Roles of Allelopathy in Plant Biodiversity and Sustainable Agriculture

Allelopathic compounds are metabolites released from plants that might be beneficial or detrimental to the growth of receptor plants. These compounds are involved in the environmental complex of managed or natural ecosystems. Allelopathic compounds have been shown to play important roles in the determination of plant diversity, dominance, succession, and climax of natural vegetation and in the plant productivity of agroecosystems. The overuse of synthetic agrochemicals often causes environmental hazards, an imbalance of soil microorganisms, nutrient deficiency, and change of soil physicochemical properties, resulting in a decrease of crop productivity. The incorporation of allelopathic substances into agricultural management may reduce the use of synthetic herbicides, fungicides, and insecticides and lessen environmental deterioration. Scientists in many different habitats around the world have demonstrated the above examples previously. It is known that most volatile compounds, such as terpenoids, are released from plants in drought areas. In contrast, water-borne phytotoxins, such as phenolics, flavonoids, or alkaloids, are released from plants in humid zone areas. Both allelopathy and autointoxication play an important mechanism in regulating plant biodiversity and plant productivity. A unique case study of a pasture-forest intercropping system, which is particularly emphasized here, could be used as a model for forest management. After the deforestation of coniferous or hardwood forests, a pasture grass, kikuyu grass (Pennisetum clandestinum), was transplanted onto the land. The grass was quickly established within 6 months. Significant suppression of weed growth by the kikuyu grass was found; however, the growth of coniferous or hardwood plants was not suppressed but stimulated. This example as well as others described in this text clearly indicate that allelopathy plays a significant role in sustainable agriculture. Nevertheless, room for allelopathic research in the next century is available for biologists, biochemists, biotechnologists, and chemists. Future allelopathic research should focus on the following tasks: (1) a continuous survey of potential allelochemicals from natural vegetation or microorganisms, (2) the establishment of practical ways of using allelochemicals in the field, (3) to understand the mode of action of allelopathic chemicals in receptor organisms, (4) to understand the role of allelopathic chemicals in biodiversity and ecosystem function, (5) to explore advanced biotechnology for allocating allelopathic chemical genes in plants or microorganisms for biological control, and (6) to challenge the natural product chemists to develop a better methodology for isolating allelopathic compounds or their degraded compounds from the environment, particularly the soil environment.     

Allelopathy in Northern Temperate and Boreal Semi-Natural Woodland

Allelopathy has been widely investigated in forest ecosystems around the world. This ecological process takes part in the vegetation dynamics and partially explains the success or failure of seedling establishment and survival. Therefore, allelopathy could be a common cause of natural regeneration failure, due to adverse impact of understory species directly on trees species (inhibition of germination and seedlings primary growth). This problem has been investigated mainly in coniferous forests, but it also occurs in deciduous forests. Furthermore, allelopathy can involve forest soil microorganisms. They can act as allelochemical mediators, where they are able to inactivate these compounds by means of metabolization, as they are able to produce biologically active compounds using inactive molecules as a substrate. Special attention is given to mycorrhizal fungi and mycor-rhizae, because, in theory, they are able to protect seedlings against allelopathy. Applied aspects of allelopathy in forest ecosystems are also presented, with two main goals: (1) how to reduce the adverse impact of such interactions (chemical and mechanical control of allelochemicals plant producer, afforestation with selected mycorrhiza), but also (2) how to use allelopathy as a tool for forest management. Suggestions to improve the study of allelopathy in forest ecosystems and prospects for future investigations conclude this review.     

Evidence for Inhibitory Allelopathic Interactions Involving Phenolic Acids in Field Soils: Concepts vs. an Experimental Model

The accepted criteria for identifying allelopathic interactions in the field that have been proposed in the literature offer heuristic function, but to date have failed as a framework for research and diagnostics. If the present criteria are to be modified to make them useful empirically, their shortcomings must be identified. For this review, data from the literature and from defined model systems consisting of plants, soil, and/or microbes are used to evaluate the applicability of the accepted criteria to defined systems in which plants are responding to known allelochemicals. Based on this evaluation, modified criteria are proposed. In many respects, however, the modified criteria are as difficult to satisfy in the field as those proposed previously. The new criteria have value as a research framework because they clearly suggest that a shift in research focus to the soil environment, specifically the barrier of the rhizosphere through which allelochemicals must pass, is essential if the role of allelopathic interactions in the field is to be established.     

不同植物对高寒草场主要杂草箭叶橐吾的化感作用

用13科31种植物地上部分的水浸液(0.05 g DW.mL-1)对高寒草场主要杂草箭叶橐吾(Ligularia sagi-tata)和同域牧草垂穗披碱草(Elymus nutans)进行种子萌发实验,旨在筛选能够抑制箭叶橐吾的植物种类。结果表明:有23种供体材料对箭叶橐吾种子萌发具较强抑制作用,并降低了萌发指数(M<-0.50);有9种供体植物显著抑制箭叶橐吾,同时对牧草的伤害较少甚至有促进作用。综合比较对2种植物的综合化感效应指数(M)差异,毛茛(Ranunculus japonicus)、高乌头(Aconitum sinomontanum)、五爪金龙(Ipomoea cairica)、露蕊乌头(Aconitumgymnandrum)和乳白香青(Anaphalis lactea)作用效果显著(其M差值分别是:-0.87、-0.82、-0.71、-0.68和-0.62),这5种植物有望开发新型植物源除草剂。     

Optimization of bioassay for tetracycline detection in milk by means of chemometric techniques

Aims: In this study, a microbiological method of dichotomous response using Bacillus cereus was designed and optimized to detect tetracyclines (TCs) at concentrations near to the maximum residue limits (MRLs). Methods and Results: In a first stage, the response time of bioassay was reduced to 5 h when the logarithm of spore concentration (log S) was increased. Later, a Plackett Burman design (2^6–3) was analysed using logistic regression model. This design indicates significant effects of log S and chloramphenicol (CAP) on the detection limit (DL) of TC. Then, the response surfaces (RS) of the TCs DTs as a function of log S and CAP were plotted using a Dohlert design and the logistic regression model. These RS show a linear decrease with the raise of CAP and a quadratic effect of log S. Finally, the DTs of TC (109 μg l^?1) and oxytetracycline (100 μg l^?1) were adjusted to their MRLs through the desirability function. Conclusions: By successive application of experimental design techniques could be optimized a bioassay for the detection of TC residues in milk. The best conditions have been achieved when the assay was made with log S = 5·12 and CAP = 470 μg l^?1. Significance and Impact of the Study: Experimental design techniques together with the logistic regression model and the desirability function represent an adequate tool for the optimization of a bioassay with binary response.     

Leaf Thickness and Water Deficit in Plants: A Tool for Field Studies

B?rquez, A. 1987. Leaf thickness and water deficit in plants:a tool for field studies.—J. exp. Bot. 38: 109–114. A technique for estimating plant water deficits using a relativelyinexpensive micrometer to measure leaf thickness was developed.A strong correlation was found between leaf thickness and relativewater content (RWC) in Brassica napus, Mirabilis jalapa, Phaseolusvulgaris and Impatiens parviflora. Although leaf thickness ata given RWC varied between plants, it increased linearly withleaf RWC, the rate of change being similar in leaves of plantsof the same age and species. Due to this relationship, the constructionof a pressure-volume curve makes possible the estimation ofleaf water potential. In this case a calibration curve is neededfor each population studied or, for the highest accuracy, foreach individual. The technique is particularly useful in fieldconditions where other techniques are not reliable because ofdifficulties in controlling temperature and where non-destructivemeasurements are required. Key words: Leaf thickness, relative water content, water potential     

橐吾属植物的研究进度

对近年来橐吾属植物的研究文献进行综述,主要内容有该属植物的化学成分、药理作用及其它方面的研究情况。     

Statistical inference and power analysis for direct and spillover effects in two-stage randomized experiments

Two-stage randomized experiments become an increasingly popular experimental design for causal inference when the outcome of one unit may be affected by the treatment assignments of other units in the same cluster. In this paper, we provide a methodological framework for general tools of statistical inference and power analysis for two-stage randomized experiments. Under the randomization-based framework, we consider the estimation of a new direct effect of interest as well as the average direct and spillover effects studied in the literature. We provide unbiased estimators of these causal quantities and their conservative variance estimators in a general setting. Using these results, we then develop hypothesis testing procedures and derive sample size formulas. We theoretically compare the two-stage randomized design with the completely randomized and cluster randomized designs, which represent two limiting designs. Finally, we conduct simulation studies to evaluate the empirical performance of our sample size formulas. For empirical illustration, the proposed methodology is applied to the randomized evaluation of the Indian National Health Insurance Program. An open-source software package is available for implementing the proposed methodology.     

农杆菌转化获得转B．t．基因水稻及其生物学鉴定

以水稻主栽品种"秀水11"和"春江11"预培养4d未成熟胚为转化受体,经农杆茵LBA4404／pGBI4A2B(含B．t．基因)感染后,筛选出抗性愈伤组织并获得转化植株。其中抗性愈伤组织产生频率达44％～70％,转化植株产生频率达27％～64％。转基因植物总DNA经PCR和Southernblot分子杂交试验表明,T-DNA上的外源基因已整合到水稻的基因组里。对转B．t．基因水稻植株进行了两种水稻主要害虫纵卷叶螟和二化螟的饲虫试验。与对照相比,7d后纵卷叶螟幼虫死亡率达31％～49％,同时纵卷叶螟对转基因水稻叶片的危害程度大大减轻。二化螟在咬食转B．t．基因水稻植株7d后的校正死亡率达15％～71％,30d后多数转基因水稻仍能正常抽穗,表明转基因水稻对上述害虫具有一定抗性。     

广州市可食用植物色彩特点及造景应用

以广州地区常见的200种(含变种、变型和品种)可食用植物为材料,对植物不同部位呈现的颜色以及不同季节色彩分布情况进行统计分析,总结可食用植物在色彩方面的特点及局限。其中,可食用植物叶、茎色以绿色为主,花、果色丰富。以色彩理论为基础,对可食用植物进行种植搭配实验,归纳相应的植物色彩搭配策略。策略包括三个方面,针对可食用植物叶色特点,提出绿色调可食用植物搭配策略;针对可食用植物色彩丰富度的差异,提出多部位色彩组合策略;针对植物时间维度的色彩分布差异及衔接空缺,提出持续的色彩植物搭配建议。     

Ecology of Microbial Saprophytes and Pathogens in Tissue Culture and Field-Grown Plants: Reasons for Contamination Problems In Vitro

This review compares published surveys of microbial populations in plant tissue and cell cultures with the microbial saprophytes and pathogens found on field grown plants and microbial populations in the laboratory environment. From this comparison and the measured reduction in contamination after improvements in working practices in the laboratory, conclusions can be drawn about the importance of the explant and the laboratory as sources of contamination.

Mechanisms of pathogenicity in vitro are described to explain why bacteria, fungi, and yeasts that are not pathogenic to plants in the field become pathogens in plant tissue cultures. Conversely, plant metabolism and its effect on the tissue culture environment are described to explain why prokaryotes, viruses, and viroids that cause disease in the field can stay latent in vitro.

Detection methods for latent contaminants in plant tissue cultures are summarized, and the strategies and methods for prevention or treatment of contamination are discussed.     

Bioaccumulation of Inorganic Chemicals from Soil by Plants: Spiked Soils vs. Field Contamination or Background

Risk assessors are often cautioned against the use of tests of highly bioavailable salt solutions added to soil to estimate the bioaccumulation of chemicals from waste site soils by plants. In this investigation, a large number of laboratory and field studies that measured the bioaccumulation of inorganic chemicals in plants were reviewed. The objective was to discern whether or not the relationship between the concentration of the element in aboveground vegetation and that in soil was different if the contamination was aged in the field rather than freshly added to soil in salt solution. For two of the eight elements, selenium and cadmium, salt solution experiments were associated with greater soil-plant uptake ratios than field measurements. Thus, these are not reliable data for use in the derivation of plant uptake regressions for screening-level ecological risk assessments at field sites. In contrast, the plant uptake of arsenic, copper, lead, mercury, nickel, and zinc, when added in salt solutions, was generally within the 95% prediction limit of regressions derived from field data. Chemical form, plant taxon, soil type, experimental methodology, and aging may be as important as the source of the chemical in predicting plant uptake of inorganic chemicals from soil.     

Pyrethroids as Promising Marine Antifoulants: Laboratory and Field Studies

Due to the regulations and bans regarding the use of traditional toxic chemicals against marine fouling organisms and the practical impediments to the commercialization of natural product antifoulants, there is an urgent need for compounds that are antifouling-active, environmentally friendly, and have a potential for commercial application. In this study, a series of common, commercially available pyrethroid products, which are generally used as environmentally safe insecticides, was evaluated for antifouling activity in the laboratory using an anti-settlement test with cyprids of the barnacle Balanus albicostatus and also in a field experiment. Laboratory assay showed that all eleven pyrethroids (namely, rich d-trans-allethrin, Es-biothrin, rich d-prallethrin, S-prallethrin, tetramethrin, rich d-tetramethrin, phenothrin, cyphenothrin, permethrin, cypermethrin, and high active cypermethrin) were able to inhibit barnacle settlement (EC₅₀ range of 0.0316 to 87.00 μg/ml) without significant toxicity. Analysis of structure–activity relationships suggested that the cyano group at the α-carbon position had a significant influence on the expression of antifouling activity in pyrethroids. In the field, the antifouling activity of pyrethroids was further confirmed, with the most potent pyrethroids being cypermethrin and high active cypermethrin, which displayed efficiency comparable with that of tributyltin. In summary, our investigation indicated that these pyrethroids have a great and practical commercial potential as antifouling agents.     

赣江流域河岸带外来入侵植物的调查分析

通过对赣江流域河岸带植物调查,发现该地有外来入侵植物17科27属31种,其中菊科最多有9种。对赣江流域河岸带入侵植物分布的分析显示:外来入侵植物发生在赣江全流域,上、中、下游河岸带植物群落中入侵植物的优势度无明显差异;河岸带植被类型对入侵植物的分布影响较大,草本群落和灌草群落中的入侵植物优势度明显高于乔木林群落;干扰对外来植物的入侵起到了积极作用,与无干扰方式下的群落相比入侵植物的优势度差异极显著,但干扰方式对入侵植物的分布无影响。     

RNAi的作用机制及其在抗病毒领域的应用

RNA干扰是外源性或内源性双链RNA诱发的mRNA水平上的基因沉默机制。RNA技术具有高效性、特异性。最近将RNA干扰应用于许多病毒性疾病的治疗研究均取得了显著的基因沉默效果,为病毒的预防和治疗开辟了一条新途径。就RNA干扰作用机制及抗病毒效应作一综述。     

植物抗细菌病害基因工程研究进展和展望

综述了利用基因工程提高植物对细菌病害抗性的各种方法,包括利用非植物抗菌蛋白,抑制细菌的致病或毒性因子,增强植物本身的抗病能力和人工诱导侵染点细胞程序化坏死。这些方法的成功都与抗菌化合物的作用机制及植物和病原细菌之间的相互作用的分子生物学的研究密切相关,还展望了这些方法的应用前景。     

Anti-Inflammatory,Antioxidant and Enzyme Inhibition Activities in Correlation with Mycochemical Profile of Selected Indigenous Ganoderma spp. from Balkan Region (Serbia)

The aim of this research work was to study the bioactivity potentials (antioxidant, anti-inflammatory, and enzyme inhibitory) of ethanol (EtOH), water (H₂O) and chloroform (CHCl₃) extracts of G. applanatum, G. lucidum, G. pfeifferi and G. resinaceum as well as their mycochemical profile: the total content of phenolics (TP) and sugars (TS) and LC/MS/MS detection of phenolics. LC/MS/MS profile showed that p-hydroxybenzoic and protocatechuic acids were mostly found. The highest ABTS and DPPH activities were detected in polar G. applanatum extracts (159.84±0.59 mg TE/g d.w., IC₅₀=0.85±0.30 μg/mL, respectively), while G. resinaceum CHCl₃ extract was the most potent in NO assay (IC₅₀=41.21±0.18−81.89±0.81 μg/mL). The highest TP and TS were generally determined in G. applanatum EtOH extracts. Enzyme inhibitory effects were determined in H₂O extracts. Generally, CHCl₃ extracts showed the most powerful anti-inflammatory potential. These results suggest that analyzed species are a promising source of bioactive compounds and may be considered as candidates for new food supplements or drug formulations.     

大血藤化学成分及药学研究进展

目的:对传统中药大血藤的化学成分及药学研究概况进行综述.方法:查阅国内外发表的文献为依据.结果:传统中药大血藤中含有鞣质、糖苷、环多酚类、三萜皂甙类、木质素类、黄酮类、甙类及有机酸类等多种化学成分;药理研究证明,其具有抗辐射;抗菌、抗炎、抗急,陛过敏、抗癌及心血管系统活性等作用,结论:大血藤具有多种药理活性,有希望从中开发出治疗心血管疾病和抗炎的现代药物.对其进行进一步的研究和开发具有重要意义.     

Effects of Temperature and Water Loss on Terrestrial Locomotor Performance in Land Crabs: Integrating Laboratory and Field Studies

SYNOPSIS. Terrestrial and semi-terrestrial crustaceans are exposedto fluctuations in ambient temperature and conditions that favorevaporative water loss. These environmental stresses alter performancelimits in the laboratory and behavior in the field. The maximalrate of oxygen consumption, maximum aerobic speed, and endurancecapacity are greater at a body temperature (T_b) of 24°Cthan at 15°C or 30°C in the ghost crab, Ocypode quadrata.The total metabolic cost to move at the same relative speedis greater at a T_b of 24°C than at 15°C. Slower aerobickinetics at 15°C result in a smaller relative contributionof oxidative metabolism to total metabolic cost. However, therelative contributions from accelerated glycolysis are similarat both temperatures. When locomotion is intermittent, the totaldistance traveled before fatigue can be similar at Tbs of 15and 24°C but result from different movement and pause durationsat these temperatures. Performance limits of the ghost crabare negatively affected by dehydration and are sensitive torates of water loss. In the laboratory, endurance capacity ofthe fiddler crab, Uca pugilator, is greater at a T_b of 30°Cthan at 25°C. In the field, freely moving fiddler crabswith a T_b of 30°C travel at faster mean preferred speeds,as determined by motion analysis, than crabs at 25°C. Datafor land crabs support and advance general ectothermic modelsfor the effects of temperature and dehydration on locomotorperformance.