Salt-stress induced physiological and proteomic changes in tomato (Solanum lycopersicum) seedlings

Soil salinity is one of the major abiotic stress limiting crop productivity and the geographical distribution of many important crops worldwide. To gain a better understanding of the salinity stress responses at physiological and molecular level in cultivated tomato (Solanum lycopersicum. cv. Supermarmande), we carried out a comparative physiological and proteomic analysis. The tomato seedlings were cultivated using a hydroponic system in the controlled environment growth chamber. The salt stress (NaCl) was applied (0, 50, 100, 150 and 200?mM), and maintained for 14 days. Salt treatment induced a plant growth reduction estimated as fresh-dry weight. Photosynthetic pigments (chlorophyll a, b) content of NaCl-treated tomato plants was significantly decreased as the salinity level increased. Proline accumulation levels in leaf and root tissues increased significantly with increasing NaCl concentration. Relative electrolyte leakage known as an indicator of membrane damage caused by salt stress was increased proportionally according to the NaCl concentrations. Roots of control and salt-stressed plants were also sampled for phenol protein extraction. Proteins were separated by two-dimensional gel electrophoresis (2-DGE). Several proteins showed up- and downregulation during salt stress. MALDI-TOF/MS analysis and database searching of some of the identified proteins indicated that the proteins are known to be in a wide range of physiological processes, that is, energy metabolism, ROS (reactive oxygen species) scavenging and detoxification, protein translation, processing and degradation, signal transduction, hormone and amino acid metabolism, and cell wall modifications. All proteins might work cooperatively to reestablish cellular homeostasis under salt stress, water deficiency, and ionic toxicity.     

Physiological and biochemical responses resulting from nitrite accumulation in tomato (Lycopersicon esculentum Mill. cv. Ibiza F1)

The sensitivity of hydroponically cultivated tomato (Lycopersicon esculentum Mill. cv. Ibiza F1) submitted to nitrite treatments (0.25-10mM KNO(2)) for 7d was studied. Increasing nitrite levels in the culture medium led to several disruptions of tomato plants, reflected by reductions of both dry matter per plant, chlorophyll concentrations and the appearance of chlorosis symptoms at the leaf surface. This behaviour was accompanied by stimulation of nitrite, nitrate and ammonia ion accumulation, mainly in roots and old leaves. Higher proteolytic and gaiacol peroxidase (GPX, EC. 1.11.1.7) activities and malonyldialdehyde content were also noted. Protein content of the different plant organs was decreased by nitrite treatment. These physiological and biochemical parameters were chosen as they are stress indicators. Taken together, our data partly explain the harmful effects of nitrite ions, when excessive in the culture medium.     

Iron uptake system mediates nitrate-facilitated cadmium accumulation in tomato (Solanum lycopersicum) plants

Nitrogen (N) management is a promising agronomic strategy to minimize cadmium (Cd) contamination in crops. However, it is unclear how N affects Cd uptake by plants. Wild-type and iron uptake-inefficient tomato (Solanum lycopersicum) mutant (T3238fer) plants were grown in pH-buffered hydroponic culture to investigate the direct effect of N-form on Cd uptake. Wild-type plants fed NO?? accumulated more Cd than plants fed NH??. Iron uptake and LeIRT1 expression in roots were also greater in plants fed NO??. However, in mutant T3238fer which loses FER function, LeIRT1 expression in roots was almost completely terminated, and the difference between NO?? and NH?? treatments vanished. As a result, the N-form had no effect on Cd uptake in this mutant. Furthermore, suppression of LeIRT1 expression by NO synthesis inhibition with either tungstate or L-NAME, also substantially inhibited Cd uptake in roots, and the difference between N-form treatments was diminished. Considering all of these findings, it was concluded that the up-regulation of the Fe uptake system was responsible for NO??-facilitated Cd accumulation in plants.     

The Solanum melongena COP1LIKE manipulates fruit ripening and flowering time in tomato (Solanum lycopersicum)

Plant Growth Regulation - The CONSTITUTIVE PHOTOMORPHOGENIC (COP) 1LIKE is a regulatory protein and repressor of photomorphogenesis; which control many processes of development in plants. Here, the...     

Plant defence induced by PGPR against Spodoptera litura in tomato (Solanum lycopersicum L.)

• The research conducted including its rationale: Spodoptera litura is the major pest of tomato causing significant reduction in tomato yield. Application of Plant growth promoting rhizobacteria(PGPR) prevent use of chemical fertilizer and synthetic pesticides through enhancement of plant growth and yield and induction of systemic resistance. Present investigation is an attempt to evaluate the role of PGPR, Pseudomonas putida and Rothia sp. on the physiology and yield of tomato fruit infested with the S. litura.
• Central methods applied : The surface sterilized seeds of tomato were inoculated with 48 h culture of P. putida and Rothia sp. At 6–7 branching stage of the plant, the larvae of S. litura at 2nd in star was used to infect the tomato plant leaves.
• Key results: The S. litura infestation decreased dry weight of shoots and roots by 46% and 22%, and significant reduction was recorded in tomato fruit yield. The P. putida and Rothia sp. inoculations alleviated the adverse effects of insect infestation and resulted in 60% increase in plant biomass and 40% increase in yield over infested plants.
• Main conclusions including key points of discussion: PGPR: Defense appears to be mediated via increase in proline production, enhanced activities of antioxidant enzymes, stimulation in the activities of protease and polyphenol oxidases, increased contents of phenolics, protein and chlorophyll. The formulation of biopesticide involving PGPR comprise an environment friendly and sustainable approach to overcome insect infestation.

     

Physiological and structural modifications induced by cadmium-calcium interaction in tomato (Lycopersicon esculentum)

Tomato seedlings (Lycopersicon esculentum), initially cultivated in a basic nutrient solution during 12 days, were treated with increasing CdCl(2) concentrations for 10 days. The results showed that cadmium inhibited the weight growth depending on the metal concentration and the plant organ. In the presence of 20 microM CdCl(2), the addition of calcium, 0.1 to 10 mM of CaCl(2) in the culture medium, improved especially the biomass production and the mineral composition of the plants in concomitance with an increase in the contents of photosynthetic pigments. Histological study at the hypocotyle level revealed that cadmium (20 microM) induced a restriction of the tissue territories as well as meristem formations differentiating in a root structure. At this concentration, the addition of CaCl(2) (5 microM) was characterized by an opposite effect with absence of meristem structures. The overall results suggest that the alteration of some plant growth process after exposure to cadmium can be attenuated by an adequate calcium contribution in culture medium.     

Gamma rays induced genetic variability in tomato (Solanum lycopersicum L.) germplasm

The present study assessed the effectiveness of gamma radiation in inducing favorable genetic variability in tomato (Solanum lycopersicum L.). An experiment was conducted in a randomized complete block design to produce M₁ generation. Significant differences were observed among the genotypes as well as between the treatments at individual plant level based on observed traits (seed germination percentage, seedling survival, plant height, number of flower clusters plant^?1, number of flowers and fruits plant^?1). All observed characters in the mutagenized population were adversely affected with increasing radiation dose. Results identified 450 Gy as the most damaging radiation dose followed by 300 Gy and 150 Gy. Moreover, 300 Gy treatment was identified as lethal dose (LD₅₀) as it caused a 50% germination inhibition in almost all the evaluated genotypes. The 150 Gy treatment showed the least damaging impact and induced maximum genetic variability in almost all the genotypes under study. Character association studies were also conducted which could be utilized in the selection of desirable mutants. Correlation studies revealed an altered association among the observed parameters from positive to negative direction in 300 Gy and 450 Gy treatments as compared to control. These deviations in correlation coefficients proved that mutagenesis can break the linkage among specific loci. Furthermore, path coefficient analysis identified the growth attributes with an effective direct and indirect contribution in yield.     

Response of photosynthesis and chlorophyll fluorescence to acute ozone stress in tomato (Solanum lycopersicum Mill.)

The crop sensitivity to ozone (O₃) is affected by the timing of the O₃ exposure, by the O₃ concentration, and by the crop age. To determine the physiological response to the acute ozone stress, tomato plants were exposed to O₃ at two growth stages. In Experiment I (Exp. I), O₃ (500 μg m^?3) was applied to 30-d-old plants (PL30). In Experiment II (Exp. II), three O₃ concentrations (200, 350, and 500 μg m^?3) were applied to 51-d-old plants (PL51). The time of the treatment was 4 h (7:30–11:30 h). Photosynthesis and chlorophyll fluorescence measurements were done 4 times (before the exposure; 20 min, 20 h, and 2–3 weeks after the end of the treatment) using a LI-COR 6400 photosynthesis meter. The stomatal pore area and stomatal conductance were reduced as the O₃ concentration increased. Ozone induced the decrease in the photosynthetic parameters of tomato regardless of the plant age. Both the photosystem (PS) II operating efficiency and the maximum quantum efficiency of PSII photochemistry declined under the ozone stress suggesting that the PSII activity was inhibited by O₃. The impaired PSII contributed to the reduced photosynthetic rate. The greater decline of photosynthetic parameters was found in the PL30 compared with the PL51. It proved the age-dependent ozone sensitivity of tomato, where the younger plants were more vulnerable. Ozone caused the degradation of photosynthetic apparatus, which affected the photosynthesis of tomato plants depending on the growth stage and the O₃ concentration.     

Investigation of tomato (Solanum lycopersicum) aminotransferases involved in biosynthesis of branched-chain-amino-acids

This study presents evidence for the role of BCAT3 and BCAT4 proteins in the synthesis of branched-chain-amino-acids in tomato Solanum lycopersicum. BCAT3 and BCAT4 genes were located on tomato chromosomal map by RFLP method (restriction fragment length polymorphism). Using confocal microscopy it was shown that BCAT3-GFP and BCAT4-GFP fusion proteins were localised in chloroplasts. It was observed that these aminotransferase isoforms exhibited distinct kinetic properties and a differential expression pattern of mRNA levels in various tomato tissues.     

Roles of ethylene and jasmonic acid in systemic induced defense in tomato (Solanum lycopersicum) against Helicoverpa zea

Inducible defenses that provide enhanced resistance to insect attack are nearly universal in plants. The defense-signaling cascade is mediated by the synthesis, movement, and perception of jasmonate (JA) and the interaction of this signaling molecule with other plant hormones and messengers. To explore how the interaction of JA and ethylene influences induced defenses, we employed the never-ripe (Nr) tomato mutant, which exhibits a partial block in ethylene perception, and the defenseless (def1) mutant, which is deficient in JA biosynthesis. The defense gene proteinase inhibitor (PIN2) was used as marker to compare plant responses. The Nr mutant showed a normal wounding response with PIN2 induction, but the def1 mutant did not. As expected, methyl JA (MeJA) treatment restored the normal wound response in the def1 mutant. Exogenous application of MeJA increased resistance to Helicoverpa zea, induced defense gene expression, and increased glandular trichome density on systemic leaves. Exogenous application of ethephon, which penetrates tissues and decomposes to ethylene, resulted in increased H. zea growth and interfered with the wounding response. Ethephon treatment also increased salicylic acid in systemic leaves. These results indicate that while JA plays the main role in systemic induced defense, ethylene acts antagonistically in this system to regulate systemic defense.     

Regulation of expression of two novel flower-specific genes from tomato (Solanum lycopersicum) by gibberellin.

Two flower-specific cDNAs have been isolated after differential screening of an anther cDNA library. This library was constructed 48 h after GA(3) treatment of buds of the GA-deficient gib-1 mutant of tomato. Northern blot analysis during flower development in tomato demonstrated that the expression of both genes is regulated by gibberellins (GAs). Application of GA(3) to developmentally arrested gib-1 flower buds induced new expression of tgas100 mRNA 48 h post-treatment, while an increased accumulation of tgas105 mRNA was found after 8 h. In situ analyses showed the spatial distribution of the expression of both genes within the tomato flower. One of the deduced polypeptides (TGAS105) displays similarities to cysteine-rich extensin-like proteins, while the other (TGAS100) shows significant homology with a stamen-specific gene of Antirrhinum majus. Based on the deduced protein sequences, the possible function of the encoded proteins is discussed.     

Diel changes in nitrogen and carbon resource status and use for growth in young plants of tomato (Solanum lycopersicum)

Background and Aims

Modellers often define growth as the development of plant structures from endogenous resources, thus making a distinction between structural (W_S) and total (W) dry biomass, the latter being the sum of W_S and the weight of storage compounds. In this study, short-term C and N reserves were characterized experimentally (forms, organ distribution, time changes) in relation to light and nutrition signals, and organ structural growth in response to reserve levels was evaluated.

Methods

Tomato plants (Solanum lycopersicum) were grown hydroponically in a growth room with a 12-h photoperiod and an adequate supply of NO₃⁻ (3 mol m⁻³). Three experiments were carried out 18 d after sowing: [NO₃⁻] was either maintained at 3 mol m⁻³, changed to 0·02 mol m⁻³ or to 0 mol m⁻³. Plants were sampled periodically throughout the light/dark cycles over 24–48 h. Organ W_S was calculated from W together with the amount of different compounds that act as C and N resources, i.e. non-structural carbohydrates and carboxylates, nitrate and free amino acids.

Key Results

With adequate nutrition, carbohydrates accumulated in leaves during light periods, when photosynthesis exceeded growth needs, but decreased at night when these sugars are the main source of C for growth. At the end of the night, carbohydrates were still high enough to fuel full-rate growth, as W_S increased at a near constant rate throughout the light/dark cycle. When nitrate levels were restricted, C reserves increased, but [NO₃⁻] decreased progressively in stems, which contain most of the plant N reserves, and rapidly in leaves and roots. This resulted in a rapid restriction of structural growth.

Conclusions

Periodic darkness did not restrict growth because sufficient carbohydrate reserves accumulated during the light period. Structural growth, however, was very responsive to NO₃⁻ nutrition, because N reserves were mostly located in stems, which have limited nitrate reduction capacity.Key words: Solanum lycopersicum, tomato, nitrogen, carbon, structural growth, reserves, nitrate, amino acids, carbohydrate, carboxylate     

Oxidative stress and antioxidants in tomato (Solanum lycopersicum) plants subjected to boron toxicity

BACKGROUND AND AIMS: Boron (B) toxicity triggers the formation of reactive oxygen species in plant tissues. However, there is still a lack of knowledge as to how B toxicity affects the plant antioxidant defence system. It has been suggested that ascorbate could be important against B stress, although existing information is limited in this respect. The objective of this study was to analyse how ascorbate and some other components of the antioxidant network respond to B toxicity. METHODS: Two tomato (Solanum lycopersicum) cultivars ('Kosaco' and 'Josefina') were subjected to 0.05 (control), 0.5 and 2 mm B. The following were studied in leaves: dry weight; relative leaf growth rate; total and free B; H(2)O(2); malondialdehyde; ascorbate; glutathione; sugars; total non-enzymatic antioxidant activity, and the activity of superoxide dismutase, catalase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, ascorbate oxidase and l-galactose dehydrogenase. KEY RESULTS: The B-toxicity treatments diminished growth and boosted the amount of B, malondialdehyde and H(2)O(2) in the leaves of the two cultivars, these trends being more pronounced in 'Josefina' than in 'Kosaco'. B toxicity increased ascorbate concentration in both cultivars and increased glutathione only in 'Kosaco'. Activities of antioxidant- and ascorbate-metabolizing enzymes were also induced. CONCLUSIONS: High B concentration in the culture medium provokes oxidative damage in tomato leaves and induces a general increase in antioxidant enzyme activity. In particular, B toxicity increased ascorbate pool size. It also increased the activity of l-galactose dehydrogenase, an enzyme involved in ascorbate biosynthesis, and the activity of enzymes of the Halliwell-Asada cycle. This work therefore provides a starting point towards a better understanding of the role of ascorbate in the plant response against B stress.     

Overexpression of GlyI and GlyII genes in transgenic tomato (Solanum lycopersicum Mill.) plants confers salt tolerance by decreasing oxidative stress

The glyoxalase system plays an important role in various physiological processes in plants, including salt stress tolerance. We report the effects of overexpressing glyoxalase I and glyoxalase II genes in transgenic tomato (Solanum lycopersicum Mill.) cv. Ailsa Craig. Stable expression of both transgenes was detected in the transformed tomato plants under salt stress. The transgenic lines overexpressing GlyI and GlyII under a high NaCl concentration (800 mM) showed reduced lipid peroxidation and the production of H₂O₂ in leaf tissues. A greater decrease in the chlorophyll a+b content in wild-type (WT) compared with transgenic lines was also observed. These results suggest that the over expression of two genes, GlyI and GlyII, may enhance salt stress tolerance by decreasing oxidative stress in transformed tomato plants. This work will help our understanding of the putative role of the glyoxalase system in the tolerance to abiotic stress in tomato plants.     

Organ-dependent oxylipin signature in leaves and roots of salinized tomato plants (Solanum lycopersicum)

Oxylipins have been extensively studied in plant defense mechanisms or as signal molecules. Depending on the stress origin (e.g. wounding, insect, pathogen), and also on the plant species or organ, a specific oxylipin signature can be generated. Salt stress is frequently associated with secondary stress such as oxidative damage. Little is known about the damage caused to lipids under salt stress conditions, especially with respect to oxylipins. In order to determine if an organ-specific oxylipin signature could be observed during salt stress, tomato (Solanum lycopersicum cv. Money Maker) plants were submitted to salt stress (100 mM of NaCl) for a 30-d period. A complete oxylipin profiling and LOX related-gene expression measurement were achieved in leaves and roots. As expected, salt stress provoked premature senescence in leaves, as revealed by a decrease in photosystem II efficiency (F(v)/F(m) ratio) and sodium accumulation in leaves. In roots, a significant decrease in several oxylipins (9- and 13-hydro(pero)xy linole(n)ic acids, keto and divinyl ether derivatives) was initiated at day 5 and intensified at day 21 after salt treatment, whereas jasmonic acid content increased. In leaves, the main changes in oxylipins were observed later (at day 30), with an increase in some 9- and 13-hydro(pero)xy linole(n)ic acids and a decrease in some keto-derivatives and in jasmonic acid. Oxylipin enantiomeric characterization revealed that almost all compounds were formed enzymatically, and therefore a massive auto-oxidation of lipids that can be encountered in abscission processes can be excluded here.     

Virus induced gene silencing of three putative prolyl 4-hydroxylases enhances plant growth in tomato (Solanum lycopersicum)

Proline hydroxylation is a major posttranslational modification of hydroxyproline-rich glycoproteins (HRGPs) that is catalyzed by prolyl 4-hydroxylases (P4Hs). HRGPs such as arabinogalactan proteins (AGPs) and extensios play significant roles on cell wall structure and function and their implication in cell division and expansion has been reported. We used tobacco rattle virus (TRV)-based virus induced gene silencing to investigate the role of three tomato P4Hs, out of ten present in the tomato genome, in growth and development. Eight-days old tomato seedlings were infected with the appropriate TRV vectors and plants were allowed to grow under standard conditions for 6 weeks. Lower P4H mRNA levels were associated with lower hydroxyproline content in root and shoot tissues indicating successful gene silencing. P4H-silenced plants had longer roots and shoots and larger leaves. The increased leaf area can be attributed to increased cell division as indicated by the higher leaf epidermal cell number in SlP4H1- and SlP4H9-silenced plants. In contrast, SlP4H7-silenced plants had larger leaves due to enhanced cell expansion. Western blot analysis revealed that silencing of SlP4H7 and SlP4H9 was associated with reduced levels of JIM8-bound AGP and JIM11-bound extensin epitopes, while silencing of SlP4H1 reduced only the levels of AGP proteins. Collectively these results show that P4Hs have significant and distinct roles in cell division and expansion of tomato leaves.     

Cloning, expression and characterization of insulin-degrading enzyme from tomato (Solanum lycopersicum)

A cDNA encoding insulin-degrading enzyme (IDE) was cloned from tomato (Solanum lycopersicum) and expressed in Escherichia coli in N-terminal fusion with glutathione S-transferase. GST-SlIDE was characterized as a neutral thiol-dependent metallopeptidase with insulinase activity: the recombinant enzyme cleaved the oxidized insulin B chain at eight peptide bonds, six of which are also targets of human IDE. Despite a certain preference for proline in the vicinity of the cleavage site, synthetic peptides were cleaved at apparently stochastic positions indicating that SlIDE, similar to IDEs from other organisms, does not recognize any particular amino acid motif in the primary structure of its substrates. Under steady-state conditions, an apparent K(m) of 62+/-7 microm and a catalytic efficiency (k(cat)/K(m)) of 62+/-15 mm(-1) s(-1) were determined for Abz-SKRDPPKMQTDLY(NO(3))-NH(2) as the substrate. GST-SlIDE was effectively inhibited by ATP at physiological concentrations, suggesting regulation of its activity in response to the energy status of the cell. While mammalian and plant IDEs share many of their biochemical properties, this similarity does not extend to their function in vivo, because insulin and the beta-amyloid peptide, well-established substrates of mammalian IDEs, as well as insulin-related signaling appear to be absent from plant systems.     

Morpho-physiological investigations in transgenic tomato (Solanum lycopersicum L.) over expressing OsRGLP1 gene

In Vitro Cellular & Developmental Biology - Plant - The OsRGLP1 gene was overexpressed under the control of CaMV 35S promoter in tomato (Solanum lycopersicum L.) plants using...