The Influence of Lead and Acyrthosiphon pisum (Harris) on Generation of Pisum sativum Defense Signaling Molecules and Expression of Genes Involved in Their Biosynthesis.

The main aim of this study was to understand the regulation of the biosynthesis of phytohormones as signaling molecules in the defense mechanisms of pea seedlings during the application of abiotic and biotic stress factors. It was important to identify this regulation at the molecular level in Pisum sativum L. seedlings under the influence of various concentrations of lead-i.e., a low concentration increasing plant metabolism, causing a hormetic effect, and a high dose causing a sublethal effect-and during feeding of a phytophagous insect with a piercing-sucking mouthpart-i.e., pea aphid (Acyrthosiphon pisum (Harris)). The aim of the study was to determine the expression level of genes encoding enzymes of the biosynthesis of signaling molecules such as phytohormones-i.e., jasmonates (JA/MeJA), ethylene (ET) and abscisic acid (ABA). Real-time qPCR was applied to analyze the expression of genes encoding enzymes involved in the regulation of the biosynthesis of JA/MeJA (lipoxygenase 1 (LOX1), lipoxygenase 2 (LOX2), 12-oxophytodienoate reductase 1 (OPR1) and jasmonic acid-amido synthetase (JAR1)), ET (1-aminocyclopropane-1-carboxylate synthase 3 (ACS3)) and ABA (9-cis-epoxycarotenoid dioxygenase (NCED) and aldehyde oxidase 1 (AO1)). In response to the abovementioned stress factors-i.e., abiotic and biotic stressors acting independently or simultaneously-the expression of the LOX1, LOX2, OPR1, JAR1, ACS3, NCED and AO1 genes at both sublethal and hormetic doses increased. Particularly high levels of the relative expression of the tested genes in pea seedlings growing at sublethal doses of lead and colonized by A. pisum compared to the control were noticeable. A hormetic dose of lead induced high expression levels of the JAR1, OPR1 and ACS3 genes, especially in leaves. Moreover, an increase in the concentration of phytohormones such as jasmonates (JA and MeJA) and aminococyclopropane-1-carboxylic acid (ACC)-ethylene (ET) precursor was observed. The results of this study indicate that the response of pea seedlings to lead and A. pisum aphid infestation differed greatly at both the gene expression and metabolic levels. The intensity of these defense responses depended on the organ, the metal dose and direct contact of the stress factor with the organ.

The Alleviation of Metal Stress Nuisance for Plants-A Review of Promising Solutions in the Face of Environmental Challenges.

Environmental changes are inevitable with time, but their intensification and diversification, occurring in the last several decades due to the combination of both natural and human-made causes, are really a matter of great apprehension. As a consequence, plants are exposed to a variety of abiotic stressors that contribute to their morpho-physiological, biochemical, and molecular alterations, which affects plant growth and development as well as the quality and productivity of crops. Thus, novel strategies are still being developed to meet the challenges of the modern world related to climate changes and natural ecosystem degradation. Innovative methods that have recently received special attention include eco-friendly, easily available, inexpensive, and, very often, plant-based methods. However, such approaches require better cognition and understanding of plant adaptations and acclimation mechanisms in response to adverse conditions. In this succinct review, we have highlighted defense mechanisms against external stimuli (mainly exposure to elevated levels of metal elements) which can be activated through permanent microevolutionary changes in metal-tolerant species or through exogenously applied priming agents that may ensure plant acclimation and thereby elevated stress resistance.

The Role of Sugars in Plant Responses to Stress and Their Regulatory Function during Development.

Due to their role as energy and carbon sources and their regulatory functions, sugars influence all phases of the plant life cycle, interact with other signaling molecules, including phytohormones, and control plant growth and development [...].

Signal Transduction in Cereal Plants Struggling with Environmental Stresses: From Perception to Response.

Cereal plants under abiotic or biotic stressors to survive unfavourable conditions and continue growth and development, rapidly and precisely identify external stimuli and activate complex molecular, biochemical, and physiological responses. To elicit a response to the stress factors, interactions between reactive oxygen and nitrogen species, calcium ions, mitogen-activated protein kinases, calcium-dependent protein kinases, calcineurin B-like interacting protein kinase, phytohormones and transcription factors occur. The integration of all these elements enables the change of gene expression, and the release of the antioxidant defence and protein repair systems. There are still numerous gaps in knowledge on these subjects in the literature caused by the multitude of signalling cascade components, simultaneous activation of multiple pathways and the intersection of their individual elements in response to both single and multiple stresses. Here, signal transduction pathways in cereal plants under drought, salinity, heavy metal stress, pathogen, and pest attack, as well as the crosstalk between the reactions during double stress responses are discussed. This article is a summary of the latest discoveries on signal transduction pathways and it integrates the available information to better outline the whole research problem for future research challenges as well as for the creative breeding of stress-tolerant cultivars of cereals.

PYR/PYL/RCAR Receptors Play a Vital Role in the Abscisic-Acid-Dependent Responses of Plants to External or Internal Stimuli.

Abscisic acid (ABA) is a phytohormone that plays a key role in regulating several developmental processes as well as in response to stressful conditions such as drought. Activation of the ABA signaling cascade allows the induction of an appropriate physiological response. The basic components of the ABA signaling pathway have been recognized and characterized in recent years. Pyrabactin resistance, pyrabactin resistance-like, and the regulatory component of ABA receptors (PYR/PYL/RCAR) are the major components responsible for the regulation of the ABA signaling pathway. Here, we review recent findings concerning the PYR/PYL/RCAR receptor structure, function, and interaction with other components of the ABA signaling pathway as well as the termination mechanism of ABA signals in plant cells. Since ABA is one of the basic elements related to abiotic stress, which is increasingly common in the era of climate changes, understanding the perception and transduction of the signal related to this phytohormone is of paramount importance in further increasing crop tolerance to various stress factors.

Resveratrol and cyclodextrins, an easy alliance: Applications in nanomedicine, green chemistry and biotechnology.

Most drugs or the natural substances reputed to display some biological activity are hydrophobic molecules that demonstrate low bioavailability regardless of their mode of absorption. Resveratrol and its derivatives belong to the chemical group of stilbenes; while stilbenes are known to possess very interesting properties, these are limited by their poor aqueous solubility as well as low bioavailability in animals and humans. Among the substances capable of forming nanomolecular inclusion complexes which can be used for drug delivery, cyclodextrins show spectacular physicochemical and biomedical implications in stilbene chemistry for their possible application in nanomedicine. By virtue of their properties, cyclodextrins have also demonstrated their possible use in green chemistry for the synthesis of stilbene glucosylated derivatives with potential applications in dermatology and cosmetics. Compared to chemical synthesis and genetically modified microorganisms, plant cell or tissue systems provide excellent models for obtaining stilbenes in few g/L quantities, making feasible the production of these compounds at a large scale. However, the biosynthesis of stilbenes is only possible in the presence of the so-called elicitor compounds, the most commonly used of which are cyclodextrins. We also report here on the induction of resveratrol production by cyclodextrins or combinatory elicitation with methyljasmonate in plant cell systems as well as the mechanisms by which they are able to trigger a stilbene response. The present article therefore discusses the role of cyclodextrins in stilbene chemistry both at the physico-chemical level as well as the biomedical and biotechnological levels, emphasizing the notion of "easy alliance" between these compounds and stilbenes.

Probing behavior of Adelges laricis Vallot (Hemiptera: Adelgidae) on Larix decidua Mill: Description and analysis of EPG waveforms.

Adelgidae are a sister group of Aphididae and Phylloxeridae within Hemiptera, Aphidoidea and occur exclusively on Pinaceae. The piercing-sucking mouthparts of Adelgidae are similar to those of aphids and it is believed that adelgids ingest sap from both the non-vascular and vascular (phloem) tissues. The aim of the present study was to identify and characterize the adelgid stylet activities during their penetration in plant tissues. The probing behavior of Adelges laricis Vallot (Hemiptera: Adelgidae) on European larch Larix decidua Mill. and sucrose diets was monitored using the DC-EPG (Electrical Penetration Graph technique = electropenetrography). The EPG waveforms were described based on amplitude, frequency, voltage level, and electrical origin of the observed traces, and associated with putative behavioral activities based on analogy with aphid activities. Waveform frequency, duration, and sequence were analysed as well. A. laricis generated EPG signals at two clearly distinct voltage levels positive and negative, suggesting extracellular and intracellular stylet penetration, respectively. The adelgid EPG patterns were ascribed to four behavioral phases, which were non-probing, pathway, phloem, and xylem phases. Non-probing referred to the position of the stylets outside the plant tissues. Pathway phase was represented by three waveform patterns that visualized extracellular stylet penetration in non-vascular tissues without potential drops (AC1), with serial short (1.2-1.5 s) potential drops (AC2), and with 'aphid-like' (5-10 s) potential drops (AC3). Phloem phase comprised three waveform patterns at intracellular level, which in all probability represented phloem salivation (AE1), and phloem sap passive (AE2) and active ingestion (AE3). AE3 was a newly described waveform, previously unreported from Hemiptera. Waveform AG represented the ingestion of xylem sap. The comparative analysis demonstrated that the gymnosperm-associated adelgids show certain similarities in probing behavior typical of aphids and phylloxerids on angiosperm plants. The present work is the first detailed analysis of specific adelgid stylet activities on gymnosperms.

Phytostilbenes as agrochemicals: biosynthesis, bioactivity, metabolic engineering and biotechnology.

Covering: 1976 to 2020. Although constituting a limited chemical family, phytostilbenes represent an emblematic group of molecules among natural compounds. Ever since their discovery as antifungal compounds in plants and their ascribed role in human health and disease, phytostilbenes have never ceased to arouse interest for researchers, leading to a huge development of the literature in this field. Owing to this, the number of references to this class of compounds has reached the tens of thousands. The objective of this article is thus to offer an overview of the different aspects of these compounds through a large bibliography analysis of more than 500 articles. All the aspects regarding phytostilbenes will be covered including their chemistry and biochemistry, regulation of their biosynthesis, biological activities in plants, molecular engineering of stilbene pathways in plants and microbes as well as their biotechnological production by plant cell systems.

The Role of Saccharides in the Mechanisms of Pathogenicity of Fusarium oxysporum f. sp. lupini in Yellow Lupine (Lupinus luteus L.).

The primary aim of this study was to determine the relationship between soluble sugar levels (sucrose, glucose, or fructose) in yellow lupine embryo axes and the pathogenicity of the hemibiotrophic fungus Fusarium oxysporum f. sp. Schlecht lupini. The first step of this study was to determine the effect of exogenous saccharides on the growth and sporulation of F. oxysporum. The second one focused on estimating the levels of ergosterol as a fungal growth indicator in infected embryo axes cultured in vitro on sugar containing-medium or without it. The third aim of this study was to record the levels of the mycotoxin moniliformin as the most characteristic secondary metabolite of F. oxysporum in the infected embryo axes with the high sugar medium and without it. Additionally, morphometric measurements, i.e., the length and fresh weight of embryo axes, were done. The levels of ergosterol were the highest in infected embryo axes with a sugar deficit. At the same time, significant accumulation of the mycotoxin moniliformin was recorded in those tissues. Furthermore, it was found that the presence of sugars in water agar medium inhibited the sporulation of the pathogenic fungus F. oxysporum in relation to the control (sporulation of the pathogen on medium without sugar), the strongest inhibiting effect was observed in the case of glucose. Infection caused by F. oxysporum significantly limited the growth of embryo axes, but this effect was more visible on infected axes cultured under sugar deficiency than on the ones cultured with soluble sugars. The obtained results thus showed that high sugar levels may lead to reduced production of mycotoxins by F. oxysporum, limiting infection development and fusariosis.

Cyst Nematode Infection Elicits Alteration in the Level of Reactive Nitrogen Species, Protein S-Nitrosylation and Nitration, and Nitrosoglutathione Reductase in Arabidopsis thaliana Roots.

Reactive nitrogen species (RNS) are redox molecules important for plant defense against pathogens. The aim of the study was to determine whether the infection by the beet cyst nematode Heterodera schachtii disrupts RNS balance in Arabidopsis thaliana roots. For this purpose, measurements of nitric oxide (NO), peroxynitrite (ONOO-), protein S-nitrosylation and nitration, and nitrosoglutathione reductase (GSNOR) in A. thaliana roots from 1 day to 15 days post-inoculation (dpi) were performed. The cyst nematode infection caused generation of NO and ONOO- in the infected roots. These changes were accompanied by an expansion of S-nitrosylated and nitrated proteins. The enzyme activity of GSNOR was decreased at 3 and 15 dpi and increased at 7 dpi in infected roots, whereas the GSNOR1 transcript level was enhanced over the entire examination period. The protein content of GSNOR was increased in infected roots at 3 dpi and 7 dpi, but at 15 dpi, did not differ between uninfected and infected roots. The protein of GSNOR was detected in plastids, mitochondria, cytoplasm, as well as endoplasmic reticulum and cytoplasmic membranes. We postulate that RNS metabolism plays an important role in plant defense against the beet cyst nematode and helps the fine-tuning of the infected plants to stress sparked by phytoparasitic nematodes.

The Role of Sugars in the Regulation of the Level of Endogenous Signaling Molecules during Defense Response of Yellow Lupine to Fusarium oxysporum.

Soluble sugars such as sucrose, glucose and fructose in plant host cells not only play the role as donors of carbon skeletons, but they may also induce metabolic signals influencing the expression of defense genes. These metabolites function in a complex network with many bioactive molecules, which independently or in dialogue, induce successive defense mechanisms. The aim of this study was to determine the involvement of sucrose and monosaccharides as signaling molecules in the regulation of the levels of phytohormones and hydrogen peroxide participating in the defense responses of Lupinus luteus L. to a hemibiotrophic fungus Fusarium oxysporum Schlecht f. sp. lupini. A positive correlation between the level of sugars and postinfection accumulation of salicylic acid and its glucoside, as well as abscisic acid, was noted. The stimulatory effect of sugars on the production of ethylene was also reported. The protective role of soluble sugars in embryo axes of yellow lupine was seen in the limited development of infection and fusariosis. These results provide evidence for the enhanced generation of signaling molecules both by sugar alone as well as during the crosstalk between sugars and infection caused by F. oxysporum. However, a considerable postinfection increase in the level of these signaling molecules under the influence of sugars was recorded. The duration of the postinfection generation of these molecules in yellow lupine was also variable.

Leaf position-dependent effect of Alternaria brassicicola development on host cell death, photosynthesis and secondary metabolites in Brassica juncea.

During the first 24 hours of infection, Alternaria brassicicola developmental parameters such as conidial germination, germ tubes and appressoria formation on each of the five mature Brassica juncea leaves, correlated with a leaf position showing stronger development of the pathogen on older leaves than on young ones. As a consequence of fungal development, the black spot disease was observed during 96 hours of infection on a macroscopic scale, as well as via confocal microscopy. Degradation of the chloroplast thylakoids and plastoglobule appearance during infection, followed by the decrease in chlorophyll a fluorescence parameters i.e. maximum quantum yield of PSII (Fv /Fm ), non-photochemical quenching (NPQ) and chlorophyll a:b ratio, have been observed. Also, after an initial increase of carbohydrates (glucose, fructose and sucrose), content far below the respective control values was found. The content of secondary metabolites such as flavonoids and glucosinolates increased in a leaf position-dependent manner in infected leaves, with a lower level in older leaves than in younger ones. Although, the total phenolic compounds (TPCs) content did not differ significantly in infected leaves compared to control leaves, TPCs level in both control and infected leaves was leaf position-dependent. To the best of our knowledge, this is the first report on leaf position-dependent effect on the B. juncea biochemical response to A. brassicicola infection.

Oxidative stress links response to lead and Acyrthosiphon pisum in Pisum sativum L.

This study demonstrates the impact of lead at hormetic (0.075 mM Pb(NO3)2) and sublethal (0.5 mM Pb(NO3)2) doses on the intensity of oxidative stress in pea seedlings (Pisum sativum L. cv. 'Cysterski'). Our first objective was to determine how exposure of pea seedlings to Pb alters the plant defence responses to pea aphid (Acyrthosiphon pisum Harris), and whether these responses could indirectly affect A. pisum. The second objective was to investigate the effects of various Pb concentrations in the medium on demographic parameters of pea aphid population and the process of its feeding on edible pea. We found that the dose of Pb sublethal for pea seedlings strongly reduced net reproductive rate and limited the number of A. pisum individuals reaching the phloem. An important defence line of pea seedlings growing on Pb-supplemented medium and next during combinatory effect of the two stressors Pb and A. pisum was a high generation of superoxide anion (O2-). This was accompanied by a considerable reduction in superoxide dismutase (SOD) activity, and a decrease in the level of Mn2+ ions. A the same time, weak activity of Mn-SOD was detected in the roots of the seedlings exposed to the sublethal dose of Pb and during Pb and aphid interaction. Apart from the marked increase in O2-, an increase in semiquinone radicals occurred, especially in the roots of the seedlings treated with the sublethal dose of Pb and both infested and non-infested with aphids. Also, hydrogen peroxide (H2O2) generation markedly intensified in aphid-infested leaves. It reached the highest level 24 h post infestation (hpi), mainly in the cell wall of leaf epidermis. This may be related to the function of H2O2 as a signalling molecule that triggers defence mechanisms. The activity of peroxidase (POX), an important enzyme involved in scavenging H2O2, was also high at 24 hpi and at subsequent time points. Moreover, the contents of thiobarbituric acid reactive substances (TBARS), products of lipid peroxidation, rose but to a small degree thanks to an efficient antioxidant system. Total antioxidant capacity (TAC) dependent on the pool of fast antioxidants, both in infested and non-infested and leaves was higher than in the control. In conclusion, the reaction of pea seedlings to low and sublethal doses of Pb and then A. pisum infestation differed substantially and depended on a direct contact of the stress factor with the organ (Pb with roots and A. pisum with leaves). The probing behavior of A. pisum also depended on Pb concentration in the plant tissues.

Defense responses of Thuja orientalis to infestation of anholocyclic species aphid Cinara tujafilina.

The aim of this study was to determine an interdependence between generation of semiquinone radicals, superoxide anion (O2-), manganese ions (Mn2+) and phenolic content in leaves of Thuja orientalis in response to infestation by varying populations of Cinara tujafilina, i.e. 40 or 80 aphids per plant. Also, superoxide dismutase (SOD) and ß-d-glucosidase activities in leaves of T. orientalis in a defense response to C. tujafilina was recorded. Analyses of electron paramagnetic resonance (EPR) showed generally a higher concentration of semiquinone radicals with g-values of 2.0051 ± 0.0005 and 20032 ± 0.0005 after C. tujafilina infestation in leaves in comparison to the control. Up to 48 h post-infestation in leaves infested by 80 aphids the level of semiquinone radicals was significantly higher than in the control, while in leaves infested by 40 aphids the highest concentrations of these radicals were recorded at later time points (i.e. at 72 and 96 hpi). In parallel, the highest total generation of O2- and low activity of SOD were recorded in 24-h leaves infested by 80 aphids. Additionally, analysis of confocal images showed that the strongest yellow fluorescence indicating O2- generation was detected in epidermal cells of leaves up to 48 hpi. Significant reduction of Mn2+ ions detected by EPR spectroscopy in relation to the control was observed in 4-w leaves infested by 80 and 40 aphids and in 48-h leaves infested by 40 aphids. Phenolic contents in leaves infested by 80 and 40 aphids at all time points were higher than in the control. The greatest ß-d-glucosidase activity and phenolic contents were recorded at 96 h of feeding. These results indicate that the perception of C. tujafilina infestation by T. orientalis leaves induces a specified sequence of defense mechanisms in the course of time.

The Role of Heavy Metals in Plant Response to Biotic Stress.

The present review discusses the impact of heavy metals on the growth of plants at different concentrations, paying particular attention to the hormesis effect. Within the past decade, study of the hormesis phenomenon has generated considerable interest because it was considered not only in the framework of plant growth stimulation but also as an adaptive response of plants to a low level of stress which in turn can play an important role in their responses to other stress factors. In this review, we focused on the defence mechanisms of plants as a response to different metal ion doses and during the crosstalk between metal ions and biotic stressors such as insects and pathogenic fungi. Issues relating to metal ion acquisition and ion homeostasis that may be essential for the survival of plants, pathogens and herbivores competing in the same environment were highlighted. Besides, the influence of heavy metals on insects, especially aphids and pathogenic fungi, was shown. Our intention was also to shed light on the relationship between heavy metals deposition in the environment and ecological communities formed under a strong selective pressure.

The Influence of Lead on Generation of Signalling Molecules and Accumulation of Flavonoids in Pea Seedlings in Response to Pea Aphid Infestation.

The aim of this study was to investigate the effect of an abiotic factor, i.e., lead at various concentrations (low causing a hormesis effect and causing high toxicity effects), on the generation of signalling molecules in pea (Pisum sativum L. cv. Cysterski) seedlings and then during infestation by the pea aphid (Acyrthosiphon pisum Harris). The second objective was to verify whether the presence of lead in pea seedling organs and induction of signalling pathways dependent on the concentration of this metal trigger defense responses to A. pisum. Therefore, the profile of flavonoids and expression levels of genes encoding enzymes of the flavonoid biosynthesis pathway (phenylalanine ammonialyase and chalcone synthase) were determined. A significant accumulation of total salicylic acid (TSA) and abscisic acid (ABA) was recorded in the roots and leaves of pea seedlings growing on lead-supplemented medium and next during infestation by aphids. Increased generation of these phytohormones strongly enhanced the biosynthesis of flavonoids, including a phytoalexin, pisatin. This research provides insights into the cross-talk between the abiotic (lead) and biotic factor (aphid infestation) on the level of the generation of signalling molecules and their role in the induction of flavonoid biosynthesis.

The Dynamics of the Defense Strategy of Pea Induced by Exogenous Nitric Oxide in Response to Aphid Infestation.

The aim of this study was to investigate the effect of exogenous nitric oxide (NO), i.e., S-nitrosoglutathione (GSNO) and sodium nitroprusside (SNP), on the metabolic status of Pisum sativum L. cv. Cysterski leaves infested by Acyrthosiphon pisum Harris, population demographic parameters and A. pisum feeding activity. A reduction in the level of semiquinone radicals in pea seedling leaves pretreated with exogenous NO occurred 24 h after A. pisum infestation, which was earlier than in non-pretreated leaves. A decrease in the level of O2•- was observed in leaves pretreated with GSNO and infested by aphids at 48 and 72 h post-infestation (hpi). Directly after the pretreatment with GSNO, an increase in the level of metal ions was recorded. NO considerably induced the relative mRNA levels for phenylalanine ammonia-lyase in 24-h leaves pretreated with NO donors, both non-infested and infested. NO stimulated the accumulation of pisatin in leaves until 24 h. The Electrical Penetration Graph revealed a reduction in the feeding activity of the pea aphid on leaves pretreated with NO. The present study showed that foliar application of NO donors induced sequentially defense reactions of pea against A. pisum and had a deterrent effect on aphid feeding and limited the population growth rate.

Brachycorynella asparagi (Mordv.) Induced-Oxidative Stress and Antioxidative Defenses of Asparagus officinalis L.

The aim of this study was to investigate whether and to what extent oxidative stress is induced in leaves of one- and two-month-old plants of Asparagus officinalis L. cv. Argenteuil infested by Brachycorynella asparagi (Mordvilko) at a varied population size. The pest B. asparagi has been described as the most damaging species feeding on asparagus. Analyses using electron paramagnetic resonance (EPR) demonstrated generally higher concentrations of semiquinone radicals with g-values of 2.0045 ± 0.0005 and 2.0026 ± 0.0005 in Asparagus officinalis (A. officinalis) leaves after Brachycorynella asparagi (B. asparagi) infestation than in the control. Observations of leaves under a confocal microscope showed a post-infestation enhanced generation of the superoxide anion radical (O2•-) and hydrogen peroxide (H2O2) in comparison to the control. Strong fluctuations in Mn2+ ion levels detected by EPR spectroscopy versus time were detected in leaves infested by aphids, which may indicate the involvement of these ions in the control of O2•- production. An enhanced superoxide dismutase activity is an important element in leaf defense against oxidative stress. Visible symptoms were found in aphid-infested A. officinalis. Damage to leaves of one- and two-month-old A. officinalis plants by the aphid B. asparagi was dependent on the intensity, duration of infestation and plant age.

Pea aphid infestation induces changes in flavonoids, antioxidative defence, soluble sugars and sugar transporter expression in leaves of pea seedlings.

The perception of aphid infestation induces highly coordinated and sequential defensive reactions in plants at the cellular and molecular levels. The aim of the study was to explore kinetics of induced antioxidative defence responses in leaf cells of Pisum sativum L.cv. Cysterski upon infestation of the pea aphid Acyrthosiphon pisum at varying population sizes, including accumulation of flavonoids, changes of carbon metabolism, and expression of nuclear genes involved in sugar transport. Within the first 96 h, after A. pisum infestation, flavonoid accumulation and increased peroxidase activity were observed in leaves. The level of pisatin increased after 48 h of infestation and reached a maximum at 96 h. At this time point, a higher concentration of flavonols was observed in the infested tissue than in the control. Additionally, strong post-infestation accumulation of chalcone synthase (CHS) and isoflavone synthase (IFS) transcription products was also found. The levels of sucrose and fructose in 24-h leaves infested by 10, 20, and 30 aphids were significantly lower than in the control. Moreover, in leaves infested by 30 aphids, the reduced sucrose level observed up to 48 h was accompanied by a considerable increase in the expression level of the PsSUT1 gene encoding the sucrose transporter. In conclusion, A. pisum infestation on pea leads to stimulation of metabolic pathways associated with defence.

Effects of endogenous signals and Fusarium oxysporum on the mechanism regulating genistein synthesis and accumulation in yellow lupine and their impact on plant cell cytoskeleton.

The aim of the study was to examine cross-talk interactions of soluble sugars (sucrose, glucose and fructose) and infection caused by Fusarium oxysporum f.sp. lupini on the synthesis of genistein in embryo axes of Lupinus luteus L.cv. Juno. Genistein is a free aglycone, highly reactive and with the potential to inhibit fungal infection and development of plant diseases. As signal molecules, sugars strongly stimulated accumulation of isoflavones, including genistein, and the expression of the isoflavonoid biosynthetic genes. Infection significantly enhanced the synthesis of genistein and other isoflavone aglycones in cells of embryo axes of yellow lupine with high endogenous sugar levels. The activity of ß-glucosidase, the enzyme that releases free aglycones from their glucoside bindings, was higher in the infected tissues than in the control ones. At the same time, a very strong generation of the superoxide anion radical was observed in tissues with high sugar contents already in the initial stage of infection. During later stages after inoculation, a strong generation of semiquinone radicals was observed, which level was relatively higher in tissues deficient in sugars than in those with high sugar levels. Observations of actin and tubulin cytoskeletons in cells of infected embryo axes cultured on the medium with sucrose, as well as the medium without sugar, showed significant differences in their organization.