The role of subcellular plant carbohydrate metabolism in heat response and acclimation

Seydel, Charlotte (2026): The role of subcellular plant carbohydrate metabolism in heat response and acclimation. Dissertation, LMU München: Faculty of Biology

Abstract

During exposure to elevated temperatures, plants employ various mechanisms to survive and maintain cellular functions, ultimately leading to increased thermotolerance. Heat affects membrane integrity, protein function, enzyme activity and transport processes, impacting photosynthesis and the primary carbohydrate metabolism. To adjust to the environmental conditions, plants regulate their metabolism to stabilise growth and development. Especially photosynthesis and the metabolism of carbohydrates, which are primary products of photosynthetic CO2 fixation, need to be adjusted to prevent irreversible tissue damage. The metabolic and photosynthetic response to transient heat exposure of differing severity was quantified in Arabidopsis thaliana accession Columbia-0 (Col-0), and two mutants deficient in enzyme activities of starch and sucrose biosynthesis, plastidial Phosphoglucomutase (PGM1) and Sucrose Phosphate Synthase A1 (SPSA1), respectively. A mathematical carbon balance model utilising Fourier polynomials was employed to analyse underlying dynamics of net carbon fluxes. Integrals and derivatives of the Fourier polynomials revealed a stabilising role of a lowered activity of SPS during transient heat exposure. To further understand the effect of carbohydrates on heat response, the acclimation of Arabidopsis to elevated temperatures was analysed. Wild type Col-0 plants before and after 7 days of acclimation to heat, ranging from moderate to severe, were analysed by photosynthesis and electrolyte leakage measurements to assess their acclimation capability. Across a temperature range from 22°C to 40°C, it was found that Arabidopsis most efficiently increases its heat tolerance during acclimation at 34°C. Leaf tissue of non-acclimated and acclimated plants was analysed using the non-aqueous fractionation (NAF) technique, which enabled the quantification of subcellular sugar distribution. Ultrastructural 3D measurements by serial block-face scanning electron microscopy (SBF-SEM) resolved compartment volumes, which enabled estimations of effective sugar concentrations. The compartment-specific concentrations of the three sugars sucrose, glucose and fructose were quantified for vacuole, cytosol and chloroplasts. In acclimated plants, cytosolic sucrose levels were stabilised by shifting invertase-catalysed sucrose cleavage into the vacuole. Further, glucose and fructose concentrations were observed to peak in the cytosol of acclimated plants, indicating a heat-induced deregulation of dissimilatory pathways, e.g., glycolysis. In summary, it is hypothesised that a coordinate heat response of sucrose transport into the vacuole and a hexose-induced inhibition of sucrose cleavage in the cytosol stabilises carbohydrate metabolism and photosynthesis.

• Item Type: Theses (Dissertation, LMU Munich)
• Subjects: 500 Natural sciences and mathematics; 500 Natural sciences and mathematics > 570 Life sciences
• Faculties: Faculty of Biology
• Language: English
• Date of oral examination: 17. February 2026
• 1. Referee: Nägele, Thomas
• Signature of the printed copy: 0001/UMC 31825