Utilizing genomic prediction to boost hybrid performance in a sweet corn breeding program.

Sweet corn breeding programs, like field corn, focus on the development of elite inbred lines to produce commercial hybrids. For this reason, genomic selection models can help the in silico prediction of hybrid crosses from the elite lines, which is hypothesized to improve the test cross scheme, leading to higher genetic gain in a breeding program. This study aimed to explore the potential of implementing genomic selection in a sweet corn breeding program through hybrid prediction in a within-site across-year and across-site framework. A total of 506 hybrids were evaluated in six environments (California, Florida, and Wisconsin, in the years 2020 and 2021). A total of 20 traits from three different groups were measured (plant-, ear-, and flavor-related traits) across the six environments. Eight statistical models were considered for prediction, as the combination of two genomic prediction models (GBLUP and RKHS) with two different kernels (additive and additive + dominance), and in a single- and multi-trait framework. Also, three different cross-validation schemes were tested (CV1, CV0, and CV00). The different models were then compared based on the correlation between the estimated breeding values/total genetic values and phenotypic measurements. Overall, heritabilities and correlations varied among the traits. The models implemented showed good accuracies for trait prediction. The GBLUP implementation outperformed RKHS in all cross-validation schemes and models. Models with additive plus dominance kernels presented a slight improvement over the models with only additive kernels for some of the models examined. In addition, models for within-site across-year and across-site performed better in the CV0 than the CV00 scheme, on average. Hence, GBLUP should be considered as a standard model for sweet corn hybrid prediction. In addition, we found that the implementation of genomic prediction in a sweet corn breeding program presented reliable results, which can improve the testcross stage by identifying the top candidates that will reach advanced field-testing stages.

Anhydrous and Stereoretentive Fluoride-Enhanced Suzuki-Miyaura Coupling of Immunomodulatory Imide Drug Derivatives.

Immunomodulatory imide drugs form the core of many pharmaceutically relevant structures, but Csp2-Csp2 bond formation via metal-catalyzed cross coupling is difficult due to the sensitivity of the glutarimide ring ubiquitous in these structures. We report that replacement of the traditional alkali base with a fluoride source enhances a previously challenging Suzuki-Miyaura coupling on glutarimide-containing compounds with trifluoroborates. These enabling conditions are reactive enough to generate these derivatives in high yields but mild enough to preserve both the glutarimide and its sensitive stereocenter. Experimental and computational data suggest a mechanistically distinct process of π-coordination of the trifluoroborate enabled by these conditions.

First report of severe tolpyralate sensitivity in corn (Zea mays) discovers a novel genetic factor conferring crop response to a herbicide.

BACKGROUND: Tolpyralate, a relatively new inhibitor of 4-hydroxyphenylpyruvate dioxygenase (HPPD), is registered for postemergence use in all types of corn (Zea mays L.) and has a record of excellent crop tolerance. A report of severe crop injury to sweet corn inbred (XSEN187) led to the following objectives: (i) determine whether sensitivity to tolpyralate in XSEN187 exists, and if confirmed, (ii) determine the genetic basis of tolpyralate sensitivity, and (iii) screen other corn germplasm for sensitivity to tolpyralate. RESULTS: Inbred XSEN187 was confirmed sensitive to tolpyralate. Inclusion of methylated seed oil or nonionic surfactant in the spray volume was necessary for severe crop injury. Tolpyralate sensitivity in XSEN187 is not conferred by alleles at Nsf1, a cytochrome P450-encoding gene (CYP81A9) conferring tolerance to many corn herbicides. Evidence suggests that tolpyralate sensitivity in XSEN187 is conferred by a single gene mapped to the Chr05: 283 240-1 222 909 bp interval. Moreover, tolpyralate sensitivity was observed in 48 other sweet corn and field corn inbreds. CONCLUSIONS: Severe sensitivity to tolpyralate exists in sweet corn and field corn germplasm when the herbicide is applied according to label directions. Whereas the corn response to several other herbicides, including HPPD-inhibitors, is conferred by the Nsf1 locus, corn sensitivity to tolpyralate is the result of a different locus. The use of tolpyralate should consider herbicide tolerance in inbred lines from which corn hybrids were derived, whereas alleles that render corn germplasm sensitive to tolpyralate should be eliminated from breeding populations, inbreds, and commercial cultivars. © 2023 Illinois Foundation Seeds, Inc and The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

A Novel 7H-[1,2,4]Triazolo[3,4-b]thiadiazine-based Cystic Fibrosis Transmembrane Conductance Regulator Potentiator Directed toward Treatment of Cystic Fibrosis.

Cystic fibrosis (CF) is an autosomal genetic disorder caused by disrupted anion transport in epithelial cells lining tissues in the human airways and digestive system. While cystic fibrosis transmembrane conductance regulator (CFTR) modulator compounds have provided transformative improvement in CF respiratory function, certain patients exhibit marginal clinical benefit or detrimental effects or have a form of the disease not approved or unlikely to respond using CFTR modulation. We tested hit compounds from a 300,000-drug screen for their ability to augment CFTR transepithelial transport alone or in combination with the FDA-approved CFTR potentiator ivacaftor (VX-770). A subsequent SAR campaign led us to a class of 7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines that in combination with VX-770 rescued function of G551D mutant CFTR channels to approximately 400% above the activity of VX-770 alone and to nearly wild-type CFTR levels in the same Fischer rat thyroid model system.

Unearthing the Subtleties of Rhodium(II)-Catalyzed Carbenoid Cycloadditions to Furans with an N-Sulfonyl-1,2,3-triazole Probe.

The rhodium(II)-catalyzed reaction of a model alkenyl donor/acceptor N-sulfonyltriazole with a wide selection of furans is reported. This investigation unearthed a range of structurally diverse carbocyclic and ring-opened products, in good to excellent yields. The products obtained are proposed to arise selectively via cyclopropanation or zwitterionic rearrangement pathways, which are highly dependent on both the structural and electronic features of the furan substrate.

Asymmetric Cyclopropanation with 4-Aryloxy-1-sulfonyl-1,2,3-triazoles: Expanding the Range of Rhodium-Stabilized Donor/Acceptor Carbenes to Systems with an Oxygen Donor Group.

Rhodium-catalyzed enantioselective synthesis of 1-phenoxycyclopropane-1-carbaldehydes by intermolecular cyclopropanation of terminal alkenes followed by imine hydrolysis is described. This methodology utilizes 4-aryloxy-1-sulfonyl-1,2,3-triazoles as the carbene precursors and the chiral dirhodium(II) tetracarboxylates Rh2(S-NTTL)4 or Rh2(S-DPCP)4 as the catalysts. These reactions are considered to proceed via rhodium-stabilized donor/acceptor carbene intermediates, and these studies demonstrate that a heteroatom donor group is compatible with an enantioselective transformation.

Genome-wide association study suggests an independent genetic basis of zinc and cadmium concentrations in fresh sweet corn kernels.

Despite being one of the most consumed vegetables in the United States, the elemental profile of sweet corn (Zea mays L.) is limited in its dietary contributions. To address this through genetic improvement, a genome-wide association study was conducted for the concentrations of 15 elements in fresh kernels of a sweet corn association panel. In concordance with mapping results from mature maize kernels, we detected a probable pleiotropic association of zinc and iron concentrations with nicotianamine synthase5 (nas5), which purportedly encodes an enzyme involved in synthesis of the metal chelator nicotianamine. In addition, a pervasive association signal was identified for cadmium concentration within a recombination suppressed region on chromosome 2. The likely causal gene underlying this signal was heavy metal ATPase3 (hma3), whose counterpart in rice, OsHMA3, mediates vacuolar sequestration of cadmium and zinc in roots, whereby regulating zinc homeostasis and cadmium accumulation in grains. In our association panel, hma3 associated with cadmium but not zinc accumulation in fresh kernels. This finding implies that selection for low cadmium will not affect zinc levels in fresh kernels. Although less resolved association signals were detected for boron, nickel, and calcium, all 15 elements were shown to have moderate predictive abilities via whole-genome prediction. Collectively, these results help enhance our genomics-assisted breeding efforts centered on improving the elemental profile of fresh sweet corn kernels.

Genome assembly and population genomic analysis provide insights into the evolution of modern sweet corn.

Sweet corn is one of the most important vegetables in the United States and Canada. Here, we present a de novo assembly of a sweet corn inbred line Ia453 with the mutated shrunken2-reference allele (Ia453-sh2). This mutation accumulates more sugar and is present in most commercial hybrids developed for the processing and fresh markets. The ten pseudochromosomes cover 92% of the total assembly and 99% of the estimated genome size, with a scaffold N50 of 222.2 Mb. This reference genome completely assembles the large structural variation that created the mutant sh2-R allele. Furthermore, comparative genomics analysis with six field corn genomes highlights differences in single-nucleotide polymorphisms, structural variations, and transposon composition. Phylogenetic analysis of 5,381 diverse maize and teosinte accessions reveals genetic relationships between sweet corn and other types of maize. Our results show evidence for a common origin in northern Mexico for modern sweet corn in the U.S. Finally, population genomic analysis identifies regions of the genome under selection and candidate genes associated with sweet corn traits, such as early flowering, endosperm composition, plant and tassel architecture, and kernel row number. Our study provides a high-quality reference-genome sequence to facilitate comparative genomics, functional studies, and genomic-assisted breeding for sweet corn.

Genetic Perturbation of the Starch Biosynthesis in Maize Endosperm Reveals Sugar-Responsive Gene Networks.

In maize, starch mutants have facilitated characterization of key genes involved in endosperm starch biosynthesis such as large subunit of AGPase Shrunken2 (Sh2) and isoamylase type DBE Sugary1 (Su1). While many starch biosynthesis enzymes have been characterized, the mechanisms of certain genes (including Sugary enhancer1) are yet undefined, and very little is understood about the regulation of starch biosynthesis. As a model, we utilize commercially important sweet corn mutations, sh2 and su1, to genetically perturb starch production in the endosperm. To characterize the transcriptomic response to starch mutations and identify potential regulators of this pathway, differential expression and coexpression network analysis was performed on near-isogenic lines (NILs) (wildtype, sh2, and su1) in six genetic backgrounds. Lines were grown in field conditions and kernels were sampled in consecutive developmental stages (blister stage at 14 days after pollination (DAP), milk stage at 21 DAP, and dent stage at 28 DAP). Kernels were dissected to separate embryo and pericarp from the endosperm tissue and 3' RNA-seq libraries were prepared. Mutation of the Su1 gene led to minimal changes in the endosperm transcriptome. Responses to loss of sh2 function include increased expression of sugar (SWEET) transporters and of genes for ABA signaling. Key regulators of starch biosynthesis and grain filling were identified. Notably, this includes Class II trehalose 6-phosphate synthases, Hexokinase1, and Apetala2 transcription factor-like (AP2/ERF) transcription factors. Additionally, our results provide insight into the mechanism of Sugary enhancer1, suggesting a potential role in regulating GA signaling via GRAS transcription factor Scarecrow-like1.

Natural variation for carotenoids in fresh kernels is controlled by uncommon variants in sweet corn.

Sweet corn (Zea mays L.) is highly consumed in the United States, but does not make major contributions to the daily intake of carotenoids (provitamin A carotenoids, lutein and zeaxanthin) that would help in the prevention of health complications. A genome-wide association study of seven kernel carotenoids and twelve derivative traits was conducted in a sweet corn inbred line association panel ranging from light to dark yellow in endosperm color to elucidate the genetic basis of carotenoid levels in fresh kernels. In agreement with earlier studies of maize kernels at maturity, we detected an association of ß-carotene hydroxylase (crtRB1) with ß-carotene concentration and lycopene epsilon cyclase (lcyE) with the ratio of flux between the α- and ß-carotene branches in the carotenoid biosynthetic pathway. Additionally, we found that 5% or less of the evaluated inbred lines possessing the shrunken2 (sh2) endosperm mutation had the most favorable lycE allele or crtRB1 haplotype for elevating ß-branch carotenoids (ß-carotene and zeaxanthin) or ß-carotene, respectively. Genomic prediction models with genome-wide markers obtained moderately high predictive abilities for the carotenoid traits, especially lutein, and outperformed models with less markers that targeted candidate genes implicated in the synthesis, retention, and/or genetic control of kernel carotenoids. Taken together, our results constitute an important step toward increasing carotenoids in fresh sweet corn kernels.

Characterizing the Physical Properties and Cell Compatibility of Phytoglycogen Extracted from Different Sweet Corn Varieties.

Owing to its unique structure and properties, the glucose dendrimer phytoglycogen is gaining interest for medical and biotechnology applications. Although many maize variants are available from commercial and academic breeding programs, most applications rely on phytoglycogen extracted from the common maize variant, sugary1. Here we characterized the solubility, hydrodynamic diameter, water-binding properties, protein contaminant concentration, and cytotoxicity of phytoglycogens from different maize sources, A632su1, A619su1, Wesu7, and Ia453su1, harboring various sugary1 mutants. A619su1-SW phytoglycogen was cytotoxic while A632su1-SW phytoglycogen was not. A632su1-Pu phytoglycogen promoted cell growth, whereas extracts from A632su1-NE, A632su1-NC, and A632su1-CM were cytotoxic. Phytoglycogen extracted from Wesu7su1-NE using ethanol precipitation was cytotoxic. Acid-treatment improved Wesu7 phytoglycogen cytocompatibility. Protease-treated Wesu7 extracts promoted cell growth. Phytoglycogen extracted from Ia453su1 21 days after pollination ("Ia435su1 21DAP") was cytotoxic, whereas phytoglycogen extracted at 40 days ("Ia435su1 40DAP") was not. In general, size and solubility had no correlation with cytocompatibility, whereas protein contaminant concentration and water-binding properties did. A632su1-CM had the highest protein contamination among A632 mutants, consistent with its higher cytotoxicity. Likewise, Ia435su1 21DAP phytoglycogen had higher protein contamination than Ia435su1 40DAP. Conversely, protease-treated Wesu7 extracts had lower protein contamination than the other Wesu7 extracts. A632su1-NE, A632su1-NC, and A632su1-CM had similar water-binding properties which differed from those of A632su1-Pu and A632su1-SW. Likewise, water binding differed between Ia435su1 21DAP and Ia435su1 40DAP. Collectively, these data demonstrate that maize phytoglycogen extracts are not uniformly cytocompatible. Rather, maize variant, plant genotype, protein contaminants, and water-binding properties are determinants of phytoglycogen cytotoxicity.

Maize sugary enhancer1 (se1) is a gene affecting endosperm starch metabolism.

sugary enhancer1 (se1) is a naturally occurring mutant allele involved in starch metabolism in maize endosperm. It is a recessive modifier of sugary1 (su1) and commercially important in modern sweet corn breeding, but its molecular identity and mode of action remain unknown. Here, we developed a pair of near-isogenic lines, W822Gse (su1-ref/su1-ref se1/se1) and W822GSe (su1-ref/su1-ref Se1/Se1), that Mendelize the se1 phenotype in an su1-ref background. W822Gse kernels have lower starch and higher water soluble polysaccharide and sugars than W822GSe kernels. Using high-resolution genetic mapping, we found that wild-type Se1 is a gene Zm00001d007657 on chromosome 2 and a deletion of this gene causes the se1 phenotype. Comparative metabolic profiling of seed tissue between these 2 isolines revealed the remarkable difference in carbohydrate metabolism, with sucrose and maltose highly accumulated in the mutant. Se1 is predominantly expressed in the endosperm, with low expression in leaf and root tissues. Differential expression analysis identified genes enriched in both starch biosynthesis and degradation processes, indicating a pleiotropic regulatory effect of se1 Repressed expression of Se1 and Su1 in RNA interference-mediated transgenic maize validates that deletion of the gene identified as Se1 is a true causal gene responsible for the se1 phenotype. The findings contribute to our understanding of starch metabolism in cereal crops.

Multiple Maize Reference Genomes Impact the Identification of Variants by Genome-Wide Association Study in a Diverse Inbred Panel.

Use of a single reference genome for genome-wide association studies (GWAS) limits the gene space represented to that of a single accession. This limitation can complicate identification and characterization of genes located within presence-absence variations (PAVs). In this study, we present the draft de novo genome assembly of 'PHJ89', an 'Oh43'-type inbred line of maize ( L.). From three separate reference genome assemblies ('B73', 'PH207', and PHJ89) that represent the predominant germplasm groups of maize, we generated three separate whole-seedling gene expression profiles and single nucleotide polymorphism (SNP) matrices from a panel of 942 diverse inbred lines. We identified 34,447 (B73), 39,672 (PH207), and 37,436 (PHJ89) transcripts that are not present in the respective reference genome assemblies. Genome-wide association studies were conducted in the 942 inbred panel with both the SNP and expression data values to map (SCMV) resistance. Highlighting the impact of alternative reference genomes in gene discovery, the GWAS results for SCMV resistance with expression values as a surrogate measure of PAV resulted in robust detection of the physical location of a known resistance gene when the B73 reference that contains the gene was used, but not the PH207 reference. This study provides the valuable resource of the Oh43-type PHJ89 genome assembly as well as SNP and expression data for 942 individuals generated from three different reference genomes.

Genome-Wide Association and Genomic Prediction Models of Tocochromanols in Fresh Sweet Corn Kernels.

Sweet corn ( L.), a highly consumed fresh vegetable in the United States, varies for tocochromanol (tocopherol and tocotrienol) levels but makes only a limited contribution to daily intake of vitamin E and antioxidants. We performed a genome-wide association study of six tocochromanol compounds and 14 derivative traits across a sweet corn inbred line association panel to identify genes associated with natural variation for tocochromanols and vitamin E in fresh kernels. Concordant with prior studies in mature maize kernels, an association was detected between γ-tocopherol methyltransferase (vte4) and α-tocopherol content, along with () and () for tocotrienol variation. Additionally, two kernel starch synthesis genes, () and (), were associated with tocotrienols, with the strongest evidence for in combination with fixed, strong and alleles, accounting for the greater amount of tocotrienols in and lines. In prediction models with genome-wide markers, predictive abilities were higher for tocotrienols than tocopherols, and these models were superior to those that used marker sets targeting a priori genes involved in the biosynthesis and/or genetic control of tocochromanols. Through this quantitative genetic analysis, we have established a key step for increasing tocochromanols in fresh kernels of sweet corn for human health and nutrition.

Effects of long-term exposure to elevated temperature on Zea mays endosperm development during grain fill.

Cereal yields decrease when grain fill proceeds under conditions of prolonged, moderately elevated temperatures. Endosperm-endogenous processes alter both rate and duration of dry weight gain, but underlying mechanisms remain unclear. Heat effects could be mediated by either abnormal, premature cessation of storage compound deposition or accelerated implementation of normal development. This study used controlled environments to isolate temperature as the sole environmental variable during Zea mays kernel-fill, from 12 days after pollination to maturity. Plants subjected to elevated day, elevated night temperatures (38°C day, 28°C night (38/28°C])) or elevated day, normal night (38/17°C), were compared with those from controls grown under normal day and night conditions (28/17°C). Progression of change over time in endosperm tissue was followed to dissect contributions at multiple levels, including transcriptome, metabolome, enzyme activities, product accumulation, and tissue ultrastructure. Integrated analyses indicated that the normal developmental program of endosperm is fully executed under prolonged high-temperature conditions, but at a faster rate. Accelerated development was observed when both day and night temperatures were elevated, but not when daytime temperature alone was increased. Although transcripts for most components of glycolysis and respiration were either upregulated or minimally affected, elevated temperatures decreased abundance of mRNAs related to biosynthesis of starch and storage proteins. Further analysis of 20 central-metabolic enzymes revealed six activities that were reduced under high-temperature conditions, indicating candidate roles in the observed reduction of grain dry weight. Nonetheless, a striking overall resilience of grain filling in the face of elevated temperatures can be attributed to acceleration of normal endosperm development.

Ovary abortion is prevalent in diverse maize inbred lines and is under genetic control.

Crop improvement programs focus on characteristics that are important for plant productivity. Typically genes underlying these traits are identified and stacked to create improved cultivars. Hence, identification of valuable traits for plant productivity is critical for plant improvement. Here we describe an important characteristic for maize productivity. Despite the fact mature maize ears are typically covered with kernels, we find that only a fraction of ovaries give rise to mature kernels. Non-developed ovaries degenerate while neighboring fertilized ovaries produce kernels that fill the ear. Abortion occurs throughout the ear, not just at the tip. We show that the fraction of aborted ovaries/kernels is genetically controlled and varies widely among maize lines, and low abortion genotypes are rare. Reducing or eliminating ovary abortion could substantially increase yield, making this characteristic a new target for selection in maize improvement programs.

The Genetics of Leaf Flecking in Maize and Its Relationship to Plant Defense and Disease Resistance.

Physiological leaf spotting, or flecking, is a mild-lesion phenotype observed on the leaves of several commonly used maize (Zea mays) inbred lines and has been anecdotally linked to enhanced broad-spectrum disease resistance. Flecking was assessed in the maize nested association mapping (NAM) population, comprising 4,998 recombinant inbred lines from 25 biparental families, and in an association population, comprising 279 diverse maize inbreds. Joint family linkage analysis was conducted with 7,386 markers in the NAM population. Genome-wide association tests were performed with 26.5 million single-nucleotide polymorphisms (SNPs) in the NAM population and with 246,497 SNPs in the association population, resulting in the identification of 18 and three loci associated with variation in flecking, respectively. Many of the candidate genes colocalizing with associated SNPs are similar to genes that function in plant defense response via cell wall modification, salicylic acid- and jasmonic acid-dependent pathways, redox homeostasis, stress response, and vesicle trafficking/remodeling. Significant positive correlations were found between increased flecking, stronger defense response, increased disease resistance, and increased pest resistance. A nonlinear relationship with total kernel weight also was observed whereby lines with relatively high levels of flecking had, on average, lower total kernel weight. We present evidence suggesting that mild flecking could be used as a selection criterion for breeding programs trying to incorporate broad-spectrum disease resistance.

A Genome-Wide Association Study for Partial Resistance to Maize Common Rust.

Quantitative resistance to maize common rust (causal agent Puccinia sorghi) was assessed in an association mapping population of 274 diverse inbred lines. Resistance to common rust was found to be moderately correlated with resistance to three other diseases and with the severity of the hypersensitive defense response previously assessed in the same population. Using a mixed linear model accounting for the confounding effects of population structure and flowering time, genome-wide association tests were performed based at 246,497 single-nucleotide polymorphism loci. Three loci associated with maize common rust resistance were identified. Candidate genes at each locus had predicted roles, mainly in cell wall modification. Other candidate genes included a resistance gene and a gene with a predicted role in regulating accumulation of reactive oxygen species.

Feeding the World Today and Tomorrow: The Importance of Food Science and Technology: An IFT Scientific Review.

by Philip E. Nelson, 2007 World Food Prize Laureate; Professor Emeritus, Food Science Dept., Purdue Univ. Just as society has evolved over time, our food system has also evolved over centuries into a global system of immense size and complexity. The commitment of food science and technology professionals to advancing the science of food, ensuring a safe and abundant food supply, and contributing to healthier people everywhere is integral to that evolution. Food scientists and technologists are versatile, interdisciplinary, and collaborative practitioners in a profession at the crossroads of scientific and technological developments. As the food system has drastically changed, from one centered around family food production on individual farms and home food preservation to the modern system of today, most people are not connected to their food nor are they familiar with agricultural production and food manufacturing designed for better food safety and quality. The Institute of Food Technologists-a nonprofit scientific society of individual members engaged in food science, food technology, and related professions in industry, academia, and government-has the mission to advance the science of food and the long-range vision to ensure a safe and abundant food supply contributing to healthier people everywhere. IFT convened a task force and called on contributing authors to develop this scientific review to inform the general public about the importance and benefits of food science and technology in IFT's efforts to feed a growing world. The main objective of this review is to serve as a foundational resource for public outreach and education and to address misperceptions and misinformation about processed foods. The intended audience includes those who desire to know more about the application of science and technology to meet society's food needs and those involved in public education and outreach. It is IFT's hope that the reader will gain a better understanding of the goals or purposes for various applications of science and technology in the food system, and an appreciation for the complexity of the modern food supply. Abstract: This Institute of Food Technologists scientific review describes the scientific and technological achievements that made possible the modern production-to-consumption food system capable of feeding nearly 7 billion people, and it also discusses the promising potential of ongoing technological advancements to enhance the food supply even further and to increase the health and wellness of the growing global population. This review begins with a historical perspective that summarizes the parallel developments of agriculture and food technology, from the beginnings of modern society to the present. A section on food manufacturing explains why food is processed and details various food processing methods that ensure food safety and preserve the quality of products. A section about potential solutions to future challenges briefly discusses ways in which scientists, the food industry, and policy makers are striving to improve the food supply for a healthier population and feed the future. Applications of science and technology within the food system have allowed production of foods in adequate quantities to meet the needs of society, as it has evolved. Today, our production-to-consumption food system is complex, and our food is largely safe, tasty, nutritious, abundant, diverse, convenient, and less costly and more readily accessible than ever before. Scientific and technological advancements must be accelerated and applied in developed and developing nations alike, if we are to feed a growing world population.

Cell wall composition in juvenile and adult leaves of maize (Zea mays L.).

Many leaf characteristics vary with position along the culm in maize (Zea mays L.) due to the existence of vegetative phase change and heteroblasty. The objective of this work was to determine if differences in cell wall composition exist among developmental phases and between Cg1, a developmental mutant, and wild-type maize. In one experiment, the middle third of fully elongated leaf blades from lower and upper regions of the shoot was harvested (midribs removed) and analyzed for several cell wall components. Averaged over five inbreds (De811, Ia5125, Mo17, P39, and Wh8584), lower leaf blades had higher levels of xylose and lower levels of total uronosyls, glucose, arabinose, and galactose (P < 0.05) than did upper leaf blades. With the exception of glucose, upper and lower leaves of Cg1 plants varied in the same manner as their near-isogenic siblings, except cell walls of Cg1 plants were more "juvenile" than cell walls of wild-type siblings at the same leaf stage. These data support the hypothesis that Cg1 delays but does not eliminate the transition from juvenile-vegetative to adult-vegetative phase. In a second experiment, juvenile (leaves 3 and 5), transition (leaf 7), and adult (leaves 9 and 11) leaves from inbreds B73 and De811 were harvested and analyzed as in the first experiment. As leaf number rose, total cell wall content of sample dry matter, total neutral sugars, glucose, xylose, and ester-linked monomers of p-coumaric acid and total ferulates including ferulate dimers increased linearly while total uronosyls acids, arabinose, and galactose declined linearly (P < 0.05). Glucose and xylose are major cell wall components released from cellulose and xylans after acid hydrolysis. Pectin, a minor component of grass cell walls, is composed of galacturonosyls, arabinose, and galactose. Secondary cell wall deposition increased between leaves 3 and 11 in a heteroblastic series, due to either increased cell wall content concomitant with decreased cell lumen size, changes in proportion of cell types (i.e., sclerenchyma), or a combination of these factors.