Priming for enhanced defense

Inner Plant Values: Diversity, Colonization and Benefits from Endophytic Bacteria

One of the most exciting scientific advances in recent decades has been the realization that the diverse and immensely active microbial communities are not only 'passengers' with plants, but instead play an important role in plant growth, development and resistance to biotic and abiotic stresses. A picture is emerging where plant roots act as 'gatekeepers' to screen soil bacteria from the rhizosphere and rhizoplane. This typically results in root endophytic microbiome dominated by Proteobacteria, Actinobacteria and to a lesser extent Bacteroidetes and Firmicutes, but Acidobacteria and Gemmatimonadetes being almost depleted. A synthesis of available data suggest that motility, plant cell-wall degradation ability and reactive oxygen species scavenging seem to be crucial traits for successful endophytic colonization and establishment of bacteria. Recent studies provide solid evidence that these bacteria serve host functions such as improving of plant nutrients through acquisition of nutrients from soil and nitrogen fixation in leaves. Additionally, some endophytes can engage 'priming' plants which elicit a faster and stronger plant defense once pathogens attack. Due to these plant growth-promoting effects, endophytic bacteria are being widely explored for their use in the improvement of crop performance. Updating the insights into the mechanism of endophytic bacterial colonization and interactions with plants is an important step in potentially manipulating endophytic bacteria/microbiome for viable strategies to improve agricultural production.

Plant Hormesis Management with Biostimulants of Biotic Origin in Agriculture

Over time plants developed complex mechanisms in order to adapt themselves to the environment. Plant innate immunity is one of the most important mechanisms for the environmental adaptation. A myriad of secondary metabolites with nutraceutical features are produced by the plant immune system in order to get adaptation to new environments that provoke stress (stressors). Hormesis is a phenomenon by which a stressor (i.e., toxins, herbicides, etc.) stimulates the cellular stress response, including secondary metabolites production, in order to help organisms to establish adaptive responses. Hormetins of biotic origin (i.e., biostimulants or biological control compounds), in certain doses might enhance plant performance, however, in excessive doses they are commonly deleterious. Biostimulants or biological control compounds of biotic origin are called "elicitors" that have widely been studied as inducers of plant tolerance to biotic and abiotic stresses. The plant response toward elicitors is reminiscent of hormetic responses toward toxins in several organisms. Thus, controlled management of hormetic responses in plants using these types of compounds is expected to be an important tool to increase nutraceutical quality of plant food and trying to minimize negative effects on yields. The aim of this review is to analyze the potential for agriculture that the use of biostimulants and biological control compounds of biotic origin could have in the management of the plant hormesis. The use of homolog DNA as biostimulant or biological control compound in crop production is also discussed.

The priming molecule β-aminobutyric acid is naturally present in plants and is induced by stress

The defense system of a plant can be primed for increased defense, resulting in an augmented stress resistance and/or tolerance. Priming can be triggered by biotic and abiotic stimuli, as well as by chemicals such as β-aminobutyric acid (BABA), a nonprotein amino acid considered so far a xenobiotic. Since the perception mechanism of BABA has been recently identified in Arabidopsis thaliana, in the present study we explored the possibility that plants do synthesize BABA. After developing a reliable method to detect and quantify BABA in plant tissues, and unequivocally separate it from its two isomers α- and γ-aminobutyric acid, we measured BABA levels in stressed and nonstressed A. thaliana plants, and in different plant species. We show that BABA is a natural product of plants and that the endogenous levels of BABA increase rapidly after infection with necrotrophic, biotrophic and hemibiotrophic pathogens, as well as after salt stress and submergence. Our results place the rise in endogenous BABA levels to a point of convergence in plant stress response and provide biological significance to the presence of a receptor in plants. These findings can explain the extremely widespread efficacy of BABA and open the way to unravel the early steps of priming.

Methylome evolution in plants

Despite major progress in dissecting the molecular pathways that control DNA methylation patterns in plants, little is known about the mechanisms that shape plant methylomes over evolutionary time. Drawing on recent intra- and interspecific epigenomic studies, we show that methylome evolution over long timescales is largely a byproduct of genomic changes. By contrast, methylome evolution over short timescales appears to be driven mainly by spontaneous epimutational events. We argue that novel methods based on analyses of the methylation site frequency spectrum (mSFS) of natural populations can provide deeper insights into the evolutionary forces that act at each timescale.

The role of DNA (de)methylation in immune responsiveness of Arabidopsis

DNA methylation is antagonistically controlled by DNA methyltransferases and DNA demethylases. The level of DNA methylation controls plant gene expression on a global level. We have examined impacts of global changes in DNA methylation on the Arabidopsis immune system. A range of hypo-methylated mutants displayed enhanced resistance to the biotrophic pathogen Hyaloperonospora arabidopsidis (Hpa), whereas two hyper-methylated mutants were more susceptible to this pathogen. Subsequent characterization of the hypo-methylated nrpe1 mutant, which is impaired in RNA-directed DNA methylation, and the hyper-methylated ros1 mutant, which is affected in DNA demethylation, revealed that their opposite resistance phenotypes are associated with changes in cell wall defence and salicylic acid (SA)-dependent gene expression. Against infection by the necrotrophic pathogen Plectosphaerella cucumerina, nrpe1 showed enhanced susceptibility, which was associated with repressed sensitivity of jasmonic acid (JA)-inducible gene expression. Conversely, ros1 displayed enhanced resistance to necrotrophic pathogens, which was not associated with increased responsiveness of JA-inducible gene expression. Although nrpe1 and ros1 were unaffected in systemic acquired resistance to Hpa, they failed to develop transgenerational acquired resistance against this pathogen. Global transcriptome analysis of nrpe1 and ros1 at multiple time-points after Hpa infection revealed that 49% of the pathogenesis-related transcriptome is influenced by NRPE1- and ROS1-controlled DNA methylation. Of the 166 defence-related genes displaying augmented induction in nrpe1 and repressed induction in ros1, only 25 genes were associated with a nearby transposable element and NRPE1- and/or ROS1-controlled DNA methylation. Accordingly, we propose that the majority of NRPE1- and ROS1-dependent defence genes are regulated in trans by DNA methylation.

Respiration activity monitoring system for any individual well of a 48-well microtiter plate

BACKGROUND

Small-scale micro-bioreactors have become the cultivation vessel of choice during the first steps of bioprocess development. They combine high cultivation throughput with enhanced cost efficiency per cultivation. To gain the most possible information in the early phases of process development, online monitoring of important process parameters is highly advantageous. One of these important process parameters is the oxygen transfer rate (OTR). Measurement of the OTR, however, is only available for small-scale fermentations in shake flasks via the established RAMOS technology until now. A microtiter plate-based (MTP) μRAMOS device would enable significantly increased cultivation throughput and reduced resource consumption. Still, the requirements of miniaturization for valve and sensor solutions have prevented this transfer so far. This study reports the successful transfer of the established RAMOS technology from shake flasks to 48-well microtiter plates. The introduced μRAMOS device was validated by means of one bacterial, one plant cell suspension culture and two yeast cultures.

RESULTS

A technical solution for the required miniaturized valve and sensor implementation for an MTP-based μRAMOS device is presented. A microfluidic cover contains in total 96 pneumatic valves and 48 optical fibers, providing two valves and one optical fiber for each well. To reduce costs, an optical multiplexer for eight oxygen measuring instruments and 48 optical fibers is introduced. This configuration still provides a reasonable number of measurements per time and well. The well-to-well deviation is investigated by 48 identical Escherichia coli cultivations showing standard deviations comparable to those of the shake flask RAMOS system. The yeast Hansenula polymorpha and parsley suspension culture were also investigated.

CONCLUSIONS

The introduced MTP-based μRAMOS device enables a sound and well resolved OTR monitoring for fast- and slow-growing organisms. It offers a quality similar to standard RAMOS in OTR determination combined with an easier handling. The experimental throughput is increased 6-fold and the media consumption per cultivation is decreased roughly 12.5-fold compared to the established eight shake flask RAMOS device.

CaLecRK-S.5, a pepper L-type lectin receptor kinase gene, confers broad-spectrum resistance by activating priming

In Arabidopsis, several L-type lectin receptor kinases (LecRKs) have been identified as putative immune receptors. However, to date, there have been few analyses of LecRKs in crop plants. Virus-induced gene silencing of CaLecRK-S.5 verified the role of CaLecRK-S.5 in broad-spectrum resistance. Compared with control plants, CaLecRK-S.5-silenced plants showed reduced hypersensitive response, reactive oxygen species burst, secondary metabolite production, mitogen-activated protein kinase activation, and defense-related gene expression in response to Tobacco mosaic virus pathotype P0 (TMV-P0) infection. Suppression of CaLecRK-S.5 expression significantly enhanced the susceptibility to Pepper mild mottle virus pathotype P1,2,3, Xanthomonas campestris pv. vesicatoria, Phytophthora capsici, as well as TMV-P0 Additionally, β-aminobutyric acid treatment and a systemic acquired resistance assay revealed that CaLecRK-S.5 is involved in priming of plant immunity. Pre-treatment with β-aminobutyric acid before viral infection restored the reduced disease resistance phenotypes shown in CaLecRK-S.5-silenced plants. Systemic acquired resistance was also abolished in CaLecRK-S.5-silenced plants. Finally, RNA sequencing analysis indicated that CaLecRK-S.5 positively regulates plant immunity at the transcriptional level. Altogether, these results suggest that CaLecRK-S.5-mediated broad-spectrum resistance is associated with the regulation of priming.

Recognizing Plant Defense Priming

Defense priming conditions diverse plant species for the superinduction of defense, often resulting in enhanced pest and disease resistance and abiotic stress tolerance. Here, we propose a guideline that might assist the plant research community in a consistent assessment of defense priming in plants.

Cas3-Derived Target DNA Degradation Fragments Fuel Primed CRISPR Adaptation

Prokaryotes use a mechanism called priming to update their CRISPR immunological memory to rapidly counter revisiting, mutated viruses, and plasmids. Here we have determined how new spacers are produced and selected for integration into the CRISPR array during priming. We show that Cas3 couples CRISPR interference to adaptation by producing DNA breakdown products that fuel the spacer integration process in a two-step, PAM-associated manner. The helicase-nuclease Cas3 pre-processes target DNA into fragments of about 30-100 nt enriched for thymine-stretches in their 3' ends. The Cas1-2 complex further processes these fragments and integrates them sequence-specifically into CRISPR repeats by coupling of a 3' cytosine of the fragment. Our results highlight that the selection of PAM-compliant spacers during priming is enhanced by the combined sequence specificities of Cas3 and the Cas1-2 complex, leading to an increased propensity of integrating functional CTT-containing spacers.

Beta-aminobutyric acid priming of plant defense: the role of ABA and other hormones

Plants are exposed to recurring biotic and abiotic stresses that can, in extreme situations, lead to substantial yield losses. With the changing environment, the stress pressure is likely to increase and sustainable measures to alleviate the effect on our crops are sought. Priming plants for better stress resistance is one of the sustainable possibilities to reach this goal. Here, we report on the effects of beta-aminobutyric acid, a priming agent with an exceptionally wide range of action and describe its way of preparing plants to defend themselves against various attacks, among others through the modulation of their hormonal defense signaling, and highlight the special role of abscisic acid in this process.

Induction of Direct or Priming Resistance against Botrytis cinerea in Strawberries by β-Aminobutyric Acid and Their Effects on Sucrose Metabolism

The specific forms of disease resistance induced by β-aminobutyric acid (BABA) and their impacts on sucrose metabolism of postharvest strawberries were determined in the present research. Treatment with 10-500 mmol L(-1) BABA inhibited the Botrytis cinerea infection, possibly directly by suppressing the fungus growth and indirectly by triggering disease resistance. Moreover, BABA-induced resistance against B. cinerea infection in strawberries was associated with either one of two mechanisms, depending upon the concentration used: BABA at concentrations higher than 100 mmol L(-1) directly induced the defense response, including a H2O2 burst, modulation of the expression of PR genes, including FaPR1, FaChi3, Faβglu, and FaPAL, and increased activities of chitinase, β-1,3-glucanase, and PAL, whereas BABA at 10 mmol L(-1) activated a priming response because the BABA-treated fruits exhibited an increased capacity to express molecular defense only when the fruits were inoculated with B. cinerea. Activation of the priming defense appeared almost as effective against B. cinerea as inducing direct defense. However, the primed strawberries maintained higher activities of SS synthesis and SPS and SPP enzymes) and lower level of SS cleavage during the incubation; these activities contributed to higher sucrose, fructose, and glucose contents, sweetness index, and sensory scores compared to fruits exhibiting the direct defense. Thus, it is plausible that the priming defense, which can be activated by BABA at relatively low concentrations, represents an optimal strategy for combining the advantages of enhanced disease protection and soluble sugar accumulation.

Cold regulation of plastid ascorbate peroxidases serves as a priming hub controlling ROS signaling in Arabidopsis thaliana

BACKGROUND

Short cold periods comprise a challenge to plant growth and development. Series of cold stresses improve plant performance upon a future cold stress. This effect could be provoked by priming, training or acclimation dependent hardening. Here, we compared the effect of 24 h (short priming stimulus) and of 2 week long cold-pretreatment (long priming stimulus) on the response of Arabidopsis thaliana to a single 24 h cold stimulus (triggering) after a 5 day long lag-phase, to test Arabidopsis for cold primability.

RESULTS

Three types of pretreatment dependent responses were observed: (1) The CBF-regulon controlled gene COR15A was stronger activated only after long-term cold pretreatment. (2) The non-chloroplast specific stress markers PAL1 and CHS were more induced by cold after long-term and slightly stronger expressed after short-term cold priming. (3) The chloroplast ROS signaling marker genes ZAT10 and BAP1 were less activated by the triggering stimulus in primed plants. The effects on ZAT10 and BAP1 were more pronounced in 24 h cold-primed plants than in 14 day long cold-primed ones demonstrating independence of priming from induction and persistence of primary cold acclimation responses. Transcript and protein abundance analysis and studies in specific knock-out lines linked the priming-specific regulation of ZAT10 and BAP1 induction to the priming-induced long-term regulation of stromal and thylakoid-bound ascorbate peroxidase (sAPX and tAPX) expression.

CONCLUSION

The plastid antioxidant system, especially, plastid ascorbate peroxidase regulation, transmits information on a previous cold stress over time without the requirement of establishing cold-acclimation. We hypothesize that the plastid antioxidant system serves as a priming hub and that priming-dependent regulation of chloroplast-to-nucleus ROS signaling is a strategy to prepare plants under unstable environmental conditions against unpredictable stresses by supporting extra-plastidic stress protection.

Pre-exposure of Arabidopsis to the abiotic or biotic environmental stimuli "chilling" or "insect eggs" exhibits different transcriptomic responses to herbivory

Plants can retain information about environmental stress and thus, prepare themselves for impending stress. In nature, it happens that environmental stimuli like ‘cold’ and ‘insect egg deposition’ precede insect herbivory. Both these stimuli are known to elicit transcriptomic changes in Arabidposis thaliana. It is unknown, however, whether they affect the plant’s anti-herbivore defence and feeding-induced transcriptome when they end prior to herbivory. Here we investigated the transcriptomic response of Arabidopsis to feeding by Pieris brassicae larvae after prior exposure to cold or oviposition. The transcriptome of plants that experienced a five-day-chilling period (4 °C) was not fully reset to the pre-chilling state after deacclimation (20 °C) for one day and responded differently to herbivory than that of chilling-inexperienced plants. In contrast, when after a five-day-lasting oviposition period the eggs were removed, one day later the transcriptome and, consistently, also its response to herbivory resembled that of egg-free plants. Larval performance was unaffected by previous exposure of plants to cold and to eggs, thus indicating P. brassicae tolerance to cold-mediated plant transcriptomic changes. Our results show strong differences in the persistence of the plant’s transcriptomic state after removal of different environmental cues, and consequently differential effects on the transcriptomic response to later herbivory.

Innate immune memory in plants

The plant innate immune system comprises local and systemic immune responses. Systemic plant immunity develops after foliar infection by microbial pathogens, upon root colonization by certain microbes, or in response to physical injury. The systemic plant immune response to localized foliar infection is associated with elevated levels of pattern-recognition receptors, accumulation of dormant signaling enzymes, and alterations in chromatin state. Together, these systemic responses provide a memory to the initial infection by priming the remote leaves for enhanced defense and immunity to reinfection. The plant innate immune system thus builds immunological memory by utilizing mechanisms and components that are similar to those employed in the trained innate immune response of jawed vertebrates. Therefore, there seems to be conservation, or convergence, in the evolution of innate immune memory in plants and vertebrates.

Pollen proteomics: from stress physiology to developmental priming

Pollen development and stress. In angiosperms, pollen or pollen grain (male gametophyte) is a highly reduced two- or three-cell structure which plays a decisive role in plant reproduction. Male gametophyte development takes place in anther locules where diploid sporophytic cells undergo meiotic division followed by two consecutive mitotic processes. A desiccated and metabolically quiescent form of mature pollen is released from the anther which lands on the stigma. Pollen tube growth takes place followed by double fertilization. Apart from its importance in sexual reproduction, pollen is also an interesting model system which integrates fundamental cellular processes like cell division, differentiation, fate determination, polar establishment, cell to cell recognition and communication. Recently, pollen functionality has been studied by multidisciplinary approaches which also include OMICS analyses like transcriptomics, proteomics and metabolomics. Here, we review recent advances in proteomics of pollen development and propose the process of developmental priming playing a key role to guard highly sensitive developmental processes.

Use of BABA and INA As Activators of a Primed State in the Common Bean (Phaseolus vulgaris L.)

To survive in adverse conditions, plants have evolved complex mechanisms that "prime" their defense system to respond and adapt to stresses. Their competence to respond to such stresses fundamentally depends on its capacity to modulate the transcriptome rapidly and specifically. Thus, chromatin dynamics is a mechanism linked to transcriptional regulation and enhanced defense in plants. For example, in Arabidopsis, priming of the SA-dependent defense pathway is linked to histone lysine methylation. Such modifications could create a memory of the primary infection that is associated with an amplified gene response upon exposure to a second stress-stimulus. In addition, the priming status of a plant for induced resistance can be inherited to its offspring. However, analyses on the molecular mechanisms of generational and transgenerational priming in the common bean (Phaseolus vulagris L.), an economically important crop, are absent. Here, we provide evidence that resistance to P. syringae pv. phaseolicola infection was induced in the common bean with the synthetic priming activators BABA and INA. Resistance was assessed by evaluating symptom appearance, pathogen accumulation, changes in gene expression of defense genes, as well as changes in the H3K4me3 and H3K36me3 marks at the promoter-exon regions of defense-associated genes. We conclude that defense priming in the common bean occurred in response to BABA and INA and that these synthetic activators primed distinct genes for enhanced disease resistance. We hope that an understanding of the molecular changes leading to defense priming and pathogen resistance will provide valuable knowledge for producing disease-resistant crop varieties by exposing parental plants to priming activators, as well as to the development of novel plant protection chemicals that stimulate the plant's inherent disease resistance mechanisms.

Jasmonate signalling in plants shapes plant-insect interaction ecology

The phytohormone jasmonic acid (JA) regulates the induction of direct and indirect defences against herbivores. By now, the biochemical pathway of JA-signalling has been well resolved, allowing the use of an interdisciplinary toolbox and spurring the mechanistic investigation of plant-insect interactions. Recent advances show that JA-mediated plant responses are involved in the competitive and trophic interactions between various organisms throughout at least four trophic levels and therefore likely shape natural communities. Moreover, JA-mediated responses can be primed or suppressed by various environmental factors that are related to herbivory or not. Yet, to integrate the complex interactions at the physiological and ecological levels into community ecology, an examination of the often onetime discoveries for general rules and new bioinformatic approaches are required.

Natural genetic variation in Arabidopsis for responsiveness to plant growth-promoting rhizobacteria

The plant growth-promoting rhizobacterium (PGPR) Pseudomonas simiae WCS417r stimulates lateral root formation and increases shoot growth in Arabidopsis thaliana (Arabidopsis). These plant growth-stimulating effects are partly caused by volatile organic compounds (VOCs) produced by the bacterium. Here, we performed a genome-wide association (GWA) study on natural genetic variation in Arabidopsis for the ability to profit from rhizobacteria-mediated plant growth-promotion. To this end, 302 Arabidopsis accessions were tested for root architecture characteristics and shoot fresh weight in response to exposure to WCS417r. Although virtually all Arabidopsis accessions tested responded positively to WCS417r, there was a large variation between accessions in the increase in shoot fresh weight, the extra number of lateral roots formed, and the effect on primary root length. Correlation analyses revealed that the bacterially-mediated increase in shoot fresh weight is related to alterations in root architecture. GWA mapping for WCS417r-stimulated changes in root and shoot growth characteristics revealed 10 genetic loci highly associated with the responsiveness of Arabidopsis to the plant growth-promoting activity of WCS417r. Several of the underlying candidate genes have been implicated in important plant growth-related processes. These results demonstrate that plants possess natural genetic variation for the capacity to profit from the plant growth-promoting function of a beneficial rhizobacterium in their rhizosphere. This knowledge is a promising starting point for sustainable breeding strategies for future crops that are better able to maximize profitable functions from their root microbiome.

Citrus Plants: A Model System for Unlocking the Secrets of NO and ROS-Inspired Priming Against Salinity and Drought

Plants treated with chemical compounds can develop an enhanced capacity to resist long after being subjected to (a)biotic stress, a phenomenon known as priming. Evidence suggests that reactive oxygen species (ROS) and reactive nitrogen species (RNS) coordinately regulate plant stress responses to adverse environmental conditions; however, the mechanisms underlying this function remain unknown. Based on the observation that pre-exposure of citrus (Citrus aurantium L.) roots to the NO donor sodium nitroprusside (SNP) or to H2O2 prior to NaCl application can induce acclimation against subsequent stress we characterized the changes occurring in primed citrus tissues using several approaches. Herein, using this experimental model system, we provide an overview of our current knowledge of the possible mechanisms associated with NO and H2O2 priming to abiotic stresses, particularly concerning salinity and drought. The data and ideas presented here introduce six aspects of priming behavior in citrus under abiotic stress that provide knowledge necessary to exploit priming syndrome in the context of sustainable agriculture.

Epigenetic Control of Defense Signaling and Priming in Plants

Immune recognition of pathogen-associated molecular patterns or effectors leads to defense activation at the pathogen challenged sites. This is followed by systemic defense activation at distant non-challenged sites, termed systemic acquired resistance (SAR). These inducible defenses are accompanied by extensive transcriptional reprogramming of defense-related genes. SAR is associated with priming, in which a subset of these genes is kept at a poised state to facilitate subsequent transcriptional regulation. Transgenerational inheritance of defense-related priming in plants indicates the stability of such primed states. Recent studies have revealed the importance and dynamic engagement of epigenetic mechanisms, such as DNA methylation and histone modifications that are closely linked to chromatin reconfiguration, in plant adaptation to different biotic stresses. Herein we review current knowledge regarding the biological significance and underlying mechanisms of epigenetic control for immune responses in plants. We also argue for the importance of host transposable elements as critical regulators of interactions in the evolutionary "arms race" between plants and pathogens.

Oxygen transfer rate identifies priming compounds in parsley cells

BACKGROUND

In modern agriculture, the call for an alternative crop protection strategy increases because of the desired reduction of fungicide and pesticide use and the continuously evolving resistance of pathogens and pests to agrochemicals. The direct activation of the plant immune system does not provide a promising plant protection measure because of high fitness costs. However, upon treatment with certain natural or synthetic compounds, plant cells can promote to a fitness cost-saving, primed state of enhanced defense. In the primed state, plants respond to biotic and abiotic stress with faster and stronger activation of defense, and this is often associated with immunity and abiotic stress tolerance. Until now, the identification of chemical compounds with priming-inducing activity (so-called plant activators) relied on tedious and invasive approaches, or required the late detection of secreted furanocoumarin phytoalexins in parsley cell cultures. Thus, simple, fast, straightforward, and noninvasive techniques for identifying priming-inducing compounds for plant protection are very welcome.

RESULTS

This report demonstrates that a respiration activity-monitoring system (RAMOS) can identify compounds with defense priming-inducing activity in parsley cell suspension in culture. RAMOS relies on the quasi-continuous, noninvasive online determination of the oxygen transfer rate (OTR). Treatment of parsley culture cells with the known plant activator salicylic acid (SA), a natural plant defense signal, resulted in an OTR increase. Addition of the defense elicitor Pep13, a cell wall peptide of Phythophthora sojae, induced two distinctive OTR peaks that were higher in SA-primed cells than in unprimed cells upon Pep13 challenge. Both, the OTR increase after priming with SA and the Pep13 challenge were dose-dependent. Furthermore, there was a close correlation of a compound's activity to enhance the oxygen consumption in parsley cells and its capacity to prime Pep13-induced furanocoumarin secretion as evaluated by fluorescence spectroscopy.

CONCLUSIONS

RAMOS noninvasively determines the OTR as a measure of the metabolic activity of plant cells. Chemical enhancement of oxygen consumption by salicylic derivatives in parsley cell suspension cultures correlates with the induction of the primed state of enhanced defense that enhances the quantity of Pep13-induced furanocoumarin phytoalexins. Treatment with the priming-active compounds methyl jasmonate and pyraclostrobin also resulted in an enhanced respiration activity. Thus, RAMOS is a novel technology for identifying priming-inducing compounds for agriculture.

The use of ECAS in plant protection: a green and efficient antimicrobial approach that primes selected defense genes

The use of highly polluting chemicals for plant and crop protection is one of the components of the negative environmental impact of agricultural activities. In the present paper, an environmentally friendly alternative to pesticide application has been studied, based on the so-called electrochemically activated solutions (ECAS). Experiments have been carried out, by applying ECAS having different contents of active ingredients, on tobacco plants at a laboratory scale and on apple trees at fruit garden scale. The results, accumulated during a couple of years, have shown that properly selected dilute solutions of chlorides, once activated by an electrochemical treatment, exhibit a very effective protecting action of plants, irrespective of their nature. Extension of the research has shown that the observed effect is the result of two distinct factors: the expected anti-microbial action of the electrochemically synthesized oxidants, and an unexpected priming of immune plant defenses, which is clearly due to the treatment with ECAS. Interestingly, the repetition of ECAS application triggers an even stronger activation of defense genes. No oxidative damages, due to the use of the activated solutions, could be detected.