Anwendung des quantitativen Fernsehmikroskopes und der Elektronenstrahlmikrosonde für die Untersuchung des Systems Eisen—Kohlenstoff—Phosphor bei 900 bis 1000°C

Neue Wege, mit geringem Aufwand an Legierungen metallische Mehrstoffsysteme im festen Zustand zu untersuchen: 1. durch Mengenmessung der Phasen mit dem quantitativen Fernsehmikroskop und Errechnung der Sättigungskonzentrationen, 2. durch Ermittlung der Phasenzusammensetzung mit der Elektronenstrahlmikrosonde. Vergleich der herkömmlichen und neuen Verfahren. Untersuchung der Eisenecke des Systems Eisen–Phosphor–Kohlenstoff bei 900, 950 und 1000°C.     

Karbidmengen und ihre örtliche Verteilung in Werkzeugstählen

Karbidmengenbestimmung mit dem quantitativen Fernsehmikroskop (QFM). Automatische Registrierung der örtlichen Karbidverteilung. Möglichkeiten sur Gewinnung einer objektiven Kennzahl der Karbidzeiligkeit. Karbidgehalte von weichgeglühten bzw. gehärteten Werkzeugstahlen.     

Messung von Karbidmengen und Größenverteilungen der Karbide in einigen Werkzeugstählen mit dem quantitativen Fernsehmikroskop

Beschreibung der Messung und Aufstellung von Summenhäufigkeitskurven der Karbidteilchendurchmesser und von Größenverteilungskurven der Anschnitte von Karbidteilchen in einer Schliffebene mit dem quantitativen Fernsehmikroskop. Errechnung von Kurven der räumlichen Größenverteilung. An einer Eisen-Kohlenstoff-Legierung mit 1,3% C, dem Schnellarbeitsstahl S 18-0-1 mit rd. 0,75% C, 4% Cr, 1,0% V und 18,0% W und dem Kaltarbeitsstahl X 40 Cr 13 mit rd. 0,4% C und 13,0% Cr Messung der Karbidmenge und der Anschnittverteilungskurven für verschiedene Austenitisierungsbedingungen sowie Errechnung von Kurven der räumlichen Größenverteilung zur Erforschung der Kinetik der Ausscheidung, Koagulation und Auflösung von Karbidteilchen.     

Flavonoids: Their Structure, Biosynthesis and Role in the Rhizosphere, Including Allelopathy

Flavonoids are biologically active low molecular weight secondary metabolites that are produced by plants, with over 10,000 structural variants now reported. Due to their physical and biochemical properties, they interact with many diverse targets in subcellular locations to elicit various activities in microbes, plants, and animals. In plants, flavonoids play important roles in transport of auxin, root and shoot development, pollination, modulation of reactive oxygen species, and signalling of symbiotic bacteria in the legume Rhizobium symbiosis. In addition, they possess antibacterial, antifungal, antiviral, and anticancer activities. In the plant, flavonoids are transported within and between plant tissues and cells, and are specifically released into the rhizosphere by roots where they are involved in plant/plant interactions or allelopathy. Released by root exudation or tissue degradation over time, both aglycones and glycosides of flavonoids are found in soil solutions and root exudates. Although the relative role of flavonoids in allelopathic interference has been less well-characterized than that of some secondary metabolites, we present classic examples of their involvement in autotoxicity and allelopathy. We also describe their activity and fate in the soil rhizosphere in selected examples involving pasture legumes, cereal crops, and ferns. Potential research directions for further elucidation of the specific role of flavonoids in soil rhizosphere interactions are considered.     

Phytohormone Regulation of Legume-Rhizobia Interactions

The symbiosis between legumes and nitrogen fixing bacteria called rhizobia leads to the formation of root nodules. Nodules are highly organized root organs that form in response to Nod factors produced by rhizobia, and they provide rhizobia with a specialized niche to optimize nutrient exchange and nitrogen fixation. Nodule development and invasion by rhizobia is locally controlled by feedback between rhizobia and the plant host. In addition, the total number of nodules on a root system is controlled by a systemic mechanism termed ’autoregulation of nodulation’. Both the local and the systemic control of nodulation are regulated by phytohormones. There are two mechanisms by which phytohormone signalling is altered during nodulation: through direct synthesis by rhizobia and through indirect manipulation of the phytohormone balance in the plant, triggered by bacterial Nod factors. Recent genetic and physiological evidence points to a crucial role of Nod factor-induced changes in the host phytohormone balance as a prerequisite for successful nodule formation. Phytohormones synthesized by rhizobia enhance symbiosis effectiveness but do not appear to be necessary for nodule formation. This review provides an overview of recent advances in our understanding of the roles and interactions of phytohormones and signalling peptides in the regulation of nodule infection, initiation, positioning, development, and autoregulation. Future challenges remain to unify hormone–related findings across different legumes and to test whether hormone perception, response, or transport differences among different legumes could explain the variety of nodules types and the predisposition for nodule formation in this plant family. In addition, the molecular studies carried out under controlled conditions will need to be extended into the field to test whether and how phytohormone contributions by host and rhizobial partners affect the long term fitness of the host and the survival and competition of rhizobia in the soil. It also will be interesting to explore the interaction of hormonal signalling pathways between rhizobia and plant pathogens.     

The Impact of Beneficial Plant-Associated Microbes on Plant Phenotypic Plasticity

Plants show phenotypic plasticity in response to changing or extreme abiotic environments; but over millions of years they also have co-evolved to respond to the presence of soil microbes. Studies on phenotypic plasticity in plants have focused mainly on the effects of the changing environments on plants’ growth and survival. Evidence is now accumulating that the presence of microbes can alter plant phenotypic plasticity in a broad range of traits in response to a changing environment. In this review, we discuss the effects of microbes on plant phenotypic plasticity in response to changing environmental conditions, and how this may affect plant fitness. By using a range of specific plant-microbe interactions as examples, we demonstrate that one way that microbes can alleviate the effect of environmental stress on plants and thus increase plant fitness is to remove the stress, e.g., nutrient limitation, directly. Furthermore, microbes indirectly affect plant phenotypic plasticity and fitness through modulation of plant development and defense responses. In doing so, microbes affect fitness by both increasing or decreasing the degree of phenotypic plasticity, depending on the phenotype and the environmental stress studied, with no clear difference between the effect of prokaryotic and eukaryotic microbes in general. Additionally, plants have the ability to modulate microbial behaviors, suggesting that they manipulate bacteria, enhancing interactions that help them cope with stressful environments. Future challenges remain in the identification of the many microbial signals that modulate phenotypic plasticity, the characterization of plant genes, e.g. receptors, that mediate the microbial effects on plasticity, and the elucidation of the molecular mechanisms that link phenotypic plasticity with fitness. The characterization of plant and microbial mutants defective in signal synthesis or perception, together with carefully designed glasshouse or field experiments that test various environmental stresses will be necessary to understand the link between molecular mechanisms controlling plastic phenotypes with the resulting effects on plant fitness.