Changes in free polyamine levels induced by salt stress in leaves of cultivated and wild tomato species

The effects of N_aCl on endogenous free levels of the poluamines putrescine, spermi dine and spermine, and the relationships between polyamines, K⁺ levels and Na⁺ accumulation were determined in leaves of the cultivated tomato ( Lycopersicon esculentum Mill.) and its wild, salt-tolerant relative L. pennellii (Correll) D' Arcy at different exposure times during a 32-day period. Both stress treatments (100 and 200 m M NaCl) decreased the levels of putrescine and spermidine, although to a different degree for the cultivated and wild tomato species. The spermine levels did not decrease with salinity in L. pennellii over the salinization period, whereas they decreased in L. esculentum , except at the first application of the 100m M NaCl treatment. In both species, the changes induced by salinity in total polyamines and K⁺ were very similar, with the accumulation of Na⁺ in the leaf being concomitant with a decrease in both total polyamines and K⁺. This suggests that the main role of the polyamines in the leaf tissues. In this sense, a direct relationship between total polyamines and K⁺, and inverse relationship between polyamines and Na⁺ and between K⁺ and Na⁺ were found for both species. In the short term (up to 4 days) a peculiar physiological behavior was found in L. pennellii , as the total polyamine and K⁺ levels decreased at 100 m M but not at 200 m M NaCl, while after this time the latter plants had values lower than those of the 100 m M NaCl-treated plants at day 11.     

Salinity effects on water relations in Lycopersicon esculentum and its wild salt-tolerant relative species L. pennellii

Cultivated tomato Lycopersicon esculentum (L.) Mill. cv. P-73 and its wild salt tolerant relative L. pennellii (Correll) D'Arcy accession PE-47, were grown during spring-summer 1989 under unheated plastic greenhouse conditions. Plants were submitted to two different salt treatments using 0 and 140 mM NaCI irrigation water. In both tomato species, salinity caused a proportionally larger reduction in leaf area than in leaf weight and, in L. esculentum , a proportionally larger decrease in stem weight than in leaf weight. Daily variations in leaf water potential (Ψ₁) were fundamentally due to changes in the evaporative demand of the atmosphere. Reductions in Ψ₁ due to salinity were consistent only in L. esculentum . In all the conditions studied, leaf turgor was maintained. Leaf conductance (g₁)was higher in L. esculentum than in L. pennellii .Salinity induced a clear reduction in g₁ levels in L. esculentum whereas, in L. pennellii , this reduction was noted only in May. In both species the Ψ^o_s (leaf osmotic potential at full turgor) levels were reduced by salinity. The bulk modulus of elasticity (E) and relative water content at turgor loss point (RWC_tlp) were not affected by salinity. The RWC_tlp values in L. pennellii seem to be controlled by E values.     

Water relations and osmotic adjustment in Lycopersicon esculentum and L. pennellii during short-term salt exposure and recovery

Cultivated tomato Lycopersicon esculentum (L.) Mill. cv. P-73 and its wild salt-tolerant relative L. pennellii (Correll) D'Arcy accession PE-47 growing on silica sand in a growth chamber were exposed to 0, 70, 140 and 210 m M NaCl nutrient solutions 35 days after sowing. The saline treatments were imposed for 4 days, after which the plants were rinsed with distilled water. Salinity in L. esculentum reduced leaf area and leaf and shoot dry weights. The reductions were more pronounced when sodium chloride was removed from the root medium. Reduction in leaf area and weight in L. pennellii was only observed after the recovery period. In both genotypes salinity induced a progressive reduction in leaf water potential and leaf conductance. During the recovery period leaf water potential (ψ₁) and leaf conductance (g₁) reached levels similar to those of control plants in wild and cultivated species, respectively. Leaf osmotic potential at full turgor (ψ_os) decreased in the salt treated plants of both genotypes, whereas the bulk modulus of elasticity was not affected by salinity. Leaf water potential at turgor loss point (ψ_tlp) and relative water content at turgor loss point (RWC_tlp) appeared to be controlled by leaf osmotic potential at full turgor (ψ_os) and by bulk modulus of elasticity, respectively. At lowest salinity, the wild species carried out the osmotic adjustment based almost exclusively on Cl⁻ and Na⁺, with a marked energy savings. Under highest salinity, this species accommodate the stress through a higher expenditure of energy due to the contribution of organic solutes to the osmotic adjustment. The domesticated species carried out the osmotic adjustment based always on an important contribution of organic solutes.     

Potassium utilization and fluxes in wild salt-tolerant relatives of the cultivated tomato

The growth of the wild tomato species Lycopersicon peruvianum (L.) Mill, and L. pennellii (Correll) D'Arcy, was compared with that of the cultivated tomato, L. esculentum Mill. cv. VE 234, under conditions of reduced K⁺ supply. Growth was impaired less in the wild than in the cultivated species. The higher efficiency of K⁺ utilization in the wild species was not associated with more efficient JC uptake from the medium. The rate of K⁺ uptake by whole plants was similar in the three species, but the rate of uptake by detached root tips was lower in the wild species. The permeability of the plasma membrane to K+ was apparently similar in root tips of the three species, but the tonoplast permeability was much lower in the wild than in the cultivated species.     

Evaluation of salt tolerance in cultivated and wild tomato species through in vitro shoot apex culture

The possibility of using in vitro shoot apex culture to evaluate salt tolerance of cultivated (Lycopersicon esculentum Mill.) and wild (Lycopersicon pennellii (Correll) D'Arcy) tomato species was determined and related to the response obtained by callus culture. Both apices and calluses were grown on media supplemented with 0, 35, 70, 105, 140, 175 and 210 mM NaCl, and growth and physiological traits were determined. Most apices of L. esculentum did not develop roots from low NaCl levels, whereas the apices of L. pennellii were able to develop roots at the different salt levels. This different degree of salt tolerance between L. esculentum and L. pennellii was not, however, clearly shown on the basis of the shoot growth of the plantlets. The callus response was similar to that shown by the rooting parameters, as callus growth in response to increased salinity was much greater in L. pennellii than in the tomato cultivar. K⁺decreased more and proline accumulated less with salinity in shoots of L. esculentum compared to L. pennellii, whereas the opposite response was obtained in calluses. The results obtained in this study suggest that rooting parameters are the most useful traits for rapid evaluation and screening of tomato species and segregating populations through in vitro shoot apex culture. This revised version was published online in June 2006 with corrections to the Cover Date.     

Responses to NaCl stress of cultivated and wild tomato species and their hybrids in callus cultures

Summary If in vitro culture is to be used for evaluating the salt tolerance of tomato hybrids and segregant populations in a breeding programme, it is previously necessary to get quick and reliable traits. In this work, growth and physiological responses to salinity of two interspecific hybrids between the cultivated tomato (Lycopersicon esculentum Mill) and its wild salt-tolerant species L pennellii are compared to those of their parents. The leaf callus of the first subculture was grown on media amended with 0, 35, 70, 105, 140, 175 and 210 mM NaCl for 40 days. Relative fresh weight growth of callus in response to increased salinity in the culture medium was much greater in L pennellii than in the tomato cultivars, and greater in the hybrids than in the wild species. Moreover, the different salt tolerance degree of hybrids was related to that of female parents. At high salt levels, only Cl^– accumulation was higher in L pennellii than in tomato cultivars, whereas in the hybrids both Cl^–, and Na⁺ accumulation were higher than in their parents. Proline increased with salinity in the callus of all genotypes; these increases were much higher in the tomato cultivars than in L pennellii, and the hybrids showed a similar response to that of the wild species. Salt-treated callus of the tomato cultivars showed significant increases in valine, isoleucine and leucine contents compared to control callus tissue. In contrast, these amino acids in callus tissues of the wild species and hybrids showed a tendency to decrease with increasing salinity.     

Toxicity of methyl ketones from tomato trichomes to Tetranychus urticae Koch

The two methyl ketones, 2-tridecanone and 2-undecanone, are constituents of type VI glandular trichomes of the wild tomato, Lycopersicon hirsutum f. glabratum (PI 134417). They are known to cause mortality in several herbivorous insect species. In this study we investigated the effects of these chemicals on two strains of the two-spotted spider mite, Tetranychus urticae Koch, collected from tomato and cucumber crops in Dutch greenhouses. The two ketones were tested separately, in combination in the ratio found in L. hirsutum f. glabratum and in several other ratios to detect any synergistic interaction between them. We measured both the direct contact and residual toxicity, as well as the viability of the eggs produced by ketone-treated females. The methyl ketones can be considered as quite toxic to spider mites because their LC50 values were comparable to that found for the formulated acaricide amitraz. 2-Tridecanone was slightly more toxic than 2-undecanone but only in the tomato strain. Synergistic effects were not detected. In the bio assays for the residual effects of the two methyl ketones no significant mortality occurred but the mites avoided feeding on the treated surface and the eggs were laid almost exclusively on the untreated area. Furthermore, there was no significant egg viability for most of the treatments and when some egg viability occurred, it was not correlated to the dose of the chemical. Based on published data on the levels of methyl ketones in the trichome tips of wild and cultivated tomato (L. hirsutum f. glabratum and Lycopersicon esculentum Mill, respectively) it was calculated how many contacts are required to reach the LD50 (ng a.i. per mite). It appeared that on wild tomato just a few contacts suffice, but many are needed on cultivated tomato. Nevertheless, it seems justified to conclude that even in cultivated tomato, 2-tridecanone represents a naturally occurring acaricide. The cucumber and tomato strains of the two-spotted spider mite did not differ in their response to the methyl ketones. Because this is surprising, given the selection pressures on their respective host plants, we formulated two hypotheses, one explaining the absence of a difference due to cross-resistance and another one proposing that bioaccumulation obscures the underlying differences between the strains. This revised version was published online in November 2006 with corrections to the Cover Date.     

Cold tolerance in tomato. II. Early seedling growth of Lycopersicon spp.

Hypocotyl and root growth elongation of etiolated seedlings was measured non-destructively for the wild tomato accessions LA 460 ( Lycopersicon chilense Dun.), PI 126435, PI 127831 and PI 127832 ( L. peruvianum Mill.) and controls PI 120256 and T3 ( L. esculentum Mill.) on slant boards at 10, 15 and 20°C. Both hypocotyl and root elongation over time were fitted by a logistic growth function with three parameters estimated for each seedling by non-linear least squares regression. Analysis of variance of these equation parameters indicated linear decreases of both hypocotyl and root growth rate parameters with temperature. All four wild accessions maintained greater hypocotyl growth rate parameters at 10°C than the fast-germinating cultivated accession PI 120256, but not significantly greater than T3. Hypocotyl growth rates of the wild accessions were less inhibited at 10°C relative to 20°C than were either cultivated accession. These results suggest that these wild accessions have greater chilling tolerance than cultivated controls for early seedling growth, and may have potential use for genetically improving emergence times for tomatoes sown in cold soil.     

The Effect of Ventilation on in vitro Response of Seedlings of the Cultivated Tomato and its Wild Salt-tolerant Relative Lycopersicon pennellii to Salt Stress

Organs or plants grown in vitro do not always exhibit the same responses to salinity as the whole plant of same species grown ex vitro. The response to salinity (100 mM NaCl) of seedlings of the wild tomato species Lycopersicon pennellii acc. Atico (Lpa) and of the cultivated tomato L. esculentum cv. M82 (Lem), the former is known as salt tolerant and the second as relatively salt sensitive under ex vitro conditions, was compared under in vitro conditions with three different ventilation regimes. It was found that under salinity shoots of the wild species accumulated the same or even more dry biomass than the control (roots somewhat less) under all ventilation levels. Growth of shoots and roots of the cultivated species was inhibited under the same conditions especially under the high ventilation. Ventilation reduced some abnormalities of leaf development related to hyperhydricity and consequently ventilated leaves exhibited a more compounded structure, increased area, increased resistance to water loss and stomata functioning. Ventilation increased K⁺, Na⁺ and Cl⁻ accumulation in shoots of both tomato species. This was more pronounced under salinity and in Lpa. This work indicates that differences that characterize whole plants of these species in response to salinity under ex vitro conditions are exhibited also in whole plants grown in vitro under high ventilation. It is suggested that ventilation is needed to evaluate well the response of whole plants to salt stress applied in vitro.     

The effect of salt stress on lipid peroxidation and antioxidants in the leaf of the cultivated tomato and its wild salt‐tolerant relative Lycopersicon pennellii

The possible involvement of the antioxidative system in the tolerance to salt stress was studied in the cultivated tomato Lycopersicon esculentum Mill. cv. M82 (M82) and its wild salt‐tolerant relative L. pennellii (Corn) D'Arcy accession Atico (Lpa). All analyses, except that of monodehydroascorbate reductase (MDHAR), were performed of the youngest fully‐expanded leaf of control and salt (100 m M NaCl) stressed plants, 4, 7, 10, 14, 18 and 22 days after completing the stress treatment. In Lpa, constitutive level of lipid peroxidation and activities of catalase (CAT) and glutathione reductase (GR) were lower while the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) were inherently higher than in M82. Relative to M82, lipid peroxidation was much lower and the activities of SOD, CAT and APX were higher in Lpa at 100 m M NaCl. The activity of DHAR decreased more in Lpa than in M82 under salt stress, and the activity of MDHAR, which was lower in Lpa than in M82 under control conditions, increased much more and to a higher level in salt‐treated Lpa plants. GR activity decreased similarly in the two species under salt stress. The results of these analyses suggest that the wild salt‐tolerant Lpa plants are better protected against active oxygen species (AOS), inherently and under salt stress, than the relatively sensitive plants of the cultivated species.     

The chilling sensitivity of root ammonium influx in a cultivated and wild tomato

A chilling episode of a few hours damaged root ammonium absorption in a cultivated tomato ( Lycopersicon esculentum cv. T-5), but not in a wild congener from high altitudes ( Lycopersicon hirsutum LA1778). In the cultivar, ammonium influx was strongly temperature dependent and showed the residual effects of chilling, whereas ammonium efflux was nearly temperature invariant and showed no persistent effects. A 2 h exposure to 5 °C significantly depressed subsequent ammonium absorption at 20 °C, and about 12 h at 20 °C was required for recovery. For both the cultivated and wild species, rerooted cuttings were slightly less sensitive to chilling than seedlings. The relative inhibition (mean ± SE) of ammonium absorption before and after chilling was 58·4 ± 2·5% for the cultivated species and 29·0 ± 9·1% for the wild species. The F₁ hybrid between the species showed a relative inhibition of 52·4 ± 3·6%, suggesting that chilling sensitivity may be dominant. In a backcross of the hybrid to L. esculentum , the phenotypic distribution of the relative inhibition of ammonium absorption indicated that this trait is segregating.     

The response to NaCl of excised fully differentiated and differentiating tissues of the cultivated tomato, Lycopersicon esculentum, and its wild relatives, L. peruvianum and Solanum pennellii

The responses to NaCl of cultured leaf discs and leaflets derived from fully differentiated leaves and of shoot apices excised from the cultivated tomato Lycopersicon esculentum Mill. and its wild salt-tolerant relatives L. peruvianum (L.) Mill, and Solanum pennellii Cor were compared. The results suggest that the tolerance of the whole plant to salt depends largely on the tolerance of plant organs containing meristematic tissues rather than on tissues already differentiated. This suggestion is based on the positive correlation found between the response to NaCl of shoot apices and of the whole plant, i.e. both whole plants and apices of the wild species were more resistant to salt than those of the cultivated species. No difference was found among the species with respect to the responses of the fully differentiated parts. The ion balance (K⁺/Na⁺ and Cl⁻/Na⁺) in detached leaves and apices exposed to salt was different from the balance in the same parts while attached to the salt-treated plant. This difference may be due to the severance of the excised parts from the major sites controlling the balance of ions in the whole plant.     

Salinity tolerance of normal-fruited and cherry tomato cultivars

The salinity tolerances (NaCl) of 8 normal-fruited tomato cultivars (Lycopersicon esculentum Mill.) and 4 cherry tomato cultivars (L. esculentum var.cerasiforme) were determined by yield-substrate EC response curves, according to the Mass-Hoffman model, modified by van Genuchten and Hoffman (1984). The same model was used to determine the response curves of leaf dry-weight, stem dry-weight, and plant height against substrate EC and also between yield and leaf concentrations of Cl- and Na ions.According to the salinity-threshold (maximum EC-value without yield reduction) and slope (yield decrease per unit EC increase) parameters, determined from the yield-EC response curves, the cherry tomato cultivars were more salt-tolerant than the normal-fruited ones. However, on the basis of vegetative growth characters-EC response curves, cherry tomato cultivars and normal-fruited ones were similarly affected by NaCl.The ranking of the cultivars by their salinity tolerance, determined from the plots of yield vs. leaf concentrations of Cl- and Na ions, was the same as that evaluated from the yield vs. substrate EC plots.     

The inheritance of chilling tolerance in tomato (Lycopersicon spp.)

During the past 25 years, chilling tolerance of the cultivated (chilling-sensitive) tomato Lycopersicon esculentum and its wild, chilling-tolerant relatives L. peruvianum and L. hirsutum (and, less intensively studied, L. chilense) has been the object of several investigations. The final aim of these studies can be seen in the increase in chilling tolerance of the cultivated genotypes. In this review, we will focus on low-temperature effects on photosynthesis and the inheritance of these traits to the offspring of various breeding attempts. While crossing L. peruvianum (male symbol) to L. esculentum (female symbol) so far has brought the most detailed insight with respect to physiological questions, for practical purposes, e.g., the readily cross ability, crossing programmes with L. hirsutum as pollen donor at present seem to be a promising way to achieve higher chilling-tolerant genotypes of the cultivated tomato. This perspective is due to the progress that has been made with respect to the genetic basis of chilling tolerance of Lycopersicon spp. over the past five years.     

Natural Occurrence of Pepino mosaic virus in Lycopersicon Species in Central and Southern Peru

Pepino mosaic virus (PepMV), a potexvirus first described in 1980 from pepino ( Solanum muricatum ) plants cultivated in Peru, was isolated from diseased tomato plants in the Netherlands in 1999, and is now the cause of an emerging tomato disease in Europe. In a survey of central and southern Peru, 65 wild and four cultivated populations of Lycopersicon , as well as six populations of other species of Solanaceae , were tested for the presence of PepMV and six other viruses. Of the Lycopersicon population sampled, 23 (35.4%) reacted positively in double antibody sandwich (DAS)-enzyme-linked immunosorbent assay (ELISA) with antisera to PepMV. DAS-ELISA tests for PepMV of other solanaceous species were negative, except for one sample of pepino ( Solanum muricatum ). Mechanical inoculation of susceptible Lycopersicon esculentum cv. NE-1 plants with crude sap extracts of 20 of these samples confirmed that 15 of them (from the Departments of Apurimac, Arequipa and Moquegua) were infected with PepMV; these inoculated plants were also DAS-ELISA positive and, in most cases, developed symptoms. Thirteen of the infective extracts were obtained from plants of wild Lycopersicon species (three L. chilense , three L. chmielewskii , two L. parviflorum and five L. peruvianum ) and one each from the cultivated species L. esculentum and S. muricatum . The wild Lycopersicon species are newly reported natural hosts of PepMV. Tests for the other six viruses were negative, except that two samples contained Tomato mosaic virus . Thus, PepMV occurs in Lycopersicon species in central and southern Peru, even in isolated wild populations. These results indicate that the virus is not new to the region and has an efficient mechanism of natural transmission.     

Fluxes of Na+, K+ and Cl-, and osmotic adjustment in Lycopersicon pimpinellifolium and L. esculentum during short- and long-term exposures to NaCl

NaCl (140 m M ) was applied to 14-day-old plants of salt-sensitive Lycopersicon esculentum Mill. cv. Volgogradskij and its wild relative L. pimpinellifolium Mill. accession PE-2. Changes in the relative growth rate of whole plant, and in the levels of inorganic and organic solutes in leaves, stems and roots were followed for 15 days after the application. Short-term salt exposure (4–6 days of salinization) resulted in enhanced relative growth rates for L. pimpinellifolium , but did not affect growth of L. esculentum , After 6 days of salinization, the relative growth rates of both species decreased significantly; leading to practically comparable growth rates for them by day 15. In all parts of both species, the contribution of organic solutes to the osmotic potential (Ψ_s) gradually decreased from 30% on day 0 to a value lower than 5% on day 4. In L. pimpinellifolium , compared to L. esculentum , short-term salt exposure resulted in (1) a higher percentage of adjustment of Ψ_s; and (2) increases in Na⁺ and K⁺ uptake rates, and in the levels of organic acids and proline (the level of which reached that of sugars, i.e., 10 μmol g^-1 dry weight. Conversely, in L. esculentum , drastic reductions of K⁺ uptake rates and organic acid levels occurred already on day 1. During long-term salt exposure, both species were able to adjust osmotically and both exhibited decreases in organic acid levels as well as in K⁺ uptake and accumulation rates in all parts. The results are discussed in an attempt to explain the adaptive responses during short-term salt exposure and the metabolic dysfunctions that lead to growth decrease after long-term exposure to salt.     

Sucrolytic activities during fruit development of Lycopersicon genotypes differing in tolerance to salinity

The different growth responses under control and moderate salinity (70 mM NaCl) in relation to the carbon partitioning and sucrose metabolism in developing tomato fruits [20 days after anthesis (DAA), start of ripening and ripe stages] were studied in the cultivated tomato Lycopersicon esculentum Mill (cv. H-324-1), in the wild relative species L. cheesmanii (ac. LA-530) (hexose-accumulators), L. chmielewskii (ac. LA-1028) (sucrose-accumulator) and in two interspecific F1 hybrids (hexose-accumulators) (F1-530: H-324-1 x A-530, F1-1028: H-324-1 x A-1028). The higher salt-tolerance of the wild species and hybrids with respect to the domestic tomatoes was also observed at the fruit level because these genotypes were less affected in the assimilation of dry weight (DW) under salinity. With the exception of the wild tomatoes, the sink strength, evaluated as the dry matter accumulation rate (mg DW day-1) and the sink activity, evaluated as a relative growth rate (mg DW mg-1 day-1), were reduced during the early fruit growing period (20 DAA-start ripening). However, a total recovery of growth was registered in the salinized hybrid fruits during the late growing period (start of ripening-ripe fruits). The early reduction in sink activity in the hybrid and domestic fruits was related to a sucrose accumulation and a decrease in the total sucrolytic activity at 20 DAA, especially the cytoplasmic sucrolytic activities sucrose synthase (EC 2.4.1.13) and neutral invertase (EC 3.2.1.26). The further recovery in sink strength of the hybrid fruits was related to the maintenance of the insoluble acid invertase (EC 3.2.1.25) and the induction of the cytoplasmic sucrolytic activities, namely at the start of ripening stage, demonstrating the existence of an inverse relationship between these activities, which suggests a regulatory mechanism in order to maintain the sink capacity. The roles of different enzymes in the control of assimilate import under salinity in relation to the sucrose transport and possible regulatory mechanisms are discussed.     

Serological studies on the accumulation and localisation of three tomato leaf curl geminiviruses in resistant and susceptible Lycopersicon species and tomato cultivars

Accessions of wild Lycopersicon spp. and selected Fl hybrid tomato cultivars were compared for their resistance to three whitefly-transmissible geminiviruses: Indian tomato leaf curl virus (ITmLCV) and tomato yellow leaf curl viruses from Sardinia (TYLCV-Sar) and Senegal (TYLCV-Sen). The resistance of different plant lines was expressed in different ways but in most instances a given line reacted similarly to graft inoculation with the three viruses. L. pimpinellifolium LA1478 produced as much virus antigen, assessed by triple antibody sandwich-ELISA, as the susceptible cv. Moneymaker but developed only very mild symptoms and is therefore tolerant of infection. In L. hirsutum LA1777 and L. peruvianum CMV-INRA, very mild or no symptoms developed but antigen concentrations were substantially less than in Moneymaker. L. chilense LA1969 remained symptomless and its antigen concentration was < 1% of that in Moneymaker. Symptoms were mild or barely evident in the Fl hybrid cultivars. Cultivars Tyking and Fiona had antigen concentrations about 5–10% of those of Moneymaker, whereas TY20, Top 21 and Tyger had intermediate antigen concentrations. In a few instances, the extent to which virus accumulation was restricted depended on the challenge virus. Accumulation of TYLCV-Sen in TY20, Top 21 and Tyger was less affected than that of the other two viruses, and accumulation of TYLCV-Sar in accessions LA1777 and CMV-INRA was less affected than that of TYLCV-Sen or ITmLCV. Tissue-printing tests showed that ITmLCV and TYLCV-Sen antigens were confined to phloem tissue. In Tyking, the number of virus antigen-containing phloem traces and the antigen content of individual traces were less than in Moneymaker but the partitioning of antigen between internal and external phloem was unaffected.