A highly digestible sorghum mutant cultivar exhibits a unique folded structure of endosperm protein bodies

The endosperm of a sorghum mutant cultivar, with high in vitro uncooked and cooked protein digestibilities, was examined by transmission electron micr oscopy and alpha-, beta-, and gamma-kafirins (storage proteins) were locali zed within its protein bodies. Transmission electron microscopy micrographs revealed that these protein bodies had a unique microstructure related to high protein digestibility. They were irregular in shape and had numerous i nvaginations. often reaching to the central area of the protein body. Prote in bodies from normal cultivars. such as P721N studied here, with much lowe r uncooked and cooked digestibilities are spherical and contain no invagina tions. Immunocytochemistry results showed that the relative location of alp ha- and beta-kafirins within the protein bodies of the highly digestible ge notype were similar to the normal cultivar. P721N. gamma-Kafirin, however, was concentrated in dark-staining regions at the base of the folds instead of at the protein body periphery, as is typical of normal cultivars. The re sulting easy accessibility of digestive enzymes to alpha-kafirin, the major storage protein, in addition to the increased surface area of the protein bodies of the highly digestible cultivar appear to account for its high in vitro protein digestibility.