Sweet heat: Organelle-specific carbohydrate metabolism in heat stress

Plant metabolism varies substantially between developmental stages, cell types, and intracellular environments. Similarly, biochemical responses to abiotic stress often deviate between neighboring cell types, but discerning what is changing where becomes more challenging in smaller and more fragile sub-compartments.  Seydel et al. investigated how carbohydrate metabolism in Arabidopsis thaliana changed in response to 7 days of elevated temperature. The authors combined serial block-face electron microscopy to quantify the volumes of subcellular compartments and non-aqueous fractionation to quantify metabolites in each organelle. Together, these methods enable an organelle-specific view of carbohydrate metabolism. Although the relative sizes of chloroplasts, the cytosol, and vacuoles, were not affected by the increase in temperature, it reduced total leaf volume and therefore the absolute volumes of each compartment. Before accounting for these absolute volumes, the relative abundance of sucrose and fructose in the cytoplasm showed no change in the elevated temperature, with a small increase in glucose levels. By contrast, the absolute concentrations (accounting for absolute organelle volumes) of cytoplasmic sucrose was lower, with higher fructose and glucose at 34 °C. Under these new conditions, invertase activity is near-completely inhibited in the cytosol. Overall, this study demonstrated a powerful method for understanding metabolism on a sub-cellular level, cautioning that relative versus absolute quantification can tell contrasting stories. (Summary by Ciara O’Brien @ciara-obrien.bsky.social) Plant Physiol. 10.1093/plphys/kiaf117