Low pH (<5.0) can significantly decrease root growth but whether this is a direct effect of H(+) or an active plant response is examined here. Tomato (Solanum lycopersicum cv Micro-Tom) roots were ...exposed directly or gradually to low pH through step-wise changes in pH over periods ranging from 4 to 24 h. Roots exposed gradually to pH 4.5 grew even less than those exposed directly, indicating a plant-coordinated response. Direct exposure to pH 4.0 suppressed root growth and caused high cell mortality, in contrast to roots exposed gradually, in which growth remained inhibited but cell viability was maintained. Total class III peroxidase activity increased significantly in all low pH treatments, but was not correlated with the observed differential responses. Use of the enzyme inhibitors salicylhydroxamic acid (SHAM) or diphenyleneiodonium chloride (DPI) suggest that peroxidase and, to a lesser extent, NADPH oxidase were required to prevent or reduce injury in all low pH treatments. However, a role for other enzymes, such as the alternative oxidase is also possible. The results with SHAM, but not DPI, were confirmed in tobacco BY-2 cells. Our results indicate that root growth inhibition from low pH can be part of an active plant response, and suggest that peroxidases may have a critical early role in reducing loss of cell viability and in the observed root growth constraint.
The adverse effects of glyphosate herbicide on plants are well recognised, however, potential hormetic effects have not been well studied. This study aimed to use tomato as a model organism to ...explore the potential hormetic effects of glyphosate in water (0–30 mg L−1) and in compost soil (0–30 mg kg−1). The growth-promoting effects of glyphosate at concentrations of 0.03–1 mg L−1 in water or 0.03–1 mg kg−1 in compost were demonstrated in tomato for the first time. These hormetic effects were manifest as increased hypocotyl and radicle growth of seedlings germinated on paper towel soaked in glyphosate solution and also in crops which had been sprayed with glyphosate. Increased rates of photosynthesis (up to 2-fold) were observed in 4-week old crops when seeds were sown in compost amended with glyphosate and also when leaves were sprayed with glyphosate. The examination of chloroplast morphology using transmission electron microscopy revealed that the hormetic effects were associated with elongation of chloroplasts, possibly due to lateral expansion of thylakoid grana.
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•Glyphosate in soil or on leaves showed hormetic effects.•Enhanced growth was associated with elevated rates of photosynthesis.•Chloroplasts in leaves sprayed with glyphosate were elongated.
L-Galactono-1,4-lactone dehydrogenase (EC 1.3.2.3) catalyzes the last step in the main pathway of vitamin C (L-ascorbic acid) biosynthesis in higher plants. In this study, we first characterized the ...spatial and temporal expression of SlGalLDH in several organs of tomato (Solanum lycopersicum) plants in parallel with the ascorbate content. P₃₅S:SlgalldhRNAi silenced transgenic tomato lines were then generated using an RNAi strategy to evaluate the effect of any resulting modification of the ascorbate pool on plant and fruit development. In all P₃₅S:SlgalldhRNAi plants with reduced SlGalLDH transcript and activity, plant growth rate was decreased. Plants displaying the most severe effects (dwarf plants with no fruit) were excluded from further analysis. The most affected lines studied exhibited up to an 80% reduction in SlGalLDH activity and showed a strong reduction in leaf and fruit size, mainly as a consequence of reduced cell expansion. This was accompanied by significant changes in mitochondrial function and altered ascorbate redox state despite the fact that the total ascorbate content remained unchanged. By using a combination of transcriptomic and metabolomic approaches, we further demonstrated that several primary, like the tricarboxylic acid cycle, as well as secondary metabolic pathways related to stress response were modified in leaves and fruit of P₃₅S:SlgalldhRNAi plants. When taken together, this work confirms the complexity of ascorbate regulation and its link with plant metabolism. Moreover, it strongly suggests that, in addition to ascorbate synthesis, GalLDH could play an important role in the regulation of cell growth-related processes in plants.
SUMMARY
A major challenge in global crop production is mitigating yield loss due to plant diseases. One of the best strategies to control these losses is through breeding for disease resistance. One ...barrier to the identification of resistance genes is the quantification of disease severity, which is typically based on the determination of a subjective score by a human observer. We hypothesized that image‐based, non‐destructive measurements of plant morphology over an extended period after pathogen infection would capture subtle quantitative differences between genotypes, and thus enable identification of new disease resistance loci. To test this, we inoculated a genetically diverse biparental mapping population of tomato (Solanum lycopersicum) with Ralstonia solanacearum, a soilborne pathogen that causes bacterial wilt disease. We acquired over 40 000 time‐series images of disease progression in this population, and developed an image analysis pipeline providing a suite of 10 traits to quantify bacterial wilt disease based on plant shape and size. Quantitative trait locus (QTL) analyses using image‐based phenotyping for single and multi‐traits identified QTLs that were both unique and shared compared with those identified by human assessment of wilting, and could detect QTLs earlier than human assessment. Expanding the phenotypic space of disease with image‐based, non‐destructive phenotyping both allowed earlier detection and identified new genetic components of resistance.
Significance Statement
Plant diseases cause complex, quantitative phenotypes that can be difficult to assess accurately by visual assessment, which leads to challenges in detecting disease resistance loci. We developed a non‐destructive disease imaging and phenotyping pipeline and used it to capture disease progression in tomato (Solanum lycopersicum) plants inoculated with the bacterial pathogen Ralstonia solanacearum. We phenotyped for 10 traits from these images and visually assessed disease over time. Quantitative trait locus mapping with image‐based phenotyping for single and multi‐traits identified new genetic loci for resistance and detected loci earlier than those detected with visual assessment.
In the present study, we investigated whether cold plasma activation affected the efficacy of aerosolized hydrogen peroxide against S. Typhimurium and L. innocua. Stem scars and smooth surfaces of ...grape tomatoes, surfaces of Granny Smith apples and Romaine lettuce (both midrib and upper leaves) and cantaloupe rinds were inoculated with two-strain cocktails of S. Typhimurium and 3-strain cocktails of L. innocua. The inoculated samples were treated with 7.8% aerosolized H2O2 with and without cold plasma for various times. For all fresh produce items and surfaces, cold plasma significantly (P < 0.05) improved the efficacy of aerosolized H2O2 against Salmonella and L. innocua. Without cold plasma activation, H2O2 aerosols only reduced populations of Salmonella by 1.54–3.17 log CFU/piece while H2O2 with cold plasma achieved 2.35–5.50 log CFU/piece reductions of Salmonella. L. innocua was more sensitive to the cold plasma-activated H2O2 than Salmonella. Cold plasma activated H2O2 aerosols reduced Listeria populations by more than 5 log CFU/piece on all types and surfaces of fresh produce except for the tomato stem scar area. Without cold plasma, the reductions by H2O2 were only 1.35–3.77 log CFU/piece. Overall, our results demonstrated that cold plasma activation significantly enhanced the efficacy of H2O2 mist against bacteria on fresh produce.
•Ionization of H2O2 mist was achieved by passing through a cold plasma.•Cold plasma enhanced the efficacy of H2O2 mist against Salmonella and Listeria.•The ionized H2O2 was more effective against Listeria than against Salmonella.•Bacteria on smooth surfaces were easier to inactivate than those on rough surfaces.
The increases in atmospheric carbon dioxide (CO₂) concentrations can enhance plant growth and change their nutrient demands. We report that when tomato (Lycopersicon esculentum 'Zheza 809') plants ...were grown in iron (Fe)-limited medium (with hydrous ferric iron oxide) and elevated CO₂ (800 μL L⁻¹), their biomass and root-to-shoot ratio were greater than plants grown in ambient CO₂ (350 μL L⁻¹). Furthermore, the associated increase in Fe concentrations in the shoots and roots alleviated Fe-deficiency-induced chlorosis. Despite the improved nutrient status of plants grown in Fe-limited medium under elevated CO₂, the Fe-deficiency-induced responses in roots, including ferric chelate reductase activity, proton secretion, subapical root hair development, and the expression of FER, FRO1, and IRT genes, were all greater than plants grown in the ambient CO₂. The biomass of plants grown in Fe-sufficient medium was also increased by the elevated CO₂ treatment, but changes in tissue Fe concentrations and Fe deficiency responses were not observed. These results suggest that the improved Fe nutrition and induction of Fe-deficient-induced responses in plants grown in Fe-limited medium under elevated CO₂ are caused by interactions between elevated CO₂ and Fe deprivation. Elevated CO₂ also increased the nitric oxide (NO) levels in roots, but treatment with the NO scavenger cPTIO inhibited ferric chelate reductase activity and prevented the accumulation of LeFRO1, LeIRT1, and FER transcripts in roots of the Fe-limited plants. These results implicate some involvement of NO in enhancing Fe-deficiency-induced responses when Fe limitation and elevated CO₂ occur together. We propose that the combination of elevated CO₂ and Fe limitation induces morphological, physiological, and molecular responses that enhance the capacity for plants to access and utilize Fe from sparingly soluble sources, such as Fe(III)-oxide.
•Cold promotes accumulation of putrescine (Put) and jasmonic acid (JA).•JA increases Put accumulation and cold tolerance.•Suppression of JA signaling reduces Put accumulation.•JA-regulated Put ...biosynthesis attenuates cold-triggered oxidative stress.
Previous studies have shown that jasmonic acid (JA) and putrescine (Put), a major polyamine, are both accumulated in tomato plants upon cold treatment. However, it is unclear whether JA regulates Put biosynthesis in tomato plants under the cold condition. The goal of the present work was to determine whether JA regulates Put biosynthesis and how JA-regulated Put accumulation affects cold tolerance in tomato plants. We found that among three major polyamines, putrescine was predominantly accumulated in cold-stressed tomato plants and exogenous putrescine markedly alleviated cold-induced oxidative stress, indicating an important role of putrescine in tomato cold response. We then identified ADC1 as a major putrescine biosynthetic gene in response to cold and JA. Further experiments using a JA biosynthesis inhibitor sodium diethyldithiocarbamate (DIECA), MeJA and an ADC (arginine decarboxylase 1) enzyme inhibitor difluoromethylarginine (DFMA) confirmed that JA functions in the putrescine biosynthesis by acting on ADC. Finally, we found that RNAi-mediated suppression of MYC2, a master regulator of JA signaling, decreased the expression of ADC1, reduced putrescine accumulation and enhanced cold-induced oxidative damages, implying that JA-induced putrescine biosynthesis relies, at least partially, on MYC2 in tomato plants. Our study thus establishes a link between JA signaling and polyamine metabolism in tomato plants under cold stress. Our data support that JA signaling is crucial for putrescine biosynthesis during cold stress and JA-induced accumulation of putrescine mitigates cold-induced oxidative stress in plants.
Physical interaction between two proteins is strong evidence that the proteins are involved in the same biological process, making Protein-Protein Interaction (PPI) networks a valuable data resource ...for predicting the cellular functions of proteins. However, PPI networks are largely incomplete for non-model species. Here, we tested to what extent these incomplete networks are still useful for genome-wide function prediction. We used two network-based classifiers to predict Biological Process Gene Ontology terms from protein interaction data in four species: Saccharomyces cerevisiae, Escherichia coli, Arabidopsis thaliana and Solanum lycopersicum (tomato). The classifiers had reasonable performance in the well-studied yeast, but performed poorly in the other species. We showed that this poor performance can be considerably improved by adding edges predicted from various data sources, such as text mining, and that associations from the STRING database are more useful than interactions predicted by a neural network from sequence-based features.
Plant sulfite reductase (SiR; Enzyme Commission 1.8.7.1) catalyzes the reduction of sulfite to sulfide in the reductive sulfate assimilation pathway. Comparison of SiR expression in tomato (Solatium ...lycopersicum 'Rheinlands Ruhm') and Arabidopsis (Arabidopsis thaliana) plants revealed that SiR is expressed in a different tissue-dependent manner that likely reflects dissimilarity in sulfur metabolism between the plant species. Using Arabidopsis and tomato SiR mutants with modified SiR expression, we show here that resistance to ectopically applied sulfur dioxide/sulfite is a function of SiR expression levels and that plants with reduced SiR expression exhibit higher sensitivity than the wild type, as manifested in pronounced leaf necrosis and chlorophyll bleaching. The sulfite-sensitive mutants accumulate applied sulfite and show a decline in glutathione levels. In contrast, mutants that overexpress SiR are more tolerant to sulfite toxicity, exhibiting little or no damage. Resistance to high sulfite application is manifested by fast sulfite disappearance and an increase in glutathione levels. The notion that SiR plays a role in the protection of plants against sulfite is supported by the rapid up-regulation of SiR transcript and activity within 30 min of sulfite injection into Arabidopsis and tomato leaves. Peroxisomal sulfite oxidase transcripts and activity levels are likewise promoted by sulfite application as compared with water injection controls. These results indicate that, in addition to participating in the sulfate assimilation reductive pathway, SiR also plays a role in protecting leaves against the toxicity of sulfite accumulation.
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