The growth of wheat plants in humic acid solutions under axenic conditions

Summary A technique is described for growing wheat plants in nutrient solutions containing C¹⁴-labelled humic acid under axenic conditions. The general appearance of axenic plants was indistinguishable from plants grown in association with microbes. C¹⁴-labelled humic acid enhanced the growth of both roots and shoots showing that by-products of microbial degradation of humic acid are unnecessary for this enhanced plant growth. Thus humic acid had a direct effect on the growth processes. The C¹⁴-labelled humic acid was taken up by the roots and virtually none was transported to the shoot. Only some 30 to 40 per cent of the incorporated radioactivity was associated with the root cell walls and thus more than 60 per cent was in the cytoplasm and may have influenced the biochemical processes involved in the regulation of plant growth.     

不同生态条件下华抗草78水稻对杂草的干扰控制作用

对不同水稻叶龄、水层深度、水稻密度和保水时间条件下水稻对杂草控制效果进行研究.结果表明,具有化感特性的水稻品系华抗草78对稗草、鳢肠、异型莎草等杂草的抑制率显著优于无化感特性品种Lemont;华抗草78对0～1.5叶期稗草和0～0.3叶期异型莎草的控制效果优于1.5～2.4叶期稗草和0.8～2.0叶期异型莎草;移栽时叶龄与栽插密度互作有利于提高华抗草78对杂草的防效,并明显高于移栽时叶龄分别与水层深度和保水时间互作效应.适当提高水稻移栽时的叶龄、增加移栽密度可显著提高华抗草78对供试杂草的抑制率.     

Two compounds from allelopathic rice accession and their inhibitory activity on weeds and fungal pathogens

A flavone (5,7,4'-trihydroxy-3',5'-dimethoxyflavone), a cyclohexenone (3-isopropyl-5-acetoxycyclohexene-2-one-1) and a liquid mixture of low polarity, containing long-chain and cyclic hydrocarbons, were isolated from leaves of allelopathic rice accession PI 312777 using column chromatography. Their structures and constituents were identified by means of HR-MS, NMR and GC/MS analyses, respectively. Bioassays showed that both the flavone and cyclohexenone significantly inhibited the growth of weeds Echinochloa crus-galli, Cyperus difformis and Cyperus iris, and the spore germination of fungal pathogens Pyricularia oryzae and Rhizoctonia solani at all tested concentrations. Moreover, the combination of the inactive mixture of low polarity and the active flavone or cyclohexenone significantly enhanced the inhibitory activities on weed growth. In addition, the two compounds and the mixture of low polarity from the leaves of PI312777 did not inhibit the rice growth at the same concentrations. It was also established that both compounds could be released into the soil, and was especially induced by E. crus-galli. The results suggest that 5,7,4'-trihydroxy-3',5'-dimethoxyflavone and 3-isopropyl- 5-acetoxycyclohexene-2-one-1 may act as allelochemicals participating in the defense of rice against weeds and pathogens.     

Promoters maintain their relative activity levels under different growth conditions

Most genes change expression levels across conditions, but it is unclear which of these changes represents specific regulation and what determines their quantitative degree. Here, we accurately measured activities of ～900 S. cerevisiae and ～1800 E. coli promoters using fluorescent reporters. We show that in both organisms 60–90% of promoters change their expression between conditions by a constant global scaling factor that depends only on the conditions and not on the promoter's identity. Quantifying such global effects allows precise characterization of specific regulation—promoters deviating from the global scale line. These are organized into few functionally related groups that also adhere to scale lines and preserve their relative activities across conditions. Thus, only several scaling factors suffice to accurately describe genome‐wide expression profiles across conditions. We present a parameter‐free passive resource allocation model that quantitatively accounts for the global scaling factors. It suggests that many changes in expression across conditions result from global effects and not specific regulation, and provides means for quantitative interpretation of expression profiles.     

化感作用水稻对无芒稗及相关田间杂草的抑制作用评价

对从500份水稻种质资源中用差时播种共培法的改进方法初步筛选出10份水稻化感抑稗材料进行了田间化感抑草评价研究.结果表明,在直播条件下,化感材料谷梅2号、吓一跳、鸡早籼、赣早籼和商糯1号等对无芒稗的抑制作用显著优于水稻无化感作用材料秀水63和春江11.化感材料Milyang54对田间总量杂草的抑制作用最强.在移栽条件下,化感材料谷梅2号、青困2号、吓一跳和鸡早籼对无芒稗的抑制作用与无化感作用材料秀水63和春江11差异及显著性水平.水稻材料间部分农艺性状差异及显著性水平,化感材料吓一跳和鸡早籼的株高较高,分蘖力较强,但顶三叶叶面积较小.     

Chemical composition of Thuja orientalis L. essential oils and study of their allelopathic potential on germination and seedling growth of weeds

The chemical composition of essential oils isolated by hydrodistillation from needles and cones of Thuja orientalis L. was analysed by gas chromatography-flame ionisation detection and gas chromatography–mass spectrometry. Twenty-one compounds were identified; quantitative differences, mainly, between cone and needle oils were observed. Both oils were rich in monoterpene hydrocarbons and the major constituents were α-pinene (64.2 and 49.3%, respectively, in cones and needles), β-phellandrene (6.7–9.6%) and α-cedrol (3.9 and 8.2%). Herbicidal properties of Thuja essential oils were assessed against three invasive weed species in crops: Sinapis arvensis L., Phalaris paradoxa L. and Lolium rigidum Gaud. The study of herbicidal activity was carried out on the weed germination, seed vigour and seedling growth. Our results showed a strong inhibitory effect on all tested weeds following a dose-dependent manner, property that could be valourised in managing biocontrol of weeds.     

Effects of application of Rhodopseudomonas sp. on seed germination and growth of tomato under axenic conditions

Purple nonsulfur bacteria were isolated from river sediments and their growth promoting capabilities on tomato were examined. Isolated strains KL9 and BL6 were identified as Rhodopseudomonas spp. by 16S rDNA sequence analysis. Rhodopseudomonas strain KL9 maximally produced 5.56 mM/ min/mg protein and 67.2 microM/min/mg protein of indole-3-acetic acid (IAA) and 5-aminolevulinic acid (ALA), respectively, which may be one of the mechanisms of plant growth enhancement. The germination percentage of tomato seed, total length, and dry mass of germinated tomato seedling increased by 30.2%, 71.1%, and 270.8%, respectively, compared with those of the uninoculated control 7 days after inoculation of strain KL9. The lengths of the root and shoot of germinated seedling treated with 3 mM tryptophan, a precursor of IAA, increased by 104.4% and 156.5%, respectively, 7 days after inoculation of strain KL9. Rhodopseudomonas KL9 increased 123.5% and 54% of the root and shoot lengths of germinated seedling, respectively, treated with 15 mM glycine and succinate, precursors of ALA. This plant growth promoting capability of purple nonsulfur bacteria may be a candidate for a biofertilizer in agriculture.     

Seasonal mycorrhizal colonization of winter wheat and its effect on wheat growth under dryland field conditions

 A field experiment was conducted to determine the seasonal patterns of arbuscular mycorrhiza (AM) in a dryland winter wheat (Triticum aestivum L.) system and to determine wheat growth and P uptake responses to inoculation with mycorrhizal fungus. Broadcast-incorporated treatments included (1) no inoculation with mycorrhizal fungus, with and without P fertilizer, and (2) mycorrhizal fungal inoculation at a rate of 5000 spores of Glomus intraradices (Schenck and Smith), per 30 cm in each row, with and without fertilizer P. Winter wheat was seeded within a day after treatments were imposed, and roots were sampled at five growth stages to quantify AM. Shoot samples were also taken for determination of dry matter, grain yield and yield components, and N and P uptake. No AM infection was evident during the fall months following seeding, which was characterized by low soil temperature, while during the spring, the AM increased gradually. Increases in wheat grain yields by enhanced AM were of similar magnitude to the response obtained from P fertilization. However, responses differed at intermediate growth stages. At the tillering stage, P uptake was mainly increased by P fertilization but not by fungal inoculation. At harvest, enhanced AM increased P uptake regardless of whether or not fertilizer P was added. The AM symbiosis increased with rising soil temperatures in the spring, in time to enhance late-season P accumulation and grain production. Accepted: 15 July 1998     

Carbohydrate utilization by Trichomonas gallinae: effects on growth and metabolic activity under nongrowth conditions

Trichomonas gallinae used 13 of 29 carbohydrates for growth. Quantitative relationships between final populations, acid production, and cellular glycogen contents varied depending on the substrate. The effect of growth on different carbohydrates on the subsequent utilization of carbohydrates by cells under nongrowth conditions was studied by measuring carbohydrate uptake, changes in cellular glycogen content, and gas production. Two major utilization patterns were found. Cells grown on maltose or starch used these substrates well, but cells grown on other sugars did not. All cells used glucose, fructose, galactose, and mannose, but cells grown on maltose or starch did not use them as well as cells grown on other sugars. All cells used ribose slightly but not xylose or arabinose. Turanose, a disaccharide yielding high populations in growth medium, was not used under nongrowth conditions.     

不同除草剂的田间杂草防效及对糜子生长发育的影响

筛选糜子适宜除草剂来防范农田药害,是糜子高效安全生产和改善生态环境亟待解决的关键问题。本研究以粳性糜子品种‘榆糜2号'为材料,探究22种除草剂对糜子田间杂草的防除效果及对糜子生长发育的影响。结果表明: 1)喷施土壤封闭型除草剂谷友、丁草胺、莠去津、苄嘧·丙草胺和茎叶型除草剂苯唑·二甲钠、阔世玛、藤净、陶氏·优先、阔菲后,基本无药害作用,糜子幼苗生长正常,其余除草剂均对糜子有不同程度的药害影响;2)参试的22种除草剂在糜子田中对杂草均表现出一定的防除效果,总体而言,土壤封闭型除草剂的杂草防效相对优于茎叶型除草剂,但所有参试除草剂对糜子株高、功能叶片叶绿素含量、单株穗重均造成不同程度的影响;3)与人工除草相比,参试除草剂均导致糜子产量有不同程度的下降;但与不除草对照相比,部分除草剂有明显的增产增效作用。土壤封闭型除草剂中,谷友、丁草胺、莠去津、苄嘧·丙草胺的杂草防效较好,较不除草对照增产60%以上;茎叶型除草剂中,阔世玛、苯唑·二甲钠的杂草防效较好,较不除草对照增产50%以上。因此,在糜子出苗前可用38%莠去津或44%单嘧磺隆进行土壤封闭处理,或在出苗后喷施茎叶型除草剂3.6%二磺·甲碘隆或55%苯唑·二甲钠,农田杂草防效较好,且对糜子生长发育的负面影响较小。     

花生根分泌物的鉴定及其化感作用

采用改进的根系分泌物循环收集系统收集花生根系分泌物,利用气相色谱/质谱联用仪(GC-MS)鉴定其结构,并研究了花生根系分泌物对花生青枯病原菌的化感作用.结果表明,花生根系分泌物中主要含有丙三醇、苯甲酸、3,5-二甲基苯甲醛、苯乙酮、硬脂酸、棕榈酸和乳酸等7种物质.7种根系分泌物中只有苯乙酮在浓度低于0.1g·L-1时,对花生青枯病原菌生长才有明显的促进作用.同时还发现,苯乙酮浓度超过0.1 gL-1后对花生青枯病原菌有显著的抑制作用.这一结论为利用苯乙酮调控花生青枯病害的发生提供了可靠的依据.     

Impact of PGPR inoculation on growth and antioxidant status of wheat under saline conditions

Two plant growth‐promoting rhizobacterial (PGPR) strains, Bacillus subtilis SU47 and Arthrobacter sp. SU18, were found to tolerate 8% NaCl. Wheat co‐inoculated with these two PGPR strains, and grown under different salinity regimes (2–6 dS m^?1), showed an increase in dry biomass, total soluble sugars and proline content. Wheat sodium content was reduced under co‐inoculated conditions but not after single inoculation with either strain or in the control. The activity of antioxidant enzymes in wheat leaves decreased under salinity stress after PGPR co‐inoculation, suggesting these PGPR species could be used for amelioration of stress in wheat plants. Activity of three antioxidant enzymes in wheat grown with both PGPR strains was reduced, most notably that of catalase activity at a salinity of 6 dS m^?1, when compared with the control. The results indicate that co‐inoculation with B. subtilis and Arthrobacter sp. could alleviate the adverse effects of soil salinity on wheat growth.     

Biological control of winter wheat pathogens with the use of antagonistic Sphingomonas bacteria under greenhouse conditions

This paper describes, for the first time, the effect of bacteria of the genus Sphingomonas on healthiness of winter wheat. The effect of the application of Sphingomonas cell suspension on development of disease symptoms of powdery mildew and Fusarium head blight (FHB) of winter wheat cv. Bogatka was studied under greenhouse conditions. The abundance of populations of yeast and fungi producing mycelium as well as bacteria of the genus Azotobacter and pseudomonads was determined on wheat kernels. The biocontrol agent reduced the population size of Fusarium poae, and it contributed to better grain filling. The tested Sphingomonas isolate reduced the severity of flag leaf infection caused by pathogenic biotroph Blumeria graminis f. sp. tritici.     

Molecular mapping of genomic regions associated with wheat seedling growth under osmotic stress

A quantitative trait loci (QTL) approach was applied to dissect the genetic control of the common wheat seedling response to osmotic stress. A set of 114 recombinant inbred lines was subjected to osmotic stress from the onset of germination to the 8^th day of seedling development, induced by the presence of 12 % polyethylene glycol. Root, coleoptile and shoot length, and root/shoot length ratio were compared under stress and control conditions. In all, 35 QTL mapping to ten chromosomes, were identified. Sixteen QTL were detected in controls, 17 under stressed conditions, and two tolerance index QTL were determined. The majority of the QTL were not stress-specific. In regions on five chromosome arms (1AS, 1BL, 2DS, 5BL and 6BL) the QTL identified under stress co-mapped with QTL affecting the same trait in controls, and these were classified as seedling vigour QTL, in addition to those expressed in controls. Tolerance-related QTL were detected on four chromosome arms. A broad region on chromosome 1AL, including five QTL, with a major impact of the gene Glu-A1 (LOD 3.93) and marker locus Xksuh9d (LOD 2.91), positively affected root length under stress and tolerance index for root length, respectively. A major QTL (LOD 3.60), associated with marker locus Xcdo456a (distal part of chromosome arm 2BS) determined a tolerance index for shoot length. Three minor QTL (LOD < 3.0) for root length and root/shoot length ratio under osmotic stress were identified in the distal parts of chromosome arms 6DL (marker locus Xksud27a) and 7DL (marker locus Xksue3b). Selecting for the favourable alleles at marker loci associated with the detected QTL for growth traits may represent an efficient approach to enhance the plants’ ability to maintain the growth of roots, coleoptile and shoots in drought-prone soils at the critical early developmental stages.     

Cultivable bacteria associated with Caribbean octocorals are active against coral pathogens but exhibit variable bioactivity when grown under different temperature conditions

Caribbean scleractinian corals have been declining in recent decades while octocorals appear to be thriving. Although microbial communities associated with scleractinians have been extensively studied, less is known about octocoral-associated communities. To investigate whether octocoral-associated microorganisms can provide resistance against coral pathogens, bacteria from the mucus and external surfaces of three common Caribbean octocoral species (Gorgonia ventalina, Eunicea flexuosa, and Antillogorgia americana) were isolated. Isolates were tested for bioactivity against six scleractinian coral pathogens at three temperatures to capture potential differences under varying conditions. Production of bioactive metabolites was evaluated using disk diffusion assays while growth competition assays determined whether the pathogen and isolate could establish simultaneously. Over half of the isolates, members of the phyla Actinobacteria, Firmicutes and Proteobacteria, produced compounds that inhibited the growth of one or more pathogens with some variation in bioactivity noted across temperatures. When inoculated simultaneously, most isolates were able to grow in presence of the pathogens while temperature did not have a significant impact. Collectively, these results demonstrate that octocorals support a diverse group of culturable bacteria capable of competing against coral pathogens. The putative protective roles of these bacteria provide insight into why Caribbean octocorals may be less susceptible to diseases and might explain their increasing prevalence on degraded reefs.

     

Influence of bovine lactoferrin on the growth of selected probiotic bacteria under aerobic conditions

Bovine lactoferrin (bLf) is a natural glycoprotein, and it shows broad-spectrum antimicrobial activity. However, reports on the influences of bLf on probiotic bacteria have been mixed. We examined the effects of apo-bLf (between 0.25 and 128 mg/mL) on both aerobic and anaerobic cultures of probiotics. We found that bLf had similar effects on the growth of probiotics under aerobic or anaerobic conditions, and that it actively and significantly (at concentrations of >0.25 mg/mL) retarded the growth rate of Bifidobacterium bifidum (ATCC 29521), B. longum (ATCC 15707), B. lactis (BCRC 17394), B. infantis (ATCC 15697), Lactobacillus reuteri (ATCC 23272), L. rhamnosus (ATCC 53103), and L. coryniformis (ATCC 25602) in a dose-dependent manner. Otherwise, minimal inhibitory concentrations (MICs) were 128 or >128 mg/mL against B. bifidum, B. longum, B. lactis, L. reuteri, and L. rhamnosus (ATCC 53103). With regard to MICs, bLf showed at least four-fold lower inhibitory effect on probiotics than on pathogens. Intriguingly, bLf (>0.25 mg/mL) significantly enhanced the growth of Rhamnosus (ATCC 7469) and L. acidophilus (BCRC 14065) by approximately 40–200 %, during their late periods of growth. Supernatants produced from aerobic but not anaerobic cultures of L. acidophilus reduced the growth of Escherichia coli by about 20 %. Thus, bLf displayed a dose-dependent inhibitory effect on the growth of most probiotic strains under either aerobic or anaerobic conditions. An antibacterial supernatant prepared from the aerobic cultures may have significant practical use.