Maria C. Bolarin

The rootstock effect on the tomato salinity response depends on the shoot genotype

Abstract With the aim of determining whether the rootstock effect depends on the shoot genotype, two distinctly different tomato ( Lycopersicon esculentum Mill) genotypes, Moneymaker with excluder character and UC-82B with includer character, were grafted onto a commercial tomato hybrid (cv. Kyndia). Self-grafted plants were used as controls. The rootstock effect was first assessed by growing plants at different NaCl concentrations (0, 50 and 100 mM) under controlled conditions, and by determining the growth and physiological responses of the grafted plants after 35 days of salt treatment. The rootstock did not affect the shoot growth when Moneymaker was used as scion. However, when UC-82B was used as scion, the shoot biomass reduction induced by salinity was lower in plants with rootstock Kyndia than in the self-grafted plants. The effectiveness of the UC-82B grafted plants onto Kyndia was also showed on the basis of fruit yield. The rootstock also induced significant physiological changes in the leaves of these plants, with the most important changes being found in the ion saline accumulation and Na + /K + ratio. The Na + and Cl − accumulation induced by salinity in leaves of UC-82B was substantially lower when the root of this cultivar had been substituted by that of the cv. Kyndia, whereas the K + concentration was less reduced by salinity, and consequently the leaf Na + /K + ratio values were much lower. These results suggest that the saline ion accumulation in leaves was controlled predominantly by the genotype of the rootstock. In addition, the characteristics of the rootstock able to induce salt tolerance to the shoot depend on the salt tolerance mechanism of the shoot genotype.

Response of tomato cultivars to salinity

The responses of five tomato cultivars (L. esculentum Mill) of different degrees of salt tolerance were examined over a range of 0 to 140 mM NaCl applied for 3 and 10 weeks. Judged by both Na and Cl accumulations and maintenance of K, Ca and Mg contents with increasing salinity, the most tolerant cultivars (Pera and GC-72) showed different responses. The greater salt tolerance of cv Pera was associated with a higher Cl and Na accumulation and a lower K content in the shoot than those found in the other cultivars, typical of a halophytic response to salinity. However, the greater salt tolerance of cv GC-72 was associated with a retention of Na and Cl in the root, restriction of their translocation to the shoot and maintenance of potassium selectivity under saline conditions. The salt tolerance mechanisms that operated in the remaining cultivars were similar to that of cv GC-72, as at first they excluded Na and Cl from the shoots, accumulating them in the roots; with longer treatment, the ability to regulate Na and Cl concentrations in the plant was lost only in the most salt sensitive cultivar (Volgogradskij), resulting in a massive influx of both ions into the shoot.The salt sensitivity of some tomato cultivars to salinity could be due to both the toxic effect of Na and Cl ions and nutritional imbalance induced by salinity, as plant growth was inversely correlated with Na and Cl contents and directly correlated with K and Ca contents. This study displays that there is not a single salt tolerance mechanism, since different physiological responses among tomato cultivars have been found.

Growth and osmotic adjustment of two tomato cultivars during and after saline stress

The effect of a short period of saline stress was studied in two phenotypically different cultivars, one of normal fruit-size (L. esculentum cv. New Yorker) and one of cherry fruit-size (L. esculentum var.cerasiforme cv. PE-62). In both cultivars the relative growth rate (RGR) and the leaf area ratio (LAR) decreased following salinisation. The leaf turgor potential (ψp) and the osmotic potential at full turgor (ψos) decreased to the same extent in both cultivars. However, the contributions of organic and inorganic solutes to the osmotic adjustment was different between cultivars. New Yorker achieved the osmotic adjustment by means of the Cl− and Na+ uptake from the substrate, and by synthesis of organic solutes. In the cherry cultivar organic solutes did not contribute to the osmotic adjustment, instead, their contribution decreased after salinisation. After the salt stress was removed, the water stress disappeared, the content of organic solutes decreased in plants of both cultivars and, therefore, their growth was not retarded by the diversion of resources for the synthesis of organic solutes. However, the toxic effects of the Cl− and Na+ did not disappear after removal of the salt stress, and the net assimilation rate (NAR) and the rate of growth (RGR) did not recover.

Short-term salt tolerance mechanisms in differentially salt tolerant tomato species

Abstract The physiological changes induced by a daily increase of NaCl level, over a period of 4 d, were studied in leaves of the salt-sensitive cultivated tomato species Lycopersicon esculentum and its wild salt-tolerant relative Lycopersicon pennellii. A higher solute contribution to the osmotic adjustment was observed in NaCl-treated leaves of L. pennellii than in those of L. esculentum. This response together with the higher accumulation of inorganic solutes in the wild species and of organic solutes in the cultivated species verified the different salt tolerance mechanisms operating in the two species in the short-term. With regard to the changes induced by salt stress on the free polyamine levels, the putrescine and spermine levels increased with salinity, whereas the spermine levels decreased in both tomato species; nevertheless, the main difference between the two species lays in an earlier and greater accumulation of putrescine induced by salinity in L. pennellii than in L. esculentum. The changes in putrescine levels were associated to changes in amino acids related to its synthesis, and the changes were different in both species. In L. esculentum, the high concentrations of some intermediate compounds (glutamate and arginine) were related to the low accumulation rate of both proline and putrescine. In contrast, in L. pennellii, important reductions in glutamate and arginine levels were found at the end of the salinization period. Moreover, in this last situation, a decline in the putrescine level ran parallel to a high proline accumulation, which suggests that the higher the stress level, the higher the deviation of glutamate to proline occurring in the salt tolerant species. It could be concluded that an early accumulation of the diamine putrescine seems to be associated with salt tolerance in the short-term.

Fast changes in soluble carbohydrates and proline contents in tomato seedlings in response to ionic and non-ionic iso-osmotic stresses

Summary Qualitative and quantitative changes in soluble carbohydrates and proline contents were studied in young plants of two tomato cultivars ( Lycopersicon esculentum L. Mill.) differing in their salt-tolerance (cvs. Pera and Volgogradskij). Seedlings were treated for 24 h with ionic (300 mmol L −1 ) and non-ionic iso-osmotic (380 g kg −1 polyethylene glycol MW 6000) stresses. Salinity provoked a decrease in the hexose contents and it also dramatically enhanced sucrose accumulation in all organs of the plants, and to a greater extent in the salt-sensitive cv. Volgogradskij. The PEG iso-osmotic stress, compared with saline conditions, only affected the hexose contents in a similar way to salinity in the cv. Volgogradskij, while it increased the sucrose content 2.5 and 4 times in the roots of Pera and Volgogradskij, respectively. Proline accumulation was more important in the salt-sensitive cultivar under both conditions. The contribution of these solutes to the osmotic potential was up to −0.3 MPa under non-ionic stress, but they had little influence under salinity compared with control plants. The fast changes observed in soluble carbohydrates and proline composition are discussed in relation to the osmotic adjustment under saline and non-permeant iso-osmotic stresses.

Overexpression of dehydrin tas14 gene improves the osmotic stress imposed by drought and salinity in tomato

One strategy to increase the level of drought and salinity tolerance is the transfer of genes codifying different types of proteins functionally related to macromolecules protection, such as group 2 of late embryogenesis abundant (LEA) proteins or dehydrins. The TAS14 dehydrin was isolated and characterized in tomato and its expression was induced by osmotic stress (NaCl and mannitol) and abscisic acid (ABA) [Godoy et al., Plant Mol Biol 1994;26:1921-1934], yet its function in drought and salinity tolerance of tomato remains elusive. In this study, transgenic tomato plants overexpressing tas14 gene under the control of the 35SCaMV promoter were generated to assess the function of tas14 gene in drought and salinity tolerance. The plants overexpressing tas14 gene achieved improved long-term drought and salinity tolerance without affecting plant growth under non-stress conditions. A mechanism of osmotic stress tolerance via osmotic potential reduction and solutes accumulation, such as sugars and K(+) is operating in tas14 overexpressing plants in drought conditions. A similar mechanism of osmotic stress tolerance was observed under salinity. Moreover, the overexpression of tas14 gene increased Na(+) accumulation only in adult leaves, whereas in young leaves, the accumulated solutes were K(+) and sugars, suggesting that plants overexpressing tas14 gene are able to distribute the Na(+) accumulation between young and adult leaves over a prolonged period in stressful conditions. Measurement of ABA showed that the action mechanism of tas14 gene is associated with an earlier and greater accumulation of ABA in leaves during short-term periods. A good feature for the application of this gene in improving drought and salt stress tolerance is the fact that its constitutive expression does not affect plant growth under non-stress conditions, and tolerance induced by overexpression of tas14 gene was observed at the different stress degrees applied to the long term.

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.

Effect of NaCl priming on increased salt tolerance in tomato

SummaryTomato seeds (Lycopersicon esculentum Mill.) cvs Pera, Muchamiel, P-73 and GC-72, were primed with 0,0.5 and 1.0 M NaCl solutions. The plants were then grown at 35,70 and 140 mM NaCl. These salt treatments were applied pre-emergence (seed sowing) and post-emergence (4 leaf stage). The effect of seed priming on yield was different depending on both the NaCl concentration used for seed priming and on the time of starting the salt treatments during the growing period of the plants. The yield increase under 1.0 M NaCl priming was mainly due to increased fruit weight, but was always reduced by increasing the NaCl treatment (35-140 mM). The effect of this seed priming on yield was higher when salt treatments were applied pre- rather than post-emergence, although it was significant only in plants treated at 35 and 70 mM NaCl. At pre-emergence, the yield increased in cvs Pera, Muchamiel and GC-72, whereas at post-emergence only cv. GC-72 increased its yield by salt priming. The increase in yield of cv. GC-...

Sucrolytic activities in relation to sink strength and carbohydrate composition in tomato fruit growing under salinity

Abstract The effects of low (control), moderate, and high salinity on sucrose metabolism, in relation to fruit growth, were assayed in a commercial F 1 tomato hybrid ( Lycopersicon esculentum L. Mill) Radja (GC-793). High salinity reduced both fruit growth rate and the mature fruit weight by 44%, while moderate salinity did not affect them significantly. The highest sink strength in control fruits was found between 20 and 30 days after anthesis (DAA). During this critical growing period, the import rate was reduced by more than 30% and 50% under moderate and high salinity, respectively, although the highest sink strength in salinized fruits was registered between 40 and 50 DAA. Starch was accumulated up to 40 DAA and to a greater extent in the salt-treated fruits, with a negative correlation between starch accumulation and the sink strength during the critical growing period (20–30 DAA). The hexose accumulation in mature fruits (60 DAA) was about 2 and 1.5 times greater in moderately salinized fruits than in control and highly salinized ones, respectively. The sucrose content, which declines in control fruits with time, was accumulated in the salinized ones during the rapid growing period. The acid invertase (E.C. 3.2.1.25) was the main sucrolytic activity in control fruits between 10 and 40 DAA, with a positive correlation between this activity and the sink strength during this period. However, the cytoplasmic sucrolytic activities, neutral invertase (E.C. 3.2.1.26) and sucrose synthase (E.C. 2.4.1.13) were more important in salinized fruits. Sucrose synthase activity increased in relation to the intensity of stress between 30 and 40 DAA coinciding with the highest starch accumulation and the depletion in the sucrose content, and preceding the highest sink strength in the salinized fruits (50 DAA). The implication of sucrolytic activities in the import of assimilates and fruit growth under these adverse conditions is discussed.

The high fruit soluble sugar content in wild Lycopersicon species and their hybrids with cultivars depends on sucrose import during ripening rather than on sucrose metabolism

Soluble sugar content has been studied in relation to sucrose metabolism in the hexose-accumulating cultivated tomato Lycopersicon esculentum Mill, the wild relative species Lycopersicon cheesmanii Riley, in the sucrose-accumulating wild relative species Lycopersicon chmielewskii Rick, Kesicky, Fobes & Holle. and in two hexose-accumulating interspecific F1 hybrids (L. esculentum × L. cheesmanii; L. esculentum × L. chmielewskii), cultivated under two irrigation regimes (control: EC = 2.1 and saline: EC = 8.4 dS m-1). Under control conditions the total soluble sugar content (as hexose equivalents) in the ripe fruits of L. cheesmanii was 3-fold higher than in L. esculentum, while L. chmielewskii and both F1 hybrids contained twice as much as the cultivar. With the exception of L. esculentum × L. cheesmanii, salinity increased the sugar content by 1.3 (wild species) and 1.7 times (cultivar and L. esculentum × L. chmielewskii) with respect to control fruits. Wild germplasm or salinity provided two different mechanisms for the increases in fruit sugar content. The hexoses accumulated in ripe fruits were strongly influenced by those accumulated at the start of ripening, but the hydrolysed starch before start of ripening only partially explained the final hexose levels and especially the increase under salinity. The early cell wall acid invertase and the late neutral invertase activities appeared to be related to the amount of hexoses accumulated in ripe fruits. However, no metabolic parameter was positively related to the amount of sugar accumulated (including sucrose). The major differences between genotypes appeared in ripe fruits, in which up to 50% of the total amount of sugars accumulated in the wild species (mainly in L. cheesmanii) and hybrids cannot be explained by the sugars accumulated and the starch hydrolysed before the start of ripening stage. As a consequence, the higher fruit quality of the wild species compared with L. esculentum may depend more on the continuation of sucrose import during ripening than on osmotic or metabolic particularities such as the hexose / sucrose-accumulator character or specific enzyme activities.