Lipid Droplets: Packing Hydrophobic Molecules Within the Aqueous Cytoplasm

Article discusses how lipid droplets, also known as oil bodies or lipid bodies, are plant organelles that compartmentalize neutral lipids as a hydrophobic matrix covered by proteins embedded in a phospholipid monolayer. The authors review the growing body of knowledge about lipid droplets in plant cells, describe the evolutionary similarity and divergence in their associated subcellular machinery, and point to gaps that deserve future attention

Quantification of Botrytis cinerea Growth in Arabidopsis thaliana

Article describes how yield losses attributed to plant pathogens pose a serious threat to plant productivity and food security. Here, the authors describe two methods to quantify B. cinerea development in Arabidopsis thaliana genotypes through measurements of lesion development and quantification of fungal genomic DNA in infected tissues

Analysis of Pectin-derived Monosaccharides from Arabidopsis Using GC–MS

Article describes how pectin is a complex polysaccharide present in the plant cell wall, whose composition is constantly remodeled to adapt to environmental or developmental changes. Here, authors describe a quick and efficient gas chromatography–mass spectrometry (GC–MS)-based method that allows the differential analysis of pectin monosaccharide composition in plants under different conditions or between mutant plants and their respective wild types

A seed-like proteome in oil-rich tubers

There are numerous examples of plant organs or developmental stages that are desiccation-tolerant and can withstand extended periods of severe water loss. One prime example are seeds and pollen of many spermatophytes. However, in some plants, also vegetative organs can be desiccation-tolerant. One example are the tubers of yellow nutsedge (Cyperus esculentus), which also store large amounts of lipids similar to seeds. Interestingly, the closest known relative, purple nutsedge (Cyperus rotundus), generates tubers that do not accumulate oil and are not desiccation-tolerant. We generated nanoLC-MS/MS-based proteomes of yellow nutsedge in five replicates of four stages of tuber development and compared them to the proteomes of roots and leaves, yielding 2257 distinct protein groups. Our data reveal a striking upregulation of hallmark proteins of seeds in the tubers. A deeper comparison to the tuber proteome of the close relative purple nutsedge (C. rotundus) and a previously published proteome of Arabidopsis seeds and seedlings indicates that indeed a seed-like proteome was found in yellow but not purple nutsedge. This was further supported by an analysis of the proteome of a lipid droplet-enriched fraction of yellow nutsedge, which also displayed seed-like characteristics. One reason for the differences between the two nutsedge species might be the expression of certain transcription factors homologous to ABSCISIC ACID INSENSITIVE3, WRINKLED1, and LEAFY COTYLEDON1 that drive gene expression in Arabidopsis seed embryos

A unified viscoplastic model for high temperature low cycle fatigue of service-aged P91 steel

The finite element (FE) implementation of a hyperbolic sine unified cyclic viscoplasticity model is presented. The hyperbolic sine flow rule facilitates the identification of strain-rate independent material parameters for high temperature applications. This is important for the thermo-mechanical fatigue of power plants where a significant stress range is experienced during operational cycles and at stress concentration features, such as welds and branched connections. The material model is successfully applied to the characterisation of the high temperature low cycle fatigue behavior of a service-aged P91 material, including isotropic (cyclic) softening and nonlinear kinematic hardening effects, across a range of temperatures and strain-rates

Unterschiedliche Funktionen von PI4P 5-Kinasen in der Kontrolle des polaren Spitzenwachstums von Pollenschläuchen

Das Phospholipid Phosphatidylinositol-4,5-bisphosphat (PI(4,5)P2) kommt in wachsenden Pollenschläuchen vorwiegend in der apikalen Plasmamembran der Spitze vor. Welche Enzyme PI(4,5)P2 an dieser Stelle synthetisieren und welche Funktionen dieses Signallipid hat, war bislang unbekannt. Daher wurden an Hand von Sequenzähnlichkeiten und publizierten Genexpressionsdaten fünf Kandidaten-gene identifiziert, welche möglicherweise Phosphatidylinositol-4-phosphat 5-Kinasen (PI4P 5-Kinasen) kodieren und in Pollenschläuchen exprimiert werden. Diese Kinasen wurden heterolog exprimiert und biochemisch charakterisiert, wobei die vermutete PI4P 5-Kinaseaktivität bestätigt wurde. Auf Grund ihrer Domänenstruktur können die Isoenzyme in zwei Unterfamilien A und B unterteilt werden. Die Analyse von Arabidopsis Mutanten, die in der Expression verschiedener PI4P 5-Kinasen gestört sind, zeigte, dass Typ A Isoenzyme essentiell für die Pollenentwicklung sind, während Typ B Kinasen eine wichtige Rolle vor allem bei der Pollenkeimung spielen. Alle fünf Enzyme waren in der apikalen Plasmamembran von Pollenschläuchen lokalisiert, wobei die Ergebnisse im parallel untersuchten Arabidopsis- und Tabakmodell ähnlich waren. Zusätzliche Information über die Rolle von PI(4,5)P2 in Pollenschläuchen konnte aus Überexpressionsstudien gewonnen werden, in denen Typ A und Typ B PI4P 5-Kinasen jeweils spezifische morphologische Veränderungen in den Pollenschläuchen bewirkten. Starke Überexpression von Typ A Enzymen unterband das polare Wachstum der Pollenschläuche und führte zu einem Anschwellen der Pollenschlauchspitze sowie zu Veränderungen des Zytoskeletts und der Zytoplasmaströmung. Typ B Isoenzyme dagegen führten zu einer massiven Verstärkung der apikalen Exozytose von Pektin, was zu verzweigten, aber auch zu deutlich verkürzten Pollenschläuchen mit stark verdickter Pektinzellwand führte. Die Veränderungen der Pollenschlauchmorphologie beruhten auf dem verstärkt synthetisierten PI(4,5)P2 und nicht auf strukturellen Eigenschaften der Enzyme, da die Überexpression inaktiver PI4P 5-Kinasen das Wachstum von Kontrollpollenschläuchen in keiner Weise veränderte. Aufgrund der unterschiedlichen Phänotypen, welche durch die verschiedenen Typen von PI4P 5-Kinasen hervorgerufen wurden, kann davon ausgegangen werden, dass diese beiden Typen von Enzymen weitestgehend unabhängige PI(4,5)P2-Pools generieren, welche auf engem Raum in der apikalen Plasmamembran von Pollenschläuchen unterschiedliche zelluläre Prozesse regulieren, wie zum Beispiel das Zytoskelett und die Pektinsekretion. Die Überexpression einer Phosphatidylinositol 4-Kkinase aus der β-Unterfamilie führte zu ähnlichen Effekten wie die Überexpression von Typ B PI4P 5-Kinasen. Die Koexpression dieser beiden Enzyme zeigte synergisitsche Effekte auf, woraus geschlossen werden kann, dass diese beiden Lipidkinasen in einem gemeinsamen Signalweg die Sekretion von Pektin regulieren

Signalling Pinpointed to the Tip: The Complex Regulatory Network That Allows Pollen Tube Growth

Plants display a complex life cycle, alternating between haploid and diploid generations. During fertilisation, the haploid sperm cells are delivered to the female gametophyte by pollen tubes, specialised structures elongating by tip growth, which is based on an equilibrium between cell wall-reinforcing processes and turgor-driven expansion. One important factor of this equilibrium is the rate of pectin secretion mediated and regulated by factors including the exocyst complex and small G proteins. Critically important are also non-proteinaceous molecules comprising protons, calcium ions, reactive oxygen species (ROS), and signalling lipids. Among the latter, phosphatidylinositol 4,5-bisphosphate and the kinases involved in its formation have been assigned important functions. The negatively charged headgroup of this lipid serves as an interaction point at the apical plasma membrane for partners such as the exocyst complex, thereby polarising the cell and its secretion processes. Another important signalling lipid is phosphatidic acid (PA), that can either be formed by the combination of phospholipases C and diacylglycerol kinases or by phospholipases D. It further fine-tunes pollen tube growth, for example by regulating ROS formation. How the individual signalling cues are intertwined or how external guidance cues are integrated to facilitate directional growth remain open questions