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.