A pivotal role for starch in the reconfiguration of 14C-partitioning and allocation in Arabidopsis thaliana under short-term abiotic stress.

Plant carbon status is optimized for normal growth but is affected by abiotic stress. Here, we used 14C-labeling to provide the first holistic picture of carbon use changes during short-term osmotic, salinity, and cold stress in Arabidopsis thaliana. This could inform on the early mechanisms plants use to survive adverse environment, which is important for efficient agricultural production. We found that carbon allocation from source to sinks, and partitioning into major metabolite pools in the source leaf, sink leaves and roots showed both conserved and divergent responses to the stresses examined. Carbohydrates changed under all abiotic stresses applied; plants re-partitioned 14C to maintain sugar levels under stress, primarily by reducing 14C into the storage compounds in the source leaf, and decreasing 14C into the pools used for growth processes in the roots. Salinity and cold increased 14C-flux into protein, but as the stress progressed, protein degradation increased to produce amino acids, presumably for osmoprotection. Our work also emphasized that stress regulated the carbon channeled into starch, and its metabolic turnover. These stress-induced changes in starch metabolism and sugar export in the source were partly accompanied by transcriptional alteration in the T6P/SnRK1 regulatory pathway that are normally activated by carbon starvation

Foraging for foundations in decision neuroscience: insights from ethology

Modern decision neuroscience offers a powerful and broad account of human behaviour using computational techniques that link psychological and neuroscientific approaches to the ways that individuals can generate near-optimal choices in complex controlled environments. However, until recently, relatively little attention has been paid to the extent to which the structure of experimental environments relates to natural scenarios, and the survival problems that individuals have evolved to solve. This situation not only risks leaving decision-theoretic accounts ungrounded but also makes various aspects of the solutions, such as hard-wired or Pavlovian policies, difficult to interpret in the natural world. Here, we suggest importing concepts, paradigms and approaches from the fields of ethology and behavioural ecology, which concentrate on the contextual and functional correlates of decisions made about foraging and escape and address these lacunae

Spatiotemporal neural characterization of prediction error valence and surprise during reward learning in humans

Reward learning depends on accurate reward associations with potential choices. These associations can be attained with reinforcement learning mechanisms using a reward prediction error (RPE) signal (the difference between actual and expected rewards) for updating future reward expectations. Despite an extensive body of literature on the influence of RPE on learning, little has been done to investigate the potentially separate contributions of RPE valence (positive or negative) and surprise (absolute degree of deviation from expectations). Here, we coupled single-trial electroencephalography with simultaneously acquired fMRI, during a probabilistic reversal-learning task, to offer evidence of temporally overlapping but largely distinct spatial representations of RPE valence and surprise. Electrophysiological variability in RPE valence correlated with activity in regions of the human reward network promoting approach or avoidance learning. Electrophysiological variability in RPE surprise correlated primarily with activity in regions of the human attentional network controlling the speed of learning. Crucially, despite the largely separate spatial extend of these representations our EEG-informed fMRI approach uniquely revealed a linear superposition of the two RPE components in a smaller network encompassing visuo mnemonic and reward areas. Activity in this network was further predictive of stimulus value updating indicating a comparable contribution of both signals to reward learning

Transportprozesse von K+- und Cs+-Ionen durch Porositäten in freistehenden Poly(para)Xylylen-Membranen

Untersucht wird der Transport von K+ und Cs+-Ionen durch Porositäten in Poly(para)Xylylen-Membranen. Diese werden hierzu freistehend präpariert und in einer UHV-Apparatur montiert. Untersuchungen zum Transportprozess erfolgen mit thermionischen Emittern welche K+ und Cs+ Ionen emittieren. Hierbei werden Untersuchungen mit kontinuierlichem und gepulstem Ionenstrahl durchgeführt. Die Apparatur besteht aus einer Ionenquelle, in welcher die Alkaliionen thermionisch erzeugt werden. Diese werden durch eine Ionenoptik geführt und in eine Zwischenkammer verbracht. Hier kann der kontinuierliche Ionenstrahl durch geeignete gepulste Spannung an einem System von Ablenkplattenpaaren in einen gepulsten Ionenstrahl gewandelt werden. Nach dem Transfer der Ionen in die Hauptkammer können dort Untersuchungen an freistehend präparierten Membranen unterschiedlicher Dicke und in Abhängigkeit von der Stoßenergie der auftreffenden Ionen durchgeführt werden. Der Transport von Alkaliionen erfolgt im Wesentlichen durch Poren und Porositäten innerhalb der Membranen bei Energien von einigen hundert Elektronenvolt. Bei einer kinetischen Energie der auftreffenden Ionen von 2000eV wird der Transport von sekundär in den Membranen erzeugten Elektronen beobachtet

Resolving the EPR Spectra in the Cytochrome bc (1) Complex from Saccharomyces cerevisiae

Quinone molecules are ubiquitous in living organisms. They are found either within the lipid phase of the biological membrane (quinone pool) or are bound in specific binding sites within membrane-bound protein complexes. The biological function of such bound quinones is determined by their ability to be reduced and/or oxidized in two successive one-electron steps. As a result, quinones are involved as one- or two-electron donors or acceptors in a large number of biological electron-transfer steps occurring during respiratory or photosynthetic processes. The intermediate formed by a one-electron reduction step is a semiquinone, which is paramagnetic and can be studied by electron paramagnetic resonance (EPR) spectroscopy. Detailed studies of such states can provide important structural information on these intermediates in such electron-transfer processes. In this study, we focus on the redox-active ubiquinone-6 of the yeast cytochrome bc (1) complex (QCR, ubiquinol: cytochrome c oxidoreductase) from Saccharomyces cerevisiae at the so-called Q(i) site. Although the location of the Q(i) binding pocket is quite well known, details about its exact binding are less clear. Currently, three different X-ray crystallographic studies suggest three different binding geometries for Q(i). Recent studies in the bacterial system (Rhodobacter sphaeroides) have suggested a direct coordination to histidine as proposed in the chicken heart crystal structure model. Using the yeast system we apply EPR and especially relaxation filtered hyperfine (REFINE) spectroscopy to study the Q(i) binding site. N-14-electron spin-echo envelope modulation spectroscopy together with an inversion-recovery filter (REFINE) is applied to resolve the question of whether N-14 modulations arise from interactions to Q (i) (center dot-) or to the Rieske iron-sulphur center. These results are discussed with regard to the location and potential function of Q(i) in the enzyme