Strategic distribution of protective proteins within bran layers of wheat protects the nutrient-rich endosperm

Aqueous phase extractable protein of wheat bran and germ for the production of liquid and semi-solid foods

To achieve a more sustainable global food production, a shift from animal to plant protein based food is necessary. At the same time, these plant proteins are preferentially derived from side-streams of industrial processes. Wheat bran and germ represent two major side-streams of the wheat milling industry, and contain aqueous-phase soluble proteins with a well-balanced amino acid composition. To successfully use wheat bran and germ proteins in novel plant-based liquid and semi-solid foods, they need to (i) be rendered extractable and (ii) contribute functionally to stabilizing the food system. Prior heat treatment and the occurrence of intact cell walls are important barriers in this regard. Several strategies have been applied to overcome these issues, including physical processing and (bio)chemical modification. We here present a comprehensive, critical overview of the aqueous-phase extraction of protein from (modified) wheat bran and germ. Moreover, we discuss the functionality of the extracted protein, specifically in the context of liquid (foam- and emulsion-type) and semi-solid (gel-type) food applications. In each section, we identify important knowledge gaps and highlight several future prospects that could further increase the application potential of wheat bran and germ proteins in the food industry.

Ultrasound application for the decontamination of roselle (Hibiscus sabdariffa L.) seeds: Influence on fungal inhibition and seed quality

Seed decay is a major problem caused by pathogens that adversely affect seed yield and quality in agricultural production. Herein, the effect of 28 KHz ultrasound treatment for 20, 40 and 60 min and 1.5% sodium hypochlorite solution for 20 min was assessed for the decontamination of roselle (Hibiscus sabdariffa L.) seeds. In addition, seed germination indices, seedling growth traits, total phenolic content and the activity of defense-related enzymes, viz. peroxidase, superoxide dismutase, catalase and malondialdehyde were measured in the treated seeds. An isolate of Fusarium solani was obtained from roselle seeds and identified as the causal agent of roselle seed rot based on morphological and molecular characteristics. After six days of seed storage, the microbial infection caused the highest seed rot in the control seeds on the average of 56.67%, whereas ultrasound treatment for 60 min could remarkably reduce the seed decay by 3.33%. At the end of seed storage, the fungal load showed the highest (7.72 Log CFU ml-1) and lowest (6.99 Log CFU ml-1) rates in the control and ultrasound treatment for 60 min, respectively. Total phenolic content was significantly increased in ultrasound treatment for 60 min compared to control and sodium hypochlorite treatments. Moreover, the activity of peroxidase, superoxide dismutase and catalase was noticeably improved in ultrasound treatment for 60 min. Furthermore, ultrasound treatment did not show any adverse effects on seed germination indices and seedling growth traits of the roselle plants. Overall, ultrasound treatment for 60 min could effectively decrease roselle seed decay and the fungal load without changing seed and seedling quality.

Mixed-Linkage Glucan Is the Main Carbohydrate Source and Starch Is an Alternative Source during Brachypodium Grain Germination

Seeds of the model grass Brachypodium distachyon are unusual because they contain very little starch and high levels of mixed-linkage glucan (MLG) accumulated in thick cell walls. It was suggested that MLG might supplement starch as a storage carbohydrate and may be mobilised during germination. In this work, we observed massive degradation of MLG during germination in both endosperm and nucellar epidermis. The enzymes responsible for the MLG degradation were identified in germinated grains and characterized using heterologous expression. By using mutants targeting MLG biosynthesis genes, we showed that the expression level of genes coding for MLG and starch-degrading enzymes was modified in the germinated grains of knocked-out cslf6 mutants depleted in MLG but with higher starch content. Our results suggest a substrate-dependent regulation of the storage sugars during germination. These overall results demonstrated the function of MLG as the main carbohydrate source during germination of Brachypodium grain. More astonishingly, cslf6 Brachypodium mutants are able to adapt their metabolism to the lack of MLG by modifying the energy source for germination and the expression of genes dedicated for its use.

Relevance of the air-water interfacial and foaming properties of (modified) wheat proteins for food systems

A shift from animal protein- to plant protein-based foods is crucial in transitioning toward a more sustainable global food system. Among food products typically stabilized by animal proteins, food foams represent a major category. Wheat proteins are ubiquitous and structurally diverse, which offers opportunities for exploiting them for food foam and air-water interface stabilization. Notably, they are often classified into those that are soluble in aqueous systems (albumins and globulins) and those that are not (gliadins and glutenins). However, gliadins are at least to an extent water extractable and thus surface active. We here provide a comprehensive overview of studies investigating the air-water interfacial and foaming properties of the different wheat protein fractions. Characteristics in model systems are related to the functional role that wheat proteins play in gas cell stabilization in existing wheat-based foods (bread dough, cake batter, and beer foam). Still, to further extend the applicability of wheat proteins, and particularly the poorly soluble glutenins, to other food foams, their modification is required. Different physical, (bio)chemical, and other modification strategies that have been utilized to alter the solubility and therefore the air-water interfacial and foaming properties of the gluten protein fraction are critically reviewed. Such approaches may open up new opportunities for the application of (modified) gluten proteins in other food products, such as plant-based meringues, whippable drinks, or ice cream. In each section, important knowledge gaps are highlighted and perspectives for research efforts that could lead to the rational design of wheat protein systems with enhanced functionality and overall an increased applicability in food industry are proposed.

Wheat bran layers: composition, structure, fractionation, and potential uses in foods

Wheat bran, the main by-product of dry milling of wheat, is currently mainly used in the animal feed industry, but has attracted attention as a food ingredient owing to its high dietary fiber and phytochemical contents, providing excellent physiological effects. The bran layers (aleurone layer, outer pericarp and intermediate layer) contain different compositions, structures, and nutrients, and have different properties. Each layer, when separated and isolated, potentially could find more extensive applications in foods. This triggered interest in isolating the bran layers using milling and wet- or dry-fractionation techniques based on their chemical or physical properties. The recent progress has allowed the production of commercial products from wheat bran layers, particularly aleurone-rich products, enhancing the value of wheat bran layers and their applications in food. The present review highlights the recent advances in studying the chemical composition including distribution of chemical components, physical structure, biopolymer matrix, and physicochemical properties of each wheat bran layer. Technologies to fractionate wheat bran layers and utilization of different bran layers in foods are discussed and reviewed, providing new strategies for improving the value of wheat bran and utilization of wheat bran in foods.

Molecular prospective on the wheat grain development

Wheat grain development is an important biological process to determine grain yield and quality, which is controlled by the interplay of genetic, epigenetic, and environmental factors. Wheat grain development has been extensively characterized at the phenotypic and genetic levels. The advent of innovative molecular technologies allows us to characterize genes, proteins, and regulatory factors involved in wheat grain development, which have enhanced our understanding of the wheat seed development process. However, wheat is an allohexaploid with a large genome size, the molecular mechanisms underlying the wheat grain development have not been well understood as those in diploids. Understanding grain development, and how it is regulated, is of fundamental importance for improving grain yield and quality through conventional breeding or genetic engineering. Herein, we review the current discoveries on the molecular mechanisms underlying wheat grain development. Notably, only a handful of genes that control wheat grain development have, thus far, been well characterized, their interplay underlying the grain development remains elusive. The synergistic network-integrated genomics and epigenetics underlying wheat grain development and how the subgenome divergence dynamically and precisely regulates wheat grain development are unknown.

Measurements of Antibacterial Activity of Seed Crude Extracts in Cultivated Rice and Wild Oryza Species

Seeds are continuously exposed to a wide variety of microorganisms in the soil. In addition, seeds contain large amounts of carbon and nitrogen sources that support initial growth after germination. Thus, seeds in the soil can easily promote microbial growth, and seeds are susceptible to decay. Therefore, seed defense against microorganisms is important for plant survival. Seed-microbe interactions are also important issues from the perspective of food production, in seed quality and shelf life. However, seed-microbe interactions remain largely unexplored. In this study, we established a simple and rapid assay system for the antibacterial activity of rice seed crude extracts by colorimetric quantification methods by the reduction of tetrazolium compound. Using this experimental system, the diversity of effects of rice seed extracts on microbial growth was analyzed using Escherichia coli as a bacterial model. We used collections of cultivated rice, comprising 50 accessions of Japanese landraces, 52 accessions of world rice core collections, and of 30 wild Oryza accessions. Furthermore, we attempted to find genetic factors responsible for the diversity by genome-wide association analysis. Our results demonstrate that this experimental system can easily analyze the effects of seed extracts on bacterial growth. It also suggests that there are various compounds in rice seeds that affect microbial growth. Overall, this experimental system can be used to clarify the chemical entities and genetic control of seed-microbe interactions and will open the door for understanding the diverse seed-microbe interactions through metabolites.

Proteome-Wide Response of Dormant Caryopses of the Weed, Avena fatua, After Colonization by a Seed-Decay Isolate of Fusarium avenaceum

Promoting seed decay is an ecological approach to reducing weed persistence in the soil seedbank. Previous work demonstrated that Fusarium avenaceum F.a.1 decays dormant Avena fatua (wild oat) caryopses and induces several defense enzyme activities in vitro. The objectives of this study were to obtain a global perspective of proteins expressed after F.a.1-caryopsis colonization by conducting proteomic evaluations on (i) leachates, soluble extrinsic (seed-surface) proteins released upon washing caryopses in buffer and (ii) proteins extracted from whole caryopses; interactions with aluminum (Al) were also evaluated in the latter study because soil acidification and associated metal toxicity are growing problems. Of the 119 leachate proteins classified as defense/stress, 80 were induced or repressed. Defense/stress proteins were far more abundant in A. fatua (35%) than in F.a.1 (12%). Avena defense/stress proteins were also the most highly regulated category, with 30% induced and 35% repressed by F.a.1. Antifungal proteins represented 36% of Avena defense proteins and were the most highly regulated, with 36% induced and 37% repressed by F.a.1. These results implicate selective regulation of Avena defense proteins by F.a.1. Fusarium proteins were also highly abundant in the leachates, with 10% related to pathogenicity, 45% of which were associated with host cell wall degradation. In whole caryopsis extracts, fungal colonization generally resulted in induction of a similar set of Avena proteins in the presence and absence of Al. Results advance the hypothesis that seed decay pathogens elicit intricate and dynamic biochemical responses in dormant seeds.

Effect of Bran Pre-Treatment with Endoxylanase on the Characteristics of Intermediate Wheatgrass (Thinopyrum intermedium) Bread

Previous work indicated that bran removal promotes network formation in breads prepared from intermediate wheatgrass (IWG) flour. However, refinement reduces yields as well as contents of nutritionally beneficial compounds such as fiber. This study evaluated xylanase pretreatment of IWG bran as a processing option to enhance the properties of bread made with half of the original bran content. Xylanase pretreatment did not affect stickiness but significantly reduced hardness and increased specific loaf volumes compared to negative (without xylanase) and positive controls (with xylanase but without pretreatment). However, the surface of breads with pretreated bran was uneven due to structural collapse during baking. Fewer but larger gas cells were present due to pretreatment. Addition of ascorbic acid modulated these effects, but did not prevent uneven surfaces. Accessible thiol concentrations were slightly but significantly increased by xylanase pretreatment, possibly due to a less compact crumb structure. Endogenous xylanases (apparent activity 0.46 and 5.81 XU/g in flour and bran, respectively) may have been activated during the pretreatment. Moreover, Triticum aestivum xylanase inhibitor activity was also detected (193 and 410 InU/g in flour and bran). Overall, xylanase pretreatment facilitates incorporation of IWG bran into breads, but more research is needed to improve bread appearance.

Maize endosperm development

Recent breakthroughs in transcriptome analysis and gene characterization have provided valuable resources and information about the maize endosperm developmental program. The high temporal-resolution transcriptome analysis has yielded unprecedented access to information about the genetic control of seed development. Detailed spatial transcriptome analysis using laser-capture microdissection has revealed the expression patterns of specific populations of genes in the four major endosperm compartments: the basal endosperm transfer layer (BETL), aleurone layer (AL), starchy endosperm (SE), and embryo-surrounding region (ESR). Although the overall picture of the transcriptional regulatory network of endosperm development remains fragmentary, there have been some exciting advances, such as the identification of OPAQUE11 (O11) as a central hub of the maize endosperm regulatory network connecting endosperm development, nutrient metabolism, and stress responses, and the discovery that the endosperm adjacent to scutellum (EAS) serves as a dynamic interface for endosperm-embryo crosstalk. In addition, several genes that function in BETL development, AL differentiation, and the endosperm cell cycle have been identified, such as ZmSWEET4c, Thk1, and Dek15, respectively. Here, we focus on current advances in understanding the molecular factors involved in BETL, AL, SE, ESR, and EAS development, including the specific transcriptional regulatory networks that function in each compartment during endosperm development.

Cascade extraction of proteins and feruloylated arabinoxylans from wheat bran

A cascade process for the sequential recovery of proteins and feruloylated arabinoxylan from wheat bran is proposed, involving a protein isolation step, enzymatic destarching and subcritical water extraction. The protein isolation step combining lactic acid fermentation and cold alkaline extraction reduced the recalcitrance of wheat bran, thus improving the total yields of the subsequent subcritical water extraction. The time evolution of subcritical water extraction of feruloylated arabinoxylan was compared at two temperatures (160 °C and 180 °C). Longer residence times enhanced the purity of target feruloylated arabinoxylans, whereas higher temperatures resulted in faster extraction at the expense of significant molar mass reduction. The radical scavenging activity of the extracted feruloylated arabinoxylans was preserved after the initial protein isolation step. This study opens new possibilities for the cascade valorization of wheat bran into enriched protein and non-starch polysaccharide fractions, which show potential to be used as functional food ingredients.

Biodegradation of crude oil using self-immobilized hydrocarbonoclastic deep sea bacterial consortium

Hydrocarbonoclastic bacterial consortium that utilizes crude oil as carbon and energy source was isolated from marine sediment collected at a depth of 2100 m. Molecular characterization by 16S rRNA gene sequences confirmed that these isolates as Oceanobacillus sp., Nesiotobacter sp., Ruegeria sp., Photobacterium sp., Enterobacter sp., Haererehalobacter sp., Exiguobacterium sp., Acinetobacter sp. and Pseudoalteromonas sp. Self-immobilized consortium degraded more than 85% of total hydrocarbons after 10 days of incubation with 1% (v/v) of crude oil and 0.05% (v/v) of Tween 80 (non-ionic surfactant) at 28 ± 2 °C. The addition of nitrogen and phosphorus sources separately i.e. 0.1% (v/v) of CO (NH₂)₂ or K₂HPO₄ enhanced the hydrocarbon utilization percentage. The pathways of microbial degradation of hydrocarbons were confirmed by FTIR, GC-MS, ¹H and ¹³C NMR spectroscopy analyses. These results demonstrated a novel approach using hydrocarbonoclastic self-immobilized deep sea bacterial consortium for eco-friendly bioremediation.

The Dead Can Nurture: Novel Insights into the Function of Dead Organs Enclosing Embryos

Plants have evolved a variety of dispersal units whereby the embryo is enclosed by various dead protective layers derived from maternal organs of the reproductive system including seed coats (integuments), pericarps (ovary wall, e.g., indehiscent dry fruits) as well as floral bracts (e.g., glumes) in grasses. Commonly, dead organs enclosing embryos (DOEEs) are assumed to provide a physical shield for embryo protection and means for dispersal in the ecosystem. In this review article, we highlight recent studies showing that DOEEs of various species across families also have the capability for long-term storage of various substances including active proteins (hydrolases and ROS detoxifying enzymes), nutrients and metabolites that have the potential to support the embryo during storage in the soil and assist in germination and seedling establishment. We discuss a possible role for DOEEs as natural coatings capable of "engineering" the seed microenvironment for the benefit of the embryo, the seedling and the growing plant.

The Iceman's Last Meal Consisted of Fat, Wild Meat, and Cereals

The history of humankind is marked by the constant adoption of new dietary habits affecting human physiology, metabolism, and even the development of nutrition-related disorders. Despite clear archaeological evidence for the shift from hunter-gatherer lifestyle to agriculture in Neolithic Europe [1], very little information exists on the daily dietary habits of our ancestors. By undertaking a complementary -omics approach combined with microscopy, we analyzed the stomach content of the Iceman, a 5,300-year-old European glacier mummy [2, 3]. He seems to have had a remarkably high proportion of fat in his diet, supplemented with fresh or dried wild meat, cereals, and traces of toxic bracken. Our multipronged approach provides unprecedented analytical depth, deciphering the nutritional habit, meal composition, and food-processing methods of this Copper Age individual.

Defense Enzyme Responses in Dormant Wild Oat and Wheat Caryopses Challenged with a Seed Decay Pathogen

Seeds have well-established passive physical and chemical defense mechanisms that protect their food reserves from decay-inducing organisms and herbivores. However, there are few studies evaluating potential biochemical defenses of dormant seeds against pathogens. Caryopsis decay by the pathogenic Fusarium avenaceum strain F.a.1 was relatively rapid in wild oat (Avena fatua L.) isoline "M73," with >50% decay after 8 days with almost no decay in wheat (Triticum aestivum L.) var. RL4137. Thus, this fungal strain has potential for selective decay of wild oat relative to wheat. To study defense enzyme activities, wild oat and wheat caryopses were incubated with F.a.1 for 2-3 days. Whole caryopses were incubated in assay reagents to measure extrinsic defense enzyme activities. Polyphenol oxidase, exochitinase, and peroxidase were induced in whole caryopses, but oxalate oxidase was reduced, in response to F.a.1 in both species. To evaluate whether defense enzyme activities were released from the caryopsis surface, caryopses were washed with buffer and enzyme activity was measured in the leachate. Significant activities of polyphenol oxidase, exochitinase, and peroxidase, but not oxalate oxidase, were leached from caryopses. Defense enzyme responses were qualitatively similar in the wild oat and wheat genotypes evaluated. Although the absolute enzyme activities were generally greater in whole caryopses than in leachates, the relative degree of induction of polyphenol oxidase, exochitinase, and peroxidase by F.a.1 was greater in caryopsis leachates, indicating that a disproportionate quantity of the induced activity was released into the environment from the caryopsis surface, consistent with their assumed role in defense. It is unlikely that the specific defense enzymes studied here play a key role in the differential susceptibility to decay by F.a.1 in these two genotypes since defense enzyme activities were greater in the more susceptible wild oat, compared to wheat. Results are consistent with the hypotheses that (1) dormant seeds are capable of mounting complex responses to pathogens, (2) a diversity of defense enzymes are involved in responses in multiple plant species, and (3) it is possible to identify fungi capable of selective decay of weed seeds without damaging crop seeds, a concept that may be applicable to weed management in the field. While earlier work on seed defenses demonstrated the presence of passive defenses, this work shows that dormant seeds are also quite responsive and capable of activating and releasing defense enzymes in response to a pathogen.

Delineation of Inheritance Pattern of Aleurone Layer Colour Through Chemical Tests in Rice

BACKGROUND

Rice aleurone layer develops different colours with various chemical tests that may help to develop some rapid tests for identification/grouping of rice varieties. Understanding the colour inheritance pattern could enable to develop chemical clues that may help for genetic purity analysis along with grow-out-test.

RESULTS

In this study, inheritance pattern of aleurone layer colour was studied in parents, F₁ and F₂ progenies derived from the crosses IR 36 × Acc. No. 2693 and IR 64 × Acc. No. 2693. The parent IR 36 showed light yellow (NaOH/KOH) and brown (phenol/modified phenol test) colour; whereas, Acc. No. 2693 revealed wine red/dark wine red (NaOH/KOH) and light brown colour/no reaction (phenol/modified phenol test). In contrary, another parent IR 64 exhibited light yellow (KOH/NaOH) and dark brown (phenol, modified phenol) colour. Both the F₁ showed an intermediate light wine red colour (NaOH/KOH) and dark brown (phenol and modified phenol) colour, which is dominant over their one of the parents. The colour pattern with standard phenol/modified phenol, NaOH and KOH tests in F₂ progenies of both the crosses showed 9:7 (complementary gene interaction) and 11:5 ratios (reciprocal dominance modification of recessive alleles), respectively.

CONCLUSIONS

Our findings clearly elucidate the colour inheritance pattern in rice that may facilitate to develop rapid chemical tests to identify/ group the varieties for genetic purity analysis.

NKD Transcription Factors Are Central Regulators of Maize Endosperm Development

NAKED ENDOSPERM1 (NKD1) and NKD2 are duplicate INDETERMINATE DOMAIN (IDD) transcription factors important for maize (Zea mays) endosperm development. RNA-seq analysis of the nkd1 nkd2 mutant endosperm revealed that NKD1 and NKD2 influence 6.4% of the transcriptome in developing aleurone and 6.7% in starchy endosperm. Processes regulated by NKD1 and NKD2 include gene expression, epigenetic functions, cell growth and division, hormone pathways, and resource reserve deposition. The NKD1 and NKD2 proteins bind a consensus DNA sequence of TTGTCGT with slightly different properties. This motif was enriched in the promoters of gene transcripts differentially expressed (DE) in mutant endosperm. DE genes with a NKD binding motif in the 5' promoter region were considered as likely direct targets of NKD1 and NKD2 regulation, and these putative direct target genes were notably enriched for storage proteins. Transcription assays demonstrate that NKD1 and NKD2 can directly regulate gene transcription, including activation of opaque2 and viviparous1 promoters. NKD2 functions as a negative regulator of nkd1 transcription, consistent with previously reported feedback regulation. NKD1 and NKD2 can homo- and heterodimerize through their ID domains. These analyses implicate NKD1 and NKD2 as central regulators of gene expression in developing maize endosperm.

Folate distribution in barley (Hordeum vulgare L.), common wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum durum Desf.) pearled fractions

BACKGROUND

Wholegrain cereals are an important source of folates. In this study, total folate was analysed in pearled fractions of barley and wheat cultivars employing AOAC Official Method 2004.05. In particular, the distribution of folate in the kernels was evaluated in three barley cultivars (two hulled types and a hulless one as well as two- and six-row types) and in a common and a durum wheat cultivar.

RESULTS

A noticeable variation in the folate content was observed between the barley [653-1033 ng g(-1) dry matter (DM)] and wheat cultivars (1024-1119 ng g(-1) DM). The highest folate content was detected in the hulless barley cultivar (1033 ng g(-1) DM). A significant reduction in total folate, from 63% to 86%, was observed in all cultivars from the outermost to the innermost pearled fractions.

CONCLUSION

Results proved that folates are mainly present in the germ and in the outer layers of the kernel. This is the first study reporting the folate distribution in kernels of both common and durum wheat and in a hulless barley cultivar. Results suggest that the pearling process could be useful for the selection of intermediate fractions that could be used in order to develop folate-enhanced ingredients and products.

Wheat (Triticum aestivum L.) Bran in Bread Making: A Critical Review

Wheat bran, a by-product of the industrial roller milling of wheat, is increasingly added to food products because of its nutritional profile and physiological effects. Epidemiological data and scientific studies have demonstrated the health benefits of consuming bran-rich or whole-grain food products. However, incorporation of wheat bran in cereal-based products negatively affects their production process. Furthermore, the organoleptic quality of the obtained products is mostly perceived as inferior to that of products based on refined wheat flour. This review summarizes the current knowledge on the impact of wheat bran on bread making, provides a comprehensive overview of the bran properties possibly involved, and discusses different strategies that have been evaluated up till now to counteract the detrimental effects of wheat bran on bread making.

Advances in plant proteomics toward improvement of crop productivity and stress resistancex

Abiotic and biotic stresses constrain plant growth and development negatively impacting crop production. Plants have developed stress-specific adaptations as well as simultaneous responses to a combination of various abiotic stresses with pathogen infection. The efficiency of stress-induced adaptive responses is dependent on activation of molecular signaling pathways and intracellular networks by modulating expression, or abundance, and/or post-translational modification (PTM) of proteins primarily associated with defense mechanisms. In this review, we summarize and evaluate the contribution of proteomic studies to our understanding of stress response mechanisms in different plant organs and tissues. Advanced quantitative proteomic techniques have improved the coverage of total proteomes and sub-proteomes from small amounts of starting material, and characterized PTMs as well as protein-protein interactions at the cellular level, providing detailed information on organ- and tissue-specific regulatory mechanisms responding to a variety of individual stresses or stress combinations during plant life cycle. In particular, we address the tissue-specific signaling networks localized to various organelles that participate in stress-related physiological plasticity and adaptive mechanisms, such as photosynthetic efficiency, symbiotic nitrogen fixation, plant growth, tolerance and common responses to environmental stresses. We also provide an update on the progress of proteomics with major crop species and discuss the current challenges and limitations inherent to proteomics techniques and data interpretation for non-model organisms. Future directions in proteomics research toward crop improvement are further discussed.

The cereal starch endosperm development and its relationship with other endosperm tissues and embryo

The cereal starch endosperm is the central part of endosperm, and it is rich in starch and protein which are the important resources for human food. The starch and protein are separately accumulated in starch granules and protein bodies. Content and configuration of starch granules and protein bodies affect the quality of the starch endosperm. The development of starch endosperm is mediated by genes, enzymes, and hormones, and it also has a close relationship with other endosperm tissues and embryo. This paper reviews the latest investigations on the starch endosperm and will provide some useful information for the future researches on the development of cereal endosperm.

Polyphenol oxidase as a biochemical seed defense mechanism

Seed dormancy and resistance to decay are fundamental survival strategies, which allow a population of seeds to germinate over long periods of time. Seeds have physical, chemical, and biological defense mechanisms that protect their food reserves from decay-inducing organisms and herbivores. Here, we hypothesize that seeds also possess enzyme-based biochemical defenses, based on induction of the plant defense enzyme, polyphenol oxidase (PPO), when wild oat (Avena fatua L.) caryopses and seeds were challenged with seed-decaying Fusarium fungi. These studies suggest that dormant seeds are capable of mounting a defense response to pathogens. The pathogen-induced PPO activity from wild oat was attributed to a soluble isoform of the enzyme that appeared to result, at least in part, from proteolytic activation of a latent PPO isoform. PPO activity was also induced in wild oat hulls (lemma and palea), non-living tissues that cover and protect the caryopsis. These results are consistent with the hypothesis that seeds possess inducible enzyme-based biochemical defenses arrayed on the exterior of seeds and these defenses represent a fundamental mechanism of seed survival and longevity in the soil. Enzyme-based biochemical defenses may have broader implications since they may apply to other defense enzymes as well as to a diversity of plant species and ecosystems.

Differentiation mechanism and function of the cereal aleurone cells and hormone effects on them

The cereal aleurone cells differentiate from the endosperm epidermis with the exception of endosperm transfer cells. Aleurone cells contain proteins, lipids, and minerals, and are important for digesting the endosperm storage products to nurse the embryo under effects of several hormones during the seed germination. The differentiation of aleurone cells is related to location effect and special gene expression. Moreover, the differentiation of aleurone cells is probably affected by the cues from maternal tissues. In the paper, differentiation mechanism and function of aleurone cells and hormone effects on them are reviewed. Some speculations about the differentiation mechanism of aleurone cells are given here.

Spatial X-ray fluorescence micro-imaging of minerals in grain tissues of wheat and related genotypes

Wheat and its related genotypes show distinct distribution patterns for mineral nutrients in maternal and filial tissues in grains. X-ray-based imaging techniques are very informative to identify genotypes with contrasting tissue-specific localization of different elements. This can help in the selection of suitable genotypes for nutritional improvement of food grain crops. Understanding mineral localization in cereal grains is important for their nutritional improvement. Spatial distribution of mineral nutrients (Mg, P, S, K, Ca, Fe, Zn, Mn and Cu) was investigated between and within the maternal and filial tissues in grains of two wheat cultivars (Triticum aestivum Cv. WH291 and WL711), a landrace (T. aestivum L. IITR26) and a related wild species Aegilops kotschyi, using micro-proton-induced X-ray emission (µ-PIXE) and micro-X-ray fluorescence (µ-XRF). Aleurone and scutellum were major storage tissues for macro (P, K, Ca and Mg) as well as micro (Fe, Zn, Cu and Mn) nutrients. Distinct elemental distribution patterns were observed in each of the four genotypes. A. kotschyi, the wild relative of wheat and the landrace, T. aestivum L. IITR26, accumulated more Zn and Fe in scutellum and aleurone than the cultivated wheat varieties, WH291 and WL711. The landrace IITR26, accumulated far more S in grains, Mn in scutellum, aleurone and embryo region, Ca and Cu in aleurone and scutellum, and Mg, K and P in scutellum than the other genotypes. Unlike wheat, lower Mn and higher Fe, Cu and Zn concentrations were noticed in the pigment strand of A. kotschyi. Multivariate statistical analysis, performed on mineral distribution in major grain tissues (aleurone, scutellum, endosperm and embryo region) resolved the four genotypes into distinct clusters.

Gibberellic acid-induced aleurone layers responding to heat shock or tunicamycin provide insight into the N-glycoproteome, protein secretion, and endoplasmic reticulum stress

The growing relevance of plants for the production of recombinant proteins makes understanding the secretory machinery, including the identification of glycosylation sites in secreted proteins, an important goal of plant proteomics. Barley (Hordeum vulgare) aleurone layers maintained in vitro respond to gibberellic acid by secreting an array of proteins and provide a unique system for the analysis of plant protein secretion. Perturbation of protein secretion in gibberellic acid-induced aleurone layers by two independent mechanisms, heat shock and tunicamycin treatment, demonstrated overlapping effects on both the intracellular and secreted proteomes. Proteins in a total of 22 and 178 two-dimensional gel spots changing in intensity in extracellular and intracellular fractions, respectively, were identified by mass spectrometry. Among these are proteins with key roles in protein processing and secretion, such as calreticulin, protein disulfide isomerase, proteasome subunits, and isopentenyl diphosphate isomerase. Sixteen heat shock proteins in 29 spots showed diverse responses to the treatments, with only a minority increasing in response to heat shock. The majority, all of which were small heat shock proteins, decreased in heat-shocked aleurone layers. Additionally, glycopeptide enrichment and N-glycosylation analysis identified 73 glycosylation sites in 65 aleurone layer proteins, with 53 of the glycoproteins found in extracellular fractions and 36 found in intracellular fractions. This represents major progress in characterization of the barley N-glycoproteome, since only four of these sites were previously described. Overall, these findings considerably advance knowledge of the plant protein secretion system in general and emphasize the versatility of the aleurone layer as a model system for studying plant protein secretion.

Use of an extruder for pre-mixing enhances xylanase action on wheat bran at low water content

The aim of the work was to test the hypothesis that at low water content enzyme action on biomass is enhanced when the raw material is in the form of a continuous mass instead of powder/granular form. Effects of two pre-mixing methods, blade-mixing and extrusion, on xylanase action were studied during stationary incubation of wheat bran of different particle sizes, also in comparison with incubation at high water content with continuous stirring. The use of an extruder enhanced arabinoxylan (AX) solubilisation at low water content (<54%), as compared to blade-mixing. AX solubilisation was highest in the high-water stirring treatment, but based on molecular weight, xylanase action on solubilised AX was similar as in the extrusion-aided process. Pre-mixing by extrusion enabled efficient enzyme action at low water content without the requirement for continuous mixing, probably due to the enhanced diffusion by the formation of a continuous mass in the extruder.