Biology subjects

Naegele, T.

Publications and source records attributed to Naegele, T..

18 recordsLinked to original sources

bioRxiv2026

Decoding plant x environment interactions through spatial gradients in leaf physiology and metabolism

Succulent leaves are well known to combine photosynthesis, carbon storage and hydraulic buffering. However, their metabolic responses to heat and drought may differ along the same leaf axis. We investigated spatial and temporal changes in leaf tissue water content, photosynthetic performance and central carbon metabolism in the CAM plant Sansevieria cylindrica across three experimental phases: (i) heat, (ii) combined heat and drought, and (iii) rewatering under continued heat. Apical, middle and basal leaf sections were sampled at midday, and chlorophyll fluorescence was monitored near the leaf tip. Fresh-weight-to-dry-weight ratios declined significantly in basal tissues under drought, whereas apical tissues showed a significant decrease only during rewatering indicating a considerable delay in tissue water supply along the leaf axis. Apical photosystem II quantum yield decreased during combined heat and drought, and sucrose accumulated transiently during heat exposure, particularly in middle and basal sections. Glucose and fructose peaked under drought conditions and declined after rewatering. Citrate decreased during the experimental time course, while apical malate increased significantly during rewatering phase. Chlorophyll varied primarily with leaf position, whereas starch and fumarate showed no significant effects. Neural network classification identified citrate and sucrose as major contributors to the discrimination of treatment phases, while chlorophyll was most informative for distinguishing leaf positions. Together, these findings demonstrate that within leaf physiological and metabolic gradients capture complementary dimensions of plant x environment interactions, distinguishing spatially structured leaf characteristics from dynamic stress responses. Integrating spatially resolved metabolic and physiological profiles thus provides a promising approach for identifying biochemical signatures of environmental stress and recovery in CAM plants.

plant biology↗

bioRxiv2026

Subcellular carbohydrate compartmentation and organic acid signatures reveal natural variation in cold acclimation of Arabidopsis thaliana

Plant cold acclimation emerges from coordinated adjustments in photosynthesis, primary metabolism, and intracellular carbon allocation. Yet, the regulatory role of subcellular metabolite compartmentation in natural variation of cold acclimation remains insufficiently understood. Here, we investigated four Arabidopsis thaliana accessions grown either individually or in bulk to determine how growth configuration and genotype shape the metabolism of sugars and organic acids during cold exposure. Using non-aqueous fractionation, we quantified plastidial, cytosolic, and vacuolar sugar pools alongside whole-cell carbohydrates, organic acids, enzyme activities, photosynthetic parameters, and stress markers. A neural-network classifier revealed that subcellular sugar distribution together with sugar amounts and organic acids provided the strongest discriminatory power among accessions, surpassing photosynthetic traits and enzyme activities. Our findings demonstrate that natural variation in cold acclimation is strongly determined by genotype-specific subcellular metabolite architectures, and that the cultivation strategy modulates these intracellular signatures. We conclude that subcellular compartmentation of metabolites represents a cellular control layer for natural variation of cold acclimation and resilience in Arabidopsis thaliana.

plant biology↗

bioRxiv2025

The functional divergence of plant ESCRT components TOL3, SNF7.1, and VPS4 during salt stress response

Salinity, a major abiotic stressor, impacts protein trafficking and alters transport routes. The endosomal sorting complex required for transport (ESCRT)is a key player for membrane protein sorting and is increasingly recognized as pivotal element in abiotic stress responses. However, the functional role of ESCRT proteins in cereal crops under salt stress remains unexplored. Using the as near as possible to nature DRD-BIBLOX (Dark-Root device Brick Black Box), barley (Hordeum vulgare, L.), although relatively salt-tolerant, exhibits impaired germination, seedling growth, and an altered root system architecture (RSA) under high salinity. Shotgun proteomic analysis revealed spatio-temporal regulation of ESCRT proteins in shoots and roots during seedling development. We identified HvSNF7.1 and HvVPS4 as critical, but differently acting modulators of salt stress responses in barley tissues. In this study we further reveal novel functions of ESCRT-0-like TOM-1-like proteins (TOLs): Previously described as gatekeepers of degradative protein sorting and as regulators of abscisic acid signaling, growth, and heat stress responses in Arabidopsis (Arabidopsis thaliana), HvTOLs had not been characterized for their role in salinity adaptation during plant development. Functional analyses demonstrated lethality in Hvtoldouble and Hvtolquadruple mutants under standard growth conditions. In Arabidopsis, loss of AtTOL3 alone impaired germination and root growth under salt stress, underscoring the essential role of individual TOL proteins in the spatio-temporal regulation of abiotic stress adaptation. These findings highlight ESCRT-mediated trafficking as a key determinant of cereal resilience under saline conditions and provide a molecular framework for improving crop stress tolerance.

plant biology↗

bioRxiv2025

The chloroplast ionome shines new light on organellar Fe homeostasis

Annually, chloroplasts fix 258 billion tons of CO2 through photosynthesis. Photosynthesis and other biochemical pathways require specific amounts of metal ions in the organelle. Transport proteins in the plastid inner envelope maintain the organellar ion homeostasis. Despite substantial progress over the last decades, many genes encoding for plastid ion channels and ion carriers or their regulators remain unknown. To fill this knowledge gap, detailed information on the elemental composition of chloroplasts i.e., a plastid ionome, is needed. This will allow to compare mutants of transporter candidates with wild-types. Here, we provide quantitative descriptions of chloroplast ionomes from Arabidopsis thaliana, the metal hyperaccumulator Arabidopsis halleri, Pisum sativum, and Nicotiana benthamiana and analyze similarities and distinctions. Using A. thaliana, we show that plastid ionomes can be genetically manipulated. Chloroplasts of oligopeptide transporter3 (opt3)-deficient mutants contain 14-fold more iron, which they deposit into stromal FERRITIN. The removal of FERRITIN in opt3 mutants leads to a substantial decrease in plastid and leaf iron pointing to important signaling linked to the chloroplast ionome. Our study reveals that chloroplasts can be turned into large iron storages. Since crop biofortification to fight hidden hunger has become a global mission, this research provides groundwork to reach this goal.

plant biology↗

bioRxiv2025

Acclimation of carbon metabolism to a changing environment across a leaf rosette of Arabidopsis thaliana

O_LIPlants need to efficiently and quickly stabilize photosynthesis and carbon metabolism under changing environmental conditions to prevent irreversible tissue damage C_LIO_LIDifferently developed leaves of Arabidopsis thaliana rosettes are typically homogenized for metabolic analyses which might result in significant over- or underestimation of metabolite dynamics. C_LIO_LIHere, photosynthesis and carbon metabolism were analysed in mature and immature leaves of rosettes of natural Arabidopsis accessions originating from southern and northern Europe. Ambient growth condition at 22 {degrees}C was compared to a combined low temperature/elevated light treatment. C_LIO_LIGradients of Fv/Fm and CO2 assimilation rates across leaf rosettes hinted towards tissue-specific acclimation capacities of photosynthesis and carbon metabolism. C_LIO_LIDynamics of carbohydrates and carboxylic acids were integrated with photosynthetic parameters in a quantitative carbon balance model. Model simulations suggested that mature leaf tissue stabilizes acclimation of carbon metabolism in immature leaf tissue and/or other sink tissue. C_LIO_LIIn conclusion, acclimation capacities of photosynthesis to low temperature and elevated light significantly differ within one leaf rosette of Arabidopsis. This directly affects carbon metabolism which shapes the metabolic acclimation capacity of the whole plant. C_LIO_LIIt is suggested to consider such tissue-specific effects which might otherwise be hidden behind a high variance of experimental data. C_LI

plant biology↗

bioRxiv2025

Metabolic Response of a Chemolithoautotrophic Archaeon to Carbon Limitation

The ubiquitously distributed ammonia-oxidizing archaea generate energy from ammonia and build cell mass from inorganic carbon sources, thereby contributing to both the global nitrogen and carbon cycles. However, little is known about the regulation of their predicted core carbon metabolism. A thermodynamic model for Nitrososphaera viennensis was developed to estimate the consumption of inorganic carbon in relation to ammonia consumed for energy and was tested experimentally by growing cells in carbon-limited and excess conditions. A combined proteomic and metabolomic approach of the experimental conditions revealed distinct metabolic adaptation depending on the amount of carbon supplied, either in a catalase or pyruvate background as a reactive oxygen species scavenger. Integration of protein and metabolite dynamics revealed a cellular strategy under carbon limitation to maintain a pool of amino acids and an upregulation of proteins necessary for translation initiation to stay primed for protein synthesis. The combination of modelling and functional genomics fills gaps in the understanding of the central metabolism and its regulation in a chemolithoautotrophic, ammonia-oxidizing archaeon even in the absence of available genetic tools.

microbiology↗

bioRxiv2024

Hexokinase 1-mediated plant immunity under abiotic stress depends on chloroplast positioning

Molecular networks involved in the responses of plants towards environmental changes are multifaceted and affect diverse metabolic and signalling pathways. Under challenging environmental conditions, such as low temperatures and high light intensities, plants need to immediately adjust their metabolism to prevent irreversible tissue damage, e.g., caused by reactive oxygen species. Regulation of photosynthesis and carbohydrate metabolism plays a crucial role in this stress response. Here, we analysed mutants of Arabidopsis thaliana, which were affected in either central enzymatic activities of carbohydrate metabolism, in chloroplast positioning or in a combination of both. Plants were exposed to a treatment of combined cold and elevated light. While mutants with deficiencies in sucrose (spsa1) or starch (pgm1) metabolism showed affected metabolic pathway regulation under abiotic stress, Hexokinase 1 mutants (hxk1) showed a severe growth phenotype with lesions and pale areas on leaf tissue. In a double mutant, which combined deficiencies in Chloroplast Unusual Positioning 1 (CHUP1)-mediated chloroplast positioning and HXK1 (chup1 x hxk1), this growth phenotype vanished resulting in wild type-like plants. Transcriptome analysis revealed a significantly affected immune response of hxk1 plants, which was suppressed in the double mutants. Our findings provide evidence for a role of HXK1 as a positive regulator of the plant immune response. Finally, we suggest that, due to its potential role as a negative regulator of plant immunity, CHUP1 deficiency counteracted the reduced immunity of hxk1 in the double mutant which rescued the plants. Future studies might now reveal whether deficiencies in CHUP1 function and/or transcription represent a conserved strategy to increase plant immunity under abiotic stress.

plant biology↗

bioRxiv2024

Regulation of plant metabolism under elevated CO2

Plant responses to changing environments afford complex regulation at transcriptome and proteome level to maintain metabolic homeostasis. Homeostasis itself constitutes a complex and dynamic equilibrium of metabolic reactions and transport processes among cellular compartments. In the present study, we aimed at the highest possible resolution of this network by combining analysis of transcriptome, proteome and subcellular resolved metabolome of plants exposed to rising carbon dioxide concentrations over a time course of one week. To prove suitability of our approach, we included mutants affected in photorespiratory metabolism and, thus, should deviate from the wildtype in their response to elevated CO2. Our multi-omics analysis revealed that the hpr1-1 mutant, defective in peroxisomal hydroxypyruvate reduction, is also affected in cytosolic pyruvate metabolism, reaching out to cysteine synthesis, while the hexokinase mutant hxk1 displays a disturbed redox balance upon changing CO2 levels. For the third mutant, defective in the mitochondrial protein BOU, we found compelling evidence that the function of this transporter is related to lipoic acid metabolism, thus challenging current interpretations. This demonstrates that the combined omics approach introduced here opens new insights into complex metabolic interaction of pathways shared among different cellular compartments.

plant biology↗

bioRxiv2024

Flavonoid metabolism and its different physiological roles in plant cold acclimation

Flavonoids represent a diverse group of plant secondary metabolites which are also discussed in context of dietary health and inflammatory response. Numerous studies have revealed that flavonoids play a central role in plant acclimation to abiotic factors like low temperature or high light, but their structural and functional diversity frequently prevents a detailed mechanistic understanding. Further complexity in analysing flavonoid metabolism arises from the different subcellular compartments which are involved in biosynthesis and storage. In the present study, non-aqueous fractionation of Arabidopsis leaf tissue was combined with metabolomics and proteomics analysis to reveal subcellular regulation during cold acclimation in two flavonoid-deficient mutants. During the first three days of a two-week cold acclimation period, flavonoid deficiency was observed to affect pyruvate, citrate and glutamate metabolism which indicated a role in stabilising C/N metabolism and photosynthesis. Also, tetrahydrofolate metabolism was found to be affected which had significant effects on regulation of the proteome of the photorespiratory pathway. In the late stage of cold acclimation, flavonoid deficiency was found to affect protein stability, folding and proteasomal degradation which resulted in a significant decrease of total protein amounts in both mutants. In summary, these findings suggest that flavonoid metabolism plays different roles in early and late stages of plant cold acclimation and significantly contributes to establishing a new protein homeostasis in a changing environment.

plant biology↗

bioRxiv2023

Temperature acclimation of photosynthesis and carbohydrate metabolism are related to the geographical origin of Arabidopsis thaliana

Acclimation is a multigenic trait by which plants adjust photosynthesis and metabolism to cope with a changing environment. Here, natural variation of photosynthetic and metabolic acclimation was analyzed in response to low and elevated temperature. For this, 18 natural accessions of Arabidopsis thaliana, originating from Africa and Europe, were grown at 22{degrees}C before being exposed to 4{degrees}C and 34{degrees}C for cold and heat acclimation, respectively. Amounts of carbohydrates were quantified together with their subcellular distribution across plastids, cytosol and vacuole. Linear electron transport rates (ETRs) were determined together with maximum quantum efficiency of photosystem II (Fv/Fm) for all growth conditions and under temperature fluctuation. Under elevated temperature, residuals of ETR under increasing photosynthetic photon flux densities were found to significantly correlate with the longitudinal gradient of the geographic origin of accessions indicating a naturally occurring east-west gradient of photosynthetic acclimation capacities. Further, in heat acclimated plants, vacuolar fructose amount was found to positively correlate with longitude while plastidial and cytosolic amounts were found to be negatively correlated. Plastidial sucrose concentrations were found to positively correlate with maximal ETRs under fluctuating temperature indicating a stabilizing role within the chloroplast. In summary, our findings revealed specific subcellular carbohydrate distributions which contribute differentially to photosynthetic efficiencies of natural Arabidopsis thaliana accessions across a longitudinal gradient. This sheds light on the relevance of subcellular metabolic regulation for photosynthetic performance in a fluctuating environment and supports the physiological interpretation of naturally occurring genetic variation of temperature tolerance and acclimation.

plant biology↗

bioRxiv2023

A bench-top dark-root device built with LEGO bricks enables a non-invasive plant root development analysis in soil conditions mirroring nature

Roots are the hidden parts of plants, anchoring their above ground counterparts in the soil. They are responsible for water and nutrient uptake, as well as for interacting with biotic and abiotic factors in the soil. The root system architecture (RSA) and its plasticity are crucial for resource acquisition and consequently correlate with plant performance, while being highly dependent on the surrounding environment, such as soil properties and therefore environmental conditions. Thus, especially for crop plants and regarding agricultural challenges, it is essential to perform molecular and phenotypic analyses of the root system under conditions as near as possible to nature (#asnearaspossibletonature). To prevent root illumination during experimental procedures, which would heavily affect root development, dark-root (D-Root) devices (DRDs) have been developed. In this article, we describe the construction and different applications of a sustainable, affordable, flexible, and easy to assemble open-hardware bench-top LEGO(R) DRD, the DRD-BIBLOX (Brick Black Box). The DRD-BIBLOX consists of one or more 3D-printed rhizoboxes which can be filled with soil, while still providing root visibility. The rhizoboxes sit in a scaffold of secondhand LEGO(R) bricks, which allows root development in the dark as well as non-invasive root-tracking with an infrared (IR) camera and an IR light emitting diode (LED) cluster. Proteomic analyses confirmed significant effects of root illumination on barley root and shoot proteome. Additionally, we confirmed the significant effect of root illumination on barley root and shoot phenotypes. Our data therefore reinforces the importance of the application of field conditions in the lab and the value of our novel device, the DRD-BIBLOX. We further provide a DRD-BIBLOX application spectrum, spanning from investigating a variety of plant species and soil conditions as well as simulating different environmental conditions and stresses, to proteomic and phenotypic analyses, including early root tracking in the dark.

plant biology↗

bioRxiv2022

The trade-off function of photorespiration in a changing environment

The photorespiratory pathway in plants comprises metabolic reactions distributed across several cellular compartments. It emerges from the dual catalytic function of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) which either carboxylates or oxygenates ribulose-1,5-bisphosphate (RuBP). Carboxylation reactions produce 3-phospho-glycerate (3PGA) molecules which are substrate for central carbohydrate metabolism while oxygenation forms 2-phosphoglycolate (2PG) molecules which are substrate for the multicompartmental recovery process of photorespiration. Further, 2PG is a strong inhibitor of several enzymes involved in the Calvin-Benson-Bassham cycle which challenges the experimental and theoretical study of carbon assimilation, photorespiration and metabolic regulation in vivo. Here, an approach of structural kinetic modeling (SKM) is presented to investigate the extend of stabilization of CBC and carbohydrate metabolism by photorespiration. Further, our approach highlights the importance of feedback regulation by 2-PG for alleviation of environmental perturbation. Our findings indicate that oxygenation of RuBP by Rubisco significantly stabilizes CBC activity and, thus, carbohydrate metabolism. Based on our findings, we suggest a trade-off function of photorespiration which reduces carbon assimilation rates but simultaneously stabilizes metabolism by increasing plasticity of metabolic regulation within the chloroplast. Furthermore, our analysis suggests a stabilizing effect of increasing the partition of newly assimilated carbon going towards sucrose biosynthesis. With this, our analysis sheds light on the role of a multicompartmental metabolic pathway in stabilizing plant metabolism within a changing environment.

plant biology↗

bioRxiv2021

Metabolic regulation inferred from Jacobian and Hessian matrices of metabolic functions

Quantitative analysis of experimental metabolic data is frequently challenged by non-intuitive, complex patterns which emerge from regulatory networks. Quantitative output of metabolic regulation can be summarised by metabolic functions which comprise information about dynamics of metabolite concentrations. They reflect the sum of biochemical reactions which affect a metabolite concentration. Derivatives of metabolic functions provide essential information about system dynamics. The Jacobian matrix of a reaction network summarises first-order partial derivatives of metabolic functions with respect to metabolite concentrations while Hessian matrices summarise second-order partial derivatives. Here, a simple model of invertase-driven sucrose hydrolysis is simulated and both Jacobian and Hessian matrices of metabolic functions are derived for quantitative analysis of kinetic regulation of sucrose metabolism. Based on previous experimental observations, metabolite dynamics are quantitatively explained in context of underlying metabolic functions. Their potential regulatory role during plant cold acclimation is derived from Jacobian and Hessian matrices.

systems biology↗

bioRxiv2021

Integration of plant carbohydrate dynamics by Fourier polynomials

Quantification of system dynamics is a central aim of mathematical modelling in biology. Defining experimentally supported functional relationships between molecular entities by mathematical terms enables the application of computational routines to simulate and analyse the underlying molecular system. In many fields of natural sciences and engineering, trigonometric functions are applied to describe oscillatory processes. As biochemical oscillations occur in many aspects of biochemistry and biophysics, Fourier analysis of metabolic functions promises to quantify, describe and analyse metabolism and its reaction towards environmental fluctuations. Here, Fourier polynomials were developed from experimental time-series data and combined with block diagram simulation of plant metabolism to study heat shock response of photosynthetic CO2 assimilation and carbohydrate metabolism. Findings suggest that increased capacities of starch biosynthesis stabilize photosynthetic CO2 assimilation under transient heat exposure. Among soluble sugars, fructose concentrations were observed to fluctuate least under heat exposure which might be the consequence of high respiration rates under elevated temperature. Finally, Col-0 and two mutants of Arabidopsis thaliana with deficiencies in starch and sucrose metabolism were discriminated by fundamental frequencies of Fourier polynomials across different experiments. This suggests balance modelling based on Fourier polynomials as a suitable approach for mathematical analysis of dynamic plant-environment interactions. HighlightA balance equation model is developed to quantify effects of transient heat exposure on plant carbon assimilation. The model is based on Fourier polynomials for quantitative assessment of system dynamics.

plant biology↗

bioRxiv2020

Plasticity of the primary metabolome in 241 cold grown Arabidopsis thaliana accessions and its relation to natural habitat temperature

In the present study, 241 natural accessions of Arabidopsis thaliana were grown under two different temperature regimes, 16 {degrees}C and 6 {degrees}C, and growth parameters were recorded together with metabolite profiles to investigate the natural variation in metabolic responses and growth rates. Primary metabolism and growth rates of accessions significantly differed between accessions and both growth conditions. Relative growth rates showed high correlations to specific metabolite pools. Metabolic distances based on whole metabolite profiles were built from principal component centroids between both growth setups. Genomic prediction using ridge-regression best linear unbiased prediction (rrBLUP) revealed a significant prediction accuracy of metabolite profiles in both conditions and metabolic distances, which suggests a tight relationship between genome and primary metabolome. GWAS analysis revealed significantly associated SNPs for a number of metabolites, especially for fumarate metabolism at low temperature. A highly significant correlation was observed between metabolic distances and maximum temperature in the original growth habitat between January and March. Inverse data-driven modelling revealed that metabolic pathway regulation and metabolic reaction elasticities distinguish accessions originating from warm and cold growth habitats.

plant biology↗

bioRxiv2020

Impaired chloroplast positioning affects photosynthetic capacity and regulation of the central carbohydrate metabolism during cold acclimation

Photosynthesis and carbohydrate metabolism of higher plants need to be tightly regulated to prevent tissue damage during environmental changes. The intracellular position of chloroplasts changes due to a changing light regime. Chloroplast avoidance and accumulation response under high and low light, respectively, are well known phenomena, and deficiency of chloroplast movement has been shown to result in photodamage and reduced biomass accumulation. Yet, effects of chloroplast positioning on underlying metabolic regulation are less well understood. Here, we analysed photosynthesis together with metabolites and enzyme activities of the central carbohydrate metabolism during cold acclimation of the chloroplast unusual positioning 1 (chup1) mutant of Arabidopsis thaliana. We compared cold acclimation under ambient and low light and found that maximum quantum yield of PSII was significantly lower in chup1 than in Col-0 under both conditions. Our findings indicated that net CO2 assimilation in chup1 is rather limited by biochemistry than by photochemistry. Further, cold-induced dynamics of sucrose phosphate synthase differed significantly between both genotypes. Together with a reduced rate of sucrose cycling derived from kinetic model simulations our study provides evidence for a central role of chloroplast positioning for photosynthetic and metabolic acclimation to low temperature.

plant biology↗

bioRxiv2020

Cold acclimation has a differential effect on leaf vascular bundle structure and carbon export rates in natural Arabidopsis accessions originating from southern and northern Europe

Acclimation to low but non-freezing temperature represents an ecologically important process for Arabidopsis thaliana but also for many other plant species from temperate regions. Cold acclimation comprises and affects numerous molecular and physiological processes and the maintenance of sugar supply of sink tissue by photosynthetically active source tissue is preliminary for plant survival. Here, we analysed the correlation of changes in vascular bundle structure at the leaf petiole and sucrose exudation rates before and after cold acclimation. We compared six natural Arabidopsis accessions originating from southern and northern Europe. Photosynthetic capacities, i.e. maximum and effective quantum yield of photosystem II, revealed a significant effect of condition but not of genotype. Only for northern accessions we observed a highly significant negative correlation between leaf sucrose exudation rates, xylem and petiole cross section areas. Further, only for northern accessions we observed a significant increase of vascular bundle and leaf petiole cross section area during cold acclimation. In contrast, variance of cross section areas of cold acclimated southern accessions was strongly reduced compared to control plants while mean areas remained similar under both conditions. In summary, our findings suggest that natural Arabidopsis accessions from northern Europe significantly adjust sink strength and leaf vascular bundle structure to stabilize plant growth and photosynthesis for survival under low and freezing temperature.

plant biology↗

bioRxiv2017

Vacuolar invertase activity shapes photosynthetic stress response of Arabidopsis thaliana and stabilizes central energy supply

Stabilization of the central carbohydrate and energy metabolism plays a key role in plant stress response. As the primary photosynthetic products, carbohydrates are substrate for numerous metabolic and stress-protective reactions. Further, they have been shown to be involved in diverse signalling processes finally affecting and regulating plant stress response on a whole plant level. Sucrose metabolism is known to be central to many stress-related processes and enzymes catalysing its biosynthesis, transport and degradation have been shown to significantly impact stress resistance and acclimation output. However, due to the cyclic structure of sucrose metabolism involving sucrose cleavage in multiple compartments as well as energy-demanding re-synthesis via hexose phosphorylation, it is challenging to derive an unambiguous picture of its contribution to stress reactions. In the present study, a combined stress experiment comprising cold and high-light identified metabolism of sucrose and fumaric acid to significantly separate the stress response of a cold susceptible and a tolerant natural accession of Arabidopsis thaliana. Kinetic modelling and simulation of subcellular rates of invertase-driven sucrose cleavage revealed a contrasting picture between the susceptible and the tolerant accession pointing to an important role of vacuolar invertase during initial stress response. Using a T-DNA insertion mutant with a dramatically reduced invertase activity provided evidence for a central role of the enzyme in stabilizing photosynthesis and the central energy metabolism during freezing and high-light stress. Reducing vacuolar invertase activity to about 3% of the wild type resulted in a strong increase of ADP and ATP levels indicating a severe effect on cytosolic and plastidial energy balance. Together with a significant decrease of maximum quantum yield of photosystem II (Fv/Fm) these results suggest that vacuolar invertase activity stabilizes cytosolic energy metabolism by supplying hexose equivalents being phosphorylated in the cytosol. Finally, the accompanying ATP consumption is essential for cytosolic phosphate balance which directly affects photosynthetic performance by the supply of ADP being crucial for photosynthetic ATP production.

plant biology↗