Abiotic and Herbivory Combined Stress in Tomato: Additive, Synergic and Antagonistic Effects and Within-Plant Phenotypic Plasticity.

BACKGROUND: Drought, N deficiency and herbivory are considered the most important stressors caused by climate change in the agro- and eco-systems and varied in space and time shaping highly dynamic and heterogeneous stressful environments. This study aims to evaluate the tomato morpho-physiological and metabolic responses to combined abiotic and herbivory at different within-plant spatial levels and temporal scales. METHODS: Leaf-level morphological, gas exchange traits and volatile organic compounds (VOCs) profiles were measured in tomato plants exposed to N deficiency and drought, Tuta absoluta larvae and their combination. Additive, synergistic or antagonistic effects of the single stress when combined were also evaluated. Morpho-physiological traits and VOCs profile were also measured on leaves located at three different positions along the shoot axes. RESULTS: The combination of the abiotic and biotic stress has been more harmful than single stress with antagonistic and synergistic but non-additive effects for the morpho-physiological and VOCs tomato responses, respectively. Combined stress also determined a high within-plant phenotypic plasticity of the morpho-physiological responses. CONCLUSIONS: These results suggested that the combined stress in tomato determined a "new stress state" and a higher within-plant phenotypic plasticity which could permit an efficient use of the growth and defense resources in the heterogeneous and multiple stressful environmental conditions.

Monoterpene Synthase Genes and Monoterpene Profiles in Pinus nigra subsp. laricio.

In the present study, we carried out a quantitative analysis of the monoterpenes composition in different tissues of the non-model conifer Pinus nigra J.F. Arnold subsp. laricio Palib. ex Maire (P. laricio, in short). All the P. laricio tissues examined showed the presence of the same fourteen monoterpenes, among which the most abundant were ß-phellandrene, α-pinene, and ß-pinene, whose distribution was markedly tissue-specific. In parallel, from the same plant tissues, we isolated seven full-length cDNA transcripts coding for as many monoterpene synthases, each of which was found to be attributable to one of the seven phylogenetic groups in which the d1-clade of the canonical classification of plants' terpene synthases can be subdivided. The amino acid sequences deduced from the above cDNA transcripts allowed to predict their putative involvement in the biosynthesis of five of the monoterpenes identified. Transcripts profiling revealed a differential gene expression across the different tissues examined, and was found to be consistent with the corresponding metabolites profiles. The genomic organization of the seven isolated monoterpene synthase genes was also determined.

Diterpene Resin Acids and Olefins in Calabrian Pine (Pinus nigra subsp. laricio (Poiret) Maire) Oleoresin: GC-MS Profiling of Major Diterpenoids in Different Plant Organs, Molecular Identification and Expression Analysis of Diterpene Synthase Genes.

A quali-quantitative analysis of diterpenoid composition in tissues obtained from different organs of Pinus nigra subsp. laricio (Poiret) Maire (Calabrian pine) was carried out. Diterpene resin acids were the most abundant diterpenoids across all the examined tissues. The same nine diterpene resin acids were always found, with the abietane type prevailing on the pimarane type, although their quantitative distribution was found to be remarkably tissue-specific. The scrutiny of the available literature revealed species specificity as well. A phylogeny-based approach allowed us to isolate four cDNAs coding for diterpene synthases in Calabrian pine, each of which belonging to one of the four groups into which the d3 clade of the plants' terpene synthases family can be divided. The deduced amino acid sequences allowed predicting that both monofunctional and bifunctional diterpene synthases are involved in the biosynthesis of diterpene resin acids in Calabrian pine. Transcript profiling revealed differential expression across the different tissues and was found to be consistent with the corresponding diterpenoid profiles. The isolation of the complete genomic sequences and the determination of their exon/intron structures allowed us to place the diterpene synthase genes from Calabrian pine on the background of current ideas on the functional evolution of diterpene synthases in Gymnosperms.

Profiling Volatile Terpenoids from Calabrian Pine Stands Infested by the Pine Processionary Moth.

Terpenoids make up the biggest and most diversified class of chemical substances discovered in plants, encompassing over 40,000 individual compounds. In conifers, the production of terpenoids, either as oleoresin or emitted as volatile compounds, play an important role in the physical and chemical defence responses against pathogens and herbivores. In the present work, we examined, for the first time to the best of our knowledge, the terpenic defensive relations of Calabrian pine (Pinus nigra subsp. laricio (Poiret) Maire), facing the attack of the pine processionary moth (Thaumetopoea pityocampa (Denis and Schiffermüller, 1775)), brought about in the open on adult plant individuals growing at two distinct forest sites. Among the volatile terpenoids emitted from pine needles, bornyl acetate [(4,7,7-trimethyl-3-bicyclo[2.2.1]heptanyl) acetate] was the most frequently and selectively associated with the infestation, increasing during the period of most intense trophic activity of the caterpillars (defoliation), and decreasing thereafter. Although further work is needed to clarify whether the observed response reflects defence reactions and/or they are involved in communication among the infested plants and their biotic environment, the present results boost the currently growing interest in the isolation and characterization of plant secondary metabolites that can be used to control pests, pathogens, and weeds.

On the Evolution and Functional Diversity of Terpene Synthases in the Pinus Species: A Review.

In the biosynthesis of terpenoids, the ample catalytic versatility of terpene synthases (TPS) allows the formation of thousands of different molecules. A steadily increasing number of sequenced plant genomes invariably show that the TPS gene family is medium to large in size, comprising from 30 to 100 functional members. In conifers, TPSs belonging to the gymnosperm-specific TPS-d subfamily produce a complex mixture of mono-, sesqui-, and diterpenoid specialized metabolites, which are found in volatile emissions and oleoresin secretions. Such substances are involved in the defence against pathogens and herbivores and can help to protect against abiotic stress. Oleoresin terpenoids can be also profitably used in a number of different fields, from traditional and modern medicine to fine chemicals, fragrances, and flavours, and, in the last years, in biorefinery too. In the present work, after summarizing the current views on the biosynthesis and biological functions of terpenoids, recent advances on the evolution and functional diversification of plant TPSs are reviewed, with a focus on gymnosperms. In such context, an extensive characterization and phylogeny of all the known TPSs from different Pinus species is reported, which, for such genus, can be seen as the first effort to explore the evolutionary history of the large family of TPS genes involved in specialized metabolism. Finally, an approach is described in which the phylogeny of TPSs in Pinus spp. has been exploited to isolate for the first time mono-TPS sequences from Pinus nigra subsp. laricio, an ecologically important endemic pine in the Mediterranean area.

Transcriptional regulation of stilbene synthases in grapevine germplasm differentially susceptible to downy mildew.

BACKGROUND: To limit the impact of the downy mildew disease of grapevine and reduce the need to recur to chemical treatments, an effective strategy might be recovering adaptive resistance traits in both cultivated and wild V. vinifera germplasm. Considering that stilbenes represent the most important class of phytoalexins in the Vitaceae, the constitutive expression and transcriptional activation of all the functional members of the stilbene synthase gene family were analysed in a group of nine grapevine genotypes following artificial infection with the oomycete Plasmopara viticola, the causal agent of the disease. In addition, in the same genotypes we analyzed the expression of genes encoding for two transcription factors involved in the transcriptional regulation of the stilbene synthase genes, namely VvMYB14 and VvMYB15, and of genes encoding for chalcone synthases. RESULTS: Downy mildew incidence and severity ranged from nihil to high in the grapevine genotypes considered, being low to moderate in a subgroup of V. vinifera genotypes. The constitutive expression of the stilbene synthase genes as well as the extent of their transcriptional activation following P. viticola inoculation appeared to be inversely related to the proneness to develop disease symptoms upon infection. In a specular manner, following P. viticola inoculation all the chalcone synthase genes were up-regulated in the susceptible grapevine genotypes and down-regulated in the resistant ones. The infection brought by P. viticola appeared to elicit a co-ordinated and sequential transcriptional activation of distinct stilbene synthase genes subsets, each of which may be regulated by a distinct and specific MYB transcription factor. CONCLUSIONS: The present results suggest that the induction of stilbene biosynthesis may contribute to the basal immunity against the downy mildew of grapevine, thus representing an adaptive resistance trait to recover, in both cultivated and wild V. vinifera germplasm. During the early stages of P. viticola infection, an antagonistic interaction between flavonol and stilbene biosynthesis might occur, whose outcome might determine the subsequent extent of disease symptoms. Further studies are needed to decipher the possible regulatory mechanisms involved in the antagonistic crosstalk between these two metabolic pathways in resistant and susceptible genotypes in response to P. viticola.

Correction to: Jasmonate-mediated defence responses, unlike salicylate-mediated responses, are involved in the recovery of grapevine from bois noir disease.

CORRECTION: Following publication of the original article [1], it came to the attention of the authors that they had omitted to acknowledge the University of Parma. The Acknowledgement section should read as follows: "The authors kindly acknowledge the University of Parma (Department of Chemistry, Life Sciences and Environmental Sustainability; formerly Department of Life Sciences/Evolutionary and Functional Biology) for the transfer of funds obtained from the Ager project: GIALLUMI DELLA VITE: TECNOLOGIE INNOVATIVE PER LA DIAGNOSI E LO STUDIO DELLE INTERAZIONI PIANTA/PATOGENO, BANDO AGER VITICOLTURA DA VINO".

On the interactions among zinc availability and responses to ozone stress in durum wheat seedlings.

Seedlings of durum wheat [Triticum turgidum subsp. durum (Desf.) Husn] were exposed to zinc nutrition and to ozone (O3) in a factorial combination: adequate (+Zn treatment) or no Zn (-Zn) in the nutrient solution, followed by exposure to either ozone-free air (filtered air, FA) or to 150 nL L-1 ozone (O3) for 4 h. Although omitting Zn from the nutrient solution failed to impose a genuine Zn deficiency, -Zn*FA durum wheat seedlings showed a typical deficiency behaviour, i.e. Zn mobilisation from root to shoot. Such inter-organ Zn redistribution, however, did not occur in -Zn*O3 plants. Exposure to each stress singly decreased the activity and the protein amount of foliar plasma membrane H+-ATPase, but not stress combination, which even increased the H+-ATPase expression with respect to control. In the -Zn*O3 plants, moreover, the foliar activities of the plasma membrane-bound NAD(P)H-dependent superoxide synthase and of Cu,Zn-superoxide dismutase, and the transcripts abundance of the luminal binding protein and of the protein disulphide isomerase, were also stimulated. It is proposed that, even in the absence of actual Zn starvation, the perception of deficiency conditions could trigger changes in redox homoeostasis at the plasma membrane level, helpful in compensating an O3-dependent oxidative damage.

Jasmonate-mediated defence responses, unlike salicylate-mediated responses, are involved in the recovery of grapevine from bois noir disease.

BACKGROUND: Bois noir is an important disease of grapevine (Vitis vinifera L.), caused by phytoplasmas. An interesting, yet elusive aspect of the bois noir disease is "recovery", i.e., the spontaneous and unpredictable remission of symptoms and damage. Because conventional pest management is ineffective against bois noir, deciphering the molecular bases of recovery is beneficial. The present study aimed to understand whether salicylate- and jasmonate-defence pathways might have a role in the recovery from the bois noir disease of grapevine. RESULTS: Leaves from healthy, bois noir-diseased and bois noir-recovered plants were compared, both in the presence (late summer) and absence (late spring) of bois noir symptoms on the diseased plants. Analyses of salicylate and jasmonate contents, as well as the expression of genes involved in their biosynthesis, signalling and action, were evaluated. In symptomatic diseased plants (late summer), unlike symptomless plants (late spring), salicylate biosynthesis was increased and salicylate-responsive genes were activated. In contrast, jasmonate biosynthesis and signalling genes were up-regulated both in recovered and diseased plants at all sampling dates. The activation of salicylate signalling in symptomatic plants might have antagonised the jasmonate-mediated defence response by suppressing the expression of jasmonate-responsive genes. CONCLUSIONS: Our results suggest that grapevine reacts to phytoplasma infection through salicylate-mediated signalling, although the resultant full activation of a salicylate-mediated response is apparently ineffective in conferring resistance against bois noir disease. Activation of the salicylate signalling pathway that is associated with the presence of bois noir phytoplasma seems to antagonise the jasmonate defence response, by failing to activate or suppressing both the expression of some jasmonate responsive genes that act downstream of the jasmonate biosynthetic pathway, as well as the first events of the jasmonate signalling pathway. On the other hand, activation of the entire jasmonate signalling pathway in recovered plants suggests the potential importance of jasmonate-regulated defences in preventing bois noir phytoplasma infections and the subsequent development of bois noir disease. Thus, on one hand, recovery could be achieved and maintained over time by preventing the activation of defence genes associated with salicylate signalling, and on the other hand, by activating jasmonate signalling and other defence responses.

Seed Oil from Ten Algerian Peanut Landraces for Edible Use and Biodiesel Production.

As a result of a recent ad hoc prospection of the Algerian territory, a collection of peanut (groundnut; Arachis hypogaea L.) landraces was established, covering a remarkable array of diversity in terms of morphological and physiological features, as well as of adaptation to local bioclimatic conditions. In the present work, the oils extracted from the seeds of these landraces were evaluated in terms of edible properties and suitability for biodiesel production. As for edible use, a low free acidity (ranging from 0.62 to 1.21%) and a high oleic acid content (44.61-50.94%) were common features, although a poor stability to oxidation [high peroxide values, high spectrophotometric indices, and low % of inhibition in the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH)· test] was observed in a few cases. As for biodiesel production, low values of acidity [1.23-2.40 mg KOH (g oil)(-1)], low iodine values [90.70-101.54 g I2 (g oil)(-1)], high cetane numbers (56.95-58.88) and high calorific values (higher heating value 37.34-39.27 MJ kg(-1)) were measured. Edible properties and suitability for biodiesel production were discussed with respect to the German standard DIN 51605 for rapeseed oil and to the EN 14214 standard, respectively. One way ANOVA and Hierarchical Cluster Analysis showed significant differences among the oils from the Algerian peanut landraces.

Gene expression induced by chronic ozone in the Mediterranean shrub Phillyrea latifolia: analysis by cDNA-AFLP.

Seedlings of Phillyrea latifolia L., a Mediterranean shrub, were exposed for 90 days to 110 nl l(-1) ozone (O(3)). Comparison of the cDNA-amplified fragment length polymorphism (cDNA-AFLP) patterns for treated and control plants allowed the identification and cloning of 88 differential sequences induced by O(3). The differential expression of 67 cloned sequences was further confirmed by RT-PCR. The functions of 36 cloned sequences, corresponding to seven of the twelve gene functional classes of Arabidopsis, were presumed on the basis of their homology with characterized gene sequences. Ozone induction of genes homologous to 24 of the clones has been reported in other plant species, whereas the induction of the 12 remaining sequences has not been observed before. Ozone activation of these newly identified genes could be a result of the chronic exposure to low O(3) concentration, because in most previous studies, acute treatments, involving high O(3) dosages, were applied. Possible roles of the cloned sequences in the response of P. latifolia to O(3) and other causes of oxidative stress are discussed.

Different compensatory mechanisms in two metal-accumulating aquatic macrophytes exposed to acute cadmium stress in outdoor artificial lakes.

Mechanisms underlying cadmium (Cd) detoxification were compared in two aquatic macrophytes commonly used in phytoremediation, namely Pistia stratiotes L. and Eichhornia crassipes (Mart.) Solms. To simulate Cd pollution in the open environment, plants growing in outdoor artificial lakes were exposed for 21d to either 25 or 100microM Cd, in two consecutive years. Toxicity symptoms were absent or mild in both species. Metal accumulation was much higher in the roots of P. stratiotes, whereas in E. crassipes a comparatively higher fraction was translocated to the leaves. In both species, Cd was neither included in phenolic polymers or Ca-oxalate crystals, nor altered the levels of Cd-complexing organic acids. Glutathione levels were constitutively remarkably higher and much more responsive to Cd exposure in P. stratiotes than in E. crassipes. Abundant phytochelatin synthesis occurred only in P. stratiotes, both in roots and in leaves. In E. crassipes, on the other side, the constitutive levels of some antioxidant enzymes and ascorbate were higher and more responsive to Cd than in P. stratiotes. Thus, in these two aquatic plants grown in the open, different detoxification mechanisms might come into play to counterbalance Cd acute stress.

On the role of H2O2 in the recovery of grapevine (Vitis vinifera cv. Prosecco) from Flavescence dorée disease.

In the present work, we compared hydrogen peroxide (H2O2) localisation and the activities/contents of antioxidant enzymes and metabolites in the leaf tissues of grapevine (Vitis vinifera L. cv. Prosecco) plants showing different sanitary status, namely diseased by Flavescence dorée, healthy or recovered. Polymerase chain reaction analysis revealed that the pathogen associated with Flavescence dorée (proposed as 'Candidatus Phytoplasma vitis') was detected in the leaf tissues of symptomatic plants, but was not observed in either the healthy or recovered plants. Hydrogen peroxide accumulated in the phloem plasmalemma of recovered grapevine leaves, but was not detected in either healthy or diseased material. When compared to diseased or healthy plants, recovered plants had distinctly lower extractable levels of catalase and ascorbate peroxidase, two enzymes primarily involved in the scavenging of excess H2O2 generated in different cell compartments. Among healthy, diseased and recovered leaves there was no significant difference in the amount of 2-thiobarbituric acid-reactive substances, which are assumed to reflect the extent of peroxidative breakdown of membrane lipids. Therefore, it is suggested that recovery from Flavescence dorée disease in grapevine might be associated with a long-term, sustained and tissue-specific accumulation of H2O2 in leaves, which reduces numbers or prevents further infection by Flavescence dorée phytoplasma. Recovered grapevine plants might be able to achieve such H2O2 accumulation through a selective and presumably stable downregulation of enzymatic H2O2 scavengers, without altering the levels of other antioxidant systems and without incurring an increased oxidative risk.

Iron deficiency induces sulfate uptake and modulates redistribution of reduced sulfur pool in barley plants.

We studied the possibility that the sulfur (S) assimilatory pathway might be modulated by iron (Fe) starvation in barley, as a consequence of plant requirement for an adequate amount of reduced S to maintain methionine and, in turn, phytosiderophore biosynthesis. Barley seedlings were grown with or without 100 µm FeIII-EDTA, at three S levels in the nutrient solution (S2 = 1200, S1 = 60, and S0 = 0 µm sulfate) in order to reproduce conditions of optimal supply, latent and severe deficiency, respectively. Fe deprivation increased root cysteine content irrespective of the S supply. However, this increase was not associated with either higher rates of 35SO42- uptake or increased expression of the gene for the high-affinity sulfate transporter, HvST1, and these roots failed to increase their activities of ATP sulfurylase (ATPS) and O-acetylserine(thiol) lyase (OASTL). We observed a significant increase in 35SO42- uptake rate (+76%) only in Fe-deficient S1 plants and we found an increase in root ATPS activity only in S0 plants. We observed an increase of ATPS enzyme activity in leaves of S1 and S2 plants, most likely suggesting increased S assimilation followed by translocation of thiols (Cys) to the root. Taken together, our results suggest that Fe deficiency affects the partitioning from the shoot to the root of the reduced S pool within the plant and can affect SO42- uptake under limited S supply.

Cadmium distribution and effects on ultrastructureand chlorophyll status in photobionts and mycobionts of Xanthoria parietina.

In this work, we tried to go deeper inside distribution and toxicity of cadmium (Cd) in the macrolichen Xanthoria parietina (L.) Th. Fr. Thalli of this species were treated with 0 (control), 4.5, 9, 18, or 36 muM Cd for 24 or 48 hours. Transmission electron microscopy, X-ray microanalysis, and electron energy loss spectroscopy were exploited to study distribution and ultrastructural effects of Cd in thalli; spectrophotometric techniques were utilized for measuring Cd effects on chlorophyll (Chl) content; light fluorescence microscopy was used to evaluate Chl autofluorescence. The highest Cd concentration caused ultrastructural alterations both in the mycobiont and in the photobiont, more severe in the latter, decreased total Chl content and progressively quenched Chl autofluorescence. Cell wall immobilization was observed in both bionts, and evidence pointing to a Cd-binding ability by the concentric bodies in the mycobiont was also obtained. Lower Cd concentrations led to slight or even no effects on thallus structures and on Chl content and autofluorescence. The results obtained suggest that: (1) among the two bionts, the algal partner appears to be more susceptible to Cd stress, probably because of the presence of delicate and sensitive components such as the chloroplast and photosynthetic pigments; (2) a concentration threshold exists for the occurrence of evident structural and functional damage in X. parietina thalli exposed to Cd.

Cell wall immobilisation and antioxidant status of Xanthoria parietina thalli exposed to cadmium.

Total and cell wall-bound cadmium and the major antioxidants were measured in thalli of the lichen Xanthoria parietina (L.) Th. Fr. exposed to two Cd concentrations, namely 4.5 or 9.0 µm, in liquid medium during exposure periods of either 24 or 48 h. Total Cd in the thalli was within the range of previous field measurements and was proportional to the exposure concentration, but less than proportional with respect to exposure duration. More than half of the total Cd was immobilised by the cell wall. The adopted conditions of Cd stress caused: (i) no changes in dry weight and protein concentration; (ii) an increase in the level of ascorbic acid and a decrease in that of reduced glutathione, as well as an increase in guaiacol peroxidase activity; (iii) no changes or moderate decreases in the activities of superoxide dismutase, catalase, dehydroascorbate-, NADPH-dependent glutathione disulfide-, and monodehydroascorbate reductases and of ascorbate peroxidase; (iv) an increase of the level of thiobarbituric acid-reactive substances, assumed to reflect malondialdehyde formation arising from membrane lipid peroxidation. Thus, X. parietina might withstand realistic levels of Cd stress by: (1) intercepting the heavy metal at cell wall level, (2) the intervention of antioxidant metabolites, and (3) a moderate increase in guaiacol peroxidase activity.

Responses of Xanthoria parietina thalli to environmentally relevant concentrations of hexavalent chromium.

Thalli of the lichen Xanthoria parietina (L.) Th. Fr. were soaked for either 24 or 48 h in a buffered medium in the presence of environmentally relevant concentrations (4.8 and 9.6 µM) of hexavalent chromium [Cr(VI)]. Treatment effects on the antioxidant status, differential distribution and fate of Cr(VI) among the mycobiont and the photobiont cells, and potential damage to cell ultrastructure in the two bionts, were evaluated. The adopted conditions of low Cr(VI) stress caused: (i) an increase in the level of ascorbic acid and a decrease in that of reduced glutathione, as well as a moderate increase in guaiacol peroxidase activity, only observed after treatment with 9.6 µM Cr(VI); (ii) no changes in malondialdehyde content; (iii) a remarkable Cr accumulation in the mycobiont cytosol and compartmentalisation in the mycobiont vacuoles;(iv) a modest apoplastic Cr immobilisation by the outer part of the cell walls, of both the mycobiont and the photobiont. The response of X.parietina to low concentrations of Cr(VI) appears to be a complex phenomenon, which might reflect maintenance of cellular homeostatic equilibria, rather than specific response pathways.

Coumarin inhibits the growth of carrot (Daucus carota L. cv. Saint Valery) cells in suspension culture.

We used a carrot (Daucus carota L. cv. Saint Valery) cell suspension culture as a simplified model system to study the effects of the allelochemical compound coumarin (1,2 benzopyrone) on cell growth and utilisation of exogenous nitrate, ammonium and carbohydrates. Exposure to micromolar levels of coumarin caused severe inhibition of cell growth starting from the second day of culture onwards. At the same time, the presence of 50 mumol/L coumarin caused accumulation of free amino acids and of ammonium in the cultured cells, and stimulated their glutamine synthetase, glutamate dehydrogenase, glucose-6-phosphate dehydrogenase and phosphoenolpyruvate carboxylase activities. Malate dehydrogenase, on the other hand, was inhibited under the same conditions. These effects were interpreted in terms of the stimulation of protein catabolism and/or interference with protein biosynthesis induced by coumarin. This could have led to a series of compensatory changes in the activities of enzymes linking nitrogen and carbon metabolism. Because coumarin seemed to abolish the exponential phase and to accelerate the onset of the stationary phase of cell growth, we hypothesise that such allelochemical compounds may act in nature as an inhibitor of the cell cycle and/or as a senescence-promoting substance.

A H2O2-forming peroxidase rather than a NAD(P)H-dependent O2•- synthase may be the major player in cell death responses controlled by the Pto-Fen complex following fenthion treatment.

Four tomato (Lycopersicon esculentum Mill.) near-isogenic lines were treated by foliar spraying with the insecticide fenthion. Two, Riogrande and Rimone, differed from each other only for the presence in the latter of the Fen gene, conferring propensity to develop foliar symptoms upon exposure to fenthion. The other two, namely RC332 and RC131, were the transgenic versions of Riogrande and Rimone, respectively, harbouring the Gox gene encoding for glucose oxidase of Aspergillus niger. The production of H2O2 as well as the activities of H+-ATPase, NAD(P)H-dependent superoxide synthase, catalase, peroxidase, and Cu,Zn-superoxide dismutase were evaluated in the foliar tissues up to 24 h after exposure to fenthion. The Fen gene conferred sensitivity to fenthion, regardless of the expression of a Gox transgene. A prolonged accumulation of H2O2 was observed in the leaves of Rimone and of RC131, which was instead transient in Riogrande and in RC332. In all the tomato lines, exposure to fenthion induced rapid but transient changes in the activities of most enzymes. The only exception was peroxidase activity in the leaves of Rimone and of RC131, which steadily increased until the end of the sampling period. It is suggested that the sensitivity of Rimone to fenthion might be due to the sustained activity of a H2O2-forming peroxidase.