No alpha-1,4-glucan hydrolase activity, including beta-amylase, alpha-amylase, a-glucosidase or alpha-amyloglucosidase. However, facilitates or regulates starch breakdown, especially at night, by a mechanism involving direct interaction with starch or other alpha-1,4-glucan. A number of isoforms are produced. According to EST sequences. Preferentially expressed in vascular tissue of cotyledons, leaves, petioles, stems, petals, siliques and roots, particularly in phloem. Also present in root tip. Slightly retarded growth rate and reduced starch breakdown in leaves during the night. Belongs to the glycosyl hydrolase 14 family. In contrast to other members of the family, lacks the conserved Glu active site in position 473, which is replaced by an Arg residue, explaining why it is inactive. Truncated N-terminus.