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

Abstract

The endosperm of a sorghum mutant cultivar, with high in vitro uncooked and cooked protein digestibilities, was examined by transmission electron microscopy and ␣-, ␤-, and ␥-kafirins (storage proteins) were localized 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 invaginations, often reaching to the central area of the protein body. Protein bodies from normal cultivars, such as P721N studied here, with much lower uncooked and cooked digestibilities are spherical and contain no invaginations. Immunocytochemistry results showed that the relative location of ␣-and ␤-kafirins within the protein bodies of the highly digestible genotype were similar to the normal cultivar, P721N. ␥-Kafirin, however, was concentrated in darkstaining regions at the base of the folds instead of at the protein body periphery, as is typical of normal cultivars. The resulting easy accessibility of digestive enzymes to ␣-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.

Effect of suppressing the synthesis of different kafirin sub-classes on grain endosperm texture, protein body structure and protein nutritional quality in improved sorghum lines

“…As explained, the improved protein digestibility of mutant sorghum lines, having highly invaginated protein bodies, is believed to be due to increased protein body surface area and easy accessibility of digestive enzymes to the more digestible alpha-kafirin proteins (Oria et al, 2000). In addition, the dense protein matrix observed in the TG lines, is probably composed of more digestible lysine-rich endogenous proteins, which would further improve the cooked IVPD of these lines.…”

“…Breeding using P721 opaque line has been undertaken to produce high-lysine genotypes with improved grain hardness and protein digestibility after cooking (Tesso et al, 2006;Weaver et al, 1998). Electron microscopy and immunological studies of these high-lysine high-protein digestibility mutants showed their grain to have modified protein bodies (irregular shapes with deep invaginations), compared to the spherical protein bodies of normal sorghums (Oria et al, 2000). The location and organisation of different kafirin sub-classes within the protein bodies also differed with the gamma-kafirins being located at the bottom of folds, exposing the more digestible alpha-kafirins to digestive enzymes.…”

Transgenic Sorghum with Altered Kafirin Synthesis: Kafirin Solubility, Polymerization, and Protein Digestion

“…However, in these HD mutants the protein bodies are very folded (invaginated) (Figure 1c), with the gammakafirin located at the base of the invaginations (14), with the effect that proteases have easy accessibility to the alpha-kafirin. Thus, it appears that reason for the high digestibility of the protein bodies the TG lines is different from that in the HD types.…”

Increasing the utilisation of sorghum, millets and pseudocereals: Developments in the science of their phenolic phytochemicals, biofortification and protein functionality

“…The higher protein digestibility of these lines was attributed to the fact that their protein bodies (the organelles of kafirin storage) are invaginated in shape, instead of being spherical (Oria et al, 2000). Recent research indicates that the invaginated shape of the .…”

“…They noted that in sorghum the protein bodies are difficult to disrupt and therefore in normal sorghum flour the protein is effectively inert as it is contained in the protein body (Goodall et al, 2012). However, in the case of the high protein digestibility mutant, the protein bodies have substantially lost their integrity (Oria et al, 2000) and the protein is much more available. Using this mutant it has been shown that doughs enriched with wheat gluten showed better rheological properties than similarly enriched doughs from normal sorghum and the resulting bread had higher loaf volume (Goodall et al, 2012).…”