Interactions of maize and Italian ryegrass in a living mulch system: (2)Nitrogen and water dynamics

Water and nitrogen availability may limit the growth of the main crop competing with a cover crop in a living mulch system. Some aspects of the dynamics of water (soil water content and deep percolation) and nitrogen (concentration in soil solution and leachate) were studied in maize (Zea mays L.) sown into a bare soil (BS, conventional cropping) or into a living Italian ryegrass (Lolium multiflorum Lam.) mulch (LM) during three years. Eight lysimeters (1.0 by 1.0m square surface area and 1.1m deep) with ceramic suction cups, TDR probes and a drainage pipe were used each. In LM a 0.3m wide strip was kept free of grass around the maize row. The living mulch reduced the soil water content between 0.3 and 0.9m soil depth, which remained lower even after intense rainfall. Deep percolation over the entire maize crop season was at least 40% lower in the LM compared to the BS treatment. In LM the nitrate concentrations in the soil solution and in the leachate (usually <10mgL−1) were very low. In BS the nitrate concentration in the leachate reached as much as 70mgL−1. Losses of N in LM did not reach 1% of the values observed in BS. Reduced water and N availability in LM contribute to explain the decrease in growth and yield of the maize plants, and are in good agreement with the dense root system developed in this cropping system as compared to BS. The challenge for the development of living mulch systems is to improve the uptake of water and nitrogen by the roots of the main crop in a competitive environment without affecting the capacity of the cover crop to prevent N losses by leachin

Rooting depth and water use efficiency of tropical maize inbred lines, differing in drought tolerance

Deep rooting has been identified as strategy for desiccation avoidance in natural vegetation as well as in crops like rice and sorghum. The objectives of this study were to determine root morphology and water uptake of four inbred lines of tropical maize (Zea mays L.) differing in their adaptation to drought. The specific questions were i) if drought tolerance was related to the vertical distribution of the roots, ii) whether root distribution was adaptive or constitutive, and iii) whether it affected water extraction, water status, and water use efficiency (WUE) of the plant. In the main experiment, seedlings were grown to the V5 stage in growth columns (0.80m high) under well-watered (WW) and water-stressed (WS) conditions. The depth above which 95 % of all roots were located (D95) was used to estimate rooting depth. It was generally greater for CML444 and Ac7729/TZSRW (P2) compared to SC-Malawi and Ac7643 (P1). The latter had more lateral roots, mainly in the upper part of the soil column. The increase in D95 was accompanied by increases in transpiration, shoot dry weight, stomatal conductance and relative water content without adverse effects on the WUE. Differences in the morphology were confirmed in the V8 stage in large boxes: CML444 with thicker (0.14mm) and longer (0.32m) crown roots compared to SC-Malawi. Deep rooting, drought sensitive P2 showed markedly reduced WUE, likely due to an inefficient photosynthesis. The data suggest that a combination of high WUE and sufficient water acquisition by a deep root system can increase drought toleranc

Einfluss von lebenden Mulchen auf die Begleitflora und die Weizenerträge unter Bedingungen des Ökolandbau

For the success of no-tillage in organic farming, new tools have to be developed to control weeds. One possible strategy could be sowing the main crop into an earlier established living mulch of easily controllable cover crops. Field trials were carried out in the Swiss midlands to investigate the impact of different legume cover crops on weed populations and grain yield of directly drilled winter wheat (Triticum aestivum L.) in a living mulch system. In general, weed suppressing effect was best with highly productive legumes. A significant reduction of the weed density of dicotyle, monocotyle, and spring germinating species was observed. Though, effective weed suppression resulted also in strong competition with the winter wheat. In order to improve the practicability of such systems, seeding technique of the main crop and living mulch management should be investigated

Investigation of oxidative protein folding in protist mitochondria and elucidation of the catalytic mechanism of glutaredoxins

Protein import into the mitochondrial intermembrane space (IMS) of parasitic protists differs from other eukaryotes despite a general conservation of mitochondrial protein import signals. Imported proteins typically carry conserved cysteine-motifs that are oxidized in the IMS. In opisthokonta such as yeast and mammals, these motifs are recognized and oxidized by the oxidoreductase Mia40 leading to the formation of intramolecular disulfide bonds. Reduced Mia40 is subsequently re-oxidized by the sulfhydryl electron transferase Erv1. In kinetoplastida, such as Leishmania tarentolae, and in apicomplexan parasites, such as Plasmodium falciparum, no Mia40 homolog could be identified so far. However, conserved substrates and an Erv homolog in these parasites suggest the existence of a Mia40 replacement. Indeed, preliminary results revealed two disulfide-bonded interaction partners of PfErv as demonstrated by western blot analyses. The major objective of this thesis was the identification of a potential Mia40 replacement in the parasite L. tarentolae. Numerous experiments were performed in order to trap mixed disulfide intermediates between the model substrate LtsTim1 or LtErv and a potential interaction partner. A variety of protocols with alkylating, oxidizing or reducing agents did not reveal mixed disulfides between LtErv and the adapter replacement in western blot analyses. In addition, even with highly enriched LtErv protein levels after denaturing or native pulldown, no mixed disulfide intermediate could be identified. In contrast, staining against LtsTim1 in western blot analyses showed disulfide-bridged intermediates indicating potential heterodimers of LtsTim1 and Mia40 replacement candidates. However, an enrichment of these intermediates by affinity chromatography and further analysis failed because of systematic problems with the hydrophobicity of the substrate and the LtsTim1-antibody. To summarize, a potential replacement for Mia40 in parasitic protists remains to be identified and the oxidative folding machinery in the IMS of kinetoplastida and apicomplexa could not be unraveled during this PhD project. Four alternative cysteine-containing substrates of the oxidative protein folding pathway in the IMS were already designed during this project and might lead to a rather fast breakthrough in further experiments. Glutaredoxins (Grx) are highly conserved enzymes that play important roles in redox catalysis and iron metabolism and are found in almost all organisms. The traditional monothiol mechanism of Grx catalysis is divided into an oxidative half-reaction with the first glutathionylated substrate and a reductive half reaction with the reduced tripeptide glutathione (GSH) as the second substrate. However, this traditional model cannot explain how exactly the two different substrates of Grx are bound. Hence, two refined models of Grx catalysis namely the “glutathione scaffold model” and the “glutathione activator model” were previously proposed and experimentally confirmed for two residues of ScGrx7. This model can help to distinguish protein areas that either interact with the disulfide substrate (a scaffold site, including Glu170 in ScGrx7) or with the reducing agent (an activator site, including Lys105 in ScGrx7). The second objective of this PhD project was to test the general applicability of this model using the non-related enzyme PfGrx. Moreover, four additional residues that were previously suggested to contribute to the glutathione activator site in ScGrx7 were characterized in this thesis. Taken together, I confirmed the existence of two distinct glutathione interaction sites with the non-related model enzyme PfGrx. Moreover, I could identify Arg153 of ScGrx7 as another potential scaffold site residue. In addition, I could show that the two charge inversion mutants with a positively charged amino acid of the helix 3 residues Asp144 and Glu147 in ScGrx7 enhanced the interaction with the second substrate GSH. Hence, the helix 3 of these “gain-offunction” mutants indeed seems to affect the glutathione activator site. Furthermore, I could show that the introduced mutations influenced the pKa value of the active site cysteine of ScGrx7 only to a minor degree, except for ScGrx7K105E. Modeling of the transition states and analyses of the different mutants by roGFP assays may help to elucidate the structure-function relationships of Grx in further analyses

QTLs for the elongation of axile and lateral roots of maize in response to low water potential

Changes in root architecture and the maintenance of root growth in drying soil are key traits for the adaptation of maize (Zea mays L.) to drought environments. The goal of this study was to map quantitative trait loci (QTLs) for root growth and its response to dehydration in a population of 208 recombinant inbred lines from the International Maize and Wheat Improvement Center (CIMMYT). The parents, Ac7643 and Ac7729/TZSRW, are known to be drought-tolerant and drought-sensitive, respectively. Roots were grown in pouches under well-watered conditions or at low water potential induced by the osmolyte polyethylene glycol (PEG 8000). Axile root length (L Ax) increased linearly, while lateral root length (L Lat) increased exponentially over time. Thirteen QTLs were identified for six seedling traits: elongation rates of axile roots (ERAx), the rate constant of lateral root elongation (k Lat), the final respective lengths (L Ax and L Lat), and the ratios k Lat/ERAx and L Lat/L Ax. While QTLs for lateral root traits were constitutively expressed, most QTLs for axile root traits responded to water stress. For axile roots, common QTLs existed for ERAx and L Ax. Quantitative trait loci for the elongation rates of axile roots responded more clearly to water stress compared to root length. Two major QTLs were detected: a QTL for general vigor in bin 2.02, affecting most of the traits, and a QTL for the constitutive increase in k Lat and k Lat/ERAx in bins 6.04-6.05. The latter co-located with a major QTL for the anthesis-silking interval (ASI) reported in published field experiments, suggesting an involvement of root morphology in drought tolerance. Rapid seedling tests are feasible for elucidating the genetic response of root growth to low water potential. Some loci may even have pleiotropic effects on yield-related traits under drought stres

Early growth of field-grown swiss flint maize landraces

Mild cold stress (chilling) limits early growth of maize (Zea mays L.) in central and northern Europe. Introgression of chilling tolerance from landraces has been proposed, because the genetic basis for chilling tolerance of European Flint x Dent hybrids is small. Therefore, the aim of this study was a detailed characterization of the chilling toler¬ance of Swiss maize landraces, hypothesizing a relatively good performance in marginal thermal environments. The environments were set up by different sowing dates in two years. A functional growth analysis of the shoot from the one-leaf to the six-leaf stage was conducted with eight Swiss landraces and a check hybrid (Magister). The mean air temperature calculated across the six environments was above 15°C. Under these conditions, none of the landraces grew consistently better than Magister. Some landrace-specific relative growth reactions were observed compared to Magister, apparently due to strong changes in the temperature course. However, based on this study direct use of Swiss maize landraces in breeding for the improvement of chilling tolerance is not recom¬mended. More detailed investigations of promising landraces are proposed

Early growth of field-grown swiss flint maize landraces

Mild cold stress (chilling) limits early growth of maize (Zea mays L.) in central and northern Europe. Introgression of chilling tolerance from landraces has been proposed, because the genetic basis for chilling tolerance of European Flint x Dent hybrids is small. Therefore, the aim of this study was a detailed characterization of the chilling toler¬ance of Swiss maize landraces, hypothesizing a relatively good performance in marginal thermal environments. The environments were set up by different sowing dates in two years. A functional growth analysis of the shoot from the one-leaf to the six-leaf stage was conducted with eight Swiss landraces and a check hybrid (Magister). The mean air temperature calculated across the six environments was above 15°C. Under these conditions, none of the landraces grew consistently better than Magister. Some landrace-specific relative growth reactions were observed compared to Magister, apparently due to strong changes in the temperature course. However, based on this study direct use of Swiss maize landraces in breeding for the improvement of chilling tolerance is not recom¬mended. More detailed investigations of promising landraces are proposed

Bone fractures in patients using tapentadol or oxycodone: an exploratory US claims database study

Aim: To explore fracture outcomes with tapentadol or oxycodone, two opioids with differing mechanisms of action. Materials &amp; methods: Retrospective cohort pilot study, using MarketScan® Commercial and Medicare Supplemental claims databases, on patients with postoperative pain, back pain, or osteoarthritis and ≥1 claim for tapentadol (n = 16,457), oxycodone (n = 1,356,920), or both (n = 15,893) between June 2009 and December 2015. Results: During 266,826 and 9,007,889 days of tapentadol and oxycodone treatment, patients evidenced 1080 and 72,275 fractures, respectively. Fracture rates per treatment-year were 1.512 for tapentadol and 3.013 for oxycodone. Conclusion: Examination of administrative claims has inherent limitations, but this exploratory analysis indicates a lower fracture rate with tapentadol than oxycodone in the analyzed dataset, which needs confirmation by further clinical trials