Inhibits papain, ficin, cathepsin B and, to a lesser extent, chymopapain, but is inactive against bromelain. Inhibits the growth of pathogenic fungi. Regulated by the DOF transcription factors SAD (activator) and BPBF (repressor). Expressed in embryos, developing endosperms, leaves, roots, flowers and pollen grains. Expressed during seed germination. Up-regulated by dark and cold shock, anaerobiosis and upon seed imbibition. Repressed by gibberellic acid treatment in aleurones, but not in leaves. Not affected by abscisic acid treatment. Belongs to the cystatin family. Phytocystatin subfamily.