Living with lethal PIP3 levels: viability of flies lacking PTEN restored by a PH domain mutation in Akt/PKB

The phosphoinositide phosphatase PTEN is mutated in many human cancers. Although the role of PTEN has been studied extensively, the relative contributions of its numerous potential downstream effectors to deregulated growth and tumorigenesis remain uncertain. We provide genetic evidence in Drosophila melanogaster for the paramount importance of the protein kinase Akt [also called protein kinase B (PKB)] in mediating the effects of increased phosphatidylinositol 3,4,5-trisphosphate (PIP3) concentrations that are caused by the loss of PTEN function. A mutation in the pleckstrin homology (PH) domain of Akt that reduces its affinity for PIP3 sufficed to rescue the lethality of flies devoid of PTEN activity. Thus, Akt appears to be the only critical target activated by increased PIP3 concentrations in Drosophila.     

Grazing regime as a tool to assess positive side effects of livestock farming systems on wading birds

Wet grasslands support large populations of waders. As these birds are very sensitive to sward height and heterogeneity, grazing management is a key issue to their conservation. On a French coastal marsh consisting of 816 fields of wet grasslands, birds were monitored in spring and grazing regimes were assessed at three periods: year, spring, autumn. Each species was associated with a particular annual grazing index lower than the mean for all grazed fields. During spring, grazing intensity was significantly lower for fields occupied by birds than for those of the entire landscape. Different species of waders showed different preferences to grazing intensity with redshanks and curlews representing two extremes of a gradient going from low to high intensity. In early spring, the more precocious species selected fields with a significantly higher mean and variance in autumn stocking rate than for all grazed fields in previous autumn. These results highlight the need to maintain a variety of grazing regimes if conservation of the waders is to be achieved at the community level. On the basis of our analysis, useful indicators related to thresholds on livestock density and turn-out date can be derived to assess positive side effects of livestock farming systems.     

Mixing history affects gluten protein recovery, purity, and glutenin re-assembly capacity from optimally developed flour–water batters

Batters, from three wheat cultivars, were mixed up to their maximal consistency (t_peak) at different mixing speeds (N) and flour/water ratios [Auger, F., Morel, M.H., Lefebvre, J., Dewilde, M., Redl, A., 2008. A parametric and microstructural study of the formation of gluten network in mixed flour–water batter. Journal of Cereal Science 48, 349–358]. Gluten and starch were extracted from those batters using a process which included two successive steps: dilution and sieving. In order to reveal the specific influence of the mixing step, a standardized gentle washing and sieving procedure was selected. Mixing the batters at t_peak guaranteed a high and stable gluten protein recovery (ca. 82%) irrespective of mixing conditions. SE-HPLC analysis of protein, from flours and batters sampled at t_peak, demonstrated that mixing led to the almost total breakdown of the unextractable glutenin polymers (ca. 80%), whereas their re-assembly occurred during gluten extraction. The extent of glutenin re-assembly in gluten was influenced by the batter mixing history and was mainly related to the number of mixing rotations (N.t_peak). Gluten protein contents were also found related to N.t_peak. We proposed that the leaching of starch from the batter during gluten extraction was controlled by the elasticity of the protein network, i.e. the gluten content in unextractable glutenin. An innovating scheme relating the glutenin re-assembly capacity to the irreversible thiol protein oxidation is proposed.     

Changes and roles of secondary structures of whey protein for the formation of protein membrane at soy oil/water interface under high-pressure homogenization

The conformational changes of whey proteins upon adsorption at the soy oil/water interface were investigated using Fourier transform infrared (FT-IR) spectroscopy. Significant changes were observed in the bands assigned to beta-sheets and alpha-helix structures following the adsorption of proteins at the oil/water interface. The remaining interfacial proteins after Tween 20 desorption revealed small changes in beta-sheet and alpha-helical structures, whereas in the desorbed whey proteins the unordered structures largely increased, and beta-sheet structures almost disappeared. These FT-IR results provide important knowledge about the conformational modifications in whey proteins occurring upon adsorption at the oil/water interface. Finally, specific conformational changes are necessary to stabilize emulsions: adsorption-induced unfolding, increase in alpha-helical structures to establish interactions with the oil phase, and aggregation between adsorbed whey proteins to form protein membranes. Moreover, the structural changes in whey protein adsorbed at the oil/water interface under high-pressure homogenization are irreversible.     

Uptake and xylem transport of fipronil in sunflower

The phenylpyrazole insecticide, fipronil, is used in seed coating against Agriotes larvae, which infest mainly corn and sunflower. Coating the seeds of the cultivated plants with fipronil has proven its effectiveness against Agriotes populations. In the case of sunflower or even corn, the possible root uptake of this insecticide may lead to a toxic effect against pollinators such as honeybees. In the present report, the uptake and transport of fipronil inside the sunflower seedling was studied in the laboratory. In a first study, sunflower was cultivated on an aqueous medium containing fipronil. An intense root uptake of fipronil occurred, leading to a transport into leaves depending upon transpiration. In a second study, plants were cultivated on a soil in which fipronil was uniformly distributed. Under our soil conditions (20% organic carbon), the partition coefficient between soil and water (K(d)) was found to be equal to 386 +/- 30. The average rate of fipronil transfer from soil water to seedlings was from 2 to 2.6 times lower than water transfer. During the 3 week experiment, 55% of recovered labeled compounds was in the parent form and 35% had been converted to lipophilic metabolites, with either a 4-CF(3)-SO(2) or 4-CF(3)-S substituant, which are also very potent lipophilic insecticides. This paper suggests that the possible uptake of fipronil by sunflower seedlings under agronomic conditions is mainly controlled by the physicochemical characteristics of the seed-coating mixture.     

Manipulating the pathway of ammonia assimilation in transgenic non-legumes and legumes

In this paper we discuss the ways in which our understanding of the nature of the molecular controls of nitrogen assimilation has been increased by the use of non-leguminous and leguminous plants with genetically-altered capacities for ammonia assimilation. Using tobacco or Lotus as model plants, Glutamine synthetase (GS) and glutamate synthase (GOGAT) activities have been altered by stimulating or inhibiting in an organ- or tissue-specific manner the expression of the corresponding genes. In a few selected examples, the physiological impact of these genetic manipulations has been studied on plants grown under different nitrogen regimes. The use of such genetically-modified plants will allow us to better understand the molecular control of this metabolic pathway. It is also potentially of great importance in agriculture if such internal and stable modifications are beneficial in terms of nitrogen use efficiency, thus avoiding an excessive utilization of fertilizers or herbicides (GS inhibitors). Our current knowledge and prospects for future development are explored.     

Iron availability from whey protein hydrogels: an in vitro study

The influence of whey protein hydrogel microstructure, filamentous versus particulate, on iron delivery was studied under different conditions, including simulated gastrointestinal conditions. Experiments were initially conducted to determine the impact of pH and enzymes on iron release. The results show that different iron release profiles can be obtained from filamentous and particulate gels. Particulate gels released more iron than filamentous gels at acidic pH, but the opposite was observed at alkaline pH. In the presence of pepsin at pH 1.2 or pancreatin at pH 7.5, both gel types showed increased protein hydrolysis, but only filamentous gels showed increased iron release, suggesting that matrix structure plays an important role in iron delivery. A dissolution test was carried out under gastrointestinal conditions to mimic the in vivo dissolution process. Filamentous gel released most of its iron during the intestinal phase of a simulated digestion, hence protecting iron during its transit in the gastric zone. Absorption of iron by the Caco-2 system, used to estimate intestinal absorption, revealed that filamentous gels favored intracellular iron absorption. These results suggest that filamentous gels show promise as matrices for transporting iron and promoting its absorption and therefore should be of major interest in the development of innovative functional foods.     

CHANGES IN CHEMICAL COMPOSITION AND THE LOSS OF NUTRIENTS IN TRIPODED AND SWATH-CURED HAY

The changes in chemical composition during haymaking, the loss of nutrients in the field and during storage, and the nutritive value of swath-cured and tripoded hay were compared. In good weather no advantage was gained by tripoding the hay. The nutritive value of the hays made by the two methods was similar and the loss of dry matter in the field slightly lower in the swath-cured hay. In a bad season, however, the nutrient loss in the swath-cured hay greatly exceeded that occurring in the tripoded hay and the starch equivalent, as shown by the results of digestibility trials, was markedly lower for the swath-cured.