Date of Award
Master of Science (MS)
Professor B. Ann Oaks
The hydrolyses of endosperm storage reserves in maize caryopses was investigated. The following points were examined in detail: 1) The enzymes responsible for hydrolysis of the reserve starch and proteins during early germination; 2) The regulation of enzyme formation and starch hydrolysis in the endosperm by gibberellic acid and 3) Isolation of protein bodies and associated protease activity.
The principle protease extracted from maize endosperm after germination had an acid pH optimum, and a high temperature optimum with the substrate haemoglobin. Alpha-amylase was also present in this tissue. Electrophoretic gels were used in identifying the development of two distinct amylases during early seedling growth. The acid protease and the amylases are absent from quiescent caryopses. These enzymes appear 2-3 days after imbibition of intact caryopses, and increase in activity throughout the course of protein and starch breakdown.
In contrast to other reported results (76) neither the embryo nor exogenous factors were necessary for initiation or continuation of amylase formation in de-embryonated endosperms. Changes in enzyme activity in excised endosperms following similar trends were compared to intact caryopses germinated at the same temperature. Neither enzyme production nor starch hydrolysis was stimulated by treating de-embryonated maize endosperms with gibberellic acid. The response to gibberellic acid of de-embryonated endosperms of barley was tested as a control. De-embryonated endosperms of this cereal had low α-amylase activities when incubated in buffer. Inclusion of gibberellic acid in the incubation medium stimulated enzyme production eight-fold.
Protein bodies were isolated from germinating maize endosperm using sucrose density gradients and were identified by electron microscopy. Acid protease activity was not associated with this fraction, and in fact over 90% of the original activity was recovered in the soluble fraction.
A second protease extracted from developing maize endosperm had a broad neutral-basic pH optimum, and a temperature optimum of 55 C. It actively degraded both α-N-benzoyl DL-arginine p-nitroanilide (BAPNA) and haemoglobin. This protease was present in all stages of developing endosperm tested with activity peaks at 25 and 57 days post fertilization. This protease was also present in quiescent and early germinating caryopses. After imbibition, activity decreased rapidly and disappeared in approximately four days. Preliminary results indicate no association of this protease with the protein body fraction
Lenz, Douglas Emil, "Hydrolysis of Maize Endosperm" (1978). Open Access Dissertations and Theses. Paper 278.