Cytosolic fumarate hydratase that catalyzes the reversible stereospecific interconversion of fumarate to L-malate (PubMed:29688630). Catalyzes the dehydration of L-malate to fumarate in the cytosol: required for the massive fumarate accumulation during the day in plants grown under high nitrogen (PubMed:20202172). Also required for acclimation of photosynthesis to cold: acts by mediating accumulation of fumarate at low temperature, leading to reduce accumulation of phosphorylated sugars (PubMed:27440755). (S)-malate = fumarate + H2O Fumarate hydratase activity (fumarate to L-malate) is strongly inhibited by phosphoenolpyruvate, citrate, oxaloacetate, ATP and ADP (PubMed:29688630). Malate dehydratase activity (malate to fumarate) is activated by oxaloacetate, Asn and Gln (PubMed:29688630). Malate dehydratase activity (malate to fumarate) is inhibited by citrate, succinate, ADP and ATP (PubMed:29688630). kcat is 23.04 sec(-1) for fumarate (at pH 7.7) (PubMed:29688630). kcat is 22.15 sec(-1) for fumarate (at pH 8.0) (PubMed:29688630). kcat is 18.3 sec(-1) for fumarate (at pH 8.2) (PubMed:29688630). kcat is 5.22 sec(-1) for (S)-malate (at pH 7.7) (PubMed:29688630). kcat is 14.79 sec(-1) for (S)-malate (at pH 8.0) (PubMed:29688630). kcat is 17.1 sec(-1) for (S)-malate (at pH 8.2) (PubMed:29688630). Homotetramer. Decreased fumarate levels, while malate levels increase (PubMed:20202172). Leaves display lower levels of many amino acids during the day, but higher levels at night, consistent with a link between fumarate and amino acid metabolism (PubMed:20202172). Plants are unable to acclimate photosynthesis in response to cold (PubMed:27440755). There are 2 substrate-binding sites: the catalytic A site, and the non-catalytic B site that may play a role in the transfer of substrate or product between the active site and the solvent. Alternatively, the B site may bind allosteric effectors. Belongs to the class-II fumarase/aspartase family. Fumarase subfamily.