Native Plant and Microbial Contributions to a Negative Plant-Plant Interaction

A number of hypotheses have been suggested to explain why invasive exotic plants dramatically increase their abundance upon transport to a new range. The novel weapons hypothesis argues that phytotoxins secreted by roots of an exotic plant are more effective against naïve resident competitors in the range being invaded. The common reed Phragmites australis has a diverse population structure including invasive populations that are noxious weeds in North America. P. australis exudes the common phenolic gallic acid, which restricts the growth of native plants. However, the pathway for free gallic acid production in soils colonized by P. australis requires further elucidation. Here, we show that exotic, invasive P. australis contain elevated levels of polymeric gallotannin relative to native, noninvasive P. australis. We hypothesized that polymeric gallotannin can be attacked by tannase, an enzymatic activity produced by native plant and microbial community members, to release gallic acid in the rhizosphere and exacerbate the noxiousness of P. australis. Native plants and microbes were found to produce high levels of tannase while invasive P. australis produced very little tannase. These results suggest that both invasive and native species participate in signaling events that initiate the execution of allelopathy potentially linking native plant and microbial biochemistry to the invasive traits of an exotic species.Invasive weeds are a major source of agricultural costs due to reduced productivity and the labor expended for weed control. In addition, the extensive use of herbicides to control weed populations has undesirable environmental consequences. Therefore, understanding mechanisms that facilitate exotic plant dispersal and displacement of natives in new ranges is critical to predicting and controlling invasions and may yield insights into the ecological processes that govern homeostasis and perturbation in natural plant communities.Phragmites australis (Cav.) Trin ex. Steud. (common reed) has been present in the United States for at least 10,000 years as a major component of mixed tidal wetland plant communities (Saltonstall, 2002). However, over the past 200 years its distribution and abundance has expanded rapidly and it is now considered one of the most aggressive invasive species in marsh communities in North America. Chloroplast DNA analysis has shown that 13 native North American Phragmites haplotypes exist, while invasive populations possess a single chloroplast DNA haplotype (M) that is also widespread in Europe and Asia (Saltonstall, 2002). These data are supported by nuclear microsatellite DNA analysis (Saltonstall, 2003) and morphological differences that distinguish native, noninvasive from exotic, invasive Phragmites in North America (Saltonstall et al., 2004). When grown under the same conditions, exotic Phragmites has significantly higher aboveground and belowground biomass than native Phragmites (Vasquez et al., 2005; Saltonstall and Stevenson, 2007), and this pattern is typically observed under field conditions as well although exceptions exist (League et al., 2006; Meadows and Saltonstall, 2007). Unfortunately today, only remnant native P. australis populations remain along the Atlantic Coast of North America, indicating the near total displacement of native populations by exotic P. australis.Various hypotheses have been forwarded to explain the rapid invasion of P. australis, of which human activities, stress regimes, and hydrologic disturbances have received the greatest attention (Chambers et al., 1999). Compared to invasion in terrestrial ecosystems, invasiveness in marsh communities is less well documented and it is still not clear how environmental factors relate to the establishment of specific dominant marsh species. Although allelopathy has been superficially suggested as the main displacing mechanism in P. australis (Kaneta and Sugiyama, 1972; Drifmeyer and Zieman, 1979), there has been minimal success in characterizing the responsible allelochemical. Interestingly, three triterpenoids (β-amacin, taraxerol, and taraxerone) and a flavone (tricin) have been identified from aerial portions of P. australis (Kaneta and Sugiyama, 1972; Drifmeyer and Zieman, 1979). Regrettably, none of these identified chemicals were tested for possible allelopathic activity.Previously, we showed that a root exudate component of P. australis roots inhibits seedling growth, and that production of the exudates is higher in the invasive P. australis haplotype (Rudrappa et al., 2007). The active fraction of this exudate was found to be composed of gallic acid (3,4,5-trihydroxybenzoic acid). Gallic acid is toxic to a variety of weeds, crop plant species, and the model plant species Arabidopsis (Arabidopsis thaliana; Rudrappa et al., 2007; Rudrappa and Bais, 2008). Our published results also show the persistence of gallic acid in soil extracts from P. australis-invaded fields, which validates our in vitro results and strongly supports the idea that P. australis'' invasive behavior may partly be due to the exudation of gallic acid in the soil/marsh (Rudrappa et al., 2007). Our studies concur with the earlier established reports of phytotoxicity and persistence of gallic acid in soil (Weidenhamer and Romeo, 2004).Biochemically, the transition from simple galloylglucoses to complex gallotannins is marked by addition of further galloyl moieties to the pentagalloylglucose (Niemetz and Gross, 2005). It is now known that free gallic acid is released from complexed gallotannins by simple hydrolysis reactions, wherein a tannase activity breaks gallate ester to form free gallic acid, ellagic acid, and Glc (Mahoney and Molyneux, 2004). Treatment of fungal tannase from Aspergillus flavus results in hydrolysis of pellicle-localized gallotannin to form gallic acid, and ellagic acid as two phenolic components (Mahoney and Molyneux, 2004). As gallic acid is often complexed as gallotannins (Niemetz and Gross, 2005), we speculated that plant- or microbial-derived tannase may facilitate free gallic acid release in salt marsh soils.Aside from allelopathy, invasive plants may deleteriously affect interactions between rhizospheric microbial communities and native plant species (Klironomos, 2002; Wardle et al., 2004; Callaway et al., 2008) to promote their expansion in new ranges. One specific example is the disruption of interactions between native species and their arbuscular mycorhizae, upon which the native species rely for nutrient acquisition (Stinson et al., 2006). Another recent study suggests that the recruitment or establishment of an altered soil microbial community may negatively impact the ability of native species to survive in the same soils (Batten et al., 2008). Evidences suggest that soil biota have several effects on the success of invasive plants and the interactions are based in part on the biochemistry, i.e. novel biochemical weapons (Callaway and Ridenour, 2004). However, to our knowledge, no previous studies have directly tested whether P. australis or any other exotic plant may exploit the biochemical potential of native plant and microbial communities to release a phytotoxin (gallic acid) from a relatively benign precursor (gallotannin) in the rhizosphere. This report presents evidence that links native plant and microbial biochemistry to the invasive traits of an exotic species.     

Interaction of Phytohormones in Regulating the Axillary Bud Growth in Pea

In the present study the interactions of GR24, a synthetic analog of newly discovered plant hormones strigolactones (SLs), with cytokinin (CK), benzyladenine (BA), auxin naphthaleneacetic acid (NAA), gibberellic acid (GA₃) and abscisic acid (ABA) in the regulation of axillary bud growth in pea (Pisum sativum L.) were investigated. The hormones were applied directly to buds at node 1 and 2 and the dose-response experiments were performed on 8–10-day-old SL-deficient rms1 and rms5–1 mutants, branching SL-sensitive rms2–1 mutants and wild-type plants. In the mutant plants the treatment with 5 μM GR24 completely inhibited bud growth while BA up to 100 μM stimulated it. The combined application of GR24 and BA showed that GR24 efficiency to reduce bud outgrowth constantly declines as CK-stimulated bud growth increased, with the inhibiting effect of GR24 abolished at 100 μM BA applied. GA₃ accelerated bud outgrowth, but did not interfere with GR24 inhibitory action. NAA reduced bud growth in intact SL-sensitive rms2–1 mutant and also in SL-insensitive rms3–2 and rms4–1 mutants. The NAA effect was observed already at 0.5 μM, however, even at a response saturating concentration of 500 μM its inhibiting effect was inferior to that of 5 μM GR24. At combined treatment the effectiveness of GR24 in suppressing bud growth decreased with a decrease in NAA-inhibited bud growth, suggesting that auxin might act as a suppressor of SL action. ABA strongly inhibited the bud outgrowth and, like CK and auxin, reduced the inhibitory effectiveness of GR24. The revealed ability of CK, ABA and auxin to suppress bud response to SLs is supposed to result from phytohormone signaling crosstalks.     

活性氧类与mTOR信号通路

哺乳动物雷帕霉素靶蛋白(mammalian target of rapamycin,mTOR)是整合细胞内外各种信号,调节蛋白质翻译与细胞生长增殖等多种生理活动的中心信号分子。活性氧类(reactive oxygen species,ROS)作为第二信使分子,可介导多种细胞信号通路并发挥广泛的生理效应。近年的研究发现ROS可通过一定的途径激活或抑制mTOR通路。而作为反馈调节,mTOR通路活性的轻度上调可促进细胞抗氧化物质的生成,而过度激活则会促进ROS生成,并增加细胞对氧化应激的敏感性,形成正反馈。本文将ROS与mTOR之间相互调节与相互作用的特点及机制的研究进展作一综述。     

活性氧介导的信号通路在衣原体感染过程中的作用机制

活性氧(reactive oxygen species,ROS)是一种重要的信号分子,能介导多条信号通路,从而影响宿主细胞的生长与增殖。衣原体为细胞内寄生菌,其感染过程会导致ROS的表达水平增加,ROS可介导多种信号通路,通过氧化修饰蛋白、改变细胞内氧化还原平衡,从而影响衣原体的生长与繁殖。对ROS介导的信号通路在衣原体感染过程中的作用机制作一综述。     

Phytohormones and Cytoskeleton

Various aspects of the interaction between phytohormones and principal components of the cytoskeleton are considered. Four levels of this interaction are discussed: (1) the spatial organization of microtubules and microfilaments; (2) the synthesis and modification of cytoskeletal proteins; (3) the cytoskeleton involvement in processes, which are under hormonal control; and (4) the cytoskeleton involvement in phytohormone functioning.     

Phytohormones in algae

In various algal taxa, essentially all known phytohormones were detected in concentrations comparable with their content in higher plants. The occurrence of diverse free and conjugated hormone forms substantiates the functioning of the complex system of metabolism and activity regulation of these compounds. In most cases, the spectrum of biological activities of algal hormones corresponds to the functions of higher plant hormones. Some physiological and biochemical processes in algal cells and tissues are under the control of several phytohormones. All these facts permit a consideration of the algal hormonal system as a full-value regulatory system.     

Phytohormones in fruit development and maturation

Phytohormones are integral to the regulation of fruit development and maturation. This review expands upon current understanding of the relationship between hormone signaling and fruit development, emphasizing fleshy fruit and highlighting recent work in the model crop tomato (Solanum lycopersicum) and additional species. Fruit development comprises fruit set initiation, growth, and maturation and ripening. Fruit set transpires after fertilization and is associated with auxin and gibberellic acid (GA) signaling. Interaction between auxin and GAs, as well as other phytohormones, is mediated by auxin-responsive Aux/IAA and ARF proteins. Fruit growth consists of cell division and expansion, the former shown to be influenced by auxin signaling. While regulation of cell expansion is less thoroughly understood, evidence indicates synergistic regulation via both auxin and GAs, with input from additional hormones. Fruit maturation, a transitional phase that precipitates ripening, occurs when auxin and GA levels subside with a concurrent rise in abscisic acid (ABA) and ethylene. During fruit ripening, ethylene plays a clear role in climacteric fruits, whereas non-climacteric ripening is generally associated with ABA. Recent evidence indicates varying requirements for both hormones within both ripening physiologies, suggesting rebalancing and specification of roles for common regulators rather than reliance upon one. Numerous recent discoveries pertaining to the molecular basis of hormonal activity and crosstalk are discussed, while we also note that many questions remain such as the molecular basis of additional hormonal activities, the role of epigenome changes, and how prior discoveries translate to the plethora of angiosperm species.     

Role of Phytohormones and Light in De-etiolation

Russian Journal of Plant Physiology - De-etiolation or transition from etiolated growth (skotomorphogenesis) to photomorphogenesis is one of the most intriguing and intricate stages of plant...     

Involvement of Reactive Nitrogen and Oxygen Species (RNS and ROS) in Sunflower-Mildew Interaction

Nitric oxide (·NO) has been shown to participate in plantresponse against pathogen infection; however, less is knownof the participation of other NO-derived molecules designatedas reactive nitrogen species (RNS). Using two sunflower (Helianthusannuus L.) cultivars with different sensitivity to infectionby the pathogen Plasmopara halstedii, we studied key componentsinvolved in RNS and ROS metabolism. We analyzed the superoxideradical production, hydrogen peroxide content, L-arginine-dependentnitric oxide synthase (NOS) and S-nitrosoglutathione reductase(GSNOR) activities. Furthermore, we examined the location andcontents of ·NO, S-nitrosothiols (RSNOs), S-nitrosoglutathione(GSNO) and protein 3-nitrotyrosine (NO₂-Tyr) by confocal laserscanning microscopy (CLSM) and biochemical analyses. In thesusceptible cultivar, the pathogen induces an increase in proteinsthat undergo tyrosine nitration accompanied by an augmentationin RSNOs. This rise of RSNOs seems to be independent of theenzymatic generation of ·NO because the L-arginine-dependentNOS activity is reduced after infection. These results suggestthat pathogens induce nitrosative stress in susceptible cultivars.In contrast, in the resistant cultivar, no increase of RSNOsor tyrosine nitration of proteins was observed, implying anabsence of nitrosative stress. Therefore, it is proposed thatthe increase of tyrosine nitration of proteins can be considereda general biological marker of nitrosative stress in plantsunder biotic conditions.     

Phytohormones in plant root-Piriformospora indica mutualism

Piriformospora indica is a mutualistic root-colonising basidiomycete that tranfers various benefits to colonized host plants including growth promotion, yield increases as well as abiotic and biotic stress tolerance. The fungus is characterized by a broad host spectrum encompassing various monocots and dicots.^1,2 Our recent microarray-based studies indicate a general plant defense suppression by P. indica and significant changes in the GA biosynthesis pathway.³ Furthermore, barley plants impaired in GA synthesis and perception showed a significant reduction in mutualistic colonization, which was associated with an elevated expression of defense-related genes. Here, we discuss the importance of plant hormones for compatibility in plant root-P. indica associations. Our data might provide a first explanation for the colonization success of the fungus in a wide range of higher plants.Key words: compatibility, plant defense, gibberellic acid, symbiosis, plant hormones     

湖南农业大学植物激素重点实验室

实验室仪器设备简介 湖南农业大学植物激素实验室是由湖南省教育厅和湖南农业大学共同资助的省级重点开放实验室,由全国留学回国人员先进个人、博士生导师、留美归国博士萧浪涛教授任主任。     

Phytohormones in soil after atrazine application

The herbicide atrazine influences the content of phytohormones (auxins, gibberellins, cytokinins) in maize-cultivated soils. The effect is probably related to variations in the metabolism of hormones in soil microorganisms.     

植物激素在氮磷养分调节根形态建成中的作用

本文介绍植物激素在氮磷养分调节根形态建成中的作用研究进展。     

植物激素与芥子油苷在生物合成上的相互作用

植物激素在植物的生长发育中起着关键性作用,芥子油苷是一类重要的次生代谢物质。植物激素与芥子油苷之间存在复杂的相互作用。生长素与吲哚类芥子油苷在生物合成上存在着相互作用。植物防卫信号分子与芥子油苷之间也存在相互作用,茉莉酸强烈诱导吲哚类芥子油苷生物合成相关基因CYP7982和CYP7983的表达,从而诱导吲哚-3-甲基芥子油苷和N-甲氧吲哚-3-甲基芥子油苷等吲哚类芥子油苷的生成,水杨酸和乙烯则能轻度诱导4-甲氧吲哚-3-甲基芥子油苷的生成。植物防卫信号转导途径相互作用以精细调节不同种类吲哚类芥子油苷的生成。     

Phytohormones signaling and crosstalk regulating leaf angle in rice

Leaf angle is an important agronomic trait in rice (Oryza sativa L.). It affects both the efficiency of sunlight capture and nitrogen reservoirs. The erect leaf phenotype is suited for high-density planting and thus increasing crop yields. Many genes regulate leaf angle by affecting leaf structure, such as the lamina joint, mechanical tissues, and the midrib. Signaling of brassinosteroids (BR), auxin (IAA), and gibberellins (GA) plays important roles in the regulation of lamina joint bending in rice. In addition, the biosynthesis and signaling of BR are known to have dominant effects on leaf angle development. In this review, we summarize the factors and genes associated with the development of leaf angle in rice, outline the regulatory mechanisms based on the signaling of BR, IAA, and GA, and discuss the contribution of crosstalk between BR and IAA or GA in the formation of leaf angle. Promising lines of research in the transgenic engineering of rice leaf angle to increase grain yield are proposed.     

Phytohormones and pigments in albino mutants of cotton and pea

The contents of chlorophylls, carotenoids, flavonoids and phytohormones (IAA, ABA and other inhibitors) were determined in green and albino seedlings of cotton (Gossypium hirsutum L.) and pea (Pisum sativum L.) The growth of green and albino seedlings during 1 –2 weeks was similar. The green and albino seedlings do not differ remarkably in phytohormonal content and in the flavonoid concentration. In the etiolated seedlings of green and albino forms the content of flavonoids was rather decreased.     

Root Secreted Metabolites and Proteins Are Involved in the Early Events of Plant-Plant Recognition Prior to Competition

The mechanism whereby organisms interact and differentiate between others has been at the forefront of scientific inquiry, particularly in humans and certain animals. It is widely accepted that plants also interact, but the degree of this interaction has been constricted to competition for space, nutrients, water and light. Here, we analyzed the root secreted metabolites and proteins involved in early plant neighbor recognition by using Arabidopsis thaliana Col-0 ecotype (Col) as our focal plant co-cultured in vitro with different neighbors [A. thaliana Ler ecotype (Ler) or Capsella rubella (Cap)]. Principal component and cluster analyses revealed that both root secreted secondary metabolites and proteins clustered separately between the plants grown individually (Col-0, Ler and Cap grown alone) and the plants co-cultured with two homozygous individuals (Col-Col, Ler-Ler and Cap-Cap) or with different individuals (Col-Ler and Col-Cap). In particularly, we observed that a greater number of defense- and stress- related proteins were secreted when our control plant, Col, was grown alone as compared to when it was co-cultured with another homozygous individual (Col-Col) or with a different individual (Col-Ler and Col-Cap). However, the total amount of defense proteins in the exudates of the co-cultures was higher than in the plant alone. The opposite pattern of expression was identified for stress-related proteins. These data suggest that plants can sense and respond to the presence of different plant neighbors and that the level of relatedness is perceived upon initial interaction. Furthermore, the role of secondary metabolites and defense- and stress-related proteins widely involved in plant-microbe associations and abiotic responses warrants reassessment for plant-plant interactions.     

植物化感作用与生物多样性

本文简要地阐释了化感作用的含义、基本特征以及作用机制,并结合生物多样性理论,综述了化感作用研究中化感物种的多样性、化感物质的多样性及其释放途径的多样性,具体讨论了化感作用对物种多样性、遗传多样性及生态系统多样性中的种群生态、协同进化、土壤生境、生态系统功能和生物入侵等方面的可能影响。文中提出了化感作用的利用、管理应与生物多样性保护相统一的看法,并指出对化感作用与生物多样性的关系以及相互影响机制进行本质的探索,特别是对植物化感作用的生态服务功能与价值评估与探讨,可为保护生物学和系统生态学提供理论基础,这也是今后工作开展的一个重要方向。