On the Robustness of the Geometrical Model for Cell Wall Deposition

All plant cells are provided with the necessary rigidity to withstand the turgor by an exterior cell wall. This wall is composed of long crystalline cellulose microfibrils embedded in a matrix of other polysaccharides. The cellulose microfibrils are deposited by mobile membrane bound protein complexes in remarkably ordered lamellar textures. The mechanism by which these ordered textures arise, however, is still under debate. The geometrical model for cell wall deposition proposed by Emons and Mulder (Proc. Natl. Acad. Sci. 95, 7215–7219, 1998) provides a detailed approach to the case of cell wall deposition in non-growing cells, where there is no evidence for the direct influence of other cellular components such as microtubules. The model successfully reproduces even the so-called helicoidal wall; the most intricate texture observed. However, a number of simplifying assumptions were made in the original calculations. The present work addresses the issue of the robustness of the model to relaxation of these assumptions, by considering whether the helicoidal solutions survive when three aspects of the model are varied. These are: (i) the shape of the insertion domain, (ii) the distribution of lifetimes of individual CSCs, and (iii) fluctuations and overcrowding. Although details of the solutions do change, we find that in all cases the overall character of the helicoidal solutions is preserved.     

Preventing introduction and spread of Dermanyssus gallinae in poultry facilities using the HACCP method

Preventing the establishment of ectoparasitic poultry red mite (Dermanyssus gallinae) populations is key in ensuring welfare and egg production of laying hens and absence of allergic reactions of workers in poultry facilities. Using the Hazard Analysis and Critical Control Point method, a panel of experts identified hazards and associated risks concerning the introduction and spread of this mite in poultry facilities. Together we provide an overview of possible corrective actions that can be taken to prevent population establishment. Additionally, a checklist of the most critical control points has been devised as management tool for poultry farmers. This list was evaluated by Dutch and British poultry farmers. They found the checklist feasible and useful.     

Characterization of Newly Formed and Aged Granules in the Neurohypophysis

Neurosecretory granules from the rat and bovine neurohypophysis were isolated and some of their biochemical and biophysical properties studied. Neurosecretory granules (NSG) from rat neurohypophysis were labeled, in vivo, with [35S]cysteine and isolated on isoosmotic gradients. Whereas 1 day after labeling most of the radioactivity was found in the lower part of the gradient, 35 days later the isotope was also located in the lighter NSG-containing fraction. Different analytical procedures showed that the lighter fraction, both in bovine and rat NSG, contain more subpopulations of neurophysin-like material than the heavier fraction. The first material to be released during stimulation of secretion, in vivo or in vitro, is mobilized from the heavy NSG. Isolation of rat NSG, at different times during and after dehydration of the animals, reveals that the newly synthesized material is found in the heavy NSG-containing fraction. Furthermore, the results indicate that the newly synthesized NSG are more resistant to lysis than the lighter granules. The results are discussed in relation to the maturation and degradation processes of the granule content and to the functional state of the NSG.     

From the Schnauzenorgan to the back: Morphological comparison of mormyromast electroreceptor organs at different skin regions of Gnathonemus petersii

The nocturnally active weakly electric fish Gnathonemus petersii is known to employ active electrolocation for the detection of objects and for orientation in its environment. The fish emits pulse‐type electric signals with an electric organ and perceives these signals with more than 3,000 epidermal electroreceptor organs, the mormyromasts, which are distributed over the animal's skin surface. In this study, we measured the metric dimensions of the mormyromasts from different body regions to find structural and functional specialization of the various body parts. We focused on the two foveal regions of G. petersii, which are located at the elongated and movable chin (the Schnauzenorgan; SO) and at the nasal region (NR), the skin region between the mouth and the nares. These two foveal regions were compared to the dorsal part (back) of the fish, which contains typical nonfoveal mormyromasts. While the gross anatomy of the mormyromasts from all skin regions is similar, the metric dimensions of the main substructures differed. The mormyromasts at the SO are the smallest and contain the smallest receptor cells. In addition, the number of receptor cells per organ is lowest at the SO. In contrast, at the back the biggest receptor organs with the highest amount of receptor cells per organ occur. The mormyromasts at the NR are in several respects intermediate between those from the back and the SO. However, mormyromasts at the NR are longer than those at all other skin regions, the canal leading from the receptor pore to the inner chambers were the longest and the overlaying epidermal layers are the thickest. These results show that mormyromasts and the epidermis they are embedded in at both foveal regions differ specifically from those found on the rest of the body. The morphological specializations lead to functional specialization of the two foveae. J. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

Über die Bedeutung des Kupfers für das Wachstum von Mikroorganismen und über eine mikrobiologische Methode zur Bestimmung des pflanzenverfügbaren Bodenkupfers

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