Function and evolution of channels and transporters in photosynthetic membranes

Chloroplasts from land plants and algae originated from an endosymbiotic event, most likely involving an ancestral photoautotrophic prokaryote related to cyanobacteria. Both chloroplasts and cyanobacteria have thylakoid membranes, harboring pigment-protein complexes that perform the light-dependent reactions of oxygenic photosynthesis. The composition, function and regulation of these complexes have thus far been the major topics in thylakoid membrane research. For many decades, we have also accumulated biochemical and electrophysiological evidence for the existence of solute transthylakoid transport activities that affect photosynthesis. However, research dedicated to molecular identification of the responsible proteins has only recently emerged with the explosion of genomic information. Here we review the current knowledge about channels and transporters from the thylakoid membrane of Arabidopsis thaliana and of the cyanobacterium Synechocystis sp. PCC 6803. No homologues of these proteins have been characterized in algae, although similar sequences could be recognized in many of the available sequenced genomes. Based on phylogenetic analyses, we hypothesize a host origin for most of the so far identified Arabidopsis thylakoid channels and transporters. Additionally, the shift from a non-thylakoid to a thylakoid location appears to have occurred at different times for different transport proteins. We propose that closer control of and provision for the thylakoid by products of the host genome has been an ongoing process, rather than a one-step event. Some of the proteins recruited to serve in the thylakoid may have been the result of the increased specialization of its pigment-protein composition and organization in green plants.     

The experimenters' regress: from skepticism to argumentation

Harry Collins' central argument about experimental practice revolves around the thesis that facts can only be generated by good instruments but good instruments can only be recognized as such if they produce facts. This is what Collins calls the experimenters' regress. For Collins, scientific controversies cannot be closed by the ‘facts’ themselves because there are no formal criteria independent of the outcome of the experiment that scientists can apply to decide whether an experimental apparatus works properly or not.No one seems to have noticed that the debate is in fact a rehearsal of the ancient philosophical debate about skepticism. The present article suggests that the way out of radical skepticism offered by the so-called mitigated skeptics is a solution to the problem of consensus formation in science.     

Marked by association: techniques for proximity-dependent labeling of proteins in eukaryotic cells

Various methods have been established for the purpose of identifying and characterizing protein–protein interactions (PPIs). This diverse toolbox provides researchers with options to overcome challenges specific to the nature of the proteins under investigation. Among these techniques is a category based on proximity-dependent labeling of proteins in living cells. These can be further partitioned into either hypothesis-based or unbiased screening methods, each with its own advantages and limitations. Approaches in which proteins of interest are fused to either modifying enzymes or receptor sequences allow for hypothesis-based testing of protein proximity. Protein crosslinking and BioID (proximity-dependent biotin identification) permit unbiased screening of protein proximity for a protein of interest. Here, we evaluate these approaches and their applications in living eukaryotic cells.     

Maternal defensive behavior of mountain goats against predation by golden eagles

Maternal defensive behavior against predators may appear risky but is common in many species. Herein we describe maternal defensive behavior of mountain goats ( Oreamnos americanus ) against Golden Eagle ( Aquila chrysaetos ) predatory attempts. We found that Golden Eagles attacked goats in 1.9% of sightings ( n = 311 sightings of active Golden Eagles over 12 years) but were never successful. Mothers always defended their young against Golden Eagle attacks. Predation by Golden Eagles on young-of-the-year appears low for most ungulate species, including mountain goats. The benefits of defending offspring against eagles are likely high in ungulates, and we would therefore expect selection to favor maternal defensive behavior.     

From Practitioner to Researcher: Designing the Dissertation Process for Part Time Coursework Masters Students

Coursework Masters degrees that are offered as block release programmes provide opportunities for access to postgraduate education for adult students while in full time employ. These students attend structured contact modules after which they return to home and work and a distance format of study. However, these courses are generally characterised by low completion rates and lengthy time to completion, particularly of the research dissertation. While various explanations for this problem have been offered, for example, students’ non-academic commitments and supervisor–student-relations, our particular concern in this paper is students’ reading and writing practices in the transition from professional work practice and Masters coursework to the research dissertation. This paper proposes a systemic design to improve student reading and writing in this transition, and the proposal is illustrated using a block release coursework Masters programme in Management at a South African university. The design draws on interpretive systems ideas to think about the different levels of institutional and disciplinary context that impact on the research dissertation. We also use an academic literacies perspective—the concepts of literacy practice, language identity and power in particular—to think about reading and writing. This design incorporates components that include system elements, relationships, purpose and feedback that facilitate interaction between the conventions of the research practice, what the student brings to the practice, and the agency of the student.     

Pyruvate kinase activity in brain,liver and brown adipose tissue and the effect of cortisone in suckling rats

Zusammenfassung Die Pyruvatkinaseaktivität wurde im Gehirn und in den Muskeln von Ratten während der Entwicklung bestimmt. Die Aktivität war in Feten höher als in säugenden Jungen und stieg dann wieder an. Kortisonacetat (5 mg · 100 g/Tag, 3 Tage) erhöht die Pyruvatkinaseaktivität am 10. Tag im braunen Fettgewebe und erniedrigt sie in der Leber. Eine hohe Fettdiät, vom 14. Tag an gefüttert, hat denselben Effekt am 30. Tag. Das Muskel- und Gehirnenzym kann man durch hohe Fettdiät oder Kortison nicht verändern.     

β-Fructofuranosidase activity in pea seeds

Zusammenfassung In trockenen Erbsensamen wurde alkalische-Fruktofuranosidase mit Transferaseaktivität gefunden. Ein angereichertes Enzympräparat, durchL-Cystein, 2-Merkaptoethanol und Glutathion aktiviert und durchp-Chlormerkuribenzoat, Iodoacetamid,N-Ethylmaleimide undL-Cystin inhibiert, wurde hergestellt.