Abdelly Chedly

Salt tolerance of the halophyte Limonium delicatulum is more associated with antioxidant enzyme activities than phenolic compounds

In this work we studied the effect of salinity (ranging from 50 to 500mM NaCl) on the physiological and the antioxidant responses of the local halophyte Limonium delicatulum Kuntze. We based our analysis on 12 biochemical assays that are commonly used to measure the antioxidant responses under stress such as oxidative stress markers, enzymes activities and polyphenolic compounds. Our aim was to study parameters that are strongly correlated with the growth response to salinity. Results showed two different growth responses depending on the concentration of NaCl in the medium. Under 50 to 200mM, the growth was stimulated before it decreased significantly at 300-500mM. L. delicatulum revealed a good aptitude to maintain photosynthetic machinery by increasing the concentrations of photosynthetic pigments, which is essential for the stabilisation of photosystems and the photosynthesis process under optimal NaCl concentration. Their breakdown at higher salinity decreased the photosynthetic performance of plants resulting in growth inhibition. Moreover, to reduce the damaging effect of oxidative stress and to tolerate the accumulation of salt ions, L. delicatulum induced the activities of their antioxidant enzymes more than their contents in polyphenolic compounds.

Scanning and transmission electron microscopy and X-ray analysisof leaf salt glands of Limoniastrum guyonianum Boiss. under NaCl salinity.

Leaf salt glands of Limoniastrum guyonianum were examined by scanning and transmission electron microscopes and energy dispersive X-ray analysis (EDAX) system, after growing for three months on sandy soil with or without 300 mM NaCl. Results showed that salt glands were irregularly scattered on both leaf sides and sunk under the epidermal level. Salt excretion occurred in both conditions and is mainly composed of calcium and magnesium in control plants, and essentially sodium and chloride in plants subjected to salt treatment. A salt gland is comprised of collecting, accumulating, and central compartments, and is made up of total thirty-two cells. The collecting cells were characterized by large central vacuoles. Accumulating cells contain numerous, large, and unshaped vacuoles and rudimentary chloroplasts. The central compartment was comprised of four basal cells and each one is surmounted by an apical cell. The basal cells are granulated, containing large nucleus, numerous mitochondria, endoplasmic reticulum, ribosomes, polyribosomes, and small vacuoles or vesicles. Equally, the apical cells are rich in organelles. Application of 300 mM NaCl to the culture medium increased vacuoles number and size, and organelles density especially the mitochondria which suggests energy requirement for ions transport. The reduction in size and number of vacuoles toward the interior of salt glands of treated plants and the fusion of the smallest ones with the plasma membrane substantiate the implication of such vacuoles in salt excretion process. The current study which is the first report on L. guyonianum salt gland has provided an in-depth understanding on structure-function relationship in the multicellular salt glands.

EFFECTS OF THE HALOPHYTES TECTICORNIA INDICA AND SUAEDA FRUTICOSA ON SOIL ENZYME ACTIVITIES IN A MEDITERRANEAN SABKHA

In the present work, we studied the effectiveness of the predominant halophytes of Soliman sabkha (Tecticornia indica and Suaeda fruticosa) to promote soil biological activities and ecosystem productivity. Soil Arylsulphatese ARY, β-glucosidase β-GLU, phosphatase PHO, invertase INV, urease URE, and dehydogenase DES activities in Extra- and Intra-tuft halophytes and plant productivity were assessed. Results revealed a high increase of microbial community and ARY, β-GLU, PHO, INV, URE and DES activities (+298%, +400%, +800%, +350%, +320%, +25% and +759%, respectively) in Intra-tuft rhizosphere as compared to Extra-tuft one, which is likely due to the significant decrease of salinity in the rhizosphere of Tecticornia indica and Suaeda fruticosa. Both perennial plants exhibited high productivities (7.4 t dry weight ha−1 and 2.2 t dry weight ha−1, respectively) and Na+-hyperaccumulating capacities (0.75 t Na+ ha−1 and 0.22 t Na+ ha−1, respectively), reducing salt constraint and favouring soil fertility. This constitutes a promising alternative to enhance productivity in such a salt-affected biotope by offering suitable microhabitat for annual glycophytes.