Stress In Tomato Plants Research Articles

Bacillus megaterium strain A12 ameliorates salinity stress in tomato plants through multiple mechanisms

ABSTRACT Plants must cope with the stress conditions to survive. Plant growth promoting rhizobacteria can improve plant growth either directly or indirectly under stress conditions. However, the possible mechanisms remain unclear. Here we report that Bacillus megaterium strain A12 (BMA12) maintains hormonal and redox homeostasis and restores the photosynthetic efficacy of tomato plants through multiple mechanisms to survive under salinity stress conditions. Tomato plants were co-cultivated with BMA12 under saline conditions. The application of BMA12 significantly increased plant growth and photosynthetic capacity. BMA12 decreased production of ROS and ethylene but increased expression levels of selected genes responsible for repairing of damaged photosynthetic apparatus and maintenance of redox homeostasis. Furthermore, BMA12 significantly altered metabolic profile to restore perturbations of tomato plant physiology impaired with salinity stress. This study proves that BMA12 can be used in the conventional agriculture system in the salinity effected fields.

Functional analyses of lipocalin proteins in tomato.

In this study, two temperature-induced lipocalin genes SlTIL1 and SlTIL2, and a chloroplastic lipocalin gene SlCHL were isolated from 'Micro-Tom' tomato. The coding sequences of SlTIL1, SlTIL2 and SlCHL were 558, 558, and 1002 bp, respectively. By TargetP analysis, no characteristic transit peptides were predicted in the proteins of SlTIL1 and SlTIL2, while a chloroplastic transit peptide was predicted in the protein of SlCHL. The subcellular localization results indicated that SlTIL1 and SlTIL2 proteins were major localized in the plasma membrane, while SlCHL was localized in chloroplast. To understand the function of lipocalins, transgenic tomato over-expressed SlTIL1, SlTIL2 and SlCHL and their virus-induced gene silencing (VIGS) plants were generated. The phenotypes were significantly affected when the SlTIL1, SlTIL2 and SlCHL were over-expressed or silenced by VIGS, which suggested that the three lipocalins played important roles in regulating the growth and development of tomato. In addition, the level of ROS (O2 - and H2O2) was low in SlTIL1, SlTIL2 and SlCHL over-expressed plants, while it was high in their silenced plants. The changes in the expression of SODs were consistent with the accumulations of ROS, which indicated that lipocalins might have an important role in abiotic oxidative stress tolerance in tomato plants. Especially SlTIL1 and SlTIL2 are localized around their membranes and protect them from ROS. The results will contribute to elucidating the functions of lipocalin in plants, and provide new strategies to improve the tolerance to abiotic stress in tomato plants.

Molecular and biochemical characterization of oxidative stress in tomato plants cultivated with lead (Pb)

Molecular and biochemical characterization of oxidative stress in tomato plants cultivated with lead (Pb)

Growth and metabolic adjustments in response to gibberellin deficiency in drought stressed tomato plants

Gibberellins (GAs) have been shown to be involved in the tolerance of plants to a range of environmental stresses. However, the physiological and metabolic implications of altered levels of GAs in plants under drought stress remain largely unknown. To understand the contribution of GAs for the responses to water deficit conditions, physiological and metabolic parameters were evaluated in tomato deficient mutants in GAs biosynthesis, gib1, gib2, and gib3. Interestingly, the mutants maintained leaf water content over a longer time period and recovered photosynthesis faster than wild-type (WT) plants. Furthermore, gib1 and gib2 plants showed no apparent wilt even after reaching low leaf water potential (-1.3 MPa). Additionally, mutants plants partitioned more biomass to the roots than shoots compared to WT. The maintenance of leaf water content and consequent increased water use efficiency observed in the mutants can be explained by the osmotic adjustment of leaf and root cells, mainly due to amino acid accumulation. Collectively, our results suggest that plants with reduced GAs content are able to cope with water deprivation by increasing proline and other amino acid levels. This response, alongside partitioning of carbon to roots allows GAs-deficient plants to maintain the leaf turgor for a longer time and thereby promotes water deficit tolerance.

Exogenous GSH protects tomatoes against salt stress by modulating photosystem II efficiency, absorbed light allocation and H2O2-scavenging system in chloroplasts

The effects of exogenous GSH (reduced glutathione) on photosynthetic characteristics, photosystem II efficiency, absorbed light energy allocation and the H2O2-scavenging system in chloroplasts of salt-stressed tomato (Solanum lycopersicum L.) seedlings were studied using hydroponic experiments in a greenhouse. Application of exogenous GSH ameliorated saline-induced growth inhibition, the disturbed balance of Na+ and Cl− ions and Na+/K+ ratios, and the reduction of the net photosynthetic rate (Pn). GSH also increased the maximal photochemical efficiency of PSII (Fv/Fm), the electron transport rate (ETR), the photochemical quenching coefficient (qP), and the non-photochemical quenching coefficient (NPQ). In addition, GSH application increased the photochemical quantum yield (Y(II)) and relative deviation from full balance between the photosystems (β/α–1) and decreased the PSII excitation pressure (1–qP) and quantum yield of non-regulated energy dissipation (Y(NO)) in leaves of salt-stressed tomatoes without BSO (L-buthionine-sulfoximine, an inhibitor of key GSH synthesis enzyme γ-glutamylcysteine synthetase) or with BSO. Further, the addition of GSH depressed the accumulation of H2O2 and malondialdehyde (MDA), induced the redistribution of absorbed light energy in PSII reaction centers, and improved the endogenous GSH content, GSH/GSSH ratio and activities of H2O2-scavenging enzymes (including superoxidase dismutase (SOD), catalase (CAT), peroxidase (POD) and key enzymes in the AsA-GSH cycle and Grx system) in the chloroplasts of salt-stressed plants with or without BSO. Therefore, GSH application alleviates inhibition of salt-induced growth and photosynthesis mainly by overcoming stomatal limitations, improving the PSII efficiency, and balancing the uneven distribution of light energy to reduce the risk of ROS generation and to mediate chloroplast redox homeostasis and the antioxidant defense system to protect the chloroplasts from oxidative damage. Thus, GSH may be used as a potential tool for alleviating salt stress in tomato plants.

Effect of abscisic acid on the calcium content for controlling blossom-end rot in tomato under water stress

ABSTRACT Water stress in tomato plants may cause the incidence of blossom-end rot. This study aimed to analyze the effect of abscisic acid leaf application for increasing the calcium uptake in irrigated tomato (‘Santa Clara' cultivar) in the field, as a possible mechanism of blossom-end rot inhibition. The treatments consisted of four irrigation levels (25 %, 50 %, 75 % and 100 % of the crop water requirements to fulfil the crop evapotranspiration) and two abscisic acid doses (0 mg L-1 and 500 mg L-1). The fruits were harvested at 15 and 30 days after the anthesis and evaluated for calcium content and percentage of blossom-end rot. The application of abscisic acid increased the calcium partition to the distal region of the fruits at 30 days after the beginning of flowering, as well as reduced the incidence of blossom-end rot by 86 %, when compared with plants not treated with abscisic acid. It is possible to conclude that the foliar application of abscisic acid can significantly reduce the incidence of blossom-end rot.

Effect of several commercial seaweed extracts in the mitigation of iron chlorosis of tomato plants (Solanum lycopersicum L.)

Commercial seaweed extracts (SWEs) have been applied in agriculture for ameliorating biotic and abiotic stress in plants. However, the mechanisms of action of these extracts are only partially known. Most of the research work with SWEs has focused on abiotic stresses such as drought, salinity or high temperatures, but little is known about SWE effects on plants with nutrient imbalances. Therefore, the goal of this study was to investigate the effects of several commercial SWEs (based on Ascophyllum nodosum and Durvillea potatorum) in the mitigation of iron chlorosis of stressed tomato plants. Tomato plants were grown in a hydroponic system initially with Fe, and then Fe was removed from the nutrient solution. SWEs were applied twice, first during the growth period (+ Fe) and second at the beginning of Fe deficiency (− Fe), following the recommended doses of manufacturers. Some of SWE treatments activated the antioxidant system in Fe-deficient tomato plants increasing SOD and CAT activity. However, SWEs application did not produce positive effects on biomass, chlorophyll content, activation of Fe acquisition strategies and Fe uptake with respect to the untreated control.

Inoculation of tomato plants with selected PGPR represents a feasible alternative to chemical fertilization under salt stress

AbstractPlant growth‐promoting rhizobacteria (PGPR) are soil bacteria that colonize the rhizosphere of plants, enhance plant growth, and may alleviate environmental stress, thus constituting a powerful tool in sustainable agriculture. Here, we compared the capacity of chemical fertilization to selected PGPR strains to promote growth and alleviate salinity stress in tomato plants (Solanum lycopersicum L.). A pot experiment was designed with two main factors: fertilization (chemical fertilization, bacterial inoculation with seven PGPR, or a non‐fertilized non‐inoculated control) and salt stress (0 or 100 mM NaCl). In the absence of stress, a clear promotion of growth, a positive effect on plant physiology (elevated Fv/Fm), and enhanced N, P, and K concentrations were observed in inoculated plants compared to non‐fertilized controls. Salinity negatively affected most variables analyzed, but inoculation with certain strains reduced some of the negative effects on growth parameters and plant physiology (water loss and K+ depletion) in a moderate but significant manner. Chemical fertilization clearly exceeded the positive effects of inoculation under non‐stressed conditions, but conversely, biofertilization with some strains outperformed chemical fertilization under salt stress. The results point at inoculation with selected PGPR as a viable economical and environment‐friendly alternative to chemical fertilization in salinity‐affected soils.

Discrimination between abiotic and biotic drought stress in tomatoes using hyperspectral imaging

Crop plants are subjected to various biotic and abiotic stresses. Both root-knot nematodes (biotic stress) and water deficiency (abiotic stress) lead to similar drought symptoms in the plant canopy. In this work, hyperspectral imaging was used for early detection of nematode infestation and water deficiency (drought) stress in tomato plants. Hyperspectral data in the range from 400 to 2500 nm of plants subjected to different watering regimes and nematode infestation levels were analysed by partial least squares – discriminant analysis (PLS-DA) and partial least squares – support vector machine (PLS-SVM) classification. PLS-SVM classification achieved up to 100% accuracy differentiating between well-watered and water-deficient plants, and between 90 and 100% when identifying nematode-infested plants. Grouping the data according to the time of imaging increased the accuracy of classification. Shortwave infrared spectral regions associated with the OH and CH stretches were most relevant for the identification of nematode infested plants and severity of infestation. This study demonstrates the capability of hyperspectral imaging to identify and discriminate between biotic and abiotic plant stresses.

Ascophyllum nodosum extract biostimulants and their role in enhancing tolerance to drought stress in tomato plants

Global changes in climate are leading to increased occurrence and duration of drought episodes with concurrent reduction in crop yields. Expansion of the irrigated land area does not appear to be a viable solution in many regions to deliver crop productivity. The development of crop drought tolerance traits by either genetic modification or plant breeding represent the principal approaches to meeting this challenge to date. Biostimulants are an emerging category of crop management products which can enhance crop productivity under abiotic stress conditions. The ability of some biostimulant products such as Ascophyllum nodosum extracts (ANE) to enhance the tolerance of crops to drought stress has been observed by growers. The objective of this study was to investigate if different commercial ANE biostimulants provided the same tolerance to tomato plants (cv. Moneymaker) subjected to a defined drought period. A compositional characterisation of the key macromolecules of ANEs was performed. In addition, the role of ANE biostimulants in inducing changes of chlorophyll and osmolytes levels, MDA production, dehydrin isoform pattern and dehydrin gene expression levels was assessed. The three ANE biostimulants evaluated were found to provide different levels of tolerance to drought stressed tomato plants. The level of drought tolerance provided was related to changes in the concentration of osmolytes and expression of tas14 dehydrin gene. Taken together, our results highlight that despite the fact all ANE biostimulants were manufactured from the same raw material, their ability to maintain crop productivity during and after drought stress was not the same.

Mitigation of abiotic stresses in Lycopersicon esculentum by endophytic bacteria

In this paper, we emphasize the role of endophytic bacterial strains viz. Bacillus subtilis, two strains of Pseudomonas sp. in mitigating drought and salinity stress in tomato plants. Uninoculated or control plants showed arrested growth; while endophytic bacteria inoculated plants had appreciably higher plant biomass and chlorophyll contents under draught and salinity stress. The improving effects of endophytic bacterial inoculation were also substantiated by the augmented water potential and diminished electrolytic leak. Endophytic bacterial treated plants had copiously present K+ and P+ ions while less Na+ ion concentration in contrast to uninoculated under stress. The oxidative stress was reduced by endophytes through lessened activities of total polyphenol and enzymes catalase, peroxidase, polyphenol oxidase, as compared to the uninoculated plants. Uninoculated plants exhibited up-regulation of stress-responsive abscisic acid as compared to endophyte treated plants, while salicylic acid (SA) and gibberellin 4 were considerably higher in endophytic treated plants. In inference, application of endophytic bacterial strains may be used in relegated agricultural lands to upsurge crop sustainability and productivity.

H2O2 mediates ALA-induced glutathione and ascorbate accumulation in the perception and resistance to oxidative stress in Solanum lycopersicum at low temperatures

BackgroundLow temperature is a crucial factor influencing plant growth and development. The chlorophyll precursor, 5-aminolevulinic acid (ALA) is widely used to improve plant cold tolerance. However, the interaction between H2O2 and cellular redox signaling involved in ALA-induced resistance to low temperature stress in plants remains largely unknown. Here, the roles of ALA in perceiving and regulating low temperature-induced oxidative stress in tomato plants, together with the roles of H2O2 and cellular redox states, were characterized.ResultsLow concentrations (10–25 mg·L− 1) of ALA enhanced low temperature-induced oxidative stress tolerance of tomato seedlings. The most effective concentration was 25 mg·L− 1, which markedly increased the ratio of reduced glutathione and ascorbate (GSH and AsA), and enhanced the activities of superoxide dismutase, catalase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase. Furthermore, gene expression of respiratory burst oxidase homolog1 and H2O2 content were upregulated with ALA treatment under normal conditions. Treatment with exogenous H2O2, GSH, and AsA also induced plant tolerance to oxidative stress at low temperatures, while inhibition of GSH and AsA syntheses significantly decreased H2O2-induced oxidative stress tolerance. Meanwhile, scavenging or inhibition of H2O2 production weakened, but did not eliminate, GSH- or AsA- induced tomato plant tolerance to oxidative stress at low temperatures.ConclusionsAppropriate concentrations of ALA alleviated the low temperature-induced oxidative stress in tomato plants via an antioxidant system. The most effective concentration was 25 mg·L− 1. The results showed that H2O2 induced by exogenous ALA under normal conditions is crucial and may be the initial step for perception and signaling transmission, which then improves the ratio of GSH and AsA. GSH and AsA may then interact with H2O2 signaling, resulting in enhanced antioxidant capacity in tomato plants at low temperatures.

Effects of Chitosan-PVA and Cu Nanoparticles on the Growth and Antioxidant Capacity of Tomato under Saline Stress.

Chitosan is a natural polymer, which has been used in agriculture to stimulate crop growth. Furthermore, it has been used for the encapsulation of nanoparticles in order to obtain controlled release. In this work, the effect of chitosan–PVA and Cu nanoparticles (Cu NPs) absorbed on chitosan–PVA on growth, antioxidant capacity, mineral content, and saline stress in tomato plants was evaluated. The results show that treatments with chitosan–PVA increased tomato growth. Furthermore, chitosan–PVA increased the content of chlorophylls a and b, total chlorophylls, carotenoids, and superoxide dismutase. When chitosan–PVA was mixed with Cu NPs, the mechanism of enzymatic defense of tomato plants was activated. The chitosan–PVA and chitosan–PVA + Cu NPs increased the content of vitamin C and lycopene, respectively. The application of chitosan–PVA and Cu NPs might induce mechanisms of tolerance to salinity.

The Impacts of Silicon and Salicylic Acid Amendments on Yield and Fruit Quality of Salinity Stressed Tomato Plants

The Impacts of Silicon and Salicylic Acid Amendments on Yield and Fruit Quality of Salinity Stressed Tomato Plants

Silver nanoparticles induced genotoxicity and oxidative stress in tomato plants

Among nanoparticles, silver nanoparticles (AgNPs) are intensively used in many materials owing to their antibacterial effects. In the present study different concentrations of AgNPs in Hoagland solution were applied to tomato seedlings. Total chlorophyll content, relative water content (RWC), antioxidant enzyme activities, and malondialdehyde content (MDA) as well as the genomic template stability (GTS) were analyzed. The intersimple sequence repeat polymerase chain reaction assay (ISSR-PCR) was used to determine the genotoxic effects of AgNPs on DNA. RWC did not change under AgNPs treatments; however, total chlorophyll content was significantly reduced by AgNPs applications. ISSR profiles demonstrated a consistent increase in polymorphic bands by the increase in the concentration of AgNPs. GTS value was also reduced depending on the concentration of AgNPs. SOD and APX activities were increased under low AgNPs treatments; however, these activities were decreased under high concentrations of AgNPs treatments. Tomato plants could be sensitive to AgNPs within the increase in MDA content in all of the AgNPs treatments. AgNPs nanotoxicity could be quite dose-dependent. AgNPs could also have negative effects on tomato plants by enhancing DNA damage and lipid peroxidation.

Overexpression of a Calvin cycle enzyme SBPase improves tolerance to chilling-induced oxidative stress in tomato plants

Sedoheptulose-1,7-bisphosphatase (SBPase) is a critical enzyme involved in photosynthetic carbon fixation in the Calvin cycle. Here, we report the effects of SBPase overexpression on the tolerance to chilling-induced oxidative stress in transgenic tomato (Solanum lycopersicum) plants. In transgenic plants overexpressing SBPase, CO2 fixation and carbohydrate accumulation were increased in comparison with equivalent wild-type plants. SBPase was found to be susceptible to oxidative stress and the activity was substantially inhibited by reactive oxygen species both in vivo and in vitro. In response to chilling stress, production of H2O2 was increased in parallel with the reduction in SBPase activity in tomato plants, however, transgenic plants maintained significantly higher SBPase activity than wild-type plants did. Under chilling stress, compared with wild-type plants, transgenic plants were found to have increased CO2 fixation and reduced electrolyte leakage. The overall tolerance could be ascribed to the enhancement of photosynthetic carbon fixation, the reductions in the level of H2O2 and the increased accumulation of carbohydrate in transgenic plants. Collectively, our data suggest that high level of SBPase activity gives an advantage to photosynthetic carbon fixation and tolerance to chilling-induced oxidative stress in tomato plants. This work presents a case study that an individual enzyme in the Calvin cycle may be a useful target for genetically engineering stress tolerance in horticultural crops.

Soil salinity increases the tolerance of excessive sulfur fumigation stress in tomato plants

To investigate the responses of plant photosynthesis and chlorophyll fluorescence to excessive sulfur fumigation stress (Sulfur) alleviated by pre-treated salt in the soil (Salt), seedlings of a tomato cultivar (Solanum lycopersicum L. ‘Money Maker’) were exposed to the Sulfur with or without the Salt treatment for 15h. Leaf fresh weight, dry weight, chlorophyll (Chl) content, carotenoid (Car) content, photosynthesis and chlorophyll fluorescence parameters were measured. The results showed that the Sulfur treatment significantly decreased leaf fresh weight, dry weight, Chl and Car contents, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum quantum efficiency of photosystem II (PSII) photochemistry (Fv/Fm), actual photochemical efficiency of PSII (ФPSII), photochemical quenching coefficient (qP), electron transport rate (ETR), and the effective quantum yield of PSII photochemistry (F′v/F′m). In addition, the Sulfur treatment significantly increased intercellular CO2 concentration (Ci) and non-photochemical quenching coefficients (qN). Plants in soil pre-treated with salt clearly experienced less damage from sulfur toxicity, and these plants were able to retain higher leaf mass per area, greater total Chl and Car contents and photosynthetic activities, and to maintain the integrity of their chlorophyll fluorescence systems than fumigated plants growing in soil that was not pre-treated. Reduced leaf photosynthesis in the Sulfur treatment was due to non-stomatal limitation, and to disturbance of the chlorophyll fluorescence system which needs more energy consumption for thermal dissipation. Our results showed that a cross-tolerance exists between the salt stress and extreme sulfur fumigation stress, and plants pre-treated with salt provided some protection against excessive sulfur toxicity.

Melatonin enhances thermotolerance by promoting cellular protein protection in tomato plants.

Melatonin is a pleiotropic signaling molecule that provides physiological protection against diverse environmental stresses in plants. Nonetheless, the mechanisms for melatonin-mediated thermotolerance remain largely unknown. Here, we report that endogenous melatonin levels increased with a rise in ambient temperature and that peaked at 40°C. Foliar pretreatment with an optimal dose of melatonin (10μmol/L) or the overexpression of N-acetylserotonin methyltransferase (ASMT) gene effectively ameliorated heat-induced photoinhibition and electrolyte leakage in tomato plants. Both exogenous melatonin treatment and endogenous melatonin manipulation by overexpression of ASMT decreased the levels of insoluble and ubiquitinated proteins, but enhanced the expression of heat-shock proteins (HSPs) to refold denatured and unfolded proteins under heat stress. Meanwhile, melatonin also induced expression of several ATG genes and formation of autophagosomes to degrade aggregated proteins under the same stress. Proteomic profile analyses revealed that protein aggregates for a large number of biological processes accumulated in wild-type plants. However, exogenous melatonin treatment or overexpression of ASMT reduced the accumulation of aggregated proteins. Aggregation responsive proteins such as HSP70 and Rubisco activase were preferentially accumulated and ubiquitinated in wild-type plants under heat stress, while melatonin mitigated heat stress-induced accumulation and ubiquitination of aggregated proteins. These results suggest that melatonin promotes cellular protein protection through induction of HSPs and autophagy to refold or degrade denatured proteins under heat stress in tomato plants.

Erratum to: Potential of Fusarium wilt-inducing chlamydospores, in vitro behaviour in root exudates and physiology of tomato in biochar and compost amended soil

Biochars are recognised for their ability to improve soil functions and to stimulate plant defense mechanisms. We evaluated the response of Fusarium oxysporum f. sp. lycopersici chlamydospores to tomato plants grown in biochar and compost amended soil to get a deeper insight into the tomato-Fusarium pathosystem. Wood chips and green waste biochar in combination with compost (‘WCBcomp and GWBcomp’ respectively) were studied for their ability to suppress the Fusarium chlamydospores infectivity. Plant growth parameters and in vitro effects on chlamydospores were determined. The ‘GWBcomp’ soil amendment stimulated plants growth and gaseous exchange rates and had a suppressive effect on the chlamydospore infectivity in comparison with the ‘WCBcomp’ treatment and the treatment containing compost only. The germination rate of chlamydospores was unaffected by the source of root exudates, whereas the mycelial growth was significantly higher in root exudates from chlamydospore inoculated plants grown in ‘WCBcomp’ amended soil unlike to ‘GWBcomp’ amended soil. Overall, our findings indicate that both biochars had a variable effect on chlamydospores. We conclude that soil amendment with garden waste biochar and compost exhibit a great potential in suppressing Fusarium chlamydospore infectivity and alleviating pathogen–induced physiological stress in tomato plants.

Melatonin mediates selenium-induced tolerance to cadmium stress in tomato plants.

Both selenium (Se) and melatonin reduce cadmium (Cd) uptake and mitigate Cd toxicity in plants. However, the relationship between Se and melatonin in Cd detoxification remains unclear. In this study, we investigated the influence of three forms of Se (selenocysteine, sodium selenite, and sodium selenate) on the biosynthesis of melatonin and the tolerance against Cd in tomato plants. Pretreatment with different forms of Se significantly induced the biosynthesis of melatonin and its precursors (tryptophan, tryptamine, and serotonin); selenocysteine had the most marked effect on melatonin biosynthesis. Furthermore, Se and melatonin supplements significantly increased plant Cd tolerance as evidenced by decreased growth inhibition, photoinhibition, and electrolyte leakage (EL). Se-induced Cd tolerance was compromised in melatonin-deficient plants following tryptophan decarboxylase (TDC) gene silencing. Se treatment increased the levels of glutathione (GSH) and phytochelatins (PCs), as well as the expression of GSH and PC biosynthetic genes in nonsilenced plants, but the effects of Se were compromised in TDC-silenced plants under Cd stress. In addition, Se and melatonin supplements reduced Cd content in leaves of nonsilenced plants, but Se-induced reduction in Cd content was compromised in leaves of TDC-silenced plants. Taken together, our results indicate that melatonin is involved in Se-induced Cd tolerance via the regulation of Cd detoxification.