Fault tree analysis for system modeling in case of intentional EMI

The complexity of modern systems on the one hand and the rising threat of intentional electromagnetic interference (IEMI) on the other hand increase the necessity for systematical risk analysis. Most of the problems can not be treated deterministically since slight changes in the configuration (source, position, polarization, ...) can dramatically change the outcome of an event. For that purpose, methods known from probabilistic risk analysis can be applied. One of the most common approaches is the fault tree analysis (FTA). The FTA is used to determine the system failure probability and also the main contributors to its failure. In this paper the fault tree analysis is introduced and a possible application of that method is shown using a small computer network as an example. The constraints of this methods are explained and conclusions for further research are drawn

Rieske FeS overexpression in tobacco provides increased abundance and activity of Cytochrome b₆f

Photosynthesis is fundamental for plant growth and yield. The Cytochrome b₆ f complex catalyses a rate-limiting step in thylakoid electron transport and therefore represents an important point of regulation of photosynthesis. Here we show that overexpression of a single core subunit of Cytochrome bA ) and plastoquinone pool and faster electron transport from the plastoquinone pool to Photosystem I upon changes in irradiance, compared to control plants. A faster establishment of qE , the energy-dependent component of non-photochemical quenching, in transgenic plants suggests a more rapid build-up of the transmembrane proton gradient, also supporting the increased in vivo Cytochrome b₆ f activity. However, there was no consistent increase in steady-state rates of electron transport or CO₂ assimilation in plants overexpressing Rieske FeS grown in either laboratory conditions or field trials, suggesting that the in vivo activity of the complex was only transiently increased upon changes in irradiance. Our results show that overexpression of Rieske FeS in tobacco enhances the abundance of functional Cytochrome b₆ f and may have the potential to increase plant productivity if combined with other traits

Biotechnological Perspective of Reactive Oxygen Species (ROS)-Mediated Stress Tolerance in Plants

All environmental cues lead to develop secondary stress conditions like osmotic and oxidative stress conditions that reduces average crop yields by more than 50% every year. The univalent reduction of molecular oxygen (O2) in metabolic reactions consequently produces superoxide anions (O2•−) and other reactive oxygen species (ROS) ubiquitously in all compartments of the cell that disturbs redox potential and causes threat to cellular organelles. The production of ROS further increases under stress conditions and especially in combination with high light intensity. Plants have evolved different strategies to minimize the accumulation of excess ROS like avoidance mechanisms such as physiological adaptation, efficient photosystems such as C4 or CAM metabolism and scavenging mechanisms through production of antioxidants and antioxidative enzymes. Ascorbate-glutathione pathway plays an important role in detoxifying excess ROS in plant cells, which includes superoxide dismutase (SOD) and ascorbate peroxidase (APX) in detoxifying O2•−radical and hydrogen peroxide (H2O2) respectively, monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) involved in recycling of reduced substrates such as ascorbate and glutathione. Efficient ROS management is one of the strategies used by tolerant plants to survive and perform cellular activities under stress conditions. The present chapter describes different sites of ROS generation and and their consequences under abiotic stress conditions and also described the approaches to overcome oxidative stress through genomics and genetic engineering

Five-coordinate Mn^IV intermediate in the activation of nature’s water splitting cofactor

Nature’s water splitting cofactor passes through a series of catalytic intermediates (S0-S4) before O-O bond formation and O2 release. In the second last transition (S2 to S3) cofactor oxidation is coupled to water molecule binding to Mn1. It is this activated, water-enriched all MnIV form of the cofactor that goes on to form the O-O bond, after the next light-induced oxidation to S4. How cofactor activation proceeds remains an open question. Here, we report a so far not described intermediate (S3') in which cofactor oxidation has occurred without water insertion. This intermediate can be trapped in a significant fraction of centers (>50%) in (i) chemical-modified cofactors in which Ca2+ is exchanged with Sr2+; the Mn4O5Sr cofactor remains active, but the S2-S3 and S3-S0 transitions are slower than for the Mn4O5Ca cofactor; and (ii) upon addition of 3% vol/vol methanol; methanol is thought to act as a substrate water analog. The S3' electron paramagnetic resonance (EPR) signal is significantly broader than the untreated S3 signal (2.5 T vs. 1.5 T), indicating the cofactor still contains a 5-coordinate Mn ion, as seen in the preceding S2 state. Magnetic double resonance data extend these findings revealing the electronic connectivity of the S3' cofactor is similar to the high spin form of the preceding S2 state, which contains a cuboidal Mn3O4Ca unit tethered to an external, 5-coordinate Mn ion (Mn4). These results demonstrate that cofactor oxidation regulates water molecule insertion via binding to Mn4. The interaction of ammonia with the cofactor is also discussed