Prediction of wheat response to an application of phosphorus under field conditions using diffusive gradients in thin-films (DGT) and extraction methods

The ability of the Diffusive Gradients in Thin Films (DGT) technique and two other established testing methods (Colwell, resin) to predict wheat responsiveness to applied P from 35 field trials across southern Australia was investigated. Regression analysis of relative early dry matter production and grain yield responses demonstrated that the DGT method predicted plant responsiveness to applied P more accurately than Colwell P and resin P at sites where maximum yields were reached with P rates used (20 out of 35). The measured concentration in soils at the DGT surface, C_DGT, explained 74% of the variation in response for both early dry matter and grain, compared to 7% for early dry matter and 35% for grain using the resin P method. No significant relationships could be obtained for Colwell P although modifying the Colwell test data using Phosphorus Buffering Index resulted in a correct response prediction for 11 of the 20 field sites compared to 18 for DGT and 14 for resin P. These observations suggest that the DGT technique can assess plant available P in soils with significantly greater accuracy than traditional soil P testing methods. The critical P threshold, expressed as C_DGT, was 255 μg L^?1 for early dry matter and 66 μg L^?1 for grain.     

Calcitriol enhances gemcitabine antitumor activity in vitro and in vivo by promoting apoptosis in a human pancreatic carcinoma model system

Gemcitabine is the standard care chemotherapeutic agent to treat pancreatic cancer. Previously we demonstrated that calcitriol (1, 25-dihydroxycholecalciferol) has significant anti-proliferative effects in vitro and in vivo in multiple tumor models and enhances the activity of a variety of chemotherapeutic agents. We therefore investigated whether calcitriol could potentiate the cytotoxic activity of gemcitabine in the human pancreatic cancer Capan-1 model system. Isobologram analysis revealed that calcitriol and gemcitabine had synergistic antiproliferative effect over a wide range of drug concentrations. Calcitriol did not reduce the cytidine deaminase activity in Capan-1 tumors nor in the livers of Capan-1 tumor bearing mice. Calcitriol and gemcitabine combination promoted apoptosis in Capan-1 cells compared with either agent alone. The combination treatment also increased the activation of caspases-8, -9, -6 and -3 in Capan-1 cells. This result was confirmed by substrate-based caspase activity assay. Akt phosphorylation was reduced by calcitriol and gemcitabine combination treatment compared to single agent treatment. However, ERK1/2 phosphorylation was not modulated by either agent alone or by the combination. Tumor regrowth delay studies showed that calcitriol in combination with gemcitabine resulted in a significant reduction of Capan-1 tumor volume compared to single agent treatment. Our study suggests that calcitriol and gemcitabine in combination promotes caspase-dependent apoptosis, which may contribute to increased anti-tumor activity compared to either agent alone.Key words: calcitriol, gemcitabine, pancreatic carcinoma, apoptosis, Akt, ERK1/2     

A novel nuclear export signal and a REF interaction domain both promote mRNA export by the Epstein-Barr virus EB2 protein

A striking characteristic of mRNA export factors is that they shuttle continuously between the cytoplasm and the nucleus. This shuttling is mediated by specific factors interacting with peptide motifs called nuclear export signals (NES) and nuclear localization signals. We have identified a novel CRM-1-independent transferable NES and two nuclear localization signals in the Epstein-Barr virus mRNA export factor EB2 (also called BMLF1, Mta, or SM) localized at the N terminus of the protein between amino acids 61 and 146. We have also found that a previously described double NES (amino acids 213-236) does not mediate the nuclear shuttling of EB2, but is an interaction domain with the cellular export factor REF in vitro. This newly characterized REF interaction domain is essential for EB2-mediated mRNA export. Accordingly, in vivo, EB2 is found in complexes containing REF as well as the cellular factor TAP. However, these interactions are RNase-sensitive, suggesting that the RNA is an essential component of these complexes.     

Peripheral oestrogen metabolism in postmenopausal women with or without breast cancer: the role of dietary lipids and growth factors

Studies we have carried out have revealed significant differences in oestrogen production and metabolism between normal women and postmenopausal women with breast cancer. The free, biologically available fraction of oestradiol is elevated in plasma from women with breast cancer and we have found that metabolic clearance rates and production rates of oestradiol are also increased. In vitro studies have suggested that lipids can influence the distribution of sex steroids in plasma and we have therefore examined the effect of dietary lipids on the distribution of sex steroids in plasma in vivo. Consumption of a meal with a high saturated fat content or the oral or i.v. administration of "Intralipid", a stabilised emulsion of soya bean oil that is high in unsaturated free fatty acids, had little effect on the available fractions of oestradiol in plasma. However, results from a preliminary study suggest that long-term changes in dietary fat intake can alter the distribution of steroids in plasma. It is concluded that dietary lipids may influence the availability of sex steroids to tissues. Such a mechanism could account for the significant correlation that has been found between dietary fat consumption and the incidence of breast cancer on a world-wide basis.     

Transepithelial potential in the Magadi tilapia, a fish living in extreme alkalinity

We investigated the transepithelial potential (TEP) and its responses to changes in the external medium in Alcolapia grahami, a small cichlid fish living in Lake Magadi, Kenya. Magadi water is extremely alkaline (pH = 9.92) and otherwise unusual: titratable alkalinity (290 mequiv L(-1), i.e. HCO(3) (-) and CO(3) (2-)) rather than Cl(-) (112 mmol L(-1)) represents the major anion matching Na(+) = 356 mmol L(-1), with very low concentrations of Ca(2+) and Mg(2+) (<1 mmol L(-1)). Immediately after fish capture, TEP was +4 mV (inside positive), but stabilized at +7 mV at 10-30 h post-capture when experiments were performed in Magadi water. Transfer to 250% Magadi water increased the TEP to +9.5 mV, and transfer to fresh water and deionized water decreased the TEP to -13 and -28 mV, respectively, effects which were not due to changes in pH or osmolality. The very negative TEP in deionized water was attenuated in a linear fashion by log elevations in [Ca(2+)]. Extreme cold (1 vs. 28°C) reduced the positive TEP in Magadi water by 60%, suggesting blockade of an electrogenic component, but did not alter the negative TEP in dilute solution. When fish were transferred to 350 mmol L(-1) solutions of NaHCO(3), NaCl, NaNO(3), or choline Cl, only the 350 mmol L(-1) NaHCO(3) solution sustained the TEP unchanged at +7 mV; in all others, the TEP fell. Furthermore, after transfer to 50, 10, and 2% dilutions of 350 mmol L(-1) NaHCO(3), the TEPs remained identical to those in comparable dilutions of Magadi water, whereas this did not occur with comparable dilutions of 350 mmol L(-1) NaCl-i.e. the fish behaves electrically as if living in an NaHCO(3) solution equimolar to Magadi water. We conclude that the TEP is largely a Na(+) diffusion potential attenuated by some permeability to anions. In Magadi water, the net electrochemical forces driving Na(+) inwards (+9.9 mV) and Cl(-) outwards (+3.4 mV) are small relative to the strong gradient driving HCO(3) (-) inwards (-82.7 mV). Estimated permeability ratios are P (Cl)/P (Na) = 0.51-0.68 and [Formula: see text] = 0.10-0.33. The low permeability to HCO(3) (-) is unusual, and reflects a unique adaptation to life in extreme alkalinity. Cl(-) is distributed close to Nernst equilibrium in Magadi water, so there is no need for lower P (Cl). The higher P (Na) likely facilitates Na(+) efflux through the paracellular pathway. The positive electrogenic component is probably due to active HCO(3) (-) excretion.     

Phase Variation of Andrewes in Salmonella enteritidis Bioserotype Paratyphi-A

The natural occurrence of a strain of Salmonella enteritidis bioserotype Paratyphi-A is reported, in which the flagellar antigens segregated readily into normal phase 2 antigens and mixtures of normal phase 1 and phase 2 antigens, and in which phase variation of Andrewes was demonstrated with ease.     

Controlling the size of organs and organisms

A key difference between yeast and metazoans is the need of the latter to regulate cell proliferation and growth to create organs (and organisms) of reproducible size and shape. Great progress has been made in understanding how growth, cell size and the cell cycle are controlled in metazoans. Recent work has shown that disruption of conserved components of the insulin and Tor kinase pathways can alter organ size, indicating that the normal functioning of these pathways is essential for organ size control. However, disruption of genes that regulate patterning and of genes that control cell adhesion and cell polarity has a much more dramatic effect on final organ size than does manipulation of the cell cycle or of basal growth control mechanisms. These data point to an 'organ-size checkpoint' that regulates cell division, cell growth and apoptosis. Recent data suggests that cell competition may play an important role in implementing the organ-size checkpoint.     

The posttranslational modification of tubulin undergoes a switch from detyrosination to acetylation as epithelial cells become polarized

Tubulin posttranslational modifications (PTMs) have been suggested to provide navigational cues for molecular motors to deliver cargo to spatially segregated subcellular domains, but the molecular details of this process remain unclear. Here we show that in Madin-Darby Canine Kidney (MDCK) epithelial cells, microtubules express several tubulin PTMs. These modifications, however, are not coordinated, and cells have multiple subpopulations of microtubules that are marked by different combinations of PTMs. Furthermore these subpopulations show differential sensitivity to both drug- and cold-induced depolymerization, suggesting that they are functionally different as well. The composition and distribution of modified microtubules change as cells undergo the morphogenesis associated with polarization. Two-dimensionally polarized spreading cells have more detyrosinated microtubules that are oriented toward the leading edge, but three-dimensionally polarized cells have more acetylated microtubules that are oriented toward the apical domain. These data suggest that the transition from 2D polarity to 3D polarity involves both a reorganization of the microtubule cytoskeleton and a change in tubulin PTMs. However, in both 2D polarized and 3D polarized cells, the modified microtubules are oriented to support vectorial cargo transport to areas of high need.