Nitrogen nutrition effects on development, growth and nitrogen accumulation of vegetables

In order to be able to match nitrogen supply and nitrogen requirement of vegetable crops, insight is necessary in the responses to nitrogen of important processes of growth and development. This study focused on effects of amount of nitrogen applied and fractionation of nitrogen supply on leaf attributes, accumulation and partitioning of dry matter and nitrogen in potato (Solanum tuberosum L.), Brussels sprouts ( Brassica oleracea L. var gemmifera DC), leek ( Allium porrum L.) and spinach ( Spinacia oleracea L.). Effects of amount of nitrogen applied were always much more important than effects of fractionation of nitrogen supply. Rate of leaf appearance varied among crops from 0. 15-0.60 leaves d -1; it increased with more nitrogen in Brussels sprouts and spinach. Rates of leaf senescence were enhanced by nitrogen in Brussels sprouts. Life span of leaves was about 70 d for all crops. Rates of leaf expansion and maximum sizes of leaves increased with leaf number until a certain leaf number after which they gradually decreased. Both characteristics increased with more nitrogen. Duration of leaf expansion varied among crops from 18-40 d and decreased in Brussels sprouts with more nitrogen. Maximum size of a leaf was mainly determined by rate of leaf expansion. Except in potato, more nitrogen increased specific leaf area. Differences among nitrogen treatments in total green leaf area reflected the effects of nitrogen on rates of leaf expansion.Total dry matter production was strongly related to leaf area duration. Although more nitrogen applied resulted in more nitrogen taken up and more total dry matter produced, considerable variation was observed in the relation between total nitrogen uptake and total dry matter production. Harvest indices for dry matter varied among crops and treatments from about 0.10-0.87; more nitrogen increased it for Brussels sprouts, but decreased it for leek. Harvest indices for nitrogen varied from about 0.22-0.86; more nitrogen increased it for Brussels sprouts. In general, organic nitrogen concentration increased with increasing node number for leaf blades, petioles and leaf sheaths but not for sprouts. The gradient with node number resulted from a decreasing nitrogen concentration during the leafs life. High nitrate concentrations in the marketable produce were only observed in spinach. Nitrate nitrogen concentrations of leaf blades, petioles and leaf sheaths decreased with increasing leaf number at any time of observation, but were not related to leaf age. However, in stems of Brussels sprouts and stems and tubers of potato, total nitrogen and nitrate nitrogen concentration were closely related.The present findings elucidate the reactions of the crops to nitrogen fertilisation. This is helpful for the fine-tuning of nitrogen fertilisation and to develop modules on plant development in crop simulation models

The role of tunneling in enzyme catalysis of C–H activation

AbstractRecent data from studies of enzyme catalyzed hydrogen transfer reactions implicate a new theoretical context in which to understand C–H activation. This is much closer to the Marcus theory of electron transfer, in that environmental factors influence the probability of effective wave function overlap from donor to acceptor atoms. The larger size of hydrogen and the availability of three isotopes (H, D and T) introduce a dimension to the kinetic analysis that is not available for electron transfer. This concerns the role of gating between donor and acceptor atoms, in particular whether the system in question is able to tune distance between reactants to achieve maximal tunneling efficiency. Analysis of enzyme systems is providing increasing evidence of a role for active site residues in optimizing the inter-nuclear distance for nuclear tunneling. The ease with which this optimization can be perturbed, through site-specific mutagenesis or an alteration in reaction conditions, is also readily apparent from an analysis of the changes in the temperature dependence of hydrogen isotope effects

De bedrijfseconoom moet mee met de tijdsgeest

●Om relevant te blijven moeten bedrijfseconomen de samenhang in het vakgebied herontdekken.● Daarnaast is kennis van datamanagement en ethisch leiderschap noodzakelijk voor succces in de toekomst

The role of red blood cell characteristics and viscosity in sickle cell retinopathy and maculopathy.

Sickle cell disease (SCD), encompassing genotypes such as HbSS and HbSC, causes chronic haemolysis and microvascular occlusion, leading to organ damage. The retina is particularly vulnerable, often resulting in sickle cell retinopathy (SCR) or sickle cell maculopathy (SCM). The precise underlying mechanisms are unclear, though various factors are suggested to contribute. This study explored the role of whole blood viscosity and red blood cell (RBC) deformability in SCR and SCM. Adult HbSS (n = 34) and HbSC patients (n = 34) were offered an ophthalmic examination to determine SCR stage. A venous ethylenediaminetetraacetic acid (EDTA) sample was collected from each participant. Whole blood viscosity was measured using a Brookfield viscometer and RBC deformability was assessed using the Oxygenscan feature of the Laser Optical Rotational Red Cell Analyser as a function of the (varying) partial oxygen pressure. HbSC patients with proliferative sickle cell retinopathy (PSCR) had a lower delta elongation index (p = 0.012) and point of sickling (p = 0.002) than those without PSCR, suggesting that RBC sickling might not play a central role in the pathogenesis of PSCR in HbSC patients. Despite hyperviscosity being a commonly proposed mechanism, no associations were found between blood viscosity, SCR and SCM. These results point to alternative mechanisms contributing to SCR and SCM, highlighting the complexity and need for further research to fully understand the underlying factors

Dynamics of salt intrusion in complex estuarine networks: an idealised model applied to the Rhine–Meuse Delta

Many deltas in the world consist of a network of connected channels. We identify and quantify the characteristics of salt intrusion in such systems using an idealised model. The Rhine–Meuse Delta is selected as a prototype example of a complex network with many channels. The model is able to capture the characteristics of the tide-dominated water level variations due to the main tidal component and the salinity time series for 1 year of observations. Quantification of tidally averaged salt transport components shows that transport related to exchange flow is dominant in the seaward, deep parts of the network, but tidal dispersion is dominant in shallower channels further inland. Close to the network junctions, a tidally averaged downgradient salt transport is generated by the tidal currents, which is explained by the phase differences between the tidal currents in the different channels. Salt overspill is confined to the most seaward part of the Rhine–Meuse Delta. The magnitudes of the response times of different channels to changes in discharge increase with the distance to the estuary mouth and with decreasing net water transport through the channel. In channels without a subtidal discharge, response times are a factor of 2–4 larger than in the other channels. The effect of changes in the depth on the extent of salt intrusion strongly depends on where the change takes place. If the change is within the salt intrusion range, deepening will locally increase salt intrusion due to an increase in salt transport by the exchange flow. If the change is outside the salt intrusion range, changes to the net water transport dominate the response of the salt intrusion.</p

Assessment of bone ingrowth potential of biomimetic hydroxyapatite and brushite coated porous E-beam structures

The bone ingrowth potential of biomimetic hydroxyapatite and brushite coatings applied on porous E-beam structure was examined in goats and compared to a similar uncoated porous structure and a conventional titanium plasma spray coating. Specimens were implanted in the iliac crest of goats for a period of 3 (4 goats) or 15 weeks (8 goats). Mechanical implant fixation generated by bone ingrowth was analyzed by a push out test. Histomorphometry was performed to assess the bone ingrowth depth and bone implant contact. The uncoated and hydroxyapatite-coated cubic structure had significantly higher mechanical strength at the interface compared to the Ti plasma spray coating at 15 weeks of implantation. Bone ingrowth depth was significantly larger for the hydroxyapatite- and brushite-coated structures compared to the uncoated structure. In conclusion, the porous E-beam surface structure showed higher bone ingrowth potential compared to a conventional implant surface after 15 weeks of implantation. Addition of a calcium phosphate coating to the E-beam structure enhanced bone ingrowth significantly. Furthermore, the calcium phosphate coating appears to work as an accelerator for bone ingrowth