Effect of various phytoimmunocorrectors on fruit and soft fruit cultures

Catalase activity and induction of delayed chlorophyll fluorescence were shown to be the markers of plant native state. The dependence of reaction of the plant to exogenous elicitors, stimulators or inhibitors of defense system, on the age, cultivar and/or species was found. Prolonged effect of the treatment with phytoimmunocorrectors was observed. The necessity of careful choice of elicitors depending on the plant state was shown.     

植食性昆虫唾液效应子和激发子的研究进展

植食性昆虫与寄主植物通过协同进化形成了复杂的防御和反防御机制。本文系统综述了昆虫唾液效应子和激发子在植物与昆虫互作中的作用及机理。昆虫取食中释放的唾液激发子被植物识别而激活植物早期免疫反应,昆虫也能从口腔分泌效应子到植物体内抑制免疫;抗性植物则利用抗性(R)蛋白识别昆虫无毒效应子,启动效应子诱导的免疫反应,而昆虫又进化出多种方式来躲避植物R蛋白的识别。总之,在这场军备竞赛中,昆虫的唾液成分决定着昆虫能否取食成功。取食过程中,咀嚼式口器害虫分泌大量酶类到植物体内,而刺吸式害虫则分泌胶状和水样唾液到植物中,它们都利用激发子和效应子去调控植物的免疫防御反应。分析现已报道的昆虫效应子发现其作用机制各有不同,具体表现为影响植物早期防御信号,调控植物激素通路及其他通路,或靶向小分子RNA通路。本文还综述了昆虫激发子的最新进展,揭示激发子可以通过诱导释放植物次生代谢物以及调控激素水平、Ca²⁺内流和活性氧爆发增强植物抗性。最后对昆虫效应子的分泌特性、寄主特异性和多功能性作了分析,并对无毒效应子及其对应的植物R基因,以及激发子的模式识别受体的研究进行了展望。     

Induced increase in chitinase activity in tomato cells (<Emphasis Type="Italic">Lycopersicon esculentum</Emphasis> L.)

The magnitude of the chitinase activity in tomato plant cells induced by elicitors is determined. It is shown that the magnitude of the enzymatic activity of cells is a function of the dimensions and concentration of the biotic elicitors.     

诱导子促进植物次生代谢产物生产的研究进展

本文简要介绍了诱导子的分类和应用概况,讨论了诱导子的筛选、作用机制、作用效果等研究热点问题,同时简要介绍了诱导子之间的互作关系以及诱导子对植物生理生化反应的影响。     

Elicitor stimulation of the defense response in cultured plant cells monitored by fluorescent dyes

Addition of fungal elicitors to plant cells in suspension is known to stimulate biochemical changes in the plant cell leading to production of defense compounds. In this paper we demonstrate that introduction of elicitors from the pathogenic fungus Verticillium dahliae to cultured cotton, tobacco, or soybean cells leads to a rapid, dramatic change in the fluorescence of several membrane-associated potentiometric or pH-sensitive dyes. The fluorescence transitions occur abruptly following a brief (0 to 10 min) lag period in apparently most cells of the suspension simultaneously. Furthermore, both the length of the lag period and the rate of the subsequent fluorescence change were shown to be highly dependent on elicitor concentration. When the crude elicitor extract was separated by gel filtration chromatography into several active fractions, the ability of each fraction to stimulate phytoalexin production in the cotton cell suspension was found to correlate directly with the rate of the fluorescence decrease in the fluorescence assay. Because the assay is rapid, simple to perform, quantitative, and reproducible, it represents an attractive alternative to the more cumbersome and perhaps less quantitative elicitor assays currently in use. The fact that membrane-potential-sensitive dyes of different structure respond to elicitation of plant cells similarly further suggests, but does not prove, that asymmetric ion fluxes into or out of the plant cell are involved in the initial events of elicitor signal transduction.     

Effects of elicitors of host plant defenses on pear psylla,Cacopsylla pyricola

Pear psylla, Cacopsylla pyricola (Foerster) (Hemiptera: Psyllidae), is a key pest of cultivated pear [Pyrus communis L. (Rosaceae)] in North America and Europe. We examined the effects of foliar applications of three commercially available chemical elicitors of host‐plant defenses — Actigard (acibenzolar‐S‐methyl), Employ (harpin protein), and ODC (chitosan) — on survival, development, feeding, and egg laying of C. pyricola. All three defense elicitors reduced the number of nymphs present on pear (cvs. Bartlett or D'Anjou) 30 days after releasing 10 adults on the trees. Choice assays showed that females settled and oviposited on untreated trees more often than on trees treated with any of the three defense elicitors. Results of no‐choice assays confirmed that the effects of Actigard, Employ, and ODC on C. pyricola were due to activation of systemic plant responses that led to reduced oviposition preference and nymph survival. However, results did not provide evidence that plant responses to elicitors led to reduced nymphal feeding rates or development. Results of our laboratory studies suggest that commercial defense elicitors may be useful in the integrated management of pear psylla once the effects of elicitors at an ecological scale are better understood.     

The Problems of Specific Phytoimmunity

Recent studies established that the specificity of phytoimmunity is shaped at the initial stages of genic interactions between a pathogen and its plant host. While elicitors, the products of pathogen avirulence genes (avr-genes), have been already investigated in great detail, there are few studies on the products of plant resistance genes (R-genes) recognizing these elicitors. This review deals with examples of nonspecific and specific elicitors of some R-genes as well as the systems that transduce the elicited signals to the plant genome and evoke immune responses in the plant cells. Several types of immunosuppressors characteristic of pathogens are considered. The molecular-genetic studies of the relations between the pathogens and their plant hosts supplement the already existing arsenal for plant protection with new technologies, such as the genetically engineered plant resistance and the resistance induced by biogenic elicitors.     

Fungal Pathogens: The Battle for Plant Infection

The attempted infection of a plant by a pathogen, such as a fungus or an Oomycete, may be regarded as a battle whose major weapons are proteins and smaller chemical compounds produced by both organisms. Indeed, plants produce an astonishing plethora of defense compounds that are still being discovered at a rapid pace. This pattern arose from a multi-million year, ping-pong?type co-evolution, in which plant and pathogen successively added new chemical weapons in this perpetual battle. As each defensive innovation was established in the host, new ways to circumvent it evolved in the pathogen. This complex co-evolution process probably explains not only the exquisite specificity observed between many pathogens and their hosts, but also the ineffectiveness or redundancy of some defensive genes which often encode enzymes with overlapping activities. Plants evolved a complex, multi-level series of structural and chemical barriers that are both constitutive or preformed and inducible. These defenses may involve strengthening of the cell wall, hypersensitive response (HR), oxidative burst, phytoalexins and pathogenesis-related (PR) proteins. The pathogen must successfully overcome these obstacles before it succeeds in causing disease. In some cases, it needs to modulate or modify plant cell metabolism to its own benefit and/or to abolish defense reactions. Central to the activation of plant responses is timely perception of the pathogen by the plant. A crucial role is played by elicitors which, depending on their mode of action, are broadly classified into nonspecific elicitors and highly specific elicitors or virulence effector/avirulence factors. A protein battle for penetration is then initiated, marking the pathogen attempted transition from extracellular to invasive growth before parasitism and disease can be established. Three major types of defense responses may be observed in plants: non-host resistance, host resistance, and host pathogenesis. Plant innate immunity may comprise a continuum from non-host resistance involving the detection of general elicitors to host-specific resistance involving detection of specific elicitors by R proteins. It was generally assumed that non-host resistance was based on passive mechanisms and that nonspecific rejection usually arose as a consequence of the non-host pathogen failure to breach the first lines of plant defense. However, recent evidence has blurred the clear-cut distinction among non-host resistance, host-specific resistance and disease. The same obstacles are also serious challenges for host pathogens, reducing their success rate significantly in causing disease. Indeed, even susceptible plants mount a (insufficient) defense response upon recognition of pathogen elicited molecular signals. Recent evidence suggests the occurrence of significant overlaps between the protein components and signalling pathways of these types of resistance, suggesting the existence of both shared and unique features for the three branches of plant innate immunity.     

Induction of resistance against pathogens by β-aminobutyric acid

Among the many types of plant stressors, pathogen attack, mainly fungi and bacteria can cause particularly severe damage both to individual plants and, on a wider scale, to agricultural productivity. The magnitude of these pathogen-induced problems has stimulated rapid progress in green biotechnology research into plant defense mechanisms. Plants can develop local and systemic wide-spectrum resistance induced by their exposure to virulent (systemic acquired resistance—SAR) or non-pathogenic microbes and various chemical elicitors (induced systemic resistance—ISR). β-Aminobutyric acid (BABA), non-protein amino acid, is though to be important component of the signaling pathway regulating ISR response in plants. After treatment with BABA or various chemicals, after infection by a necrotizing pathogen, colonization of the roots by beneficial microbes many plants establish a unique physiological state that is called the “primed” state of the plant. This review will focus on the recent knowledge about the role of BABA in the induction of ISR against pathogens mainly against fungi.     

寡糖诱导植物抗病性研究进展

寡糖在植物中可作为早期信息分子,激活植物防御系统,诱导植物产生抗病性。综述近年来对寡糖激发子受体、信号转导、基因表达等方面的研究进展。     

Perception, signaling and molecular basis of oviposition-mediated plant responses

Eggs deposited on plants by herbivorous insects represent a threat as they develop into feeding larvae. Plants are not a passive substrate and have evolved sophisticated mechanisms to detect eggs and induce direct and indirect defenses. Recent years have seen exciting development in molecular aspects of egg-induced responses. Some egg-associated elicitors have been identified, and signaling pathways and egg-induced expression profiles are being uncovered. Depending on the mode of oviposition, both the jasmonic acid and salicylic acid pathways seem to play a role in the induction of defense responses. An emerging concept is that eggs are recognized like microbial pathogens and innate immune responses are triggered. In addition, some eggs contain elicitors that induce highly specific defenses in plants. Examples of egg-induced suppression of defense or, on the contrary, egg-induced resistance highlight the complexity of plant–egg interactions in an on-going arms race between herbivores and their hosts. A major challenge is to identify plant receptors for egg-associated elicitors, to assess the specificity of these elicitors and to identify molecular components that underlie various responses to oviposition.     

Parents lend a helping hand to their offspring in plant defence

Plants under attack by pathogens and pests can mount a range of inducible defences, encompassing both chemical and structural changes. Although few reports exist, it appears that plants responding to pathogen or herbivore attack, or chemical defence elicitors, may produce progeny that are better able to defend themselves against attack, compared with progeny from unthreatened or untreated plants. To date, all research on transgenerational effects of biotic stress has been conducted on dicotyledenous plants. We examined the possibility that resistance induced by application of chemical defence elicitors to the monocot plant barley, could be passed on to the progeny. Plants were treated with acibenzolar-S-methyl (ASM) or saccharin, and grain harvested at maturity. Germination was unaffected in seed collected from plants treated with saccharin, while germination was reduced significantly in seed collected from ASM-treated plants. The subsequent growth of the seedlings was not significantly different in any of the treatments. However, plants from parents treated with both ASM or saccharin exhibited significantly enhanced resistance to infection by Rhynchosporium commune, despite not being treated with elicitor themselves. These data hint at the possibility of producing disease-resistant plants by exposing parent plants to chemical elicitors.     

Stimulation of plant natural defenses

Some defense mechanisms of plants are of the passive type while others are induced after perception of the pathogenic microorganism (very specific gene-for-gene recognition) or of microbial components (non specific elicitors). These recognition events trigger an array of plant signals and a cascade of signalling pathways which activate a battery of metabolic alterations responsible for the observed induced resistance. These include the stimulated production of low molecular weight molecules with antibiotic activity, cell wall reinforcement by deposition and cross-linking of various macromolecules, and accumulation of a wide range of PR ('pathogenesis-related') proteins that exhibit direct and/or indirect antimicrobial activities. The present studies aim to characterize natural elicitors or design chemical messengers capable of triggering an array of plant defense responses. Treatments of plants with elicitors could be an alternative strategy of crop protection with a more satisfactory preservation of the environment.     

Phaseollin production in cell suspensions and whole plants of Phaseolus vulgaris

Production of phaseollin was measured in cell suspension cultures and whole plants of Phaseolus vulgaris. In suspension cultures phaseollin appeared when there was no further increase in cell mass. Cells transferred to a medium without auxins yielded three times higher phaseollin concentrations than cells grown in their presence. Addition of autoclaved fungal mycelia or polysaccharides as elicitors resulted in an increased phaseollin concentration in the cell suspension.In whole plants phaseollin could be detected only after the plants were challenged by a fungus which caused lesions (browning) of the upper root neck region, Rhizoctonia solani. Treatment of non-infected plants with autoclaved fungal mycelia or other elicitors did not induce phaseollin production. However, when they were added before or together with the pathogenic fungus, the elicitors further increased phaseollin concentration in the root neck regions of the plants. This indicated that the pathogenic fungus was important for the penetration of the elicitors to inner plant tissues where phaseollin (and probably other phytoalexins) is produced.     

The induced increase of chitinase activity in tomato (Lycopersicon esculentum L) cells

The levels of chitinase activity induced with elicitors in tomato cells have been detected. It was shown that enzymatic activity depended on degree of polymerization and concentration of biotic elicitors.     

刺激剂(elicitor)在植物细胞培养次生代谢物生产中的应用

刺激剂（ｅｌｉｃｉｔｏｒ）在植物细胞培养中被用来作为提高次生代谢物产量的手段。文中概括介绍了微生物、寡聚糖、蛋白质、第二信使及其他物质作为刺激剂在植物细胞培养中的应用及其研究成果。     

Oligogalacturonic Acid and Chitosan Reduce Stomatal Aperture by Inducing the Evolution of Reactive Oxygen Species from Guard Cells of Tomato and Commelina communis

Stomatal opening provides access to inner leaf tissues for many plant pathogens, so narrowing stomatal apertures may be advantageous for plant defense. We investigated how guard cells respond to elicitors that can be generated from cell walls of plants or pathogens during pathogen infection. The effect of oligogalacturonic acid (OGA), a degradation product of the plant cell wall, and chitosan (beta-1,4-linked glucosamine), a component of the fungal cell wall, on stomatal movements were examined in leaf epidermis of tomato (Lycopersicon esculentum L.) and Commelina communis L. These elicitors reduced the size of the stomatal aperture. OGA not only inhibited light-induced stomatal opening, but also accelerated stomatal closing in both species; chitosan inhibited light-induced stomatal opening in tomato epidermis. The effects of OGA and chitosan were suppressed when EGTA, catalase, or ascorbic acid was present in the medium, suggesting that Ca(2+) and H(2)O(2) mediate the elicitor-induced decrease of stomatal apertures. We show that the H(2)O(2) that is involved in this process is produced by guard cells in response to elicitors. Our results suggest that guard cells infected by pathogens may close their stomata via a pathway involving H(2)O(2) production, thus interfering with the continuous invasion of pathogens through the stomatal pores.     

The case for the defense: plants versus Pseudomonas syringae

Incredible progress has been made over the last 20 years in understanding the components and mechanisms governing plant innate immunity. The most important discoveries concern pathogen recognition mechanisms, which divide perception of conserved elicitors at the cell periphery, and recognition of variable elicitors within the host cytoplasm. The underlying mechanisms of immunity post elicitation are complex and poorly defined. This review highlights emergent themes in plant–microbe interactions with a particular focus on the plant immune responses against infection by the bacterium Pseudomonas syringae.