Vascular signalling mediated by ZWILLE potentiates WUSCHEL function during shoot meristem stem cell development in the Arabidopsis embryo

Stem cells are maintained in an undifferentiated state by signals from their microenvironment, the stem cell niche. Despite its central role for organogenesis throughout the plant's life, little is known about how niche development is regulated in the Arabidopsis embryo. Here we show that, in the absence of functional ZWILLE (ZLL), which is a member of the ARGONAUTE (AGO) family, stem cell-specific expression of the signal peptide gene CLAVATA3 (CLV3) is not maintained despite increased levels of the homeodomain transcription factor WUSCHEL (WUS), which is expressed in the organising centre (OC) of the niche and normally promotes stem cell identity. Tissue-specific expression indicates that ZLL acts to maintain the stem cells from the neighbouring vascular primordium, providing direct evidence for a non-cell-autonomous mechanism. Furthermore, mutant and marker gene analyses suggest that during shoot meristem formation, ZLL functions in a similar manner but in a sequential order with its close homologue AGO1, which mediates RNA interference. Thus, WUS-dependent OC signalling to the stem cells is promoted by AGO1 and subsequently maintained by a provascular ZLL-dependent signalling pathway.Matthew R. Tucker, Annika Hinze, Elise J. Tucker, Shinobu Takada, Gerd Jürgens and Thomas Lau

Guided Bone Regeneration with Application of Titanium Membrane (Clinical experience)

U implantologiji i parodontologiji se u svrhu kontrole regeneracije koštanoga tkiva rabe resorptivne i neresorptivne membrane.U ovome radu prikazana su iskustva dobivena uporabom neresorptivne titan neperforirane membrane. U slučajevima velikih koštanih defekata s namjerom ugradnje usadaka “Paraplant 2000” simultano smo upotrebljavali titan membrane kako bi se dobio koštani volumen odmah nakon ugradnje usadka u defekt. Fiksacija titan membrane provedena je s pomoću “Currasan” seta. Kod obrađenih i prikazanih slučajeva ustanovili smo opsežnu koštanu regeneraciju nakon 75 dana. Time i opravdanost uporabe titan membrane.Resorbable and non-resorbable membranes are used in implantology and periodontology for guided bone regeneration. This paper shows experience that has been gained from using non-resorbable titanium non-perforated membrane. In case of large bone defects with intention to place an implant “Paraplant 2000” we simultaneously use titanium membrane for building up bone volume immediately after positioning implant into the defect. Fixation of titanium membrane has been performed with “Currasan” fixation set. In the processed and presented cases we have determined significant volume of bone regeneration after 75 days which validate application of titanium membrane

Nonequilibrium radiation measurements and modelling relevant to Titan entry

An update to a collisional-radiative model developed by Magin1 for Huygens Titan atmospheric entry is proposed. The model is designed to predict the nonequilibrium populations and the radiation emitted from cyanogen and nitrogen during the entry of the Huygens probe into the Titan atmosphere. Radiation during Titan entry is important at lower speeds (around 5 – 6 km/s) more so than other planetary entries due to the formation of cyanogen in the shock layer, which is a highly radiative species. The model has been tested against measurements obtained with the EAST shock tube of NASA Ames Research Centre.1,2 The motivation for the update is due to the large discrepancies shown in the postshock fall-off rates of the radiation when compared to the experimental EAST shock tube test results. Modifications were made to the reaction rates used to calculate the species concentrations in the flow field. The reaction that was deemed most influential for the radiation fall off rate was the dissociation of molecular nitrogen. The model with modified reaction rates showed significantly better agreement with the EAST data. This paper also includes experimental results for radiation and spectra for Titan entry. Experiments were performed on the University of Queensland's X2 expansion tube. Spectra were recorded at various positions behind the shock. This enabled the construction of radiation profiles for Titan entry, as well as wavelength plots to identify various radiating species, in this case, predominately CN violet. This paper includes radiation profiles to compare with experiments performed at NASA Ames. It is planned that further experiments will be performed to cover a larger pressure range than NASA Ames. Good qualitative agreement has so far been obtained between our data and NASA Ames, however, it should be noted at the time of printing, the experimental spectrum have not been calibrated absolutely