Fumaric acid: an overlooked form of fixed carbon in Arabidopsis and other plant species

Photoassimilates ale used by plants for production of energy, as carbon ske letons and in transport of fixed carbon between different plant organs. Man y studies have been devoted to characterizing the factors that regulate pho toassimilate concentrations in different plant species. Most studies examin ing photoassimilate concentrations in C-3 plants have focused on analyzing starch and soluble sugars. However, work presented here demonstrates that a number of C-3 plants, including the popular model organism Arabidopsis tha liana (L.) Heynh., and agriculturally important plants. such as soybean, Gl ycine max (L.) Merr., contain significant quantities of fumaric acid. In fa ct, fumaric acid can accumulate to levels of several milligrams per grain f resh weight in Arabidopsis leaves, often exceeding those of starch and solu ble sugars. Fumaric acid is a component of the tricarboxylic acid cycle and , like starch and soluble sugars, can be metabolized to yield energy and ca rbon skeletons for production of other compounds. Fumaric acid concentratio ns increase with plant age and light intensity in Arabidopsis leaves. Moreo ver, Arabidopsis phloem exudates contain significant quantities of fumaric acid, raising the possibility that fumaric acid may function in carbon tran sport.