Phytate metabolism in Petunia pollen

Phytic acid has been detected in the anthers of young flower buds of Petunia hybrida, the amount increasing slowly as the flower develops until anther dehydration, when there was a more rapid increase in phytic acid content. In mature pollen, the phytic acid content was found to be 2.0 % by weight, of which 90 % was water soluble, while free myo-inositol was a relatively low 0.06 % by weight. Breakdown of phytic acid was initiated soon after pollen germination began, and its degradation products, myo-inositol and inorganic phosphate, were rapidly mobilized for phospholipid and pectin biosynthesis. Both are in high demand during pollen tube elongation. Utilization of myo-[2-³H]inositol for phospholipid biosynthesis was about five times that for pectin synthesis during the first few hours of pollen germination. The label in the phospholipid was identified as the myo-inositol moiety of phosphaltidylinositol, while the pectin material contained predominantly labelled arabinose, with smaller amounts of label in galacturonic acid, glucose and xylose. A chase experiment showed that the myo-inositol moiety of phosphatidylinositol was subject to a relatively rapid turnover, while the label in pectin was not. Labelling germinating pollen with [³²P]orthophosphate gave label in phosphatidic acid, phosphatidylinositol, phosphatidylethanolamine and phosphatidylcholine of the phospholipids. Phosphatidylinositol contained 30 % of this label initially, a proportion which declined to 10 % over longer periods of germination.     

小麦籽粒中植酸、戊聚糖含量及其与相关性状关系的研究

选用不同基因型小麦,测定了籽粒中植酸、蛋白质及戊聚糖的含量,并对其进行遗传相关分析,结果表明：(1)各性状在品种间存在显著性差异,且植酸的广义遗传力比较低;(2)植酸含量与蛋白质含量呈极显著的正相关,与戊聚糖呈极显著负相关。通过对参试的18个不同基因型小麦中植酸和戊聚糖含量进行聚类分析,可以将18个基因型小麦聚为四类,并初步认为豫麦47是参试品种中最适宜于用作饲用小麦。     

Enhancement of ABA responsiveness in wheat embryos by high temperature*†

Abstract. Mature wheat (Triticum aestivum L.) grain often possesses high-temperature dormancy which restricts the grain from germinating at warm temperatures (25–30°C). Isolated embryos from such grain exhibited little high-temperature dormancy when germinated in water. Dormancy was restored by the application of abscisic acid (ABA) to the embryos. The ability of ABA to block germination in isolated embryos was enhanced significantly by elevating the germination temperature. ABA was 100 times more effective in reducing embryonic germination at 30°C than at 15°C. These temperature effects on embryonic response to ABA are a useful system for studying the mechanism of ABA action in seed dormancy.     

Wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) multiple inositol polyphosphate phosphatases (MINPPs) are phytases expressed during grain filling and germination

At present, little is known about the phytases of plant seeds in spite of the fact that this group of enzymes is the primary determinant for the utilization of the major phosphate storage compound in seeds, phytic acid. We report the cloning and characterization of complementary DNAs (cDNAs) encoding one of the groups of enzymes with phytase activity, the multiple inositol phosphate phosphatases (MINPPs). Four wheat cDNAs (TaPhyIIa1, TaPhyIIa2, TaPhyIIb and TaPhyIIc) and three barley cDNAs (HvPhyIIa1, HvPhyIIa2 and HvPhyIIb) were isolated. The open reading frames ranged from 1548 to 1554 bp and the level of homology between the barley and wheat proteins ranged from 90.5% to 91.9%. All cDNAs contained an N-terminal signal peptide encoding sequence, and a KDEL-like sequence, KTEL, was present at the C-terminal, indicating that the enzyme was targeted to and retained within the endoplasmic reticulum. Expression of TaPhyIIa2 and HvPhyIIb in Escherichia coli revealed that the MINPPs possessed a significant phytase activity with narrow substrate specificity for phytate. The pH and temperature optima for both enzymes were pH 4.5 and 65 degrees C, respectively, and the K(m) values for phytate were 246 and 334 microm for the wheat and barley recombinant enzymes, respectively. The enzymes were inhibited by several metal ions, in particular copper and zinc. The cDNAs showed significantly different temporal and tissue-specific expression patterns during seed development and germination. With the exception of TaPhyIIb, the cDNAs were present during late seed development and germination. We conclude that MINPPs constitute a significant part of the endogenous phytase potential of the developing and germinating barley and wheat seeds.     

Effect of Germination on Vomitoxin Level in Grain

The present investigation clarified the effect of enzymes or other substances formed during the germination process on the vomitoxin level of contaminated oats. The studies found that oats containing vomitoxin germinated very poorly; the decrease in toxins was also slight. The amount of pure vomitoxin added to toxin-free grain decreased (barley 53 %, oats 40 %, wheat 20 %) during germination (5 d). In homogenized mixture of germinated grain (2.4 and 7 d) and toxic grain no decrease in toxin amount occurred during a 1–7 day period. In contrast, when germinating toxin free grains and toxic oats in a grain mixture the toxin level decreased at first, but later rose considerably. On the basis of these results, the utilization of germination processes for the improvement of grain containing vomitoxin is of questionable value.     

Identification and characterization of the soybean IPK1 ortholog of a low phytic acid mutant reveals an exon-excluding splice-site mutation

Phytic acid (myo-inositol 1, 2, 3, 4, 5, 6 hexakisphosphate) is an important constituent of soybean meal. Since phytic acid and its mineral salts (phytates) are almost indigestible for monogastrics, their abundance in grain food/feed causes nutritional and environmental problems; interest in breeding low phytic acid has therefore increased considerably. Based on gene mapping and the characteristics of inositol polyphosphates profile in the seeds of a soybean mutant line Gm-lpa-ZC-2, the soybean ortholog of inositol 1,3,4,5,6 pentakisphosphate (InsP₅) 2-kinase (IPK1), which transforms InsP₅ into phytic acid, was first hypothesized as the candidate gene responsible for the low phytic acid alteration in Gm-lpa-ZC-2. One IPK1 ortholog (Glyma14g07880, GmIPK1) was then identified in the mapped region on chromosome 14. Sequencing revealed a G?→?A point mutation in the genomic DNA sequence and the exclusion of the entire fifth exon in the cDNA sequence of GmIPK1 in Gm-lpa-ZC-2 compared with its wild-type progenitor Zhechun No. 3. The excluded exon encodes 37 amino acids that spread across two conserved IPK1 motifs. Furthermore, complete co-segregation of low phytic acid phenotype with the G?→?A mutation was observed in the F₂ population of ZC-lpa x Zhexiandou No. 4 (a wild-type cultivar). Put together, the G?→?A point mutation affected the pre-mRNA splicing and resulted in the exclusion of the fifth exon of GmIPK1 which is expected to disrupt the GmIPK1 functionality, leading to low phytic acid level in Gm-lpa-ZC-2. Gm-lpa-ZC-2, would be a good germplasm source in low phytic acid soybean breeding.     

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.     

Reduced phytic Acid content does not have an adverse effect on germination of soybean seeds

Altering the level of phytic acid phosphorus by nutritional means had no effect on the ability of soybean (Glycine max L. [Merr.], cv `Williams 79') seeds to germinate under laboratory or greenhouse conditions. Dry matter moved out of the cotyledons at similar rates whether the germinating seeds initially contained low (0.19), medium (0.59), or high (1.00 milligram per seed) phytic acid phosphorus. Growth of roots and shoots from 3 to 9 days after planting was similar for seeds containing low and medium levels of phytic acid phosphorus. The medium level of phytic acid resembles that found in field-grown seed, so it is clear that soybean seeds normally contain a phosphorus reserve far above that needed for germination and early seedling growth.     

The pattern and control of isoprenoid quinone and tocopherol metabolism in the germinating grain of wheat (Triticum vulgare)

1. The syntheses of ubiquinone-9 and plastoquinone-9 were used as parameters respectively of mitochondrial and proplastid development in the germinating wheat grain. 2. The changes in the amounts of the tocopherols were also studied and the possible biological significance of these changes is discussed. During germination, the dimethyl tocopherols of the resting grain are probably not utilized for the synthesis of α-tocopherol. 3. It was demonstrated that ubiquinone synthesis, and hence probably mitochondrial development, in the aleurone cells during germination, is independent of control by gibberellic acid from the embryo. 4. The influence of light on the syntheses of the isoprenoid quinones in the etiolated wheat shoot was investigated. In particular, illumination did not stimulate the synthesis of either α-tocopherol or α-tocopherolquinone.     

Mitochondrial Efficiency and Grain Yield in Wheat

Mitochondrial ADP/O and RC ratios have been determined in two-day-oldshoots of nine wheat (Triticum aestivum) varieties of knownaverage grain yield. Both ratios were highly correlated withaverage grain yield. ADP/O and RC ratios of germinating shootswere also correlated with yield within a variety when yieldwas varied by irrigation and different nitrogen fertilizer treatments.It is proposed that the observed correlations are the resultof mitochondrial ADP/O and RC ratios being partly controlledduring germination directly or indirectly by seed-based metabolismwhich reflects the metabolic activity and total carbohydratedeposited in seed during seed formation.     

The role of phytic acid in legumes: antinutrient or beneficial function?

This review describes the present state of knowledge about phytic acid (phytate), which is often present in legume seeds. The antinutritional effects of phytic acid primarily relate to the strong chelating associated with its six reactive phosphate groups. Its ability to complex with proteins and particularly with minerals has been a subject of investigation from chemical and nutritional viewpoints. The hydrolysis of phytate into inositol and phosphates or phosphoric acid occurs as a result of phytase or nonenzymatic cleavage. Enzymes capable of hydrolysing phytates are widely distributed in micro-organisms, plants and animals. Phytases act in a stepwise manner to catalyse the hydrolysis of phytic acid. To reduce or eliminate the chelating ability of phytate, dephosphorylation of hexa- and penta-phosphate forms is essential since a high degree of phosphorylation is necessary to bind minerals. There are several methods of decreasing the inhibitory effect of phytic acid on mineral absorption (cooking, germination, fermentation, soaking, autolysis). Nevertheless, inositol hexaphosphate is receiving increased attention owing to its role in cancer prevention and/or therapy and its hypocholesterolaemic effect.     

Formation of [3H, 32P]phytic acid in germinating wheat

Doubly labeled phytic acid of high specific activity was prepared by incubating whole wheat seeds with [32P]phosphoric acid and [3H]myoinositol for 48 h and purifying by anion-exchange chromatography on AG 1- X 8 resin. Both degradation and synthesis of phytic acid were inhibited by KF to a similar extent, yet the catabolic and anabolic pathways involved distinctly different enzyme systems, as no [3H, 32P]myoinositol tetra- or pentaphosphate could be detected.     

Induction of chilling tolerance in wheat during germination by pre-soaking seed with nitric oxide and gibberellin

Chilling depresses seed germination and seedling establishment, and is one major constraint to grain yield formation in late sown winter wheat. Seeds of winter wheat (Triticum aestivum L.) were separately pre-soaked with sodium nitroprusside (SNP, as nitric oxide donor) and Gibberellic acid (GA₃) before germination and then germinated under low temperature. SNP and GA₃ pre-treatment increased seed germination rate, germination index, weights and lengths of coleoptile and radicle, while they decreased mean germination time and weight of seeds germinating under low temperature. Exogenous NO and GA₃ increased seed respiration rate and promoted starch degradation along with increased amylase activities. In addition, efficient antioxidant systems were activated by NO, and which effectively reduced concentrations of malondialdehyde and hydrogen peroxide (H₂O₂). Seedling growth was also enhanced by exogenous NO and GA₃ as a result of improved seed germination and maintenance of better reactive oxygen species homeostasis in seedling growing under chilling temperatures. It is indicated that exogenous NO was more effective than GA₃ in alleviating chilling stress during seed germination and seedling establishment in wheat.     

Timing, localization, and control of wheat germ agglutinin synthesis in developing wheat embryos

The lectin, wheat germ agglutinin (WGA), is synthesized de novo by developing wheat (Triticum aestivum, L.) embryos but is not synthesized or localized in developing endosperm as shown by radioimmunoassay. Young embryos removed from the grain and cultured on a defined medium germinate precociously and concomitantly cease WGA synthesis. In vitro precocious germination of young embryos is reversibly inhibited by low levels (1–100 μM) of the plant growth substance abscisic acid (ABA). Embryos inhibited from germinating by this growth regulator not only continue synthesizing WGA, but do so at an accelerated rate when compared with embryos left associated with the grain.     

Localization of carboxypeptidase I in germinating barley grain

Activity measurements and Northern blot hybridizations were used to study the temporal and spatial expression of carboxypeptidase I in germinating grains of barley (Hordeum vulgare L. cv Himalaya). In the resting grain no carboxypeptidase I activity was found in the aleurone layer, scutellum, or starchy endosperm. During germination high levels of enzyme activity appeared in the scutellum and in the starchy endosperm but only low activity was found in the aleurone layer. No mRNA for carboxypeptidase I was observed in the resting grain. By day 1 of germination the mRNA appeared in the scutellum where its level remained high for several days. In contrast, little mRNA was observed in the aleurone layer. These results indicate that the scutellum plays an important role in the production of carboxypeptidase I in germinating barley grain.     

Alterations in the relative abundance of Haptoglobin (Hp) transcripts in total milk somatic cells during different stages of lactation cycle in high yielding cross-bred cows

The expression profile of Haptoglobin (Hp) gene in total milk somatic cells (SCC) of high-yielding cross-bred Karan Fries (KF) was studied during early, mid, and late lactation cycle. Milk samples (200 ml/animals) were collected from 10 high-yielding and 10 low-yielding cows throughout the lactation cycle (from day 7 to day 300) with an interval of one month. Relative mRNA expression profiles of Hp by RT polymerase chain reaction was studied in high-yielding cows, whereas low-yielding cows were taken as control. The folds of induction of Hp was significantly (p < 0.001) downregulated by a mean factor of 0.207 in milk SCC during early lactating cows. Whereas, it was significantly (p < 0.01) upregulated by a mean factor of 20.888 during mid lactation. The expression was unaltered during the late lactation. The study demonstrates that Hp is synthesized within the mammary gland and significantly upregulated during mid-lactation period compared to other stages of lactation cycle.     

Increased erythritol production in Torula sp. with inositol and phytic acid

Of the vitamins tested, inositol was the most effective for erythritol production. To increase erythritol production by Torula sp., inositol and a related compound, phytic acid (myoinositol hexaphosphate), were added to the culture media. Erythritol production in the presence of phytic acid was greater than that in the presence of inositol, due to the synergistic effects of phosphate and inositol. Supplementation with phosphate and inositol increased cell growth, erythritol production, and the activity of erythrose reductase in cells. Inositol was a more effective stimulator of cell growth and erythritol production than was phosphate.     

(1→4)-α-d-glucan phosphorylase [(1→4)-α-d-glucan:orthophosphate glucosyltransferase] isoenzymes from sweet corn seed embryo

The presence of multiple forms of phosphorylase [(1→4)-α-d-glucan:orthophosphate glucosyltransferase] in sugary maize seeds was demonstrated by polyacrylamide-gel-disc electrophoresis. The patterns of phosphorylase isoenzymes from immature and from germinating seeds were different. Most of the isoenzymes from embryo of germinated seeds precipitated at an ammonium sulfate concentration above 45% of saturation. The most cathodic band of the zymograms appeared on the third day of germination, then disappeared. This form of phosphorylase occurred only in the embryo of germinating seeds and it was absent both in the immature embryo and in the endosperm at any stage of development. The slow-moving embryo isoenzyme was purified through chromatography on DEAE-cellulose. Its kinetic properties and enlargement mechanism were studied.     

Development of functional foods using psyllium husk and wheat bran fractions: Phytic acid contents

Wheat grain is a rich source of phosphorus which is present mostly as phytic acid and is distributed mainly in the bran and germ fractions. Phytic acid has now been recognized as an important phytochemical having antioxidant properties. This study deals with the determination of total as well as phytic phosphorus contents of psyllium (PS), course (CB) and fine wheat bran (FB) enriched pan bread and Arabic flat bread. The concentration of phytic acid in CB, FB, wheat germ, wholegrain wheat flour (WGF), white wheat flour (WWF), and psyllium were found to be 8.86 mg/g, 8.52 mg/g, 6.05 mg/g, 1.74 mg/g, 0.46 mg/g and 0.02 mg/g, respectively. Most of the phosphorus existed as phytic phosphorus (74.7–90.8%) in FB, CB, germ, and WGF as compared to only 42.6% in WWF. The level of phytic phosphorus in pan bread containing 10% CB, 20% FB (both containing with 5% PS) was found to be 0.63 mg/g and 1.53 mg/g respectively, as compared to only 0.34 mg/g in WWF pan bread, and 0.90 mg/g in WGF pan bread. The phytic phosphorus content in Arabic bread made with WGF and 3% psyllium was 1.32 mg/g as compared to only 0.48 mg/g in WWF Arabic flat bread. The results obtained indicate that the level of phytic phosphorus significantly increased in bread formulations containing CB, FB, and WGF, but no change with psyllium addition was observed. Adding these wheat mill fractions, and psyllium will enable bakeries not only to produce fiber-enriched pan bread and Arabic bread but would also benefit consumers to increase their dietary fiber intakes, and health-promoting phytochemicals coming from wheat bran and germ fractions.