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

Unraveling the potential of bacterial phytases for sustainable management of phosphorous

Phosphorous actively participates in numerous metabolic and regulatory activities of almost all living organisms including animals and humans. Therefore, it is considered as an essential macronutrient required supporting their proper growth. On contrary, phytic acid (PA), an antinutritional substance, is widely known for its strong affinity to chelate essential mineral ions including PO4 3- , Ca2+ , Fe2+ , Mg2+ , and Zn2+ . Being one the major reservoir of PO4 3- ions, PA has great potential to bind PO4 3- ions in diverse range of foods. Once combined with P, PA transforms into an undigested and insoluble complex namely phytate. Produced phytate leads to a notable reduction in the bioavailability of P due to negligible activity of phytases in monogastric animals and humans. This highlights the importance and consequent need of enhancement of phytase level in these life forms. Interestingly, phytases, catalyzing the breakdown of phytate complex and recycling the phosphate into ecosystem to its available form, have naturally been reported in a variety of plants and microorganisms over past few decades. In pursuit of a reliable solution, the focus of this review is to explore the keynote potential of bacterial phytases for sustainable management of phosphorous via efficient utilization of soil phytate. The core of the review covers detailed discussion on bacterial phytases along with their widely reported applications viz. biofertilizers, phosphorus acquisition, and plant growth promotion. Moreover, meticulous description on fermentation-based strategies and future trends on bacterial phytases have also been included.

Phytic acid accumulation in plants: Biosynthesis pathway regulation and role in human diet

Phytate or phytic acid (PA), is a phosphorus (P) containing compound generated by the stepwise phosphorylation of myo-inositol. It forms complexes with some nutrient cations, such as Ca, Fe and Zn, compromising their absorption and thus acting as an anti-nutrient in the digestive tract of humans and monogastric animals. Conversely, PAs are an important form of P storage in seeds, making up to 90% of total seed P. Phytates also play a role in germination and are related to the synthesis of abscisic acid and gibberellins, the hormones involved in seed germination. Decreasing PA content in plants is desirable for human dietary. Therefore, low phytic acid (lpa) mutants might present some negative pleiotropic effects, which could impair germination and seed viability. In the present study, we review current knowledge of the genes encoding enzymes that function in different stages of PA synthesis, from the first phosphorylation of myo-inositol to PA transport into seed reserve tissues, and the application of this knowledge to reduce PA concentrations in edible crops to enhance human diet. Finally, phylogenetic data for PA concentrations in different plant families and distributed across several countries under different environmental conditions are compiled. The results of the present study help explain the importance of PA accumulation in different plant families and the distribution of PA accumulation in different foods.

Globoids and Phytase: The Mineral Storage and Release System in Seeds

Phytate and phytases in seeds are the subjects of numerous studies, dating back as far as the early 20th century. Most of these studies concern the anti-nutritional properties of phytate, and the prospect of alleviating the effects of phytate with phytase. As reasonable as this may be, it has led to a fragmentation of knowledge, which hampers the appreciation of the physiological system at hand. In this review, we integrate the existing knowledge on the chemistry and biosynthesis of phytate, the globoid cellular structure, and recent advances on plant phytases. We highlight that these components make up a system that serves to store and-in due time-release the seed's reserves of the mineral nutrients phosphorous, potassium, magnesium, and others, as well as inositol and protein. The central component of the system, the phytate anion, is inherently rich in phosphorous and inositol. The chemical properties of phytate enable it to sequester additional cationic nutrients. Compartmentalization and membrane transport processes regulate the buildup of phytate and its associated nutrients, resulting in globoid storage structures. We suggest, based on the current evidence, that the degradation of the globoid and the mobilization of the nutrients also depend on membrane transport processes, as well as the enzymatic action of phytase.

Phytic Acid and Transporters: What Can We Learn from low phytic acid Mutants

Phytic acid has two main roles in plant tissues: Storage of phosphorus and regulation of different cellular processes. From a nutritional point of view, it is considered an antinutritional compound because, being a cation chelator, its presence reduces mineral bioavailability from the diet. In recent decades, the development of low phytic acid (lpa) mutants has been an important goal for nutritional seed quality improvement, mainly in cereals and legumes. Different lpa mutations affect phytic acid biosynthetic genes. However, other lpa mutations isolated so far, affect genes coding for three classes of transporters: A specific group of ABCC type vacuolar transporters, putative sulfate transporters, and phosphate transporters. In the present review, we summarize advances in the characterization of these transporters in cereals and legumes. Particularly, we describe genes, proteins, and mutants for these different transporters, and we report data of in silico analysis aimed at identifying the putative orthologs in some other cereal and legume species. Finally, we comment on the advantage of using such types of mutants for crop biofortification and on their possible utility to unravel links between phosphorus and sulfur metabolism (phosphate and sulfate homeostasis crosstalk).

Genetic dissection of grain elements predicted by hyperspectral imaging associated with yield-related traits in a wild barley NAM population

Enhancing the accumulation of essential mineral elements in cereal grains is of prime importance for combating human malnutrition. Biofortification by breeding holds great potential for improving nutrient accumulation in grains. However, conventional breeding approaches require element analysis of many grain samples, which causes high costs. Here we applied hyperspectral imaging to estimate the concentration of 15 grain elements (C, B, Ca, Cd, Cu, Fe, K, Mg, Mn, Mo, N, Na, P, S, Zn) in high-throughput in the wild barley nested association mapping (NAM) population HEB-25, comprising 1,420 BC₁S₃ lines derived from crossing 25 wild barley accessions with the cultivar 'Barke'. Nutrient concentrations varied largely with a multitude of lines having higher micronutrient concentration than 'Barke'. In a genome-wide association study (GWAS), we located 75 quantitative trait locus (QTL) hotspots, whereof many could be explained by major genes such as NO APICAL MERISTEM-1 (NAM-1) and PHOTOPERIOD 1 (Ppd-H1). The GWAS approach revealed exotic alleles that were able to increase grain element concentrations. Remarkably, a QTL linked to GIBBERELLIN 20 OXIDASE 2 (HvGA20ox₂) significantly increased several grain elements without yield loss. We conclude that introgressing promising exotic alleles into elite breeding material can assist in improving the nutritional value of barley grains.

A decrease in phytic acid content substantially affects the distribution of mineral elements within rice seeds

Phytic acid (myo-inositol hexakisphosphate; InsP6) is the storage compound of phosphorus and many mineral elements in seeds. To determine the role of InsP6 in the accumulation and distribution of mineral elements in seeds, we performed fine mappings of mineral elements through synchrotron-based X-ray microfluorescence analysis using developing seeds from two independent low phytic acid (lpa) mutants of rice (Oryza sativa L.). The reduced InsP6 in lpa seeds did not affect the translocation of mineral elements from vegetative organs into seeds, because the total amounts of phosphorus and the other mineral elements in lpa seeds were identical to those in the wild type (WT). However, the reduced InsP6 caused large changes in mineral localization within lpa seeds. Phosphorus and potassium in the aleurone layer of lpa greatly decreased and diffused into the endosperm. Zinc and copper, which were broadly distributed from the aleurone layer to the inner endosperm in the WT, were localized in the narrower space around the aleurone layer in lpa mutants. We also confirmed that similar distribution changes occurred in transgenic rice with the lpa phenotype. Using these results, we discussed the role of InsP6 in the dynamic accumulation and distribution patterns of mineral elements during seed development.

Antiepileptogenic effect of curcumin on kainate-induced model of temporal lobe epilepsy

CONTEXT

Temporal lobe epilepsy (TLE) is an intractable neurological disorder. Curcumin is the bioactive component of turmeric with anti-epileptic and neuroprotective potential.

OBJECTIVE

The beneficial effect of curcumin on the intrahippocampal kainate-induced model of TLE was investigated.

MATERIALS AND METHODS

Rats were divided into sham, curcumin-pretreated sham, kainate and curcumin-pretreated kainate groups. The rat model of TLE was induced by unilateral intrahippocampal injection of 4 μg of kainate. Rats received curcumin p.o. at a dose of 100 mg/kg/d starting 1 week before the surgery. Seizure activity (SE) and oxidative stress-related markers were measured. Furthermore, the Timm index for evaluation of mossy fiber sprouting (MFS) and number of Nissl-stained neurons were quantified.

RESULTS

All rats in the kainate group had SE, while 28.5% of rats showed seizures in the curcumin-pretreated kainate group. Malondialdehyde and nitrite and nitrate levels significantly increased in the kainate group (p < 0.01 and p < 0.05, respectively), and curcumin significantly lowered these parameters (p < 0.05). Superoxide dismutase activity significantly decreased in the kainate group (p < 0.05) and curcumin did not improve it. Rats in the kainate group showed a significant reduction of neurons in Cornu Ammonis 1 (CA1) (p < 0.05), CA3 (p < 0.005) and hilar (p < 0.01) regions, and curcumin significantly prevented these changes (p < 0.05-0.005). The Timm index significantly increased in the kainate group (p < 0.005), and curcumin significantly lowered this index (p < 0.01).

DISCUSSION AND CONCLUSION

Curcumin pretreatment can attenuate seizures, lower some oxidative stress markers, and prevent hippocampal neuronal loss and MFS in the kainate-induced model of TLE.

Low phytic acid 1 mutation in maize modifies density, starch properties, cations, and fiber contents in the seed

Monogastric animals are unable to digest phytic acid, so it represents an antinutritional factor and also an environmental problem. One strategy to solve this problem is the utilization of low phytic acid (lpa) mutants that accumulate low levels of phytic P and high levels of free phosphate in the seeds; among the lpa maize mutants lpa1 exhibited the highest reduction of phytic acid in the seed. This study indicated that the low phytic acid mutations exerted pleiotropic effects not directly connected to the phytic acid pathway, such as on seed density, content of ions, and the antioxidant compounds present in the kernels. Furthermore some nutritional properties of the flour were altered by the lpa1 mutations, in particular lignin and protein content, while the starch does not seem to be modified as to the total amount and in the amylose/amylopectin ratio, but alterations were noticed in the structure and size of granules.

Compositional equivalence of barleys differing only in low- and normal-phytate levels

Recent breeding advances have led to the development of several barley lines and cultivars with significant reductions (50% or greater) in phytate levels. Low-phytate (LP) grain is distinguished by containing not only a reduced level of phytate P but also an increased level of inorganic P, resulting in greater bioavailability of P and mineral cations in animal diets. It is important to determine whether other nutritional characteristics are altered by breeding for the low-phytate trait. This study was designed to investigate if breeding for reduced phytate content in barleys had any effect on the contents of other attributes measured by comparing mean and range values of the levels of protein, oil, ash, total carbohydrate, starch, and β-glucan, fatty acid composition, and levels of tocopherols and tocotrienols between five LP and five normal-phytate barleys grown in three Idaho locations. Results show that only the phytate level in the LP group was substantially lower than that of the normal-phytate group and that all other attributes measured or calculated were substantially equivalent between the two groups of barleys. Therefore, the phytate level had little effect on the levels of protein, oil, ash, total carbohydrate, starch, and β-glucan, fatty acid composition, and levels of tocopherols and tocotrienols in barley seeds.

Comparison of lipid content and fatty acid composition and their distribution within seeds of 5 small grain species

Barley, oats, rice, sorghum, and wheat, each with two genotypes, were sequentially abraded by an electric seed scarifier. The pearling fines (PF) and pearled kernels (PK) at each cycle were analyzed for lipid (mostly nonpolar) content and fatty acid (FA) composition. The oil content in whole or dehulled grains ranged from 2.18% of a wheat variety to 6.38% of an oat line. Compared with barley and wheat, rice, oat, and sorghum had higher relative % of C18:1 (31.60 to 36.64 compared with 12.15 to 15.61) and lower % of C18:2 (35.69 to 45.44 compared with 50.79 to 61.50). The relationship between oil content in PF and the cumulative level of surface removal essentially describes the distribution pattern of oil content within a seed. Barley, rice, and sorghum had a similar distribution pattern, characterized by a rapid rate of decreasing for the first few outer layers and then by gradual decrease to a flat value toward the inner core. In contrast, distribution within oats was characterized by a gradual reduction in oil content across the seed. The distribution of oil within wheat fell between the former 2 types. For all 10 grains, from seed surface to inner core, C16:0 and C18:0 increased, C18:1 and C18:3 decreased, and C18:2 changed slightly, providing a new reason for improved oxidative stability for pearled kernels. The differences in the changing intensity of FA composition among grain species correspond to those in oil distribution within a seed, while varietal difference in distribution patterns of content and FA composition of lipids within a species was insignificant.

PRACTICAL APPLICATION

This study was the first to document fatty acid distribution across a grain seed. Results provide 2 major reasons for improved oxidative stability of pearled grains: reduced oil content and shift of fatty acids toward more saturated and less unsaturated composition.

Moving micronutrients from the soil to the seeds: genes and physiological processes from a biofortification perspective

The micronutrients iron (Fe), zinc (Zn), and copper (Cu) are essential for plants and the humans and animals that consume plants. Increasing the micronutrient density of staple crops, or biofortification, will greatly improve human nutrition on a global scale. This review discusses the processes and genes needed to translocate micronutrients through the plant to the developing seeds, and potential strategies for developing biofortified crops.

Changes in mineral concentrations and phosphorus profile during dry-grind processing of corn into ethanol

For determining variation in mineral composition and phosphorus (P) profile among streams of dry-grind ethanol production, samples of ground corn, intermediate streams, and distillers dried grains with solubles (DDGS) were obtained from three commercial plants. Most attributes (dry matter concentrations) increased significantly from corn to cooked slurry but fermentation caused most significant increase in all attributes. During centrifugation, more minerals went into thin stillage than wet grains, making minerals most concentrated in the former. Mineral increase in DDGS over corn was about 3 fold, except for Na, S, Ca, and Fe. The first three had much higher fold of increase, presumably due to exogenous addition. During fermentation, phytate P and inorganic P had 2.54 and 10.37 fold of increase over corn, respectively, while relative to total P, % phytate P decreased and % inorganic P increased significantly. These observations suggest that phytate underwent some degradation, presumably due to activity of yeast phytase.

Megapixel imaging of (micro)nutrients in mature barley grains

Understanding the accumulation and distribution of essential nutrients in cereals is of primary importance for improving the nutritional quality of this staple food. While recent studies have improved the understanding of micronutrient loading into the barley grain, a detailed characterization of the distribution of micronutrients within the grain is still lacking. High-definition synchrotron X-ray fluorescence was used to investigate the distribution and association of essential elements in barley grain at the micro scale. Micronutrient distribution within the scutellum and the embryo was shown to be highly variable between elements in relation to various morphological features. In the rest of the grain, the distribution of some elements such as Cu and Zn was not limited to the aleurone layer but extended into the endosperm. This pattern of distribution was less marked in the case of Fe and, in particular, Mn. A significant difference in element distribution was also found between the ventral and dorsal part of the grains. The correlation between the elements was not consistent between and within tissues, indicating that the transport and storage of elements is highly regulated. The complexity of the spatial distribution and associations has important implications for improving the nutritional content of cereal crops such as barley.

The low phytic acid1-241 (lpa1-241) maize mutation alters the accumulation of anthocyanin pigment in the kernel

The lpa1 mutations in maize are caused by lesions in the ZmMRP4 (multidrug resistance-associated proteins 4) gene. In previous studies (Raboy et al. in Plant Physiol 124:355-368, 2000; Pilu et al. in Theor Appl Genet 107:980-987, 2003a; Shi et al. Nat Biotechnol 25:930-937, 2007), several mutations have been isolated in this locus causing a reduction of phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate, or InsP(6)) content and an equivalent increasing of free phosphate. In particular, the lpa1-241 mutation causes a reduction of up to 90% of phytic acid, associated with strong pleiotropic effects on the whole plant. In this work, we show, for the first time to our knowledge, an interaction between the accumulation of anthocyanin pigments in the kernel and the lpa mutations. In fact the lpa1-241 mutant accumulates a higher level of anthocyanins as compared to wild type either in the embryo (about 3.8-fold) or in the aleurone layer (about 0.3-fold) in a genotype able to accumulate anthocyanin. Furthermore, we demonstrate that these pigments are mislocalised in the cytoplasm, conferring a blue pigmentation of the scutellum, because of the neutral/basic pH of this cellular compartment. As a matter of fact, the propionate treatment, causing a specific acidification of the cytoplasm, restored the red pigmentation of the scutellum in the mutant and expression analysis showed a reduction of ZmMRP3 anthocyanins' transporter gene expression. On the whole, these data strongly suggest a possible interaction between the lpa mutation and anthocyanin accumulation and compartmentalisation in the kernel.

Biofortification of crops with seven mineral elements often lacking in human diets--iron, zinc, copper, calcium, magnesium, selenium and iodine

The diets of over two-thirds of the world's population lack one or more essential mineral elements. This can be remedied through dietary diversification, mineral supplementation, food fortification, or increasing the concentrations and/or bioavailability of mineral elements in produce (biofortification). This article reviews aspects of soil science, plant physiology and genetics underpinning crop biofortification strategies, as well as agronomic and genetic approaches currently taken to biofortify food crops with the mineral elements most commonly lacking in human diets: iron (Fe), zinc (Zn), copper (Cu), calcium (Ca), magnesium (Mg), iodine (I) and selenium (Se). Two complementary approaches have been successfully adopted to increase the concentrations of bioavailable mineral elements in food crops. First, agronomic approaches optimizing the application of mineral fertilizers and/or improving the solubilization and mobilization of mineral elements in the soil have been implemented. Secondly, crops have been developed with: increased abilities to acquire mineral elements and accumulate them in edible tissues; increased concentrations of 'promoter' substances, such as ascorbate, beta-carotene and cysteine-rich polypeptides which stimulate the absorption of essential mineral elements by the gut; and reduced concentrations of 'antinutrients', such as oxalate, polyphenolics or phytate, which interfere with their absorption. These approaches are addressing mineral malnutrition in humans globally.

Phytate: impact on environment and human nutrition. A challenge for molecular breeding

Phytic acid (PA) is the primary storage compound of phosphorus in seeds accounting for up to 80% of the total seed phosphorus and contributing as much as 1.5% to the seed dry weight. The negatively charged phosphate in PA strongly binds to metallic cations of Ca, Fe, K, Mg, Mn and Zn making them insoluble and thus unavailable as nutritional factors. Phytate mainly accumulates in protein storage vacuoles as globoids, predominantly located in the aleurone layer (wheat, barley and rice) or in the embryo (maize). During germination, phytate is hydrolysed by endogenous phytase(s) and other phosphatases to release phosphate, inositol and micronutrients to support the emerging seedling. PA and its derivatives are also implicated in RNA export, DNA repair, signalling, endocytosis and cell vesicular trafficking. Our recent studies on purification of phytate globoids, their mineral composition and dephytinization by wheat phytase will be discussed. Biochemical data for purified and characterized phytases isolated from more than 23 plant species are presented, the dephosphorylation pathways of phytic acid by different classes of phytases are compared, and the application of phytase in food and feed is discussed.