The regulatory network adjusting light-harvesting in the model green alga Chlamydomonas reinhardtii

Berger H. The regulatory network adjusting light-harvesting in the model green alga Chlamydomonas reinhardtii. Bielefeld: Bielefeld University; 2015.In photosynthetic organisms, control of light-harvesting is a key component of acclimation mechanisms that optimize photon conversion efficiencies. In this thesis, the interrelation of short- and long-term regulation of light-harvesting at photosystem II (PSII) was analyzed in the green alga Chlamydomonas reinhardtii. This model organism is able to gain carbon and energy through photosynthetic carbon dioxide fixation as well as heterotrophic feeding. A lowered inorganic or increased organic carbon supply reduces the rate of NADPH consumption by the Calvin cycle, resulting in an over-reduced photosynthetic electron transport chain and increased excitation pressure at photosystem II. A combination of molecular biology, biochemistry, chlorophyll fluorescence and physiological analyses revealed that a reduction in functional antenna size efficiently relieved excitation pressure on PSII under these conditions. Particularly, translation control on PSII-associated major light-harvesting proteins (LHCII) replaced state transitions as an initial protection mechanism in the long term. The LHCII translation repressor NAB1 emerged as key factor implicated in the acclimation to the prevailing carbon assimilation mode. The level of NAB1 was increased under carbon dioxide limitation, and expression control based on modulated promoter activity. Application of a photosynthetic electron transport inhibitor and a perturbed NAB1 accumulation in a state transition mutant suggested that chloroplast retrograde signals control nuclear NAB1 expression. To further investigate this retrograde signaling, a reporter system was developed that enables detailed promoter analyses. Systematic truncation studies identified a promoter fragment of 152 bases, which comprised essential regulatory elements and can be used as tool for the identification of cis-regulatory elements in future studies. Furthermore, chloroplast redox poise was shown to modulate the extent of LHCII translation repression in the cytosol via cysteine based redox control of NAB1. In response to moderate light intensity changes, a fine-tuning system comprising specific single cysteine nitrosylation and thioredoxin mediated re-reduction adjusted NAB1 activity to the demand for light-harvesting antenna proteins. This is the first mechanistic description of redox based translation control of nuclear encoded photosynthesis associated genes. Overall, this thesis describes regulatory circuits that adjust light-harvesting capacity over a range of time scales, involving nuclear and cytosolic expression control as well as short-term responses in the chloroplast, and provides new insights into interorganellar communication that ensures optimal photon capture

Public subsidies and the sources of venture capital

Research suggests that public subsidies for newly founded firms have a positive effect on follow-on financing, in particular, Venture Capital (VC). This study differentiates between Government VC, Independent VC, Corporate VC, and Business Angels and shows that public subsidies are not relevant for all of these sources. When accounting for firm characteristics that drive both selection into public subsidies as well as into VC financing through econometric matching techniques, we find that subsidies are only linked to Government VC and Business Angel financin

Resilience trinity: safeguarding ecosystem functioning and services across three different time horizons and decision contexts

Ensuring ecosystem resilience is an intuitive approach to safeguard the functioning of ecosystems and hence the future provisioning of ecosystem services (ES). However, resilience is a multi‐faceted concept that is difficult to operationalize. Focusing on resilience mechanisms, such as diversity, network architectures or adaptive capacity, has recently been suggested as means to operationalize resilience. Still, the focus on mechanisms is not specific enough. We suggest a conceptual framework, resilience trinity, to facilitate management based on resilience mechanisms in three distinctive decision contexts and time‐horizons: 1) reactive, when there is an imminent threat to ES resilience and a high pressure to act, 2) adjustive, when the threat is known in general but there is still time to adapt management and 3) provident, when time horizons are very long and the nature of the threats is uncertain, leading to a low willingness to act. Resilience has different interpretations and implications at these different time horizons, which also prevail in different disciplines. Social ecology, ecology and engineering are often implicitly focussing on provident, adjustive or reactive resilience, respectively, but these different notions of resilience and their corresponding social, ecological and economic tradeoffs need to be reconciled. Otherwise, we keep risking unintended consequences of reactive actions, or shying away from provident action because of uncertainties that cannot be reduced. The suggested trinity of time horizons and their decision contexts could help ensuring that longer‐term management actions are not missed while urgent threats to ES are given priority

Reviews

Reviews Carolyn E. Hill. Token Professionals and Master Critics: A Critique of Orthodoxy in Literary Studies. (James Sosnoski, 1994). Michael Kuhne. Releasing the Imagination: Essays on Education, the Arts, and Social Change. (Maxine Greene, 1995). Felicia M. Briscoe. Artwork of the Mind: An Interdisciplinary Description of Insight and the Search for it in Student Writing. (Mary M. Murray, 1996). Hanna Berger. If You Want to Write: A Book about Art, Independence and Spirit. (Brenda Ueland, 1997). Candace Walworth. The Rag and Bone Shop of the Heart: Poems for Men. (Robert Bly, James Hillman, Michael Meade, Eds., 1992)

The automatic gain-matching in the PIBETA CsI calorimeter

Segmented electromagnetic calorimeters are used to determine both the total energy and direction (momentum components) of charged particles and photons. A trade off is involved in selecting the degree of segmentation of the calorimeter as the spatial and energy resolutions are affected differently. Increased number of individual detectors reduces accidental particle pile-up per detector but introduces complications related to ADC pedestals and pedestal variations, exacerbates the effects of electronic noise and ground loops, and requires summing and discrimination of multiple analog signals. Moreover, electromagnetic showers initiated by individual ionizing particles spread over several detectors. This complicates the precise gain-matching of the detector elements which requires an iterative procedure. The PIBETA calorimeter is a 240-module pure CsI non-magnetic detector optimized for detection of photons and electrons in the energy range 5-100 MeV. We present the computer-controlled, automatic, in situ gain-matching procedure that we developed and used routinely in several rare pion and muon decay experiments with the PIBETA detector.Comment: 28 pages, 13 postscript figures, LaTeX, submitted to Nucl. Instrum. Meth.

Local networks and new business formation

New business formation is a key driver of regional transformation and development. While we know that a region’s attractiveness for new businesses depends on its resources, infrastructure, and human capital, we know little about the role of local business networks in promoting or impeding the birth of new firms. We construct local business networks connecting more than 350 million nodes consisting of managers, owners and firms using administrative data on all German businesses from 2002 to 2020. Differentiating between serial and de-novo entrepreneurs, we show a positive but decreasing relation between a region’s connectedness and firm entry of serial entrepreneurs. Networks are, moreover, positively linked to firm survival. Relating our findings to a measure of ownership concentration, we show that networks provide additional explanations for regional variation in new business formations. These patterns are robust to synthetic instrumental variable estimation

The role of the chemical composition of monetite on the synthesis and properties of α-tricalcium phosphate

Peer reviewedPublisher PD