Possesses alpha-amylase activity in vitro, but seems not required for breakdown of transitory starch in leaves. Endohydrolysis of (1->4)-alpha-D-glucosidic linkages in polysaccharides containing three or more (1->4)-alpha-linked D-glucose units. Binds 3 Ca(2+) ions per subunit. Monomer. Expressed in leaves, stems, flowers and developing siliques. Up-regulated during leaf senescence. By gibberellin, abscisic acid (ABA), heat shock and infection with the bacterial pathogen P.syringae. Not regulated by transition from dark to light. Triggered by NAC072/RD26 during senescence (PubMed:29659022). Early flowering. Belongs to the glycosyl hydrolase 13 family.