Response of antioxidative enzymes to plum pox virus in two apricot cultivars

Quick Decline and Stem Pitting Citrus tristeza virus Isolates Induce a Distinct Metabolomic Profile and Antioxidant Enzyme Activity in the Phloem Sap of Two Citrus Species

Susceptibility to the severe Citrus tristeza virus (CTV), T36, is higher for Citrus macrophylla (CM) than for C. aurantium (CA). How host-virus interactions are reflected in host physiology is largely unknown. In this study, the profile of metabolites and the antioxidant activity in the phloem sap of healthy and infected CA and CM plants were evaluated. The phloem sap of quick decline (T36) and stem pitting (T318A) infected citrus, and control plants was collected by centrifugation, and the enzymes and metabolites analyzed. The activity of the antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), in infected plants increased significantly in CM and decreased in CA, compared to the healthy controls. Using LC-HRMS² a metabolic profile rich in secondary metabolites was assigned to healthy CA, compared to healthy CM. CTV infection of CA caused a drastic reduction in secondary metabolites, but not in CM. In conclusion, CA and CM have a different response to severe CTV isolates and we propose that the low susceptibility of CA to T36 may be related to the interaction of the virus with the host's metabolism, which reduces significantly the synthesis of flavonoids and antioxidant enzyme activity.

Seed Endophyte bacteria enhance drought stress tolerance in Hordeum vulgare by regulating, physiological characteristics, antioxidants and minerals uptake

Growth stimulating bacteria help remediate dry arid soil and plant stress. Here, Pseudomonas sp. and Pantoea sp. we used to study the stress ecology of Hordeum vulgare and the environmental impact of water deficit on soil characteristics, growth, photosynthesis apparatus, mineral acquisition and antioxidiant defense. Plants inoculated with Pseudomonas or Pantoea had significantly higher (about 2 folds) soil carbon flux (soil respiration), chlorophyll levels (18%), net photosynthetic rate (33% in Pantoea and 54% in Pseudomonas), (44%) stomatal conductance than uninoculated plants in stressed conditions. Both bacterial strains improved leaf growth (23-29%) and root development under well-watered conditions but reduced around (25%) root biomass under drought. Plants inoculated with Pseudomonas or Pantoea under drought also increased of about 27% leaf respiration and transpiration (48%) but decreased water use efficiency, photoinhibition (91%), and the risk of oxidative stress (ETR/A) (49%). Drought stress increased most of the studied antioxidant enzymatic activities in the plants inoculated with Pseudomonas or Pantoea, which reduce the membrane damage and protect plants form oxidative defenses. Drought stress increased K⁺ acquisition around 50% in both shoots inoculated with Pseudomonas or Pantoea relative to non-stressed plants. Plants inoculated with Pseudomonas or Pantoea increased shoot Na⁺ while root Na⁺ only increased in plants inoculated with Pseudomonas in stressed conditions. Drought stress increased shoot Mg²⁺ in plants inoculated with Pseudomonas or Pantoea but did not affect Ca²⁺ relative to non-stressed plants. Drought stress increased about 70% K⁺/Na⁺ ratio only in plants inoculated with Pseudomonas relative to non-stressed plants. Our results indicate that inoculating barley with the studied bacterial strains increases plant biomass and can therefore play a role in the environmental remediation of drylands for food production.

Systemic reprogramming of phytohormone profiles and metabolic traits by virulent Diplodia infection in its pine (Pinus sylvestris L.) host

The widespread ascomycetous fungus Diplodia pinea is a latent, necrotrophic pathogen in Pinus species causing severe damages and world-wide economic losses. However, the interactions between pine hosts and virulent D. pinea are largely not understood. In the present study, systemic defence responses were investigated in non-inoculated, asymptomatic needles and roots of D. pinea infected saplings of two P. sylvestris provenances under controlled greenhouse conditions. Here, we show that D. pinea infection induced a multitude of systemic responses of the phytohormone profiles and metabolic traits. Shared systemic responses of both pine provenances in needles and roots included increased abscisic acid and jasmonic acid levels. Exclusively in the roots of both provenances, enhanced salicylic acid and reduced indole-3-acetic acid levels, structural biomass, and elevated activities of anti-oxidative enzymes were observed. Despite these similarities, the two pine provenances investigated different significantly in the systemic responses of both, phytohormone profiles and metabolic traits in needles and roots. However, the different systemic responses did not prevent subsequent destruction of non-inoculated needles, but rather prevented damage to the roots. Our results provide a detailed view on systemic defence mechanisms of pine hosts that are of particular significance for the selection of provenances with improved defence capacity.

Deciphering Prunus Responses to PPV Infection: A Way toward the Use of Metabolomics Approach for the Diagnostic of Sharka Disease

Sharka disease, caused by Plum pox virus (PPV), induces several changes in Prunus. In leaf tissues, the infection may cause oxidative stress and disrupt the photosynthetic process. Moreover, several defense responses can be activated after PPV infection and have been detected at the phytohormonal, transcriptomic, proteomic, and even translatome levels. As proposed in this review, some responses may be systemic and earlier to the onset of symptoms. Nevertheless, these changes are highly dependent among species, variety, sensitivity, and tissue type. In the case of fruit tissues, PPV infection can modify the ripening process, induced by an alteration of the primary metabolism, including sugars and organic acids, and secondary metabolism, including phenolic compounds. Interestingly, metabolomics is an emerging tool to better understand Prunus–PPV interactions mainly in primary and secondary metabolisms. Moreover, through untargeted metabolomics analyses, specific and early candidate biomarkers of PPV infection can be detected. Nevertheless, these candidate biomarkers need to be validated before being selected for a diagnostic or prognosis by targeted analyses. The development of a new method for early detection of PPV-infected trees would be crucial for better management of the outbreak, especially since there is no curative treatment.

Biochemical study of the effect of stress conditions on the mandelonitrile-associated salicylic acid biosynthesis in peach

Salicylic acid (SA) plays a central role in plant responses to environmental stresses. In a recent study, we suggested a third pathway for SA biosynthesis from mandelonitrile (MD) in peach plants. This pathway is an alternative to the phenylalanine ammonia-lyase pathway and links SA biosynthesis and cyanogenesis. In the present work, using biochemical approaches, we studied the effect of salt stress and Plum pox virus (PPV) infection on this proposed SA biosynthetic pathway from MD. Peach plants were submitted to salt stress and Plum pox virus (PPV) infection. We studied the levels of SA and its intermediates/precursors (phenylalanine, MD, amygdalin and benzoic acid) in in vitro shoots. Moreover, in peach seedlings, we analysed the content of H₂ O₂ -related enzymes, SA and the stress-related hormones abscisic acid and jasmonic acid. We showed that the contribution of this SA biosynthetic pathway from MD to the total SA pool does not seem to be important under the stress conditions assayed. Nevertheless, MD treatment not only affected the SA content, but also had a pleiotropic effect on abscisic acid and jasmonic acid levels. Furthermore, MD modulates the antioxidative metabolism via SA-dependent or -independent redox-related signalling pathways. Even though the proposed SA biosynthetic pathway seems to be functional under stress conditions, MD, and hence cyanogenic glycosides, may be operating more broadly than by influencing SA pathways and signalling. Thus, the physiological function of the proposed SA biosynthetic pathway remains to be elucidated.

The Respiratory Burst Oxidase Homolog D (RbohD) Cell and Tissue Distribution in Potato-Potato Virus Y (PVYNTN) Hypersensitive and Susceptible Reactions

The respiratory burst oxidase homolog D (RbohD) acts as a central driving force of reactive oxygen species signaling in plant cells by integrating many different signal transduction pathways in plants, including incompatible interactions with pathogens. This study demonstrated the localization and distribution of RbohD in two types of potato–potato virus Y (PVY) interactions: Compatible and incompatible (resistant). The results indicated a statistically significant induction of the RbohD antigen signal in both interaction types. In the hypersensitive response (resistant reaction) of potato with a high level of resistance to the potato tuber necrotic strain of PVY (PVY^NTN), RbohD localization followed by hydrogen peroxide (H₂O₂) detection was concentrated in the apoplast. In contrast, in the hypersensitive response of potato with a low resistance level to PVY^NTN, the distribution of RbohD was concentrated more in the plant cell organelles than in the apoplast, resulting in the virus particles being present outside the inoculation area. Moreover, when compared to mock-inoculated plants and to the hypersensitive response, the PVY^NTN-compatible potato interaction triggered high induction in the RbohD distribution, which was associated with necrotization. Our findings indicated that RbohD and hydrogen peroxide deposition was associated with the hypersensitive response, and both were detected in the vascular tissues and chloroplasts. These results suggest that the RbohD distribution is actively dependent on different types of PVY ^NTN-potato plant interactions. Additionally, the RbohD may be involved in the PVY^NTN tissue limitation during the hypersensitive response, and it could be an active component of the systemic signal transduction in the susceptible host reaction.

Effects of Rhizophagus clarus and P availability in the tolerance and physiological response of Mucuna cinereum to copper

Arbuscular mycorrhizal fungi (AMF) improve plant ability to uptake P and tolerate heavy metals. This study aimed to evaluate the effect of available P and the inoculation of Rhizophagus clarus in a Cu-contaminated soil (i) on the activity of acid phosphatases (soil and plant), the presence of glomalin, and (ii) in the biochemical and physiological status of Mucuna cinereum. A Typic Hapludalf soil artificially contaminated by adding 60 mg kg^-1 Cu was used in a 3 × 2 factorial design with three replicates. Treatments consisted of three P levels: 0, 40, and 100 mg kg^-1 P. Each P treatment level was inoculated (+AMF)/non-inoculated (-AMF) with 200 spores of R. clarus per pot, and plants grown for 45 days. The addition of at least 40 mg kg^-1 P and the inoculation of plants with R. clarus proved to be efficient to reduce Cu phytotoxicity and increase dry matter yield. Mycorrhization and phosphate fertilization reduced the activity of enzymes regulating oxidative stress (SOD and POD), and altered the chlorophyll a fluorescence parameters, due to the lower stress caused by available Cu. These results suggest a synergism between the application of P and the inoculation with R. clarus, favoring the growth of M. cinereum in a Cu-contaminated soil. This study shows that AMF inoculation represents an interesting alternative to P fertilization to improve plant development when exposed to excess Cu.

Biochemical changes in the leaves of mungbean (Vigna radiata) plants infected by phytoplasma

Objective:

Phyllody disease caused by phytoplasma is an emerging problem in mungbean worldwide. However, the alterations in the host physiology and its associated biochemical components induced by the infection with phytoplasma in mungbean plant remain unknown. Hence the present study was performed with the diseased plants in order to determine the patho-physiological changes that take place.

Methods:

Under present study, the changes in total phenolic compounds, total soluble proteins, peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), Chlorophyll a, Chlorophyll b, and total chlorophyll were studied in leaves of phytoplasma-infected and healthy plants of six mungbean genotypes.

Results:

Total phenols were decreased significantly in four but increased in one genotype. Protein contents were increased significantly in two genotypes, POD in four, PPO in one and PAL in two genotypes. However, activity of CAT and amount of

Conclusion:

These results suggest that phytoplasma can interfere with host metabolism and photosynthesis to induce disease. In conclusion, this study provides new insights into the mungbean response to phytoplasma infection.

Drought increases cowpea (Vigna unguiculata [L.] Walp.) susceptibility to cowpea severe mosaic virus (CPSMV) at early stage of infection

The physiological and biochemical responses of a drought tolerant, virus-susceptible cowpea genotype exposed to drought stress (D), infected by Cowpea severe mosaic virus (CPSMV) (V), and to these two combined stresses (DV), at 2 and 6 days post viral inoculation (DPI), were evaluated. Gas exchange parameters (net photosynthesis, transpiration rate, stomatal conductance, and internal CO₂ partial pressure) were reduced in D and DV at 2 and 6 DPI compared to control plants (C). Photosynthesis was reduced by stomatal and biochemical limitations. Water use efficiency increased at 2 DPI in D, DV, and V, but at 6 DPI only in D and DV compared to C. Photochemical parameters (effective quantum efficiency of photosystem II and electron transport rate) decreased in D and DV compared to C, especially at 6 DPI. The potential quantum efficiency of photosystem II did not change, indicating reversible photoinhibition of photosystem II. In DV, catalase decreased at 2 and 6 DPI, ascorbate peroxidase increased at 2 DPI, but decreased at 6 DPI. Hydrogen peroxide increased at 2 and 6 DPI. Peroxidase increased at 6 DPI and chitinase at 2 and 6 DPI. β-1,3-glucanase decreased in DV at 6 DPI compared to V. Drought increased cowpea susceptibility to CPSMV at 2 DPI, as verified by RT-PCR. However, at 6 DPI, the cowpea plants overcome this effect. Likewise, CPSMV increased the negative effects of drought at 2 DPI, but not at 6 DPI. It was concluded that the responses to combined stresses are not additive and cannot be extrapolated from the study of individual stresses.

Eclipta yellow vein virus enhances chlorophyll destruction, singlet oxygen production and alters endogenous redox status in Andrographis paniculata

The infection of Eclipta yellow vein virus [EcYVV-IN, Accession No. KC476655], recently reported for the first time, on Andrographis paniculata was studied for redox-mediated alteration mechanism in infected plants. A. paniculata, an important medicinal plant, is used in traditional Indian, Chinese and modern system of medicine. Andrographolide, one of the foremost components of this plant, is known for its varied pharmacological properties. Our investigation provides insight into the effect of virus-induced changes in the singlet oxygen quenching due to the alteration in pigment content (chlorophyll and carotenoids) as well as activation of plant secondary metabolism along with defense activation leading to changes in enzymatic and non-enzymatic redox status. Due to infection, a reduction in carotenoid content was observed which leads to reduced quenching of singlet oxygen. An increased level of enzymatic (SOD and APX) and non-enzymatic antioxidant (DPPH, FRAP, RP, NO, TAC and TP) activities were also observed in virus-infected plants with a positive correlation (>0.9). However, CAT activity was diminished which could be either due to its proteolytic degradation or inactivation by superoxide anions (O(2-.)), NO or peroxynitrite radicals. A significant (p < 0.05) increase in total phenolic content was observed in the infected plants while no considerable difference was seen in the total flavonoid content. Our results highlighted the alteration in redox status caused by virus-induced biotic stress on the plants and could be useful for understanding the after effects of viral infection This study could also be helpful in developing biomimetic methods for improving the production of secondary metabolites of pharmaceutical importance.

Leaf crinkle disease in urdbean (Vigna mungo L. Hepper): An overview on causal agent, vector and host

Urdbean leaf crinkle disease (ULCD) is an economically significant widespread and devastating disease resulting in extreme crinkling, puckering and rugosity of leaves inflicting heavy yield losses annually in major urdbean-producing countries of the world. This disease is caused by urdbean leaf crinkle virus (ULCV). Urdbean (Vigna mungo L. Hepper) is relatively more susceptible than other pulses to leaf crinkle disease. Urdbean is an important and useful crop cultivated in various parts of South-East Asia and well adapted for cultivation under semi-arid and subtropical conditions. Aphids, insects and whiteflies have been reported as vectors of the disease. The virus is also transmitted through sap inoculation, grafting and seed. The loss in seed yield in ULCD-affected urdbean crop ranges from 35 to 81%, which is dependent upon type of genotype location and infection time. The diseased material and favourable climatic conditions contribute for the widespread viral disease. Anatomical and biochemical changes take place in the affected diseased plants. Genetic variations have been reported in the germplasm screening which suggest continuous screening of available varieties and new germplasm to search for new traits (new genes) and identify new sources of disease resistance. There are very few reports on breeding programmes for the development and release of varieties tolerant to ULCD. Mostly random amplified polymorphic DNA (RAPD) as well as inter-simple sequence repeat (ISSR) molecular markers have been utilized for fingerprinting of blackgram, and a few reports are there on sequence-tagged micro-satellite site (STMS) markers. There are so many RNA viruses which have also developed strategies to counteract silencing process by encoding suppressor proteins that create hindrances in the process. But, in the case of ULCV, there is no report available indicating which defence pathway is operating for its resistance in the plants and whether same silencing suppression strategy is also followed by this virus causing leaf crinkle disease in urdbean. The antiviral principles (AVP) present in leaf extracts of several plants are known to inhibit infection by many viruses. Many chemicals have been reported as inhibitors of virus replication in plants. Raising the barrier crops also offers an effective solution to control the spread of virus.

Changes in the Antioxidant System in Soybean Leaves Infected by Corynespora cassiicola

Considering the importance of target spot, caused by the fungus Corynespora cassiicola, to reduce soybean yield in Brazil and that more basic information regarding the soybean-C. cassiicola interaction is needed, the present study aimed to investigate whether the cellular damage caused by C. cassiicola infection could activate the antioxidant system and whether a more efficient antioxidant system could be associated with an increase in soybean resistance to target spot. The activities of the antioxidant enzymes superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, glutathione peroxidase, glutathione reductase, glutathione S-transferase as well as the concentrations of ascorbate (AsA), hydrogen peroxide (H2O2), superoxide (O2•-), and malondialdehyde (MDA) were measured in soybean plants from two cultivars differing in resistance to the pathogen. The number of lesions per square centimeter was significantly reduced by 14% in plants from cultivar Fundacep 59 compared with plants from cultivar TMG 132. The area under the disease progress curve was significantly lower, by 15%, in plants from Fundacep 59 than in plants from TMG 132. Generally, antioxidant enzyme activities and AsA concentration significantly increased in response to C. cassiicola infection in plants from both cultivars, however more prominent increases were recorded for plants from Fundacep 59. The concentrations of MDA, H2O2, and O2•- also increased, particularly for plants from TMG 132. The results from this study highlight the importance of a more efficient antioxidative system in the removal of reactive oxygen species generated in soybean plants during C. cassiicola infection, contributing to the resistance to target spot.

Sharka: how do plants respond to Plum pox virus infection?

Plum pox virus (PPV), the causal agent of sharka disease, is one of the most studied plant viruses, and major advances in detection techniques, genome characterization and organization, gene expression, transmission, and the description of candidate genes involved in PPV resistance have been described. However, information concerning the plant response to PPV infection is very scarce. In this review, we provide an updated summary of the research carried out to date in order to elucidate how plants cope with PPV infection and their response at different levels, including the physiological, biochemical, proteomic, and genetic levels. Knowledge about how plants respond to PPV infection can contribute to the development of new strategies to cope with this disease. Due to the fact that PPV induces an oxidative stress in plants, the bio-fortification of the antioxidative defences, by classical or biotechnological approaches, would be a useful tool to cope with PPV infection. Nevertheless, there are still some gaps in knowledge related to PPV-plant interaction that remain to be filled, such as the effect of PPV on the hormonal profile of the plant or on the plant metabolome.

Histochemical visualization of ROS and antioxidant response to viral infections of vegetable crops grown in Azerbaijan

Extremes of environmental conditions, such as biotic stresses, strongly affect plant growth and development and may adversely affect photosynthetic process. Virus infection is especially problematic in crops, because unlike other diseases, its impact cannot be reduced by phytosanitary treatments. The vegetable crops (Solanum lycopеrsicum L, Cucurbita melo L., Cucumis sativus L., Piper longum L., Solánum melongéna L., Vicia faba L.) showing virus-like symptoms were collected from fields located in the main crop production provinces of Azerbaijan. Infection of the plants were confirmed by Enzyme-linked immunosorbent assay using commercial kits for the following viruses: Tomato yellow leaf curl virus, Tomato mosaic virus, Tomato chlorosis virus, Melon necrotic spot virus and Cucumber mosaic virus, Bean common mosaic virus and Bean yellow mosaic virus. Generation sites of superoxide and hydrogen peroxide radicals and activities of enzymes involved in the detoxification of reactive oxygen species (catalase, glutathione reductase, ascorbate peroxidase, guaiacol peroxidase and superoxide dismutase) were examined in uninfected leaves and in leaves infected with viruses. High accumulation of superoxide and hydrogen peroxide radicals was visualized in infected leaves as a purple discoloration of nitro blue tetrazolium and 3,3'-diaminobenzidine tetrahydrochloride. It was found that the activities of APX and CAT significantly increased in all infected samples compared with non-infected ones. Dynamics of GR and Cu/Zn-SOD activities differed from those of CAT and APX, and slightly increased in stressed samples. Electrophoretic mobility profiling of APX, GPX and CAT isoenzymes was also studied.

Biochemical changes in the leaves of wheat plants infected by Pyricularia oryzae

Blast, caused by the fungus Pyricularia oryzae, is a major disease of the wheat crop in the Brazilian Cerrado and represents a potential threat to world wheat production. However, information about the wheat-P. oryzae interaction is still limited. In this work, the activities of the enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), glutathione-S-transferase (GST), ascorbate peroxidase (APX), glutathione reductase (GR), and glutathione peroxidase (GPX) and the concentrations of superoxide (O₂(-)), hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) as well as the electrolyte leakage (EL) were studied in wheat plants 'BR 18' and 'BRS 229', which are susceptible and partially resistant, respectively, to leaf blast at the vegetative growth stage, during the infection process of P. oryzae. The blast severity in BRS 229 was 50% lower than in BR 18 at 96 h after inoculation (hai). The activities of SOD, POX, APX, and GST increased for both cultivars in the inoculated plants compared with noninoculated plants and the increases were more pronounced for BRS 229 than for BR 18 at 96 hai. The GR and CAT activities only increased in inoculated plants from BRS 229 at 96 hai. For BR 18, the GR activity was not influenced by plant inoculation, and the CAT activity was lower in inoculated plants. The GPX activity only increased in inoculated plants from BR 18 at 48 and 72 hai. The P. oryzae infection increased the O₂(-), H₂O₂, and MDA concentrations and EL. However, the greater increases of the SOD, POX, APX, GST, GR, and CAT activities for BRS 229 compared with BR 18 contributed to the lower O₂(-), H₂O₂, and MDA concentrations and EL verified in the former. These results show that a more efficient antioxidative system in the removal of excess of reactive oxygen species generated during the infection process of P. oryzae limits the cellular damage caused by the fungus, thus contributing to greater wheat resistance to blast.

Sharka: the past, the present and the future

Members the Potyviridae family belong to a group of plant viruses that are causing devastating plant diseases with a significant impact on agronomy and economics. Plum pox virus (PPV), as a causative agent of sharka disease, is widely discussed. The understanding of the molecular biology of potyviruses including PPV and the function of individual proteins as products of genome expression are quite necessary for the proposal the new antiviral strategies. This review brings to view the members of Potyviridae family with respect to plum pox virus. The genome of potyviruses is discussed with respect to protein products of its expression and their function. Plum pox virus distribution, genome organization, transmission and biochemical changes in infected plants are introduced. In addition, techniques used in PPV detection are accentuated and discussed, especially with respect to new modern techniques of nucleic acids isolation, based on the nanotechnological approach. Finally, perspectives on the future of possibilities for nanotechnology application in PPV determination/identification are outlined.

Unconventional protein secretion

It is generally believed that protein secretion or exocytosis is achieved via a conventional ER (endoplasmic reticulum)-Golgi-TGN (trans-Golgi network)-PM (plasma membrane) pathway in the plant endomembrane system. However, such signal peptide (SP)-dependent protein secretion cannot explain the increasing number of SP-lacking proteins which are found outside of the PM in plant cells. The process by which such leaderless secretory proteins (LSPs) gain access to the cell exterior is termed unconventional protein secretion (UPS) and has been well-studied in animal and yeast cells, but largely ignored by the plant community. Here, we review the evidence for UPS in plants especially in regard to the recently discovered EXPO (exocyst-positive-organelle).

Analysis of the antioxidant response of Nicotiana benthamiana to infection with two strains of Pepper mild mottle virus

The present study was carried out to investigate the role of reactive oxygen species (ROS) metabolism in symptom development and pathogenesis in Nicotiana benthamiana plants upon infection with two strains of Pepper mild mottle virus, the Italian (PMMoV-I) and the Spanish (PMMoV-S) strains. In this host, it has been shown that PMMoV-I is less virulent and plants show the capability to recover 21 d after inoculation. Analyses of oxidative stress biomarkers, ROS-scavenging enzyme activities, and antioxidant compounds were conducted in plants at different post-infection times. Only PMMoV-I stimulated a defence response through: (i) up-regulation of different superoxide dismutase isozymes; (ii) maintenance of adequate levels of three peroxiredoxins (2-Cys Prx, Prx IIC, and Prx IIF); and (iii) adjustments in the glutathione pool to maintain the total glutathione content. Moreover, there was an increase in the level of oxidized glutathione and ascorbate in the recovery phase of PMMoV-I-infected plants. The antioxidant response and the extent of oxidative stress in N. benthamiana plants correlates to: (i) the severity of the symptoms elicited by either strain of PMMoV; and (ii) the high capacity of PMMoV-I-infected plants for symptom recovery and delayed senescence, compared with PMMoV-S-infected plants.

Plant growth stimulation in Prunus species plantlets by BTH or OTC treatments under in vitro conditions

The effects of benzothiadiazole (BTH) and L-2-oxothiazolidine-4-carboxylic acid (OTC) on the growth and viral content of micropropagated, Plum pox virus (PPV)-infected peach [(Prunus persica (L.) Batsch] 'GF305' plantlets were analyzed. Low BTH and OTC concentrations resulted in a significant increase in the growth of GF305 peach and plum plants, with greater effects in PPV-infected than in healthy GF305 peach plantlets. Neither BTH nor OTC reduced the virus content. In fact, the highest growth and viral contents coincided, especially with the 10 μM BTH treatment. Differing effects on the antioxidative metabolism of PPV-infected GF305 peach plantlets were observed, depending on the compound and the concentration used: BTH decreased GSH, whereas OTC increased it. In PPV-infected plants, the 50 μM OTC treatment produced a decrease in ascorbate peroxidase, catalase, and glutathione peroxidase, but an increase in superoxide dismutase. However, BTH produced a rise in peroxidase activity. Both 10 μM BTH and 50 μM OTC produced H₂O₂ accumulation that was correlated with the histochemical detection of H₂O₂ by 3,3'-diaminobenzidine staining. PPV infection induced NPR1 expression and a synergistic effect occurred in the presence of 50 μM OTC, since this compound produced an up-regulation of NPR1 in both healthy and PPV-infected GF305 peach plantlets. The results showed that GSH, as previously suggested, and/or H₂O₂ could be involved in the regulation of NPR1 expression. Globally, the results show that both OTC and BTH improved the vigor of Prunus species, including peach and plum, under in vitro conditions, producing positive effects on growth, antioxidative metabolism and NPR1 expression. All of these improvements could be critical for more successful ex vitro acclimatization as well as for improved responses to different stresses.

Effects of cucumber mosaic virus infection on electron transport and antioxidant system in chloroplasts and mitochondria of cucumber and tomato leaves

We examined the responses of the photosynthetic and respiratory electron transport and antioxidant systems in cell organelles of cucumber (Cucumis sativus L.) and tomato (Lycopersicon esculentum Mill.) leaves to infection of cucumber mosaic virus (CMV) by comparing the gas exchange, Chl fluorescence, respiratory electron transport, superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate-glutathione (AsA-GSH) cycle enzymes and the production of H(2)O(2) in chloroplasts, mitochondria and soluble fraction in virus-infected and non-infected leaves. Long-term CMV infection resulted in decreased photosynthesis and respiration rates. Photosynthetic electron flux to carbon reduction, respiratory electron transport via both complex I and complex II and also the Cyt respiration rate all significantly decreased, while photosynthetic alternative electron flux and alternative respiration significantly increased. These changes in electron transport were accompanied by a general increase in the activities of SOD/AsA-GSH cycle enzymes followed by an increased H(2)O(2) accumulation in chloroplasts and mitochondria. These results demonstrated that disturbance of photosynthetic and respiratory electron transport by CMV also affected the antioxidative systems, thereby leading to oxidative stress in various organelles.

Exopolysaccharides produced by plant pathogenic bacteria affect ascorbate metabolism in Nicotiana tabacum

The role of the exopolysaccharides (EPSs) produced by plant pathogenic bacteria has not completely clarified, they are considered either molecules able to avoid or delay the activation of plant defences, or acting as signal in the plant-pathogen cross-talk. In order to understand whether EPSs are recognized by infected plant cells and are able to induce the activation of plant defence responses, their capability to induce metabolic alteration in tobacco cells has been analysed. The results indicate that several EPSs, even if not chemically related, induce increases in phenylalanine ammonia-lyase, a marker enzyme of defence responses of plants against stress; but others are completely ineffective. The EPSs affecting phenylalanine ammonia-lyase also induce an increase in hydrogen peroxide production. Moreover, they alter the metabolism of ascorbate, another parameter indicative of the presence of stress conditions and the involvement of which in the hypersensitive reaction has been recently reported. The possibility that specific EPSs could act as signals in the plant-pathogenic bacteria interaction is discussed.

Antioxidant systems and O(2)(.-)/H(2)O(2) production in the apoplast of pea leaves. Its relation with salt-induced necrotic lesions in minor veins

The present work describes, for the first time, the changes that take place in the leaf apoplastic antioxidant defenses in response to NaCl stress in two pea (Pisum sativum) cultivars (cv Lincoln and cv Puget) showing different degrees of sensitivity to high NaCl concentrations. The results showed that only superoxide dismutase, and probably dehydroascorbate reductase (DHAR), were present in the leaf apoplastic space, whereas ascorbate (ASC) peroxidase, monodehydroascorbate reductase (MDHAR), and glutathione (GSH) reductase (GR) seemed to be absent. Both ASC and GSH were detected in the leaf apoplastic space and although their absolute levels did not change in response to salt stress, the ASC/dehydroascorbate and GSH to GSH oxidized form ratios decreased progressively with the severity of the stress. Apoplastic superoxide dismutase activity was induced in NaCl-treated pea cv Puget but decreased in NaCl-treated pea cv Lincoln. An increase in DHAR and GR and a decrease in ASC peroxidase, MDHAR, ASC, and GSH levels was observed in the symplast from NaCl-treated pea cv Lincoln, whereas in pea cv Puget an increase in DHAR, GR, and MDHAR occurred. The results suggest a strong interaction between both cell compartments in the control of the apoplastic ASC content in pea leaves. However, this anti-oxidative response does not seem to be sufficient to remove the harmful effects of high salinity. This finding is more evident in pea cv Lincoln, which is characterized by a greater inhibition of the growth response and by a higher rise in the apoplastic hydrogen peroxide content, O(2)(.-) production and thiobarbituric acid-reactive substances, and CO protein levels. This NaCl-induced oxidative stress in the apoplasts might be related to the appearance of highly localized O(2)(.-)/H(2)O(2)-induced necrotic lesions in the minor veins in NaCl-treated pea plants. It is possible that both the different anti-oxidative capacity and the NaCl-induced response in the apoplast and in the symplast from pea cv Puget in comparison with pea cv Lincoln contributes to a better protection of pea cv Puget against salt stress.