Glycine betaine protects tomato (Solanum lycopersicum) plants at low temperature by inducing fatty acid desaturase7 and lipoxygenase gene expression

Cold stress is among the environmental stressors limiting productivity, yield and quality of agricultural plants. Tolerance to cold stress is associated with the increased unsaturated fatty acids ratio in the plant membranes which are also known to be substrates of octadecanoid pathway for jasmonate and other oxylipins biosynthesis. Accumulation of osmoprotectant, glycine betaine (GB) is well known to be effective in the protecting membranes and mitigating cold stress effects but, the mode of action is poorly understood. We studied the role of GB in cold stress responses of two tomato cultivated varieties; Gerry (cold stress sensitive) and T47657 (moderately cold stress tolerant) and compared the differences in lypoxygenase-13 (TomLOXF) and fatty acid desaturase 7 (FAD7) gene expression profiles and physiological parameters including relative growth rates, relative water content, osmotic potential, photosynthetic efficiency, membrane leakage, lipid peroxidation levels. Our results indicated that GB might have a role in inducing FAD7 and LOX expressions for providing protection against cold stress in tomato plants which could be related to the desaturation process of lipids leading to increased membrane stability and/or induction of other genes related to stress defense mechanisms via octadecanoid pathway or lipid peroxidation products.     

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.     

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.     

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.     

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     

Growth Inhibition Occurs Independently of Cell Mortality in Tomato （Solanum lycopersicum） Exposed to High Cadmium Concentrations

In order to analyze the adaptation potential of tomato shoots to a sudden increase in Cd concentration, tomato plants (Solanum lycopersicum L. var. Ailsa Craig) were exposed under controlled environmental conditions to a high dose of this heavy metal (250 μM CdCl2>) in nutrient solution for 7 and 14 d. Both root and shoot growth was completely inhibited but all plants remained alive until the end of the treatment. Cell viability remained unaffected but the activity of the mitochondrial alternative pathway was stimulated by Cd stress at the expense of the cytochrome pathway. Cadmium concentration was higher in roots than in shoots and a decrease In the rate of net Cd translocation was noticed during the second week of stress. Cadmium decreased both leaf conductance (g1>) and chlorophyll concentration. However, the effect on net CO2 assimilation remained limited and soluble sugars accumulated in leaves. Photochemical efficiency of PSll (FvlFm) was not affected despite a decrease in the number of reaction centers and an inhibition of electron transfer to acceptors of PSII. It is concluded that tomato shoot may sustain short term exposure to high doses of cadmium despite growth inhibition. This property implies several physiological strategies linked to both avoidance and tolerance mechanisms.     

The influence of a reduced gibberellin biosynthesis and nitrogen supply on the morphology and anatomy of leaves and roots of tomato (Solanum lycopersicum)

We investigated how the differences in growth and morphology, between fast-growing wildtype (Wt) tomato ( Solanum lycopersicum L.) plants and slow-growing gibberellin (GA) deficient W335 mutants, were reflected in cell numbers and cell sizes. We also studied whether the differences between the Wt and the low-GA mutant would persist at a growth-limiting supply of nitrate. Both a low endogenous GA concentration and a low supply of nitrate reduced the number and size of leaf cells, whereas they increased the size and number of root cortex cells. The effects of low N-supply on the size and number of leaf and root cells did not depend on endogenous GA concentrations. The mutant's higher allocation to roots seemed to be the result of the strongly reduced growth of the shoot.     

Inoculation of tomato plants (Solanum lycopersicum) with growth-promoting Bacillus subtilis retards whitefly Bemisia tabaci development

Root inoculation of tomato (Solanum lycopersicum) plants with a Bacillus subtilis strain BEB-DN (BsDN) isolated from the rhizosphere of cultivated potato plants was able to promote growth and to generate an induced systemic resistance (ISR) response against virus-free Bemisia tabaci. Growth promotion was evident 3 weeks after inoculation. No changes in oviposition density, preference and nymphal number in the early stages of B. tabaci development were observed between BsDN-treated plants and control plants inoculated with a non-growth promoting Bs strain (PY-79), growth medium or water. However, a long-term ISR response was manifested by a significantly reduced number of B. tabaci  pupae developing into adults in BsDN-treated plants. The observed resistance response appeared to be a combination of jasmonic acid (JA) dependent and JA-independent responses, since the BsDN-related retardation effect on B. tabaci development was still effective in the highly susceptible spr2 tomato mutants with an impaired capacity for JA biosynthesis. A screening of 244 genes, 169 of which were previously obtained from subtractive-suppressive-hybridization libraries generated from B. tabaci-infested plants suggested that the BsDN JA-dependent ISR depended on an anti-nutritive effect produced by the simultaneous expression of genes coding principally for proteases and proteinase inhibitors, whereas the JA-independent ISR observed in the spr2 background curiously involved the up-regulation of several photosynthetic genes, key components of the phenyl-propanoid and terpenoid biosynthetic pathways and of the Hsp90 chaperonin, which probably mediated pest resistance response(s), in addition to the down-regulation of pathogenesis and hypersensitive response genes.     

Differential gene expression in whitefly Bemisia tabaci-infested tomato (Solanum lycopersicum) plants at progressing developmental stages of the insect's life cycle

A suppression-subtractive-hybridization (SSH) strategy was used to identify genes whose expression was modified in response to virus-free whitefly Bemisia tabaci ( Bt , biotype A) infestation in tomato ( Solanum lycopersicum ) plants. Thus, forward and reverse SSH gene libraries were generated at four points in the whitefly's life cycle, namely at (1) 2 days (adult feeding and oviposition: phase I); (2) 7 days (mobile crawler stage: phase II); (3) 12 days (second to third instar nymphal transition: phase III) and (4) 18 days (fourth instar nymphal stage: phase IV). The 169 genes with altered expression (up and downregulated) that were identified in the eight generated SSH libraries, together with 75 additional genes that were selected on the basis of their involvement in resistance responses against phytofagous insects and pathogens, were printed on a Nexterion^® Slide MPX 16 to monitor their pattern of expression at the above phases. The results indicated that Bt infestation in tomato led to distinctive phase-specific expression/repression patterns of several genes associated predominantly with photosynthesis, senescence, secondary metabolism and (a)biotic stress. Most of the gene expression modifications were detected in phase III, coinciding with intense larval feeding, whereas fewer changes were detected in phases I and IV. These results complement previously reported gene expression profiles in Bt -infested tomato and Arabidopisis, and support and expand the opinion that Bt infestation leads to the downregulation of specific defense responses in addition to those controlled by jasmonic acid.     

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.     

Identification and localization of a lipase-like acyltransferase in phenylpropanoid metabolism of tomato (Solanum lycopersicum)

We have isolated an enzyme classified as chlorogenate: glucarate caffeoyltransferase (CGT) from seedlings of tomato (Solanum lycopersicum) that catalyzes the formation of caffeoylglucarate and caffeoylgalactarate using chlorogenate (5-O-caffeoylquinate) as acyl donor. Peptide sequences obtained by trypsin digestion and spectrometric sequencing were used to isolate the SlCGT cDNA encoding a protein of 380 amino acids with a putative targeting signal of 24 amino acids indicating an entry of the SlCGT into the secretory pathway. Immunogold electron microscopy revealed the localization of the enzyme in the apoplastic space of tomato leaves. Southern blot analysis of genomic cDNA suggests that SlCGT is encoded by a single-copy gene. The SlCGT cDNA was functionally expressed in Nicotiana benthamiana leaves and proved to confer chlorogenate-dependent caffeoyltransferase activity in the presence of glucarate. Sequence comparison of the deduced amino acid sequence identified the protein unexpectedly as a GDSL lipase-like protein, representing a new member of the SGNH protein superfamily. Lipases of this family employ a catalytic triad of Ser-Asp-His with Ser as nucleophile of the GDSL motif. Site-directed mutagenesis of each residue of the assumed respective SlCGT catalytic triad, however, indicated that the catalytic triad of the GDSL lipase is not essential for SlCGT enzymatic activity. SlCGT is therefore the first example of a GDSL lipase-like protein that lost hydrolytic activity and has acquired a completely new function in plant metabolism, functioning in secondary metabolism as acyltransferase in synthesis of hydroxycinnamate esters by employing amino acid residues different from the lipase catalytic triad.     

Colonization with arbuscular mycorrhizal fungi improves salinity tolerance of tomato (Solanum lycopersicum L.) plants

The purpose of this study was to investigate the mechanisms underlying alleviation of salt stress by mycorrhization. Solanum lycopersicum L. cultivars Behta and Piazar with different salinity tolerance were cultivated in soil without salt (EC?=?0.63 dSm^?1), with low (EC?=?5 dSm^?1), or high (EC?=?10 dSm^?1) salinity. Plants inoculated with the arbuscular mycorrhizal fungi Glomus intraradices (+AMF) were compared to non-inoculated plants (?AMF). Under salinity, AMF-mediated growth stimulation was higher in more salt tolerant Piazar than in sensitive Behta. Mycorrhization alleviated salt-induced reduction of P, Ca, and K uptake. Ca/Na and K/Na ratios were also better in +AMF. However, growth improvement by AMF was independent from plant P nutrition under high salinity. Mycorrhization improved the net assimilation rates through both elevating stomatal conductance and protecting photochemical processes of PSII against salinity. Higher activity of ROS scavenging enzymes was concomitant with lowering of H₂O_2, less lipid peroxidation, and higher proline in +AMF. Cultivar differences in growth responses to salinity and mycorrhization could be well explained by differences in ion balance, photochemistry, and gas exchange of leaves. Function of antioxidant defenses seemed responsible for different AMF-responsiveness of cultivars under salinity. In conclusion, AMF may protect plants against salinity by alleviating the salt-induced oxidative stress.     

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.     

Viscoelastic nature of isolated tomato (Solanum lycopersicum) fruit cuticles: a mathematical model

Viscoelastic behaviour of isolated tomato fruit cuticle (CM) is well known and extensively described. Temperature and hydration conditions modify the mechanical properties of CM. Mechanical data from previous transient‐creep analysis developed in tomato fruit cuticle under different temperature and hydration conditions have been used to propose a rheological model that describes the viscoelastic nature of CM. As a composite material, the biomechanical behaviour of the plant cuticle will depend not only on the mechanical characteristics of the individual components by themselves but also on the sum of them. Based on this previous information, we proposed a two‐element model to describe the experimental behaviour: an elastic hookean element connected in parallel to a viscous element or Voigt element that will describe the mechanical behaviour of the isolated CM and cutin under the studied conditions. The main parameters of the model, E₁ and E₂ will reflect the elastic and viscoelastic behaviour of the cuticle. Relationship between these physical parameters and the change in CM properties were discussed in order to elucidate the rheological processes taking place in CM. This model describes both the influence of temperature and hydration and the behaviour of the isolated cutin and the inferred contribution of the cuticle fraction of polysaccharides when the whole cuticle is tested.     

Growth and shoot:root partitioning of spinach plants as affected by nitrogen supply

Spinach plants (Spinacia oleracea L.) were grown hydroponically in fixed environmental conditions either at full nitrate availability (11·8mol m^-3) or at a suboptimum relative nitrate addition rate of 0·20d^-1, 0·15d^-1 or 0·10d^-1 respectively, the other nutrients being adequately provided. The relative growth rate (RGR) of the plants varied significantly with the nutrition treatment and decreased during development in all treatments. The concentration of reduced nitrogen in the plants grown at full nitrate availability did not change significantly during the experimental growth period and nitrate accumulation was substantial. After an adaptation period, the concentration of reduced nitrogen in the plants at the suboptimum nitrate addition rates increased during growth and was lowest at the lowest relative nitrate addition rate. Nitrate uptake was almost complete in the suboptimum treatments and nitrate accumulation was negligible as long as the concentration of reduced nitrogen was below 2·0 mmol (g dry weight)^-1. The RGR of all plants was proportional to the concentration of reduced nitrogen in the plant minus a minimal tissue concentration required for growth. However, the proportionality factor was inversely related to the plant mass. This relationship was summarized in an empirical model which explained 98·7% of the variance of the dry weight (log scale) data of all treatments at all harvests. The model was compared with other growth models found in the literature. The shoot/root weight ratio increased from 2 to 4 if nitrate provision was not limiting, and initially, this ratio decreased at suboptimum nitrate provision but increased at higher growth stages. Possible explanations of the dynamics of dry matter partitioning are discussed in relation to models.