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.     

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.     

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.     

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.     

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.     

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.

     

Phases in potassium transport and their regulation under near-equilibrium conditions in wheat seedlings

Potassium uptake and release in roots and translocation to the shoots were studied in 14-day-old winter wheat ( Tritictum aestivum L. cv. Martonvásári 8) of different K status. Transport processes were measured in the growth solutions for 5 h ensuring near-equilibrium conditions. The uptake showed three phases: (1) at low external K⁺ concentrations it increased with increasing concentrations and culminated at 0.1 m M : (2) between 0.1 and 1 m M it decreased, and (3) it increased again above 1 m M : The release of K⁺ showed a constant low level below 1 m M while paralleling the uptake above that. The uncoupler 2,4-dinitrophenol inhibited uptake phases (1) and (2), whereas it did not affect either phase (3) or K⁺ release. Translocation showed similar patterns. It is concluded that phases (1) and (2) depend on metabolic energy while phase (3) is mostly passive. It is emphasized that different types of regulation seem to operate in the transport mechanism: i.e. limitation by transport sites, control by negative feedback and by K⁺/K⁺ exchange, respectively.     

Fungi associated with Eichhornia crassipes in South Africa and their pathogenicity under controlled conditions

Eichhornia crassipes Mart. Solms-Laubach (Pontederiaceae), water hyacinth, continues to be the world's worst aquatic weed. In South Africa, considerable research has been conducted on biological control agents associated with water hyacinth, with the release of six arthropods and one fungus, but little is known about the occurrence and impacts of native phytopathogenic fungi. Nation-wide surveys were conducted in 2010 and 2011 on various aquatic bodies of South Africa to identify the fungal pathogens associated with water hyacinth. Diseased plant parts were collected and fungi were isolated and identified. Some 250 isolates belonging to more than 25 genera were collected. Some of these represent new host records, as well as undescribed taxa. Isolates of Acremonium zonatum (Sawada) Gams, Alternaria eichhorniae Nag Raj and Ponnappa, Bipolaris hawaiiensis (M.B. Ellis) Uchida and Aragaki, Fusarium Link, Myrothecium roridum Tode ex Fr. and Ulocladium sp., showed the highest pathogenicity and have the potential to be useful in complementing the ongoing biocontrol programme on water hyacinth in South Africa.     

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.     

Effect of exogenous siderophores on iron uptake activity of marine bacteria under iron-limited conditions

More than 60% of species examined from a total of 421 strains of heterotrophic marine bacteria which were isolated from marine sponges and seawater were observed to have no detectable siderophore production even when Fe(III) was present in the culture medium at a concentration of 1.0 pM. The growth of one such non-siderophore-producing strain, alpha proteobacterium V0210, was stimulated under iron-limited conditions with the addition of an isolated exogenous siderophore, N,N'-bis (2,3-dihydroxybenzoyl)-O-serylserine from a Vibrio sp. Growth was also stimulated by the addition of three exogenous siderophore extracts from siderophore-producing bacteria. Radioisotope studies using (59)Fe showed that the iron uptake ability of V0210 increased only with the addition of exogenous siderophores. Biosynthesis of a hydroxamate siderophore by V0210 was shown by paper electrophoresis and chemical assays for the detection of hydroxamates and catechols. An 85-kDa iron-regulated outer membrane protein was induced only under iron-limited conditions in the presence of exogenous siderophores. This is the first report of bacterial iron uptake through an induced siderophore in response to exogenous siderophores. Our results suggest that siderophores are necessary signaling compounds for growth and for iron uptake by some non-siderophore-producing marine bacteria under iron-limited conditions.     

Performance of transgenic spring wheat plants and effects on non-target organisms under glasshouse and semi-field conditions

Abstract:  A convertible glasshouse was established to study annual transgenic plants under near-field environmental conditions while simultaneously ensuring a high level of biological containment. This system can provide a useful step in the assessment of transgenic plants prior to open-field experiments. Two transgenic wheat lines (cv. Bobwhite) were investigated and compared with their corresponding non-transformed wildtypes with respect to plant performance, expression of the transgenic trait and interactions with antagonists. The first line expressed snowdrop lectin [ Galanthus nivalis agglutinin (GNA)] for enhanced resistance to aphids, and the second one overexpressed the endogenous Lr10 gene to enhance resistance to leaf rust. Interestingly, 1000-kernel weight of Lr10 -transgenic plants was significantly reduced, indicating that the overexpression of the Lr10 gene caused a significant fitness cost for the plant. GNA-transgenic plants expressed the lectin at levels too low to affect the target aphids. A detached leaf bioassay with Lr10 -transgenic plants revealed an increased resistance to leaf rust. No differences in the performance of aphids or cereal leaf beetles on transgenic and non-transformed plants were recorded in the convertible glasshouse and in complementary glasshouse studies. Similarly, infection levels with powdery mildew did not differ between transgenic and non-transformed plants but Bobwhite plants were significantly more infected when compared with conventional Swiss spring wheat cultivars. Overall, the assessment revealed that for the plants investigated here, their genetic background had a stronger impact on the performance of a plant and its interactions with insect herbivores and pathogens than the expression of the transgene.     

Sodium exclusion QTL associated with improved seedling growth in bread wheat under salinity stress

Worldwide, dryland salinity is a major limitation to crop production. Breeding for salinity tolerance could be an effective way of improving yield and yield stability on saline-sodic soils of dryland agriculture. However, this requires a good understanding of inheritance of this quantitative trait. In the present study, a doubled-haploid bread wheat population (Berkut/Krichauff) was grown in supported hydroponics to identify quantitative trait loci (QTL) associated with salinity tolerance traits commonly reported in the literature (leaf symptoms, tiller number, seedling biomass, chlorophyll content, and shoot Na⁺ and K⁺ concentrations), understand the relationships amongst these traits, and determine their genetic value for marker-assisted selection. There was considerable segregation within the population for all traits measured. With a genetic map of 527 SSR-, DArT- and gene-based markers, a total of 40 QTL were detected for all seven traits. For the first time in a cereal species, a QTL interval for Na⁺ exclusion (wPt-3114-wmc170) was associated with an increase (10%) in seedling biomass. Of the five QTL identified for Na⁺ exclusion, two were co-located with seedling biomass (2A and 6A). The 2A QTL appears to coincide with the previously reported Na⁺ exclusion locus in durum wheat that hosts one active HKT1;4 (Nax1) and one inactive HKT1;4 gene. Using these sequences as template for primer design enabled mapping of at least three HKT1;4 genes onto chromosome 2AL in bread wheat, suggesting that bread wheat carries more HKT1;4 gene family members than durum wheat. However, the combined effects of all Na⁺ exclusion loci only accounted for 18% of the variation in seedling biomass under salinity stress indicating that there were other mechanisms of salinity tolerance operative at the seedling stage in this population. Na⁺ and K⁺ accumulation appear under separate genetic control. The molecular markers wmc170 (2A) and cfd080 (6A) are expected to facilitate breeding for salinity tolerance in bread wheat, the latter being associated with seedling vigour.     

Generation of Leishmania donovani axenic amastigotes: their growth and biological characteristics

In this report, we describe an in vitro culture system for the generation and propagation of axenic amastigotes from the well characterised 1S-CL2D line of Leishmania donovani. Fine structure analyses of these in vitro-grown amastigotes demonstrated that they possessed morphological features characteristic of L. donovani tissue-derived amastigotes. Further, these axenic amastigotes (LdAxAm) were shown to synthesise and release a secretory acid phosphatase isoform similar to that produced by intracellular amastigotes. Such LdAxAm also expressed surface membrane 3'-nucleotidase enzyme activity similar to that of tissue-derived amastigotes. Moreover, LdAxAm, in contrast to promastigotes, expressed significant levels of the amastigote-specific A2 proteins. In addition, LdAxAm, derived from long term cultures of Ld 1S-CL2D promastigotes, had significant infectivity for both human macrophages in vitro and for hamsters in vivo. Thus, the in vitro culture system described herein provides a useful tool for the generation of large quantities of uniform populations of axenic amastigotes of the L. donovani 1S-CL2D line. The availability of such material should greatly facilitate studies concerning the cell and molecular biology of this parasite developmental stage.