A core set of metabolite sink/source ratios indicative for plant organ productivity in Lotus japonicus

Plant growth is an important process in physiological as well as ecological respect and a number of metabolic parameters (elemental ratios as well as steady-state levels of individual metabolites) have been demonstrated to reflect this process on the whole plant level. Since plant growth is highly localized and is the result of a complex interplay of metabolic activities in sink and source organs, we propose that ratios in metabolite levels of sink and source organs are particularly well suited to characterize this process. To demonstrate such a connection, we studied organ-specific metabolite ratios from Lotus japonicus treated with mineral nutrients, salt stress or arbuscular mycorrhizal fungi. The plants were displaying a wide range of biomass and of flower/biomass ratios. In the analysis of our data we looked for correlations between shifts in sink/source metabolite ratios and plant productivity (biomass accumulated at the time of harvest). In addition we correlated shifts in metabolite ratios comparing competing generative and vegetative sink organs with shifts in productivity of the two organs (changes in flower/biomass ratios). In our analyses we observed clear shifts of carbohydrates and of compounds connected to nitrogen metabolism in favour of sink organs of particularly high productivity. These shifts were in agreement with general differences in metabolite steady-state levels when comparing sink and source organs. Our findings suggest that differentiation of sink and source organs during sampling for metabolomic experiments substantially increases the amount of information obtained from such experiments.     

Optimization of speed and accuracy of decoding in translation

The speed and accuracy of protein synthesis are fundamental parameters for understanding the fitness of living cells, the quality control of translation, and the evolution of ribosomes. In this study, we analyse the speed and accuracy of the decoding step under conditions reproducing the high speed of translation in vivo. We show that error frequency is close to 10⁻³, consistent with the values measured in vivo. Selectivity is predominantly due to the differences in k_cat values for cognate and near-cognate reactions, whereas the intrinsic affinity differences are not used for tRNA discrimination. Thus, the ribosome seems to be optimized towards high speed of translation at the cost of fidelity. Competition with near- and non-cognate ternary complexes reduces the rate of GTP hydrolysis in the cognate ternary complex, but does not appreciably affect the rate-limiting tRNA accommodation step. The GTP hydrolysis step is crucial for the optimization of both the speed and accuracy, which explains the necessity for the trade-off between the two fundamental parameters of translation.     

Morphological embedding and phonetic reduction: the case of triconstituent compounds

In this paper we propose that the internal bracketing of a word with more than two morphemes is reflected in the phonetic implementation. We hypothesize that embedded forms show more phonetic reduction than forms at higher structural levels (‘Embedded Reduction Hypothesis’). This paper tests the prediction of the Embedded Reduction Hypothesis with triconstituent compounds. The analysis of the durational properties of almost 500 compound tokens shows that there is a lengthening effect on the non-embedded constituent, and a shortening effect on the adjacent embedded constituent. Yet, this predicted effect of embedding interacts with other lexical factors, above all the bigram frequency of the embedded compound. At a theoretical level, these effects mean that the durational properties of the cross-boundary constituents are indicative of the hierarchical structure and of the strength of the internal boundary of triconstituent compounds. Hence, morphological structure is reflected in the speech signal.     

Issue Information ‐ Referees List

Rapid developments in remote‐sensing of vegetation and high‐throughput precision plant phenotyping promise a range of real‐life applications using leaf optical properties for non‐destructive assessment of plant performance. Use of leaf optical properties for assessing plant performance requires the ability to use photosynthetic pigments as proxies for physiological properties and the ability to detect these pigments fast, reliably and at low cost. We describe a simple and cost‐effective protocol for the rapid analysis of chlorophylls, carotenoids and tocopherols using high‐performance liquid chromatography (HPLC). Many existing methods are based on the expensive solvent acetonitrile, take a long time or do not include lutein epoxide and α‐carotene. We aimed to develop an HPLC method which separates all major chlorophylls and carotenoids as well as lutein epoxide, α‐carotene and α‐tocopherol. Using a C₃₀‐column and a mobile phase with a gradient of methanol, methyl‐tert‐butyl‐ether (MTBE) and water, our method separates the above pigments and isoprenoids within 28 min. The broad applicability of our method is demonstrated using samples from various plant species and tissue types, e.g. leaves of Arabidopsis and avocado plants, several deciduous and conifer tree species, various crops, stems of parasitic dodder, fruit of tomato, roots of carrots and Chlorella algae. In comparison to previous methods, our method is very affordable, fast and versatile and can be used to analyze all major photosynthetic pigments that contribute to changes in leaf optical properties and which are of interest in most ecophysiological studies.     

Membrane–drug interactions studied using model membrane systems

The direct interaction of drugs with the cell membrane is often neglected when drug effects are studied. Systematic investigations are hindered by the complexity of the natural membrane and model membrane systems can offer a useful alternative. Here some examples are reviewed of how model membrane architectures including vesicles, Langmuir monolayers and solid supported membranes can be used to investigate the effects of drug molecules on the membrane structure, and how these interactions can translate into effects on embedded membrane proteins.