to date on the relationships between cool season grasses and Neotyphodium fungal endophytes has focused on the physiological, biochemical, and genetic ramifications of the host-fungus relationship and the subsequent influence these effects have on ruminant nutrition, plant adaptation to environmental stresses, and aboveground ecological processes. Relatively little attention has been paid to effects on belowground parameters. In this paper, we review the research evaluating the impact of one endophyte-grass association, the Neotyphodium – tall fescue symbiosis, on underground ecological and biogeochemical processes. We also present some preliminary data showing that the quantity and nature of tall fescue root exudates are influenced by the plant cultivar and fungal genotype. This body of work clearly indicates that effects of the Neotyphodium-tall fescue symbiosis extend to belowground processes; however, additional research is needed to understand the mechanisms driving many of the observed root and soil endophyte effects

Does Fungal Endophyte Infection Improve Tall Fescue’s Growth Response to Fire and Water Limitation?

Invasive species may owe some of their success in competing and co-existing with native species to microbial symbioses they are capable of forming. Tall fescue is a cool-season, non-native, invasive grass capable of co-existing with native warm-season grasses in North American grasslands that frequently experience fire, drought, and cold winters, conditions to which the native species should be better-adapted than tall fescue. We hypothesized that tall fescue’s ability to form a symbiosis with Neotyphodium coenophialum, an aboveground fungal endophyte, may enhance its environmental stress tolerance and persistence in these environments. We used a greenhouse experiment to examine the effects of endophyte infection (E+ vs. E−), prescribed fire (1 burn vs. 2 burn vs. unburned control), and watering regime (dry vs. wet) on tall fescue growth. We assessed treatment effects for growth rates and the following response variables: total tiller length, number of tillers recruited during the experiment, number of reproductive tillers, tiller biomass, root biomass, and total biomass. Water regime significantly affected all response variables, with less growth and lower growth rates observed under the dry water regime compared to the wet. The burn treatments significantly affected total tiller length, number of reproductive tillers, total tiller biomass, and total biomass, but treatment differences were not consistent across parameters. Overall, fire seemed to enhance growth. Endophyte status significantly affected total tiller length and tiller biomass, but the effect was opposite what we predicted (E−\u3eE+). The results from our experiment indicated that tall fescue was relatively tolerant of fire, even when combined with dry conditions, and that the fungal endophyte symbiosis was not important in governing this ecological ability. The persistence of tall fescue in native grassland ecosystems may be linked to other endophyte-conferred abilities not measured here (e.g., herbivory release) or may not be related to this plant-microbial symbiosis

Grassland productivity limited by multiple nutrients

Terrestrial ecosystem productivity is widely accepted to be nutrient limited1. Although nitrogen (N) is deemed a key determinant of aboveground net primary production (ANPP)2,3, the prevalence of co-limitation by N and phosphorus (P) is increasingly recognized4,​5,​6,​7,​8. However, the extent to which terrestrial productivity is co-limited by nutrients other than N and P has remained unclear. Here, we report results from a standardized factorial nutrient addition experiment, in which we added N, P and potassium (K) combined with a selection of micronutrients (K+μ), alone or in concert, to 42 grassland sites spanning five continents, and monitored ANPP. Nutrient availability limited productivity at 31 of the 42 grassland sites. And pairwise combinations of N, P, and K+μ co-limited ANPP at 29 of the sites. Nitrogen limitation peaked in cool, high latitude sites. Our findings highlight the importance of less studied nutrients, such as K and micronutrients, for grassland productivity, and point to significant variations in the type and degree of nutrient limitation. We suggest that multiple-nutrient constraints must be considered when assessing the ecosystem-scale consequences of nutrient enrichment

Soil net nitrogen mineralisation across global grasslands

Soil nitrogen mineralisation (N-min), the conversion of organic into inorganic N, is important for productivity and nutrient cycling. The balance between mineralisation and immobilisation (net N-min) varies with soil properties and climate. However, because most global-scale assessments of net N-min are laboratory-based, its regulation under field-conditions and implications for real-world soil functioning remain uncertain. Here, we explore the drivers of realised (field) and potential (laboratory) soil net N-min across 30 grasslands worldwide. We find that realised N-min is largely explained by temperature of the wettest quarter, microbial biomass, clay content and bulk density. Potential N-min only weakly correlates with realised N-min, but contributes to explain realised net N-min when combined with soil and climatic variables. We provide novel insights of global realised soil net N-min and show that potential soil net N-min data available in the literature could be parameterised with soil and climate data to better predict realised N-min