Ryegrass-based diet and barley supplementation: Partition of nitrogenous nutrients among splanchnic tissues and hind limb in finishing lambs1

Local-scale dynamics of plant-pesticide interactions in a northern Brittany agricultural landscape

Soil pollution by anthropogenic chemicals is a major concern for sustainability of crop production and of ecosystem functions mediated by natural plant biodiversity. Understanding the complex effects of soil pollution requires multi-level and multi-scale approaches. Non-target and agri-environmental plant communities of field margins and vegetative filter strips are confronted with agricultural xenobiotics through soil contamination, drift, run-off and leaching events that result from chemical applications. Plant-pesticide dynamics in vegetative filter strips was studied at field scale in the agricultural landscape of a long-term ecological research network in northern Brittany (France). Vegetative filter strips effected significant pesticide abatement between the field and riparian compartments. However, comparison of pesticide usage modalities and soil chemical analysis revealed the extent and complexity of pesticide persistence in fields and vegetative filter strips, and suggested the contribution of multiple sources (yearly carry-over, interannual persistence, landscape-scale contamination). In order to determine the impact of such persistence, plant dynamics was followed in experimentally-designed vegetative filter strips of identical initial composition (Agrostis stolonifera, Anthemis tinctoria/Cota tinctoria, Centaurea cyanus, Fagopyrum esculentum, Festuca rubra, Lolium perenne, Lotus corniculatus, Phleum pratense, Trifolium pratense). After homogeneous vegetation establishment, experimental vegetative filter strips underwent rapid changes within the following two years, with Agrostis stolonifera, Festuca rubra, Lolium perenne and Phleum pratense becoming dominant and with the establishment of spontaneous vegetation. Co-inertia analysis showed that plant dynamics and soil residual pesticides could be significantly correlated, with the triazole fungicide epoxiconazole, the imidazole fungicide prochloraz and the neonicotinoid insecticide thiamethoxam as strong drivers of the correlation. However, the correlation was vegetative-filter-strip-specific, thus showing that correlation between plant dynamics and soil pesticides likely involved additional factors, such as threshold levels of residual pesticides. This situation of complex interactions between plants and soil contamination is further discussed in terms of agronomical, environmental and health issues.

Herbicide-related signaling in plants reveals novel insights for herbicide use strategies, environmental risk assessment and global change assessment challenges

Herbicide impact is usually assessed as the result of a unilinear mode of action on a specific biochemical target with a typical dose-response dynamics. Recent developments in plant molecular signaling and crosstalk between nutritional, hormonal and environmental stress cues are however revealing a more complex picture of inclusive toxicity. Herbicides induce large-scale metabolic and gene-expression effects that go far beyond the expected consequences of unilinear herbicide-target-damage mechanisms. Moreover, groundbreaking studies have revealed that herbicide action and responses strongly interact with hormone signaling pathways, with numerous regulatory protein-kinases and -phosphatases, with metabolic and circadian clock regulators and with oxidative stress signaling pathways. These interactions are likely to result in mechanisms of adjustment that can determine the level of sensitivity or tolerance to a given herbicide or to a mixture of herbicides depending on the environmental and developmental status of the plant. Such regulations can be described as rheostatic and their importance is discussed in relation with herbicide use strategies, environmental risk assessment and global change assessment challenges.

Nutritional regulation of the anabolic fate of amino acids within the liver in mammals: concepts arising from in vivo studies

At the crossroad between nutrient supply and requirements, the liver plays a central role in partitioning nitrogenous nutrients among tissues. The present review examines the utilisation of amino acids (AA) within the liver in various physiopathological states in mammals and how the fates of AA are regulated. AA uptake by the liver is generally driven by the net portal appearance of AA. This coordination is lost when demands by peripheral tissues is important (rapid growth or lactation), or when certain metabolic pathways within the liver become a priority (synthesis of acute-phase proteins). Data obtained in various species have shown that oxidation of AA and export protein synthesis usually responds to nutrient supply. Gluconeogenesis from AA is less dependent on hepatic delivery and the nature of nutrients supplied, and hormones like insulin are involved in the regulatory processes. Gluconeogenesis is regulated by nutritional factors very differently between mammals (glucose absorbed from the diet is important in single-stomached animals, while in carnivores, glucose from endogenous origin is key). The underlying mechanisms explaining how the liver adapts its AA utilisation to the body requirements are complex. The highly adaptable hepatic metabolism must be capable to deal with the various nutritional/physiological challenges that mammals have to face to maintain homeostasis. Whereas the liver responds generally to nutritional parameters in various physiological states occurring throughout life, other complex signalling pathways at systemic and tissue level (hormones, cytokines, nutrients, etc.) are involved additionally in specific physiological/nutritional states to prioritise certain metabolic pathways (pathological states or when nutritional requirements are uncovered).

Net portal and hepatic flux of nutrients in growing wethers fed high-concentrate diets with oscillating protein concentrations

We hypothesized that oscillating dietary CP would improve N retention by increasing the uptake of endogenous urea N by portal drained viscera (PDV), compared with static dietary CP regimens. Chronic indwelling catheters were surgically implanted in the abdominal aorta, a mesenteric vein, a hepatic vein, and the portal vein of 18 growing Dorset x Suffolk wethers (44.6 +/- 3.6 kg of BW). Wethers had ad libitum access to the following diets in a completely randomized block design: 1) Low (9.9% CP), 2) Medium (12.5% CP), or 3) Low and High (14.2% CP) diets oscillated on a 48-h interval (Osc). Dry matter intake was greater (P = 0.04) for the Osc diet (1,313 g/d) than the Low diet (987 g/d) and was intermediate for the Medium diet (1,112 g/d). Nitrogen intake was not different between the wethers fed the Osc (25.4 g/d) and Medium diets (22.2 g/d), but was lower (P < 0.01) in wethers fed the Low diet (16.0 g/d). Wethers fed the Osc diet (6.7 g/d) retained more (P < 0.04) N than did those fed the Medium diet (4.0 g/d). Hepatic arterial blood flow was not different (P = 0.81) between wethers fed the Osc (31 L/h) or Medium diet (39 L/h) but was greater (P = 0.05) in wethers fed the Low diet (66 L/h). Net release of alpha-amino N by the PDV did not differ (P = 0.90) between the Low (37.8 mmol/h) and Medium diets (41.5 mmol/h) or between the Osc (53.0 mmol/h) and Medium diets (P = 0.29). Net PDV release of ammonia N was less (P = 0.05) for the Low diet than for the Medium diet, and this was accompanied by a similar decrease (P = 0.04) in hepatic ammonia N uptake. Urea N concentrations tended to be (P = 0.06) less in arterial, portal, and hepatic blood in wethers fed the Low diet compared with those fed the Medium diet. Wethers fed the Osc diet tended (P = 0.06) to have a greater PDV uptake of urea N than did those fed the Medium diet, but there was no difference between the Osc and Medium diets (P = 0.72) in hepatic urea N release. Net PDV uptake of glutamine tended to be greater (P < 0.07) in wethers fed the Low diet (6.7 mmol/h) than those fed the Medium diet (2.7 mmol/h). These data indicate that oscillating dietary protein may improve N retention by increasing endogenous urea N uptake by the gastrointestinal tract.