Two carbon fluxes to reserve starch in potato (Solanum tuberosum L.) tuber cells are closely interconnected but differently modulated by temperature

Parenchyma cells from tubers of Solanum tuberosum L. convert several externally supplied sugars to starch but the rates vary largely. Conversion of glucose 1-phosphate to starch is exceptionally efficient. In this communication, tuber slices were incubated with either of four solutions containing equimolar [U-14C]glucose 1-phosphate, [U-14C]sucrose, [U-14C]glucose 1-phosphate plus unlabelled equimolar sucrose or [U-14C]sucrose plus unlabelled equimolar glucose 1-phosphate. 14C-incorporation into starch was monitored. In slices from freshly harvested tubers each unlabelled compound strongly enhanced 14C incorporation into starch indicating closely interacting paths of starch biosynthesis. However, enhancement disappeared when the tubers were stored. The two paths (and, consequently, the mutual enhancement effect) differ in temperature dependence. At lower temperatures, the glucose 1-phosphate-dependent path is functional, reaching maximal activity at approximately 20 °C but the flux of the sucrose-dependent route strongly increases above 20 °C. Results are confirmed by in vitro experiments using [U-14C]glucose 1-phosphate or adenosine-[U-14C]glucose and by quantitative zymograms of starch synthase or phosphorylase activity. In mutants almost completely lacking the plastidial phosphorylase isozyme(s), the glucose 1-phosphate-dependent path is largely impeded. Irrespective of the size of the granules, glucose 1-phosphate-dependent incorporation per granule surface area is essentially equal. Furthermore, within the granules no preference of distinct glucosyl acceptor sites was detectable. Thus, the path is integrated into the entire granule biosynthesis. In vitro 14C-incorporation into starch granules mediated by the recombinant plastidial phosphorylase isozyme clearly differed from the in situ results. Taken together, the data clearly demonstrate that two closely but flexibly interacting general paths of starch biosynthesis are functional in potato tuber cells

Reduction of the cytosolic phosphoglucomutase in Arabidopsis reveals impact on plant growth, seed and root development, and carbohydrate partitioning

Phosphoglucomutase (PGM) catalyses the interconversion of glucose 1-phosphate (G1P) and glucose 6-phosphate (G6P) and exists as plastidial (pPGM) and cytosolic (cPGM) isoforms. The plastidial isoform is essential for transitory starch synthesis in chloroplasts of leaves, whereas the cytosolic counterpart is essential for glucose phosphate partitioning and, therefore, for syntheses of sucrose and cell wall components. In Arabidopsis two cytosolic isoforms (PGM2 and PGM3) exist. Both PGM2 and PGM3 are redundant in function as single mutants reveal only small or no alterations compared to wild type with respect to plant primary metabolism. So far, there are no reports of Arabidopsis plants lacking the entire cPGM or total PGM activity, respectively. Therefore, amiRNA transgenic plants were generated and used for analyses of various parameters such as growth, development, and starch metabolism. The lack of the entire cPGM activity resulted in a strongly reduced growth revealed by decreased rosette fresh weight, shorter roots, and reduced seed production compared to wild type. By contrast content of starch, sucrose, maltose and cell wall components were significantly increased. The lack of both cPGM and pPGM activities in Arabidopsis resulted in dwarf growth, prematurely die off, and inability to develop a functional inflorescence. The combined results are discussed in comparison to potato, the only described mutant with lack of total PGM activity

Carbohydrate analysis of Col-0 and <i>pgm2/3</i> plants.

<p>A<b>–</b>E, Plants were grown under 12 h light/12 h dark conditions and after five weeks 7–8 plants were collected and homogenized per line. Values are means of four technical replicates (A–C), and three technical parallels (D–E) ± SD, respectively. A, Starch content. B–C, Soluble sugar content. D–E, Sugar phosphate content. Asterisks denote the significance levels comparing <i>pgm2/3</i> mutants to Co1-0: <b>*</b><i>p</i>≤0.01;<b>**</b><i>p</i>≤0.05.</p

Phenotype of Col-0 and <i>pgm2/3</i> plants in 12 h light/12 h dark regime.

<p>A, Growth phenotypes. Photographs were taken of six-week-old plants. Bar = 1 cm. B, Fresh weight of plant rosettes. Values are means ± SD (n = 29−30). Plants were harvested after five weeks. Asterisks indicate significant difference from Col-0 (Student Test, P≤0.01). C, Leaf form from Col-0 and transgenic plants. Leaves were harvested from the middle of rosettes from six-week-old plants. Bar = 1 cm. D, Phosphoglucomutase activity in Col-0 and <i>pgm2/3</i> plants. Crude extracts were subjected to native PAGE and subsequent PGM activity staining. Separation gel was 7.5% [T] and 25 µg protein was loaded per lane.</p

Starch and soluble sugar content in Col-0 and PGM knock-out mutants.

<p>Plants were grown under long day conditions (14 h light/10 h dark). Plants were five-week-old. Values are means of three biological replicates (two technical replicates each) ± SD. Asterisks indicate values significantly different from <i>pgm1</i> and <i>pgm2 pgm1</i> (Student Test, <i>p</i>≤0.05).</p><p>Starch and soluble sugar content in Col-0 and PGM knock-out mutants.</p

Carbohydrate content.

<p>Leaves were harvested one hour before beginning of the dark phase. Values are means of four replicates representing a mix of 7–10 plants ± SD. Asterisks denote the significance levels as comparing mutants to Co1-0 : <b>*</b><i>p</i>≤0.01;<b>**</b><i>p</i>≤0.05.</p><p>Carbohydrate content.</p

Characterization of knock-out mutants lacking one cytosolic and the plastidial PGM.

<p>A, Analysis of PGM activity in the Col-0 and <i>pgm3 pgm1</i> and <i>pgm2 pgm1</i> mutants using native PAGE and PGM activity staining. Separation gel 7.5% [T]. 35 µg proteins were loaded per lane. 1– Col-0, 2– <i>pgm3</i>, 3– <i>pgm2</i>, 4– <i>pgm1</i>, 5– <i>pgm3 pgm1</i>, 6– <i>pgm2 pgm1.</i> B, Analysis of floral stems development in Col-0 and different PGM knock-out plants. Plants were grown under long day conditions (14 h light/10 h dark). Days after germination were registered, when plants developed floral stems 1 cm long. Values are means ± SD (n = 24). a - significant difference from Col-0 (Student Test, <i>p</i>≤0.01), b - significant difference from <i>pgm1</i> (Student Test, <i>p</i>≤0.01).</p

Overlay heat map of the metabolite changes in <i>pgm2/3</i> mutants in comparison with control (Co1-0) using false-color scale.

<p>Red or blue indicate that the metabolite content is increased or decreased, respectively. Five-week-old plants were grown under 12 h light/12 h dark conditions and harvested at the end of light phase (EL) and dark phase (ED), and three replicates represented 3–4 plants were analyzed (two technical replicates each); asterisks denote the significance levels as comparing <i>pgm2/3</i> mutants to Co1-0 : <b>*</b><i>p</i>≤0.01;<b>**</b><i>p</i>≤0.05.</p

Denkwerkstatt „Osnabrück 2030 – Demokratie leben“ – Handlungs- und Aktionsfelder II

Zukünftige Nonprofit-Manager*innen sind mit komplexen Herausforderungen in einem sich stetig wandelnden Umfeld konfrontiert. Themen wie Klimaschutz, soziale Ungleichheit oder auch Demokratieförderung haben einen starken Einfluss auf die Arbeitsfelder der Nonprofit-Organisationen. Eine zentrale Aufgabe der Führungskräfte ist daher in dieser Komplexität konstruktiv agieren zu können. Dafür sind Kompetenzen erforderlich: Ganz zentral ist die Fähigkeit, sich initiativ und eigenverantwortlich mit den Herausforderungen unserer Zeit auseinanderzusetzen und im besten Fall geeignete Lösungen dafür zu finden sowie diese zielführend kommunizieren zu können. Aus diesem Grund wird genau diese Fähigkeit bei Studierenden aus den Masterstudiengängen Management in Nonprofit-Organisationen und Soziale Arbeit der Hochschule Osnabrück gefördert. Im Rahmen des Moduls Handlungsfelder II entwickelten rund 30 Studierende im Wintersemester 2022/2023 in einer Denkwerkstatt Forschungsergebnisse und Lösungsideen zum Thema „Osnabrück 2030 – Demokratie leben“. Die Studierenden wählten in einem partizipativen Prozess ihre eigenen Schwerpunktthemen wie zum Beispiel Mobilität oder Bildung aus und arbeiteten dann ein Semester lang an den Inhalten. Bei der Erarbeitung wurden sie durch Marlene Eimterbäumer begleitet, die Modelle, Methoden und Coaching zur Unterstützung bereit stellte. Die Modelle und Methoden finden sich teilweise in den Beiträgen der Studierenden wieder (unter anderem das Social Ecological Model und der Business Model Canvas). Am Ende des Semesters stand eine Präsentation vor den Kommiliton*innen, der Lehrenden und auch vor externen Gästen, die aus unterschiedlichen Expertisegebieten im Themenbereich „Demokratie“ kamen und dementsprechend Feedback aus der Praxis geben konnten. Das Modul selbst wurde von der Hochschule im Rahmen der Innovativen Lehre an der Fakultät Wirtschafts- und Sozialwissenschaften gefördert. Für die Studierenden stellte das Modul durchaus eine Herausforderung dar, denn in der Denkwerkstatt musste unter hoher Komplexität stark prozessbezogen gearbeitet werden im Gegensatz zu der sonstigen hohen Ergebnisorientierung. Die durchweg sehr guten Ergebnisse zeigen, dass der Einsatz und die kontinuierliche Kommunikation und Zusammenarbeit sich gelohnt haben. Aufgeteilt ist das vorliegende Buch in die fünf Themen: Wahlen, Partizipation, Partizipative Raumentwicklung, Politische Bildung und Medienkompetenz. Zu diesen Themen finden Sie jeweils erst einen Beitrag der Forscher*innen und darauffolgend einen Beitrag zur Darstellung einer Lösungsidee