Starch is synthesized in plant leaves during the day, in order to serve as an energy source at night. Starch is stored as granulates. These insoluble highly branched chains have to be phosphorylated in order to be accessible for degrading enzymes. The enzyme glucan, water dikinase (GWD) phosphorylates at the C-6 position of a glucose molecule, close to the chains 1,6-alpha branching bonds. A second enzyme, phosphoglucan, water dikinase (PWD) phosphorylates the glucose molecule at the C-3 position. A loss of these enzymes, for example a loss of the GWD, leads to a starch excess (sex) phenotype. Because starch cannot be phosphorylated, it accumulates in the plastid.