β-Amylase is not Involved in Degradation of Endosperm Starch During Seed Germination of Maize

Abstract

For species of Triticeae, e.g., barley, β-amylase was synthesized in endosperm during seed development and processed to active form during seed germination. Thus, β-amylase was suggested to be one of the enzymes to degrade endosperm starch for seed germination. β-Amylase expression in maize kernels apparently is different from that of barley. By immunolocalization, we found that maize β-amylase is expressed in the pericarp but not in the endosperm during seed development; and is synthesized in the aleurone cells but not in the scutellar epithelium cells during seed germination. The newly synthesized maize β-amylase is retained inside of the aleurone cells. On the contrary, maize α-amylase is synthesized and secreted from the aleurone cells to the starchy endosperm. By PAS and iodine stain, we showed that starch is present in the starchy endosperm and absent in the aleurone cells of maize seeds. Results of starch film assay and native activity gel analysis indicated that α-amylases are the enzymes for endosperm starch degradation during maize seed germination. Because maize β-amylase is synthesized and retained in the aleurone cells, it is unlikely that β-amylase acts on endosperm starch during seed germination.