Salinity is one of the rising problems causing tremendous yield losses in many regions of the world especially in arid and semiarid regions. To maximize crop productivity, these areas should be brought under utilization where there are options for removing salinity or using the salt-tolerant crops. Use of salt-tolerant crops does not remove the salt and hence halophytes that have capacity to accumulate and exclude the salt can be an effective way. Methods for salt removal include agronomic practices or phytoremediation. The first is cost- and labor-intensive and needs some developmental strategies for implication; on the contrary, the phytoremediation by halophyte is more suitable as it can be executed very easily without those problems. Several halophyte species including grasses, shrubs, and trees can remove the salt from different kinds of salt-affected problematic soils through salt excluding, excreting, or accumulating by their morphological, anatomical, physiological adaptation in their organelle level and cellular level. Exploiting halophytes for reducing salinity can be good sources for meeting the basic needs of people in salt-affected areas as well. This review focuses on the special adaptive features of halophytic plants under saline condition and the possible ways to utilize these plants to remediate salinity.

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Potential Use of Halophytes to Remediate Saline Soils

Mentha pulegium L. is a medicinal and aromatic plant belonging to the Labiatae family present in the humid to the arid bioclimatic regions of Tunisia. We studied the effect of different salt concentrations on plant growth, mineral composition and antioxidant responses. Physiological and biochemical parameters were assessed in the plant organs after 2 weeks of salt treatment with 25, 50, 75 and 100 mM NaCl. Results showed that, growth was reduced even by 25 mM, and salt effect was more pronounced in shoots (leaves and stems) than in roots. This growth decrease was accompanied by a restriction in tissue hydration and K+ uptake, as well as an increase in Na+ levels in all organs. Considering the response of antioxidant enzymes to salt, leaves and roots reacted differently to saline conditions. Leaf and root guaiacol peroxidase activity showed an increase by different concentration of NaCl, but superoxide dismutase activity in the same organs showed a slight modification in NaCl-treated leaves and roots. Moreover, polyphenol contents and antioxidant activity were analysed in M. pulegium leaves and roots under salt constraint. The analysis showed an increase of total polyphenol content (2.41–8.17 mg gallic acid equivalent g−1 dry weight) in leaves. However, methanol extract of leaves at 100 mM NaCl displayed the highest DPPH· scavenging ability with the lowest IC50 value (0.27 μg ml−1) in comparison with control which exhibited IC50 equal to 0.79 μg ml−1.

Physiological and antioxidant responses of Mentha pulegium (Pennyroyal) to salt stress

Phytodesalination of a salt-affected soil with the halophyte Sesuvium portulacastrum L. to arrange in advance the requirements for the successful growth of a glycophytic crop.

Nitrogen is the most important element for plant growth and development. In the cell, it is present as constituent of proteins, amino acids, nucleic acids, coenzymes, vitamins, chlorophylls, hormones, and functional groups of enzymes. It is a major part of chlorophyll and the green color of plants. It is a key constituent of nucleic acids that serve as genetic material and regulate vital processes like growth, reproduction, and heredity. Being a principal macronutrient, N has a special place in plant nutrition, and plants require it in large amounts. Though N is the most abundant element in our atmosphere, majority of the plants cannot utilize it directly in the elemental form. An adequate supply of N in the soil is essential to maintain proper growth and yield of crops. The availability of N in the soil is due to N2 fixation by symbiotic and nonsymbiotic bacteria; mineralization of organic matter, manure, and animal waste products; or application of inorganic N fertilizers. Though the natural sources can make significant contributions to soil N levels, with the advent of modern agricultural practices, to CONTENTS

Physiological Mechanisms of Nitrogen Absorption and Assimilation in Plants Under Stressful Conditions

In the sabkha of Soliman (N-E Tunisia), soil samples of the upper 20 cm were taken during the driest period of the year (July–August) from inside and outside tufts of two perennial halophytes: Arthrocnemum indicum (Willd.) Moq. and Suaeda fruticosa Forssk., both from family Chenopodiaceae. Samples were analysed for electrical conductivity of the saturation paste extract (ECe) and soluble sodium (Na+) content. Then, tufts were divided into three size categories and their shoot biomass production and Na+ content were determined. Our results showed a considerable contribution of shoot Na+ accumulation to rhizosphere desalination. The capacity of the two native halophytes A. indicum. and S. fruticosa to desalinize saline soils was compared with that of an introduced halophyte, Sesuvium portulacastrum L. (Aizoaceae). Seedlings were grown under greenhouse conditions in pots containing 8 kg of saline soil each. Pots were irrigated with tap water during 170 days without leaching. Our results confirmed the contribution of shoot Na+ accumulation to soil desalination. They showed also that among the three studied species, Sesuvium portulacastrum L. seems to be the most convenient to be used for this purpose in arid and semi-arid regions where precipitation is too low to leach salts from rhizosphere.

Resume

Dans la sebkha de Soliman (N-E de la Tunisie), des echantillons de sol ont ete preleves dans les 20 cm superieurs pendant la periode la plus seche de l’annee (juillet-aout) a l’interieur et a l’exterieur des touffes de deux halophytes perennes, Arthrocnemum indicum (Willd) Moq. et Suaeda fructicosa Forsk., appartenant tous deux a la famille des Chenopodiaceae. L’analyse des echantillons s’est basee sur la conductiviteelectrique de la pâte saturee (ECe) et le contenu en sodium (Na+) soluble. Par ailleurs, les touffes d’halophytes ont ete reparties en trois categories selon leur taille, puis des touffes representatives de chaque categorie ont ete recoltees pour la determination de la biomasse et la charge en Na+ de leurs parties aeriennes. Nos resultats ont montre que l’accumulation de ces ions au niveau des organes aeriens contribue considerablement au dessalement de la rhizosphere. La capacite des deux halophytes locales A. indicum et S. fructicosa de dessaler des sols salins a ete comparee a celle d’un halophyte introduite, Sesuvium portulacastrum L. (Aizoaceae). De jeunes plantules ont ete cultivees sous serre dans des pots contenant chacun huit kilos de sol salin. Les pots ont ete irrigues a l’eau de ville pendant 170 jours sans lessivage. Nos resultats ont confirme la contribution de l’accumulation de Na+ par les organes photosynthetiques au dessalement du sol. Ils ont montre, egalement, que, parmi les trois especes etudiees, S. portulacastrum semble etre la plus prometteuse pour un tel programme dans les regions arides et semi-arides ou les precipitations sont assez faibles pour lessiver les sels de la rhizosphere.

Evaluation of the capacity of three halophytes to desalinize their rhizosphere as grown on saline soils under nonleaching conditions.

Growth and nutrient acquisition in sour orange (Citrus aurantium L.) were studied under salt stress in vitro. Microshoots were transferred to Murashige and Skoog (MS) solid proliferation media containing 8.9 µM BA (6‐Benzyladenine) and 0.5 µM NAA (naphthaline acetic acid). Salinity was induced by incorporating different concentrations [0.0 (control), 50, 100, 150, 200, or 300 mM] of sodium chloride (NaCl) to the culture media. Microshoots were exposed to direct or gradual salinity shock. Slight reduction was obtained in growth (shoot length, shoot number, leaf number, and dry weight) when microshoots were directly exposed to NaCl stress from 0.0 to 150 mM. At 200 and 300 mM NaCl, growth parameters were adversly affected and microshoots died thereafter. Gradual NaCl shock was studied by transferring microshoots sequentialy every week to different NaCl concentraions (0.0, 50, 100, 150, 200, or 300 mM). Growth was monitored at each concentration until the end of the last week of incubation at 300 mM...

Munir M. Mohammad

Papers

Influence of sodium chloride salt stress on growth and nutrient acquisition of sour orange in vitro