Mobilization of protein and phytin in aleurone grains of germinating castor beans

The mobilization of protein and phytin was studied in aleurone grains of th e endosperm of germinating castor beans (Ricinus communis L.). Differential staining of protein and phytin zones of aleurone grains indicated that mob ilization of phytin preceded that of proteins. Biochemical assays demonstra ted that, after 64 h of seed imbibition, phytin content decreased by 14%, a nd, after six days, phytin was digested by 87%. This process was correlated with increasing phytase activity. At the same time, phytin content increas ed in cotyledons and axial organs. The breakdown of storage proteins began after radicle emergence. The activities of two proteolytic enzymes accelera ted after three and five days of germination, respectively, in correlation with the degradation of storage proteins and conversion of aleurone grains into aleurone vacuoles by the third day. We concluded that the mobilization of phytin and protein in the endosperm preceded the mobilization of storag e lipids, and this determined the composition of metabolites flowing from t he endosperm to the seedling.