Choline-Mediated Lipid Reprogramming as a Dominant Salt Tolerance Mechanism in Grass Species Lacking Glycine Betaine

Choline, as a precursor of glycine betaine (GB) and phospholipids, is known to play roles in plant tolerance to salt stress, but the downstream metabolic pathways regulated by choline conferring salt tolerance are still unclear for non-GB-accumulating species. The objectives were to examine how choline affects salt tolerance in a non-GB-accumulating grass species and to determine major metabolic pathways of choline regulating salt tolerance involving GB or lipid metabolism. Kentucky bluegrass (Poa pratensis) plants were subjected to salt stress (100 mM NaCl) with or without foliar application of choline chloride (1 mM) in a growth chamber. Choline or GB alone and the combined application increased leaf photochemical efficiency, relative water content and osmotic adjustment and reduced leaf electrolyte leakage. Choline application had no effects on the endogenous GB content and GB synthesis genes did not show responses to choline under nonstress and salt stress conditions. GB was not detected in Kentucky bluegrass leaves. Lipidomic analysis revealed an increase in the content of monogalactosyl diacylglycerol, phosphatidylcholine and phosphatidylethanolamine and a decrease in the phosphatidic acid content by choline application in plants exposed to salt stress. Choline-mediated lipid reprogramming could function as a dominant salt tolerance mechanism in non-GB-accumulating grass species.

Drought-induced injury is associated with hormonal alteration in Kentucky bluegrass

Plant hormones play an important role in plant adaptation to abiotic stress, but hormonal responses of cool-season turfgrass species to drought stress are not well documented. This study was to investigate responses of hormones and photosynthesis to drought stress and examine if drought stress - induced hormone alteration is associated with stress tolerance in kentucky bluegrass (KBG, Poa pratensis L.). The grass was grown in a growth chamber for 6 weeks and then subjected to drought stress [40%-50% evapotranspiration (ET) replacement)] for 28 d. Drought stress caused cell membrane damage, resulting in decline in photosynthetic rate (Pn), chlorophyll content, and visual quality in KBG. Drought stressed grass had higher leaf abscisic acid (ABA), lower leaf trans-zeatin riboside (ZR), isopentenyl adenosine (iPA), and indole-3-acetic acid (IAA), but similar level of leaf gibberellin A4 (GA4) when compared to the control (well-watered). On average, drought stress treatment reduced leaf ZR by 59.1%, iPA by 50.4%, IAA by 26.7%, while increased ABA by 108.5% when compared to the control at the end of drought stress (28 d). The turf quality and photosynthetic rate was positively correlated with cytokinins and IAA, but negatively correlated with ABA and ABA/cytokinins (CK) ratio under drought stress. The results of this study suggest drought stress-induced injury to Kentucky bluegrass may be associated with hormonal alteration, and the plants with higher cytokinins and IAA and less ABA under drought stress may have better photosynthetic function and performance.

Water transport properties of root cells contribute to salt tolerance in halophytic grasses Poa juncifolia and Puccinellia nuttalliana

Plant water uptake and aquaporin-mediated root water transport are among the most salt-sensitive processes in most plants, but even relatively high salt concentrations do not appear to impair water transport processes in halophytes. To develop better understanding of these processes in halophytic plants, we compared the responses to NaCl of the two halophytic grasses varying in salt tolerance, Puccinellia nuttalliana and Poa juncifolia, with the glycophytic grass Poa pratensis. The plants were hydroponically grown and subjected to different NaCl concentrations for up to 10 days. At the lower NaCl concentrations, shoot and root dry weights were drastically reduced in Poa pratensis, but increased in Puccinellia nuttalliana and Poa juncifolia. The examined treatment concentrations of up to 300 mM NaCl had either no effect (Puccinellia nuttalliana) or little effect (Poa juncifolia) on the net photosynthesis and transpiration rates in plants, but severely decreased the gas exchange parameters in Poa pratensis. Similarly, to growth and gas exchange, leaf water content in Puccinellia nuttalliana was not affected even by the highest, 300 mM NaCl concentration, while Poa pratensis showed decreased shoot water content in all examined NaCl treatments and Poa juncifolia in 150 and 300 mM NaCl. Cell hydraulic conductivity in roots of Poa pratensis also showed high sensitivity to NaCl and was drastically reduced in all examined NaCl concentrations. Cell hydraulic conductivity in Poa juncifolia roots was less affected by NaCl compared with Poa pratensis and in Puccinellia nuttalliana, cell hydraulic conductivity increased in response to NaCl treatments. Both Puccinellia nuttalliana and Poa juncifolia accumulated less Na in their shoot tissues compared with Poa pratensis. The concentrations of K in the roots of Poa pratensis sharply decreased with increasing NaCl treatment concentrations while in Puccinellia nuttalliana, K root concentrations remained high in all NaCl treatments and in Poa juncifoila, root K decreased only in the 300 mM NaCl treatment. Since K efflux from the cytoplasm can contribute to the acidification of the cytoplasm, this process could potentially lead to the inhibition of aquaporin function and reduction of root hydraulic conductivity. The, significance of stable K root concentrations in the roots of halophytes should be further investigated as a possible salt tolerance mechanism that could contribute to the maintenance of aquaporin function and root water transport under salt stress conditions.

Differential effects of citric acid on cadmium uptake and accumulation between tall fescue and Kentucky bluegrass

Organic acids play an important role in cadmium availability, uptake, translocation, and detoxification. A sand culture experiment was designed to investigate the effects of citric acid on Cd uptake, translocation, and accumulation in tall fescue and Kentucky bluegrass. The results showed that two grass species presented different Cd chemical forms, organic acid components and amount in roots. The dormant Cd accumulated in roots of tall fescue was the pectate- and protein- integrated form, which contributed by 84.85%. However, in Kentucky bluegrass, the pectate- and protein- integrated Cd was only contributed by 35.78%, and the higher proportion of Cd form was the water soluble Cd-organic acid complexes. In tall fescue, citric acid dramatically enhanced 2.8 fold of Cd uptake, 3 fold of root Cd accumulation, and 2.3 fold of shoot Cd accumulation. In Kentucky bluegrass, citric acid promoted Cd accumulation in roots, but significantly decreased Cd accumulation in shoots. These results suggested that the enhancements of citric acid on Cd uptake, translocation, and accumulation in tall fescue was associated with its promotion of organic acids and the water soluble Cd-organic acid complexes in roots.

5-Aminolevulinic acid modulates antioxidant defense systems and mitigates drought-induced damage in Kentucky bluegrass seedlings

Drought stress occurs frequently and severely as a result of global climate change, and it exerts serious effects on plants. 5-Aminolevulinic acid (5-ALA) plays a crucial role in conferring abiotic stress tolerance in plants. To enhance the drought tolerance of turfgrass and investigate the effects of 5-ALA on antioxidant metabolism and gene expression under drought stress conditions, exogenous 5-ALA was applied by foliar spraying before Kentucky bluegrass (Poa pratensis L.) seedlings were exposed to drought [induced by 10% polyethylene glycol (PEG)] stress for 20 days. 5-ALA pretreatment increased turf quality (TQ) and leaf relative water content (RWC) while reducing reactive oxygen species (ROS) production including H2O2 content and O2•- generation rate, lipoxygenase (LOX) activity, and malondialdehyde (MDA) content under drought stress. 5-ALA pretreatment maintained ascorbate (AsA) and glutathione (GSH) contents and the ASA/DHA and GSH/GSSG ratios at high levels, and it enhanced the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione peroxidase (GPX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR), which are crucial for scavenging drought-induced ROS. In addition, 5-ALA upregulated the relative expression levels of Cu/ZnSOD, APX, GPX, and DHAR but downregulated those of CAT and GR under drought stress. These results indicated that the application of 5-ALA might improve turfgrass quality and promote drought tolerance in Kentucky bluegrass through reducing oxidative damage and increasing non-enzyme antioxidant levels and antioxidant enzyme activity at transcriptional and posttranscriptional levels.

Silicate application increases the photosynthesis and its associated metabolic activities in Kentucky bluegrass under drought stress and post-drought recovery

Drought stress is the most pervasive threat to plant growth, which disrupts the photosynthesis and its associated metabolic activities, while silicate (Si) application may have the potential to alleviate the damaging effects of drought on plant growth. In present study, the role of Si in regulating the photosynthesis and its associated metabolic events in Kentucky bluegrass (cv. Arcadia) were investigated under drought stress. Drought stress and four levels (0, 200, 400, 800 mg L(-1)) of Si (Na2SiO3.9H2O) were imposed on 1-year-old plants removed from field and cultured under glasshouse conditions. After 20 days of drought stress, the plants were re-watered to reach soil field capacity for the examination of recovery on the second and the seventh day. The experiment was arranged in completely randomized design replicated four times. Drought stress severely decreased the photosynthesis, water use efficiency, stomatal conductance, cholorophyll contents, Rubisco activity, and Rubisco activation state in Kentucky bluegrass. Nevertheless, application of Si had a positive influence on all these attributes, particularly under stress conditions. As compared to control, Si application at 400 mg L(-1) recorded 78, 64, and 48 % increase in photosynthesis, Rubisco initial activity, and Rubisco total activity, respectively, at 20 days of drought. Higher photosynthesis and higher Rubisco activity in Si-applied treatments suggest that Si may have possible (direct or indirect) role in maintenance of more active Rubisco enzyme and Rubisco activase and more stable proteins for carbon assimilation under stress conditions, which needs to be elucidated in further studies.

A new amino acid substitution (Ala-205-Phe) in acetolactate synthase (ALS) confers broad spectrum resistance to ALS-inhibiting herbicides

This is a first report of an Ala-205-Phe substitution in acetolactate synthase conferring resistance to imidazolinone, sulfonylurea, triazolopyrimidines, sulfonylamino-carbonyl-triazolinones, and pyrimidinyl (thio) benzoate herbicides. Resistance to acetolactate synthase (ALS) and photosystem II inhibiting herbicides was confirmed in a population of allotetraploid annual bluegrass (Poa annua L.; POAAN-R3) selected from golf course turf in Tennessee. Genetic sequencing revealed that seven of eight POAAN-R3 plants had a point mutation in the psbA gene resulting in a known Ser-264-Gly substitution on the D1 protein. Whole plant testing confirmed that this substitution conferred resistance to simazine in POAAN-R3. Two homeologous forms of the ALS gene (ALSa and ALSb) were detected and expressed in all POAAN-R3 plants sequenced. The seven plants possessing the Ser-264-Gly mutation conferring resistance to simazine also had a homozygous Ala-205-Phe substitution on ALSb, caused by two nucleic acid substitutions in one codon. In vitro ALS activity assays with recombinant protein and whole plant testing confirmed that this Ala-205-Phe substitution conferred resistance to imidazolinone, sulfonylurea, triazolopyrimidines, sulfonylamino-carbonyl- triazolinones, and pyrimidinyl (thio) benzoate herbicides. This is the first report of Ala-205-Phe mutation conferring wide spectrum resistance to ALS inhibiting herbicides.

Methiozolin sorption and mobility in sand-based root zones

BACKGROUND

Methiozolin is a herbicide currently used for annual bluegrass control in golf course putting greens. Previous research indicates that maximum weed control efficacy requires root exposure; however, soil sorption and mobility of methiozolin have not been established. Research was conducted to investigate soil sorption and subsequent desorption by dilution of methiozolin, as well as soil mobility using batch equilibrium experiments and thin-layer chromatography in nine root zones. Evaluations focused on sand-based systems typical of many golf course putting greens.

RESULTS

Sorption coefficients (Kd values) ranged from 0.4 to 29.4 mL g(-1) and averaged 13.8 mL g(-1) . Sorption was most influenced by organic matter content; conversely, soil pH had a negligible effect. Methiozolin desorption did not occur with a 0.01 M CaCl2 dilution. Methiozolin mobility was low; retardation factors (Rf values) were <0.05 for all media with ≥0.3% organic matter. Sand (0.1% organic matter) resulted in an Rf value of 0.46.

CONCLUSION

Approximately 24% of applied methiozolin is available for root uptake, and mobility is limited, suggesting resistance to loss through leaching displacement.

Utilizing next-generation sequencing to study homeologous polymorphisms and herbicide-resistance-endowing mutations in Poa annua acetolactate synthase genes

BACKGROUND

Detection of single nucleotide polymorphisms (SNPs) related to herbicide resistance in non-model polyploid weed species is fraught with difficulty owing to the gene duplication and lack of reference sequences. Our research seeks to overcome these obstacles by Illumina HiSeq read mapping, SNP calling and allele frequency determinations. Our focus is on the acetolactate synthase (ALS) gene, the target site of ALS-inhibiting herbicides, in Poa annua, an allotetraploid weed species originating from two diploid parents, P. supina and P. infirma.

RESULTS

ALS contigs with complete coding regions of P. supina, P. infirma and P. annua were assembled and compared with ALS genes from other plant species. The ALS infirma-homeolog of P. annua showed higher levels of nucleotide sequence variability than the supina-homeolog. Comparisons of read mappings of P. annua and a simulated P. supina × P. infirma hybrid showed high resemblance. Two homeolog-specific primer pairs were designed and used to amplify a 1860 bp region covering all resistance-conferring codons in the ALS gene. Four P. annua populations, GN, RB, GW and LG, showed high resistance to two ALS inhibitors, bispyribac-sodium and foramsulfuron, and two populations, HD and RS, showed lower resistance in the rate-response trial. Mutations conferring Trp-574-Leu substitution were observed in the infirma-homeolog of GN and RB and in the supina-homeolog of GW and LG, but no resistance-conferring mutation was observed in the two populations of lower resistance, HD and RS.

CONCLUSION

In this study we have demonstrated the use of NGS data to study homeologous polymorphisms, parentage and herbicide resistance in an allotetraploid weed species, P. annua. Complete coding sequences of the ALS gene were assembled for P. infirma, P. supina, infirma-homeolog and supina-homeolog in P. annua. A pipeline consisting of read mapping, SNP calling and allele frequency calculation was developed to study the parentage of P. annua, which provided a new perspective on this topic besides the views of morphology, karyotype and phylogeny. Our two homeolog-specific primer pairs can be utilized in future research to separate the homeologs of the ALS gene in P. annua and cover all the codons that have been reported to confer herbicide resistance.

Protective effect of spermidine on salt stress induced oxidative damage in two Kentucky bluegrass (Poa pratensis L.) cultivars

To improve the salinity tolerance of turfgrass and investigate the effect of spermidine (Spd) on antioxidant metabolism and gene expression under salinity stress condition, exogenous Spd was applied before two kentucky bluegrass (Poa pratensis L.) cultivars ('Kenblue' and 'Midnight') were exposed to 200 mM sodium chloride (NaCl) stress for 28 d. Salinity stress decreased the turfgrass quality, increased the content of malonyldialdehyde (MDA), superoxide anion (O₂(·-)) and hydrogen peroxide (H₂O₂), and enhanced activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD) and ascorbate peroxidase (APX) and isozymes intensity in both cultivars. In addition, the expression level of Cu/ZnSOD was down-regulated in 'Kenblue' but up-regulated in 'Midnight' after salt treatment. Salinity stress also enhanced the expression of APX but inhibited the expression of CAT and POD in both cultivars. Exogenous Spd treatment alleviated the salinity-induced oxidative stress through decreasing MDA, H₂O₂ and O₂(·-) contents in both cultivars. Besides, exogenous Spd further enhanced the activities of SOD, CAT, POD and APX accompanied with the increased intensity of specific isozymes of SOD, CAT and APX in both cultivars and POD in 'Kenblue'. Moreover, Spd further up-regulated expression levels of Cu/ZnSOD and APX, but down-regulated those of CAT and POD in both cultivars. These results indicated that exogenous Spd might improve turfgrass quality and promote the salinity tolerance in the two cultivars of kentucky bluegrass through reducing oxidative damages and increasing enzyme activity both at protein and transcriptional levels.

Physiological effects of temperature on turfgrass tolerance to amicarbazone

BACKGROUND

Amicarbazone effectively controls annual bluegrass (Poa annua L.) in bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy] and tall fescue (Festuca arundinacea Schreb.) with spring applications, but summer applications may excessively injure tall fescue. The objective of this research was to investigate physiological effects of temperature on amicarbazone efficacy, absorption, translocation and metabolism in annual bluegrass, bermudagrass and tall fescue.

RESULTS

At 25/20 °C (day/night), annual bluegrass absorbed 58 and 40% more foliar-applied amicarbazone than bermudagrass and tall fescue, respectively, after 72 h. Foliar absorption increased at 40/35 °C in all species, compared with 25/20 °C, and tall fescue had similar absorption to annual bluegrass at 40/35 °C. At 6 days after treatment, annual bluegrass metabolized 54% of foliar-applied amicarbazone, while bermudagrass and tall fescue metabolized 67 and 64% respectively.

CONCLUSION

Tall fescue is more tolerant to amicarbazone than annual bluegrass at moderate temperatures (≈25/20 °C) owing to less absorption and greater metabolism. However, tall fescue susceptibility to amicarbazone injury at high temperatures (40/35 °C) results from enhanced herbicide absorption compared with lower temperatures (25/20 °C). Bermudagrass is more tolerant to amicarbazone than annual bluegrass and tall fescue owing to less herbicide absorption, regardless of temperature.

Potential ecological roles of flavonoids from Stellera chamaejasme

Stellera chamaejasme L. (Thymelaeaceae), a perennial weed, distributes widely in the grasslands of Russia, Mongolia and China. The plant synthesizes various secondary metabolites including a group of flavonoids. To our knowledge, flavonoids play important roles in the interactions between plants and the environment. So, what are the benefits to S. chamaejasme from producing these flavonoids? Here, we discuss the potential ecological role of flavonoids from S. chamaejasme in protecting the plant from insects and other herbivores, as well as pathogens and competing plant species, and new data are provided on the phytotoxicity of flavonoids from S. chamaejasme toward Poa annua L.

Indaziflam herbicidal action: a potent cellulose biosynthesis inhibitor

Cellulose biosynthesis is a common feature of land plants. Therefore, cellulose biosynthesis inhibitors (CBIs) have a potentially broad-acting herbicidal mode of action and are also useful tools in decoding fundamental aspects of cellulose biosynthesis. Here, we characterize the herbicide indaziflam as a CBI and provide insight into its inhibitory mechanism. Indaziflam-treated seedlings exhibited the CBI-like symptomologies of radial swelling and ectopic lignification. Furthermore, indaziflam inhibited the production of cellulose within <1 h of treatment and in a dose-dependent manner. Unlike the CBI isoxaben, indaziflam had strong CBI activity in both a monocotylonous plant (Poa annua) and a dicotyledonous plant (Arabidopsis [Arabidopsis thaliana]). Arabidopsis mutants resistant to known CBIs isoxaben or quinoxyphen were not cross resistant to indaziflam, suggesting a different molecular target for indaziflam. To explore this further, we monitored the distribution and mobility of fluorescently labeled CELLULOSE SYNTHASE A (CESA) proteins in living cells of Arabidopsis during indaziflam exposure. Indaziflam caused a reduction in the velocity of YELLOW FLUORESCENT PROTEIN:CESA6 particles at the plasma membrane focal plane compared with controls. Microtubule morphology and motility were not altered after indaziflam treatment. In the hypocotyl expansion zone, indaziflam caused an atypical increase in the density of plasma membrane-localized CESA particles. Interestingly, this was accompanied by a cellulose synthase interacting1-independent reduction in the normal coincidence rate between microtubules and CESA particles. As a CBI, for which there is little evidence of evolved weed resistance, indaziflam represents an important addition to the action mechanisms available for weed management.

Phytoremediation of hydrocarbon contaminants in subantarctic soils: an effective management option

Accidental fuel spills on world heritage subantarctic Macquarie Island have caused considerable contamination. Due to the island's high latitude position, its climate, and its fragile ecosystem, traditional methods of remediation are unsuitable for on-site clean up. We investigated the tolerance of a subantarctic native tussock grass, Poa foliosa (Hook. f.), to Special Antarctic Blend (SAB) diesel fuel and its potential to reduce SAB fuel contamination via phytoremediation. Toxicity of SAB fuel to P. foliosa was assessed in an 8 month laboratory growth trial under growth conditions which simulated the island's environment. Single seedlings were planted into 1 L pots of soil spiked with SAB fuel at concentrations of 1000, 5 000, 10,000, 2000 and 40,000 mg/kg (plus control). Plants were harvested at 0, 2, 4 and 8 months and a range of plant productivity endpoints were measured (biomass production, plant morphology and photosynthetic efficiency). Poa foliosa was highly tolerant across all SAB fuel concentrations tested with respect to biomass, although higher concentrations of 20,000 and 40,000 mg SAB/kg soil caused slight reductions in leaf length, width and area. To assess the phytoremediation potential of P. foliosa (to 10 000 mg/kg), soil from the planted pots was compared with that from paired unplanted pots at each SAB fuel concentration. The effect of the plant on SAB fuel concentrations and the associated microbial communities found within the soil (total heterotrophs and hydrocarbon degraders) were compared between planted and unplanted treatments at the 0, 2, 4 and 8 month harvest periods. The presence of plants resulted in significantly less SAB fuel in soils at 2 months and a return to background concentration by 8 months. Microbes did not appear to be the sole driving force behind the observed hydrocarbon loss. This study provides evidence that phytoremediation using P. foliosa is a valuable remediation option for use at Macquarie Island, and may be applicable to the management of fuel spills in other cold climate regions.

Resistance to ACCase-inhibiting herbicides in an Asia minor bluegrass (Polypogon fugax) population in China

Asia minor bluegrass (Polypogon fugax) is a common annual grass weed of winter crops distributed across China. We conducted a study on the resistance level and the mechanism of resistance to ACCase-inhibiting herbicides in a P. fugax population from China. Whole-plant dose-response experiments in greenhouse showed that the resistant P. fugax population was 1991, 364, 269, 157, and 8-fold resistant to clodinafop-propargyl, fluazifop-p-butyl, haloxyfop-R-methyl, quizalofop-p-ethyl and fenoxaprop-p-ethyl relative to the reference susceptible population, which was susceptible to all the five AOPP herbicides. Much lower R/S values of 3.5, 2.4 and 3.5, respectively, were detected for clethodim, sethoxydim and pinoxaden. Molecular analysis of resistance confirmed that the Ile2041 to Asn mutation in the resistant population conferred resistance to AOPP herbicides, but not to CHD and DEN herbicides. This is the first report of a target site mutation that corresponded to resistance to AOPP herbicides in P. fugax. Proper resistance management practices are necessary to prevent ACCase-inhibiting herbicides from becoming ineffective over wide areas.

The role of cytochrome P450 monooxygenase in the different responses to fenoxaprop-P-ethyl in annual bluegrass (Poa annua L.) and short awned foxtail (Alopecurus aequalis Sobol.)

Herbicide resistance or tolerance in weeds mediated by cytochrome P450 monooxygenase is a considerable problem. However, cytochrome P450 mediated resistance or tolerance in weeds was less studied. Thus, in this work, the role of the cytochrome P450 monooxygenase in the different responses of Poa annua and Alopecurus aequalis to fenoxaprop-P-ethyl was studied. We found that the effect of fenoxaprop-P-ethyl could be synergized by piperonyl butoxide (PBO) in P. annua, but not by malathion. After being treated with fenoxaprop-P-ethyl (containing mefenpyr-diethyl), the contents of cytochrome P450 and cytochrome b5 in P. annua increased significantly compared to plants treated with mefenpyr-diethyl only or untreated plants. However, the increase was less in A. aequalis, which was susceptible to fenoxaprop-P-ethyl. The activities of ρ-nitroanisole O-demethylase (PNOD), ethoxyresorufin O-deethylase (EROD), ethoxycoumarin oxidase (ECOD) and NADPH-dependent cytochrome P450 reductase mediated by cytochrome P450 monooxygenase increased in P. annua after treatment with fenoxaprop-P-ethyl, especially the activities of ECOD and cytochrome P450 reductase. Besides this, cytochrome P450 monooxygenase activity toward fenoxaprop-P-ethyl in P. annua increased significantly compared to untreated or treated with mefenpyr-diethyl plants and treated or untreated A. aequalis. Cytochrome P450 monooxygenase may play an important role in the different responses to fenoxaprop-P-ethyl in P. annua and A. aequalis.

The Pseudomonas aeruginosa antimetabolite L-2-amino-4-methoxy-trans-3-butenoic acid inhibits growth of Erwinia amylovora and acts as a seed germination-arrest factor

The Pseudomonas aeruginosa antimetabolite L-2-amino-4-methoxy-trans-3-butenoic acid (AMB) shares biological activities with 4-formylaminooxyvinylglycine, a related molecule produced by Pseudomonas fluorescens WH6. We found that culture filtrates of a P. aeruginosa strain overproducing AMB weakly interfered with seed germination of the grassy weed Poa annua and strongly inhibited growth of Erwinia amylovora, the causal agent of the devastating orchard crop disease known as fire blight. AMB was active against a 4-formylaminooxyvinylglycine-resistant isolate of E. amylovora, suggesting that the molecular targets of the two oxyvinylglycines in Erwinia do not, or not entirely, overlap. The AMB biosynthesis and transport genes were shown to be organized in two separate transcriptional units, ambA and ambBCDE, which were successfully expressed from IPTG-inducible tac promoters in the heterologous host P. fluorescens CHA0. Engineered AMB production enabled this model biocontrol strain to become inhibitory against E. amylovora and to weakly interfere with the germination of several graminaceous seeds. We conclude that AMB production requires no additional genes besides ambABCDE and we speculate that their expression in marketed fire blight biocontrol strains could potentially contribute to disease control.

Invasive knotweed affects native plants through allelopathy

PREMISE OF STUDY

There is increasing evidence that many plant invaders interfere with native plants through allelopathy. This allelopathic interference may be a key mechanism of plant invasiveness. One of the most aggressive current plant invaders is the clonal knotweed hybrid Fallopia × bohemica, which often forms monocultures in its introduced range. Preliminary results from laboratory studies suggest that allelopathy could play a role in this invasion.

METHODS

We grew experimental communities of European plants together with F. × bohemica. We used activated carbon to test for allelopathic effects, and we combined this with single or repeated removal of Fallopia shoots to examine how mechanical control can reduce the species' impact.

KEY RESULTS

Addition of activated carbon to the soil significantly reduced the suppressive effect of undamaged F. × bohemica on native forbs. The magnitude of this effect was similar to that of regular cutting of Fallopia shoots. Regular cutting of Fallopia shoots efficiently inhibited the growth of rhizomes, together with their apparent allelopathic effects.

CONCLUSIONS

The ecological impact of F. × bohemica on native forbs is not just a result of competition for shared resources, but it also appears to have a large allelopathic component. Still, regular mechnical control successfully eliminated allelopathic effects. Therefore, allelopathy will create an additional challenge to knotweed management and ecological restoration only if the allelochemicals are found to persist in the soil. More research is needed to examine the mechanisms underlying Fallopia allelopathy, and the long-term effects of soil residues.

Plants growing on contaminated and brownfield sites appropriate for use in Organisation for Economic Co-operation and Development terrestrial plant growth test

The Organisation for Economic Co-operation and Development (OECD) terrestrial plant test is often used for the ecological risk assessment of contaminated land. However, its origins in plant protection product testing mean that the species recommended in the OECD guidelines are unlikely to occur on contaminated land. Six alternative species were tested on contaminated soils from a former Zn smelter and a metal fragmentizer with elevated concentrations of Cd, Cu, Pb, and Zn. The response of the alternative species was compared with that of two species recommended by the OECD: Lolium perenne (perennial ryegrass) and Trifolium pratense (red clover). Urtica dioica (stinging nettle) and Poa annua (annual meadowgrass) had low emergence rates in the control soil and so may be considered unsuitable. Festuca rubra (Chewings fescue), Holcus lanatus (Yorkshire fog), Senecio vulgaris (common groundsel), and Verbascum thapsus (great mullein) offer good alternatives to the OECD species. In particular, H. lanatus and S. vulgaris were more sensitive to the soils with moderate concentrations of Cd, Cu, Pb, and Zn than the OECD species.

4-Formylaminooxyvinylglycine, an herbicidal germination-arrest factor from Pseudomonas rhizosphere bacteria

A new oxyvinylglycine has been identified as a naturally occurring herbicide that irreversibly arrests germination of the seeds of grassy weeds, such as annual bluegrass (Poa annua), without significantly affecting the growth of established grass seedlings and mature plants or germination of the seeds of broadleaf plant species (dicots). Previously, Pseudomonas fluorescens WH6 and over 20 other rhizosphere bacteria were isolated and selected for their ability to arrest germination of P. annua seeds. The germination-arrest factor (GAF, 1) responsible for this developmentally specific herbicidal action has now been isolated from the culture filtrate of P. fluorescens WH6. Purification of this highly polar, low molecular weight natural product allowed its structure to be assigned as 4-formylaminooxy-l-vinylglycine on the basis of NMR spectroscopic and mass spectrometric data, in combination with D/L-amino acid oxidase reactions to establish the absolute configuration. Assay results for P. annua inhibition by related compounds known to regulate plant growth are presented, and a cellular target for 1 is proposed. Furthermore, using bioassays, TLC, and capillary NMR spectroscopy, it has been shown that GAF (1) is secreted by all other herbicidally active rhizosphere bacteria in our collection.

Exposure to cadmium-contaminated soils increases allergenicity of Poa annua L. pollen

BACKGROUND

Pollution is considered as one main cause for the increase of allergic diseases. Air pollutants may cause and worsen airway diseases and are probably able to make pollen allergens more aggressive. Previous studies looked at traffic-related air pollution, but no data about the effects of polluted soils on pollen allergens are available. We aimed to assess the effects of plant exposure to cadmium-contaminated soil on allergenicity of the annual blue grass, Poa annua L, pollen.

METHODS

Poa plants were grown in soil contaminated or not contaminated (control) with cadmium. At flowering, mature pollen was analyzed by microscopy, to calculate the percentage of pollen grains releasing cytoplasmic granules, and by proteomic techniques to analyze allergen proteins. Allergens were identified by sera from grass pollen-allergic patients and by mass spectrometry.

RESULTS

Pollen from Cd-exposed plants released a higher amount of allergenic proteins than control plants. Moreover, Cd-exposed pollen released allergens-containing cytoplasmic grains much more promptly than control pollen. Group 1 and 5 allergens, the major grass pollen allergens, were detected both in control and Cd-exposed extracts. These were the only allergens reacting with patient's sera in control pollen, whereas additional proteins strengthening the signal in the gel region reacting with patient's sera were present in Cd-exposed pollen. These included a pectinesterase, a lipase, a nuclease, and a secretory peroxydase. Moreover, a PR3 class I chitinase-like protein was also immunodetected in exposed plants.

CONCLUSION

Pollen content of plants grown in Cd-contaminated soils is more easily released in the environment and also shows an increased propensity to bind specific IgE.

Selecting tolerant grass seedlings and analyzing the possibility for using aged refuse as sward soil

In order to test the possibility for recycling use of aged refuse as sward soil, the study determined the responses of Lolium perenne L. (perennial ryegrass), Festuca arundinacea (tall fescue), and Poa annua (annual bluegrass) to its leaching. The growth of three seedlings was significantly inhibited after treatment, especially for longer treatment duration and higher concentration leaching; however, with the better growth and chlorophyll content for shorter time and lower concentration, tall fescue was more tolerant to the stress. Afterwards, several physiological responses of tall fescue were determined. For shorter treatment duration, antioxidant enzyme activities remained unchanged, and no obvious oxidative damage was observed. Prolonging exposure time, lipid peroxidation and protein oxidation occurred after treatment of higher concentration leaching, accompanying by changes of antioxidant status. It implicates that it is possible for using aged refuse as sward soil, and the critical point focused on selecting tolerant grass and controlling exposure condition.

Effect of compost-, sand-, or gypsum-amended waste foundry sands on turfgrass yield and nutrient content

To prevent the 7 to 11 million metric tons of waste foundry sand (WFS) produced annually in the USA from entering landfills, current research is focused on the reuse of WFSs as soil amendments. The effects of different WFS-containing amendments on turfgrass growth and nutrient content were tested by planting perennial ryegrass (Lolium perenne L.) and tall fescue (Schedonorus phoenix (Scop.) Holub) in different blends containing WFS. Blends of WFS were created with compost or acid-washed sand (AWS) at varying percent by volume with WFS or by amendment with gypsum (9.6 g gypsum kg(-1) WFS). Measurements of soil strength, shoot and root dry weight, plant surface coverage, and micronutrients (Al, Fe, Mn, Cu, Zn, B, Na) and macronutrients (N, P, K, S, Ca, Mg) were performed for each blend and compared with pure WFS and with a commercial potting media control. Results showed that strength was not a factor for any of the parameters studied, but the K/Na base saturation ratio of WFS:compost mixes was highly correlated with total shoot dry weight for perennial ryegrass (r = 0.995) and tall fescue (r = 0.94). This was further substantiated because total shoot dry weight was also correlated with shoot K/Na concentration of perennial ryegrass (r = 0.99) and tall fescue (r = 0.95). A compost blend containing 40% WFS was determined to be the optimal amendment for the reuse of WFS because it incorporated the greatest possible amount of WFS without major reduction in turfgrass growth.

Using a selectivity index to evaluate logarithmic spraying in grass seed crops

BACKGROUND

Grass seed crops are minor crops that cannot support the development of selective herbicides for grass weed control in grass seed crops. An option is to screen for selective herbicides with the use of logarithmic spraying technology. The aim of this paper is to assess selectivity of various herbicides in grass seed crops by using dose-response curves.

RESULTS

Six grass species were subjected to logarithmic spraying with 11 herbicides and with Poa pratensis L. as a weed. The ratio between the doses that caused 10% of damage to the crop and 90% of damage to the weed was used as a selectivity index. Compounds with selectivity indices above 2 can be safely used in a crop. The two ACCase herbicides clodinafop-propargyl and fenoxaprop-P-ethyl and a mixture of the two ALS herbicides mesosulfuron and iodosulfuron could be used selectively to control P. pratensis in Festuca rubra L., although the selectivity indices in no instances were greater than the desired 2.0.

CONCLUSION

The logarithmic sprayer can be a rapid screening tool for identifying compounds with favourable selectivity indices. Good experimental design is needed to alleviate rates being systematically distributed and confounded with growth rate and soil fertility gradients.

Regulation of summer dormancy by water deficit and ABA in Poa bulbosa ecotypes

BACKGROUND AND AIMS

Survival of many herbaceous species in Mediterranean habitats during the dry, hot summer depends on the induction of summer dormancy by changes in environmental conditions during the transition between the winter (growth) season to the summer (resting) season, i.e. longer days, increasing temperature and drought. In Poa bulbosa, a perennial geophytic grass, summer dormancy is induced by long days, and the induction is enhanced by high temperature. Here the induction of summer dormancy in a Mediterranean perennial grass by water deficit under non-inductive photoperiodic conditions is reported for the first time.

METHODS

Plants grown under 22/16 degrees C and non-inductive short-day (9 h, SD) were subjected to water deficit (WD), applied as cycles of reduced irrigation, or sprayed with ABA solutions. They were compared with plants in which dormancy was induced by transfer from SD to inductive long-day (16 h, LD). Responses of two contrasting ecotypes, from arid and mesic habitats were compared. Dormancy relaxation in bulbs from these ecotypes and treatments was studied by comparing sprouting capacity in a wet substrate at 10 degrees C of freshly harvested bulbs to that of dry-stored bulbs at 40 degrees C. Endogenous ABA in the bulbs was determined by monoclonal immunoassay analysis.

KEY RESULTS

Dormancy was induced by WD and by ABA application in plants growing under non-inductive SD. Dormancy induction by WD was associated with increased levels of ABA. Bulbs were initially deeply dormant and their sprouting capacity was very low, as in plants in which dormancy was induced by LD. Dormancy was released after 2 months dry storage at 40 degrees C in all treatments. ABA levels were not affected by dormancy relaxation.

CONCLUSIONS

Summer dormancy in P. bulbosa can be induced by two alternative and probably additive pathways: (1) photoperiodic induction by long-days, and (2) water deficit. Increased levels of endogenous ABA are involved in both pathways.

N-(2-bromophenyl)-2-(4,6-dimethoxypyrimidin-2-yloxy)benzylamine, a new selective postemergent herbicide for weed control in winter oilseed rape

N-(2-Bromophenyl)-2-(4,6-dimethoxypyrimidin-2-yloxy)benzylamine is a highly active herbicide, which belongs to a novel class of chemistry. The compound is de novo synthesized in good yield, and the structure is confirmed by (1)H NMR, IR, MS, microanalysis, and X-ray. Its herbicidal activity is assessed under greenhouse conditions. It is effective against many grass weed species, as well as broadleaf weeds, under greenhouse conditions. Field trials indicate that it controls major weeds with a good tolerance on oilseed rape by postemergence application at rates of 15-90 g of active ingredient/ha. This compound possesses low mammalian toxicity and favorable environmental profile. These results suggest that the compound has potential as a new selective postemergent herbicide in winter oilseed rape.

Growth and nutritive quality of Poa pratensis as influenced by ozone and competition

Interspecific plant competition has been hypothesized to alter effects of early-season ozone (O3) stress. A phytometer-based approach was utilized to investigate O3 effects on growth and nutritive quality of Poa pratensis grown in monoculture and in mixed cultures with four competitor-plant species (Anthoxanthum odoratum, Achillea millefolium, Rumex acetosa and Veronica chamaedrys). Mesocosms were exposed during April/May 2000-2002 to charcoal-filtered air+25 ppb O3 (control) or non-filtered air+50 ppb O3 (elevated O3). Biomass production was not affected by O3, but foliar injury symptoms were observed in May 2002. Early-season O3 exposure decreased relative food value of P. pratensis by an average of 8%, which is sufficient to have nutritional implications for its utilization by herbivores. However, forage quality response to O3 was not changed by interspecific competition. Lack of injury and nutritive quality response in P. pratensis harvested in September may reflect recovery from early-season O3 exposure.

Generation of large numbers of transgenic Kentucky bluegrass (Poa pratensis L.) plants following biolistic gene transfer

A very efficient transformation system, using biolistic bombardment, has been developed for the production of transgenic plants of Kentucky bluegrass (Poa pratensis L.). Embryogenic calli, initiated from immature embryos, were transformed either with pAct1IHPT-4 containing the hygromycin phosphotransferase (hpt) gene or with pDM803 containing the phosphinothricin acetyltransferase (bar) gene and the beta-glucuronidase (uidA) gene. In total 119 independent transgenic plants were recovered from 153 hygromycin-resistant lines. Bialaphos selection yielded a total of 99 bialaphos-resistant lines and from these 34 independent transgenic plants were recovered. Southern blot analysis demonstrated the independent nature of the transgenic plants and also revealed a complex transgene integration pattern with multiple insertions.

Effects of commercial diazinon and imidacloprid on microbial urease activity in soil and sod

Diazinon [O,O-diethyl O-2-isopropyl-6-methyl(pyrimidine-4-yl) phosphorothioate] and imidacloprid [1-(1-[6-chloro-3-pyridinyl]methyl)-N-nitro-2-imidazolidinimine] are applied to lawns for insect control simultaneously with nitrogenous fertilizers such as urea, but their potential effect on urease activity and nitrogen availability in turfgrass management has not been evaluated. Urease activity in enzyme assays, washed cell assays, and soil slurries was examined as a function of insecticide concentration. Intact cores from field sites were used to assess the effect of insecticide application on urease activity in creeping bentgrass (Agrostis palustris Huds.) and bluegrass (Poa pratensis L.) sod. Bacterial urease from Bacillus pasteurii and plant urease from jack bean [Canavalia ensiformis (L.) DC.] were unaffected by the insecticides. Both insecticides inhibited the growth of Proteus vulgaris, a urease-producing bacterium, but only diazinon significantly reduced urease activity in washed cells; neither insecticide inhibited urease activity in sonicated cells. Neither diazinon nor imidacloprid inhibited urease activity in Woolper soil (fine, mixed, mesic Typic Argiudoll) slurries, but diazinon slightly inhibited urease activity in Maury soil (fine, mixed, semiactive, mesic Typic Paleudalf) slurries. Imidacloprid had no effect on urease activity in creeping bentgrass or bluegrass sod at up to 10 times the commercial application rate. Diazinon briefly, but significantly, reduced urease activity in bluegrass sod. Co-application of imidacloprid and urea appears to be benign with respect to urease activity in soil and sod. Diazinon, in contrast, appears to have a significant, short-term, inhibitory effect on the microbial urease-producing community, but that effect depends on soil type.

No difference in activity of Sod-1 genotypes of Poa annua to short-term treatment of ambient gaseous organic pollution

Our previous studies indicated that genotypes at locus Sod-1 of Poa annua changed clinally along a gradient of gaseous organic pollution. In the present study, we aimed to know whether there were differential responses of activities of different superoxide dismutase (SOD) genotypes to short-term treatment of ambient gaseous organic pollution. Significant bias from Hardy-Weinberg equibrium was observed on locus Sod-1, and no genotype Sod-1-BB was found. Significantly increased activities were observed in most treatments for genotype Sod-1-AA and in one treatment for genotype Sod-1-AB. However, no significant difference in SOD activities was found between the two genotypes. It was interpreted that fitness difference between the two genotypes was small and treatment duration was too short or extent of ambient organic pollution was too low to lead to differential responses. Other environmental factor effects on activities of superoxide dismutases can also explain the results.

Short-term exposure to elevated atmospheric CO2 benefits the growth of a facultative annual root hemiparasite, Rhinanthus minor (L.), more than that of its host, Poa pratensis (L.)

The effects of elevated CO2 (650 ppm) on interactions between a chlorophyllous parasitic angiosperm, Rhinanthus minor (L.) and a host, Poa pratensis (L.) were investigated. R. minor benefited from elevated CO2, with both photosynthesis and biomass increasing, and transpiration and tissue N concentration remaining unaffected. However, this did not alleviate the negative effect of the parasite on the host; R. minor reduced host photosynthesis, transpiration, leaf area and biomass, irrespective of CO2 concentration. Elevated CO2 resulted in increased host photosynthesis, but there was no concomitant increase in biomass and foliar N decreased. It appears that the parasite may reduce host growth more by competition for nitrogen than for carbon. Contrary to expectation, R. minor did not reduce the productivity of the host-parasite association, and it actually contributed to the stimulation of productivity of the association by elevated CO2.

Use of plant cell cultures to study graminicide effects on lipid metabolism

Graminicides belonging to the cyclohexanedione and aryloxyphenoxypropionate classes are well established to act by disrupting acyl lipid biosynthesis via specific inhibition of acetyl-CoA carboxylase. Species of grass inherently resistant to such herbicides, or biotypes of grassy weed species which display acquired resistance to recommended rates of graminicide application, are known to possess an altered plastidic multifunctional acetyl-CoA carboxylase showing reduced sensitivity to these herbicides in vitro. Studies reported here demonstrate that cell suspension cultures of maize, a graminicide-sensitive species and Poa annua, a graminicide-insensitive species, display a similar differential sensitivity of acyl lipid biosynthesis as tissue from corresponding intact plants. Acyl lipid biosynthesis in P. annua can be inhibited if sufficiently high concentrations of graminicide are used. The major plastidic form and the minor cytosolic forms of acetyl-CoA carboxylase were successfully purified from maize cell suspensions, were compared to those from leaf tissue and were shown to be differentially inhibited by graminicides in a similar manner to their counterparts from leaf tissue. These studies demonstrate that cell suspensions are useful for studying the mode of action of graminicides, especially in view of the limited amount of material obtainable from many grassy species which are very fine-growing.

Pseudoviviparous reproduction of Poa alpina var. vivipara L. (Poaceae) during long-term exposure to elevated atmospheric CO2

Pseudovivipary is an asexual reproductive strategy exhibited by some arctic/alpine grasses in which leafy plantlets are produced in place of seeds, with genetic conservation an advantage for stress tolerators in these nutrient-poor habitats. Photosynthetic metabolism and the development of this reproductive system were investigated under varying nutrient availability and predicted future CO(2) partial pressure (pCO(2)). Poa alpina var. vivipara L., grown at present ambient pCO(2) or ambient plus 340 micro mol mol(-1) CO(2) (elevated pCO(2)), was supplied with either 0.05 mol m(-3) phosphorus and 0.2 mol m(-3) nitrogen, or 0.2 mol m(-3) phosphorus and 1.0 mol m(-3) nitrogen. Gas exchange measurements and determination of total non-structural carbohydrate (TNC), nitrogen and phosphorus contents revealed that parent plant leaf blade tissues experienced acclimatory loss of photosynthetic capacity after long-term growth at elevated pCO(2) (particularly so when nutrient availability was low); there were associated reductions in photosynthetic nitrogen and phosphorus use efficiencies (PNUE and PPUE). In addition, decreased PNUE and PPUE were exhibited by plantlets grown at elevated pCO(2) with low nutrient availability. Decreased reproductive dry matter in this treatment also resulted from a lack of reproductive initiation in daughter tillers, and altered phenology. Pseudoviviparous P. alpina is likely to be at a disadvantage in both vegetative and reproductive phases at predicted future elevated atmospheric CO(2) concentrations, particularly where nutrients are scarce and when in competition with species experiencing less acclimatory loss of photosynthetic capacity.

Genetic structure along a gaseous organic pollution gradient: a case study with Poa annua L

The population genetic composition of Poa annua L. was studied by starch electrophoresis along a transect running NE from an organic reagents factory at Shanghai, China. Five enzyme systems were stained. We have reached the following preliminary conclusions: (1). Organic pollution has dramatically changed genotypic frequencies at some loci of Poa annua populations. At polluted sites, significant deviations from Hardy-Weinberg equilibrium were observed on loci Sod-1 and Me due to the excess of heterozygote. Especially in the two nearest sites to pollution source, all the individuals were heterozygous at locus Sod-1. The data suggests that heterozygotes were more tolerant to organic pollution than homozygotes, indicating the fitness superiority of heterozygotes. (2). A tendency towards clinal changes of allele frequencies was found at some polymorphic loci. Frequencies of the common alleles at loci Sod-1, Me and Fe-1 increased as the distance to the pollution source increased. (3). The effective number of alleles per locus, and the observed and expected heterozygosity were much higher in the pollution series than in the clear control site (Botanic Park population), but genetic multiplicity (number of alleles per locus) was lower than for the control. (4). Most genetic variability was found within populations, and only 2.56% were among populations of the polluted series. However, 9.48% of the total genetic variation occurred among populations when including the Botanic Park population. The genetic identity between populations of the pollution series (0.9869-1.0000, mean 0.9941) was higher than those between the pollution series and the Botanic Park population. UPGMA divided the five populations into two groups. One contained the four polluted populations, and the other only contained the Botanic Park population.

Nitrogen dynamics in the intact grasses Poa trivialis and Panicum maximum receiving contrasting supplies of nitrogen

The C(3) grass Poa trivialis and the C(4) grass Panicum maximum were grown in sand culture and received a complete nutrient solution with nitrogen supplied as 1.5 mol m(-3) NH(4)NO(3). (15)N tracer techniques were used to quantify the relative use of root uptake and mobilization in supplying nitrogen to growing leaves in intact plants which either continued to receive nitrogen or which received the complete nutrient solution without nitrogen. The allocation of both (15)N-labelled nitrogen uptake and unlabelled mobilized nitrogen indicated that, under their conditions of growth, the sink strength of growing leaves was relatively greater in P. maximum than P. trivialis. The supply of nitrogen by mobilization to side tillers of P. trivialis was completely stopped as the external nitrogen supply was reduced, whilst in P. maximum some allocation of mobilized nitrogen to side tillers, roots and growing leaves was maintained. In both plant species receiving an uninterrupted supply of nitrogen the allocation pattern of mobilized nitrogen differed from that of nitrogen derived from root uptake. Differences exist in the degree to which P. trivialis and P. maximum utilized uptake and mobilization to supply nitrogen to the growing leaves. In P. trivialis roots were always a net sink of mobilized nitrogen, irrespective of the external nitrogen supply. In P. maximum, roots were a net sink of mobilized nitrogen when external nitrogen was withdrawn, but exhibited both source and sink behaviour when nitrogen supply was continued.