Storage Proteins in Zea mays (L.): Interrelationship of Albumins, Globulins and Zeins in the Opaque‐2 Mutation

Abstract

Mature endosperms from opaque-2 mutant seeds with various genetic background (B 37, W 64A, R 802A and Oh 43) contained twice as much globulin as the corresponding normals, reduced amounts of zein and an increased amount of albumin. The latter is caused by a diminished disappearance of albumins in mutant endosperms during the final phases of development as compared to normal endosperms. Albumins from the opaque-2 endosperms appeared on gel electrophoresis as a similar but heterogenous polypeptide population comparable to that of normal endosperms except that in all opaque-2 forms a 70-kDa polypeptide was increased. Similarly, 1-3 specific globulin polypeptides (47, 52 and 58 kDa) were, depending on the genotype, increased in the mutant lines. The accumulation of albumins, globulins and zeins, studied in developing W 64A opaque-2 mutant and corresponding normal maize kernels from 10 days after pollination until maturity, demonstrated 2-phasic accumulation patterns for all proteins in the mutant, the 1st phase extending to .apprx. 30 days post pollination and the 2nd from there on until maturity. The transition time-point from 1st to 2nd phase was characterized in mutant endosperm by a sudden reduction in accumulating albumins (also seen in normal endosperm), by an enhanced accumulation of globulins and the cessation of further accumulation of zein. Preferential accumulation of certain globulins was found in the mutant during the 2nd phase of globulin formation. The increased accumulation of globulins in the opaque-2 mutant endosperm is considered a response to the arrest in zein synthesis.