Subcellular plant carbohydrate metabolism under elevated temperature
In many plant species, exposure to a changing environmental temperature regime induces an acclimation response which ultimately increases a plants thermotolerance. Under elevated temperature, membrane systems need remodelling to counteract de-stabilising thermodynamic effects. This also affects photosynthesis and carbohydrate metabolism due to heat affected protein functions, enzyme activities and transport processes across membrane systems. In the present study, a combination of electrolyte leakage assays and chlorophyll fluorescence measurements was applied to quantify heat tolerance before and after heat acclimation of Arabidopsis thaliana at different temperature regimes. Subcellular carbohydrate concentrations were determined in a combined approach of non-aqueous fractionation and 3D reconstruction of mesophyll cells and subcellular compartments using serial block-face scanning electron microscopy. Across temperature regimes between 32 {degrees}C and 38 {degrees}C, 7 days heat acclimation at 34 {degrees}C was found to most efficiently increase tissue heat tolerance. Under such conditions, cytosolic sucrose concentrations were stabilised by a shift of sucrose cleavage rates into the vacuolar compartment while invertase-driven cytosolic sucrose cleavage was found to be efficiently quenched by fructose and glucose acting as competitive and non-competitive inhibitors, respectively. Finally, this study provides strong evidence for a sucrose concentration gradient from the cytosol into the vacuole which might directly affect the physiological role and direction of proton gradient-driven sugar transport across the tonoplast.