Grafting raises the salt tolerance of tomato through limiting the transport of sodium and chloride to the shoot

With the aim of determining whether grafting could improve salinity tolerance of tomato (Lycopersicon esculentum Mill.), and what characteristics of the rootstock were required to increase the salt tolerance of the shoot, a commercial tomato hybrid (cv. Jaguar) was grafted onto the roots of several tomato genotypes with different potentials to exclude saline ions. The rootstock effect was assessed by growing plants at different NaCl concentrations (0, 25, 50, and 75 mM NaCl) under greenhouse conditions, and by determining the fruit yield and the leaf physiological changes induced by the rootstock after 60 d and 90 d of salt treatment. The grafting process itself did not affect the fruit yield, as non-grafted plants of cv. Jaguar and those grafted onto their own root showed the same yield over time under non-saline conditions. However, grafting raised fruit yield in Jaguar on most rootstocks, although the positive effect induced by the rootstock was lower at 25 mM NaCl than at 50 and 75 mM NaCl. At these higher levels, the plants grafted onto Radja, Pera and the hybrid VolgogradskijxPera increased their yields by approximately 80%, with respect to the Jaguar plants. The tolerance induced by the rootstock in the shoot was related to ionic rather than osmotic stress caused by salinity, as the differential fruit yield responses among graft combinations were mainly related to the different abilities of rootstocks to regulate the transport of saline ions. This was corroborated by the high negative correlation found between fruit yield and the leaf Na(+) or Cl(-) concentrations in salt-treated plants after 90 d of salt treatment. In conclusion, grafting provides an alternative way to enhance salt tolerance, determined as fruit yield, in the tomato, and evidence is reported that the rootstock is able to reduce ionic stress.     

Improving melon and cucumber photosynthetic activity, mineral composition, and growth performance under salinity stress by grafting onto Cucurbita hybrid rootstocks

The aim of the current work was to determine whether grafting could improve salinity tolerance of melon and cucumber, and whether possible induction of tolerance to salt stress was associated with the protection of the photosynthetic apparatus. Two greenhouse experiments were carried out to determine gas exchange, mineral composition, growth and yield of melon (Cucumis melo L. cv. Cyrano) and cucumber (Cucumis sativus L. cv. Akito) plants, either ungrafted or grafted onto the Cucurbita hybrid rootstocks (Cucurbita maxima Duch. × Cucurbita moschata Duch.), ??P360??, and ??PS1313??, respectively. Plants were grown hydroponically and supplied with two nutrient solutions ?? a nonsalinized control and a salinized solution which contained 40 mmol L^?1 of NaCl. Salinity induced a smaller decrease in leaf area index (LAI), in grafted-compared to ungrafted plants. Similarly, the P _N and g _s reduction in NaCl treatment compared to control were significantly lower in grafted plants (34% and 34%, respectively, for melon and 14% and 15.5%, respectively, for cucumber) compared to ungrafted plants (42% and 40%, respectively, for melon and 30% and 21%, respectively, for cucumber). In all grafting combinations, negative correlations were recorded between Na⁺ and Cl^? in the leaf tissue and P _N. Grafting reduced concentrations of sodium, but not chloride, in leaves. Under saline conditions a smaller reduction in melon and cucumber shoot biomass dry mass and fruit yield were recorded, with positive correlations between shoot biomass, yield and P _N. These results suggest that the use of salt tolerant Cucurbita rootstock can improve melon and cucumber photosynthetic capacity under salt stress and consequently crop performance.     

Stock-Scion Interactions of Normal and Fruit Ripening Mutants rin and nor in Tomato

Scions of the non-ripening rin and nor tomato strains (Lycopersicum esculentum Mill.) were grafted on normal understock plants (cv. Rutgers) in an effort to study the influence of roots and vegetative tissue on the ripening behavior of the tomato fruit. Receiprocal grafts of ‘Rutgers’ scions on rin and nor understocks as well as grafted and ungrafted controls were also established. No alteration in the ethylene, and CO₂ evolution and color development of either mutant fruits on normal understock or of normal fruits on mutant understock occurred. We suggest that the inability of rin and nor mutant fruits to ripen normally stems either from the presence in mutant fruit of a non-translocatable ripening inhibitor, or from the absence of a non-translocatable ripening factor.     

Antisense-mediated suppression of tomato zeaxanthin epoxidase alleviates photoinhibition of PSII and PSI during chilling stress under low irradiance

A tomato (Lycopersicon esculentum Mill.) zeaxanthin epoxidase gene (LeZE) was isolated and antisense transgenic tomato plants were produced. Northern, southern, and western blot analyses demonstrated that antisense LeZE was transferred into the tomato genome and the expression of LeZE was inhibited. The ratio of (A+Z)/(V+A+Z) in antisense transgenic plants was maintained at a higher level than in the wild type (WT) plants under high light and chilling stress with low irradiance. The value of non-photochemical quenching (NPQ) in WT and transgenic plants was not affected during the stresses. The oxidizable P700 and the maximal photochemical efficiency of PSII (F_v/F_m) in transgenic plants decreased more slowly at chilling temperature under low irradiance. These results suggested that suppression of LeZE caused zeaxanthin accumulation, which was helpful in alleviating photoinhibition of PSI and PSII in tomato plants under chilling stress.     

Bemisia tabaci (Gennadius) population density and pupal size are dependent on rootstock and nitrogen in hydroponic tomato crop

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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.     

Apical correlative effects in leaf epinasty of tomato

The influence of the stem apex on leaf curvature was investigated using debudded tomato (Lycopersicon esculentum Mill. cv Anahu) plants and petiole explants, consisting of a section of petiole attached to a section of stem.     

Phenotypic expression of wild-type tomato and three wilty mutants in relation to abscisic Acid accumulation in roots and leaflets of reciprocal grafts

Lycopersicon esculentum Mill. cv Rheinlands Ruhm (RR) and cv Moneymaker and the three wilty mutants flacca (flc), sitiens (sit), and sitiens^w (sit^w), together with most reciprocal grafts, were grown in pots and in solution culture. Detached leaflets, and control and steam-girdled intact plants, were left turgid or were wilted in air. Detached leaflets and the leaflets and roots of the intact plants were analyzed for their abscisic acid (ABA) content. Turgid RR leaflets contained about 2.9 ng ABA per milligram dry weight. On average, the flc and sit leaflets contained 33 and 11% of this amount, respectively. The lack of ABA approximately correlated with the severity of the mutant phenotype. Mutant roots also contained less ABA than wild-type roots. Wild-type scions on mutant stocks (wild type/mutant) maintained the normal phenotype of ungrafted plants. Mutant scions grafted onto wild-type stocks reverted to a near wild-type phenotype. After the wild-type leaves were excised from solution culture-grown mutant/wild-type plants, the revertive morphology of the mutant scions was maintained, although endogenous ABA levels in the leaflets fell to typical mutant levels and the leaflets became wilty again. When stressed in air, both leaflets and roots of RR plants produced stress-induced ABA, but the mutant leaflets and roots did not. The roots and leaflets of the grafted plants behaved according to their own genotype, with the notable exception of mutant roots grown with wild-type scions. Roots of flc and sit^w recovered the ability to accumulate stress-induced ABA when grafted with RR scions before the stress was imposed.     

Overexpression of tomato chloroplast omega-3 fatty acid desaturase gene alleviates the photoinhibition of photosystems 2 and 1 under chilling stress

In transgenic (TG) tomato (Lycopersicon esculentum Mill.) overexpressed ω-3 fatty acid desaturase gene (LeFAD7) was identified, which was controlled by the cauliflower mosaic virus 35S promoter and induced increased contents of unsaturated fatty acids in thylakoid membrane. Under chilling stress at low irradiance (4 °C, 100 μmol m⁻² s⁻¹) TG plants with higher linolenic acids (18: 3) content maintained a higher O₂ evolution rate, oxidizable P700 content, and maximal photochemical efficiency (F_v/F_m) than wild type (WT) plants. Low temperature treatment for 6 h resulted in extensive changes of chloroplast ultrastructure: in WT plants most chloroplasts became circular, the number of amyloids increased, appressed granum stacks were dissolved, grana disappeared, and the number of grana decreased, while only a few grana were found in leaves of TG plants. Hence the overexpression of LeFAD7 could increase the content of 18: 3 in thylakoid membrane, and this increase alleviated the photoinhibition of photosystem (PS) 1 and PS2 under chilling at low irradiance.     

Effect of day/night temperature difference on chlorophyll content,photosynthesis and fluorescence parameters of tomato at fruit stage

In order to investigate the effect of day/night temperature difference (DIF) on photosynthetic characteristics of tomato plants (Solanum lycopersicum, cv. Jinguan 5) at fruit stage, an experiment was carried out in climate chambers. Five day/night temperature regimes (16/34, 19/31, 25/25, 31/19, and 34/16°C) with respective DIFs of -18, -12, 0, +12, and +18 were used and measured at mean daily temperature of 25°C. The results showed that chlorophyll (Chl) a, Chl b, net photosynthetic rate (P_N), stomatal conductance (g_s), maximum quantum yield of PSII photochemistry (F_v/F_m), effective quantum yield of PSII photochemistry (?_PSII), and photochemical quenching (qp) significantly increased under positive DIF, while they decreased with negative DIF. In contrast, the Chl a/b ratio and nonphotochemical quenching (NPQ) decreased under positive DIF, while increased with negative DIF. Chl a, Chl b, P_N, g_s, F_v/F_m, ?_PSII, and qp were larger under +12 DIF than those at +18 DIF, while Chl a/b and NPQ showed an opposite trend.     

Responses of grafted tomato (Solanum lycopersiocon L.) to abiotic stresses in Saudi Arabia

Quantity and quality of irrigation water are considered the most imperative limiting factors for plant production in arid environment. Adoptions of strategies can minimize crop water consumption while nonexistent yield reduction is considered challenge for scholars especially in arid environment. Grafting is regarded as a promising tool to avoid or reduce yield loss caused by abiotic stresses. Tomato (Solanum lycopersium Mill.), commercial cultivar Faridah was grafted on Unifort rootstock and grown under regulated deficit irrigation (RDI) (100%, 80% and 60% ETc), using two types of irrigation water, fresh (EC = 0.86 dS/m) and brackish (EC = 3.52 dS/m). The effects of grafting and RDI on water use efficiency, vegetative growth, yield, fruit quality were investigated. Plant vegetative growth was reduced under water and salinity stresses. Grafting the plant significantly improves the vegetative growth under both conditions. The results showed that crop yield, Ca⁺² and K⁺ were considerably increased in grafted tomato compared to non-grafted plants under water and salinity stresses. Grafted tomato plants accumulated less Na⁺ and Cl⁻, especially under high levels of salinity compared to non-grafted plants. Grafting tomato plants showed a slight decrease on the fruit quality traits such as vitamin C, titratable acidity (TA) and total soluble solids (TSS). This study confirmed that grafted tomato plants can mitigate undesirable impact of salt stress on growth and fruit quality.     

Enhancement of low-temperature tolerance in transgenic tomato plants overexpressing Lefad7 through regulation of trienoic fatty acids

We studied how tomato (Lycopersicon esculentum Mill.) chloroplast omega-3 fatty acid desaturase gene (Lefad7) overexpression enhanced low-temperature (LT) tolerance in transgenic tomato plants. In these plants, the content of linolenic acid (18:3) markedly increased and, correspondingly, the content of linoleic acid (18:2) decreased. Similar changes were found after 6 h under LT (4°C) treatment. Under LT stress, wild type (WT) tomato plants showed a much greater increase in relative electrolyte leakage and malondialdehyde (MDA) contents compared with transgenic plants. Transgenic plants exhibited higher activities of antioxidative enzymes and a lower content of reactive oxygen species (ROS). Transgenic plants maintained a relatively higher level of the net photosynthetic rate (P _N) and chlorophyll (Chl) content than WT plants under LT stress. Taken together, we suggested that overexpression of Lefad7 enhanced LT tolerance by changing the composition of membrane lipids in tomato plants, with the increased content of trienoic fatty acids and reduced content of dienoic fatty acids that led to series of physiological alterations.     

Grafting influence on the weight and quality of tomato fruit under salt stress

Two commercial tomato cultivars were used to determine whether grafting could prevent decrease of fruit weight and quality under salt stress conditions. The cultivars Buran F1 and Berberana F1 were grafted onto rootstock ‘Maxifort’ and grown under three levels of elevated soil salinity (EC 3.80 dS m^?1, 6.95 dS m^?1 and 9.12 dS m^?1). Fruit weight reduction of grafted plants was lower (about 20–30%) in comparison with non‐grafted ones. Salt stress at the second salinity level (EC 6.95 dS m^?1) induced the highest alteration of examined growth and quality parameters. The total increase of phenols, flavonoids, ascorbate and lycopene content in the fruits of both grafted and non‐grafted plants for both cultivars had a similar trend and intensity, though some inter‐cultivar variation was observed. The possibility of grafting tomato plants to improve salt tolerance without fruit quality loss is discussed.     

Response of tomato plants to chilling stress in association with nutrient or phosphorus starvation

The experiments were conducted on two tomato cultivars: Garbo and Robin. Mineral starvation due to plant growth in 20-fold diluted nutrient solution (DNS) combined with chilling reduced the rate of photosynthesis (P _N) and stomatal conductance (g) to a greater extent than in plants grown in full nutrient solution (FNS). In phosphate-starved tomato plants the P _N rate and stomatal conductance decreased more after chilling than in plants grown on FNS. In low-P plants even 2 days after chilling the recovery of CO₂ assimilation rate and stomatal conductance was low. A resupply of phosphorus to low-P plants (low P + P) did not improve the rate of photosynthesis in non-chilled plants (NCh) but prevented P_N inhibition in chilled (Ch) plants. The greatest effect of P resupply was expressed as a better recovery of photosynthesis and stomatal conductance, especially in non-chilled low P + P plants. The F _v/F _m (ratio of variable to maximal chlorophyll fluorescence) decreased more during P starvation than as an effect of chilling. Supplying phosphorus to low-P plants caused the slight increase in the F _v/F _mratio. In conclusion, after a short-term chilling in darkness a much more drastic inhibition of photosynthesis was observed in nutrient-starved or P-insufficient tomato plants than in plants from FNS. This inhibition was caused by the decrease in both photochemical efficiency of photosystems and the reduction of stomatal conductance. The presented results support the hypothesis that tomato plants with limited supply of mineral nutrients or phosphorus are more susceptible to chilling.     

Nicotine-free and salt-tolerant tobacco plants obtained by grafting to salinity-resistant rootstocks of tomato

In this work we present the first study of the behaviour of tobacco plants, under saline conditions, grafted to salinity-resistant rootstocks of tomato cultivars. To test the viability and efficiency of this grafting technique in tobacco plants subjected to salinity, we analyse the production of foliar biomass and different quality parameters in this crop. With this aim, Nicotiana tabacum cv. Sevilla (scion) was grafted to two cultivars of Lycopersicum esculentum (rootstocks): cv. Jaguar (Sevilla/Jaguar) and cv. Brillante (Sevilla/Brillante). Furthermore, as controls, tobacco plants of cv. Sevilla were used grafted to themselves (Sevilla/Sevilla) and non-grafted plants of cv. Sevilla. Plants were grafted by needle graft following the procedure described by Rivero RM, Ruiz JM, Romero L (2002) Role of grafting in horticultural plants, pp 229–254. In the present work, we demonstrate that the graft of tobacco scions with tomato rootstocks is an effective agricultural approach to improve production and quality in tobacco leaves under conditions of saline stress. Our results show that the rootstock of the cv. Brillante best induced salt resistance in tobacco cv. Sevilla, registering the lowest foliar concentrations of Na⁺ and Cl^–, the lowest lipid peroxidation and the highest proline and sugar concentrations. Overall, this is reflected in better biomass production of the aerial part of the plant. Finally, it is noteworthy that grafting in tobacco plants to tomato rootstocks essentially eliminates foliar nicotine levels (reduced to 1%). These results are of great importance, as this technique implies a rapid, efficient and natural alternative in increasing tobacco-leaf quality and thus reducing harmful effects of this alkaloid on the health of smokers.     

Effects of Tomatex /Triacontanol/ on chlorophyll fluorescence and tomato (Lycopersicon esculentum Mill.) yields

The influence of triacontanol in a form of Tomatex preparation on basic indices of chlorophyll fluorescence in tomato leaves (Delfina cv.), yield of fruits, and dry matter content in fruits was evaluated in a pot experiment situated in vegetation hall in 1999. Tomatex was applied into roots at seedling stage (6–7 leaves) or at the stage of seedling and flowering of the 2^nd inflorescence bunch. Plants were given by 0.3, 3.0, and 30 μg triacontanol per pot at a single dosage. Results obtained have shown that triacontanol regardless of the dose applied, significantly increased the maximal efficiency of PSII photochemistry in the dark (F_v/Fm), the efficiency of excitation capture by open PSII reaction centers (F_v’/F_m’), the actual quantum yield of PSII electron transport in the light-adapted state (Φ_PSII), the photochemical quenching coefficient (Q_p). However, nonphotochemical quenching coefficient (Q_n) and non-radiative dissipation (NPQ) were decreased. Plants treated with triacontanol at the doses of 0.3 and 3.0 μg had significantly higher yields of fruits than control. No differences were found between plants treated once and twice with the growth regulator. Triacontanol did not show univocal effects on dry matter content in fruits either.     

Overexpression of chloroplastic monodehydroascorbate reductase enhanced tolerance to temperature and methyl viologen‐mediated oxidative stresses

A tomato (Lycopersicon esculentum Mill.) monodehydroascorbate reductase gene (LeMDAR) was isolated. The LeMDAR–green fluorescence protein (GFP) fusion protein was targeted to chloroplast in Arabidopsis mesophyll protoplast. RNA and protein gel blot analyses confirmed that the sense‐ and antisense‐ LeMDAR were integrated into the tomato genome. The MDAR activities and the levels of reduced ascorbate (AsA) were markedly increased in sense transgenic lines and decreased in antisense transgenic lines compared with wild‐type (WT) plants. Under low and high temperature stresses, the sense transgenic plants showed lower level of hydrogen peroxide (H₂O₂), lower thiobarbituric acid reactive substance (TBARS) content, higher net photosynthetic rate (P_n), higher maximal photochemical efficiency of PSII (F_v/F_m) and fresh weight compared with WT plants. The oxidizable P700 decreased more obviously in WT and antisense plants than that in sense plants at chilling temperature under low irradiance. Furthermore, the sense transgenic plants exhibited significantly lower H₂O₂ level, higher ascorbate peroxidase (APX) activity, greater P_n and F_v/F_m under methyl viologen (MV)‐mediated oxidative stresses. These results indicated that overexpression of chloroplastic MDAR played an important role in alleviating photoinhibition of PSI and PSII and enhancing the tolerance to various abiotic stresses by elevating AsA level.     

Ornithine decarboxylase and arginine decarboxylase activities in meristematic tissues of tomato and potato plants

Ornithine decarboxylase and arginine decarboxylase activities were measured in roots and buds of tomato (Lycopersicon esculentum Mill. cv. Pearson ms-35) and potato (Solanum tuberosum cv. Desire) plants. In both tomato and potato, the activity of ornithine decarboxylase was the highest at the root tip, decreasing proximally. The same was true for potato buds. In vegetative buds of tomato, the highest activity was found in the youngest leaves. The older the leaf, the lower was orithine decarboxylase activity. Arginine decarboxylase, on the other hand, did not display a similar gradient. These findings are in accordance with the suggestion that in tomato and potato elevated ornithine decarboxylase activity is associated with intense mitotic activity.     

Comparative effects of NaCl and NaHCO3 stresses on respiratory metabolism,antioxidant system,nutritional status,and organic acid metabolism in tomato roots

Physiological responses of tomato roots to NaCl and NaHCO₃ stresses were investigated in a hydroponic setting. The relative growth rate of tomato plants was significantly reduced in both NaCl and NaHCO₃ treatments, especially under NaHCO₃ stress. Tomato root respiration increased under low concentrations of NaCl and NaHCO₃ stresses. However, high concentrations of both NaCl and NaHCO₃ significantly inhibited respiration, especially in the NaHCO₃ treatment. With increasing concentration of NaCl and NaHCO₃ treatment, root Na accumulation increased, while accumulation of N, P, K, Fe, and Mg was significantly lower. Compared to NaCl, NaHCO₃ treatment resulted in more dramatic changes in these nutrients. All organic acids investigated were increased by NaHCO₃ after 5 days of treatment, but only oxalate, tartrate and malate were induced by NaCl. This implies that global regulation of organic acids might play an important role in tomato’s alkali stress tolerance. Compared to NaCl treatments, NaHCO₃ treatments induced much higher levels of reactive oxygen species (ROS) and lipid peroxidation after 5 days of treatment, which was accompanied by higher activities of antioxidant enzymes and higher concentrations of ascorbate–glutathione. However, after 10 days of treatment, 100 mM NaHCO₃ stress led to lower accumulation of ROS, antioxidant enzyme activities, and ascorbate–glutathione content. This may have been because root metabolism had almost completely stopped, as indicated by lower root respiration and activity.     

Pathogenesis-related proteins of tomato : p-69 as an alkaline endoproteinase

An endoproteinase induced by citrus exocortis viroid has been purified from tomato (Lycopersicon esculentum Mill, cv “Rutgers”) leaves. The proteinase corresponds to one of the major pathogenesis-related proteins of tomato plants and was designated proteinase P-69 as it has a molecular weight of 69,000 to 70,000. The proteinase was purified in four steps: (NH₄)₂SO₄ fractionation, chromatography on Bio-Gel P-60, DEAE-Sepharose chromatography, and casein-Sepharose affinity chromatography. The proteinase had a pH optimum of 8.5 to 9.0 when assayed with either fluorescein thiocarbamoyl derivative (FTC)-casein or FTC-ribulose 1,5-bisphosphate carboxylase/oxygenase as substrates. The proteinase activity was inhibited by pCMB and strongly activated by calcium and magnesium ions as well as by DTT. When analyzed by electrofocusing, the activity showed a pI around 9.0.