Allelopathy in wheat (Triticum aestivum)

Wheat (Triticum aestivum) allelopathy has potential for the management of weeds, pests and diseases. Both wheat residue allelopathy and wheat seedling allelopathy can be exploited for managing weeds, including resistant biotypes. Wheat varieties differ in allelopathic potential against weeds, indicating that selection of allelopathic varieties might be a useful strategy in integrated weed management. Several categories of allelochemicals for wheat allelopathy have been identified, namely, phenolic acids, hydroxamic acids and short‐chain fatty acids. Wheat allelopathic activity is genetically controlled and a multigenic model has been proposed. Research is underway to identify genetic markers associated with wheat allelopathy. Once allelopathic genes have been located, a breeding programme could be initiated to transfer the genes into modern varieties for weed suppression. The negative impacts of wheat autotoxicity on agricultural production systems have also been identified when wheat straws are retained on the soil surface for conservation farming purposes. A management package to avoid such deleterious effects is discussed. Wheat allelopathy requires further study in order to maximise its allelopathic potential for the control of weeds, pests and diseases, and to minimise its detrimental effects on the growth of wheat and other crops.     

Influence of ozone on ribonuclease activity in wheat (Triticum aestivum) leaves

Ribonucleases (RNases) degrade RNA and exert a major influence on gene expression during development and in response to biotic and abiotic stresses. RNase activity typically increases in response to pathogen attack, wounding and phosphate (P(i)) deficiency. Activity also increases during senescence and other programmed cell death processes. The air pollutant ozone (O(3)) often induces injury and accelerated senescence in many plants, but the biochemical mechanisms involved in these responses remain unclear. The objective of this study was to determine whether RNase activity and isozyme expression was stimulated in wheat (Triticum aestivum L.) flag leaves following treatment with O(3). Plants were treated in open-top chambers with charcoal-filtered air (27 nmol O(3) mol(-1)) (control) or non-filtered air plus O(3) (90 nmol O(3) mol(-1)) (O(3)) from seedling to reproductive stage. After exposure for 56 days, RNase activity was 2.1 times higher in flag leaf tissues from an O(3)-sensitive cultivar in the O(3) treatment compared with the control, which generally coincided with foliar injury and lower soluble protein concentration, but not soluble leaf [P(i)]. Soluble [P(i)] in leaf tissue extracts from the O(3) and control treatments was not significantly different. RNase activity gels indicated the presence of three major RNases and two nucleases, and their expression was enhanced by the O(3) treatment. Isozymes stimulated in the O(3) treatment were also stimulated in naturally senescent flag leaf tissues from plants in the control. However, soluble [P(i)] in extracts from naturally senescent flag leaves was 50% lower than that found in green flag leaves in the control treatment. Thus, senescence-like pathological responses induced by O(3) were accompanied by increased RNase and nuclease activities that also were observed in naturally senescent leaves. However, [P(i)] in the leaf tissue samples suggested that O(3)-induced injury and accelerated senescence was atypical of normal senescence processes in that P(i) export was not observed in O(3)-treated plants.     

低磷和干旱胁迫对小麦生长发育影响的研究初探

研究了低磷和干旱胁迫对小麦（Triticum aestivum L.）生长发育的影响。结果表明,低磷胁迫能显著降低小麦的分蘖数、叶片相对含水量和叶绿素含量,进而抑制小麦的生长发育,降低其生物产量和经济产量,不耐低磷品种中国春受影响的程度要大于耐低磷品种烟中144。在相同条件下,干旱能够强化磷胁迫效应,表现出明显的胁迫叠加现象。     

小麦化感作用研究进展

小麦是世界第一大粮食作物,在农业生产中占有重要地位.然而,由于人们为保证小麦产量往往施用大量的除草剂和杀菌剂,对环境造成了极大的危害.小麦化感作用是利用小麦活体或残体向环境中释放次生代谢物质对自身或其他生物产生作用,它克服了除草剂和杀菌剂等引起的环境污染问题,具有抑制杂草控制病害的潜力.本文对已有的小麦化感作用的研究进展情况进行了综合评述.其中小麦对杂草、虫害及病害产生防御功能的主要化感物质为异羟肟酸和酚酸类物质.小麦化感物质活性的发挥除了取决于化感物质的种类外,还由小麦自身的遗传因素、环境因素和生物因素的共同作用所决定.小麦化感物质在根际土壤中的滞留、迁移和转化过程、小麦化感作用与土壤生物的关系以及相关的作用机理是小麦化感作用研究的薄弱环节,其研究方法还需进一步探索改进.小麦化感作用在植物保护、环境保护以及作物育种等方面具有广泛的应用前景,促进了小麦抗逆性的增强以及产量和品质的提高.     

小麦化感作用研究进展

小麦是世界第一大粮食作物,在农业生产中占有重要地位．然而,由于人们为保证小麦产量往往施用大量的除草剂和杀菌剂,对环境造成了极大的危害．小麦化感作用是利用小麦活体或残体向环境中释放次生代谢物质对自身或其他生物产生作用,它克服了除草剂和杀菌剂等引起的环境污染问题,具有抑制杂草控制病害的潜力．本文对已有的小麦化感作用的研究进展情况进行了综合评述．其中小麦对杂草、虫害及病害产生防御功能的主要化感物质为异羟肟酸和酚酸类物质．小麦化感物质活性的发挥除了取决于化感物质的种类外,还由小麦自身的遗传因素、环境因素和生物因素的共同作用所决定．小麦化感物质在根际土壤中的滞留、迁移和转化过程、小麦化感作用与土壤生物的关系以及相关的作用机理是小麦化感作用研究的薄弱环节。其研究方法还需进一步探索改进．小麦化感作用在植物保护、环境保护以及作物育种等方面具有广泛的应用前景,促进了小麦抗逆性的增强以及产量和品质的提高．     

Effects of shade on root characters associated with lodging in wheat (Triticum aestivum)

Previous work has shown that as the density of wheat plants increase, the spread of the root plate, root length and root number per plant decrease, leading to reduced anchorage strength and increased lodging susceptibility. The aim of this study was to determine which aspect of mutual plant shading [reduction of photosynthetically active radiation (PAR) or the ratio of red to far red light (R : FR)] is associated with this reduction in anchorage strength. Field experiments were conducted at Sutton Bonington, Leicestershire, UK, in two seasons using a range of plant densities in conjunction with shading materials to manipulate PAR and R : FR independently. The spread of the root plate, which has been linked most strongly with anchorage strength, was almost exclusively influenced by PAR intercepted per plant at the beginning of stem extension. Root number and root length were influenced by both PAR and R : FR. When structural roots (defined as thicker than 0.5 mm) and nonstructural roots were considered separately, it was discovered that increasing plant density and PAR shading reduced the length of both structural and nonstructural roots. However, reducing R : FR only reduced the length of structural roots without affecting the length of nonstructural roots.     

Genetic control of in vitro response in wheat (Triticum aestivum L.)

Summary The present state of genetic control of in vitro responses of wheat and of the prospeets of its improvement and practical use are presented. The genetic factors affecting different stages of callus induction and of organogenesis in immature embryos are discussed. The dominant genotypie role in the in vitro processes and the cytoplasmic influence on the latter are shown. Genotype × environment and nucleus × cytoplasm interactions were observed. Some unsolved problems needing further investigations of cereals at the tissue culture level are pointed out.     

Genetics of yellow berry in wheat (Triticum aestivum)

Summary The inheritance of yellow berry, a grain disorder in durum and bread wheats, was studied in six intervarietal crosses in bread wheat. The trait was found to be controlled by either two or three dominant genes. Monosomic analysis using Chinese Spring monosomic series showed the presence of two major dominant genes on chromosomes 1A and 7A, and four modifiers on 4A, 4B, 6A and 6D, which influence the expression of yellow berry in bread wheat.     

Modelling potassium uptake by wheat (Triticum aestivum) crops

Spring wheat was grown in the field under deficient and sufficient levels of soil K and with high and low supplies of fertiliser nitrogen. Measurements were made of K uptake, soil nutrient supply parameters, root growth and, in solution culture, root influx parameters. Mechanistic models predicted uptake reasonably well under K-deficient conditions, but over-predicted uptake, by as much as 4 times, under K-sufficient conditions. The over-prediction was apparently due to poor characterisation of plant demand.     

Identification and verification of microRNA in wheat (Triticum aestivum)

MicroRNAs (miRNAs) are small, endogenous RNAs that regulate gene expression in both plants and animals. A large number of miRNAs has been identified from various animals and model plant species such as Arabidopsis thaliana and rice (Oryza sativa); however, characteristics of wheat (Triticum aestivum) miRNAs are poorly understood. Here, computational identification of miRNAs from wheat EST sequences was preformed by using the in-house program GenomicSVM, a prediction model for miRNAs. This study resulted in the discovery of 79 miRNA candidates. Nine out of 22 miRNA representatives randomly selected from the 79 candidates were experimentally validated with Northern blotting, indicating that prediction accuracy is about 40%. For the 9 validated miRNAs, 59 wheat ESTs were predicted as their putative targets. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Weibo Jin and Nannan Li contributed equally to the work.     

Effects of pressure on germination of seeds of wheat (Triticum aestivum cv. Barqai) in saline and in non-saline media

The effects of an increase in the absolute environmental pressure (air, N₂, O₂ or hydrostatic), up to 1 MPa, on the germination of wheat seeds and the survival of wheat seedlings were studied. Seeds were exposed to saline and non-saline media, in Petri dishes, on a double layer of filter paper. They were then introduced for different time periods into a pressure chamber and pressurized by the addition of N₂ to the chamber in the range of ambient to 1 MPa. Subsequently the seeds were left to germinate under normal atmospheric conditions. Seed germination and subsequent growth decreased during the first 6 h and then regained the control levels. Nevertheless, application of similar pressures to seeds which had been submerged under water was highly inhibitory. Such effects of pressure seem to be the result of flooding with water of some crucial intercellular spaces and a consequent disturbance of O₂ supply to the germinating embryo. The additional flood-water comprised only 1–3% of the total water content of 24-h-old seedlings. Sensitivity of the submerged seeds and the germinating seedlings to pressure varied with age and developmental stage. Highest sensitivity to pressure was obtained with 12 to 72-h-old submerged seedlings. Removal of the excess water after the pressure treatment restored the germinability of the seeds.     

Translocation and utilization of carbon in wheat (Triticum aestivum)

Wheat ( Triticum aestivum L. cv. SUN 9E) was grown in a growth chamber under conditions of low soil nitrogen. Translocation of carbon to the roots and the subsequent utilization of these carbohydrates was determined. In vegetative plants (22 days old), 21.5 mg C day⁻¹ were translocated to the roots. 29% of this was incorporated into dry matter, 32% was respired (28% via the cytochrome and 4% via a SHAM-sensitive, presumably the alternative nonphosphorylating, pathway) and 39% was translocated back to the shoots, mainly in the form of amino acids. – The rote of root maintenance respiration during the vegetative phase was estimated to be 0.7 mg O₂ h⁻¹ (g dry weight of roots)⁻¹ and the root growth respiration to be 0.41 g O₂ (g dry weight of roots)⁻¹. Total carbohydrate utilization due to root respiration via the alternative, nonphosphorylating pathway during the major part of the growth period was calculated to be only ca 6% of carbohydrate utilization for grain growth. The rate of specific mass transfer (SMT) of sugars in the sieve tubes was estimated from the data on C-translocation and data on the total area occupied by sieve tubes in a cross section of the root system. SMT was calculated to be 0.8 mg sucrose s⁻¹ cm⁻², which is very similar to the published value on SMT for other organs, except roots.     

Chaotropic effects on 2,4,6-trinitrotoluene uptake by wheat (Triticum aestivum)

Previous research in our laboratory investigated the effectiveness of a common agrochemical, urea used as a chaotropic agent to facilitate 2,4,6-trinitrotoluene (TNT) removal by vetiver grass (Vetiveria zizanioides L.). Chaotropic agents disrupt water structure, increasing solubilization of hydrophobic compounds (TNT), and enhancing plant TNT uptake. Our findings showed that urea significantly enhanced TNT uptake kinetics by vetiver. We hypothesized that the beneficial effect of urea on the overall TNT uptake by vetiver grass was not plant-specific. We explored this hypothesis by testing the ability of wheat (Triticum aestivum L.) in removing TNT from aqueous media in the presence of urea. Results showed that untreated (no urea) wheat exhibited a slow, kinetically limited TNT uptake that was nearly half of the urea-treated wheat TNT capacity (250 mg kg⁻¹). Chaotropic effects of urea were illustrated by the significant (P < 0.001) increase in the TNT second-order reaction rate constants over those of the untreated (no urea) controls. Plant TNT speciation showed that TNT and several of its metabolites were detected in both root and shoot compartments of the plant, allowing for 110 and 36% recovery for the untreated and 0.1% urea treated plants. The lower % recovery of the urea-treated plants was attributed to a number of unknown polar TNT metabolites. Responsible Editor: Hans Lambers.     

Influence of Rhizobial inoculation on yield of wheat (Triticum aestivum L.)

Summary Soil + charcoal (1∶3) carrier based and liquid cultures of Rhizobia were used to inoculate wheat seed cv. HD2329. The plants received 100 kg N in two equal splits and 60 kg P₂O₅ and 40 kg K₂₀ ha⁻¹. Inoculation with rhizobia had little effect on grain yield of wheat. Significant increase in straw yield and N-uptake occurred due to inoculation. A comparison of results of a similar experiment conducted during 1983–84, showed that inoculation with the same strains of rhizobia and application 50 kg N ha⁻¹ as basal dressing, was more effective in increasing yield and N-uptake in wheat cv. HD2329. It appears reasonable to assume occurrence of nitrogen fixation by root nodule bacteria in rhizosphere of wheat.     

Intrachromosomal mapping of crossability genes in wheat (Triticum aestivum)

Summary Intrachromosomal mapping studies were used to locate the positions of the genes Kr1 and Kr2, which control the crossability of wheat with Hordeum bulbosum, on chromosomes 5B and 5A, respectively. The location of Kr1 was established using the telocentric mapping technique and found to be on the long arm of chromosome 5B, distal to the centromere with a mean recombination frequency of 44.8±3.28%. Kr2 was located on the long arm of chromosome 5A by linkage with the major gene markers Vrn1, controlling vernalization requirement, and q, controlling ear morphology. Kr2 is closely linked to Vrn1, with a mean recombination frequency of 4.8±4.66%, and is distal to q with a mean recombination frequency of 38.1±10.60%. The similar locations of Kr1 and Kr2 on homoeologous chromosomes suggest that these two loci are homoeoallelic. Significant correlations between Hordeum bulbosum and rye crossability confirmed that Kr1 and Kr2 control the crossability of wheat with both species.     

Changes in activity of antioxidative enzymes in wheat (Triticum aestivum) seedlings under cold acclimation

Activated oxygen species such as superoxide radicals, singlet oxygen, hydrogen peroxide and hydroxyl radicals can be produced in plants exposed to low, non-freezing, non-injurious temperatures. To prevent or alleviate oxidative injury, plants have evolved several mechanisms which include scavenging by natural antioxidants and enzymatic antioxidant systems such as superoxide dismutases, catalase and peroxidases. Although overproduction of hydrogen peroxide and increased tolerance to oxidative stress can be induced in wheat by low-temperature treatments, data concerning changes in the enzymatic antioxidant systems are almost absent. With the aim to provide this information, antioxidant enzyme (superoxide dismutases, catalase and peroxidases) activities were analysed in leaves and roots of Triticum aestivum cvs Brasilia (frost resistant in field) and Eridano (less frost resistant in field) seedlings grown at day/night temperatures of 24/22°C (control treatment) and 12/5°C (low-temperature treatment). Our data showed that superoxide dismutase activities were unaffected by low-temperature treatment both in leaves and roots. Catalase activity in leaves and roots was decreased in 12/5°C-grown seedlings, but Brasilia maintained higher catalase activity than Eridano. Differences were also observed in guaiacol peroxidase activities between control and acclimated seedlings: Higher guaiacol peroxidase activities were found in the leaves of 12/5°C-grown seedlings while in roots these activities were lower. Moreover, Brasilia guaiacol peroxidase activities were higher than Eridano. Superoxide dismutase and peroxidase zymogram analyses showed that synthesis of new isoforms was not induced by low-temperature treatment. Changes in the activities of antioxidant enzymes induced by cold acclimation support the hypothesis that a frost-resistant wheat cultivar, in comparison with a less frost-resistant one, maintains a better defence against activated oxygen species during low-temperature treatment.     

Sucrose metabolism during endosperm development in wheat (Triticum aestivum)

This work reports changes in sucrose synthase and invertase activities throughout endosperm development in wheat, together with the associated substrates and metabolites, sucrose, UDP, glucose, fructose and UDP-glucose. Throughout endosperm development, sucrose synthase had consistently higher activity than invertase and indeed invertase activity did not change appreciably. The observed variation in pattern and amounts of glucose and fructose present during the mid- and late stages of endosperm development confirmed the suggestion that invertase was not the preferred pathway of sucrose catabolism. Kinetic parameters for sucrose synthase were determined in crude extracts. Estimates of UDP and sucrose concentrations suggest that sucrose synthase is unlikely to achieve its potential maximum velocity. This limitation may however be overcome in part by the apparent excess catalytic activity measured during endosperm development.     

Effects of Eu and Ca on yield and mineral nutrition of wheat (Triticum aestivum) seedlings

Although fertilisers enriched in rare earth elements (REE) are widely used in agricultural practice, little is known yet about behaviour of the REE in soil–plant system. Among REE, europium (Eu) may be of highest interest. Eu may serve as an indicator of biogeochemical processes due to a change of its valence state under different environmental conditions. Since chemical characteristics of Ca and REE are similar, Eu may compete with Ca for organic ligands. In the present work we studied the influence of Eu and Ca on the growth and mineral nutrition of wheat seedlings. An application of Eu favoured germination and root growth, whereas in combination with Ca it produced a more sustained leaf growth. Eu affected uptake and distribution of certain nutrients in different parts of a plant. The content of Eu in all parts of wheat seedlings at the end of germination significantly increased. Transfer of the seedlings germinated in the Eu-rich medium into soil resulted in the release of Eu from the plants. Nevertheless, 9 days after the sowing, Eu concentration in the seedlings was still much higher than in the control plants.