ZEIN DEGRADATION IN THE ENDOSPERM OF MAIZE SEEDS DURING GERMINATION

Abstract

The pattern and sequence of zein degradation in the endosperm of germinating maize seeds were investigated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) and by immunostaining Western blots with a monoclonal antibody to α‐zein and polyclonal antibodies to β‐, γ‐, and δ‐zeins. The results indicated: 1) the degradation of the predominant α‐zein fraction (23.8 and 26.7 kD) started on the 5th day after germination (DAG) and continued gradually until the 10th DAG with a small amount remaining undegraded up to the 26th DAG; 2) β‐zein (17 kD) began to be degraded on the 2d DAG, and the degradation of the 17 kD polypeptide was completed by the 7th DAG; 3) γ‐zeins (27 and 18 kD) were the first zeins to be degraded, and the degradations of γ‐zeinl (27 kD) and γ‐zein2 (18 kD) were complete by the 3rd and 4th DAG, respectively; and 4) the degradation of δ‐zein (10 kD) began on the 4th DAG and was complete by the 7th DAG. Based on these results, the following arrangement of zein polypeptides within the protein bodies is postulated, assuming that the proteolytic events start at the periphery and processed towards the core of the protein body: 1) γ‐zeins are situated around the periphery of the protein bodies and are possibly a structural component of the protein body membrane or directly anchored in the membrane; 2) β‐zein would be internal to γ‐zeins; and 3) α‐zein and δ‐zein would be in the protein body core. This arrangement is largely consistent with published data on the immunocytochemical localization of zeins, and it indicates that the different classes of zein are not randomly organized within the matrix of the protein body.