Regulation of Leaf Senescence by Cytokinin, Sugars, and Light : Effects on NADH-Dependent Hydroxypyruvate Reductase

The aim of this study was to investigate the interactions between cytokinin, sugar repression, and light in the senescence-related decline in photosynthetic enzymes of leaves. In transgenic tobacco (Nicotiana tabacum) plants that induce the production of cytokinin in senescing tissue, the age-dependent decline in NADH-dependent hydroxypyruvate reductase (HPR), ribulose-1,5-bisphosphate carboxylase/oxygenase, and other enzymes involved in photosynthetic metabolism was delayed but not prevented. Glucose (Glc) and fructose contents increased with leaf age in wild-type tobacco and, to a greater extent, in transgenic tobacco. To study whether sugar accumulation in senescing leaves can counteract the effect of cytokinin on senescence, discs of wild-type leaves were incubated with Glc and cytokinin solutions. The photorespiratory enzyme HPR declined rapidly in the presence of 20 mm Glc, especially at very low photon flux density. Although HPR protein was increased in the presence of cytokinin, cytokinin did not prevent the Glc-dependent decline. Illumination at moderate photon flux density resulted in the rapid synthesis of HPR and partially prevented the negative effect of Glc. Similar results were obtained for the photosynthetic enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase. It is concluded that sugars, cytokinin, and light interact during senescence by influencing the decline in proteins involved in photosynthetic metabolism.     

Repeat unit polysaccharides of bacteria: a model for polymerization resembling that of ribosomes and fatty acid synthetase, with a novel mechanism for determining chain length

We report the identification and sequence from Escherichia coli and Salmonella enterica strains of the cld gene, encoding the chain-length determinant (CLD) which confers a modal distribution of chain length on the O-antigen component of lipopolysaccharide (LPS). The distribution of chain lengths in the absence of this gene fits a model in which as the chain is extended there is a constant probability of 0.165 of transfer of growing chain to LPS core, with termination of chain extension. The data for E. coli 0111 fit a model in which the CLD reduces this probability for short chains and increases it to 0.4 for longer chains, leading to a reduced number of short chain molecules but an increase in numbers of longer molecules and transfer of essentially all molecules by chain length 21. We put forward a model for O-antigen polymerase which resembles the ribosome and fatty acid synthetase in having two sites, with the growing chain being transferred from a D site onto the new unit at the R site to extend the chain and then back to the D site to repeat the process. It is proposed that the CLD protein and polymerase form a complex which has two states:‘E’facilitating extension and T facilitating transfer to core. The complex is postulated to enter the E state as O-antigen polymerization starts, and to shift to the T state after a predetermined time, the CLD acting as a molecular clock. The CLD is not O-antigen or species-specific but the modal value does depend on the source of the cld gene.     

Always being well prepared for defense: The production of deterrents by juvenile Chrysomelina beetles (Chrysomelidae)

In response to herbivores, plants produce a variety of natural compounds. Many beetle species have developed ingenious strategies to cope with these substances, including colonizing habitats not attractive for other organisms. Leaf beetle larvae of the subtribe Chrysomelina, for example, sequester plant-derived compounds and use them for their own defense against predators. Using systematically modified structural mimics of plant-derived glucosides, we demonstrated that all tested Chrysomelina larvae channel compounds from the gut lumen into the defensive glands, where they serve as intermediates in the synthesis of deterrents. Detailed studies of the sequestration process revealed a functional network of transport processes guiding phytochemicals through the larval body. The initial uptake by the larvae’s intestine seems to be fairly unspecific, which contrasts sharply with the specific import of precursors into the defensive glands. The Malpighian tubules and hind-gut organs facilitate the rapid clearing of body fluid from excess or unusable compounds. The network exists in both sequestering species and species producing deterrents de novo. Transport proteins are also required for de novo synthesis to channel intermediates from the fat body to the defensive glands for further conversion. Thus, all the tools needed to exploit host plants’ chemistry by more derived Chrysomelina species are already developed by iridoid–de novo producers. Early intermediates from the iridoid–de novo synthesis which also can be sequestered are able to regulate the enzyme activity in the iridoid metabolism.     

Pectin May Hinder the Unfolding of Xyloglucan Chains during Cell Deformation： Implications of the Mechanical Performance of Arabidopsis Hypocotyls with Pectin Alterations

Plant cell walls, like a multitude of other biological materials, are natural fiber-reinforced composite materials. Their mechanical properties are highly dependent on the interplay of the stiff fibrous phase and the soft matrix phase and on the matrix deformation itself. Using specific Arabidopsis thaliana mutants, we studied the mechanical role of the matrix assembly in primary cell walls of hypocotyls with altered xyloglucan and pectin composition. Standard microtensile tests and cyclic loading protocols were performed on tour1 hypocotyls with affected RGII borate diester cross-links and a hindered xyloglucan fucosylation as well as qua2 exhibiting 50% less homogalacturonan in comparison to wild-type. As a control, wild-type plants （Col-0） and mur2 exhibiting a specific xyloglucan fucosylation and no differences in the pectin network were utilized. In the standard tensile tests, the ultimate stress levels （-tensile strength） of the hypocotyls of the mutants with pectin alterations （mur1, qua2） were rather unaffected, whereas their tensile stiffness was noticeably reduced in comparison to Col-0. The cyclic loading tests indicated a stiffening of all hypocotyls after the first cycle and a plastic deformation during the first straining, the degree of which, however, was much higher for tour1 and qua2 hypocotyls. Based on the mechanical data and current cell wall models, it is assumed that folded xyloglucan chains between cellulose fibrils may tend to unfold during straining of the hypocotyls. This response is probably hindered by geometrical constraints due to pectin rigidity.     

ElePhant: an anatomic-electronic simulation system for the evaluation of computer assisted interventions and surgical education]

BACKGROUND: Suitable simulation systems providing realistic conditions are required for preclinical evaluation of computer assisted interventions and surgical training. Techniques are necessary for an objective detection of injuries to the structures at risk. The aim of this study was the technical realization of a simulation system for the ENT intervention, mastoidectomy.MATERIALS AND METHODS: The basis of the simulation system was a CT scan of a cadaver skull. Using 3D printing, an anatomical phantom with realistic bone-like properties was created. Electronic detection systems were integrated into the structures at risk. A study with 16 ENT surgeons was conducted to prove the system's suitability for surgical training.RESULTS: The creation of simulation systems for the objective evaluation of surgical intervention qualities is feasible. A modular structure enables economic and simple replacement of the simulation area. The modules are cost effective and reproducible with high accuracy. The present study shows that the simulation system can be applied in surgical education and evaluation as an alternative to cadavers.CONCLUSION: Objective evaluation of injured structures at risk can be realized in real time. The simulation system permits preclinical evaluation studies of computer assisted instruments and surgical education. Reproducibility of the results makes multi-center studies possible.     

An automated, highly sensitive LC-MS/MS assay for the quantification of the opiate antagonist naltrexone and its major metabolite 6beta-naltrexol in dog and human plasma

To support animal studies and clinical pharmacokinetic trials, we developed and validated an automated, specific and highly sensitive LC-MS/MS method for the quantification of naltrexone and 6beta-naltrexol in the same run. In human plasma, the assay had a lower limit of quantitation of only 5pg/mL. This was of critical importance to follow naltrexone pharmacokinetics during its terminal elimination phase. The assay had the following key performance characteristics for naltrexone in human plasma: range of reliable quantification: 0.005-100ng/mL (r2>0.99), inter-day accuracy (0.03ng/mL): 103.7% and inter-day precision: 10.1%. There were no ion suppression, matrix interferences or carry-over.     

The bleomycin animal model: a useful tool to investigate treatment options for idiopathic pulmonary fibrosis?

Different animal models of pulmonary fibrosis have been developed to investigate potential therapies for idiopathic pulmonary fibrosis (IPF). The most common is the bleomycin model in rodents (mouse, rat and hamster). Over the years, numerous agents have been shown to inhibit fibrosis in this model. However, to date none of these compounds are used in the clinical management of IPF and none has shown a comparable antifibrotic effect in humans. We performed a systematic review of publications on drug efficacy studies in the bleomycin model to evaluate the value of this model regarding transferability to clinical use. Between 1980 and 2006 we identified 240 experimental studies describing beneficial antifibrotic compounds in the bleomycin model. 222 of those used a preventive regimen (drug given < or =7 days after last bleomycin application), only 13 were therapeutic trials (>7 days after last bleomycin application). In 5 studies we did not find enough details about the timing of drug application to allow inter-study comparison. It is critical to distinguish between drugs interfering with the inflammatory and early fibrogenic response from those preventing progression of fibrosis, the latter likely much more meaningful for clinical application. All potential antifibrotic compounds should be evaluated in the phase of established fibrosis rather than in the early period of bleomycin-induced inflammation for assessment of its antifibrotic properties. Further care should be taken in extrapolation of drugs successfully tested in the bleomycin model due to partial reversibility of bleomycin-induced fibrosis over time. The use of alternative and more robust animal models, which better reflect human IPF, is warranted.