Plant immunization

Plant immunization is the process of activating natural defense system present in plant induced by biotic or abiotic factors. Plants are pre-treated with inducing agents stimulate plant defense responses that form chemical or physical barriers that are used against the pathogen invasion. Inducers used usually give the signals to rouse the plant defense genes ultimately resulting into induced systemic resistance. In many plant-pathogen interactions, R-Avr gene interactions results in localized acquired resistance or hypersensitive response and at distal ends of plant, a broad spectrum resistance is induced known as systemic acquired resistance (SAR). Various biotic or abiotic factors induce systemic resistance in plants that is phenotypically similar to pathogen-induced systemic acquired resistance (SAR). Some of the biotic or abiotic determinants induce systemic resistance in plants through salicylic acid (SA) dependent SAR pathway, others require jasmonic acid (JA) or ethylene. Host plant remains in induced condition for a period of time, and upon challenge inoculation, resistance responses are accelerated and enhanced. Induced systemic resistance (ISR) is effective under field conditions and offers a natural mechanism for biological control of plant disease.     

Ethylene and plant responses to nutritional stress

Although ethylene is known to be involved in plant response to a number of biotic and abiotic stresses, relatively little is known concerning its role in nutritional stress arising from nutrient deficiency or mineral toxicity. There is clear evidence for involvement of ethylene in the symbiosis between Rhizobium and legumes, and in the 'Strategy 1' response to Fe deficiency. Ethylene may also be generated during tissue necrosis induced by severe toxicities and deficiencies. Metal toxicity may generate ethylene through oxidative stress. Evidence for a more general role for ethylene in regulating plant responses to macronutrient deficiency is suggestive but incomplete. Few studies have addressed this interaction, and most published reports are difficult to interpret because of the unrealistic way that nutrient treatments were imposed. Deficiency of N and P appear to interact with ethylene production and sensitivity. A role for ethylene in mediating adaptive responses to P stress is suggested by the fact that P stress can induce a variety of morphological changes in root systems that are also affected by ethylene, such as gravitropism, aerenchyma formation, and root hair development. Other adaptive responses include senescence or abscission of plant parts which cannot be supported by the plant. Ethylene and other plant hormones may be involved in mediating the stress signal to generate these responses. Although existing literature is inconclusive, we speculate that ethylene may play an important role in mediating the morphological and physiological plasticity of plant responses to nutrient patches in time and space, and especially root responses to P stress.     

Is there a plant interferon?

Plants appear to have a mechanism of acquired resistance to virus infection resembling the one which involves the interferon in mammals. In some virus-infected plants, anti-viral agents are produced which show similarities to animal interferon but it is not certain whether these are analogous to the anti-viral protein which is induced by interferon in animal cells. Acquired resistance to virus infection in plants also can be produced by a variety of non-viral agents—biotic and abiotic. In a few cases, interferon-like substances may mediate the resistance. Although many virus inhibitors of higher plant origin differ from the typical interferon because of their preformed (endogenous) character, some show other physico-chemical and biological similarities to the interferon. This is particularly true of a glycoprotein obtained fromPhytolacca spp. whose mechanism of virus inhibition closely resembles a mechanism postulated for the anti-viral protein induced by the interferon in animal cells. Many virus-plant combinations which produce local lesions and an acquired resistance to virus infection remain to be tested for their potential synthesis of induced anti-viral agents. These could be valuable in the therapy of plant and animal disease. The Caryophyllales (Centrospermae) are particularly promising in this regard.     

Getting the interactions right: Will higher O3 levels interfere with induced defenses to aphid feeding?

Induced defenses in response to biotic and abiotic agents share signalling and response pathways with many interaction points. Ozone (O₃)-exposed plants show an increased production and rapid accumulation of salicylic acid (SA), which amplifies the initial oxidative signal. SA is also involved in the defense pathway induced by aphid attack. The signal is transmitted throughout the plant, establishing communication among different plant tissues. Here, we discuss experimental and conceptual advances and limitations of cross talk between responses to O₃ and aphids and we make a case for the need of studies at a large scale with enough and sufficient complexity to assess interactions at the individual organism and population levels. We further hypothesize that stress frequency, intensity, duration and timing, will affect the direction of response to aphid herbivory of increased-O₃-exposed plants. In the long term, frequent high O₃ exposures might allow the selection of O₃-resistant plants that do not accumulate reactive oxygen species, preventing the induction of defenses against aphid attack.     

Geranium robertianum L., plant form adapted to the specific conditions along railway: “railway-wandering plant”

The question of whether any specific plant species are typically growing along railway tracks (the so-called “railway-wandering plants”) has been discussed for many years. This study proves the existence of a form of Geranium robertianum species growing along railway tracks in North–Eastern Poland. Floristic studies have been carried out in 246 areas along railway tracks. This particular species was found in 70 studied areas (28 %). Comparative studies were carried out on 12 plant populations growing in the fieldwork and in glasshouse cultivation. Plants growing along the railway tracks in Wali?y were different from all other studied populations. They were small (smaller by 31 %, max. by 57 % than other plants), with little leaf blades representing different shapes and colour. In studies of light absorption by photosynthetic apparatus (chlorophyll fluorescence) under conditions of exposure to high light intensity, the plants from Wali?y were proved to have a better adaptation capacity to stress conditions. Increased levels of anthocyanins—which provided better protection of the photosynthetic apparatus against insolation—were shown. The protective properties against water deficiencies and excessive insolation were genetically preserved and were found in the second generation of plants cultivated in a glasshouse. For the first time, a new plant form of G. robertianum—a “railway-wandering plant” adapted to the conditions prevailing along railway tracks—was confirmed to exist. The form has developed probably after 1886, when the Bia?ystok–Zubki railway was built, featuring the Wali?y railway station.     

COSTS OF INDUCED RESPONSES AND TOLERANCE TO HERBIVORY IN MALE AND FEMALE FITNESS COMPONENTS OF WILD RADISH

Theory predicts that plant defensive traits are costly due to trade-offs between allocation to defense and growth and reproduction. Most previous studies of costs of plant defense focused on female fitness costs of constitutively expressed defenses. Consideration of alternative plant strategies, such as induced defenses and tolerance to herbivory, and multiple types of costs, including allocation to male reproductive function, may increase our ability to detect costs of plant defense against herbivores. In this study we measured male and female reproductive costs associated with induced responses and tolerance to herbivory in annual wild radish plants (Raphanus raphanistrum). We induced resistance in the plants by subjecting them to herbivory by Pieris rapae caterpillars. We also induced resistance in plants without leaf tissue removal using a natural chemical elicitor, jasmonic acid; in addition, we removed leaf tissue without inducing plant responses using manual clipping. Induced responses included increased concentrations of indole glucosinolates, which are putative defense compounds. Induced responses, in the absence of leaf tissue removal, reduced plant fitness when five fitness components were considered together; costs of induction were individually detected for time to first flower and number of pollen grains produced per flower. In this system, induced responses appear to impose a cost, although this cost may not have been detected had we only quantified the traditionally measured fitness components, growth and seed production. In the absence of induced responses, 50% leaf tissue removal, reduced plant fitness in three out of the five fitness components measured. Induced responses to herbivory and leaf tissue removal had additive effects on plant fitness. Although plant sibships varied greatly (49–136%) in their level of tolerance to herbivory, costs of tolerance were not detected, as we did not find a negative association between the ability to compensate for damage and plant fitness in the absence of damage. We suggest that consideration of alternative plant defense strategies and multiple costs will result in a broader understanding of the evolutionary ecology of plant defense.     

Kinase-dead mutation: A novel strategy for improving soybean resistance to soybean cyst nematode Heterodera glycines

Protein kinases phosphorylate proteins for functional changes and are involved in nearly all cellular processes, thereby regulating almost all aspects of plant growth and development, and responses to biotic and abiotic stresses. We generated two independent co-expression networks of soybean genes using control and stress response gene expression data and identified 392 differentially highly interconnected kinase hub genes among the two networks. Of these 392 kinases, 90 genes were identified as “syncytium highly connected hubs”, potentially essential for activating kinase signalling pathways in the nematode feeding site. Overexpression of wild-type coding sequences of five syncytium highly connected kinase hub genes using transgenic soybean hairy roots enhanced plant susceptibility to soybean cyst nematode (SCN; Heterodera glycines) Hg Type 0 (race 3). In contrast, overexpression of kinase-dead variants of these five syncytium kinase hub genes significantly enhanced soybean resistance to SCN. Additionally, three of the five tested kinase hub genes enhanced soybean resistance to SCN Hg Type 1.2.5.7 (race 2), highlighting the potential of the kinase-dead approach to generate effective and durable resistance against a wide range of SCN Hg types. Subcellular localization analysis revealed that kinase-dead mutations do not alter protein cellular localization, confirming the structure–function of the kinase-inactive variants in producing loss-of-function phenotypes causing significant decrease in nematode susceptibility. Because many protein kinases are highly conserved and are involved in plant responses to various biotic and abiotic stresses, our approach of identifying kinase hub genes and their inactivation using kinase-dead mutation could be translated for biotic and abiotic stress tolerance.     

Fossil forms of Amentiferae

Review of the procedures used in determining fossil plant organs indicates that the many Cretaceous records of extant genera of “Amentiferae” based on leaves should be rejected as theoretically unreliable. Palynological data, in combination with some valid megafossil data, indicate that most recognizable members of “Amentiferae” are no older than the later part of the Late Cretaceous. Juglandales appear to be derivatives of the ancient Normapolles complex and unrelated to other “Amentiferae.” A preliminary account of some of the comparative foliar morphology of extant “Amentiferae” indicates that some—particularly Betulaceae and Fagaceae—are closely related to Hamamelidales but that other families—notably Rhoipteleaceae, Juglandaceae, Didymelaceae, and Leitneriaceae—are unrelated to this order.     

Risposte Fotomorfogeniche Indotte Dalla Radiazione UV-B in Brassica Oleracea var. Capitata

Abstract

Photomorphogenic responses induced by UV-B radiation in Brassica oleracea var. capitata.—Ultraviolet radiation can induce a plethora of “damaging” and “non damaging” effects in higher plants. We analyzed two possible photomorphogenic responses to UV-B radiation, the anthocyanin accumulation and the inhibition of hypocotyl elongation by modifying the UV spectral range with specific cut-off filters, under two levels of photon fluence rate. Experimental results suggest that detrimental effects are due to shorter wavelenghts of UV-B region (less than 305 nm); in contrast some adaptative responses may be induced by longer wavelenghts of UV-B region (between 305 and 320 nm). We attempted to determine the involvment of endogenous anthocyanin content in the UV-B photoprotection. Our experiments suggest a secondary role of anthocyanin accumulation in UV-B plant adaptation.     

Natural and artificial floral damage induces resistance in Nemophila menziesii (Hydrophyllaceae) flowers

Resistance to leaf herbivory is well-documented in plants. In contrast, resistance to herbivory in flowers has received very little attention, even though reproductive tissues are often essential for plant reproduction. Plants may protect reproductive tissues with a range of defenses from constitutive to induced, although ecological costs associated with constitutive defense or resistance are expected to be higher than costs associated with induced responses. Induced responses in flowers may be effective against floral herbivores while minimizing the negative impacts of resistance on pollinators. This study examines induced responses in Nemophila menziesii (Hydrophyllaceae), a plant that frequently receives high levels of floral herbivory. I report that natural caterpillar herbivory increased levels of resistance against caterpillars later in the season. Similarly, artificial clipping to flowers consistently reduced natural damage to flowers vs unclipped controls over two years. Neither whole-plant nor individual seed set was affected by the reduction of floral damage. Induced resistance in reproductive tissues may benefit plants that are exposed to both floral herbivory and pollinator activity and can be an important link between plant antagonists and plant mutualists.     

Action of jasmonates in plant stress responses and development — Applied aspects

Jasmonates (JAs) are lipid-derived compounds acting as key signaling compounds in plant stress responses and development. The JA co-receptor complex and several enzymes of JA biosynthesis have been crystallized, and various JA signal transduction pathways including cross-talk to most of the plant hormones have been intensively studied. Defense to herbivores and necrotrophic pathogens are mediated by JA. Other environmental cues mediated by JA are light, seasonal and circadian rhythms, cold stress, desiccation stress, salt stress and UV stress. During development growth inhibition of roots, shoots and leaves occur by JA, whereas seed germination and flower development are partially affected by its precursor 12-oxo-phytodienoic acid (OPDA). Based on these numerous JA mediated signal transduction pathways active in plant stress responses and development, there is an increasing interest in horticultural and biotechnological applications. Intercropping, the mixed growth of two or more crops, mycorrhization of plants, establishment of induced resistance, priming of plants for enhanced insect resistance as well as pre- and post-harvest application of JA are few examples. Additional sources for horticultural improvement, where JAs might be involved, are defense against nematodes, biocontrol by plant growth promoting rhizobacteria, altered composition of rhizosphere bacterial community, sustained balance between growth and defense, and improved plant immunity in intercropping systems. Finally, biotechnological application for JA-induced production of pharmaceuticals and application of JAs as anti-cancer agents were intensively studied.     

Role of Pathogen-Related Protein 10 (PR 10) under Abiotic and Biotic Stresses in Plants

Members of the Pathogenesis Related (PR) 10 protein family have been identified in a variety of plant species and a wide range of functions ranging from defense to growth and development has been attributed to them. PR10 protein possesses ribonuclease (RNase) activity, interacts with phytohormones, involved in hormone-mediated signalling, afforded protection against various phytopathogenic fungi, bacteria, and viruses particularly in response to biotic and abiotic stresses. The resistance mechanism of PR10 protein may include activation of defense signalling pathways through possible interacting proteins involved in mediating responses to pathogens, degradation of RNA of the invading pathogens. Moreover, several morphological changes have been shown to accompany the enhanced abiotic stress tolerance. In this review, the possible mechanism of action of PR10 protein against biotic and abiotic stress has been discussed. Furthermore, our findings also confirmed that the in vivo Nitric oxide (NO) is essential for most of environmental abiotic stresses and disease resistance against pathogen infection. The proper level of NO may be necessary and beneficial, not only in plant response to the environmental abiotic stress, but also to biotic stress. The updated information on this interesting group of proteins will be useful in future research to develop multiple stress tolerance in plants.     

The plant-growth-promoting rhizobacterium Paenibacillus polymyxa induces changes in Arabidopsis thaliana gene expression: a possible connection between biotic and abiotic stress responses.

This paper addresses changes in plant gene expression induced by inoculation with plant-growth-promoting rhizobacteria (PGPR). A gnotobiotic system was established with Arabidopsis thaliana as model plant, and isolates of Paenibacillus polymyxa as PGPR. Subsequent challenge by either the pathogen Erwinia carotovora (biotic stress) or induction of drought (abiotic stress) indicated that inoculated plants were more resistant than control plants. With RNA differential display on parallel RNA preparations from P. polymyxa-treated or untreated plants, changes in gene expression were investigated. From a small number of candidate sequences obtained by this approach, one mRNA segment showed a strong inoculation-dependent increase in abundance. The corresponding gene was identified as ERD15, previously identified to be drought stress responsive. Quantification of mRNA levels of several stress-responsive genes indicated that P. polymyxa induced mild biotic stress. This suggests that genes and/or gene classes associated with plant defenses against abiotic and biotic stress may be co-regulated. Implications of the effects of PGPR on the induction of plant defense pathways are discussed.     

Proteomic dissection of plant responses to various pathogens

During their growth and development, plants are vulnerable to the effects of a variety of pathogens. Proteomics technology plays an important role in research studies of plant defense mechanisms by mining the expression changes of proteins in response to various biotic stresses. This review article provides a comprehensive overview of the latest developments in international proteomic research on plant biotic stress. It summarizes the methods commonly used in plant proteomic research to investigate biotic stress, analyze the protein responses of plants in adverse conditions, and reviews the applications of proteomics combined with transgenic technology in plant protection.     

Lags in the response of mountain plant communities to climate change

Rapid climatic changes and increasing human influence at high elevations around the world will have profound impacts on mountain biodiversity. However, forecasts from statistical models (e.g. species distribution models) rarely consider that plant community changes could substantially lag behind climatic changes, hindering our ability to make temporally realistic projections for the coming century. Indeed, the magnitudes of lags, and the relative importance of the different factors giving rise to them, remain poorly understood. We review evidence for three types of lag: “dispersal lags” affecting plant species’ spread along elevational gradients, “establishment lags” following their arrival in recipient communities, and “extinction lags” of resident species. Variation in lags is explained by variation among species in physiological and demographic responses, by effects of altered biotic interactions, and by aspects of the physical environment. Of these, altered biotic interactions could contribute substantially to establishment and extinction lags, yet impacts of biotic interactions on range dynamics are poorly understood. We develop a mechanistic community model to illustrate how species turnover in future communities might lag behind simple expectations based on species’ range shifts with unlimited dispersal. The model shows a combined contribution of altered biotic interactions and dispersal lags to plant community turnover along an elevational gradient following climate warming. Our review and simulation support the view that accounting for disequilibrium range dynamics will be essential for realistic forecasts of patterns of biodiversity under climate change, with implications for the conservation of mountain species and the ecosystem functions they provide.     

Bacillus subtilis: A plant-growth promoting rhizobacterium that also impacts biotic stress

Plants encounter many biotic agents, such as viruses, bacteria, nematodes, weeds, and arachnids. These entities induce biotic stress in their hosts by disrupting normal metabolism, and as a result, limit plant growth and/or are the cause of plant mortality. Some biotic agents, however, interact symbiotically or synergistically with their host plants. Some microbes can be beneficial to plants and perform the same role as chemical fertilizers and pesticides, acting as a biofertilizer and/or biopesticide. Plant growth promoting rhizobacteria (PGPR) can significantly enhance plant growth and represent a mutually helpful plant-microbe interaction. Bacillus species are a major type of rhizobacteria that can form spores that can survive in the soil for long period of time under harsh environmental conditions. Plant growth is enhanced by PGPR through the induction of systemic resistance, antibiosis, and competitive omission. Thus, the application of microbes can be used to induce systemic resistance in plants against biotic agents and enhance environmental stress tolerance. Bacillus subtilis exhibits both a direct and indirect biocontrol mechanism to suppress disease caused by pathogens. The direct mechanism includes the synthesis of many secondary metabolites, hormones, cell-wall-degrading enzymes, and antioxidants that assist the plant in its defense against pathogen attack. The indirect mechanism includes the stimulation of plant growth and the induction of acquired systemic resistance. Bacillus subtilis can also solubilize soil P, enhance nitrogen fixation, and produce siderophores that promote its growth and suppresses the growth of pathogens. Bacillus subtilis enhances stress tolerance in their plant hosts by inducing the expression of stress-response genes, phytohormones, and stress-related metabolites. The present review discusses the activity of B. subtilis in the rhizosphere, its role as a root colonizer, its biocontrol potential, the associated mechanisms of biocontrol and the ability of B. subtilis to increase crop productivity under conditions of biotic and abiotic stress.     

Mechanisms of plant defense against insect herbivores

Plants respond to herbivory through various morphological, biochemicals, and molecular mechanisms to counter/offset the effects of herbivore attack. The biochemical mechanisms of defense against the herbivores are wide-ranging, highly dynamic, and are mediated both by direct and indirect defenses. The defensive compounds are either produced constitutively or in response to plant damage, and affect feeding, growth, and survival of herbivores. In addition, plants also release volatile organic compounds that attract the natural enemies of the herbivores. These strategies either act independently or in conjunction with each other. However, our understanding of these defensive mechanisms is still limited. Induced resistance could be exploited as an important tool for the pest management to minimize the amounts of insecticides used for pest control. Host plant resistance to insects, particularly, induced resistance, can also be manipulated with the use of chemical elicitors of secondary metabolites, which confer resistance to insects. By understanding the mechanisms of induced resistance, we can predict the herbivores that are likely to be affected by induced responses. The elicitors of induced responses can be sprayed on crop plants to build up the natural defense system against damage caused by herbivores. The induced responses can also be engineered genetically, so that the defensive compounds are constitutively produced in plants against are challenged by the herbivory. Induced resistance can be exploited for developing crop cultivars, which readily produce the inducible response upon mild infestation, and can act as one of components of integrated pest management for sustainable crop production.     

环境胁迫下植物MAPK多叠级联响应

植物MAP(mitogen-activated protein)激酶涉及植物的生长发育、对内源和外界环境刺激的反应.MAP激酶能将胞外感受器引起的刺激传递到胞内引起细胞的反应.拟南芥(Arabidopsis thaliana)作为模式植物,其全部的MAP激酶已经列出并进行了分类.根据已分类的拟南芥MAP激酶家族,已经分离出大量的MAP激酶基因,并将它们进行分类,发现它们大多能被包括病原、创伤、温度、干旱、盐、渗透、紫外线辐射、臭氧和活性氧等胁迫刺激激活.通过研究在不同环境胁迫下的功能和信号路径,发现植物MAP激酶信号传递系统是复杂且相互交错的.需要开发一些新的工具和策略去阐明MAPK信号传递路径,以及如何利用MAPK系统去改善农作物对生物和非生物胁迫的抗性.