María E. Balibrea

Agronomical and physiological characterization of salinity tolerance in a commercial tomato hybrid

The salt tolerance of the commercial F1 tomato hybrid (Lycopersicon esculentum Mill) Radja (GC-793) has been agronomically and physiologically evaluated under greenhouse conditions, using a control (nutrient solution), a moderate (70 mM NaCl added to the nutrient solution) and a high salt level (140 mM NaCl), applied for 130 days. The results show that Radja is a Na+-excluder genotype, tolerant to moderate salinity. Fruit yield was reduced by 16% and 60% and the shoot biomass by 30% and more than 75% under moderate and high salinities, respectively. At 90 days of salt treatment (DST), the mature leaves feeding the 4th truss at fruiting accumulated little Na+ (178 mmol kg-1 DW). At this time, the sucrose concentration in these leaves even increased with moderate salinity and the amino acid proline was not accumulated under salt conditions as compared to control. At 130 DST, Na+ was accumulated mainly by the roots in proportion to the salt level applied, while in leaves appreciable amounts were found only at high salinity (452 mmol kg-1 DW). In the leaves, Cl- was always accumulated in proportion to the salt level and in a very much greater amounts than Na+ (until 1640 mmol kg-1 DW). The sucrose content was reduced in all plants by salinity, and was distributed preferentially toward the distal stem and peduncle of a truss at fruiting under moderate salinity, and toward the basal stem and root at high salinity. Moreover, proline was accumulated in different organs of the plant only at high salinity, coinciding with Na+ accumulation in leaves. Attempts are made to find a clear relationship between physiological behaviour triggered by stress and the agronomical behaviour, in order to assess the validity of physiological traits used for salt-tolerance selection and breeding in tomato.

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.

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.

Composition of xylem and phloem exudates in relation to the salt-tolerance of domestic and wild tomato species.

Summary Plants of Lycopersicon esculentum cv. Volgogradskij ( Le ) and L. pennellii accession PE-47 ( Lp ) were cultivated for 22 days under control and saline (100 mmol/L NaCl) conditions. Besides growth parameters and leaf water content, toxic ions (Na + , Cl − ), major nutrients (K + , Ca 2+ , Mg 2+ and sPO 4 3− ) and assimilates (carbohydrates and amino acids) were determined weekly in xylem and phloem exudates. Salinity reduced plant dry weight by 55 % and 29 % in Le and Lp , respectively, while a 46 % increase in the root biomass was found in the latter. An earlier and higher Na + and Cl − accumulation in the xylem and a greater Na + retranslocation through phloem was found in Lp . The better nutritional status found in the xylem of the salinized plants of the wild species at the end of the salinization period seems also to be linked to phloem-xylem retranslocation. Thereafter, a more rapid and higher transport of carbohydrates and amino acids from roots to shoot through xylem was found in Lp than in Le under salinity. The implication of these parameters in the salt-tolerance of tomato has been discussed.

Hormonal and metabolic regulation of tomato fruit sink activity and yield under salinity

Summary Cytokinins and cell wall invertase are positive players in regulating fruit sink strength, growth, and yield under salinity as components of the same signalling cascade establishing and developing sink organs.

Ectopic overexpression of the cell wall invertase gene CIN1 leads to dehydration avoidance in tomato

Highlight Overexpression of a cell wall invertase gene promotes dehydration avoidance and WUE, and delays senescence in tomato through limiting stomatal conductance and inducing sink metabolism and photosynthesis in source leaves.