Tolerance Of Tomato Plants Research Articles

Inoculation with Rhizobacteria Enhanced Tolerance of Tomato (Solanum lycopersicum L.) Plants in Response to Cadmium Stress

In this study, cadmium (Cd)-tolerant bacteria Serratia sp. D23 (D23) and Sphingomonas sp. D36 (D36) were isolated from Cd-contaminated rhizospheric soil. Both strains have indole-3-acetic acid production, phosphate solubilization and siderophores production ability. A hydroponic experiment was performed to evaluate the effect of D23 and D36 on Cd toxicity and Cd content in tomato plants. The results indicated that under Cd-stressed condition, D23 and D36 inoculation increased photosynthetic pigment content in tomato leaves and decreased malonyldialdehyde level in tomato roots (p < 0.05). Both strains could alleviate Cd-induced inhibition of dry mass accumulation, D23 inoculation increased the root and leaf dry mass by 44.95% and 99.13%, while D36 treatment increased the root and leaf dry mass by 41.56% and 46.81%, respectively. Besides, D23 treatment reduced the Cd content in tomato root by 46.70%, and D36 inoculation reduced the Cd content in root and leaf by and 27.63% and 35.41%. Moreover, the expression of stress-related genes, including Hsp90, MT2 and Nramp3 were enhanced by bacterial inoculation. The subcellular localization of Cd and the activity of antioxidant enzyme were also influenced by D23 and D36 colonization. Taken together, rhizobacteria D23 and D36 could alleviate Cd toxicity and reduce Cd concentration in tomato plants via alleviating oxidative stress, modulating Cd subcellular localization and upregulating stress-related gene expression. This study provides evidence of enhancing Cd tolerance in tomato plants via rhizosphere bacteria and will be helpful to establish bacterial-assisted approach for alleviating heavy metal toxicity in plants.

Coumarin improves tomato plant tolerance to salinity by enhancing antioxidant defence, glyoxalase system and ion homeostasis.

Salinity is a severe threat to crop growth, development and even to world food sustainability. Plant possess natural antioxidant defense tactics to mitigate salinity-induced oxidative stress. Phenolic compounds are non-enzymatic antioxidants with specific roles in protecting plant cells against stress-mediated reactive oxygen species (ROS) generation. Coumarin (COU) is one of these compounds, however, to date, little is known about antioxidative roles of exogenous COU in enhancing plant tolerance mechanisms under salt stress. The involvement of COU in increasing tomato salt tolerance was examined in the present study using COU as a pre-treatment at 20 or 30µM for 2days against salt stress (100 or 160 NaCl; 5days). The COU-mediated stimulation of plant antioxidant defence and glyoxalase systems to suppress salt-induced ROS and methylglyoxal (MG) toxicity, respectively, were the main hypotheses examined in the present study. Addition of COU suppressed salt-induced excess accumulation of ROS and MG, and significantly reduced membrane damage, lipid peroxidation and Na+ toxicity. These results demonstrate COU-improved plant growth, biomass content, photosynthetic pigment content, water retention and mineral homeostasis upon imposition of salinity. Finally, this present study suggests that COU has potential roles as a phytoprotectant in stimulating plant antioxidative mechanisms and improving glyoxalase enzyme activity under salinity stress.

Exogenous Application of Nitric Oxide Mitigates Water Stress and Reduces Natural Viral Disease Incidence of Tomato Plants Subjected to Deficit Irrigation

The present work reveals the beneficial role of sodium nitroprusside (SNP; NO donor concentration: 50 and 100 µM) in mitigation of water stress accompanied by a reduction in viral disease incidence in tomato plants subjected to deficit irrigation. The plants were grown under two irrigation regimes: well-watered (WW; irrigated after the depletion of 55–60% of available soil water) and water deficit (WD; irrigated after the depletion of 85–90% of available soil water) in two seasons of 2018 and 2019. The results indicated that under water stress conditions, plant growth, chlorophyll, relative water content (RWC), and fruit yield were decreased. Conversely, water stress significantly increased the MDA, proline, soluble sugars, and antioxidant enzymes’ activities. Moreover, it was obvious a negligible increase in the fruit content from NO2 and NO3. Water-deficit stress, however, had a positive impact on reducing the percentage of viral disease (TMV and TYLCV) incidence on tomato plants. Similarly, SNP application in the form of foliar spray significantly reduced the disease incidence, the severity, and the relative concentrations of TMV and TYLCV in tomato plants raised under both WW and WD conditions. The treatment of SNP at 100 µM achieved better results and could be recommended to induce tomato plant tolerance to water stress. Thus, the present work highlights the role of NO (SNP) in the alleviation of water stress in tomato plants and subsequent reduction in viral disease incidence during deficit irrigation.

Overexpression of tomato RING E3 ubiquitin ligase gene SlRING1 confers cadmium tolerance by attenuating cadmium accumulation and oxidative stress.

Heavy metal pollution not only decreases crop yield and quality, but also affects human health via the food chain. Ubiquitination-dependent protein degradation is involved in plant growth, development, and environmental interaction, but the functions of ubiquitin-ligase (E3) genes are largely unknown in tomato (Solanum lycopersicum L.). Here, we functionally characterized a RING E3 ligase gene, SlRING1, which positively regulates cadmium (Cd) tolerance in tomato plants. An in vitro ubiquitination experiment shows that SlRING1 has E3 ubiquitin ligase activity. The determination of the subcellular localization reveals that SlRING1 is localized at both the plasma membrane and the nucleus. Overexpression of SlRING1 in tomato increased the chlorophyll content, the net photosynthetic rate, and the maximal photochemical efficiency of photosystem II (Fv/Fm), but reduced the levels of reactive oxygen species and relative electrolyte leakage under Cd stress. Moreover, SlRING1 overexpression increased the transcript levels of CATALASE (CAT), DEHYDROASCORBATE REDUCTASE (DHAR), MONODEHYDROASCORBATE REDUCTASE (MDHAR), GLUTATHIONE (GSH1), and PHYTOCHELATIN SYNTHASE (PCS), which contribute to the antioxidant and detoxification system. Crucially, SlRING1 overexpression also reduced the concentrations of Cd in both shoots and roots. Thus, SlRING1-overexpression-induced enhanced tolerance to Cd is ascribed to reduced Cd accumulation and alleviated oxidative stress. Our findings suggest that SlRING1 is a positive regulator of Cd tolerance, which can be a potential breeding target for improving heavy metal tolerance in horticultural crops.

Defense Enzymes in Mycorrhizal Tomato Plants Exposed to Combined Drought and Heat Stresses

As a result of climate change, drought and heat significantly reduced plant growth. Therefore, this study aims to explore and provide more insight into the effect of different arbuscular mycorrhizal fungi (AMF) strains (Rhizophagus irregularis, Funneliformis mosseae, and Funneliformis coronatum) on tomato plant tolerance against combined drought and heat stress, as well as combined drought and heat shock. A pot experiment was performed under controlled conditions in a growth chamber at 26/20 °C with a 16/8 h photoperiod. After six weeks of growth, one-third of plants were put in non-stress conditions, while another one-third were subjected to combined drought and heat stress (40% field capacity for two weeks and 38 °C/16 h and 30 °C/8 h for 5 days). The rest of the plants were exposed to combined drought and heat shock (40% of field capacity for two weeks and 45 °C for 6 h at the end of the drought period). All data were evaluated by one- and two-way analysis of variance (ANOVA). Means were compared by Duncan’s post hoc test at p &lt; 0.05. The obtained results showed that combined drought and heat stresses had no significant impact on root colonization. Furthermore, stressed AMF plants exhibited a decrease in hydrogen peroxide and malondialdehyde content in the cells and showed changes in defense enzyme activities (peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), and glutathione S-transferase (GST)) in leaves as well as in roots compared with their relative non-mycorrhizal plants.

Cold-regulated gene LeCOR413PM2 confers cold stress tolerance in tomato plants.

Tomato (Lycopersicon esculentum Mill) is an important food plant that has been used as a model plant in genetic evolution and molecular biology research. The plant is originated from the tropics; thus, it is sensitive to cold. Its growth and development can be easily affected by cold stress. In this study, cold-regulated gene LeCOR413PM2 was cloned from tomato leaves and then used to generate two types of transgenic tomato plants: LeCOR413PM2-overexpressing transgenic plants and RNA-interference-expressing transgenic plants. The functions and expression of LeCOR413PM2 gene in response to cold stress were subsequently assessed. The results showed that LeCOR413PM2 localized in the plasma membrane. Expression of LeCOR413PM2 gene in the leaf of transgenic tomato plant was highest compared to that in other organs (i.e., root, stem, flower and fruit); it was elevated when plants were treated with cold stress. Overexpression of LeCOR413PM2 gene was found to not only reduce damage to cell membrane, accumulation of ROS, and photoinhibition of PSII, but also maintain high activity of antioxidant enzymes and content of osmotic regulators. The results also reveal that high activities of antioxidant enzymes were caused by the up-regulation of their gene expressions. This study demonstrates that the overexpression of LeCOR413PM2 could increase cold tolerance of transgenic tomato plants, while the suppressed expression of LeCOR413PM2 by RNA interference could increase the sensitivity of plants to cold.

Effect of foliar application of amino acids on the salinity tolerance of tomato plants cultivated under hydroponic system

Salinity is one of the most critical problems faced by agriculture in all the arid and semi-arid climates in the world. Many biostimulant-producing companies utilize different raw materials to palliate the negative effects of salinity on crops. Some of these active materials are amino acids (AAs). In this study, the effect of the foliar application of free amino acids or as a mixture of them was studied in tomato plants cv “Optima”, grown in a controlled environment growth chamber in a hydroponic system with Hoagland’s solution with added 50 mM NaCl. The following treatments were applied: i) Control (-salt), ii) salt (+salt), and the salt treatments with amino acids (AAs + salt): iv) L-Arg, v) L-Pro, vi) Glu, vii) L-Trp, viii) L-Met + L-Arg, ix) L-Met + L-Trp, x) Glu + L-Pro. At the end of the assay, vegetative growth parameters, relative water content, mineral nutrient content, carbohydrates and organic solutes and chlorophylls were measured. The results showed that salinity decreased the growth of the plants, but those treated with the L-Met, Pro + Glu and Met + Trp reversed the negative effect of salinity. Also, this result was not due to differences in the concentration of Cl- or Na+ in the leaves, or to changes in the water status of the plants, but to a greater accumulation of total soluble sugars induced by the application of AAs, which could have de-activated the reactive oxygen species created by the toxicity of these ions. The results of this experiment also highlight the antagonistic or synergistic effects between the AAs, which should be taken into account by fertilizer producers.

Overexpression of LeNHX4 improved yield, fruit quality and salt tolerance in tomato plants (Solanum lycopersicum L.).

The function of the tomato K+, Na+/H+ antiporter LeNHX4 has been analyzed using 35S-driven gene construct for overexpressing a histagged LeNHX4 protein in Solanum lycopersicum L. Compared to wild-type plants, the expression of LeNHX4 was enhanced in most of plants transformed with a gene construct for LeNHX4 overexpression although some plants showed a decreased LeNHX4 expression. Overexpression of LeNHX4 was associated to an increased fruit size while silencing of this gene was related to a decreased fruit size. We have investigated the effect of LeNHX4 overexpression on fruit production and quality and we have also evaluated salt tolerance in two different overexpression lines by measuring proline, protein and glucose concentrations in tomato leaves grown either under control (0mM NaCl) or saline (125mM NaCl) conditions. Plants overexpressing LeNHX4 showed a higher amount of fruits than WT plants and accumulated higher contents of sugars and cations (Na+ and K+). The application of 125mM NaCl, affected negatively fruit production and quality of WT plants. However the transgenic lines overexpressing LeNXH4 increased fruit quality and yield. In relation to salt tolerance, overexpression lines showed higher levels of leaf proline, glucose and proteins under NaCl treatment. The overexpression of LeNHX4 in tomato plants, improved salinity tolerance and increased fruit yield and quality under both normal and salinity stress conditions.

SlWRKY81 reduces drought tolerance by attenuating proline biosynthesis in tomato

In plants, WRKY transcription factors (TFs) regulate a number of biological processes and responses to biotic and abiotic stresses. In this study, we used a reverse-genetic approach (virus-induced gene silencing) to unveil the role of tomato WRKY81 in drought tolerance. When non-silenced control (TRV:TRV) and SlWRKY81-silenced plants were grown in 30 % and 15 % substrate water content (SWC) for 7 days, TRV:TRV plants, but not SlWRKY81-silenced plants, showed severe wilting phenotype, which was closely associated with increased transcript abundance of SlWRKY81 in TRV:TRV plants compared with that in SlWRKY81-silenced plants. Although the concentrations of proline drastically increased in response to water deficit in both genotypes, the leaf proline content in SlWRKY81-silenced plants under 15 % SWC was significantly higher than that in TRV:TRV plants. The transcript levels of proline biosynthetic gene SlP5CS1 encoding delta 1-pyrroline-5-carboxylate synthetase (P5CS) were consistent with the changes in the proline contents under different SWC in TRV:TRV and TRV:SlWRKY81 plants. Inspection of 2-kb sequences upstream of the predicted translational start sites of the SlP5CS1 identified two copies of the core W-box (TTGACC/T) sequence in the promoter of SlP5CS1, which correlates well with the expression of SlP5CS1 in response to water deficit, indicating a possible target of SlWRKY81 transcription factor. Taken together, our results suggest that SlWRKY81 acts as a repressor of SlP5CS1 transcription and thus reduces proline biosynthesis to abate drought tolerance in tomato plants.

Gibberellic acid-induced generation of hydrogen sulfide alleviates boron toxicity in tomato (Solanum lycopersicum L.) plants

It was aimed to examine the role of gibberellic acid (GA) induced production of hydrogen sulfide (H2S) in alleviating boron toxicity (BT) in tomato plants. Two weeks after germination, a solution consisting of GA (100 mg L−1) was sprayed once a week for 14 days to the leaves of cv. “SC 2121” of tomato under BT stress (BT; 2.0 mM). Before starting BT treatment, half of the seedlings were retained in a solution containing a scavenger of H2S, 0.1 mM hypotaurine (HT), for 12 h. Boron toxicity led to a substantial decrease in dry biomass, leaf water potential, leaf relative water content, chlorophyll a, chlorophyll b, photosynthetic quantum yield (Fv/Fm), ascorbate (AsA) and glutathione (GSH) in the tomato plants. However, it increased the accumulation of hydrogen peroxide (H2O2), malondialdehyde (MDA), endogenous hydrogen sulfide (H2S), and free proline as well as the activities of catalase, superoxide dismutase and peroxidase. The supplementation of GA mitigated BT by increasing the endogenous H2S, and leaf Ca2+ and K+, and reducing the contents of leaf H2O2, MDA, and B as well as membrane leakage. GA-induced BT tolerance was further enhanced by the supplementation of sodium hydrosulfide (0.2 mM NaHS), an H2S donor. A scavenger of H2S, hypotaurine (0.1 mM HT) was supplied along with the GA and NaHS treatments to assess if H2S was involved in GA-induced BT tolerance of tomato plants. Addition of HT reversed the beneficial effect of GA on oxidative stress and antioxidant defence system by reducing the endogenous H2S without changing L-DES activity, suggesting that H2S participates in GA-induced tolerance to BT of tomato plants.

Exogenous Ascorbic Acid Induced Chilling Tolerance in Tomato Plants Through Modulating Metabolism, Osmolytes, Antioxidants, and Transcriptional Regulation of Catalase and Heat Shock Proteins.

Chilling, a sort of cold stress, is a typical abiotic ecological stress that impacts the development as well as the growth of crops. The present study was carried to investigate the role of ascorbic acid root priming in enhancing tolerance of tomato seedlings against acute chilling stress. The treatments included untreated control, ascorbic acid-treated plants (AsA; 0.5 mM), acute chilling-stressed plants (4 °C), and chilling stressed seedlings treated by ascorbic acid. Exposure to acute chilling stress reduced growth in terms of length, fresh and dry biomass, pigment synthesis, and photosynthesis. AsA was effective in mitigating the injurious effects of chilling stress to significant levels when supplied at 0.5 mM concentrations. AsA priming reduced the chilling mediated oxidative damage by lowering the electrolyte leakage, lipid peroxidation, and hydrogen peroxide. Moreover, up regulating the activity of enzymatic components of the antioxidant system. Further, 0.5 mM AsA proved beneficial in enhancing ions uptake in normal and chilling stressed seedlings. At the gene expression level, AsA significantly lowered the expression level of CAT and heat shock protein genes. Therefore, we theorize that the implementation of exogenous AsA treatment reduced the negative effects of severe chilling stress on tomato.

Biofilms Positively Contribute to Bacillus amyloliquefaciens 54-induced Drought Tolerance in Tomato Plants.

Drought stress is a major obstacle to agriculture. Although many studies have reported on plant drought tolerance achieved via genetic modification, application of plant growth-promoting rhizobacteria (PGPR) to achieve tolerance has rarely been studied. In this study, the ability of three isolates, including Bacillus amyloliquefaciens 54, from 30 potential PGPR to induce drought tolerance in tomato plants was examined via greenhouse screening. The results indicated that B. amyloliquefaciens 54 significantly enhanced drought tolerance by increasing survival rate, relative water content and root vigor. Coordinated changes were also observed in cellular defense responses, including decreased concentration of malondialdehyde and elevated concentration of antioxidant enzyme activities. Moreover, expression levels of stress-responsive genes, such as lea, tdi65, and ltpg2, increased in B. amyloliquefaciens 54-treated plants. In addition, B. amyloliquefaciens 54 induced stomatal closure through an abscisic acid-regulated pathway. Furthermore, we constructed biofilm formation mutants and determined the role of biofilm formation in B. amyloliquefaciens 54-induced drought tolerance. The results showed that biofilm-forming ability was positively correlated with plant root colonization. Moreover, plants inoculated with hyper-robust biofilm (ΔabrB and ΔywcC) mutants were better able to resist drought stress, while defective biofilm (ΔepsA-O and ΔtasA) mutants were more vulnerable to drought stress. Taken altogether, these results suggest that biofilm formation is crucial to B. amyloliquefaciens 54 root colonization and drought tolerance in tomato plants.

Crosstalk of PIF4 and DELLA modulates CBF transcript and hormone homeostasis in cold response in tomato.

SummaryThe ability to interpret daily and seasonal fluctuations, latitudinal and vegetation canopy variations in light and temperature signals is essential for plant survival. However, the precise molecular mechanisms transducing the signals from light and temperature perception to maintain plant growth and adaptation remain elusive. We show that far‐red light induces PHYTOCHROME‐INTERACTING TRANSCRIPTION 4 (SlPIF4) accumulation under low‐temperature conditions via phytochrome A in Solanum lycopersicum (tomato). Reverse genetic approaches revealed that knocking out SlPIF4 increases cold susceptibility, while overexpressing SlPIF4 enhances cold tolerance in tomato plants. SlPIF4 not only directly binds to the promoters of the C‐REPEAT BINDING FACTOR (SlCBF) genes and activates their expression but also regulates plant hormone biosynthesis and signals, including abscisic acid, jasmonate and gibberellin (GA), in response to low temperature. Moreover, SlPIF4 directly activates the SlDELLA gene (GA‐INSENSITIVE 4, SlGAI4) under cold stress, and SlGAI4 positively regulates cold tolerance. Additionally, SlGAI4 represses accumulation of the SlPIF4 protein, thus forming multiple coherent feed‐forward loops. Our results reveal that plants integrate light and temperature signals to better adapt to cold stress through shared hormone pathways and transcriptional regulators, which may provide a comprehensive understanding of plant growth and survival in a changing environment.

Investigating the potential use of mono-potassium phosphate (MKP: 0-52-34) applied through fertigation as a method to improve salinity tolerance of tomato plants

ISHS XXX International Horticultural Congress IHC2018: International Symposium on Water and Nutrient Relations and Management of Horticultural Crops Investigating the potential use of mono-potassium phosphate (MKP: 0-52-34) applied through fertigation as a method to improve salinity tolerance of tomato plants

Downregulation of SL-ZH13 transcription factor gene expression decreases drought tolerance of tomato

Zinc finger-homeodomain proteins (ZF-HDs) are transcription factors that regulate plant growth, development, and abiotic stress tolerance. The SL-ZH13 gene was found to be significantly upregulated under drought stress treatment in tomato (Solanum lycopersicum) leaves in our previous study. In this study, to further understand the role that the SL-ZH13 gene plays in the response of tomato plants to drought stress, the virus-induced gene silencing (VIGS) method was applied to downregulate SL-ZH13 expression in tomato plants, and these plants were treated with drought stress to analyze the changes in drought tolerance. The SL-ZH13 silencing efficiency was confirmed by quantitative real-time PCR (qRT-PCR) analysis. In SL-ZH13-silenced plants, the stems wilted faster, leaf shrinkage was more severe than in control plants under the same drought stress treatment conditions, and the mean stem bending angle of SL-ZH13-silenced plants was smaller than that of control plants. Physiological analyses showed that the activity of superoxide dismutase (SOD) and peroxidase (POD) and the content of proline (Pro) in SL-ZH13-silenced plants were lower than those in control plants after 1.5 and 3 h of drought stress treatment. The malondialdehyde (MDA) content in SL-ZH13-silenced plants was higher than that in control plants after 1.5 and 3 h of drought stress treatment, and H2O2 and O2–· accumulated much more in the leaves of SL-ZH13-silenced plants than in the leaves of control plants. These results suggested that silencing the SL-ZH13 gene affected the response of tomato plants to drought stress and decreased the drought tolerance of tomato plants.

ABA signaling rather than ABA metabolism is involved in trehalose-induced drought tolerance in tomato plants.

Trehalose increased drought tolerance of tomato plants, accompanied by reduced water loss and closed stomata, which was associated with the upregulated ABA signaling-related genes expression, but not in ABA accumulation. Drought is one of the principal abiotic stresses that negatively influence the growth of plant and yield. Trehalose has great agronomic potential to improve the stress tolerance of plants. However, little information is available on the role of ABA and its signaling components in trehalose-induced drought tolerance. The aim of this study is to elucidate the potential mechanism by which trehalose regulates ABA in response to drought stress. In this study, 6-week-old tomato (Solanum lycopersicum cv. Ailsa Craig) plants were treated with 0 or 15.0mM trehalose solution. Results showed that trehalose treatment significantly enhanced drought tolerance of tomato plants, accompanied by encouraged stomatal closure and protected chloroplast ultrastructure. Compared with controls, trehalose-treated plants showed lower hydrogen peroxide content and higher antioxidant enzymes activities, which contributed to alleviate oxidative damage caused by drought. Moreover, trehalose treatment decreased ABA content, which was followed by the downregulation of ABA biosynthesis genes expression and the upregulation of ABA catabolism genes expression. In contrast, exogenous trehalose upregulated transcript levels of ABA signaling-related genes, including SlPYL1/3/4/5/6/7/9, SlSnRK2.3/4, SlAREB1/2, and SlDREB1. These results suggested that trehalose treatment enhanced drought tolerance of tomato plants, and it's ABA signaling rather than ABA metabolism that was involved in trehalose-induced drought tolerance in tomato plants. These findings provide evidence for the physiological role of trehalose and bring about a new understanding of the possible relationship between trehalose and ABA.

Interactive role of epibrassinolide and hydrogen peroxide in regulating stomatal physiology, root morphology, photosynthetic and growth traits in Solanum lycopersicum L. under nickel stress

Nickel (Ni) is a fundamental component that assumes a vital role in managing plant growth and development. Its acquisition in soil is presently viewed as a consequential ecological issue imperilling crop productivity globally. Brassinosteroid and low concentration of H2O2 as signalling molecule could modify stomatal movement, root morphology, photosynthetic effectiveness and generation of antioxidants and finally growth traits to make the tomato plants more tolerant to Ni stress. Therefore, a study was conducted to study the effect of exogenously applied epibrassinolide (EBL; foliar spray) and H2O2 (root dipping) to nickel (Ni) stressed plants. EBL and H2O2 applied through different modes modified stomatal movement, root morphology, photosynthetic effectiveness and growth traits of Solanum lycopersicum L. plants grown under stress free and surplus Ni. The increased Ni- tolerance of tomato plants caused by EBL and H2O2 could be attributed to its capability to restrict Ni uptake, reduce Ni- inflicted oxidative burst as illustrated by lower levels of hydrogen peroxide, superoxide and electrolyte leakage in Ni- stressed plants. In addition, EBL and H2O2 increased the antioxidant capability in Ni stressed plants by sustaining increased activities of enzymes for ROS-detoxification, particularly catalase (CAT), guaiacol peroxidase (GPOX) and superoxide dismutase (SOD) and proline accumulation. These improved activities of antioxidant enzymes and accumulation of proline (osmolyte) elicited by the blend of EBL and H2O2, would have retained the ability to confer resilience to Solanum lycopersicum plants exposed to higher doses of Ni. This study further affirms that the combined application of EBL and H2O2 in various ways proved very effective to ameliorate the effects of Ni toxicity in tomato plants through modification of stomatal movement, root morphology, photosynthetic effectiveness and growth traits.

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.

RBOH1-dependent apoplastic H2O2 mediates epigallocatechin-3-gallate-induced abiotic stress tolerance in Solanum lycopersicum L.

Responses of plants to abiotic stimuli are mediated by a plethora of bioactive compounds. Flavonoids are a large group of plant secondary metabolites, playing diverse roles in plant growth, development and responses to stress. Despite the recent report on epigallocatechin-3-gallate (EGCG, a bioactive flavonoids)-induced enhanced tolerance to salt stress, the underlying molecular mechanisms of stress tolerance remain unclear. Moreover, whether such stress protective role of EGCG is common for other environmental stressors also remains elusive. In the current study, we showed that EGCG functions as a broad spectrum stress protectant that alleviates a variety of abiotic stresses such as cold, heat, salinity and drought in tomato plants. While those abiotic stresses inhibited leaf photosynthetic activity by enhancing reactive oxygen species (ROS) production and membrane damage, exogenous EGCG protected photosynthetic apparatus by reducing ROS accumulation. Furthermore, EGCG-induced attenuation of ROS accumulation was largely attributed to the enhanced activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX). Analysis of sub-cellular localization of ROS revealed that EGCG preferentially induced apoplastic H2O2 production by activation of RESPIRATORY BURST OXIDASE HOMOLOG1 (RBOH1)-encoded NADPH oxidase. Further investigation using virus-induced gene silencing showed that suppression of RBOH1 expression aggravated abiotic stress-induced ROS accumulation and compromised EGCG-induced ROS scavenging, implying that RBOH1-dependent H2O2 production is critical for the EGCG-induced tolerance to abiotic stress. This study advances our current understanding of stress protective role of flavonoids and unveils a critical mechanism of EGCG-induced abiotic stress tolerance in tomato plants.

Impacts of Paraburkholderia phytofirmans Strain PsJN on Tomato (Lycopersicon esculentum L.) Under High Temperature.

Abnormal temperatures induce physiological and biochemical changes resulting in the loss of yield. The present study investigates the impact of the PsJN strain of Paraburkholderia phytofirmans on tomato (Lycopersicon esculentum Mill.) in response to heat stress (32°C). The results of this work showed that bacterial inoculation with P. phytofirmans strain PsJN increased tomato growth parameters such as chlorophyll content and gas exchange at both normal and high temperatures (25 and 32°C). At normal temperature (25°C), the rate of photosynthesis and the photosystem II activity increased with significant accumulations of sugars, total amino acids, proline, and malate in the bacterized tomato plants, demonstrating that the PsJN strain had a positive effect on plant growth. However, the amount of sucrose, total amino acids, proline, and malate were significantly affected in tomato leaves at 32°C compared to that at 25°C. Changes in photosynthesis and chlorophyll fluorescence showed that the bacterized tomato plants were well acclimated at 32°C. These results reinforce the current knowledge about the PsJN strain of P. phytofirmans and highlight in particular its ability to alleviate the harmful effects of high temperatures by stimulating the growth and tolerance of tomato plants.