John D. Axtell

Nutritional quality of sorghum and sorghum foods from Sudan

The nutritional quality of whole and decorticated sorghum grains (Tetron, Dabar, Feterita) from Sudan, and various dishes prepared from sorghum, was determined in rat balance tests. From these tests it is concluded that sorghum is low in lysine, and, therefore, has a low biological value. On the other hand, the true digestibility of protein, as well as digestible energy, is very high with values above 90%. True digestibility of the protein decreased when a porridge (ugali) was cooked from the variety Dabar (low polyphenol) but there was an increase in biological value compared with the raw grain. These changes were eliminated if the pH was adjusted to 3·9 before cooking. These effects of cooking were much more pronounced for the variety Feterita (high polyphenol). In pancakes (Kisra) fermented at pH 3·9, there were only minor effects on the nutritional quality due to cooking for all sorghum varieties studied. Cooked, fermented and cooked, unfermented, acid-adjusted Aceda (a thin fermented gruel) had slightly lower digestible energies and lower true protein digestibilities, but higher biological values, than uncooked, fermented Aceda, snowing that the protective effect of acidification observed with Ugali did not occur with Aceda. Marissa, a sorghum beer, had a higher biological value after sieving than did the unsieved brew but true protein digestibility was negatively affected by Marissa preparation.

Discovery of grain sorghum germ plasm with high uncooked and cooked in vitro protein digestibilities

ABSTRACT Grain sorghum has been documented to have low protein digestibility relative to other cereal grains. Low protein digestibility of sorghum is most pronounced in cooked foods and is ranked slightly lower than corn as a feed grain. In this article, sorghum germ plasm is identified that has substantially higher uncooked and cooked flour in vitro protein digestibility than normal cultivars. Sorghum lines were found within a high-lysine opulation derived from the mutant P721Q that have ≈10–15% higher uncooked and ≈25% higher cooked protein digestibilities using a pepsin assay. Highly digestible sorghum grain showed little reduction in digestibility after cooking, compared to the large reduction that is typical of normal sorghum cultivars. Using the three-enzyme pH-stat method, we showed that the highly digestible lines had the same degree of peptide bond hydrolysis in ≈5 min, as was found in 60 min in the normal cultivar, P721N. Differences in protein digestibility were related to enyzme susceptibility...

Agrobacterium-mediated transformation of sorghum: factors that affect transformation efficiency

The results presented in this work support the hypothesis that Agrobacterium-mediated transformation of sorghum is feasible, analogous to what has been demonstrated for other cereals such as rice, maize, barley and wheat. The four factors that we found most influenced transformation were: the sensitivity of immature sorghum embryos to Agrobacterium infection, the growth conditions of the donor plant, type of explant and co-cultivation medium. A major problem during the development of our protocol was a necrotic response which developed in explants after co-cultivation. Immature sorghum embryos proved to be very sensitive to Agrobacterium infection and we found that the level of embryo death after co-cultivation was the limiting step in improving transformation efficiency. The addition of coconut water to the co-cultivation medium, the use of vigorous and actively growing immature embryos and the removal of excess bacteria significantly improved the survival rate of sorghum embryos and was critical for successful transformation. Hygromycin phosphotransferase (hpt) proved to be a good selectable marker for sorghum. We also found that β-glucuronidase (GUS) activity was low in most of the transgenic plant tissues tested, although it was very high in immature inflorescences. Although promising, the overall transformation efficiency of the protocol is still low and further optimization will require particular attention to be given to the number of Agrobacterium in the inoculum and the selection of sorghum genotypes and explants less sensitive to Agrobacterium infection.

A Rapid Protein Digestibility Assay for Identifying Highly Digestible Sorghum Lines

ABSTRACT Protein digestibility in sorghum (Sorghum bicolor (L.) Moench) lines was determined using two standard procedures (pepsin digestibility and pH-stat) and compared with a newly developed, rapid electrophoresis-based screening assay. The new assay was based on the rate of α-kafirin disappearance after pepsin digestion. α-Kafirin, the major sorghum storage protein, makes up ≈60–70% of the total protein in the grain. In the new assay, samples were first digested with pepsin for 1 hr, and undigested proteins were then analyzed by SDS-PAGE. The intensitizes of the undigested α-kafirin bands were measured. Higher band intensity indicated lower protein digestibility. The new assay was significantly correlated with the standard pepsin digestibility assay (r = −0.96, n = 16) after which it was patterned. The same was true of the pH-stat procedure (r = −0.85, n = 16). This implies that the new assay is comparable to existing procedures and can be used for screening sorghum lines for protein digestibility. Tw...

Epicuticular Wax Morphology of Bloomless (bm) Mutants in Sorghum bicolor

Sorghum bicolor mutants for cuticular wax production provide a model system for analysis of epicuticular wax (EW) physiology, biochemistry, and genetics. Mutants produced from seeds treated with the chemical mutagens diethyl sulfate (DES) and ethyl methanesulfonate (EMS) were selected in the M2 generation and self-pollinated to produce near-isogenic mutants of two classes: bloomless (lacking visible EW) and sparse bloom (possessing little visible EW). Scanning electron microscopy was used to further divide 33 selected lines into 14 unique classes based on altered EW structure. Mutations have affected the structure of cork silica (CS) cell associated EW or both CS cell and cuticle EW. The resulting spectrum of altered EW structure indicates unique alterations in EW biosynthesis or deposition which may correlate with specific EW alleles and loci within the Sorghum genome.

A Novel Modified Endosperm Texture in a Mutant High-Protein Digestibility/High-Lysine Grain Sorghum (Sorghum bicolor (L.) Moench)

ABSTRACT Development of high-protein digestibility (HPD)/high-lysine (hl) sorghum mutant germplasm with good grain quality (i.e., hard endosperm texture) has been a major research objective at Purdue University. Progress toward achieving this objective, however, has been slow due to challenges posed by a combination of genetic and environmental factors. In this article, we report on the identification of a sorghum grain phenotype with a unique modified endosperm texture that has near-normal hardness and possesses superior nutritional quality traits of high digestibility and enhanced lysine content. These modified endosperm lines were identified among F6 families developed from crosses between hard endosperm, normal nutritional quality sorghum lines, and improved HPD/hl sorghum mutant P721Q-derived lines. A novel vitreous endosperm formation originated in the central portion of the kernel endosperm with opaque portions appearing both centrally and peripherally surrounding the vitreous portion. Kernels exhi...

Somaclonal variation in high tannin sorghums

SummaryGenetic variants were found among over 6,000 primary plants (R1) regenerated from embryogenic tissue cultures of eight high tannin sorghums [Sorghum bicolor (L.) Moench]. Field assessment of somaclonal variation has progressed to the R2 population, with over 48,000 R2 seedlings (27,000 plants) in 1,126 rows from 1,055 R1 plants. A total of 43 variant phenotypes was recovered, including several types of chlorophyll deficiencies, dwarfism, short culm, sterility, narrow leaf, and several previously unreported variants, such as ragged leaf, multibranched heads, and Hydra, a developmental variant which produces large numbers of panicles. Variation production greatly depends on parent genotype and appears to increase with increasing time in cultures. The toal average somaclonal variation rate (based per 100 R1 plants) and somaclonal variant frequency (based per 100 R2 plants) estimated in the tested population were 11.3 and 1.6, respectively. Chimerism was found in regenerants. The estimated size of the mutated sector carried by mutant regenerants ranged from the whole plant to less than 3% of a single head. The average proportion of mutated R1 heads carrying large (80%–100%), medium (40%–80%), and small (<40%) mutated sectors was 38.7%, 26.0% and 35.3%, respectively. Some sector mutations do not appear until the R3 generation. In order to avoid losing variants, the population for selecting somaclonal variation should be as large as possible. Some of these variants found may be useful for further study or for use in breeding programs.

Turbidity assay for rapid and efficient identification of high protein digestibility sorghum lines

ABSTRACT Recently, our laboratory reported a protein digestibility assay based on SDS-PAGE that distinguishes mutant high protein digestibility from wild-type sorghum lines. Using that assay, high protein digestibility sorghum lines were identified both qualitatively (visual observation) and quantitatively by measuring the SDS-PAGE band intensity of the undigested α-kafirin protein. Here, we report on a new turbidity assay that can be used for an even quicker quantitation of the undigested proteins with much higher throughput for screening purposes. Proteins remaining after 1 hr of pepsin digestion were extracted with a buffer of SDS, 2-mercaptoethanol, and borate and an aliquot of the extract was precipitated using 72% trichloroacetic acid (TCA). Absorbance of the resulting turbid solution was then read at 562 nm. Lower readings corresponded to more digestible lines. The turbidity of the suspensions developed quickly and reached a plateau at ≈5 min for high protein digestibility lines and 10 min for wild...

Evidence for an evolutionarily conserved interaction between cell wall biosynthesis and flowering in maize and sorghum

BackgroundFactors that affect flowering vary among different plant species, and in the grasses in particular the exact mechanism behind this transition is not fully understood. The brown midrib (bm) mutants of maize (Zea mays L.), which have altered cell wall composition, have different flowering dynamics compared to their wild-type counterparts. This is indicative of a link between cell wall biogenesis and flowering. In order to test whether this relationship also exists in other grasses, the flowering dynamics in sorghum (Sorghum bicolor (L.) Moench) were investigated. Sorghum is evolutionarily closely related to maize, and a set of brown midrib (bmr) mutants similar to the maize bm mutants is available, making sorghum a suitable choice for study in this context.ResultsWe compared the flowering time (time to half-bloom) of several different bmr sorghum lines and their wild-type counterparts. This revealed that the relationship between cell wall composition and flowering was conserved in sorghum. Specifically, the mutant bmr7 flowered significantly earlier than the corresponding wild-type control, whereas the mutants bmr2, bmr4, bmr6, bmr12, and bmr19 flowered later than their wild-type controls.ConclusionThe change in flowering dynamics in several of the brown midrib sorghum lines provides evidence for an evolutionarily conserved mechanism that links cell wall biosynthesis to flowering dynamics. The availability of the sorghum bmr mutants expands the germplasm available to investigate this relationship in further detail.

Genetic and molecular characterization of Candystripe1 transposition events in sorghum

In sorghum, the Candystripe1 (Cs1) transposable element causes a variegated pericarp phenotype due to its excision activity from the y1 (yellow seed1) locus. The Y1 is a transcription regulator which is required for the biosynthesis of red 3-deoxyflavonoid pigments. Somatic variability in the transposition behavior of Cs1 was observed via biochemical analysis of 3-deoxyflavonoids in the leaf tissues of the Y1-cs alleles. Using somatic excisions of Cs1 as a tool, we establish that the Cs1 is active in young seedlings and the y1 locus is also functional in these tissues. Several somatic and germinal excision events were characterized and sequence analysis of independent events predominantly showed 2-bp footprints. Further, with the goal of understanding the properties of Cs1 that would facilitate the development of a transposon tagging system in sorghum, germinal excisions of Cs1 from y1 were used as a marker. Transposition of Cs1 was followed by characterization of putative insertion events. Genetic linkage between mutant phenotypes and the co-segregating restriction fragments of Cs1 provided additional evidence that Cs1 is an active transposable element in sorghum.