The genetic basis of heat tolerance in temperate maize (Zea mays L.)

The global mean temperature and probability of heat waves are expected to increase in the future, which has the potential to cause severe damages to maize production. To elucidate the genetic mechanisms of the response of temperate maize to heat stress and for the tolerance to heat stress, in a first experiment I applied gene expression profiling. Therewith, I investigated the transcriptomic response of temperate maize to linearly increasing heat levels. Further, I identified genes associated with heat tolerance in a set of eight genotypes with contrasting heat tolerance behavior. I identified 607 heat responsive genes, which elucidate the genetic pathways behind the response of maize to heat stress and can help to expand the knowledge of plant responses to other abiotic stresses. Further, I identified 39 genes which were differentially regulated between heat tolerant and heat susceptible inbreds and, thus, are putative heat tolerance candidate genes. Two of these candidate genes were located in genome regions which were associated with heat tolerance during seedling and adult stage that have been detected in QTL studies in the frame of this thesis. Their exact molecular functions, however, are still unknown. The statistical approach to identify heat tolerance genes, presented in my thesis, enables researchers to investigate the transcriptomic response of multiple genotypes to changing conditions across several experiments, considering their natural variation for a quantitative trait. In order to develop more heat tolerant cultivars, knowledge of natural variation for heat tolerance in temperate maize is indispensable. Therefore, heat tolerance was assessed in a set of intra- and interpool Dent and Flint populations on a multi-environment level. Usually, heat stress in temperate Europe occurs during the adult stage of maize. However, as maize is of increasing importance as a biogas crop, farmers can reduce the growth period by postponed sowing after the harvest of the winter cereals in early summer and, thus, sensitive maize seedlings can be exposed to heat stress. Therefore, I aimed to assess heat tolerance in six connected segregating Dent and Flint populations during both developmental stages considering besides multiple environments also multiple traits. At heat stress, I observed an average decrease of 20% of the shoot dry weight during seedling stage and an average of 50% of yield loss, when heat stress was present during adult stage. At the heat locations heat stress was present in the year, when the experiments were conducted as temperatures exceeded 32°C there for more than 400 hours during the growing period in contrast to less than 30 hours at the standard locations. This emphasizes that maize crop production can suffer with the increasing number and intensity of summer heat waves. Furthermore, the study revealed strong differences between genotypes, which was indispensable to differentiate between heat tolerant and heat susceptible inbred lines. The tested genotypes originating from the Flint pool turned out to possess higher heat tolerance during seedling stage, whereas the genotypes derived from the Dent pool possessed higher heat tolerance during adult stage. This fact could be exploited by the maintenance of two pools with contrasting heat tolerance and could be beneficial for hybrid breeding. A direct selection of more heat tolerant genotypes in terms of grain yield is expensive and time-consuming. To facilitate the selection process in order to develop more heat tolerant cultivars, breeders could make use of marker assisted selection. To lay the foundation for this technique, in my thesis, QTL for heat tolerance during adult and during seedling stage were identified with the previously mentioned populations. Two QTL explained 19% of the total variance for heat tolerance with respect to grain yield in a simultaneous fit. Furthermore each two QTL were identified for two principal components, which accounted for heat tolerance during seedling stage. They explained 14 and 12% of the respective variance. The results can be used by breeding companies to develop marker assays in order to select heat tolerant genotypes from their proprietary genetic material during both stages in an initial screening. This would reduce the field capacities considerably, which are needed to test heat tolerance on a field level.Es wird erwartet, dass der Klimawandel global zu einer Erhöhung der Temperatur als auch der Wahrscheinlichkeit von Hitzewellen führt. Um die genetischen Mechanismen der Reaktion von Mais auf Hitzestress aufzuklären, untersuchte ich die Genexpressionsänderung von Mais mit steigendem Hitzestress in acht Inzuchtlinien mit gegensätzlicher Hitzetoleranz. Um Gene zu identifizieren, die mit der Hitzetoleranz von Mais in Verbindung stehen, wurde außerdem die natürliche phänotypische Variation dieser Inzuchtlinien bezüglich ihrer Hitzetoleranz in die statistische Analyse miteinbezogen. In meiner Studie wurden 607 Gene identifiziert, die ein Bild der Stoffwechselveränderungen ergaben, die in Mais mit steigendem Hitzestress stattfinden. Die Ergebnisse können des Weiteren hilfreich sein, um genetische Mechanismen von Pflanzen in Reaktion auf andere Arten abiotischen Stresses zu erklären. Insgesamt 39 Kandidatengene wurden identifiziert, die in hitzetoleranten und hitzeempfindichen Genotypen unterschiedliche Expressionsänderung mit steigendem Hitzestress erfuhren. Zwei dieser Kandidatengene für Hitzetoleranz wurden Genomregionen zugeordnet, die im Zuge von QTL-Studien mit der Hitzetoleranz im Jungpflanzen- und adulten Stadium assoziiert wurden. Die genaue molekulare Funktion dieser beiden Kandidatengene ist bisher unbekannt. Der neue statistische Ansatz, mit dem Hitzetoleranzgene in meiner Studie ermittelt wurden, erlaubt es Wissenschaftlern die Genexpression von multiplen Genotypen unter sich verändernden Bedingungen über mehrere Experimente hin zu untersuchen und dabei die natürliche Variation der Genotypen bezüglich eines quantitativen Merkmals in die Analyse miteinzubeziehen. Hitzetolerante Maissorten für mitteleuropäische Bedingungen können nur dann entwickelt werden, wenn natürliche Variation für Hitzetoleranz in lokalem genetischem Matrial vorhanden ist. Um dies zu ermitteln, wurde Hitzetoleranz in einem mehrortigen Versuch mit sechs, durch gemeinsame Elternlinien verbundene, Populationen erhoben, die aus den europäischen Flint und Dent Pools stammen. In Mitteleuropa treten Hitzewellen normalerweise während des adulten Stadiums von Maispflanzen auf. Dadurch dass Mais immer öfter als Biomassepflanze genutzt wird und damit kürzere Wachstumsphasen benötigt, kann die Aussaat auf den Zeitpunkt nach der Ernte der Wintergetreide hinausgezögert werden. Somit können Maiskeimlinge starkem Hitzestress im Frühsommer ausgesetzt werden. Deswegen war mein Ziel, die Hitzetoleranz der Populationen während beider Entwicklungsstadien zu testen, wobei ich bei der Bewertung der Hitzetoleranz neben mehreren Orten auch mehrere Merkmale in Betracht zog. In den Versuchen beobachtete ich bei Hitzestress einen durchschnittlichen 20-prozentigen Verlust an Gesamtsprossmasse im Jungpflanzenstadium sowie einen durchschnittlichen Ertragsverlust von 50%, wenn Hitzestress im adulten Stadium auftrat. Diese Ergebnisse unterstreichen die Problematik, dass der Anbau von Mais unter Hitzewellen leidet. Es wurde außerdem beobachtet, dass es starke Unterschiede zwischen den getesteten Genotypen bezüglich ihrer Hitzetoleranz gab, was es erst ermöglichte effektiv zwischen hitzetoleranten und hitzeanfälligen Genotypen unterscheiden zu können. Ein Vergleich der heterotischen Pools ergab, dass Flint-Linien hitzetoleranter im Jungpflanzen, jedoch Dent-Linien hitzetoleranter im adulten Stadium waren. Diese Tatsache kann ausgenutzt werden, indem zwei Pools mit gegensätzlicher Hitzetoleranz erhalten werden, was sich als vorteilhaft für die Erzeugung von Hybriden erweisen könnte. Eine direkte Selektion hitzetoleranterer Genotypen anhand deren Ertragsverlust bei Hitzestress ist teuer und zeitaufwändig. Um die Selektion im Zuge der Entwicklung von hitzetoleranteren Sorten zu vereinfachen, können Züchter auf markergestützte Selektion zurückgreifen. Um die Grundlage für die Markerentwicklung zu legen, wurden in meiner Studie QTL für Hitzetoleranz im Jungpflanzen- und adulten Stadium mithilfe der letztgenannten Populationen identifiziert. Zwei QTL für Hitzetoleranz mit Hinblick auf den Kornertrag wurden ermittelt, die zusammen 19% der Gesamtvarianz erklärten. Außerdem wurden je zwei QTL für zwei Hauptkomponenten identifiziert, die für die Hitzetoleranz im Jungpflanzenstadium stehen. Diese erklärten 14 und 12% der jeweiligen Gesamtvarianz. Die Ergebnisse dieser Studien können durch Züchtungsunternehmen verwendet werden, um ihr genetisches Material mithilfe von Markeranalysen auf deren Hitzetoleranz während beider Entwicklungsstadien zu untersuchen. Diese Vorgehensweise könnte einen ersten Selektionsschritt darstellen und die benötigten Feldkapazitäten einer anschließende phänotypische Selektion auf Hitzetoleranz erheblich reduzieren

Critical dynamics of ballistic and Brownian particles in a heterogeneous environment

The dynamic properties of a classical tracer particle in a random, disordered medium are investigated close to the localization transition. For Lorentz models obeying Newtonian and diffusive motion at the microscale, we have performed large-scale computer simulations, demonstrating that universality holds at long times in the immediate vicinity of the transition. The scaling function describing the crossover from anomalous transport to diffusive motion is found to vary extremely slowly and spans at least 5 decades in time. To extract the scaling function, one has to allow for the leading universal corrections to scaling. Our findings suggest that apparent power laws with varying exponents generically occur and dominate experimentally accessible time windows as soon as the heterogeneities cover a decade in length scale. We extract the divergent length scales, quantify the spatial heterogeneities in terms of the non-Gaussian parameter, and corroborate our results by a thorough finite-size analysis.Comment: 14 page

Localization Transition of the Three-Dimensional Lorentz Model and Continuum Percolation

The localization transition and the critical properties of the Lorentz model in three dimensions are investigated by computer simulations. We give a coherent and quantitative explanation of the dynamics in terms of continuum percolation theory, an excellent matching of both the critical density and exponents is obtained. Upon exploiting a dynamic scaling Ansatz employing two divergent length scales we find data collapse for the mean-square displacements and identify the leading-order corrections to scaling. The non-Gaussian parameter is predicted to diverge at the transition.Comment: extended introduction, minor changes in Fig. 2b and one reference adde

A narrative review on endopancreatic interventions: an innovative access to the pancreas

The natural connection between the duodenum and the pancreatic duct enables a minimally invasive access to the pancreas. Endoscopically this access is already regularly used, mainly for diagnostic and even for certain therapeutic purposes. With per-oral pancreatoscopy the endopancreatic approach allows the direct visualization of the pancreatic duct system potentially improving the diagnostic work-up of pancreatic cystic neoplasms, intrapancreatic strictures and removal of pancreatic duct stones. However, the endopancreatic access can equally be applied for surgical interventions. The objective of this review is to summarize endoscopic and surgical interventions using the endopancreatic access. Endopancreatic surgery stands for a further development of the endoscopic technique: a rigid endoscope is transabdominally introduced over the duodenum and the papilla to enable resections of strictures and inflamed tissue from inside the pancreas under visual control. While the orientation and localization of target structures using this minimally invasive approach is difficult, the development of an accurate image guidance system will play a key role for the clinical implementation and widespread use of endoscopic and surgical endopancreatic interventions

Forces during cellular uptake of viruses and nanoparticles at the ventral side

Many intracellular pathogens, such as mammalian reovirus, mimic extracellular matrix motifs to specifically interact with the host membrane. Whether and how cell-matrix interactions influence virus particle uptake is unknown, as it is usually studied from the dorsal side. Here we show that the forces exerted at the ventral side of adherent cells during reovirus uptake exceed the binding strength of biotin-neutravidin anchoring viruses to a biofunctionalized substrate. Analysis of virus dissociation kinetics using the Bell model revealed mean forces higher than 30 pN per virus, preferentially applied in the cell periphery where close matrix contacts form. Utilizing 100 nm-sized nanoparticles decorated with integrin adhesion motifs, we demonstrate that the uptake forces scale with the adhesion energy, while actin/myosin inhibitions strongly reduce the uptake frequency, but not uptake kinetics. We hypothesize that particle adhesion and the push by the substrate provide the main driving forces for uptake

Variability in urinary oxalate measurements between six international laboratories

Background. Hyperoxaluria is a major risk factor for kidney stone formation. Although urinary oxalate measurement is part of all basic stone risk assessment, there is no standardized method for this measurement. Methods. Urine samples from 24-h urine collection covering a broad range of oxalate concentrations were aliquoted and sent, in duplicates, to six blinded international laboratories for oxalate, sodium and creatinine measurement. In a second set of experiments, ten pairs of native urine and urine spiked with 10 mg/L of oxalate were sent for oxalate measurement. Three laboratories used a commercially available oxalate oxidase kit, two laboratories used a high-performance liquid chromatography (HPLC)-based method and one laboratory used both methods. Results. Intra-laboratory reliability for oxalate measurement expressed as intraclass correlation coefficient (ICC) varied between 0.808 [95% confidence interval (CI): 0.427-0.948] and 0.998 (95% CI: 0.994-1.000), with lower values for HPLC-based methods. Acidification of urine samples prior to analysis led to significantly higher oxalate concentrations. ICC for inter-laboratory reliability varied between 0.745 (95% CI: 0.468-0.890) and 0.986 (95% CI: 0.967-0.995). Recovery of the 10 mg/L oxalate-spiked samples varied between 8.7 ± 2.3 and 10.7 ± 0.5 mg/L. Overall, HPLC-based methods showed more variability compared to the oxalate oxidase kit-based methods. Conclusions. Significant variability was noted in the quantification of urinary oxalate concentration by different laboratories, which may partially explain the differences of hyperoxaluria prevalence reported in the literature. Our data stress the need for a standardization of the method of oxalate measuremen

Energy Metabolites as Biomarkers in Ischemic and Dilated Cardiomyopathy

With more than 25 million people affected, heart failure (HF) is a global threat. As energy production pathways are known to play a pivotal role in HF, we sought here to identify key metabolic changes in ischemic- and non-ischemic HF by using a multi-OMICS approach. Serum metabolites and mRNAseq and epigenetic DNA methylation profiles were analyzed from blood and left ventricular heart biopsy specimens of the same individuals. In total we collected serum from n = 82 patients with Dilated Cardiomyopathy (DCM) and n = 51 controls in the screening stage. We identified several metabolites involved in glycolysis and citric acid cycle to be elevated up to 5.7-fold in DCM (p = 1.7 × 10−6 ). Interestingly, cardiac mRNA and epigenetic changes of genes encoding rate-limiting enzymes of these pathways could also be found and validated in our second stage of metabolite assessment in n = 52 DCM, n = 39 ischemic HF and n = 57 controls. In conclusion, we identified a new set of metabolomic biomarkers for HF. We were able to identify underlying biological cascades that potentially represent suitable intervention targets

Artesunate-mefloquine combination therapy in acute Plasmodium falciparum malaria in young children: a field study regarding neurological and neuropsychiatric safety

BACKGROUND: Mefloquine-artesunate combination therapy for uncomplicated falciparum malaria is one of the treatments used in African children. Data concerning neurological safety in adults and children treated with mefloquine and artesunate combination therapy is well documented in Asia. Safety data for neurological and neuropsychiatric side effects of mefloquine and artesunate combination therapy in African children are scarce, although WHO recommends this therapy in Africa. METHODS: A phase IV, open label, single arm study was conducted among African children between 10 and 20 kg with acute uncomplicated falciparum malaria. They were treated over three consecutive days with a paediatric fixed-dose combination of artesunate (50 mg/d) and mefloquine (125 mg/d). Parasitological, clinical and neurological examinations and standardized questions about neuropsychiatric symptoms were carried out on days 0, 4, 7, 28 and 63. The primary objective was to assess the neurological and neuropsychiatric safety of artesunate-mefloquine combination therapy in young children. RESULTS: From December 2007 to March 2009, 220 children with uncomplicated Plasmodium falciparum malaria were treated with artesunate and mefloquine. 213 children were analysed according to study protocol. 50 neurological and neuropsychiatric adverse events occurred in 28 patients. Eleven drug-related neurological and neuropsychiatric adverse events occurred in eight patients. Sleeping disorders were present in 2.3%, neurological disorders in 1.4%, neuropsychiatric disorders in 1% and eating disorders in 0.5% of the patients. Adverse events were of mild to moderate intensity and resolved spontaneously. CONCLUSION: African children showed a low percentage of self-limited neurological and neuropsychiatric adverse events, confirming studies on neurological safety in Asian children treated with artesunate and mefloquine. Sleeping disorders were most frequently observed

High Salt Intake Down-Regulates Colonic Mineralocorticoid Receptors, Epithelial Sodium Channels and 11β-Hydroxysteroid Dehydrogenase Type 2

Besides the kidneys, the gastrointestinal tract is the principal organ responsible for sodium homeostasis. For sodium transport across the cell membranes the epithelial sodium channel (ENaC) is of pivotal relevance. The ENaC is mainly regulated by mineralocorticoid receptor mediated actions. The MR activation by endogenous 11β-hydroxy-glucocorticoids is modulated by the 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2). Here we present evidence for intestinal segment specific 11β-HSD2 expression and hypothesize that a high salt intake and/or uninephrectomy (UNX) affects colonic 11β-HSD2, MR and ENaC expression. The 11β-HSD2 activity was measured by means of 3H-corticosterone conversion into 3H-11-dehydrocorticosterone in Sprague Dawley rats on a normal and high salt diet. The activity increased steadily from the ileum to the distal colon by a factor of about 3, an observation in line with the relevance of the distal colon for sodium handling. High salt intake diminished mRNA and protein of 11β-HSD2 by about 50% (p<0.001) and reduced the expression of the MR (p<0.01). The functionally relevant ENaC-β and ENaC-γ expression, a measure of mineralocorticoid action, diminished by more than 50% by high salt intake (p<0.001). The observed changes were present in rats with and without UNX. Thus, colonic epithelial cells appear to contribute to the protective armamentarium of the mammalian body against salt overload, a mechanism not modulated by UNX

Variability in urinary oxalate measurements between six international laboratories

Hyperoxaluria is a major risk factor for kidney stone formation. Although urinary oxalate measurement is part of all basic stone risk assessment, there is no standardized method for this measurement