Effects of Light and Nutrients on Tomato Plant Compensation for Herbivory by \u3ci\u3eManduca Sexta\u3c/i\u3e (Lepidoptera: Sphingidae)

This preliminary study examined how two resources (light and nutrients) influence the ability of tomato plants to show growth compensation for defoliation by the tobacco homworm (Manduca sexta). Growth rate and biomass of plants grown under high and low levels of light and nutrients, and exposed to 4 levels of defoliation by Manduca sexta were measured. Nutrients affected plant growth rate much more strongly than did light. Light and nutrients, however, each influenced how herbivory affected plant growth. Defoliation significantly decreased growth rate only under conditions of low light and high nutrients. Biomass, on the other hand. was low under all resource treatments except high levels of both light and nutrients, and defoliation significantly decreased biomass only under high levels of both resources. Thus, plants appeared to compensate for damage. in terms of biomass, only under conditions of either low light and/or low nutrients

Small but crucial : the novel small heat shock protein Hsp21 mediates stress adaptation and virulence in Candida albicans

Peer reviewedPublisher PD

Characteristics of E. coli K12 strains carrying both an F prime and an R factor

The interrelationship between an F prime and an F-like or I-like R factor was studied in Escherichia coli K 12 strains carrying both. The donorability of such strains suggested that these plasmids were transferred independently by their own transfer systems. Plaque formation by several male- and female-specific phage was tested; the inhibition by Flac of several female-specific phage was not affected by an F-like R factor. Neither did an R factor affect the incompatibility between Flac and Fhis. However, the surface exclusion characteristic of Flac was lost in the presence of an F-like R factor. This is probably closely related to the simultaneous loss of donorability, the F-pilus, and the f+ antigen: all may be the result of the inhibition by an R product of the formation or activity of a single F product

Hydrology, light and the use of organic and inorganic materials as structuring factors of biological communities in Mediterranean streams

Hydrological disturbances, light availability and nutrients are the most relevant factors determining the structure of the biological communities in Mediterranean rivers. While some hydrological disturbances are able to induce catastrophic effects, which may cause a complete reset in physical and biological conditions, continued enrichment or changes in light availability are factors leading to the progressive shift in the communities of autotrophs and heterotrophs in the systems. Primary production in Mediterranean streams shows relevant seasonal changes which mainly follows the variations in light availability. In most forested streams, the algal community is shade-adapted. Nutrient enrichment (especially phosphorus) leads to marked increases in primary production, but this increase is not lineal and there is a saturation of algal biomass even in the most enriched systems. The heterotrophs (bacteria, fungi) are related to the pattern of DOC availability (which most depends on the seasonal discharge and leaf fall dynamics) and to the available substrata in the stream. It has been repeatedly observed that shorttime increases of extracellular enzyme activities are related to the accumulation of autochthonous (algal) and/or allochthonous (leaves) organic matter on the streambed during spring and summer, this being more remarkable in dry than in wetter years. Flow reduction favours detritus concentration in pools, and the subsequent increase in the density and biomass of the macroinvertebrate community. In Mediterranean streams collectors are accounting for the highest density and biomass, this being more remarkable in the least permanent systems, in accordance with the effect of floods on the organic matter availability. Nutrients, through the effect on the primary producers, also affect the trophic food web in the streams by favouring the predominance of grazers.Los cambios hidrológicos, la disponibilidad de la luz y los nutrientes son los factores más importantes que determinan la estructura y función de la comunidad en los ríos Mediterráneos. Mientras los cambios hidrológicos pueden causar un total reestablecimiento en las condiciones físicas y biológicas, un aumento continuo de la concentración de nutrientes o cambios en la disponibilidad de la luz, son factores que favorecen un cambio progresivo de las comunidades de autótrofos y heterótrofos. La producción primaria en los ríos Mediterráneos presenta cambios estacionales en función de la luz. En los ríos forestados, las algas están adaptadas a la baja intensidad de la luz. El aumento de la concentración de nutrientes, especialmente el fósforo, favorece la producción primaria pero no de forma lineal, ya que aparece una saturación de la biomasa algal en los sistemas más eutróficos. Los heterótrofos (bacterias y hongos) están más relacionados con la disponibilidad de DOC (que a su vez depende de las variaciones estacionales del caudal y de la dinámica de la caída de las hojas) y de sustrato. Se ha observado, repetidamente, una relación entre el aumento a corto plazo de la actividad exoenzimática y la acumulación de biomasa autóctona algal y/o alóctona (hojas) en el lecho del río, durante la primavera y el verano. Esta relación es más evidente en los años más secos. La reducción del caudal favorece la concentración del detritus en las áreas de menor velocidad de corriente ("pools") y se observa un aumento en la densidad y biomasa de los macroinvertebrados. En los ríos Mediterráneos los recolectores alcanzan las mayores densidades y biomasas, especialmente en los sistemas menos permanentes, en relación con el efecto de las variaciones de caudal sobre la disponibilidad de materia orgánica. Los nutrientes, a través de la producción primaria, tienen un efecto también sobre la estructura de la red trófica, favoreciendo a los ramoneadores

Serine- and threonine/valine-dependent activation of PDK and Tor orthologs converge on Sch9 to promote aging

Dietary restriction extends longevity in organisms ranging from bacteria to mice and protects primates from a variety of diseases, but the contribution of each dietary component to aging is poorly understood. Here we demonstrate that glucose and specific amino acids promote stress sensitization and aging through the differential activation of the Ras/cAMP/PKA,PKH1/2 and Tor/S6K pathways. Whereas glucose sensitized cells through a Ras-dependent mechanism, threonine and valine promoted cellular sensitization and aging primarily by activating the Tor/S6K pathway and serine promoted sensitization via PDK1 orthologs Pkh1/2. Serine, threonine and valine activated a signaling network in which Sch9 integrates TORC1 and Pkh signaling via phosphorylation of threonines 570 and 737 and promoted intracellular relocalization and transcriptional inhibition of the stress resistance protein kinase Rim15. Because of the conserved pro-aging role of nutrient and growth signaling pathways in higher eukaryotes, these results raise the possibility that similar mechanisms contribute to aging in mammals

Can uptake length in strams be determined by nutrient addition experiments? Results from an interbiome comparison study

Nutrient uptake length is an important parnmeter tor quantifying nutrient cycling in streams. Although nutrient tracer additions are the preierred method for measuring uptake length under ambient nutrient concentrations, short-term nutrient addition experiments have more irequently been used to estimate uptake length in streams. Theoretical analysis of the relationship between uptake length determined by nutrient addition experiments (Sw\u27) and uptake length determined by tracer additions (Sw)predicted that Sw\u27 should be consistently longer than 5, , and that the overestimate of uptake length by Sw( should be related to the level of nutrient addition above ambient concentrations and the degree of nutrient limitation. To test these predictions, we used data irom an interbiorne study of NH,- uptake length in which 15NH,- tracer and short-term NH,-a ddition experiments were performed in 10 streams using a uniform experimental approach. The experimental results largely contirmed the theoretical predictions: sw\u27 was consistently longer than Sw and Sw\u27:Sw ratios were directly related to the level of NH,- addition and to indicatvrs of N limitation. The experimentally derived Sw\u27:Sw, ratios were used with the theoretical results to infer the N limitation status of each stream. Together, the theoretical and experimental results showed the tracer experiments should be used whenever possible to determine nutrient uptake length in streams. Nutrient addition experiments may be useful for comparing uptake lengths between different streams or cliiferent times in the same stream. however, provided that nutrient additions are kept as low as possible and of similar miagnitude

Efficient Computational Design of a Scaffold for Cartilage Cell Regeneration

Due to the sensitivity of mammalian cell cultures, understanding the influence of operating conditions during a tissue generation procedure is crucial. In this regard, a detailed study of scaffold based cell culture under a perfusion flow is presented with the aid of mathematical modelling and computational fluid dynamics (CFD). With respect to the complexity of the case study, this work focuses solely on the effect of nutrient and metabolite concentrations, and the possible influence of fluid-induced shear stress on a targeted cell (cartilage) culture. The simulation set up gives the possibility of predicting the cell culture behavior under various operating conditions and scaffold designs. Thereby, the exploitation of the predictive simulation into a newly developed stochastic routine provides the opportunity of exploring improved scaffold geometry designs. This approach was applied on a common type of fibrous structure in order to increase the process efficiencies compared with the regular used formats. The suggested topology supplies a larger effective surface for cell attachment compared to the reference design while the level of shear stress is kept at the positive range of effect. Moreover, significant improvement of mass transfer is predicted for the suggested topology

Influence of land use and landscape setting on the ecological status of rivers

The development of bioassessment methods for lotic ecosystems, combined with advances in geographic information systems and spatial analysis, has resulted in a rapidly expanding literature linking land use to river condition. Such studies provide evidence that declines in forested land and increases in agricultural and urban land frequently are predictors of a degraded state of the habitat and biota. However, further research should address a number of challenges to our current knowledge. Both linear and non-linear relationships have been described, and it will be useful to know when to expect non-linear or threshold responses. Legacy effects, where historical impacts may be stronger than present-day impacts, may be common but can be difficult to recognize. There is ample evidence that landscape factors influence lotic ecosystems across a wide range of spatial scales, but the roles of near-stream vs. larger spatial scales can be difficult to separate. This is part of the larger issue that multiple, interacting factors link landscape change to stream response, and the pathways or mechanisms are rarely identified. Natural and anthropogenic gradients often co-vary, because human activities are most intense in certain landscape settings, making it difficult to determine how much of the variation in stream condition should be attributed to human actions. Finally, because bioassessment methods are intended to detect impairment rather than diagnose cause, it is important to establish mechanisms that more precisely link land-use activities to stream condition, in order to prescribe appropriate restoration action. Future research that combines landscape-stream condition analyses with a basic understanding of the pathways whereby human alteration of landscapes influences river condition can serve the dual function of advancing both the management and the understanding of lotic ecosystems.El desarrollo de métodos de evaluación biológica para ecosistemas lóticos, combinados con los avances en los sistemas de información geográfica y de análisis espacial, han originado un rápido incremento en las publicaciones sobre la relación de los usos del suelo con el estado de los ríos. Tales estudios aportan evidencias de que una disminución en la superficie forestal y un incremento en el suelo agrícola y urbano, frecuentemente suponen una degradación del hábitat y la biota. No obstante, las futuras investigaciones deberían conducir hacia nuevos retos para nuestro actual conocimiento. Se han descrito relaciones tanto lineares como no lineares, por lo que será útil conocer cuando prever respuestas límites o no lineares. Los efectos heredados, donde los impactos históricos pueden ser más fuertes que los actuales, pueden ser comunes pero difíciles de reconocer. Hay una amplia evidencia de que los factores del paisaje influyen en los ecosistemas lóticos en un amplio rango a escala espacial, aunque puede resultar difícil separar los papeles de las escalas espaciales locales vs. grandes escalas. Esto es parte de una cuestión mayor en la que múltiples factores que interaccionan relacionan cambios en el paisaje con las respuestas de los ríos, y donde las vías o mecanismos son raramente identificados. Los gradientes naturales y antropogénicos a menudo covarían, debido a que las actividades humanas son más intensas en determinadas formaciones del paisaje, haciendo difícil determinar que grado de la alteración en las condiciones del río serían debidas a las acciones humanas. Finalmente, ya que los métodos de evaluación biológica están dirigidos a detectar impactos más que a diagnosticar las causas, es importante establecer mecanismos que relacionen de forma más precisa las actividades en los usos del suelo con el estado de los ríos, con el fin de prescribir las actuaciones adecuadas de restauración. La investigación futura que sea capaz de combinar los análisis de las condiciones del paisaje y del río con una interpretación básica de los caminos por los que la alteración humana del paisaje influye en el estado del río, puede servir para la doble función de avanzar tanto en la gestión como en el entendimiento de los ecosistemas lóticos

Comparison of resource and consumer dynamics in Atlantic and Mediterranean streams

This study integrates a wide range of ecological data into a comprehensive framework describing the functional and structural dynamics of streams located under different climatic conditions in Spain. Standing stocks of particulate organic matter, algal biomass and macroinvertebrate communities are examined and compared between Atlantic streams of North-West Spain and Mediterranean temporary streams of the island of Majorca. This data set, which link potential food sources to consumer dynamics, allows explanation for the structural and functional variability exhibited by these two fluvial systems. Results indicate that the differences in the dynamics of community trophic structure of the two types of streams are a reflection of their hydrology and climate characteristics.En este estudio se proporciona un marco conceptual que contrasta la dinámica estructural y funcional de ríos localizados en distintas regiones climáticas existentes en España. Con este propósito se examina un amplio rango de datos de materia orgánica particulada bentónica, de biomasa algal y de comunidades de invertebrados en ríos atlánticos del Noroeste de la Península y en ríos temporales Mediterráneos localizados en la isla de Mallorca. Esta serie de datos ecológicos, que relacionan las fuentes de alimentación potenciales con sus consumidores, suministra una base que permite diferenciar no sólo la estructura, si no también el funcionamiento fluvial de ambos sistemas. Los resultados indican que las variaciones en la importancia y dinámica de la estructura trófica en ambos tipos de ríos son un reflejo de sus características hidrológicas y climáticas