Purification and immunocytochemical localization of kafirins inSorghum bicolor (L. Moench) endosperm

Summary

Kafirins are the storage proteins of sorghum and are found in protein bodies in the seed endosperm. They have been classified as α-, β-, and γ-kafirins according to differences in molecular weight, solubility, and structure. The kafirins were purified, amino acid composition was determined, and immunolocalization methods were used to determine the organization of the protein bodies and distribution of kafirins throughout the endosperm. All three groups of kafirins were low in lysine. β-Kafirins and γ-kafirins were relatively high in cysteine, and β-kafirins were relatively high in methionine. Transmission electron microscopy showed that protein bodies in the peripheral endosperm were spheroid with concentric rings and few darkly stained inclusions. In contrast, protein bodies of the central endosperm were irregularly shaped with a higher proportion of darkly stained material. The light staining regions of the protein bodies are composed primarily of α-kafirins with minor portions of β- and γ-kafirins. The dark staining regions, however, are composed primarily of β- and γ-kafirins. Immunoelectron microscopy showed that protein bodies in the peripheral endosperm contain predominantly a-kafirin with minor amounts of β- and γ-kafirin. Central endosperm protein bodies are also predominantly α-kafirin, but have a higher proportion of β-kafirin and γ-kafirin than the peripheral endosperm protein bodies.