The timing and rate of phytic Acid accumulation in developing soybean seeds

The time-course of phosphorus (P) accumulation in the phytic acid fraction of developing soybean (Glycine max [L.] Merr. cv `Williams 79') seeds as well as the relation of phytic acid P to total P content were determined. Phytic acid was detected early in embryogenesis in field-grown soybeans and accumulated in a linear fashion throughout most of seed development. Although the observed rates of accumulation ranged from 18.7 micrograms phytic acid P per seed per day in pods positioned low on the plant to 33.6 micrograms in pods positioned high on the plant, the final concentrations were the same in all cases. Nearly all of the P translocated to developing seeds was incorporated into phytic acid from the third week after flowering until physiological maturity, with the sum of nonphytic acid P compounds remaining constant. Phytic acid accumulation was also linear throughout development when soybean plants were grown in solutions having nutrient P levels that ranged from severely limiting (2.0 milligrams P per liter) to excess (50 milligrams P per liter). However, there was a pronounced effect on rate of accumulation, which ranged from 7.2 micrograms phytic acid per seed per day with limiting nutrient P to 44.7 micrograms with excess P. The change in level of phytic acid accounted for most of the alteration in total seed P that was caused by altering the P status of the plants. These results support the view that phytic acid synthesis is involved in P homeostasis of the developing soybean seed.     

植物种子植酸研究进展

磷是植物生长发育所必需的大量营养元素。在种子发育过程中,植酸是磷的贮存库,对维持植物体内磷平衡有重要的作用。在种子萌发过程中,植酸酶分解植酸盐,释放磷、矿质营养和肌醇供幼苗生长。本文综述了近年来植物(作物)种子中植酸的生物合成途径、种子植酸含量的遗传、低植酸作物的育种等研究进展。首先,植酸生物合成途径中最初的反应底物为葡萄糖-6-磷酸,形成肌醇后,以肌醇为底物合成植酸共有两条路径:依赖脂类与不依赖脂类,目前,已分离鉴定若干植酸合成所需的关键酶及其编码基因,包括肌醇-3-磷酸合成酶、肌醇激酶、肌醇多磷酸盐激酶,以及参与植酸运输的ATP结合盒转运子。其次,利用作图群体及关联分析群体,分别在水稻(Oryza sativa L.)、白菜(Brassica rapa L.)、菜豆(Phaseolus vulgaris L.)等植物中鉴定出多个与种子植酸磷含量相关的遗传位点。第三,筛选获得有价值的低植酸突变体是培育低植酸作物的主要途径。当把低植酸作为育种目标时,可能会忽略种子植酸含量的降低给植物带来的不利影响,如何消除低植酸造成的不利影响,成为科学家们亟需解决的问题。     

Phytic acid and raffinose series oligosaccharides metabolism in developing chickpea seeds

Phytic acid and raffinose series oligosaccharides (RFOs) have anti-nutritional properties where phytic acid chelates minerals and reduces their bioavailability to humans and other animals, and RFOs cause flatulence. Both phytic acid and RFOs cannot be digested by monogastric animals and are released as pollutant-wastes. Efforts are being made to reduce the contents of these factors without affecting the viability of seeds. This will require a thorough understanding of their metabolism in different crops. Biosynthetic pathways of both metabolites though are interlinked but not well described. This study was made on metabolism of these two contents in developing chickpea (Cicer arietinum L cv GL 769) seeds. In this study, deposition of RFOs was found to occur before deposition of phytic acid. A decline in inorganic phosphorus and increase in phospholipid phosphorus and phytic acid was observed in seeds during development. Acid phosphatase was the major phosphatase in seed as well as podwall and its activity was highest at early stage of development, thereafter it decreased. Partitioning of ¹⁴ C label from ¹⁴ C-glucose and ¹⁴ C-sucrose into RFOs and phytic acid was studied in seeds in presence of inositol, galactose and iositol and galactose, which favored the view that galactinol synthase is not the key enzyme in RFOs synthesis.     

Fine mapping of the rice low phytic acid (Lpa1) locus

Phytic acid is the primary storage form of phosphorus (P) in cereal grains. In addition to being essential for normal seedling growth and development, phytic acid plays an important role in human and animal nutrition. The rice low phytic acid mutation lpa1 results in a 45% reduction in seed phytic acid with a molar equivalent increase in inorganic P. The Lpa1 locus was previously mapped to the long arm of chromosome 2. Using microsatellite markers and a recombinant inbred line population, we fine mapped this locus between the markers RM3542 and RM482, which encompass a region of 135 kb. Additional markers were developed from the DNA sequence of this region. Two of these markers further delimited the locus to a 47-kb region containing eight putative open reading frames. Cloning and molecular characterization of the Lpa1 gene will provide insight into phytic acid biosynthesis in plants. The markers reported here should also be useful in introgressing the low phytic acid phenotype into other rice cultivars.The mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.     

Phytic acid in green leaves

Phytic acid or phytate, the free‐acid form of myo‐inositolhexakiphosphate, is abundant in many seeds and fruits, where it represents the major storage form of phosphorus. Although also known from other plant tissues, available reports on the occurrence of phytic acid, e.g. in leaves, have never been compiled, nor have they been critically reviewed. We found 45 published studies with information on phytic acid content in leaves. Phytic acid was almost always detected when studies specifically tried to detect it, and accounted for up to 98% of total P. However, we argue that such extreme values, which rival findings from storage organs, are dubious and probably result from measurement errors. Excluding these high values from further quantitative analysis, foliar phytic acid‐P averaged 2.3 mg·g^?1, and represented, on average, 7.6% of total P. Remarkably, the ratio of phytic acid‐P to total P did not increase with total P, we even detected a negative correlation of the two variables within one species, Manihot esculenta. This enigmatic finding warrants further attention.     

Effect of phosphorus and zinc nutrition on soybean seed phytic Acid and zinc

The relationships between nutrient P and Zn levels and the phytic acid, P, and Zn concentrations in soybean (Glycine max L. Merr. cv `Williams 79') seed were studied. Phytic acid increased linearly from 4.2 to 19.2 milligrams per gram as nutrient P treatment was varied from 2.0 to 50 milligrams per liter and Zn was held constant at 0.05 milligrams per liter. Leaf P concentration during seed development was found to be closely related to the concentrations of seed P and phytic acid. Leaf and seed Zn concentrations both responded positively to increasing nutrient Zn treatment. The effects of P treatment on plant and seed P and phytic acid were largely independent of the effects of Zn treatment on leaf and seed Zn. Phytic acid to Zn molar ratios ranging from 3.6 to 33.8 were observed.

The effects of nutrient P treatments on the concentrations of phytic acid, seed P, and leaf P were also studied in the P-sensitive (gene np) cultivars `Harosoy' and `Clark' and their respective P-tolerant (gene Np) near-isogenic lines L66-704 and L63-1677. In general, the positive relationships observed among nutrient P, leaf P, seed P, and phytic acid concentrations were similar to those observed in the studies with Williams 79. When fertilized with low or moderate nutrient P (2.5 and 25.0 milligrams P per liter, respectively) no significant differences in any parameter were observed between Harosoy or Clark and their respective P-tolerant isolines. When fertilized with high nutrient P (100 milligrams P per liter), Harosoy seed had a significantly higher concentration of phytic acid (30 milligrams per gram) than did seed of its P-tolerant near-isogenic line L66-704 (24.2 milligrams per gram phytic acid), whereas no significant difference was observed between Clark and its P-tolerant near-isogenic line L63-1677 (22.8 and 21.6 milligrams per gram, respectively). Variation in the phytic acid concentrations in the mature seed of the cultivars and isolines more closely paralleled leaf P concentrations observed during seed development (49 days after flowering), than those observed at the onset of seed development (14 days after flowering). Electrophoresis and ion-exchange chromatography revealed that partially phosphorylated intermediates do not appear when phytic acid accumulation is greatly reduced by limiting the nutrient P or when accumulation is greatly accelerated by excess P.

     

Origin and seed phenotype of maize low phytic acid 1-1 and low phytic acid 2-1

Phytic acid (myo-inositol-1, 2, 3, 4, 5, 6-hexakisphosphate or Ins P(6)) typically represents approximately 75% to 80% of maize (Zea mays) seed total P. Here we describe the origin, inheritance, and seed phenotype of two non-lethal maize low phytic acid mutants, lpa1-1 and lpa2-1. The loci map to two sites on chromosome 1S. Seed phytic acid P is reduced in these mutants by 50% to 66% but seed total P is unaltered. The decrease in phytic acid P in mature lpa1-1 seeds is accompanied by a corresponding increase in inorganic phosphate (P(i)). In mature lpa2-1 seed it is accompanied by increases in P(i) and at least three other myo-inositol (Ins) phosphates (and/or their respective enantiomers): D-Ins(1,2,4,5,6) P(5); D-Ins (1,4,5,6) P(4); and D-Ins(1,2,6) P(3). In both cases the sum of seed P(i) and Ins phosphates (including phytic acid) is constant and similar to that observed in normal seeds. In both mutants P chemistry appears to be perturbed throughout seed development. Homozygosity for either mutant results in a seed dry weight loss, ranging from 4% to 23%. These results indicate that phytic acid metabolism during seed development is not solely responsible for P homeostasis and indicate that the phytic acid concentration typical of a normal maize seed is not essential to seed function.     

玉米中植酸代谢研究的策略

作物尤其是玉米的种子中积累了丰富的植酸。早先的研究侧重于降低种子中植酸的含量,但是随着人们对植酸认识的深入,发现植酸对于动、植物而言具有不可替代的生物功能。对于人和动物而言,植酸有抗营养作用,但也是重要的健康因子;对于植物而言,植酸及其代谢中间体的生物学功能却缺乏明确的研究。若要明确把握植酸的育种方向,就必须对植酸在植物中的合成过程有明确的认识。但自植酸被发现至今,人们对于其在高等植物中的合成过程仍然知之甚少,对其生物学功能更是缺乏全面的了解。本文综述了植酸代谢研究的现状,分析并总结了植酸的代谢通路,指出了植酸代谢研究的突破点,结合植酸代谢的研究特点和进展,比较了基因同源克隆、关联分析等4种最具潜力的研究策略。     

A novel phytase with sequence similarity to purple acid phosphatases is expressed in cotyledons of germinating soybean seedlings

Phytic acid (myo-inositol hexakisphosphate) is the major storage form of phosphorus in plant seeds. During germination, stored reserves are used as a source of nutrients by the plant seedling. Phytic acid is degraded by the activity of phytases to yield inositol and free phosphate. Due to the lack of phytases in the non-ruminant digestive tract, monogastric animals cannot utilize dietary phytic acid and it is excreted into manure. High phytic acid content in manure results in elevated phosphorus levels in soil and water and accompanying environmental concerns. The use of phytases to degrade seed phytic acid has potential for reducing the negative environmental impact of livestock production. A phytase was purified to electrophoretic homogeneity from cotyledons of germinated soybeans (Glycine max L. Merr.). Peptide sequence data generated from the purified enzyme facilitated the cloning of the phytase sequence (GmPhy) employing a polymerase chain reaction strategy. The introduction of GmPhy into soybean tissue culture resulted in increased phytase activity in transformed cells, which confirmed the identity of the phytase gene. It is surprising that the soybean phytase was unrelated to previously characterized microbial or maize (Zea mays) phytases, which were classified as histidine acid phosphatases. The soybean phytase sequence exhibited a high degree of similarity to purple acid phosphatases, a class of metallophosphoesterases.     

The role of phytic Acid in the wheat grain

The concentrations of adenosine triphosphate and phytic acid in testa, embryo plus scutellum, aleurone, and endosperm fractions from grain of Triticum vulgare cv. Insignia have been determined during development under both normal conditions and those of water stress. Phytic acid was not detected in the endosperm. In the embryo plus scutellum and aleurone fractions there was a rapid build-up of phytic acid, but the adenosine triphosphate level did not change markedly at this time. These results are not consistent with physiological roles previously suggested for phytic acid other than the role of phytin as a phosphorus and cation store for the germinating seed.     

Embryo-specific silencing of a transporter reduces phytic acid content of maize and soybean seeds

Phytic acid in cereal grains and oilseeds is poorly digested by monogastric animals and negatively affects animal nutrition and the environment. However, breeding programs involving mutants with less phytic acid and more inorganic phosphate (P(i)) have been frustrated by undesirable agronomic characteristics associated with the phytic acid-reducing mutations. We show that maize lpa1 mutants are defective in a multidrug resistance-associated protein (MRP) ATP-binding cassette (ABC) transporter that is expressed most highly in embryos, but also in immature endosperm, germinating seed and vegetative tissues. Silencing expression of this transporter in an embryo-specific manner produced low-phytic-acid, high-Pi transgenic maize seeds that germinate normally and do not show any significant reduction in seed dry weight. This dominant transgenic approach obviates the need for incorporating recessive lpa1 mutations to create maize hybrids with reduced phytic acid. Suppressing the homologous soybean MRP gene also generated low-phytic-acid seed, suggesting that the strategy might be feasible for many crops.     

转基因植物表达植酸酶研究进展

植酸是植物体内磷的主要存在形式,其绝大部分不能被单胃动物消化吸收,而随粪便排出体外造成环境污染;同时,植酸又是一种抗营养因子,它通过络合植物体内的一些营养成分而降低植物的营养价值。通过植物转基因方法使植物自身表达足量的植酸酶,以减小植酸带来的不利影响,是提高植物性饲料营养价值和控制环境磷污染的一种经济有效的措施。就转基因植物植酸酶的优势、研究现状、存在的问题及其发展前景进行了综述。     

Effect of phytic acid on postprandial serum uric acid level in healthy volunteers: a randomized,double-blind,crossover study

Abstract

Phytic acid, a constituent of various plants, has been related to health benefits. Phytic acid has been shown to inhibit purine nucleotide metabolism in vitro and suppress elevation of plasma uric acid levels after purine administration in animal models. This study investigated the effect of phytic acid on postprandial serum uric acid (SUA) in humans. This randomized, double-blind, crossover design study included 48 healthy subjects with normal fasting SUA. Subjects consumed a control drink and a phytic acid drink with purine-rich food, and serum and urine uric acid levels were measured for 360?min after purine loading. Phytic acid lowered the incremental area under the curve (0–360?min) and incremental maximum concentration of SUA after purine loading (p?<?0.05); tended to lower cumulative urinary uric acid excretion (0–360?min) after purine loading (p?<?0.10); and suppressed postprandial SUA in this clinical study. Altogether, our findings suggest that phytic acid may play a beneficial role in controlling postprandial SUA.     

Dephytinisation with Intrinsic Wheat Phytase and Iron Fortification Significantly Increase Iron Absorption from Fonio (Digitaria exilis) Meals in West African Women

Low iron and high phytic acid content make fonio based meals a poor source of bioavailable iron. Phytic acid degradation in fonio porridge using whole grain cereals as phytase source and effect on iron bioavailability when added to iron fortified fonio meals were investigated. Grains, nuts and seeds collected in Mali markets were screened for phytic acid and phytase activity. We performed an iron absorption study in Beninese women (n = 16), using non-dephytinised fonio porridge (FFP) and dephytinised fonio porridge (FWFP; 75% fonio-25% wheat), each fortified with ⁵⁷Fe or ⁵⁸Fe labeled FeSO₄. Iron absorption was quantified by measuring the erythrocyte incorporation of stable iron isotopes. Phytic acid varied from 0.39 (bambara nut) to 4.26 g/100 g DM (pumpkin seed), with oilseeds values higher than grains and nuts. Phytase activity ranged from 0.17±1.61 (fonio) to 2.9±1.3 phytase unit (PU) per g (whole wheat). Phytic acid was almost completely degraded in FWFP after 60 min of incubation (pH≈5.0, 50°C). Phytate∶iron molar ratios decreased from 23.7∶1 in FFP to 2.7∶1 in FWFP. Iron fortification further reduced phytate∶iron molar ratio to 1.9∶1 in FFP and 0.3∶1 in FWFP, respectively. Geometric mean (95% CI) iron absorption significantly increased from 2.6% (0.8–7.8) in FFP to 8.3% (3.8–17.9) in FWFP (P<0.0001). Dephytinisation of fonio porridge with intrinsic wheat phytase increased fractional iron absorption 3.2 times, suggesting it could be a possible strategy to decrease PA in cereal-based porridges.     

Determination of phytic acid by gas chromatography–mass spectroscopy: application to biological samples

A GC–MS method is reported for the determination of phytic acid based on purification by anion-exchange chromatography, enzymatic hydrolysis of phytic acid to myo-inositol and derivation to trimethylsilyl derivative, with scyllo-inositol as an internal standard. Analytical features of the method are: limit of detection 9 μg l⁻¹ phytic acid, linear working range 18–500 μg l⁻¹ phytic acid, and coefficient of variation 1.9%. The method has been successfully applied to a variety of biological samples: various rat organs (kidney, liver, brain and bone), human plasma and urine and kidney stones. A comparative study of sample treatments, including deproteization, lipid extraction and the presence of a chelator, is also reported. Phytic acid amounts found in rat organs ranged from 1.07 g kg⁻¹ for bone to 32.0 g kg⁻¹ for brain. Phytic acid in human plasma was of the order of 0.14 mg l⁻¹. In kidney stones, phytic acid was found in calcium containing stones.     

Application of 31P NMR to Monitor Phosphorus Compounds and their Changes During Germination of Legume Seeds

Extracts of embryonic axes and cotyledons of 19 species of legumeswere analysed by ³¹P nuclear magnetic resonance; the effectof different extraction procedures on the solubilization ofthe several phosphocompounds was investigated. The contentsof phytic acid, inorganic phosphate, phosphomonoesters and phosphodiesterswere determined. The relative contents of these phosphocompoundswere very different when embryonic axes and cotyledons werecompared, and were greatly influenced by the taxonomic affiliationof the corresponding species. Phytic acid and inorganic phosphatewere by far the major phosphocompounds found in cotyledon extracts;an unusual phosphodiester component was detected only in embryonicaxes and was particularly abundant in species belonging to theLotoideae sub-family. The changes in the amount of the phosphodiestercompound were followed during germination and the results suggestthat it is not a phosphorus reserve. Furthermore, this componentwas preferentially present in the roots of the new plants. Itwas partially hydrolysed by RNAse and to a smaller extent byproteases, but not affected by DNAse. The hypothesis that thisunusual component might be a ribonucleoprotein is discussed. Key words: ³¹P NMR, legumes, seed components, phosphorus compounds, solubilization