Mineral Distributions in Milling Fractions of Low Phytic Acid Wheat

Low phytic acid (LPA) wheat (Triticum aestivum L.) is one approach to improving nutritional quality of wheat by reducing the major storage form of P and increasing the level of inorganic P (Pi), which is more readily absorbed by humans and other monogastric animals. A LPAmutant of wheat, designated Js-12-LPAwas isolated following mutagenesis. LPA and wild-type (WT) sib selections of hard red spring wheat families with the pedigree ‘Grandin’*4/Js-12-LPA were grown in replicated field trials in 2003 and 2004. Grain was milled on an experimental mill, and the distribution of P, phytic acid P (PAP), and Pi was measured in milling fractions. Mineral concentrations also were determined. LPA selections had elevated concentrations of Pi and Mg in flour fractions. The concentration of Pi in LPA flour was three times the concentration in WT flour, and Mg concentration in LPA flour was 25% greater than in WT flour. Therefore, P and Mg in LPAwheat appear to be redistributed within the kernel. The increase in Pi is similar to that observed for other LPA mutants and should improve the mineral nutrition of monogastric animals fed whole grain LPA wheat. As most wheat is milled for flour and bran, the detailed distribution of minerals in the LPAwheat should assist geneticists and nutritionists in assessing the value of this mutation. PHYTIC ACID (myo-inositol [1,2,3,4,5,6] hexakisphosphate, abbreviated PA) is the major storage form of P in grain. We have identified a low phytic acid (LPA) mutant of wheat (Guttieri et al., 2004). Previous reports of LPA crops include barley (Hordeum vulgare L.; Larson et al., 1998), rice (Oryza sativa L.; Larson et al., 2000), soybean [Glycine max (L.) Merr.; Wilcox et al., 2000], and maize (Zea mays L.; Raboy et al., 2000). Low phytic acid wheat is of interest as one approach to improving the nutritional quality of wheat fed to humans and livestock. Animals fed diets with LPA corn and barley have demonstrated greater feed efficiency, improved digestibility, better retention of P, Ca, and N, and significant decrease in P excretion (reviewed by Mendoza 2002). Human diets high in PA can lead to Zn deficiency, as PA is negatively correlated with Zn absorption. Phytic acid does not affect Cu absorption in humans, but slightly inhibits Mn absorption (reviewed by Lönnerdal 2002). PA forms insoluble complexes with Fe that are nutritionally unavailable at the pH of the small intestine. Diets high in PA and low in Fe can lead to Fe deficiency. However, in human populations with high Fe diets, the formation of PA–Fe complexes may provide protection against colon cancer by reducing Feinduced oxidative injury (reviewed by Minihane and Rimbach 2002). Raboy et al. (1991) evaluated the quantitative relationship between grain PAP and total P in two winter wheat populations. Variation in PAP was observed, ranging from 30 to 48% of the population means. However, this variation in PAP was highly and positively correlated with variation in grain total P (r 5 0.93 to 0.96). They did not observe redistribution of the storage form of P in the grain. To date, the only mechanism for altering the composition of P storage in wheat has been through the LPA mutant (Guttieri et al., 2004). Phytic acid is accumulated in globoid bodies in the aleurone of wheat. Upon milling, PA concentration is highest in bran. For example, six Pakistani wheat cultivars were surveyed for PA and mineral content in whole wheat flour, bran, and straight grade flour (Anjum et al., 2002). (Straight grade flour is the flour that is produced after the bran and germ have been removed.) Phytic acid content of bran ranged from 4.2 to 6.1%; PA content of whole wheat flour ranged from 1.2 to 2.2%; and PA content of straight grade flour ranged from 0.2 to 0.5%.Mineral concentrations also were greatest in bran. Copper in bran ranged from 29 to 52 mg kg, in straight grade flour from 5 to 12 mg kg, and in whole wheat flour from 10 to 18 mg kg. Iron concentration in bran, whole wheat flour, and straight grade flour ranged from 128 to 146 mg kg, 46 to 99 mg kg, and 26 to 46 mg kg, respectively. Zinc concentration in bran, whole wheat, and straight grade flour ranged from 44 to 81 mg kg, 21 to 28 mg kg, and 9 to 34 mg kg, respectively. Manganese similarly was of higher concentration in the bran. As PA forms insoluble complexes with nutritionally important minerals, decreasing the PA/ Pi ratio may alter the distribution of minerals among bran and flour fractions. Our initial characterization of the Js-12-LPA wheat and its WT sib selection suggested that mineral distribution was altered among milling fractions of LPA wheat (Guttieri et al., 2004). However, the number of genotypes sampled (one WT and one LPA) and the number of environments evaluated (one) in the initial description of the LPA mutant, while appropriate for initial characterization of the mutant, were insufficient to describe the effects of the trait through time and space. In addition, the mutagenesis of Js-12 caused mutations to the selected line beyond the LPA trait, as evidenced by short stature, friable straw, and poor yield; the previous report did not attempt to isolate the effects of the LPA mutant from the background effects of the mutagenized Js-12-LPA line. A similar analysis was conducted by Bryant et al. (2005), which measured P and mineral concentrations in milled ‘Kaybonnet’ rice and a LPA mutant of Kaybonnet produced in unreplicated Univ. of Idaho Research and Extension Ctr., P.O. Box 870, Aberdeen, ID 83210. E. Souza, current address: USDA-ARS Soft Wheat Quality Lab., 1640 Williams Way, Wooster, OH 44691. Received 25 Jan. 2006. *Corresponding author ([email protected]). Published in Crop Sci. 46:2692–2698 (2006). Crop Breeding & Genetics doi:10.2135/cropsci2006.01.0054 a Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: HIP, high inorganic P; LPA, low phytic acid; PA, phytic acid; PAP, phytic acid P; Pi, inorganic P; WT, wild-type. R e p ro d u c e d fr o m C ro p S c ie n c e . P u b lis h e d b y C ro p S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . 2692 Published online November 21, 2006