Growth and development of root systems: Geometrical and structural aspects

The agronomist who wants to study the nutrient and water uptake of roots needs a quantitative three-dimensional dynamic model of the structure of root systems.The model presented takes into account current knowledge about the morphogenesis of root systems. It describes the root system as a set of root axes, characterised by their orders. The morphogenetic properties of root axes differ according to their order. The axes of order 1 are directly inserted on the stem, the axes of order 2 are inserted on axes of order 1, and so on. They tend to be more plagiotropec and to have less vascular bundles as the order increases.The evolution of the simulated structure is achieved by three processes: emission of new root axes from the shoot, growth and branching of existing root axes. The elongation of an axis depends on its order and on local growing conditions. Branches appear acropetally at a specified distance from the apex and from former branches, along ranks facing xylem poles, with a branching angle specific of their order.From the three-dimensional branched structures simulated by the model, various outputs, such as kinetics of growth and development, root profiles or cross-section maps can be computed, compared to observed data and used as inputs in uptake models. Some examples of such possible outputs are presented.

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Résumé L'agronome qui veut étudier l'absorption hydrique et minérale des racines a besoin d'un modèle dynamique tri-dimensionnel de la structure du système racinaire.Le modèle présentd est fondé sur les connaissances actuelles sur la morphogenèse racinaire. Le système racinaire y est représenté comme un ensemble d'axes caractérisés par leur ordre. En effet, les propriétés morphogénétiques des racines varient d'un ordre d l'autre. Les axes d'ordre 1 sont insérés directement sur la tige, les axes d'ordre 2 sur les axes d'ordre 1, et ainsi de suite. Les axes tendent à être de plus en plus plagiotropes et à avoir de moins en moins de faisceaux vasculaires quand l'ordre augmente.Trois processus interviennent pour faire évoluer la structure racinaire simulée au cours du temps: l'émission de nouveaux axes racinaires à partir des tiges, la croissance, et la ramification des axes

     

Comments on oral grooming by patas monkeys,including a comparison with rhesus macaques

Observations of the motor patterns used by patas monkeys during allogrooming indicate that this species uses oral movements much more than previously believed. Compared to rhesus macaques, patas show more mouthpicks and licks, and fewer handpicks. Despite behavioral and anatomical evidence for good precision gripping, patas usually remove debris from a partner's fur orally rather than manually.     

Recovery of copepod, but not cladoceran, zooplankton from severe and chronic effects of multiple stressors

In the mid‐twentieth century, many lakes near Sudbury, Canada, were severely contaminated by acid and metal emissions from local smelters. For example, in the early 1970s, Middle Lake had pH of 4.2, and Cu and Ni levels both >0.5 mg L^?1 . To determine if crustacean zooplankton could recover from such severe and chronic damage, Middle Lake was neutralized in 1973. A comparison of its zooplankton with that of 22 reference (pH > 6) lakes indicates that the planktonic Copepoda completely recovered by 2001. In contrast, the cladoceran assemblage improved but did not recover. Colonist sources existed – Cladocera and Copepoda occurred with equal frequency in area lakes – but six separate colonizations by cladoceran species failed. We argue that local factors, metal toxicity and predation by yellow perch, have, to date, prevented cladoceran recovery. Nonetheless, the complete copepod recovery is encouraging, given the severity and duration of pre‐neutralization stress.     

Primary culture of gill epithelial cells from the sea bassDicentrarchus Labrax

Summary We have developed the first explant technique that allows the in vitro study of gill physiology and biochemistry in marine species. Gill fragments were cultured at 17° C, in atmospheric Pco₂, with nutrient medium (Leibovitz L15), pH 7.8, supplemented with 10% fetal bovine serum and adjusted to the osmolarity of fish plasma (350 mOsm/liter). Coating plates with collagen, gelatin, or polylysin did not improve our results. Decrease in osmotic pressure, removal of bovine serum, or its replacement by fish serum inhibited growth from the explants. Approximately 50% of the explants produced cell growth, and after 4 days of culture a monolayer of contiguous cells was formed. This technique is rapid and does not require the use of enzymes. The cells appeared flat and thin with an epithelioid shape. They looked polygonal with a maximum length of 10 to 50 μm. Evidence that they are unique gill cells is the presence of polymorphic surface crenelations (microplicae), prominent Golgi apparatus, tight junctions and desmosomes. Comparison with in vivo tissue showed them to be epithelial cells having differentiated in a homogeneous population of respiratorylike (pavement) cells. They are polarized with their apical surface facing the culture medium. The development of this culture system represents a new tool for cellular approaches to determine precisely the functions and transport mechanism of gill cells.     

Tracking Molecular Interactions in Membranes by Simultaneous ATR-FTIR-AFM

In situ atomic force microscopy (AFM) is an exceedingly powerful and useful technique for characterizing the structure and assembly of proteins in real-time, in situ, and especially at model membrane interfaces, such as supported planar lipid bilayers. There remains, however, a fundamental challenge with AFM-based imaging. Conclusions are inferred based on morphological or topographical features. It is conventionally very difficult to use AFM to confirm specific molecular conformation, especially in the case of protein-membrane interactions. In this case, a protein may undergo subtle conformational changes upon insertion in the membrane that may be critical to its function. AFM lacks the ability to directly measure such conformational changes and can, arguably, only resolve features that are topographically distinct. To address these issues, we have developed a platform that integrates in situ AFM with attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. This combination of tools provides a unique means of tracking, simultaneously, conformational changes, not resolvable by in situ AFM, with topographical details that are not readily identified by conventional spectroscopy. Preliminary studies of thermal transitions in supported lipid bilayers and direct evidence of lipid-induced conformational changes in adsorbed proteins illustrates the potential of this coupled in situ functional imaging strategy.     

The phospholipid requirement of the (Ca + Mg)-ATPase from human platelets

The phospholipid requirement of the (Ca²⁺ + Mg²⁺)-ATPase present in a membrane fraction from human platelets was studied using various purified phospholipases. Only those phospholipases, which hydrolyse the negatively charged phospholipids, inhibited the (Ca²⁺ + Mg²⁺)-ATPase activity. The ATPase activity could be restored by adding mixed micelles of Triton X-100 and phosphatidylserine or phosphatidylinositol. Micelles with phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine or sphingomyelin could not be used for reconstitution and inhibited the activity of the native enzyme.     

Control of Dog Mediated Human Rabies in Haiti: No Time to Spare

The American region has pledged to eliminate dog-mediated human rabies by 2015. As part of these efforts, we describe the findings of a desk and field mission review of Haiti’s rabies situation by the end of 2013. While government officials recognize the importance of dog-mediated rabies control, and the national rabies plan adequately contemplates the basic capacities to that effect, regular and sufficient implementation, for example, of dog vaccination, is hampered by limited funding. Compounding insufficient funding and human resources, official surveillance figures do not accurately reflect the risk to the population, as evidenced by the large number of rabid dogs detected by focalized and enhanced surveillance activities conducted by the Ministry of Agriculture, Natural Resources and Rural Development (MARNDR) and the Health and Population Ministry (MSPP) with the technical assistance of the United States Centers for Disease Control and Prevention. Although international support is common, either in the form of on-the-ground technical support or donations of immunobiologicals, it is not comprehensive. In addition, there is limited coordination with MARNDR/MSPP and with other actors at the strategic or operational level due to human resources limitations. Given these findings, the 2015 elimination goal in the region is compromised by the situation in Haiti where control of the disease is not yet in sight despite the best efforts of the resolute national officials. More importantly, dog-mediated rabies is still a threat to the Haitian population.