Toxin production by a rhizobacterialPseudomonas sp. that inhibits wheat root growth

We studied the production of a toxin inhibitory to both winter wheat (Triticum aestivum L.) root growth andEscherichia coli that was produced by a rhizobacterial pseudomonad. Of several carbon sources tested, the most rapid growth and highest toxin concentrations were obtained with glucose, glycerol, or trehalose. Toxin production was repressed with L-cysteine as the nitrogen source. Toxin was produced during the late exponential and early stationary phase of growth by the bacterium and, contrary to studies with other toxins, was unaffected by Fe and P concentrations in the growth medium. Toxin production by the bacterium was the same at growth temperatures of 25 and 15°C while it produced less at 5°C. If the bacterium was able to grow, it produced toxin. No compound tested induced an increase in toxin production indicating toxin production is constitutive.Contribution from the Agric. Res. Serv., U.S. Dept. of Agriculture in cooperation with the College of Agric. and Home Econ., Res. Ctr., Washington State University, Pullman, Washington 99164.     

Characterization of a toxin produced by a rhizobacterialPseudomonas sp. that inhibits wheat growth

A toxin produced by a deleterious rhizobacterial pseudomonad that inhibits both winter wheat (Triticum aestivum L.) root andEscherichia coli growth was characterized. The toxin was rapidly deactivated at pH 2 and 12 and by autoclaving (121°C, 15 minutes). Less toxin was destroyed as the temperature and time of exposure decreased, and at 40°C it was stable for at least 24 hours. The toxin was extremely polar and could not be extracted from culture filtrates with organic solvents. The compound eluted after the void volume from a Sephadex G-10 column indicating a molecular weight of less than 700. The toxin adsorbed to Dowex 50W strong cation exchange resin and eluted with 2M NH₄OH. Numerous thin layer chromatography solvent systems were unsuccessful at purifying the toxin. The partially purified toxin inhibited several different microorganisms while the producing strains were resistant. The toxin appears unique to toxins produced by recognized plant pathogenic bacteria.Contribution from the Agric. Res. Serv., U.S. Dept. of Agriculture in cooperation with the College of Agric. and Home Econ., Res. Ctr., Washington State University, Pullman, WA 99164, USA     

Incidence of inhibitory pseudomonads in the Pacific Northwest

Incidence of pseudomonads inhibitory to the root growth of till and no-till seeded crops winter wheat (Triticum aestivum L.), pea (Pisum sativum), lentil (Lens culinaris), and no-till winter barley (Hordeum vulgare), top and bottom of a seeded slope, and on the weed downy brome (Bromus tectorum) was investigated. Pseudomonads on the rhizoplane of these plants ranged from 10⁶ to 10⁸ colony-forming units (cfu) per gram dry weight of root. Neither tillage management nor site on a seeded slope affected colonizing numbers. Total numbers of pseudomonads were reduced in a second sampling, particularly on winter barley roots. However, more inhibitory pseudomonads were found in the second sampling. Several of the isolates, both inhibitory and stimulatory from different host plants, were bioassayed against winter wheat seedlings. Generally, the effect was different on the winter wheat than on the host plant indicating the organisms had some specificity. Several pseudomonads were isolated that severely reduced downy brome root growth and not that of winter wheat. Contribution from Agric. Res. Serv., U S Dep. of Agric., in cooperation with the College of Agric, and Home Economics, Agric. Res. Center, Washington State Univ., Pullman, WA 99164. Scientific Paper No. 7491.     

Effects of crop residues,soil type and temperature on emergence and early growth of wheat

Summary Two controlled environment experiments were conducted to examine the germination and early growth of wheat (Triticum aestivum L. cv. Songlen) growing under crop residues of rape, sorghum, field pea and wheat. Additional treamments also included were soil type (Lithic Vertic Ustochrept and Plinthustalf) and temperature (8°C and 24°C to simulate winter and autumn sowing conditions). At low temperature, wheat and sorghum residues produced the most adverse effects on germination with all residues reducing emergence at high temperatures. Shoot lengths were also reduced by most residues at high temperatures whilst root lengths and shoot and root dry weights were unaffected by residue treatments. These results suggest major phytotoxic effects of residues during early growth (up to 14 days after sowing) with, in general, few interactions with soil type or temperature.     

Root colonization and growth promotion of winter wheat and pea by Cellulomonas spp. at different temperatures

Plant-growth-promoting bacteria isolated from the rhizosphere andphyllosphere were analysed for their colonization and growth-promoting effectson winter wheat and pea at different temperatures. The investigations werecarried out in pot experiments using loamy sand in Germany. The colonization ofstrains Cellulomonas sp. 21/2 andCellulomonas sp. 43 in the rhizosphere of winter wheat andpea were much better at 16 °C than that at 26°C. The inoculation with effective bacterial strainssignificantly increased the root and shoot growth of winter wheat and pea at 16more than at 26 °C. Bacterial inoculation also resulted insignificantly higher amount of N, P, and K contents of plant components.     

The effect of available carbon and nitrogen in straw on soil and ash aggregation and acetic acid production

Summary Aerobically decomposed straws containing various contents of available C and N were tested for resultant aggregating effect on Mt. St. Helen's ash and Palouse silt loam. Aggregation decreased when straw N content increased in the range 0.25–1.09% w/w. These results suggest that microbial extra-cellular products are very important for stabilizing soils. Microbial production of acetic acid, which can be phytotoxic to wheat plant seedlings, was greatest initially from the 1.09% N w/w straw. After the first three days of aerobic decomposition, acetic acid production was not linked to the straw N content. The potential of barley and wheat straw to serve as a substrate for acetic acid production was greater than that of the remains of the flowering heads (chaff). However, the chaff might pack more tightly than the straw in the field, which would increase effectively its acetic acid concentration over that of the straw. Contribution from Agric. Res. Serv., U.S. Dep. of Agric., in cooperation with the College of Agric. Res. Center, Washington State Univ., Pullman, WA 99164; and Agricultural Research Council, Letcombe Laboratory, Wantage, Oxon, Great Britain. WSU Scientific Paper No. 6556. Research was conducted at Letcombe Laboratory.     

Effects on winter wheat seedling growth by toxin-producing rhizobacteria

Summary Root-colonizing pseudomonads capable of inhibiting seedling winter wheat (Triticum aestivum L.) root growth in an agar seedling bioassay also significantly inhibited wheat root growth in vermiculite; however, the inhibitory trait is quite labile in laboratory culturing. The extent of inhibition in both the agar and vermiculite medium depended on inoculum level. These pseudomonads were found to produce a toxin capable of inhibiting growth ofEscherichia coli C-la andBacillus subtilis. Field isolates that strongly inhibit growth of indicator bacteria also inhibited root growth. Toxin production by the bacteria appeared necessary for inhibition of root growth and indicator bacteria as toxin-negative (TOX^–) mutants no longer inhibited either. Antibiosis towardsE. coli as well as wheat seedling root inhibition in agar was reversed by L-methionine, providing further evidence that a toxin, produced by these organisms, is involved in growth retardation.Contribution in cooperation with the College of Agric. Res. Center, Washington State Univ., Pullman, WA 99164. Scientific Paper No. 6837.     

Selective production of hemicellulose-derived carbohydrates from wheat straw using dilute HCl or FeCl3 solutions under mild conditions. X-ray and thermo-gravimetric analysis of the solid residues

The present work explores the combined production of hemicellulose-derived carbohydrates and an upgraded solid residue from wheat straw using a dilute-acid pretreatment at mild temperature. Dilute aqueous HCl solutions were studied at temperatures of 100 and 120 °C, and they were compared to dilute FeCl₃ under the same conditions. Comparable yields of soluble sugars and acetic acid were obtained, affording an almost complete removal of pentoses when using 200 mM aqueous solutions at 120 °C. The solid residues of pretreatment were characterized showing a preserved crystallinity of the cellulose, and a almost complete removal of ash forming matter other than Si. Results showed upgraded characteristic of the residues for thermal conversion applications compared to the untreated wheat straw.     

The manipulation of polar head group composition of phospholipids in the wheat Miranovskaja 808 affects frost tolerance

Caryopses of the frost-resistant cultivar of the wheat Triticum aestivum L., Miranovskaja 808, were germinated and grown in the presence of various concentrations of choline chloride. Changes in the composition of leaf total phospholipids and leaf total fatty acids at two extreme temperatures (25°C and 2°C) as well as changes in frost resistance were followed. A choline chloride concentration-dependent accumulation of phosphatidyl choline was observed in the leaves. Seedlings grown at 2°C accumulated more phosphatidyl choline at each choline chloride concentration than those grown at 25°C. There was an inverse relationship between the contents of phosphatidyl choline and phosphatidic acid in the leaves. Neither the temperature nor choline chloride seemed to affect fatty-acid composition. Modification of polar-head group composition of phospholipids affected frost tolerance: Seedlings grown in the presence of 15 mM choline chloride at 25°C exhibited a freezing resistance equal to that of hardened controls. The data indicate that the polar-head group composition of membrane phospholipids in plants can be easily manipulated and point to the importance of phosphatidyl choline in cold adaptation processes.     

The regulatory role of vernalization in the expression of low-temperature-induced genes in wheat and rye

Low temperature is one of the primary stresses limiting the growth and productivity of wheat (Triticum aestivum L.) and rye (Secale cereale L.). Winter cereals low-temperature-acclimate when exposed to temperatures colder than 10°C. However, they gradually lose their ability to tolerate below-freezing temperatures when they are maintained for long periods of time in the optimum range for low-temperature acclimation. The overwinter decline in low-temperature response has been attributed to an inability of cereals to maintain low-temperature-tolerance genes in an up-regulated state once vernalization saturation has been achieved. In the present study, the low-temperature-induced Wcs120 gene family was used to investigate the relationship between low-temperature gene expression and vernalization response at the molecular level in wheat and rye. The level and duration of gene expression determined the degree of low-temperature tolerance, and the vernalization genes were identified as the key factor responsible for the duration of expression of low-temperature-induced genes. Spring-habit cultivars that did not have a vernalization response were unable to maintain low-temperature-induced genes in an up-regulated condition when exposed to 4°C. Consequently, they were unable to achieve the same levels of low-temperature tolerance as winter-habit cultivars. A close association between the point of vernalization saturation and the start of a decline in the Wcs120 gene-family mRNA level and protein accumulation in plants maintained at 4°C indicated that vernalization genes have a regulatory influence over low-temperature gene expression in winter cereals.     

Effect of environment and formulation on the absorption and translocation of fenridazon in wheat (Triticum aestivum L.)

Fenridazon [potassium 1-(p-chlorophenyl)-1,4-dihydro-6-methyl-4-oxopyridazine-3-carboxylate] is a registered chemical hybridizing agent causing male floral sterility and is used for the production of hybrid wheat (Triticum aestivum L.). Foliar absorption and translocation of fenridazon to the floral primordia was decreased at 4°C compared to 24°C. At 24°C, an increase in relative humidity from 40% to 85% increased fenridazon absorption 2.5 and 1.7 times when surfactants A and B, respectively, were used. Because of the increased absorption of fenridazon with increased relative humidity, the amount of fenridazon in the floral primordia was similarly increased 2.2 and 1.5 times for surfactant A and B, respectively. Although the amount of fenridazon in the floral primordia was increased with increased relative humidity, fenridazon translocation rate was not altered by relative humidity. The effects of irradiance on fenridazon absorption were minimal, but its translocation was decreased with low irradiances.J. Paper No. 11320, Purdue Agric. Exp. Station.     

The effect of soil warming on bulk soil vs. rhizosphere respiration

There has been considerable debate on whether root/rhizosphere respiration or bulk soil respiration is more sensitive to long-term temperature changes. We investigated the response of belowground respiration to soil warming by 3 °C above ambient in bare soil plots and plots planted with wheat and maize. Initially, belowground respiration responded more to the soil warming in bare soil plots than in planted plots. However, as the growing season progressed, a greater soil-warming response developed in the planted plots as the contribution of root/rhizosphere respiration to belowground respiration declined. A negative correlation was observed between the contribution of root/rhizosphere respiration to total belowground respiration and the magnitude of the soil-warming response indicating that bulk soil respiration is more temperature sensitive than root/rhizosphere respiration. The dependence of root/rhizosphere respiration on substrate provision from photosynthesis is the most probable explanation for the observed lower temperature sensitivity of root/rhizosphere respiration. At harvest in late September, final crop biomass did not differ between the two soil temperature treatments in either the maize or wheat plots. Postharvest, flux measurements during the winter months indicated that the response of belowground respiration to the soil-warming treatment increased in magnitude (response equated to a Q ₁₀ value of 5.7 compared with ∼2.3 during the growing season). However, it appeared that this response was partly caused by a strong indirect effect of soil warming. When measurements were made at a common temperature, belowground respiration remained higher in the warmed subplots suggesting soil warming had maintained a more active microbial community through the winter months. It is proposed that any changes in winter temperatures, resulting from global warming, could alter the sink strength of terrestrial ecosystems considerably.     

The fate of residual 15N-labelled fertilizer in arable soils: its availability to subsequent crops and retention in soil

An earlier paper (Macdonald et al., 1997; J. Agric. Sci. (Cambridge) 129, 125) presented data from a series of field experiments in which ¹⁵N-labelled fertilizers were applied in spring to winter wheat, winter oilseed rape, potatoes, sugar beet and spring beans grown on four different soils in SE England. Part of this N was retained in the soil and some remained in crop residues on the soil surface when the crop was harvested. In all cases the majority of this labelled N remained in organic form. In the present paper we describe experiments designed to follow the fate of this `residual' <sup>15</sup>N over the next 2 years (termed the first and second residual years) and measure its value to subsequent cereal crops. Averaging over all of the initial crops and soils, 6.3% of this `residual' ¹⁵N was taken up during the first residual year when the following crop was winter wheat and significantly less (5.5%) if it was spring barley. In the second year after the original application, a further 2.1% was recovered, this time by winter barley. Labelled N remaining after potatoes and sugar beet was more available to the first residual crop than that remaining after oilseed rape or winter wheat. By the second residual year, this difference had almost disappeared. The availability to subsequent crops of the labelled N remaining in or on the soil at harvest of the application year decreased in the order: silty clay loam>sandy loam>chalky loam>heavy clay. In most cases, only a small proportion of the residual fertilizer N available for plant uptake was recovered by the subsequent crop, indicating poor synchrony between the mineralization of ¹⁵N-labelled organic residues and crop N uptake. Averaging over all soils and crops, 22% of the labelled N applied as fertilizer was lost (i.e., unaccounted for in harvested crop and soil to a depth of 100 cm) by harvest in the year of application, rising to 34% at harvest of the first residual year and to 35% in the second residual year. In the first residual year, losses of labelled N were much greater after spring beans than after any of the other crops.     

Thermal stress evaluation of suspension cell cultures in winter wheat

Summary The objectives of this study were to compare thermotolerance in whole plants vs. suspension cell cultures of winter wheat, and to evaluate the synthesis of heat shock proteins in relation to genotypic differences in thermotolerance in suspension cells. Whole plant genetic differences in the development of heat tolerance were identified for three wheat genotypes (ND 7532, KS 75210 and TAM 101). Suspension cell cultures of these genotypes were used to evaluatein vitro response to heat stress. Viability tests by triphenyl tetrazolium chloride (TTC) and by fluorescein diacetate (FD) were utilized to determine the relationship of cellular response to heat stress (37°C/24 h, 50°C/1h). KS 75210 and ND 7532 are relatively heat susceptible. TAM 101 is heat tolerant. Both tests at the cellular level were similar to the whole plant response. Thus, cellular selection for enhancing heat tolerance seems feasible. Heat shock protein (HSP) synthesis of two genotypes, ND 7532 and TAM 101 were determined for suspension cultured cells. In suspension cultures, HSPs of molecular weight 16 and 17 kD were found to be synthesized at higher levels in the heat tolerant genotype (TAM 101) than the susceptible genotype (ND 7532), both at 34° and 37°C treatments for 2 hours and 5 hours. HSP 22 kD was synthesized more at 34°C for TAM 101 than ND 7532, but not at 37°C; whereas, HSP 33 kD was synthesized at 37°C at similar abundance for both genotypes, but not at 34°C.These results indicated that there is a differential expression of HSP genes in wheat suspension cells at different temperature stress durations and between heat tolerant and heat susceptible genotypes. It appears that the levels of synthesis of HSPs 16 and 17 kD are correlated with genotypic differences in thermal tolerance at the cellular level in two genotypes of wheat.     

Effects of salicylic acid and cold on freezing tolerance in winter wheat leaves

The effects of salicylic acid (SA) (0.01, 0.1 and 1 mM) and cold on freezing tolerance (freezing injury and ice nucleation activity) were investigated in winter wheat (Triticum aestivum cv. Dogu-88) grown under control (20/18 °C for 15, 30 and 45-day) and cold (15/10 °C for 15-day, 10/5 °C for 30-day and 5/3 °C for 45-day) conditions. Cold acclimatisation caused a decrease of injury to leaf segments removed from the plants and subjected to freezing conditions. Exogenous SA also decreased freezing injury in the leaves grown under cold (15/10 °C) and control (15 and 30-day) conditions. Cold conditions (10/5 and 5/3 °C) caused an increase in ice nucleation activity by apoplastic proteins, which were isolated from the leaves. For the first time, it was shown that exogenous SA caused an increase in ice nucleation activity under cold (15/10 and 10/5 °C) and control conditions. These results show that salicylic acid can increase freezing tolerance in winter wheat leaves by affecting apoplastic proteins.     

Equilibrium patterns of slash pine water potentials using thermocouple psychrometry as influenced by bath temperature

The progressive changes in measured water potential and the time to equilibration was investigated forPinus elliotii varelliotii needles in thermocouple psychrometer chambers held at 15°C, 22.5°C, and 30°C. Needles at 30°C appeared to loose semi-permeable membrane integrity after 14 hours. Needles held at 22.5°C had similar problems after 48 hours while those at 15°C were not affected. time to equilibrium was shortest at 30°C and longest at 15°C.Ethanol in the chambers had the same effect on measured water potential as did >14 hours at 30°C. Needle color, chamber odor, and pattern of measured water potential suggested an anaerobic condition in the chamber was the cause of reduced membrane integrity.Journal series paper No 7187 of the Florida, Agric. Exp. Sta.At the time the work was in progress the senior author was a graduate research assistant at University of Florida.     

Response of wheatgrasses and wheat × wheatgrass hybrids to barley yellow dwarf virus

Summary Resistance to barley yellow dwarf virus (BYDV), manifested by low enzyme-linked immunosorbent assay (ELISA) values in plants exposed to viruliferous aphids, was identified in several wheatgrasses (Agropyron spp.). ELISA results were similar for root and leaf extracts of infested plants. No difference in reaction to BYDV was found between plants grown in the field and those in the growth chamber. Interspecific hybrids were generated using pollen from single resistant plants of Agropyron spp. to pollinate soft red winter wheat spikes. Resistance in hybrids appeared to be at the level of virus replication rather than at the level of vector inoculation. The hybrids varied in their reaction to BYDV. Expression of BYDV resistance in hybrids was influenced not only by wheat genotype and Agropyron species but, in some cases, reaction varied even among hybrids between the same wheat genotype and Agropyron plant. Implications of these results are discussed.Contribution from the Purdue Univ. Agric. Exp. Stn., West Lafayette, IN 47907, and USDA-ARS. The research was supported in part by Public Varieties of Indiana. Purdue Univ. Agric. Exp. Stn. Journal No. 11656     

冬小麦小RNA高通量测序及生物信息学分析

东农冬麦1号是我国首例可在黑龙江高寒地区种植的强抗寒冬小麦(Triticum aestivum)品种。鉴于分蘖节的耐寒程度直接影响植株的安全越冬, 且MicroRNAs是一类生物体内普遍存在的非编码内源小分子RNA, 在植物的生长发育和适应胁迫等过程中具有重要作用, 该文基于HiSeq深度测序原理, 对5°C和–10°C胁迫下的东农冬麦1号分蘖节进行测序, 并开展生物信息学分析。结果表明, 在5°C文库中有2 229 955条特有小分子RNA序列, 并检测到35条已知miRNA, 属于30个miRNA家族, 其表达丰度介于1–173 810之间; 在–10°C文库中有3 721 449条特有小分子RNA序列, 并发现29条已知miRNA, 属于24个miRNA家族, 其表达丰度为1–105 868。靶基因预测结果表明, 5°C文库的30个miRNA家族中共预测到53个靶基因。功能分析结果显示, 这些基因主要参与转录调节、新陈代谢、胁迫响应和信号转导等过程。已知小麦miRNA的类型和表达丰度在5°C和–10°C两个文库中均有较大差异。     

Growth of Bacteria Degrading Naphthalene and Salicylate at Low Temperatures

A total of 58 bacterial strains degrading naphthalene and salicylate were isolated from soil samples polluted with oil products, collected in different regions of Russia during winter and summer. The isolates were assessed for their ability to grow at low temperatures (4, 8, and 15°C); bacteria growing at 4°C in the presence of naphthalene or salicylate accounted for 65 and 53%, respectively, of the strains isolated. The strains differed in the temperature dependence of their growth rates. It was demonstrated that the type of expression of the Nah⁺ phenotype at low temperatures depended on the combination of host bacterium and plasmid.     

Digital imaging analysis of size and shape of wheat and pea upon heating under anoxic conditions as a function of the temperature

Three types of experiments were carried out. In the first series of experiments emmer wheat grains (Triticum dicoccum Schübl), var. AR, and peas (Pisum sativum L.), var. RE, were heated at temperatures ranging from 130–700 °C under controlled anoxic conditions for a maximum of 120 min. For each temperature a separate experiment was carried out in a pre-heated tube oven. Image acquisition was carried out on a flat bed scanner with a transparency adapter; for the analysis the image program IMAGE J 1.27 was used. Various size and shape factors are discussed and the definitions of the selected size and shape factors are given. The size and shape were measured and the mean calculated from thirty of the untreated specimens and the charred residues heated at each temperature. The results show a change of size and shape as a function of the temperature. The changes for wheat grains and peas are not identical. It is suggested that the presence of the pericarp enclosing the wheat grains causes this difference. In a second series of experiments it was shown that untreated grains of emmer wheat, bread wheat and macaroni wheat can be separated by measuring the shape, but size varies too much within each species, probably the result of different growing conditions, to be useful for separation purposes. As a result of heating at temperatures higher than 290 °C the shape of the three species becomes identical. This implies that the three species can no longer be separated after being heated, solely on the basis of size and shape. Finally, both emmer wheat grains enclosed by chaff and without chaff were heated under similar conditions. After removal of the chaff from the former, the size and shape of the grains were measured. The results show no significant difference in size and shape between both types.