Drought‐stress and plant resistance affect herbivore performance and proteome: the case of the green peach aphid Myzus persicae (Hemiptera: Aphididae)

Little is known about the simultaneous effects of drought stress and plant resistance on herbivorous insects. By subjecting the green peach aphid Myzus persicae Sulzer to well‐watered and drought‐stressed plants of both susceptible and resistant peach (Prunus persica), the effects of both stressors on aphid performance and proteomics are tested. Overall, the influence of the water treatment on aphid performance is less pronounced than the effect of host plant genetic resistance. On the susceptible cultivar, aphid survival, host acceptance and ability to colonize the plant do not depend on water treatment. On the resistant cultivar, aphid survival and ability to colonize are higher on drought‐stressed than on well‐watered plants. A study examining the pattern of protein expression aiming to explain the variation in aphid performance finds higher protein expression in aphids on the drought‐stressed susceptible cultivars compared with the well‐watered ones. In the susceptible cultivar, the regulated proteins are related to energy metabolism and exoskeleton functionality, whereas, in the resistant cultivar, the proteins are involved with the cytoskeleton. Comparison of the protein expression ratios for resistant versus susceptible plants reveals that four proteins are down‐regulated in well‐watered plants and 15 proteins are down‐regulated in drought‐stressed plants. Drought stress applied to the susceptible cultivar induces the regulation of proteins in M. persicae that enable physiological adaptation to maintain an almost unaltered aphid performance. By contrast, for aphids on the resistant cultivar subjected to drought stress, the down‐regulation of proteins responds to an induced host susceptibility effect.     

Optimal chemostat cascades for periplasmic protein production.

This theoretical work predicts the optimal system design for the steady-state production of secreted protein in a chemostat cascade, using bakers' yeast (Saccharomyces cerevisiae) as the host organism. The protein of interest, mutant invertase, is secreted to the periplasmic space instead of the culture medium on account of its large size. This work uses the secretion model developed and tested by Park and Ramirez (1988). It is shown that the highest productivity is achieved when the chemostat cascade contains two stages, although the improvement over the single-stage productivity is small. When no recycle is used, the advantage of two stages results from the tradeoff between maximizing the cell concentration and maximizing the rate of protein production per cell. When recycle is used, the cell concentration and protein productivity are increased, and the advantage of two stages results from the tradeoff between maximizing the specific protein production rate and maximizing the specific protein secretion rate. Cascades with three stages were also investigated, but these were found to have no improvement over the corresponding two-stage cascades.     

Behavioral thermoregulation of Bulla gouldiana (Gastropoda: Opisthobranchia: Cephalaspidea)

1. 1. The preferred temperature of Bulla gouldiana is 26.7–28.7°C.

2. 2. In constant scotophase, photophase, and light and dark photoperiod the organisms do not have a diel cycle of thermoregulation.

3. 3. It takes the animal 6–16 h to reach the preferred temperature.

4. 4. The lowest and highest temperatures visited were 11 and 33°C.

5. 5. Spawning of the species occurred in the thermal gradient between 27 and 28.5°C.

     

Corona chemistry in Titan.

The atmosphere of Titan is constantly bombarded by galactic cosmic rays and Saturnian magnetospheric electrons causing the formation of free electrons and primary ions, which are then stabilized by ion cluster formation and charging of aerosols. These charged particles accumulate in drops in cloud regions of the troposphere. Their abundance can substantially increase by friction, fragmentation or collisions during convective activity. Charge separation occurs with help of convection and gravitational settling leading to development of electric fields within the cloud and between the cloud and the ground. Neutralization of these charged particles leads to corona discharges which are characterized by low current densities. We have therefore, experimentally studied the corona discharge of a simulated Titan's atmosphere (10% methane and 2% argon in nitrogen) at 500 Torr and 298 K by GC-FTIR-MS techniques. The main products have been identified as hydrocarbons (ethane, ethyne, ethene, propane, propene+propyne, cyclopropane, butane, 2-methylpropane, 2-methylpropene, n-butane, 2-butene, 2,2-dimethylpropane, 2-methylbutane, 2-methylbutene, n-pentane, 2,2-dimethylbutane, 2-methylpentane, 3-methylpentane, n-hexane, 2,2-dimethylhexane, 2,2-dimethylpentane, 2,2,3-trimethylbutane, 2,3-dimethylpentane and n-heptane), nitriles (hydrogen cyanide, cyanogen, ethanenitrile, propanenitrile, 2-methylpropanenitrile and butanenitrile) and a highly branched hydrocarbon deposit. We present the trends of hydrocarbons and nitriles formation as a function of discharge time in an ample interval and have derived their initial yields of formation. The results clearly demonstrate that a complex organic chemistry can be initiated by corona processes in the lower atmosphere. Although photochemistry and charged particle chemistry occurring in the stratosphere can account for many of the observed hydrocarbon species in Titan, the predicted abundance of ethene is too low by a factor of 10 to 40. While some ethene will be produced by charged-particle chemistry, the production of ethene by corona processes and its subsequent diffusion into the stratosphere appears to be an adequate source. Because little UV penetrates to the lower atmosphere to destroy the molecules formed there, the corona-produced species may be long-lived and contribute significantly to the composition of the lower atmosphere and surface.     

Imagerie des tumeurs endocrines digestives : le point de vue du radiologue

Endocrine tumor (ET) can produce and secrete hormones to a variable degree. These neoplasms present a diagnostic challenge, both clinically and radiologically. ET is classified as either syndromic or nonsyndromic on the basis of their clinical manifestations, as differentiated and undifferentiated according to their histological patterns and as pancreatic or extra-pancreatic. Multi-detector row computed tomography (CT) plays an important role in the diagnosis and staging of these lesions. In general, syndromic ET are less than 3 cm in size. They are typically hyperenhancing on CT scans during arterial phase. Nonsyndromic ET tend to be larger than syndromic one and are more likely heterogeneous. Detection of pancreatic localisation and staging of hepatic metastasis could benefit to magnetic resonance imaging (MRI). Endoscopic ultrasound and somatostatin receptor scintigraphy are the two main tools for diagnosis and staging ET. This work presents the role of imaging in the staging and the treatment of these patients.     

The two pathways for oxygen exchange by actomyosin and myofibrils and their dependence on temperature

At an intermediate stage in the hydrolysis of MgATP by actomyosin there is an exchange of oxygen between water and the terminal phosphoryl group of MgATP, tightly bound to the myosin active site. This intermediate oxygen exchange results from the reversible hydrolysis of the bound MgATP. The rate of the exchange cycle (hydrolysis and the reverse) is assumed to be determined by the rate of reverse hydrolysis; and the average time available for exchange is determined by the post-exchange reaction that immediately follows the cycle. Past analytical studies of the exchange, using actomyosin mixtures and myofibrils at room temperature, have revealed two pathways for hydrolysis, operating at a comparable flux but differing greatly in the extent of exchange they support. It is shown here that these pathways also appear over a range of temperatures from 5 to 30 degrees C and that temperature had little effect on their relative fluxes. At each temperature, the flux ratio (%) for the low exchange pathway: high exchange pathway was near 50:50 for actomyosin mixtures and 60:40 for myofibrils. Apparently, the rate-limiting steps that determine the fluxes of the two pathways have a similar temperature dependence. However, the analysis indicates that one or both of the steps that determine the extent of exchange (reverse-hydrolysis and/or the post-exchange reaction) shows a different temperature dependence for the two pathways. We interpret this to reflect a difference in the temperature dependence of the post-exchange reaction, which we propose is exceedingly fast and independent of actin concentration along the low exchange route, but slow and dependent on the actin concentration along the high exchange route. Thus at all temperatures over a broad range of actin concentration there are two pathways of comparable flux that differ primarily in the time available for exchange.