Physiological control of exo- and endoproteolytic activities in germinating wheat and their relationship to storage protein hydrolysis.

The effects of gibberellic acid, abscisic acid, cycloheximide, actinomycin D, and cordycepin upon exo- and endoproteolytic activities and storage (gluten) protein hydrolysis in germinating wheat and in incubated embryoless wheat seeds have been studied. Early increases in endoproteolytic activity were insensitive to the addition of gibberellic acid and inhibitors of protein and RNA synthesis. Later increases in endoproteolytic activity were enhanced by gibberellic acid, strongly inhibited by abscisic acid and cycloheximide, and partially inhibited by actinomycin D and cordycepin. Increases in exoproteolytic activity were insensitive to the addition of gibberellic acid, abscisic acid, actinomycin D, and cordycepin but were inhibited in whole seeds when cycloheximide was added in the steeping medium. However, cycloheximide did not inhibit increases in exoproteolytic activity when added to embryoless seeds, to germinating whole seeds, or to seeds which had been stored at 4 C for extended periods of time. Comparison of the effects of gibberellic acid, abscisic acid, and inhibitors of protein and RNA synthesis upon storage protein hydrolysis and their effects upon proteolytic activity indicated that storage protein hydrolysis in germinating wheat is controlled by the rate of hormonally induced de novo synthesis of endoproteolytic enzymes.