Corrigendum: Will epigenetics be a key player in crop breeding?

[This corrects the article DOI: 10.3389/fpls.2022.958350.].

Will epigenetics be a key player in crop breeding?

If food and feed production are to keep up with world demand in the face of climate change, continued progress in understanding and utilizing both genetic and epigenetic sources of crop variation is necessary. Progress in plant breeding has traditionally been thought to be due to selection for spontaneous DNA sequence mutations that impart desirable phenotypes. These spontaneous mutations can expand phenotypic diversity, from which breeders can select agronomically useful traits. However, it has become clear that phenotypic diversity can be generated even when the genome sequence is unaltered. Epigenetic gene regulation is a mechanism by which genome expression is regulated without altering the DNA sequence. With the development of high throughput DNA sequencers, it has become possible to analyze the epigenetic state of the whole genome, which is termed the epigenome. These techniques enable us to identify spontaneous epigenetic mutations (epimutations) with high throughput and identify the epimutations that lead to increased phenotypic diversity. These epimutations can create new phenotypes and the causative epimutations can be inherited over generations. There is evidence of selected agronomic traits being conditioned by heritable epimutations, and breeders may have historically selected for epiallele-conditioned agronomic traits. These results imply that not only DNA sequence diversity, but the diversity of epigenetic states can contribute to increased phenotypic diversity. However, since the modes of induction and transmission of epialleles and their stability differ from that of genetic alleles, the importance of inheritance as classically defined also differs. For example, there may be a difference between the types of epigenetic inheritance important to crop breeding and crop production. The former may depend more on longer-term inheritance whereas the latter may simply take advantage of shorter-term phenomena. With the advances in our understanding of epigenetics, epigenetics may bring new perspectives for crop improvement, such as the use of epigenetic variation or epigenome editing in breeding. In this review, we will introduce the role of epigenetic variation in plant breeding, largely focusing on DNA methylation, and conclude by asking to what extent new knowledge of epigenetics in crop breeding has led to documented cases of its successful use.

Network Inference of Transcriptional Regulation in Germinating Low Phytic Acid Soybean Seeds

The low phytic acid (lpa) trait in soybeans can be conferred by loss-of-function mutations in genes encoding myo-inositol phosphate synthase and two epistatically interacting genes encoding multidrug-resistance protein ATP-binding cassette (ABC) transporters. However, perturbations in phytic acid biosynthesis are associated with poor seed vigor. Since the benefits of the lpa trait, in terms of end-use quality and sustainability, far outweigh the negatives associated with poor seed performance, a fuller understanding of the molecular basis behind the negatives will assist crop breeders and engineers in producing variates with lpa and better germination rate. The gene regulatory network (GRN) for developing low and normal phytic acid soybean seeds was previously constructed, with genes modulating a variety of processes pertinent to phytic acid metabolism and seed viability being identified. In this study, a comparative time series analysis of low and normal phytic acid soybeans was carried out to investigate the transcriptional regulatory elements governing the transitional dynamics from dry seed to germinated seed. GRNs were reverse engineered from time series transcriptomic data of three distinct genotypic subsets composed of lpa soybean lines and their normal phytic acid sibling lines. Using a robust unsupervised network inference scheme, putative regulatory interactions were inferred for each subset of genotypes. These interactions were further validated by published regulatory interactions found in Arabidopsis thaliana and motif sequence analysis. Results indicate that lpa seeds have increased sensitivity to stress, which could be due to changes in phytic acid levels, disrupted inositol phosphate signaling, disrupted phosphate ion (Pi) homeostasis, and altered myo-inositol metabolism. Putative regulatory interactions were identified for the latter two processes. Changes in abscisic acid (ABA) signaling candidate transcription factors (TFs) putatively regulating genes in this process were identified as well. Analysis of the GRNs reveal altered regulation in processes that may be affecting the germination of lpa soybean seeds. Therefore, this work contributes to the ongoing effort to elucidate molecular mechanisms underlying altered seed viability, germination and field emergence of lpa crops, understanding of which is necessary in order to mitigate these problems.

Characteristics and Quality of Japanese Traditional Fermented Soybean (Natto) from a Low-phytate Line

The Japanese traditional fermented soybean or "natto", a cheap and nutrient-rich food, is very popular in Japan. The low-phytate (LP) soybeans exhibit higher mineral bioavailability; however, their use in preparing natto has not been reported. Therefore, in this study, characteristics and quality of natto prepared using LP soybean were investigated. The findings revealed a better color, lower stickiness, and lower hardness and taste of LP natto with lower phytate and higher inorganic phosphorus (Pi) concentrations than those in the normal-phytate (NP) natto. However, the Ca, Mg, and K concentrations were not significantly different between LP and NP natto, whereas the protein level in NP natto was slightly higher than that in LP natto. These findings indicate that the lower phytate content in LP natto than that in NP natto, could facilitate a higher bioavailability of P and other minerals. Moreover, the improved color and lower stickiness, in addition to lower hardness and taste of LP natto, imparted through improved manufacturing process could increase its acceptability overseas, thereby increasing its commercial value. These improved qualities of LP natto could contribute to improving human health as well as increasing sustainable food and nutrient security.

Genetic interactions regulating seed phytate and oligosaccharides in soybean (Glycine max L.)

Two low-phytate soybean (Glycine max (L.) Merr.) mutant lines- V99-5089 (mips mutation on chromosome 11) and CX-1834 (mrp-l and mrp-n mutations on chromosomes 19 and 3, respectively) have proven to be valuable resources for breeding of low-phytate, high-sucrose, and low-raffinosaccharide soybeans, traits that are highly desirable from a nutritional and environmental standpoint. A recombinant inbred population derived from the cross CX1834 x V99-5089 provides an opportunity to study the effect of different combinations of these three mutations on soybean phytate and oligosaccharides levels. Of the 173 recombinant inbred lines tested, 163 lines were homozygous for various combinations of MIPS and two MRP loci alleles. These individuals were grouped into eight genotypic classes based on the combination of SNP alleles at the three mutant loci. The two genotypic classes that were homozygous mrp-l/mrp-n and either homozygous wild-type or mutant at the mips locus (MIPS/mrp-l/mrp-n or mips/mrp-l/mrp-n) displayed relatively similar ~55% reductions in seed phytate, 6.94 mg g -1 and 6.70 mg g-1 respectively, as compared with 15.2 mg g-1 in the wild-type MIPS/MRP-L/MRP-N seed. Therefore, in the presence of the double mutant mrp-l/mrp-n, the mips mutation did not cause a substantially greater decrease in seed phytate level. However, the nutritionally-desirable high-sucrose/low-stachyose/low-raffinose seed phenotype originally observed in soybeans homozygous for the mips allele was reversed in the presence of mrp-l/mrp-n mutations: homozygous mips/mrp-l/mrp-n seed displayed low-sucrose (7.70%), high-stachyose (4.18%), and the highest observed raffinose (0.94%) contents per gram of dry seed. Perhaps the block in phytic acid transport from its cytoplasmic synthesis site to its storage site, conditioned by mrp-l/mrp-n, alters myo-inositol flux in mips seeds in a way that restores to wild-type levels the mips conditioned reductions in raffinosaccharides. Overall this study determined the combinatorial effects of three low phytic acid causing mutations on regulation of seed phytate and oligosaccharides in soybean.

Seedling growth, physiological characteristics, nitrogen fixation, and root and nodule phytase and phosphatase activity of a low-phytate soybean line

Understanding the influence of the valuable "low-phytate" trait on soybean seedling growth, physiology, and biochemistry will facilitate its future exploitation. The aim was to elucidate the physiological and biochemical characteristics of low-phytate (LP) soybean at the seedling stage. To this end, seed P and mineral content and seedling dry weight, carbon (C) and nitrogen (N) accumulation, nitrogen fixation, and root and nodule phytase and phosphatase activity levels were measured at 21 d after sowing LP and normal-phytate (NP) soybean lines. Seedling dry weight, and C and N accumulation were 31%, 38% and 54% higher, respectively, in the LP line than the NP line. The total and specific nitrogen fixation levels in the LP nodules were 46% and 78% higher, respectively, than those in the NP nodules. The phytase, phosphatase, and specific phytase levels were 1.4-folds, 1.3-folds, and 1.3-folds higher, respectively, in the LP roots than the NP roots. The phosphatase and specific phosphatase levels in LP nodules were 1.5-folds and 1.3-folds higher, respectively, than those in the NP nodules. The mineral levels were substantially higher in the LP seeds and seedings than in those of the NP line. The HCl extractabilities of P, S, Fe, Cu and Mn were higher in the LP seeds than the NP seeds. These results indicate that the LP line presented with superior seedling growth and nitrogen fixation relative to the NP line. The LP line had relatively higher root phytase and root and nodule phosphatase activity levels than the NP line and could, therefore, be better suited and more readily adapt to low P conditions.

Implications of phytate in plant-based foods for iron and zinc bioavailability, setting dietary requirements, and formulating programs and policies

Plant-based diets in low-income countries (LICs) have a high content of phytic acid (myo-inositol hexaphosphate [InsP6]) and associated magnesium, potassium, and calcium salts. Together, InsP6 acid and its salts are termed "phytate" and are potent inhibitors of iron and zinc absorption. Traditional food processing can reduce the InsP6 content through loss of water-soluble phytate or through phytase hydrolysis to lower myo-inositol phosphate forms that no longer inhibit iron and zinc absorption. Hence, some processing practices can reduce the need for high-dose iron fortificants in plant-based diets and alleviate safety concerns. Dietary phytate-to-iron and phytate-to-zinc molar ratios are used to estimate iron and zinc bioavailability and to identify dietary iron and zinc requirements according to diet type. The European Food Safety Authority has set adult dietary zinc requirements for 4 levels of phytate intake, highlighting the urgent need for phytate food composition data. Such data will improve the ability to estimate the prevalence of inadequate zinc intakes in vulnerable groups in LICs, which will facilitate implementation of targeted policies to alleviate zinc deficiency.

Inference of Transcription Regulatory Network in Low Phytic Acid Soybean Seeds

A dominant loss of function mutation in myo-inositol phosphate synthase (MIPS) gene and recessive loss of function mutations in two multidrug resistant protein type-ABC transporter genes not only reduce the seed phytic acid levels in soybean, but also affect the pathways associated with seed development, ultimately resulting in low emergence. To understand the regulatory mechanisms and identify key genes that intervene in the seed development process in low phytic acid crops, we performed computational inference of gene regulatory networks in low and normal phytic acid soybeans using a time course transcriptomic data and multiple network inference algorithms. We identified a set of putative candidate transcription factors and their regulatory interactions with genes that have functions in myo-inositol biosynthesis, auxin-ABA signaling, and seed dormancy. We evaluated the performance of our unsupervised network inference method by comparing the predicted regulatory network with published regulatory interactions in Arabidopsis. Some contrasting regulatory interactions were observed in low phytic acid mutants compared to non-mutant lines. These findings provide important hypotheses on expression regulation of myo-inositol metabolism and phytohormone signaling in developing low phytic acid soybeans. The computational pipeline used for unsupervised network learning in this study is provided as open source software and is freely available at https://lilabatvt.github.io/LPANetwork/.

Upregulation of Zinc Absorption Matches Increases in Physiologic Requirements for Zinc in Women Consuming High- or Moderate-Phytate Diets during Late Pregnancy and Early Lactation

Background: Estimated physiologic requirements (PRs) for zinc increase in late pregnancy and early lactation, but the effect on dietary zinc requirements is uncertain.Objective: The aim of this study was to determine changes in daily fractional absorbed zinc and total absorbed zinc (TAZ) from ad libitum diets of differing phytate contents in relation to physiologic zinc requirements during pregnancy and lactation.Methods: This was a prospective observational study of zinc absorption at 8 (phase 1) and 34 (phase 2) wk of gestation and 2 (phase 3) and 6 (phase 4) mo of lactation. Participants were indigenous Guatemalan women of childbearing age whose major food staple was maize and who had been randomly assigned in a larger study to either of 2 ad libitum feeding groups: low-phytate maize (LP; 1.6 mg/g; n = 14) or control maize (C; 7.1 mg/g; n = 8). Total dietary zinc (milligrams per day, TDZ) and phytate (milligrams per day) were determined from duplicate diets and fractional absorption (FAZ) by dual isotope ratio technique (TAZ = TDZ × FAZ). All variables were examined longitudinally and by group and compared with PRs. TAZ values at later phases were compared with phase 1. Measured TAZ was compared with predicted TAZ for nonpregnant, nonlactating (NPNL) women.Results: TAZ was greater in the LP group than in the C group at all phases. All variables increased from phase 1 to phases 2 and 3 and declined at phase 4. TAZ increased by 1.25 mg/d (P = 0.045) in the C group and by 0.81 mg/d (P = 0.058) in the LP group at phase 2. At phase 3, the increases were 2.66 mg/d (P = 0.002) in the C group and 2.28 mg/d (P = 0.0004) in the LP group, compared with a 1.37-mg/d increase in PR. Measured TAZ was greater than predicted values in phases 2-4.Conclusions: Upregulation of zinc absorption in late pregnancy and early lactation matches increases in PRs of pregnant and lactating women, regardless of dietary phytate, which has implications for dietary zinc requirements of pregnant and lactating women.

Low-phytic-acid Grains

As one approach to the improvement of the nutritional quality of crops for both foods and feeds, low-phytic-acid (lpa) mutants of maize and other cereals have been isolated. An important advantage of lpa mutants is that the bioavailability of a range of minerals may be improved, although phytic acid can also function as an antioxidant. Livestock producers are primarily concerned with excretion of feed phytic acid phosphorus by livestock and fish. This contributes to water pollution and is a major environmental issue in developed countries. In these mutants, phytic acid phosphorus is reduced by 55% to 66%, which is matched by an equal increase in inorganic phosphorus. Greater reductions in phytic acid, as high as 95% to 99%, may be desirable and are possible. The first two studies of an lpa maize in human nutrition found increased fractional absorption of iron and zinc in the lpa maize as compared with the control maize.

Yields of the best lpa lines, first developed in the mid-1990s, now range between 5% and 15% below those of the highest-yielding commercial varieties. Because of benefits for animal nutrition, lpa crops could become highly profitable for use as animal feeds. All lpa lines to date have been developed using classical genetic methods; these classically obtained mutants affect the expression of a given gene throughout the tissues and organs of a plant. BY using a biotechnology approach, it may be possible to achieve optimal levels of phytic acid reduction and target the desired effect to the seed, thereby reducing any undesirable agronomic effects of whole-plant mutants.

Hulled and hull-less barley grains with the genetic trait for low-phytic acid increased the apparent total-tract digestibility of phosphorus and calcium in diets for young swine

A 35-d experiment was conducted using 63 crossbred pigs (35 barrows and 28 gilts) with an initial average BW of 7.0 kg and age of 28 d to evaluate the efficacy of the low-phytic acid (LPA) genetic trait in hulled or hull-less barley in isocaloric diets. Hulled barleys were the normal barley (NB) cultivar Harrington and the near-isogenic LPA mutant 955 (M955) with P availabilities of 36 and 95%, respectively. Hull-less lines were produced by crossing NB and the LPA mutant 422 line with a hull-less line, producing hull-less NB (HNB) and hull-less mutant 422 (HM422) with P availabilities of 41 and 66%, respectively. Pigs were in individual metabolism cages or pens for Phase 1 (d 0 to 14) and Phase 2 (d 14 to 35). Diets defined as NB, HNB, HM422, or M955 with no added inorganic P (iP) had available P (aP) concentrations of 0.27, 0.28, 0.35, and 0.40% for Phase 1 and 0.15, 0.17, 0.23, and 0.31% for Phase 2, respectively. Only diet M955 was adequate in aP. Therefore, iP was added to the P-deficient diets to make diets NB + iP, HNB + iP, and HM422 + iP with aP equal to that in diet M955. Overall (d 0 to 35), ADG and G:F were greater ( < 0.01) for pigs fed diet M955 or the diets with added iP than for pigs fed the NB diet. Serum tartrate-resistant acid phosphatase activity on d 34 was greater ( < 0.01) for pigs fed the NB or HNB diets than for pigs fed the other diets. Bone breaking strength and P absorption (g/d) were greater ( < 0.01) for pigs fed diet M955 or the diets with iP than for pigs fed the NB or HNB diets. Pigs fed diet M955 absorbed greater ( < 0.01) percentages of P and Ca and had less ( < 0.01) fecal excretion of P (g/d and %) and Ca (%) than pigs fed the other diets. In conclusion, the LPA genetic trait was effective in hulled and hull-less barley in isocaloric diets fed to young pigs. Pigs fed the diet with LPA M955 consumed 31% less P and excreted 78% less fecal P and 30% less fecal Ca than pigs fed the diet with NB + iP that was equal to diet M955 in aP. Therefore, LPA barley, especially M955 with 95% aP, will reduce the use of iP in swine diets, reduce P pollution from swine manure, and support the goal of achieving global P sustainability.

Two inositol hexakisphosphate kinases drive inositol pyrophosphate synthesis in plants

Inositol pyrophosphates are unique cellular signaling molecules with recently discovered roles in energy sensing and metabolism. Studies in eukaryotes have revealed that these compounds have a rapid turnover, and thus only small amounts accumulate. Inositol pyrophosphates have not been the subject of investigation in plants even though seeds produce large amounts of their precursor, myo-inositol hexakisphosphate (InsP6 ). Here, we report that Arabidopsis and maize InsP6 transporter mutants have elevated levels of inositol pyrophosphates in their seed, providing unequivocal identification of their presence in plant tissues. We also show that plant seeds store a little over 1% of their inositol phosphate pool as InsP7 and InsP8 . Many tissues, including, seed, seedlings, roots and leaves accumulate InsP7 and InsP8 , thus synthesis is not confined to tissues with high InsP6 . We have identified two highly similar Arabidopsis genes, AtVip1 and AtVip2, which are orthologous to the yeast and mammalian VIP kinases. Both AtVip1 and AtVip2 encode proteins capable of restoring InsP7 synthesis in yeast mutants, thus AtVip1 and AtVip2 can function as bonafide InsP6 kinases. AtVip1 and AtVip2 are differentially expressed in plant tissues, suggesting non-redundant or non-overlapping functions in plants. These results contribute to our knowledge of inositol phosphate metabolism and will lay a foundation for understanding the role of InsP7 and InsP8 in plants.

Barley (Hordeum vulgare L.) low phytic acid 1-1: an endosperm-specific, filial determinant of seed total phosphorus

Inositol hexaphosphate (Ins P6 or "phytic acid") typically accounts for 75 (± 10%) of seed total phosphorus (P). In some cases, genetic blocks in seed Ins P6 accumulation can also alter the distribution or total amount of seed P. In nonmutant barley (Hordeum vulgare L.) caryopses, ~80% of Ins P6 and total P accumulate in the aleurone layer, the outer layer of the endosperm, with the remainder in the germ. In barley low phytic acid 1-1 (Hvlpa1-1) seed, both endosperm Ins P6 and total P are reduced (~45% and ~25%, respectively), but germs are phenotypically wild type. This translates into a net reduction in whole-seed total P of ~15%. Nutrient culture studies demonstrate that the reduction in endosperm total P is not due to a reduction in the uptake of P into the maternal plant. Genetic tests (analyses of testcross and F2 seed) reveal that the Hvlpa1-1 genotype of the filial seed conditions the seed total P reduction; sibling seed in the same head of barley that differ in their Hvlpa1-1 genotype (heterozygous vs. homozygous recessive) differ in their total P (normal vs. reduced, respectively). Therefore, Hvlpa1 functions as a seed-specific or filial determinant of barley endosperm total P.

Increasing CO2 threatens human nutrition

Dietary deficiencies of zinc and iron are a substantial global public health problem. An estimated two billion people suffer these deficiencies, causing a loss of 63 million life-years annually. Most of these people depend on C3 grains and legumes as their primary dietary source of zinc and iron. Here we report that C3 grains and legumes have lower concentrations of zinc and iron when grown under field conditions at the elevated atmospheric CO2 concentration predicted for the middle of this century. C3 crops other than legumes also have lower concentrations of protein, whereas C4 crops seem to be less affected. Differences between cultivars of a single crop suggest that breeding for decreased sensitivity to atmospheric CO2 concentration could partly address these new challenges to global health.

The Effects of Inorganic Nitrogen form and CO(2) Concentration on Wheat Yield and Nutrient Accumulation and Distribution

Inorganic N is available to plants from the soil as ammonium [Formula: see text] and nitrate [Formula: see text]. We studied how wheat grown hydroponically to senescence in controlled environmental chambers is affected by N form ([Formula: see text] vs. [Formula: see text]) and CO(2) concentration ("subambient," "ambient," and "elevated") in terms of biomass, yield, and nutrient accumulation and partitioning. Wheat supplied with [Formula: see text] as a sole N source had the strongest response to CO(2) concentration. Plants exposed to subambient and ambient CO(2) concentrations typically had the greatest biomass and nutrient accumulation under both N forms. In general [Formula: see text]-supplied plants had higher concentrations of total N, P, K, S, Ca, Zn, Fe, and Cu, while [Formula: see text]-supplied plants had higher concentrations of Mg, B, Mn, and [Formula: see text][Formula: see text]-supplied plants contained amounts of phytate similar to [Formula: see text]-supplied plants but had higher bioavailable Zn, which could have consequences for human health. [Formula: see text]-supplied plants allocated more nutrients and biomass to aboveground tissues whereas [Formula: see text]-supplied plants allocated more nutrients to the roots. The two inorganic nitrogen forms influenced plant growth and nutrient status so distinctly that they should be treated as separate nutrients. Moreover, plant growth and nutrient status varied in a non-linear manner with atmospheric CO(2) concentration.

Mapping of quantitative trait loci for phytic acid and phosphorus contents in seed and seedling of mungbean (Vigna radiata (L.) Wilczek)

Phytic acid (PA) is the storage form of phosphorus (P) in seeds and plays an important role in the nutritional quality of food crops. There is little information on the genetics of seed and seedling PA in mungbean [Vigna radiata (L.) Wilczek]. Quantitative trait loci (QTL) were identified for phytic acid P (PAP), total P (TP), and inorganic P (IP) in mungbean seeds and seedlings, and for flowering, maturity and seed weight, in an F(2) population developed from a cross between low PAP cultivated mungbean (V1725BG) and high PAP wild mungbean (AusTRCF321925). Seven QTLs were detected for P compounds in seed; two for PAP, four for IP and one for TP. Six QTLs were identified for P compounds in seedling; three for PAP, two for TP and one for IP. Only one QTL co-localized between P compounds in seed and seedling suggesting that low PAP seed and low PAP seedling must be selected for at different QTLs. Seed PAP and TP were positively correlated with days to flowering and maturity, indicating the importance of plant phenology to seed P content.

Zinc absorption from low phytic acid genotypes of maize (Zea mays L.), Barley (Hordeum vulgare L.), and Rice (Oryza sativa L.) assessed in a suckling rat pup model

Dietary phytic acid is a major causative factor for low Zn bioavailability in many cereal- and legume-based diets. The bioavailability of Zn in seed of low phytic acid (lpa) variants of maize ( Zea mays L.), rice ( Oryza sativa L.), and barley ( Hordeum vulgare L.) was evaluated using a suckling rat pup model. Suckling rat pups (14 days old, n = 6-8/treatment) were fasted for 6 h and intubated with (65)Zn-radiolabeled suspensions prepared using seed produced by either wild-type (normal phytic acid) or lpa genotypes of each cereal. Test solutions were radiolabeled overnight (all genotypes) or immediately prior to intubation (barley genotypes). Pups were killed 6 h postintubation and tissues removed and counted in a gamma counter. Zn absorption was low from wild-type genotypes of maize (21, 33%) and rice (26%), and phytic acid reduction resulted in significantly higher Zn absorption, 47-52 and 35-52%, respectively. Zn absorption from wild-type barley incubated overnight was high (86-91%), and phytate reduction did not improve Zn absorption (84-90%), which is likely due to endogenous phytase activity. When the wild-type barley solutions were prepared immediately before intubation, Zn absorption was significantly lower (63, 78%) than from the lpa cultivars (92, 96%). Variation in seed or flour phenolic acid levels did not affect Zn absorption. Differences in seed Zn levels did not substantially affect Zn absorption. Thus, when phytic acid is abundant in a diet, it has a larger effect on Zn absorption than the level of Zn. Therefore, reducing the phytic acid content of staple cereal grains may contribute to enhancing Zn nutrition of populations consuming these staple foods.

Deletions in a dspm insert in a maize bronze-1 allele alter RNA processing and gene expression

The bz-m13 allele of the bronze-1 (bz) locus in maize contains a 2.2-kb defective Suppressor-mutator (dSpm) transposable element inserted in the second exon. We compared bz expression in bz-m13 and five derivatives in which the dSpm insertion had sustained deletions ranging from 2 to 1300 bp. Tissues homozygous for bz-m13 in the absence of Spm-s activity were found to contain from 5 to 13% of the enzymatic activity conditioned by a wild-type allele at the bz locus. Tissues homozygous for the deletion derivatives contained enzymatic activities ranging from less than 1% to 67%. These differences are closely correlated with the steady-state level of one of two alternatively spliced transcripts. In all alleles bz transcription proceeds through the dSpm insert. Subsequent RNA processing uses the donor site of the single bz intron and either one of two alternative acceptor splice sites (AS1 and AS2) located within the dSpm sequence. Use of the AS1 removes all but 2 bp of dSpm sequence and produces the 1.8-kb transcript whose level corresponds closely to the level of enzymatic activity. Use of AS2 produces a transcript which retains more than 600 bp of dSpm sequence. Those derivatives in which AS2 is either deleted or inactivated have substantially increased levels of both the 1.8-kb transcript and enzymatic activity. We therefore document one sequence of events which began with the insertion of a transposable element and resulted in novel and stable introns which retain element-derived sequence and which in certain cases permit substantial host-gene expression.

Neither a zinc supplement nor phytate-reduced maize nor their combination enhance growth of 6- to 12-month-old Guatemalan infants

After age 6 mo, the combination of breast-feeding and unfortified plant-based complementary feeding provides inadequate zinc (Zn). Additionally, high phytate intakes compromise the bioavailability of zinc. Our principal objective in this randomized controlled, doubly masked trial was to determine the effect of substituting low-phytate maize, a daily 5-mg zinc supplement, or both, in infants between ages 6-12 mo on impaired linear growth velocity, a common feature of zinc deficiency. In the Western Highlands of Guatemala, 412 infants were randomized to receive low-phytate or control maize. Within each maize group, infants were further randomized to receive a zinc supplement or placebo. Length, weight, and head circumference were measured at 6, 9, and 12 mo of age. There were no significant differences between the 2 maize groups or between the Zn supplement and placebo groups and no treatment interaction was observed for length-for-age (LAZ), weight-for-length (WLZ) or head circumference Z-scores. Overall mean (+/- SD) Z-scores at 6 mo for combined treatment groups were: LAZ, -2.1 +/- 1.1; WLZ, 0.7 +/- 1.0; and head circumference Z-score, -0.7.0 +/- 1.0. At 12 mo, these had declined further to: LAZ, -2.5 +/- 1.1; WLZ, -0.0 +/- 0.9; and head circumference Z-score, -0.9 +/- 1.1; 83.3% were stunted and 2% were wasted. Low linear growth in older Guatemalan infants was not improved with either low-phytate maize or a daily 5-mg zinc supplement. Low contribution of maize to the complementary food of the infants negated any potential advantage of feeding low-phytate maize.

Effect of graded levels of iron, zinc, and copper supplementation in diets with low-phytate or normal barley on growth performance, bone characteristics, hematocrit volume, and zinc and copper balance of young swine1

Fifty crossbred barrows with an average initial age of 31 d and BW of 9.94 kg were used in a 28-d experiment to evaluate the effect of a low-phytic acid (LPA) barley mutant (M) M955, a near-isogenic progeny of the normal barley (NB) cultivar Harrington with about 90% less phytate than NB, to increase the utilization of Fe, Zn, and Cu compared with diets containing NB. The response criteria were growth performance, hematocrit volume, metacarpal bone characteristics, and the apparent absorption, retention, and excretion of Zn and Cu. The 2 barley cultivars (NB and M955) and the 5 trace mineral (TM) treatment concentrations of Fe and Zn (0, 25, 50, 75, and 100% of the requirement as FeSO(4) and ZnSO(4)) and Cu (0, 40, 80, 120, and 160% of the requirement as CuSO(4)) made 10 treatments in a factorial arrangement. Available P was equalized at 0.33% in all diets by adding monosodium phosphate to the basal diet containing NB, and all diets contained 0.65% Ca. Diets were adequate in all other nutrients. Barley and soybean meal were the only sources of phytate in the practical diets that also contained spray-dried whey. The barrows were fed the diets to appetite in meal form twice daily in individual metabolism crates. There were no barley cultivar x TM treatment interactions, and there were no differences between the NB and M955 barley cultivars for any of the response criteria measured. However, for the TM treatments, there were linear increases (P < or = 0.05) in ADFI, ADG, hematocrit volume, metacarpal bone breaking strength and ash weight, and the apparent absorption, retention, and excretion (mg/d) of Zn and Cu. In conclusion, the LPA barley had no effect on the response criteria in this experiment, apparently because of the small increase in the availability of the endogenous trace minerals in the practical diets containing M955 compared with NB. However, increasing the supplementation of Fe and Zn from 0 to 100% (160% for Cu) of the requirement resulted in linear increases in growth performance, hematocrit volume, metacarpal bone strength and ash weight, and the apparent absorption, retention, and excretion of Zn and Cu. Therefore, these results indicate that the inorganic trace mineral supplementation of practical diets for young pigs should not be less than the National Research Council requirements for swine.

Barley (Hordeum vulgare L.) inositol monophosphatase: gene structure and enzyme characteristics

The cellular myo-inositol (Ins) pool is important to many metabolic and signaling pathways in plants. Ins monophosphatase (IMPase; EC 3.1.3.25) activity is essential for the de novo synthesis of myo-Inositol (Ins), and for recycling of Ins in Ins(1,4,5)P3. However, proteins encoded by at least one family of IMP genes also have L-galactose-1-P phosphatase activity important to ascorbic acid synthesis, indicating a bifunctionality that links these two branches of carbon metabolism. As part of research into the regulation of Ins synthesis and supply during seed development, the barley IMP-1 gene and gene products were studied. The 1.4 kb barley IMP-1 promoter contains one low temperature response element (RE), two heat shock REs, one gibberellin and two auxin REs, and five sugar REs. Barley IMP-1 is expressed in all tissues assayed, and expression levels were not greatly altered by abiotic stress treatments. Reduced use of Ins for Ins P6 synthesis in developing seed of barley low phytic acid (lpa) mutants results in Ins accumulation, and IMP-1 expression is reduced in proportion to the increase in Ins level. The barley recombinant enzyme had a lower Km, indicating higher affinity, for D/L-Ins(3)P1 (Km = 9.7 microM) as compared with reported Km (Ins P1) values for other eukaryotic IMPases (43-330 microM) or with a reported Km (L-Gal-1P) of 150 microM for a kiwifruit (Actinidia deliciosa) enzyme. These and other data indicate that the barley IMP-1 gene is regulated at least in part in response to Ins metabolic needs, and that the enzyme it encodes displays catalytic properties well suited for a role in Ins synthesis, in addition to other roles as an L-gal-1-P phosphatase important to ascorbate synthesis, or as an IMPase important to Ins(1,4,5)P3 signal recycling.

Intestinal excretion of endogenous zinc in Guatemalan school children

The intestine is the major route of excretion of endogenous zinc (Zn) and has a key role in maintaining Zn homeostasis. The principal objective of this paper is to provide an interpretative report of quantities of endogenous fecal Zn (EFZ) excreted by rural Guatemalan school children fed either normal or low phytate maize as their principal food staple. EFZ was measured by a Zn stable isotope technique. EFZ did not differ between control and low phytate maize groups. The overall EFZ (n = 53) was (mean +/- SD) 1.56 +/- 0.69 mg Zn/d or 0.07 +/- 0.03 mg Zn x kg body wt(-1) x d(-1). EFZ was not correlated with the quantity of Zn absorbed. The estimated EFZ at the level of absorption that matched the physiologic requirement (EFZ(PR)) did not differ from the above mean value. The EFZ(PR) of 0.07 +/- 0.03 mg Zn/kg body wt is twice the value currently used in the estimation of Dietary Reference Intakes. Supported by other recent childhood data, these results suggest that the current estimates of EFZ(PR) used in the calculation of Zn requirements for children are misleadingly low.

Comparison of the phosphorus and mineral concentrations in bran and abraded kernel fractions of a normal barley (Hordeum vulgare) cultivar versus four low phytic acid isolines

Phytic acid consists of 65-80% of the total phosphorus (P) in cereal grains. Its salts are concentrated in the germ and aleurone layers, which are typically removed during milling. We hypothesize that concentrations of different types of P and minerals in milled products will be greatly altered in low phytic acid (lpa) barleys. Seeds of cv. Harrington (control) and four lpa isolines-lpa1-1, lpa2-1, lpa3-1, and M955-were abraded by a laboratory method into five surface layer and four remaining kernel fractions. Results show that phytic acid in the four lpa lines ranged from 75% to 5% of the control. The decrease in phytic acid P concentration was matched almost equally by an increase in inorganic P, so that the rest of P (the sum of all P-containing compounds other than phytic acid P and inorganic P) and total P levels remained relatively unchanged among the five genotypes. These trends were also observed for the processed fractions. The major mineral elements in barley seeds were P, K, Mg, S, and Ca, while minor ones were Fe, Zn, Mn, Cu, and Ba. All types of P and other minerals measured were generally concentrated in the outer layers of the grain. Although there were substantial differences in mineral contents of bran fractions among genotypes, the level of phytic acid P had little effect on mineral contents in whole or abraded kernels. One major exception was Fe, which had the highest level in all tissues of M955 genotype. The above findings were all confirmed by analyzing another set of barley samples grown in a different environment. Thus, in general, breeding lpa barleys does not lead to reduced mineral contents in whole grains or elevated mineral levels in milled products.

Effects of low phytate barley (Hordeum vulgare L.) on zinc utilization in young broiler chicks

Two 21-d experiments were conducted to evaluate the effects of low phytate barley (LPB) on Zn utilization by young broiler chicks and to determine the contribution of endogenous phytase, present in LPB. In the first experiment, ninety-six 1-d-old male chicks were assigned to a 2 x 3 factorial arrangement of treatments (4 pens of 4 chicks/treatment). Factors were barley type [wild-type barley (WTB) and LPB mutant M 955] and supplemental Zn (0, 10, or 20 mg of Zn/kg). In the second experiment, two hundred forty 1-d-old straight-run broiler chicks were assigned to a 2 x 2 x 3 factorial arrangement of treatments (4 pens of 5 chicks/treatment). Factors were barley type (WTB and LPB), autoclave treatment [nonautoclaved or autoclaved (121 degrees C, 20 kg/cm(2), 20 min)], and supplemental Zn (0, 10 or 20 mg of Zn/kg). Barley made up 60% of the diets and was the only source of phytate. On average, basal diets contained 26 mg of Zn/kg. Feed intake and body weight gain were greater (P < 0.05) in broilers fed LPB compared with WTB in experiment 2. Zinc concentration in toes and tibias were affected (P < 0.0001) by barley type (LPB > WTB) and supplemented Zn levels (20 > 10 > 0 mg of Zn/kg), and significant barley type x Zn interactions were also observed in both experiments. Substitution of LPB for WTB increased tibia and toe Zn by 46 and 25%, respectively, an increase comparable to that achieved with supplementing the diet with 20 mg of Zn/kg. No effect of autoclaving was observed for any variable in experiment 2. Retention of P and Zn was higher (P < 0.001) in chicks fed LPB compared with WTB in both experiments. Zinc retention was influenced (P < 0.0001) by dietary Zn, and barley type x Zn level interactions (P < 0.05) were observed in both experiments. Chicks fed LPB utilized more dietary Zn and P than those fed WTB, and this improved mineral utilization was not due to endogenous phytase present in barley.

Low-phytate barley cultivars improve the utilization of phosphorus, calcium, nitrogen, energy, and dry matter in diets fed to young swine

A 28-d experiment was conducted using 45 crossbred barrows with an average initial BW of 9.5 kg and age of 35 d to evaluate low-phytate barley (LPB) mutants (M) M422, M635, and M955, which were hulled, near-isogenic progeny of the normal barley (NB) Harrington and had 47, 66, and 80% less phytic acid, respectively, than NB. A hull-less LPB, M422-H, which was not near-isogenic to the other cultivars, was also evaluated. Apparent nutrient balance, bone measurements, and growth performance were the response criteria evaluated. The barrows were fed the diets to appetite in meal form in individual metabolism crates. Barley and soybean meal were the only sources of phytic acid. Dietary protein supplementation and ME/kg were equalized in all diets. The treatments were diets containing NB, M422, M635, or M422-H without or with added inorganic P (iP), or M955 without added iP. Diets with added iP contained 0.30% available P (aP), the same concentration of aP provided by the diet containing M955 without added iP. There were linear increases (P < or = 0.02) in ADG, G:F, metacarpal and radius bone strength, and fat-free dry weight, and in the absorption and retention (g/d and % of intake) of P and Ca with increasing dietary concentration of aP from the near-isogenic cultivars NB, M422, M635, or M955 without added iP. There were linear decreases in the grams (P < or = 0.02) and percentages (P < 0.001) of P and Ca excreted per day with increasing dietary concentration of aP without added iP. There were no responses for N or energy balance. Growth performance and bone response criteria did not differ for barrows fed the diet containing M955 or the near-isogenic diets containing NB, M422, or M635 with added iP. However, barrows fed the diet containing M955 had greater (P < or = 0.02) percentages of P, N, and energy absorption and retention, Ca absorption, and DM digestibility and had less (P < or = 0.02, g/d and %) excretion of P, N, energy, and Ca (g) per day than barrows fed the diets containing the near-isogenic NB or LPB cultivars with added iP. When dietary aP was equalized with iP, the excretion of P in feces plus urine (g/d) was reduced by 20.2, 27.9, and 44.6%, respectively, in barrows fed the diets containing M422 + iP, M635 + iP, or M955 compared with barrows fed the diet containing NB + iP. Energy utilization did not differ for barrows fed the diets containing hulled or hull-less LPB when ME/kg was equalized with lard. In conclusion, the apparent utilization of P and Ca, the bone strength and fat-free dry weight, and growth performance increased with increasing dietary concentration of aP provided by LPB, in association with linear decreases in P and Ca excretion. Barrows fed the diet containing M955 also had greater utilization and less excretion of P, Ca, N, energy, and DM than barrows fed the diets containing the near-isogenic NB or LPB cultivars with added iP to equalize aP at 0.30%.

The effects of phytase supplementation on nutrient digestibility, plasma parameters, performance and carcass traits of pigs fed diets based on low-phytate barley without inorganic phosphorus

A total of 80 crossbred pigs (25.5 ± 2.6 kg) were assigned to one of eight dietary treatments. A positive control, based on Harrington barley, was formulated to meet requirements for total phosphorus. Three experimental diets (low in total phosphorus) were formulated based on either Harrington barley (0.28% phytate phosphorus) or the low phytate genotypes LP422 (0.14% phytate phosphorus) and LP 635 (0.09% phytate phosphorus). The four diets were fed with and without 1000 FTU kg-1 phytase. Calcium and phosphorus digestibility were significantly higher (P < 0.05) as a result of supplementation with phytase. For the barley diets formulated without dicalcium phosphate, calcium digestibility averaged 69.6, 73.3 and 72.2% while phosphorus digestibility averaged 36.5, 50.5 and 57.7% for pigs fed the Harrington, LP 422 and LP 635 diets, respectively. The addition of phytase to the diet consistently reduced the percentage of phosphorus excreted in feces and fecal phosphorus excretion declined as the level of phytate in the barley declined. The addition of phytase tended to improve weight gain (P < 0.10) and significantly improved feed conversion (P < 0.05). For pigs fed the barley diets formulated without dicalcium phosphate, daily gain averaged 0.90, 0.99 and 1.01 kg d-1 while feed conversion averaged 2.70, 2.39 and 2.38 for the Harrington, LP 422 and LP 635 diets, respectively. The overall results of this experiment indicate that the performance of pigs fed diets containing low-phytate barley formulated without a source of inorganic phosphorus is at least equal to that of pigs fed diets containing normal-phytate barley and inorganic phosphorus. In addition, the increased availability of organic phosphorus reduced the amount of phosphorus excreted thus reducing the amount of phosphorus that can potentially pollute the environment. Key words: Low phytate barley, phytase, pigs, performance, digestibility

Zinc absorption in Guatemalan schoolchildren fed normal or low-phytate maize

BACKGROUND

Poor bioavailability of zinc from high-phytate diets is an important contributory factor to zinc deficiency in low-income populations.

OBJECTIVE

The objective of this study was to determine the effect of low-phytate maize consumption on zinc absorption.

DESIGN

The participants were apparently healthy children from the Central Highlands of Guatemala. Sixty children (20 per group) were randomly assigned to be fed only the low-phytate maize or 1 of 2 control maizes, the isohybrid wild-type maize or a local maize, for a 10-wk period. During the final week, the fractional absorption of zinc for all meals was measured during 1 d with the use of zinc stable isotopes and a dual isotope ratio technique based on urine enrichment data.

RESULTS

Mean (+/-SD) phytate intakes for the low-phytate, wild-type, and local maize groups were 1536 +/- 563, 2056 +/- 517, and 2253 +/- 687 mg/d, respectively. Corresponding zinc intakes were 8.6 +/- 2.5, 8.1 +/- 2.0, and 9.7 +/- 2.6 mg/d, and the dietary phytate:zinc molar ratios were 18 +/- 5, 26 +/- 6, and 23 +/- 5. Corresponding fractional absorptions of zinc were 0.32 +/- 0.07, 0.28 +/- 0.07, and 0.29 +/- 0.06. The respective values for total absorbed zinc were 2.72 +/- 0.88, 2.30 +/- 0.96, and 2.78 +/- 1.04 mg/d. No significant differences in either the fractional absorption of zinc or total absorbed zinc were seen between the maize groups.

CONCLUSION

Under the conditions of the present study, zinc absorption was not increased by the long-term use of low-phytate maize in children whose major dietary staple is maize.

The concentrations and distributions of phytic acid phosphorus and other mineral nutrients in wild-type and low phytic acid Js-12-LPA wheat (Triticum aestivum) grain parts

Concentrations of P, phytic acid (myo-inositol hexakisphosphate, IP6), and other mineral storage elements were studied in wild-type and low phytic acid (lpa) genotype Js-12-LPA wheat (Triticum aestivum L.) embryos and rest-of-grain fractions. Environmental scanning electron microscopy images revealed a decreased average size and an increased number of aleurone layer globoids in lpa grains compared with the wild type. Energy-dispersive X-ray analyses of unfixed aleurone layer and scutellum cell cytoplasm revealed mainly C, O, P, K, and Mg in both grain types. The starchy endosperm contained virtually no P, K, or Mg, demonstrating no shift of mineral nutrients to that compartment. Scanning transmission electron microscopy – energy-dispersive X-ray analyses of scutellum and aleurone layer globoids in both genotypes revealed that P, K, and Mg were the main mineral nutrients in globoids with low amounts of Ca, Fe, and Zn. Traces of Mn were only in scutellum globoids. Total P was similar between genotypes for the rest-of-grain fractions, which are 97% of grain mass. The main inositol phosphate was IP6, but a small amount of IP5 was present. Both lpa grain fractions exhibited major reductions in IP6 compared with the wild type and a threefold increase in inorganic P. The concentration of K decreased in both fractions, while Ca increased 25% in the Js-12-LPA rest-of-grain compared with the wild type. The lack of large differences in mineral concentration and distribution between the wild type and Js-12-LPA indicates that there is no direct role of localization of IP6 synthesis in mineral distribution.

Absorption of calcium from tortilla meals prepared from low-phytate maize

BACKGROUND

Calcium fortification of maize has been achieved for millennia in Central America by the process of nixtamalization. Bioavailability of calcium is, however, compromised by phytate, which is present in large quantities in maize kernels and is only modestly reduced by nixtamalization.

OBJECTIVE

The objective was to compare the absorption of calcium from tortilla meals prepared from low-phytate maize with that from meals prepared from maize with typical phytate content.

DESIGN

At 1-mo intervals, 5 healthy adult women were fed 2 test meals of approximately 140 g tortillas in lieu of breakfast. On one occasion, the tortillas were prepared from maize with approximately 60% phytate reduction, and, on the other occasion, they were prepared from the matching isohybrid wild-type maize. Beginning midway through the test meal, (44)Ca (0.3 mg/kg body wt) was administered in water as an extrinsic label; (42)Ca (0.06 mg/kg body wt) was administered intravenously immediately after the test meal. Isotope ratios of (42)Ca to (43)Ca and of (44)Ca to (43)Ca were measured by inductively coupled plasma mass spectrometry in urine collected as an 8-h pool from the period 16-24 h after intravenous tracer administration and prepared by the oxalate precipitation method. Fractional absorption of calcium was determined by using a dual-isotope ratio technique.

RESULTS

Mean fractional absorption of calcium from tortillas prepared from the low-phytate maize (0.50 +/- 0.03) was significantly (P = 0.003) greater than that from tortillas prepared from the control maize (0.35 +/- 0.07).

CONCLUSION

The increase in the quantity of calcium absorbed could be of practical importance for calcium nutriture when the intake of dairy products is limited.

myo-Inositol and sucrose concentrations affect the accumulation of raffinose family oligosaccharides in seeds

Raffinose family oligosaccharides (RFOs) fulfil multiple functions in plants. In seeds, they possibly protect cellular structures during desiccation and constitute carbon reserves for early germination. Their biosynthesis proceeds by the transfer of galactose units from galactinol to sucrose. Galactinol synthase (GolS), which mediates the synthesis of galactinol from myo-inositol and UDP-galactose, has been proposed to be the key enzyme of the pathway. However, no significant relationship was detected between the extractable GolS activity and the amount of RFOs in seeds from seven pea (Pisum sativum L.) genotypes selected for high variation in RFO content. Instead, a highly significant correlation was found between the levels of myo-inositol and RFOs. Moderately strong relationships were also found between sucrose and RFO content as well as between myo-inositol and galactinol. Further evidence for a key role of myo-inositol for the synthesis of galactinol was obtained by feeding exogenous myo-inositol to intact pea seeds and by the analysis of four barley (Hordeum vulgare L.) low phytic acid mutants. In seeds of three of these mutants, the reduced demand for myo-inositol for the synthesis of phytic acid (myo-inositol 1,2,3,4,5,6-hexakisphosphate) was associated with an increased level in myo-inositol. The mutants seeds also contained more galactinol than wild-type seeds. The results suggest that the extent of RFO accumulation is controlled by the levels of the initial substrates, myo-inositol and sucrose, rather than by GolS activity alone.

Zinc absorption from low-phytate hybrids of maize and their wild-type isohybrids

BACKGROUND

Identification of allelic variants in a single gene that determine the phytate content of maize kernels and the subsequent breeding of low-phytate maize have facilitated studies designed to determine quantitatively the effects of maize phytate on the bioavailability of minerals in maize.

OBJECTIVE

The objective was to determine the relation between the fractional absorption of zinc (FAZ) and the phytate content and phytate:zinc molar ratios of maize tortillas prepared from hybrids with different phytate contents.

DESIGN

Six healthy adults were fed, as the only food for 2 d, maize tortillas prepared from 1 of 2 low-phytate mutants: lpa1-1 (lpa1-1-LP) or Nutridense Low Phytate (ND-LP), which have phytate reductions of approximately 60% and approximately 80%, respectively, compared with their respective wild-type isohybrids. Four additional subjects were fed tortillas prepared from the corresponding wild-type isohybrids (lpa1-1-WT and ND-WT) according to the same study design. Meals were extrinsically labeled with zinc stable isotopes, and FAZ was determined with a dual-isotope-tracer ratio technique. Overall FAZ values were examined in relation to dietary phytate and phytate:zinc molar ratios by using a mixed nonlinear regression model.

RESULTS

The mean (+/-SD) FAZ values from tortillas prepared from ND-LP, lpa1-1-LP, lpa1-1-WT, and ND-WT were 0.38 +/- 0.07, 0.28 +/- 0.04, 0.15 +/- 0.07, and 0.13 +/- 0.05, respectively. A negative relation (P < 0.001) was found between FAZ and both dietary phytate and the phytate:zinc molar ratio. The effect of dietary zinc (8-14 mg Zn/d) under these experimental conditions was not significant.

CONCLUSIONS

FAZ from maize tortillas is positively related to the extent of phytate reduction achieved with low-phytate hybrids.

Effect of phytase supplementation on phosphorus digestibility in low-phytate barley fed to finishing pigs

Forty crossbred barrows (Camborough 15 Line female x Canabred sire) weighing an average of 79.6 +/- 8.0 kg were used in a factorial design experiment (5 barleys x 2 enzyme levels) conducted to determine the effects of phytase supplementation on nutrient digestibility in low-phytate barleys fed to finishing pigs. The pigs were assigned to one of 10 dietary treatments comprised of a normal 2-rowed, hulled variety of barley (CDC Fleet, 0.26% phytate) or 2 low-phytate hulled genotypes designated as LP422 (0.14% phytate) and LP635 (0.09% phytate). A normal, hulless barley (CDC Dawn, 0.26% phytate) and a hulless genotype designated as LP422H (0.14% phytate) were also included. All barleys were fed with and without phytase (Natuphos 5000 FTU/kg). The diets fed contained 98% barley, 0.5% vitamin premix, 0.5% trace mineral premix, 0.5% NaCl and 0.5% chromic oxide but no supplemental phosphorus. The marked feed was provided for a 7-day acclimatization period, followed by a 3-day faecal collection. In the absence of phytase, phosphorus digestibility increased substantially (P < 0.05) as the level of phytate in the barley declined. For the hulled varieties, phosphorus digestibility increased from 12.9% for the normal barley (0.26% phytate) to 35.3 and 39.8% for the two low-phytate genotypes (0.14 and 0.09% phytate respectively). For the hulless varieties, phosphorus digestibility increased from 9.2% for the normal barley (0.26% phytate) to 34.7% for the hulless variety with 54% of the normal level of phytate (0.14% phytate). In contrast, when phytase was added to the diet, there was little difference in phosphorus digestibility between pigs fed normal barley and those fed the low-phytate genotypes (significant barley x enzyme interaction, P = 0.01). For the hulled varieties, phosphorus digestibility was 50.1% for the barley with the normal level of phytate (0.26% phytate) compared with 51.1 and 52.4% for the varieties with 54 and 35% of the normal level of phytate (0.14 and 0.09% phytate respectively). For the hulless varieties, phosphorus digestibility increased from 47.1% for the normal barley (0.26% phytate) to 54.4% for the hulless variety with 54% of the normal level of phytate (0.14% phytate). In conclusion, both supplementation with phytase and selection for low-phytate genotypes of barley were successful in increasing the digestibility of phosphorus for pigs. Unfortunately, the effects did not appear to be additive. Whether or not swine producers will choose low-phytate barley or supplementation with phytase as a means to improve phosphorus utilization, will likely depend on the yield potential of low-phytate barley and the additional costs associated with supplementation with phytase.

Evaluation of low-phytate corn and barley on broiler chick performance

Grains produced by low-phytate barley and corn isolines homozygous for each species' respective low phytic acid 1-1 allele were compared to grain produced by near-isogenic normal or wild-type barley and corn in broiler chick feeds. Cobb x Cobb (384) chicks were used in a 10-d study. A randomized complete block design with a factorial arrangement of 2 x 2 x 3 was used with 4 replicates (8 chicks / replicate) per treatment. Twelve isocaloric and isonitrogenous treatment diets were formulated to contain 2 types of grain (barley and corn), 2 levels of grain (40% and 60%), and 3 sources of available P (wild-type grain, wild-type P-supplemented grain, and low-phytate grain). Growth parameters, bone parameters, total bone mineral, and apparent digestibilities were measured. The mean growth and bone responses were 1) higher for barley diets compared to corn diets, 2) higher for 60% grain inclusion compared to 40%, 3) higher for low-phytate compared to wild-type grains, and 4) not different for low-phytate compared to P-supplemented wild-type grain diets. Chicks fed low-phytate-based diets excreted 33 and 43% less P than chicks fed wild-type and P-supplemented wild-type diets, respectively. Correlations between percentage bone ash, total bone ash, and bone strength indicated a strong relationship and appear to support the use of bone strength analysis as a simpler method than ash content determination as an indication of P status. Feeding low-phytate grains will reduce the need for supplemental P in chick diets.

myo-Inositol-1,2,3,4,5,6-hexakisphosphate

myo-Inositol-1,2,3,4,5,6-hexakisphosphate (Ins P(6)) was first described as an abundant form of phosphorus in plant seeds and other plant tissues and dubbed "phytic acid". Subsequently it was found to be a common constituent in eukaryotic cells, its metabolism a basic component of cellular housekeeping. In addition to phosphate, myo-inositol (Ins) and mineral storage and retrieval in plant organs and tissues, other roles for Ins P(6) include service as a major metabolic pool in Ins phosphate and pyrophosphate pathways involved in signaling and regulation; possibly as an effector or ligand in these processes; as a form of energy currency and in ATP regeneration; in RNA export and DNA repair; and as an anti-oxidant. The relatively recent demonstration that pyrophosphate-containing derivatives of Ins P(6) can function as phosphate donors in the regeneration of ATP is reminiscent of the proposal, made four decades ago in studies of seed development, that Ins P(6) itself may serve in this function. Studies of Ins P(6) in non-plant systems rarely include the consideration that this compound might represent a significant fraction of cellular P; cellular phosphate nutrition has been viewed as either not interesting or of little importance. However, there may be few fundamental differences among diverse eukaryotes in both the metabolic pathways involving Ins P(6) and the spectrum of possible roles for it and its metabolites.

Phosphorus digestibility in low-phytate barley fed to finishing pigs

Twenty-four crossbred barrows (Camborough 15 Line female × Canabred sire) weighing an average of 51.3 ± 5.1 kg were used in a trial conducted during two periods according to a completely randomized block design. The pigs were assigned to one of six dietary treatments comprised of a normal two-rowed, hulled variety of barley (CDC Bold) or three low-phytate genotypes selected to contain approximately 68, 41 or 3% of the normal level of phytate. A normal hulless barley (CDC Dawn) and a hulless genotype selected to contain 54% of the normal phytate content were also included. The diets fed contained 99.5% barley and 0.5% chromic oxide. The marked feed was provided for a 7-d acclimatization period, followed by a 3-d fecal collection. At the conclusion of the first replicate, the pigs were assigned to different treatments and the procedure was repeated resulting in eight observations per treatment. Selection for phytate content had no effects on the apparent fecal digestibility of dry matter, crude protein or gross energy (P > 0.05). The digestibility coefficients for dry matter and energy were significantly higher for the hulless varieties of barley than the hulled genotypes. Phosphorus digestibility increased as the level of phytate in the barley declined. The linear relationship relating phosphorus digestibility (y) to phytate content (x) was: y = 67.7 − 12.54x       (r2= 0.64; P < 0.0001).

Seed phosphorus and inositol phosphate phenotype of barley low phytic acid genotypes

myo-Inositol-1,2,3,4,5,6-hexakisphosphate (Ins P(6) or "phytic acid") typically represents approximately 75% of the total phosphorus and >80% of soluble myo-inositol (Ins) phosphates in seeds. The seed phosphorus and Ins phosphate phenotypes of four non-lethal barley (Hordeum vulgare L.) low phytic acid mutations are described. In seeds homozygous for M 635 and M 955 reductions in Ins P(6), approximately 75 and >90% respectively, are accompanied by reductions in other Ins phosphates and molar-equivalent increases in Pi. This phenotype suggests a block in supply of substrate Ins. In seeds homozygous for barley low phytic acid 1-1 (lpa1-1), a 45% decrease in Ins P(6) is mostly matched by an increase in Pi but also accompanied by small increases in Ins(1,2,3,4,6)P(5). In seeds homozygous for barley lpa2-1, reductions in seed Ins P(6) are accompanied by increases in both Pi and in several Ins phosphates, a phenotype that suggests a lesion in Ins phosphate metabolism, rather than Ins supply. The increased Ins phosphates in barley lpa2-1 seed are: Ins(1,2,3,4,6)P(5); Ins(1,2,4,6)P(4) and/or its enantiomer Ins(2,3,4,6)P(4); Ins(1,2,3,4)P(4) and/or its enantiomer Ins(1,2,3,6)P(4); Ins(1,2,6)P(3) and/or its enantiomer Ins(2,3,4)P(3); Ins(1,5,6)P(3) and/or its enantiomer Ins(3,4,5)P(3) (the methods used here cannot distinguish between enantiomers). This primarily "5-OH" series of Ins phosphates differs from the "1-/3-OH" series observed at elevated levels in seed of the maize lpa2 genotype, but previous chromosomal mapping data indicated that the maize and barley lpa2 loci might be orthologs of a single ancestral gene. Therefore one hypothesis that might explain the differing lpa2 phenotypes is that their common ancestral gene encodes a multi-functional, Ins phosphate kinase with both "1-/-3-" and "5-kinase" activities. A putative pyrophosphate-containing Ins phosphate, possibly an Ins P(7), was also observed in the mature seed of all barley genotypes except lpa2-1. Barley M 955 indicates that at least for this species, the ability to accumulate Ins P(6) can be nearly abolished while retaining at least short-term ( approximately 1.0 years) viability.

Low-phytic acid barley improves calcium and phosphorus utilization and growth performance in growing pigs

Thirty-five crossbred barrows averaging 13.5 kg starting BW were used in a 35-d experiment to compare the availability of P and the nutritional value of two near-isogenic progeny of the barley cultivar 'Harrington'. Low-phytic acid barley (LPB, 0.35% total P, 0.14% phytic acid P) was homozygous for the low-phytic acid 1-1 allele, and the normal barley (NB, 0.35% total P, 0.24% phytic acid P) was homozygous for the normal allele of that gene. Pigs were fed individually twice daily in metabolism pens. Barley was the only source of phytate in semipurified diets, 1 to 3. Diet 1 contained 75% NB, 0.14% estimated available P (aP), and 0.50% Ca. Diet 2 contained 75% LPB, 0.22% aP, and 0.50% Ca. No inorganic P (iP) was added to Diets 1 and 2 in order to measure the animal response to the different concentrations of aP in these cultivars. Diet 3 was NB Diet 1 supplemented with iP to equal the concentration of aP in LPB Diet 2. Practical barley-soybean meal (SBM)-type diets, NB Diet 4 and LPB Diet 5, were formulated to meet all minimum nutrient requirements, and contained 0.30% aP and 0.65% Ca. For the semipurified diets, pigs fed LPB Diet 2 had higher (P < or = 0.05) bone ash weight, bone breaking strength, P absorption and retention, and Ca absorption and retention compared with pigs fed NB Diet 1, with a trend (P = 0.10) for pigs fed LPB Diet 2 to have a higher ADG and gain:feed ratio than pigs fed NB Diet 1. However, pigs fed LPB Diet 2 or NB Diet 3 were not different (P > or = 0.3) in growth performance, fresh bone weight, fat-free dry bone weight, bone ash, bone breaking strength, or N utilization. This indicates that LPB and NB were equal in nutritional value after supplementation of NB with iP to equal the estimated aP in LPB. For the practical barley-SBM diets, there were no differences (P > or = 0.4) between pigs fed NB Diet 4 or LPB Diet 5 for growth performance, fresh bone weight, bone breaking strength, the percentages of P and Ca utilization, or N, DE, and ME utilization. The use of LPB in pig diets reduced P excretion in swine waste by 55% and 16% in our semipurified and practical diets, respectively, compared with NB. Using our in vitro procedure designed to mimic the digestive system of the pig, the availability of P for pigs was estimated at 52% for LPB and 32% for NB.