The development of waterlogging damage in wheat seedlings (Triticum aestivum L.)

Summary Decreases in the concentrations of nitrogen, phosphorus, potassium, calcium and magnesium, in the shoots of wheat seedlings soon after the start of waterlogging were mainly attributed to an inhibition of ion uptake and transport by roots in the oxygen deficient soil. There was a small net accumulation of nitrogen, phosphorus and potassium by the aerial tissues, principally the tillers rather than the main shoot. By contrast, calcium and magnesium accumulated in both tillers and main shoot. With waterlogging, nitrogen, phosphorus and potassium were translocated from the older leaves to the younger growing leaves, and in the case of nitrogen this was associated with the onset of premature senescence. Calcium and magnesium were not translocated from the older leaves, the younger leaves acquiring these cations from the waterlogged soil. The promotion of leaf senescence by waterlogging was counteracted by applications of nitrate or ammonium to the soil surface, or by spraying the shoots with solutions of urea, but the beneficial effects on shoot growth were small.The role of mineral nutrition in relation to waterlogging damage to young cereal plants is discussed.     

The development of waterlogging damage in wheat seedlings (Triticum aestivum L.)

Summary The effects of waterlogging on concentrations of gases and various solutes dissolved in the soil water were investigated in the laboratory, to determine whether the early disruption to the growth of wheat was most closely associated with depletion of dissolved oxygen, accumulation of toxins, or changes in concentrations of nutrient ions in the soil water. Waterlogging slowed shoot fresh weight accumulation, leaf extension and nodal root growth; it also caused death of the seminal root system and early senescence of the lower leaves. However, the shoot dry weight initially increased above that of the non-waterlogged controls, and thus was not a reliable indicator of the early restriction to plant growth and development. The symptoms of damage to shoots and roots were attributed to the fall in soil oxygen concentrations, rather than to any decrease in concentration of inorganic nutrients in the soil water, or to the accumulation of any other measured solutes to toxic concentrations.     

The wheat (Triticum aestivum L.) leaf proteome

The wheat leaf proteome was mapped and partially characterized to function as a comparative template for future wheat research. In total, 404 proteins were visualized, and 277 of these were selected for analysis based on reproducibility and relative quantity. Using a combination of protein and expressed sequence tag database searching, 142 proteins were putatively identified with an identification success rate of 51%. The identified proteins were grouped according to their functional annotations with the majority (40%) being involved in energy production, primary, or secondary metabolism. Only 8% of the protein identifications lacked ascertainable functional annotation. The 51% ratio of successful identification and the 8% unclear functional annotation rate are major improvements over most previous plant proteomic studies. This clearly indicates the advancement of the plant protein and nucleic acid sequence and annotation data available in the databases, and shows the enhanced feasibility of future wheat leaf proteome research.     

Lead phytotoxicity on wheat (Triticum aestivum L.) seed germination and seedlings growth

Lead (Pb) is an environmental pollutant extremely toxic to plants and other living organisms including humans. To assess Pb phytotoxicity, experiments focusing on germination of wheat seeds were germinated in a solution containing Pb (NO(3))(2) (0.05; 0.1; 0.5; 1g/L) during 6 days. Lead accumulation in seedlings was positively correlated with the external concentrations, and negatively correlated with morphological parameters of plant growth. Lead increased lipid peroxidation, enhanced soluble protein concentrations and induced a significant accumulation of proline in roots. Esterase activity was enhanced in the presence of lead, whereas α-amylase activity was significantly inhibited. Antioxidant enzymes activities, such as, ascorbate peroxidase, peroxidase, superoxide dismutase, catalase and glutathione S-transferase were generally significantly increased in the presence of lead in a dose-dependent manner. The present results thus provide a model system to screen for natural compounds able to counteract the deleterious effects of lead.     

Silicon absorption by wheat (Triticum aestivum L.)

Although silicon (Si) is a quantitatively major inorganic constituent of higher plants the element is not considered generally essential for them. Therefore it is not included in the formulation of any of the solution cultures widely used in plant physiological research. One consequence of this state of affairs is that the absorption and transport of Si have not been investigated nearly as much as those of the elements accorded 'essential' status. In this paper we report experiments showing that Si is rapidly absorbed by wheat (Triticum aestivum L.) plants from solution cultures initially containing Si at 0.5 mM, a concentration realistic in terms of the concentrations of the element in soil solutions. Nearly mature plants (headed out) 'preloaded' with Si absorbed it at virtually the same rate as did plants grown previously in solutions to which Si had not been added. The rate of Si absorption increased by more than an order of magnitude between the 2-leaf and the 7-8 leaf stage, with little change thereafter. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effect of ovary-conditioned medium on microspore embryogenesis in common wheat (Triticum aestivum L.)

Microspores were isolated from wheat (Triticum aestivum L.) spikes of various genotypes following an effective pretreatment that induced microspore embryogenesis. The isolated microspores were cultured with or without live ovaries, and with or without medium pre-conditioned by ovaries for varying periods of time. Live ovaries alone increased androgenic embryoid yields up to 4.5-fold over the control for microspores isolated from responsive genotypes. While live ovary co-culture alone was not effective for microspores isolated from recalcitrant genotypes, the addition of medium preconditioned by ovaries to microspore cultures increased embryoid yield by more than 100-fold. Without ovary-conditioned medium, no embryoids could be obtained from some recalcitrant genotypes. Ovary-conditioned medium apparently functions to increase embryoid yields by providing essential substance(s) for elaboration of the embryogenic program already triggered during pretreatment.     

Prevalence and control of wheat (Triticum aestivum L.) seed borne fungi in farmer-saved seeds

High incidence of diseases associated with the use of seeds saved from previous harvests as desire of maintaining local varieties with special attributes is of increased concern in wheat industry worldwide. Prevalent of seed-borne fungi in farmer-saved seeds and seed dressing fungicides to prevent infection from seeds to seedlings was studied in Northern Tanzania. One hundred and thirty five untreated farmer-saved seed lots were collected randomly from farmers. Alternaria alternata, Bipolaris sorokiniana, Drechslera tritici, Fusarium graminearum, Fusarium moniliforme, Aspergillus flavus, Cladosporium sphaerospermum, Epicoccum purpurascens, Pyricularia oryzae and Penicillium corylophilum were fungi isolated in farmer-saved seeds. Mean seed infection was 29% causing average grain yield loss of 1.2 mt/ha^?1. Seed dressing with Metalaxy plus (Methyl carboxaitide), Mancozeb (Manganase-zinc salt) and Baytan (Chlorophenoxy ethanol) increased seed germination by 14, 13 and 17%, respectively, and grain yield by 28, 20 and 18%, respectively. Farmer-saved seeds were heavily infected by fungi with low grain yield performance.     

The control of respiration in wheat (Triticum aestivum L.) leaves

The aim of this work was to discover whether the respiration of wheat (Triticum aestivum L. cv. Huntsman) leaves, transferred to darkness after 7 h photosynthesis, showed an initial period of wasteful respiration. For young and old leaves, CO₂ production and O₂ uptake after 7 h photosynthesis were up to 56% higher than at the end of an 8-h night. The maximum catalytic activities of citrate synthase (EC 4.1.3.7), aconitase (EC 4.2.1.3), fumarase (EC 4.2.1.2) and cytochrome-c oxidase (EC 1.9.3.1) at the end of the day did not differ from those at the end of the night. Changes in the contents of glucose 6-phosphate, fructose-1,6-bisphosphate, dihydroxyacetone phosphate, and -ketoglutarate did not as a group parallel the changes in the rate of respiration. The detailed distribution of label from [U-¹⁴C] sucrose supplied to leaves in the dark was similar at the end of the day and the end of the night. No correlation was observed between the rates of leaf respiration and extension growth. It is argued that the higher rate of respiration at the beginning of the night cannot be attributed to wasteful respiration.Abbreviation RQ respiratory quotient We thank Dr H. Thomas and Professor C.J. Pollock, Institute for Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, UK for their generous help in measuring leaf extension. R.H.A. thanks the Science and Engineering Research Council for a studentship.     

The effect of humus fractions on the phosphorylase activity of wheat (Triticum aestivum L.)

The liberation of phosphoric acid from glucose-1-phosphate, catalyzed by phosphorylase was studied in wheat growing in sand cultures with an addition of humic acid and hymatomelanic acid. It was found that the phosphorylase activity of tissues changes under the influence of humic acid very significantly. The maximum activity is reached at 10 mg humic acid/liter. The overground organs are less sensitive, as a stimulation effect is reached there only at 400 mg/liter. The effect of hymatomelanic acid is negligible in comparison with that of humic acid. The observed phenomenon is related to the effect of humus substances on the equilibrium of saccharides and on the distribution of dry matter in the plant.     

Hydrogen peroxide scavenging regulates germination ability during wheat (Triticum aestivum L.) seed maturation

Hydrogen peroxide (H₂O₂) promotes seed germination of cereal plants and ascorbic acid which acts as antioxidant suppresses the germination of wheat seeds, but the role of H₂O₂ scavenging on germination during seed maturation has not been demonstrated. We investigated relationship of germination, ascorbate, H₂O₂ scavenging enzymes and sensitivity to ascorbic acid (AsA) maturing seeds of two typical wheat (Triticum aestivum L.) cultivars, cvs. Shirogane-Komugi and Norin61. Shirogane-Komugi had marked high germination ability than Norin61 during seed maturation. Although the H₂O₂ content had no difference in the two culti-vars, sensitivity to AsA of Norin61 seeds was higher than that of Shirogane-Komugi seeds during seed maturation. The sensitivity to AsA closely correlated with germination characteristic in the two cultivars. Especially, at 28 days after pollination (DAP), sensitivity to AsA in Norin61 seeds was remarkably high. At that stage, no significant differences were observed in endogenous AsA level, ascorbate peroxidase (APX, EC 1.11.1.11) and dehydroascorbate reductase (DHAR, EC 1.8.5.1) activities in the two cultivars. However, catalase (CAT, EC 1.11.1.6) activity and CAT mRNA in Norin61 were remarkably higher than in Shirogane-Komugi. Sensitivity to AsA at 35 and 42 DAPs kept high levels in Norin61, and endogenous AsA and CAT activity in the seeds were significantly higher than in Shirogane-Komugi. These results revealed a direct correlation between germination and antioxidant sensitivity during the developmental stages of wheat seeds.Key words: ascorbic acid, germination, hydorogen peroxide, maturation, wheat seed     

Association mapping of kernel size and milling quality in wheat (Triticum aestivum L.) cultivars

Association mapping is a method for detection of gene effects based on linkage disequilibrium (LD) that complements QTL analysis in the development of tools for molecular plant breeding. In this study, association mapping was performed on a selected sample of 95 cultivars of soft winter wheat. Population structure was estimated on the basis of 36 unlinked simple-sequence repeat (SSR) markers. The extent of LD was estimated on chromosomes 2D and part of 5A, relative to the LD observed among unlinked markers. Consistent LD on chromosome 2D was <1 cM, whereas in the centromeric region of 5A, LD extended for approximately 5 cM. Association of 62 SSR loci on chromosomes 2D, 5A, and 5B with kernel morphology and milling quality was analyzed through a mixed-effects model, where subpopulation was considered as a random factor and the marker tested was considered as a fixed factor. Permutations were used to adjust the threshold of significance for multiple testing within chromosomes. In agreement with previous QTL analysis, significant markers for kernel size were detected on the three chromosomes tested, and alleles potentially useful for selection were identified. Our results demonstrated that association mapping could complement and enhance previous QTL information for marker-assisted selection.     

The duration and rate of grain growth, and harvest index, of wheat (Triticum aestivum L.) in response to temperature and CO2

Winter wheat (Triticum aestivum L. cv. Hereward) was grown inthe field inside polyethylene-covered tunnels at a range oftemperatures at either 380 or 684 µmol mol^–1 CO₂.Serial harvests were taken from anthesis until harvest maturity.Grain yield was reduced by warmer temperatures, but increasedby CO₂ enrichment at all temperatures. During grain-filling,individual grain dry weight was a linear function of time fromanthesis until mass maturity (attainment of maximum grain dryweight) within each plot. The rate of progress to mass maturity(the reciprocal of time to mass maturity) was a positive linearfunction of mean temperature, but was not affected by CO₂ concentration.The rate of increase in grain dry weight per ear was 2.0 mgd^–1 greater per 1 C rise, and was 8.0 mg d^–1 greaterat 684 compared with 380 µmol mol^–1 CO₂ at a giventemperature. The rate of increase in harvest index was 1.0%d^–1 in most plots at 380 µmol mol^–1 CO₂ andin open field plots, compared with 1.18% d^–1 in all plotsat 684 µmol mol^–1 CO₂. Thus, the increased rateof grain growth observed at an elevated CO₂ concentration couldbe attributed partly to a change in the partitioning of assimilatesto the grain. In contrast, the primary effect of warmer temperatureswas to shorten the duration of grain-filling. The rate of graingrowth at a given temperature and the rate of increase in harvestindex were only independent of the number of grains per earabove a critical grain number of 23–24 grains per ear({small tilde}20 000 grains m^–2). Key words: Winter wheat, grain growth, temperature, CO₂, harvest index, critical grain number     

The Golgi apparatus in developing endosperm of wheat (Triticum aestivum L.)

The ultrastructure and distribution of the Golgi apparatus in developing wheat endosperm was investigated using a zinc iodide-osmium tetroxide staining complex in conjunction with low and high voltage electron microscopy. Dictyosomes were numerous in starchy endosperm and aleurone at 15 days after anthesis, and during the period of rapid storage protein deposition 25 d after anthesis. Fewer dictyosomes were seen in maturing endosperm. Two types of vesicles were associated with the dictyosomes; small, heavily-stained vesicles were sited at the ends of fine tubules which extend from the cisternae, and larger less-stained vesicles were associated with the periphery of the cisternae. Stereo-pairs of micrographs up to 1 m thick were taken to demonstrate the interconnections between cisternal and tubular endoplasmic reticulum. Elements of tubular ER were closely associated with dictyosomes, but connections were not observed. These results are discussed in relation to the transport of endosperm storage proteins from their site of synthesis on the cisternal ER to their site of storage, the protein bodies.     

Agrobacterium-mediated In-planta transformation of bread wheat (Triticum aestivum L.)

Journal of Plant Biochemistry and Biotechnology - Agrobacterium-mediated in-planta transformation method allows efficient plant transformation without tissue culture. In the present study, a tissue...     

Accelerated production of transgenic wheat (Triticum aestivum L.) plants

We have developed a method for the accelerated production of fertile transgenic wheat (Triticum aestivum L.) that yields rooted plants ready for transfer to soil in 8–9 weeks (56–66 days) after the initiation of cultures. This was made possible by improvements in the procedures used for culture, bombardment, and selection. Cultured immature embryos were given a 4–6 h pre-and 16 h post-bombardment osmotic treatment. The most consistent and satisfactory results were obtained with 30 g of gold particles/bombardment. No clear correlation was found between the frequencies of transient expression and stable transformation. The highest rates of regeneration and transformation were obtained when callus formation after bombardment was limited to two weeks in the dark, with or without selection, followed by selection during regeneration under light. Selection with bialaphos, and not phosphinothricin, yielded more vigorously growing transformed plantlets. The elongation of dark green plantlets in the presence of 4–5 mg/l bialaphos was found to be reliable for identifying transformed plants. Eighty independent transgenic wheat lines were produced in this study. Under optimum conditions, 32 transformed wheat plants were obtained from 2100 immature embryos in 56–66 days, making it possible to obtain R3 homozygous plants in less than a year.     

Combined effect of salinity and hypoxia in wheat (Triticum aestivum L.) and wheat-Thinopyrum amphiploids

The effects of sodium chloride salinity and hypoxia were studied in eight wheat lines and three wheat-Thinopyrum amphiploids in vermiculite-gravel culture. The lines were treated with either 100 or 150 mol m^–3 NaCl with and without hypoxia. Saline hypoxic conditions significantly reduced the vegetative growth, water use, grain and straw yields for all wheat varieties except the amphiploids, whereas NaCl or hypoxia alone had less pronounced effects. In addition, saline hypoxic stress reduced K⁺ concentration and increased significantly the Na⁺ and Cl^– concentrations in cell sap expressed from leaves. There was more Na⁺ and Cl^– accumulation in wheats than the amphiploids in hypoxic conditions at 150 mol m^–3 NaCl. Of the wheats, Pato was the most sensitive at all stress levels while aTriticum aestivum cv. Chinese Spring ×Thinopyrum elongatum amphiploid was the most tolerant of the three amphiploids.     

The origin of the B-genome of bread wheat (Triticum aestivum L.)

Understanding the origin of cultivated wheats would further their genetic improvement. The hexaploid bread wheat (Triticum aestivum L., AABBDD) is believed to have originated through one or more rare hybridization events between Aegilops tauschii (DD) and the tetraploid T. turgidum (AABB). Progenitor, of the A-genome of the tetraploid and hexaploid wheats has generally been accepted to be T. urartu. In spite of the large number of attempts and published reports about the origin of the B-genome in cultivated wheats, the donor of the B-genome is still relatively unknown and controversial and, hence, remains open. This genome has been found to be closely related to the S-genome of the Sitopsis section (Ae. speltoides, Ae. longissima, Ae. sharonensis, Ae. searsii, and Ae. bicornis) of the genus Aegilops L. Among Sitopsis species, the most positive evidence has been accumulated for Ae. speltoides as the progenitor of the B-genome. Therefore, one or more of the Sitopsis species were proposed frequently as the B-genome donor. Although several reviews have been written on the origin of the genomes of wheat over the years, this paper will attempt for the first time to review the immense literature on the subject, with a particular emphasis on the B-genome which has attracted a huge attention over some 100 years. The ambiguity and conflicting results in most of the methods employed in deducing the precise B-genome donor/s to bread wheat are also discussed.     

Suspension and protoplast culture of hexaploid wheat (Triticum aestivum L.)

Suspension cultures have been initiated from embryogenic callus of hexaploid wheat (Triticum aestivum L.). Most commonly, these suspensions are composed of callus-like clusters (up to 2 mm in diameter). Two rapidly-growing lines (MBE6 and C82d) have been obtained, which consist of smaller aggregates of cytoplasmic cells, and these have been maintained for more than 4 years. These lines show very limited morphogenetic capacity and only a single plantlet has been regenerated, from line MBE6, after 9 months in culture. Protoplasts isolated from line MBE6 are unable to divide, but protoplasts from line C82d consistently undergo sustained divisions to form callus or secondary cell suspensions.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - MS Murashige and Skoog (1962) medium