Chedly Abdelly

Early effects of salt stress on the physiological and oxidative status of Cakile maritima (halophyte) and Arabidopsis thaliana (glycophyte)

Early changes in physiological and oxidative status induced by salt stress were monitored in two Brassicaceae plants differing in their tolerance to salinity, Cakile maritima (halophyte) and Arabidopsis thaliana (glycophyte). Growth response and antioxidant defense of C. maritima under 400 mM NaCl were compared with those of A. thaliana exposed to 100 mM NaCl. Salinity induced early growth reduction that is less pronounced in C. maritima than in A. thaliana. Maximum hydrogen peroxide (H₂O₂) level occurred in the leaves of both species 4 h after the onset of salt treatment. A rapid decline in H₂O₂ concentration was observed thereafter in C. maritima, whereas it remained high in A. thaliana. Correlatively, superoxide dismutase, catalase and peroxidase activities increased at 4 h of treatment in C. maritima and decreased thereafter. However, the activity of these enzymes remained higher in treated plants than that in controls, regardless of the duration of treatment, in A. thaliana. The concentrations of malondialdehyde (MDA) reached maximum values at 24 h of salt stress in both species. Again, MDA levels decreased later in C. maritima, but remained high in A. thaliana. The contents of α-tocopherol remained constant during salt stress in C. maritima and decreased during the first 24 h of salt stress and then remained low in A. thaliana. The results clearly showed that C. maritima, in contrast to A. thaliana, can rapidly evolve physiological and antioxidant mechanisms to adapt to salt and manage the oxidative stress. This may explain, at least partially, the difference in salt tolerance between halophytes and glycophytes.

Potential utilisation of halophytes for the rehabilitation and valorisation of salt-affected areas in Tunisia

In arid and semi-arid regions, irrigation water contributes to salinisation of the upper layer of the soil, where most root activity takes place. Along the path of plant domestication, many crop species have lost resistance mechanisms to various stress conditions [1], including salt stress [2]. Thus, most crop plants do not fully express their original genetic potential for growth, development and yield under salt stress, and their economic value declines as salinity levels increase [3, 4]. Improving salt resistance of crop plants is, therefore, of major concern in agricultural research. A potential genetic resource for the improvement of salt resistance in crop plants resides among wild populations of halophytes [5, 6]. These can be either domesticated into new, salt-resistant crops, or used as a source of genes to be introduced into crop species by classical breeding or molecular methods.

Salt and seawater effects on the germination of Crithmum maritimum

Crithmum maritimum (Apiaceae), also called sea fennel, is a perennial halophyte that thrives on saline environments (rocky coasts, piers and breakwaters) along the Mediterranean countries, Pacific and Atlantic coasts [1]. Several uses are known for this plant: for culinary purposes, fresh leaves and young branches are pickled in vinegar and used as condiments. Leaves have also medicinal applications, as antiscorbutic, tonic, diuretic, and vermifuge substances [2].

Diversity in the response of two potential halophytes (Batis maritima and Crithmum maritimum) to salt stress

In this study, we compared the response to NaCl of Batis maritima and Crithmum maritimum, two potential halophytes with a different range of salinity tolerance. At high NaCl concentrations (800 mM for B. maritima and 300 mM for C. maritimum), the growth of both plants was significantly reduced. A split root experiment aimed at determining whether high NaCl conditions limit growth of plants through toxic effects of excessive salt accumulation in shoots or through impairment of some essential nutrient acquisition. The split root experiment was performed with three treatments. In the first treatment (B/S), half of the roots were immersed in a basal medium (B) and the other half in the same medium supplemented with NaCl (S). In the two other treatments, the two halves of the root system were immersed either in salt-free medium (B/B) or in the basal medium containing salt (S/S). Under split-root conditions, B. maritima and C. maritimum accumulated Na in their shoots, and displayed improved growth as compared to control plants. In C. maritimum, the B/S treatment partially restored K provision to the shoots but not that of Ca, suggesting that the inhibition of K+ uptake by salt could only limit its growth under high salinity. In B. maritima (B/S plants), the concentration of K+ and Ca2+ were diluted by growth. The inhibition of K+ and Ca2+ uptake by salt did not seem to limit growth of B. maritima growth under high salinity. The growth of B. maritima and C. maritimum could be also limited by the restriction imposed by NaCl on N uptake.

Increased sensitivity to salt stress in tocopherol-deficient Arabidopsis mutants growing in a hydroponic system

Recent studies suggest that tocopherols could play physiological roles in salt tolerance but the mechanisms are still unknown. In this study, we analyzed changes in growth, mineral and oxidative status in vte1 and vte4 Arabidopsis thaliana mutants exposed to salt stress. vte1 and vte4 mutants lack α-tocopherol, but only the vte1 mutant is additionally deficient in γ-tocopherol. Results showed that a deficiency in vitamin E leads to reduced growth and increased oxidative stress in hydroponically-grown plants. This effect was observed at early stages, not only in rosettes but also in roots. The vte1 mutant was more sensitive to salt-induced oxidative stress than the wild type and the vte4 mutant. Salt sensitivity was associated with (i) high contents of Na+, (ii) reduced efficiency of PSII photochemistry (Fv/Fm ratio) and (iii) more pronounced oxidative stress as indicated by increased hydrogen peroxide and malondialdeyde levels. The vte 4 mutant, which accumulates γ- instead of α-tocopherol showed an intermediate sensitivity to salt stress between the wild type and the vte1 mutant. Contents of abscisic acid, jasmonic acid and the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid were higher in the vte1 mutant than the vte4 mutant and wild type. It is concluded that vitamin E-deficient plants show an increased sensitivity to salt stress both in rosettes and roots, therefore indicating the positive role of tocopherols in stress tolerance, not only by minimizing oxidative stress, but also controlling Na+/K+ homeostasis and hormonal balance.

Selection of a halophyte that could be used in the bioreclamation of salt-affected soils in arid and semi-arid regions

Vegetative bioremediation or bioreclamation of salt-affected soils is an economic solution mainly for developing countries since chemical additions are becoming increasingly expensive. However, to be efficient, this approach needs sufficient irrigation. In this investigation, we evaluated the ability of some halophytes to desalinize a saline soil under non-leaching conditions with the aim of selecting appropriate species that could be used for this purpose in arid and semi-arid regions where precipitation is too low to leach salts from the rhizosphere. Three perennial species were used in this experiment: Arthrocnemum indicum (Willd.) Moq., Suaeda fruticosa Forsk., and Sesuvium portulacastrum L. Seedlings were grown on a saline soil under greenhouse conditions and irrigated with tap water for 170 days. Irrigations were carried out with almost no leaching. Soil salinity was significantly reduced in halophyte-grown soil as compared to the control. Plants were able to decrease the soil electrical conductivity by absorbing soluble salts, mainly sodium ions. Among the three studied species, Sesuvium portulacastrum L. was the most productive and was able to accumulate in shoots nearly 30% of the sodium content of each pot over the 170 days. Thus, Sesuvium portulacastrum L. seems to be the most promising species for saline soil desalination in arid and semi-arid regions.

Effect of salinity on growth, leaf-phenolic content and antioxidant scavenging activity in Cynara cardunculus L.

Cynara cardunculus L. (cardoon) is a medicinal plant widespread in arid and semi-arid regions where high salinity frequently occurs. Cardoon leaves are known for their high content of natural bioactive molecules, notably polyphenols, that exhibit pharmacological activities such as antioxidant, antibacterial, and metal chelating activity. We studied the effect of different salt concentrations on plant growth, phenolic content and superoxide scavenging activity in locally grown C. cardunculus L. leaves (El Jem locality). No significant effect on leaf growth (leaf biomass, length and number) was found at moderate salinity (25—50 mM NaCl). However, these parameters were severely reduced (-30 to -90% as compared to the control) at 150 mM NaCl. Leaf phenolic content was significantly increased at 25-50 mM NaCl, and decreased at 150 mM NaCl. The superox-ide anion scavenging capacity of leaf extracts was stimulated by salt treatment, with a maximum at the highest NaCl level. Our findings indicate that the two studied characteristics of C. cardunculus leaves (polyphenol content and O2- quenching capacity) were not modified in parallel with increasing salinity, and that only the polyphenol content was correlated with leaf growth.

Environmental and Economical Opportunities for the Valorisation of the Genus Atriplex : New Insights

Atriplex species are members of the Chenopodiaceae. There are more than 400 species growing naturally in arid and semi arid regions of the world, most of which are highly tolerant to drought and salt. Atriplex species contain high levels of protein and economically valuable compounds. These characteristics could make Atriplex a suitable food for livestock in saline or arid/ semi-arid area. Furthermore, Atriplex can take up salt ions from saline soil and sequester it into the salt glands at the leaf surface. This trait is of high significance since it allows them to be used for revegetation of saline or arid/semi-arid lands. Atriplex species have also been used for cloning some genes related to drought and salt tolerance. This review is a new contribution that updates knowledge on the ecological and socio-economical potential of some plant genus Atriplex.

Nutrient uptake and management under saline conditions in the xerohalophyte: Tecticornia indica (Willd.) subsp. indica

In the present investigation, we studied uptake and management of the major cations in the xerohalophyte, Tecticornia indica (Willd.) subsp. indica as subjected to salinity. Plants were grown under greenhouse conditions at various salinity levels (0, 100, 200 and 400 mM NaCl) over 110 days. At harvest, they were separated into shoots and roots then analyzed for water contents, dry weights (DW), and Na+, K+, Ca²+, and Mg²+ contents. Plants showed a growth optimum at 200 mM NaCl and much better tissue hydration under saline than non-saline conditions. At this salt concentration (200 mM NaCl), shoot Na+ content reached its highest value (7.9 mmol · g-⁻¹ DW). In spite of such stressful conditions, salt-treated plants maintained adequate K+, Ca²+, and Mg²+ status even under severe saline conditions. This was mainly due to their aptitude to selectively acquire these essential cations and efficiently use them for biomass production.

Halophyte-Fodder Species Association May Improve Nutrient Availability and Biomass Production of the Sabkha Ecosystem

Sabkhas are often regarded as marginal non productive areas. Yet, a wide range of halophytes together with less salt-tolerant fodder species thrive in these ecosystems. In the present study, the potential of halophytes in improving biomass production and nutrient uptake ofan un-grazed parcel edging an inland sabkha (100 km south-east of Tunis) was addressed. The vegetation of studied area was characterised by perennial halophytes tufts in association with fodder annuals, mainly Medicago species. Halophytes grew slowly and accumulated low contents of mineral nutrients (N, Pi, K+) and high Na+ concentrations in their shoots. Depending on the precipitation, the annual fodder species showed high growth activity (up to 40% of the plant annual biomass production of the ecosystem), which was sustained by a high capacity of nutrient uptake (up to 70% of the total nutrient uptake). The annuals were almost exclusively clustered under the halophyte tufts, or at their immediate vicinity, where soil N and Pi levels were significantly higher, and salinity significantly lower than between the tufts. The perennial halophytes provided optimal conditions for the growth of these annual Leguminosae, which valorised the nutrients accumulated around the halophytes, owing to their high growth rate, nutrient-absorption rate and use-efficiency. These data are of high ecological significance and suggest that the salt tolerant-fodder species association may constitute a low-cost and valuable approach for the restoration and reclamation of the marginal saline ecosystems.