Peptide hydrolase activities in seedlings and hormone-treated cotyledons of pumpkin (Cucurbita pepo).

Enzymes hydrolyzing Gly-Ala-, Met-Met- and Pro-4-phenylazo-phenylamides, and N-benzoyl-L-arginine-4-nitroanilide have been identified in germinating seeds and cotyledons of pumpkin (Cucurbita pepo). The enzyme activities per cotyledon increase markedly during the germination process, but the proportion of enhancement depends on the type of enzyme species. The increase in enzyme activities is due to de novo synthesis as shown by cycloheximide treatment and is influenced by phytohormones (cytokinins and abscissic acid). In isolated cotyledons exogenous cytokinin (benzyladenine) obviously can replace the effect of the embryo as the source of endogenous hormone. Abscissic acid counteracts the cytokinin effect. It is suggested that aminopeptidases have a biological function in reserve protein degradation of the cotyledons during seed germination. Our results do not support the assumption that the embryonic axis of the growing seedling serves as a "sink" of proteolytic products resulting in an activation of peptide hydrolases in the cotyledons, but rather de novo synthesis of these enzymes seems to be controlled by substances (phytohormones) originating from the embryo.