Role of extracellular polymeric substances in resistance to allelochemical stress on Microcystis aeruginsosa and its mechanism

Using allelochemicals to suppress cyanobacteria growth is a prospective method for its high efficiency and ecological safety.However,the suppression efficiency is affected inevitably by the extracellular polymeric substances(EPS)produced by cyanobacteria,and the knowledge about the roles of EPS in resistance to allelochemical stress is scarce.For the study,two typical anti-cyanobacterial allelochemicals were adopted to investigate the role of EPS in resistance to allelochemical stress on Microcystis aeruginosa.Results show that EPS was crucial in alleviating the toxicity of allelochemicals to algae,especially in stabilizing the metabolism and photosynthetic activity of algal cells.The aggregation rate of algal cells increased with the increase of EPS secretion,which alleviated the stress of allelopathy.Tryptophan proteins and humic acids in EPS provided a binding site for allelochemicals,and the EPS-allelochemicals complex were formed by chemical bonding.This study improved our comprehension of the role of EPS in algal inhibition by allelochemicals.

Effects of Two Potential Allelochemicals on the Photosystem II of Nitzschia closterium and Monostroma nitidum

In aquaculture,high-density seaweed farming brings higher economic benefits but also increases outbreaks of diatom felt.The effective control of diatom felt in high-density seaweed farming has always been a research hotspot.This study selected two potential allelochemicals 2-hydroxycinnamic acid and quinic acid to explore their effects on a diatom Nitzschia closterium and an economic seaweed Monostroma nitidum.The results showed that 2-hydroxycinnamic acid had better inhibitory effects than quinic acid on the growth,pigment content and photosynthetic efficiency of N.closterium.Their half-maximal inhibitory concentrations at 120 h(IC_(50–120 h))were 0.9000 and 1.278 mM,respectively.Additionally,these allelochemicals had limited inhibitory effects on the growth,pigment content and photosynthetic efficiency of M.nitidum before 24 h.To further explore the allelopathic effect of these chemicals,this study focused on the photosystem II energy fluxes of N.closterium.It was found that 3 mM 2-hydroxycinnamic acid could destroy the whole photosynthetic system by devastating the PSII reaction centre(RC)before 24 h;however,the same concentration of quinic acid could only down-regulate the electron transport efficiency by changing the effective antenna size of an active RC and downregulating the PSII reaction centre density.These experimental results are expected to provide a new strategy to control diatom felt blooms on the high-density seaweed farming areas.

The Study of Allelochemicals of the Melon Fly (Myiopardalis pardalina Bigot.)

This study describes the isolation, identification of allelochemicals of the melon fly (Myiopardalis pardalina Bigot.), using the GC-MS method. A food attractant has been identified and a method for the synthesis of its synthetic analogue has been developed. Also, a route for the synthesis of para pheromone, raspberry ketone, has been proposed.

Allelochemicals of Panax notoginseng and their effects on various plants and rhizosphere microorganisms

Panax notoginseng(Araliaceae)is an important ginseng herb with various health benefits and a history of cultivation in southwestern China over 400 years.In recent years?.notoginseng has faced serious continuous-cropping obstacles due to its large-scale cultivation.In this study,we aim to explore the allelochemicals of P.notoginseng and their interactions with various plants and rhizosphere microor-ganisms.The chemical constituents of the soil cultivated with 3-year-old P.notoginseng were studied by column chromatography,spectroscopic and GC-MS analyses.We identified 13 volatile components and isolated six triterpenes(1-4,6-7)and one anthraquinone(5).Compounds 1-7 were tested for their effects on seed germination and root elongation in P.notoginseng,corn,wheat,turnip,water spinach and Arabidopsis thaliana.We also examined the effect of compounds 1-7on the growth of ten rhizosphere microorganisms of P.notoginseng.At a concentration of 1.0 ug mL',compounds 3 and 5-7 caused the death of P.notoginseng root cells and compounds 2,6 and 7 induced the death of root cells of A.thaliana.Compounds 1-5and 7 inhibited elongation of A.thaliana root tip cells at a concentration of 10.0μg mL^-1.Moreover,at a concentration of 0.1 mg mL^-1,compounds 3,4,6 and 7 inhibited the growth of probiotics and promoted the growth of pathogens of P.notoginseng.These results suggest that these isolated ursane-type triterpenoid acids and anthraquinone are potential allelochemicals that contribute to continuous-cropping obstacles of P.notoginseng.

Allelochemicals and allelopathy from microorganisms in wheat rhizosphers

Allelochemicals from fungi and bacteria in wheat rhizosphere,as well as their allelo-pathic effects on wheat and maize have been conducted.Fungi and bacteria were incubated at tem-perature 28-30℃.The extracts were tested for bioassay.Some samples identified to be responsi-ble for allelopathy have been determined by GC-MS.Some chemicals identified were selected to testagain their bioactivity.The results showed that acidic extracts were more toxic to germination ofwheat and maize seeds(statistic significant difference P【0.01 or P【0.05)and basic extractswere less toxic and stimulated effects on germination in some cases.A good relationship has beenobserved between the data of chemical analysis and bioassay.A wide variety of chemicals such as phenolic acids,organic acids,aldehydes,alcohol,ke-tones,nitrogen-containing chemicals,were identified by GC-MS.Some phenols and organic acidswere identified to be inhibit and nitrogens-containing compounds were to be stimulate to germina-tion of seeds and extension of root and shoot of wheat and maize.

Effects of allelochemicals on activity of nitrate reductase

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The impact of allelochemicals on the differential expression of symbiotic bacteria in cotton aphids

Insects have developed a good adaptive mechanism in response to environmental stresses in the long-term evolution. They have developed a helpful metabolism system to resist plant allelochemicals. Insects also harbor different kinds of symbiotic bacteria, which provide them a competitive advantage. Here, using cotton aphid as an example, we investigated the effects of four plant allelochemicals on the differential expression of symbiotic bacteria based on transcriptome data. We also studied the composition of symbiotic bacteria and function on pathway level in three kinds of aphids. We found that the bacteria have a significant role in resisting the plant allelochemicals stress and host plant selection by aphids. These results should be useful to investigate the environmental adaption mechanism of aphids in the view of symbiotic bacteria. These results would offer a new insight for improving strategy of aphids and developing new pest control systems.

Identification and Quantification of Allelochemicals from Selected Sweet Potato (<i>Ipomoea batatas</i>(L.) Lam.) Cultivars

Allelopathic compounds have the potential to inhibit the growth and development of other organisms in a diverse manner ranging from shifting nutrients and enhancing their growth to inflicting diseases. In addition, these compounds influence seedling growth and seed germination of various crops. The goal of this study was to identify and quantify different allelochemicals in various sweet potato cultivars through high-performance liquid chromatography techniques. Selected sweet potato slips (weight: 2.0 - 2.5 grams/slip) were propagated in separate glass tubes filled with 10.0 mL distilled water. Water extract from each glass tube was collected after 2, 4, and 6 weeks after transplanting (WAP) to identify and quantify allelochemical compounds by comparing their peaks with the retention time of standards. Results show that the concentration of allelochemicals in water extract was increased from 2 to 4 WAP but remained constant in the sixth week. Quantitative analysis revealed that the amount of chlorogenic acid was higher in all sweet potato cultivars compared to other allelochemicals. Some sweet potato cultivars, A5 and A39, exhibited higher allelopathy (18.28 - 19.37 ppm/slip) and reduced the height and biomass of Palmer amaranth the most due to the presence of increased concentration of combined allelochemicals, while other cultivars produced lesser allelochemicals (10.90 ppm/slip) and did not reduce the growth of the weed species. Allelopathic sweet potato cultivars high in chlorogenic acid production can effectively suppress Palmer amaranth with minimal dependence on chemicals to manage weeds and harmful pests under sustainable agricultural system.

Effect of allelochemicals sustained-release microspheres on the ingestion, incorporation, and digestion abilities of Daphnia magna Straus

Allelochemicals sustained-release microspheres(ACs-SMs)exhibited great inhibition effect on algae,however,few studies have focused on ACs-SMs toxicity on invertebrate.In this study,the effects of single high-concentration ACs(15 mg/L,SH-ACs),repeated lowconcentration ACs(3×5 mg/L,RL-ACs)and ACs-SMs containing 15 mg/L ACs exposure on the ingestion,incorporation,and digestion of Daphniamagna Straus(DS)were investigated by stable isotope 15N labeling method.Meanwhile,the diversity and abundance of microflora in DS guts were determined by 16S rRNA genes and cloning methods.The results showed that SH-ACs exposure caused 50%and 33.3%death rates for newborn and adult DS,while RL-ACs exposure caused 10%death rate for newborn DS and no obvious effect on the activity of adult DS.And ACs-SMs exposure did not diminish the motility of both newborn and adult DS,indicating the lower acute toxicity of ACs-SMs.Furthermore,SH-ACs inhibited the ingestion(-6.45%),incorporation(-47.1%)and digestion(-53.8%)abilities of DS and reduced the microbial abundance(-27.7%)in DS guts.Compared with SH-ACs,RL-ACs showed relatively low impact on the ingestion(-3.23%),incorporation(-5.89%)and digestion(-23.9%)abilities of DS.Interestingly,ACs-SMs enhanced the ingestion(+9.68%),incorporation(+52.9%)and digestion(+51.3%)abilities of DS and increased the microbial abundance(+10.7%)in DS guts.Overall ACs and ACs-SMs reduced the diversity of microflora in DS guts.In conclusion,ACs-SMs can release ACs sustainably and prolong the sustained release time,which not only effectively reduce the toxicity of ACs,but also had positive effects on DS.

Inductive and synergistic interactions between plant allelochemical flavone and Bt toxin Cry1 Ac in Helicoverpa armigera

Genetically engineered crops simultaneously produce defensive allelochemi-cals and Bacillus thuringiensis(Bt)toxin proteins to kill some of the world's most devastating insect pests.How the two types of toxins,when ingested sequentially or simultaneously,interact at both lethal and sublethal doses in these pests remains underexplored.Here,we examined the toxicological interactions between the Bt toxin Cry 1 Ac and the flavonoid allelochemical flavone in Helicoverpa armigera.Simultaneous exposure of H.armigera neonates to lethal doses(LC25)of Cry 1 Ac and flavone caused a mortality significantly higher than that of either toxin alone and their expected additive mortality.Preexposure for 24 h to a sublethal dose(LC10)of Cry 1 Ac followed by 6-d simultaneous exposure to the same dose of Cry 1 Ac plus a lethal dose(1.6 mg/g diets,LC50)of flavone resulted in a mortality significantly higher than that of the LC50 dose of flavone alone and the expected additive mortality of the LC50 dose of flavone plus the LC10 dose of Cry 1 Ac.One-day preexposure to the sublethal dose(LC10)of flavone followed by 6-d simultaneous exposure to the LC50 dose(6 ng/cm2)of Cry 1 Ac plus the LC25 dose of flavone yielded a mortality significantly higher than that of the LC50 dose of Cry 1 Ac but similar to the expected additive mortality of the LC50 dose of Cry 1 Ac plus the LC50 dose of flavone.The results suggest that Cry 1 Ac induces and synergizes the toxicity of flavone against H.armigera larvae.

Extraction of allelochemicals from poplar alkaline peroxide mechanical pulping effluents and their allelopathic effects on Microcystis aeruginosa

In this study,allelochemicals were extracted from pulping effluents rather than from the raw ma-terial of plants.Herein,five organic solvents(ethyl acetate(EAC),methyl tert-butyl ether(MTBE),dichloromethane(DCM),carbon tetrachloride(CTC),and petroleum(PE))were applied to sep-arately extracting the allelochemicals from alkaline peroxide mechanical pulp(APMP)effluents.The results from the algal density,inhibition ratio,and optical density of 446 nm(OD 446nm)concluded that the extractives from the APMP effluents can act as effective allelochemicals and showed noticeable allelopathic inhibition effects on Microcystis aeruginosa growth.The results in-dicated that organic solvent extraction could be a practical approach to isolate the allelochemicals from the APMP effluents,which would broaden the potential application of the APMP effluents in the production of antimicrobial agents and other value-added materials.

Do Aqueous Extracts from Buckwheat Compromise Seed Germination and Initial Development of Bidens pilosa and Euphorbia heterophylla?

Fagopyrum esculentum Moench (buckwheat) is a dicot species from the Polygonaceae family used as a cover crop in agricultural systems featured with a remarkable allelopathic potential for weed control, helping herbicide-resistance management and promoting substantial reductions in herbicide applications. The aim of this research was to examine the allelopathic potential of aqueous extracts from seeds and aerial part of buckwheat on seed germination and initial development of Bidens pilosa and Euphorbia heterophylla. Bioassay experiments were conducted under a completely randomized experimental design with four replications, containing 50 seeds each. Both weed seed species were harvested in a soybean field, and seed viability was previously assessed. Seeds were exposed to four concentrations (0, 25, 50, and 100%) from extracts of seeds (ES) and aerial part (EAP) of buckwheat. Germination speed index (GSI) in B. pilosa and E. heterophylla was daily evaluated throughout 14 and 16 days, respectively, whereas percentage of germination, abnormal seedlings, as well as non-germinated seeds, root (RL) and aerial part length (APL), and total dry matter (TDM) were rated at final germination test. EAP reduced the GSI, especially under the 100% concentration. Germination percentage was lower and abnormal seedlings increased for both weed species when seeds were exposed to EAP concentrations greater than 25%. However, ES did not impinge upon E. heterophylla germination. EAP and ES reduced the APL, RL, and TDM for concentrations greater than 50%, except for ES which did not affect E. heterophylla development. Both extracts from buckwheat have a high capacity to inhibit germination and compromise seedling development, culminating in such a potential alternative for B. pilosa and E. heterophylla management in agricultural systems.

Allelopathic Effect of Seed and Leaf Aqueous Extracts of <i>Datura stramonium</i>on Leaf Chlorophyll Content, Shoot and Root Elongation of <i>Cenchrus ciliaris</i>and <i>Neonotonia wightii</i>

Pot experiment was carried out to determine the allelopathic effects of Datura?stramonium on leaf chlorophyll content, root and shoot elongation, fresh and dry weight of two wild plant species: Cenchrus ciliaris and Neonotonia wightii. Different concentrations (0%, 25%, 50%, 75% and 100%) from seed and leaf extracts of D. stramonium were used to investigate the allelopathic effects of D. stramonium on growth of tested species.?The total chlorophyll content of N. wightii was significantly reduced in all plants treated with both aqueous seed and leaf extracts of D. stramonium. In C. ciliaris, the total chlorophyll content was also significantly reduced for those plants treated with aqueous seed extract and leaf extract from D. stramonium. Relative to the control treatments, there was greater reduction in root and shoot length which was observed in higher concentrations of aqueous seed and leaf extracts. Fresh and dry weight of tested species significantly decreased after being treated with both seed and leaf aqueous extracts of D. stramonium. It was found that the allelopathic effect of aqueous seed and leaf extracts from D. stramonium on tested species was concentration-dependent. The inhibitory effects on all tested species increased as the concentration of both extracts increased from 0% to 100%. This study concluded that aqueous seed and leaf extract of D. stramonium have allelopathic effects on leaf chlorophyll content, root and shoot length, fresh and dry weight of grass (C. ciliaris) and legume (N. wightii) species.

Beneficial rhizobacterium provides positive plant–soil feedback effects to Ageratina adenophora

Rhizosphere microbial communities play important roles in facilitating or inhibiting the establishment of exotic species.Since some invasive plants interact with soil microbial communities such as rhizosphere bacteria,changes triggered by rhizosphere bacteria may alter competitive interactions between exotic and native plants.This study compared the Bacillus cereus content in soils with different degrees of Ageratina adenophora invasion,and investigated the effects of A.adenophora allelochemicals on B.cereus growth and soil characteristics and the feedback effects of B.cereus on A.adenophora growth.Bacillus cereus content in the rhizosphere of A.adenophora increased with intensification of the invasion process,and newly invaded soil contained almost twice as much bacteria as noninvaded soil.When rhizosphere soil was added to the root exudates of A.adenophora,the contents of B.cereus were twice as much as the control,except on the first day.Certain soil parameters increased significantly,such as ammonium nitrogen(NH_(4)^(+)-N)and available phosphorus(AP),which were increased by 41 and 27%,respectively.Soil treatment with B.cereus promoted the degradation of two allelochemicals from the rhizosphere of A.adenophora,amorpha-4,7(11)-dien-8-one and 6-hydroxy-5-isopropy1-3,8-dimethyl-4 a,5,6,7,8,8 ahexahydraphthalen-2(1 H)-one,to varying degrees;and increased the germination rate by 50%,root length by 117%,shoot length by 48%and fresh weight by 81%for A.adenophora compared to those of untreated soil.Our results confirmed that the invasion of A.adenophora will promote an increase of B.cereus,a beneficial rhizosphere bacterium,which in turn induces a positive feedback effect on A.adenophora.

Sustainable Utilization of Agricultural Straw for Harmful Algal Blooms Control:A Review

The use of agricultural straw for algal bloom control has been studied for more than 30 years.In this article,we have reviewed the promising potentials of using agricultural straw as source of anti-algal agents,including the effectiveness of each major straw type so far used in this regard,and the investigated algal species.Various pre-treatment methods have also been widely reviewed.Significant progress has been made in natural product chemistry and molecular biology with regards to agricultural straw,especially in relation to the extraction of antialgal allelochemicals,degradation processes of agricultural straws and the mechanisms through which these inhibitions occur.The development of biotechnologies using agricultural straw to successfully inhibit growth of bloom forming algae has been generally accepted as environmentally friendly.The current research status and that of the future should include isolation and discovery of antialgal allelochemicals,development of models that would illustrate the sequence of physiologic events that match the species-specific inhibitor phenomenon,and products fit in the field applications.

Adverse Effects of Allelopathy from Legume Crops and Its Possible Avoidance

Plant releases many bioactive chemicals from its various parts such as leaves, stem, root and sometimes decomposed body through different mechanism into its surrounding environment. These bioactive chemicals are often termed as allelochemicals because they interact with the surrounding environment. This interaction is either positive or negative. Effects of allelochemicals to the agricultural and biological ecosystem are well documented. In leguminosae family many species are involved in releasing of allelochemicals. Many researchers found that this allelochemicals have both positive and detrimental effects on the successive legume crops. Legume monoculture is common in many parts of the world where they cause a numbers of ecological and economic problems such as decline in crop yield due to soil sickness, regeneration failure and replant problem. These negative effects of allelochemicals open a great concern on allelopathy research. This article reviews the adverse effects of allelochemicals, their extraction and isolation, mechanism inside the plant body. These all are done to find out the possible selection methods of succeeding crops to avoid the allelopathic effects in the next crop of a monoculture farm field. The main purpose of this article is to highlight the adverse allelopathic effects of legume crops to provide ways for sustainable development in agro-ecosystem.

Screening of the Growth-Inhibitory Effects of 168 Plant Species against Lettuce Seedlings

The methanol extracts of 168 plant species from 68 families were evaluated for their inhibitory activity against lettuce seedling elongation. Among the plant species tested, 12 species had EC50 values for radicle growth inhibition ranging from 0.01 to 5.00 mg fresh weight equivalent mL-1. Enterolobium contortisiliquum, a traditionally used herbal medicine, exhibited the strongest inhibitory activity (estimated EC50: 0.28 fresh weight equivalent mL-1). Among the 12 species, Pachysandra terminalis, Tamarindus indica, and Albizia guachapele required investigation, because only little has been reported about their chemical constituents to date. The data in the present study would be useful in finding new lead compounds for natural herbicides.

Allelopathic Effects of <i>Argemone mexicana</i>to Growth of Native Plant Species

Argemone mexicana is known to have significant effects on cultivated agricultural fields. However, there is little information about allelopathic effect of A. mexicana on the growth of wild plant species such as those found in wildlife protected areas. This review presents evidence that allelochemicals present in A. mexicana may affect the overall growth of other plant species.

Does Soil under Natural <i>Tithonia diversifolia </i>Vegetation Inhibit Seed Germination of Weed Species?

Pot experiment was carried out in the screen house, Ladoke Akintola University Technology Ogbomosho, Nigeria to determine the possible impact of Tithonia diversifolia on the growth of thirteen selected weed species weeds growing in its surroundings. The study consisted of two treatments (Tithonia diversifolia infested and Non-Tithonia diversifolia infested soils) and from the two media, the growth of A. hispidium, B. pilosa E. heterophylla, P. maximum and P. polystachion was significantly affected in soil infested by T. diversifolia. The number of weed seedling emergence afore mentioned was significantly lower than what was obtained in soil not infested with T. diversifolia and this accounted for about 38% of the tested weed species. Germination of four of these weeds species (23%) (A. spinosus, C. viscosa, T. procumbens and D. gayana) was enhanced by the presence of T. diversifolia. The study further revealed that weed counts in T. diversifolia infested soil is significantly lower than the ones in soil without T. diversifolia infestation. Likewise, the vegetative growth of some species (A. spinosus, C. viscosa, T. procumbens and D. gayana) was improved in this soil. This shows that T. diversifolia infested soil contains allelochemicals that performed both stimulatory and inhibitory functions.

The Allelopathic Potential of <i>Conocarpus lancifolius</i>(Engl.) Leaves on Dicot (<i>Vigna sinensis</i>L.), Monocot (<i>Zea mays</i>L.) and Soil-Borne Pathogenic Fungi

Aqueous leaf extract and pulverized leaf tissue were tested for allelopathic effects on seed germination, seedling growth traits and net photosynthesis of corn (Zea mays L.) and bean (Vigna sinensis L.) The chemical constituents of the leaf extract were determined by GC-MS and the efficacy of the leaf extract to control some soil-borne fungal pathogens was also evaluated. The leaf extract inhibited germination, radicle and plumule lengths, root and shoot growth, chlorophyll content, photosynthesis and nutrient uptake in both crops. In corn and bean plants growth inhibition was proportional to the concentrations of the extracts (2.5% - 7.5%). Seed germination was associated with water uptake and the solute potential of the extracts. Leaf extracts also reduced of chlorophyll content, and stressed photosynthetic function by reducing photochemical efficiency (Fv/Fm) and electron transport rate (ETR) of PS II in corn and bean plants. Corn was more tolerant to the leaf extract than bean plants. The GC-MS analysis detected thirty one and thirty three compounds in winter and summer leaf extracts, respectively. The majority was phenolic compounds. Mycelia growth of Fusarium oxysporum f. sp. lycopersicon, Sclerotinia sclerotiorum, and Rhizoctonia solani was inhibited and in 10% extract the fungi died. The extract however, had no effect on Trichoderma harzianum. Leaf extract of C. lancifolius exhibited both herbicidal and fungicidal properties but cannot be recommended for biological control of soil borne fungal plant pathogens because it has the potential to physiologically stress or damage cultivated plants or crops.