Developmental Expression of Genetically Defined Peptidases in Maize

The activities of genetically defined amino- and endopeptidases of maize were compared in pericarp, endosperm, and embryonic tissue of the maize kernel from 5 days postpollination until harvest. Activities were highest in the immature stages and declined as drying progressed. The expression of some of the peptidase genes contributed by the pollen parent was examined during early endosperm development in an F(1) cross. The paternally contributed peptidase variants could first be detected 7 days after pollination.During germination and early seedling growth the peptidase activities continued to decline in the endosperm but maintained high levels in the scutellum. The maize peptidases probably have no direct role in hydrolysis of endosperm storage proteins during germination and growth.The peptidase isozymes were associated with the soluble cytoplasmic fraction of the maize scutellum during early growth. Only one tissue specificity was found for the peptidases. Occurrence of a particular aminopeptidase isozyme, AMP2, is limited to endosperm tissue during kernel maturation.