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.

Chemically induced brown midrib (bmr) mutants sorghum (Sorghum bicolor (L.) Moench) were characterized with regard to phenotype, fiber composition, and in vitro dry matter disappearance (IVDMD). The recessive bmr genes produced brown pigmentation in the leaf midrib and stem of mature plants. Pigmentation varied among mutants in intensity, time of appearance, and degree of fading as plants matured.Stem and leaf samples of mutant and normal plants were analyzed in the laboratory to determine percent cell wall constituents (CWC), acid detergent fiber, (ADF), cellulose, hemicellulose, permanganate lignin (PL), vitro dry matter, and in vitro cell wall constituent disappearance (IVDMD and IVCWCD). Ten of the 13 mutants had significantly less stem lignin than the normal counterparts. Reductions in lignin ranged from 5 to 51% in stems and from 5 to 25% in leaves. In the case of other fiber components, only occasional differences were observed between normal and mutant plants. Increases in IVDMD and IVCWCD of as much as 33 and 43%, respectively, were associated with the presence of bmr genes.Variation among mutants in lignin concentration probably indicates that several different bmr genes were involved. Similarities between the bmr genes of sorghum and the bm genes of maize (Zea mays L.) suggest the possible existence of similar genes in other grasses, although their identification may be more complicated because of polyploidy.

We have shown previously that sorghum is highly digestible in the rat. However, other workers have shown that sorghum is much less digestible than wheat, maize, and rice in young children. Because the rat does not show these digestibility differences, we developed an empirical pepsin digestion method, furst reported in 1981, which simulates the digestion values found in children. In this report the method has been improved and used to analyze wheat, maize, rice, millet, and sorghum and certain processed samples of millet and sorghum. The pepsin digestion values parallel those found in children for wheat, maize, rice, and sorghum. In addition, a processed sorghum product that gave a high digestion value in children also gave a high value with the in vitro pepsin method.Sorghum [Sorghum bicolor (L.) Moench] is an important source of calories and protein for a large segment of the human population in the semiarid tropics.In a previous publication (1), the apparent digestibility of the proteins in four (cooked) sorghum gruels varied from 76.5% to 83.0% (average, 80.4%) in young rats. The same four sorghum flours, when cooked and fed to children of age 6-27 months, gave an average apparent digestibility value of only 46%, compared with values of 81%, 73%, and 66% for wheat, maize, and rice, respectively (2). Because the rat gave values for cooked sorghum that were the same as those MacLean et al. (2) found for cooked wheat in the child, we developed an empirical in vitro pepsin method (1) that more closely simulates MacLean's values in children. In this report we present improvements in our original method and data on the pepsin digestibility of the major cereals. We also include data on processed sorghum and millet products [sorghum and millet nasha (fermented baby foods) and extruded decorticated sorghum].MATERIALS AND METHODS found on the grain in Sudan), was added, and the mixture was incubated at 30'C for 12 hr. The slurry was fed to a laboratory drum dryer or was freeze-dried, and the dry residue was used for digestibility studies.Pepsin. The pepsin used was porcine pepsin 1:10,000 (Sigma). It had an activity of 1,200-2,000 units/mg of protein (A28) (3).Modified Pepsin Method (Residue Method). Ground cereal samples (200 mg) prepared with a Udy grinder and 0.4-mm screen were suspended in 35 ml of a solution of pepsin (1.5 mg/ml) in 0.1 M phosphate buffer (pH 2.0); the mixture was incubated with gentle shaking at 370C for 2 hr. Incubation for 3 hr raises all values about 10% above the 2-hr values; incubation for 1 hr lowers all values about 10% below the 2-hr values. Therefore, time of incubation is critical in the assay. After incubation the suspension was centrifuged (12,000 x g for 15 min at 40C), and the residue was suspended in 10 ml of 0.1 M phosphate buffer (pH 2.0) and centrifuged as before. The low-pepsin moist residue was freed from the walls of the centrifuge tube with a spatula and dumped in the center of Whatman filter paper no. 3 on a 43-mm Buchner funnel. Suction (aspirator) was applied, an...

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Analysis of Sorghum bicolor bloomless (bm) mutants with altered epicuticular wax (EW) structure uncovered a mutation affeding both EW and cuticle deposition. l h e cuticle of mutant bm-22 was about 60% thinner and approximately one-fifth the weight of the wild-type parent P954035 (Wl-P954035) cuticles. Reduced cuticle deposition was associated with increased epidermal conductance to water vapor. The reduction in EW and cuticle deposition increased susceptibility to the funga1 pathogen Exserohilum turcicum. Evidence suggests that this recessive mutation occurs at a single locus with pleiotropic effects. l h e independently occurring gene mutations of bm-2, bm-6, bm-22, and bm-33 are allelic. These chemically induced mutants had essentially identical EW strudure, water loss, and cuticle deposition. Furthermore, 138 Fz plants from a bm-22 x WT-P954035 backcross showed no recombination of these traits. This unique mutation in a near-isogenic background provides a useful biological system to examine plant cuticle biosynthesis, physiology, and function.EW provides the outermost bamer between plants and their environment. Previous studies have implicated EW layers in tolerance to various kinds of biotic and abiotic environmental stress (Eglinton and Hamilton, 1967; Thomas and Barber, 1974;Blum, 1975; Webster, 1977; Bengston et al., 1978;Jordan et al., 1984; El-Otmani et al., 1989;Jefferson et al., 1989;Percy and Baker, 1990; Stoner, 1990;Bergman et al., 1991). Near-isogenic mutants provide a model system for the dissection of biochemical (Koorneef et al., 1989; Somerville and Browse, 1991) and biophysical (Blum, 1975;Jordan et al., 1984; Saneoka and Ogata, 1987) under drought stress and disease pressure in southwestem Mexico suggested that mutants bm-2, bm-6, bm-22, and bm-33, making up an individual allelic group, were more susceptible to drought and more susceptible to leaf blight. Since individuals in this allelic group had EW structures and total EW load similar to other bm mutants that were not susceptible to drought and disease, we suspected that these responses were due to alterations in the cuticle proper. To test this hypothesis, cuticle ultrastructures and depositions on the wild-type and bm mutants were analyzed and then compared with water loss rates and disease resistance. Our results suggest that allelic mutants bm-2, bm-6, bm-22, and bm-33 possessa mutation affecting cuticle deposition. To our knowledge, a cuticle mutation in plants has not been previously reported. MATERIALS AND METHODS Plant MaterialThe mutagenesis program was initiated using two droughtresistant inbred lines of Sorghum bicolor (L.) Moench. These inbred lines, designated P954035 and P898012, were produced in the Purdue Sorghum Improvement Program (Dr. Gebisa Ejeta, Department of Agronomy). Seeds (Mo) were exposed to the chemical mutagens diethyl sulfate (J. T. Baker, Phillipsburg, NJ) or ethyl methanesulfate (Eastman Kodak Co., Rochester, NY). Seeds treated with diethyl sulfate were submerged in either a 5.7, 7.7, or 11.5 mM solut...