@phdthesis{vonBismarck2023,
  author    = {von Bismarck, Thekla},
  title     = {The influence of long-term light acclimation on photosynthesis in dynamic light},
  school      = {Universit{\"a}t Potsdam},
  pages     = {x, 163},
  year      = {2023},
  abstract  = {Photosynthesis converts light into metabolic energy which fuels plant growth. In nature, many factors influence light availability for photosynthesis on different time scales, from shading by leaves within seconds up to seasonal changes over months. Variability of light energy supply for photosynthesis can limit a plant´s biomass accumulation. Plants have evolved multiple strategies to cope with strongly fluctuation light (FL). These range from long-term optimization of leaf morphology and physiology and levels of pigments and proteins in a process called light acclimation, to rapid changes in protein activity within seconds. Therefore, uncovering how plants deal with FL on different time scales may provide key ideas for improving crop yield. Photosynthesis is not an isolated process but tightly integrates with metabolism through mutual regulatory interactions. We thus require mechanistic understanding of how long-term light acclimation shapes both, dynamic photosynthesis and its interactions with downstream metabolism. To approach this, we analyzed the influence of growth light on i) the function of known rapid photosynthesis regulators KEA3 and VCCN1 in dynamic photosynthesis (Chapter 2-3) and ii) the interconnection of photosynthesis with photorespiration (PR; Chapter 4). We approached topic (i) by quantifying the effect of different growth light regimes on photosynthesis and photoprotection by using kea3 and vccn1 mutants. Firstly, we found that, besides photosynthetic capacity, the activities of VCCN1 and KEA3 during a sudden high light phase also correlated with growth light intensity. This finding suggests regulation of both proteins by the capacity of downstream metabolism. Secondly, we showed that KEA3 accelerated photoprotective non-photochemical quenching (NPQ) kinetics in two ways: Directly via downregulating the lumen proton concentration and thereby de-activating pH-dependent NPQ, and indirectly via suppressing accumulation of the photoprotective pigment zeaxanthin. For topic (ii), we analyzed the role of PR, a process which recycles a toxic byproduct of the carbon fixation reactions, in metabolic flexibility in a dynamically changing light environment. For this we employed the mutants hpr1 and ggt1 with a partial block in PR. We characterized the function of PR during light acclimation by tracking molecular and physiological changes of the two mutants. Our data, in contrast to previous reports, disprove a generally stronger physiological relevance of PR under dynamic light conditions. Additionally, the two different mutants showed pronounced and distinct metabolic changes during acclimation to a condition inducing higher photosynthetic activity. This underlines that PR cannot be regarded purely as a cyclic detoxification pathway for 2PG. Instead, PR is highly interconnected with plant metabolism, with GGT1 and HPR1 representing distinct metabolic modulators. In summary, the presented work provides further insight into how energetic and metabolic flexibility is ensured by short-term regulators and PR during long-term light acclimation.},
  language  = {en}
}
@phdthesis{FloresCastellanos2023,
  author    = {Flores Castellanos, Junio},
  title     = {Potato tuber (Solanum tuberosum L. cv Desiree) — characterization of starch interacting proteins and maltodextrin metabolism},
  doi       = {10.25932/publishup-61505},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-615055},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XV, 69},
  year      = {2023},
  abstract  = {Starch is a biopolymer for which, despite its simple composition, understanding the precise mechanism behind its formation and regulation has been challenging. Several approaches and bioanalytical tools can be used to expand the knowledge on the different parts involved in the starch metabolism. In this sense, a comprehensive analysis targeting two of the main groups of molecules involved in this process: proteins, as effectors/regulators of the starch metabolism, and maltodextrins as starch components and degradation products, was conducted in this research work using potato plants (Solanum tuberosum L. cv. Desiree) as model of study. On one side, proteins physically interacting to potato starch were isolated and analyzed through mass spectrometry and western blot for their identification. Alternatively, starch interacting proteins were explored in potato tubers from transgenic plants having antisense inhibition of starch-related enzymes and on tubers stored under variable environmental conditions. Most of the proteins recovered from the starch granules corresponded to previously described proteins having a specific role in the starch metabolic pathway. Another set of proteins could be grouped as protease inhibitors, which were found weakly interacting to starch. Variations in the protein profile obtained after electrophoresis separation became clear when tubers were stored under different temperatures, indicating a differential expression of proteins in response to changing environmental conditions. On the other side, since maltodextrin metabolism is thought to be involved in both starch initiation and degradation, soluble maltooligosaccharide content in potato tubers was analyzed in this work under diverse experimental variables. For this, tuber disc samples from wild type and transgenic lines strongly repressing either the plastidial or cytosolic form of the -glucan phosphorylase and phosphoglucomutase were incubated with glucose, glucose-6-phosphate, and glucose-1-phosphate solutions to evaluate the influence of such enzymes on the conversion of the carbon sources into soluble maltodextrins, in comparison to wild-type samples. Relative maltodextrin amounts analyzed through capillary electrophoresis equipped with laser-induced fluorescence (CE-LIF) revealed that tuber discs could immediately uptake glucose-1-phosphate and use it to produce maltooligosaccharides with a degree of polymerization of up to 30 (DP30), in contrast to transgenic tubers with strong repression of the plastidial glucan phosphorylase. The results obtained from the maltodextrin analysis support previous indications that a specific transporter for glucose-1-phosphate may exist in both the plant cells and the plastidial membranes, thereby allowing a glucose-6-phosphate independent transport. Furthermore, it confirms that the plastidial glucan phosphorylase is responsible for producing longer maltooligosaccharides in the plastids by catalyzing a glucan polymerization reaction when glucose-1-phosphate is available. All these findings contribute to a better understanding of the role of the plastidial glucan phosphorylase as a key enzyme directly involved in the synthesis and degradation of glucans and their implication on starch metabolism.},
  language  = {en}
}