Involved in the hydrolysis of arabinan. Can hydrolyze (1,3)-alpha-, (1,2)-alpha-linked side group residues and non-reducing terminal L-arabinofuranose residues of debranched (1,5)-alpha-L-arabinan backbone. Acts also as a beta-D-xylosidase, releasing D-xylose from arabinoxylan and xylan. Hydrolysis of terminal non-reducing alpha-L-arabinofuranoside residues in alpha-L-arabinosides. Optimum pH is 4.7. Optimum temperature is 65 degrees Celsius. Expressed in flowers and siliques, in the early stage of seed formation and not at seed maturation. Detected exclusively in the endosperm of very young seeds when the embryo is at the globular stage. Reduced seeds size and delayed germination. Belongs to the glycosyl hydrolase 3 family.