beta-Amylases in Cereals : A Study of the Maize beta-Amylase System

beta-Amylase of maize (Zea mays L.) caryopses was studied during development and germination by means of enzymic, electrophoretic, and immunochemical techniques. beta-Amylase activity increased during caryopsis development to a maximum value at the beginning of the water content plateau (at this stage the enzyme was located primarily within the pericarp) and then decreased. Almost no beta-amylase (activity or antigen) was found in either free or bound forms in the mature maize caryopsis. The activity increased again during seedling growth and reached much higher values. Both the aleurone layer (to a major extent) and the scutellum produced and secreted beta-amylase during germination, the secretion being stimulated by Ca(2+). No posttranslational modification of the enzyme was detected during germination. The molecular specific activity of the enzyme remained unchanged during the observed periods, indicating that the regulation of the activity is based essentially on protein turnover. The enzyme from developing and germinating caryopses was found to be identical in terms of antigenicity, isoelectric point, and molecular mass to the beta-amylases extracted from the roots and the leaves of the maize seedling. The maize beta-amylase resembles in all respects the ubiquitous beta-amylase described for rye and wheat, whereas the major beta-amylase of those cereals appears to be lacking in the maize caryopsis.