Raoudha Abdellaoui

Comparative Study of Chemical Composition of the Essential Oils from Three Calligonum Species Growing-Wild in Tunisian Desert

Abstract The essential oils of three wild species of Calligonum (C. azel, C. arich and C. comosum) growing in the Tunisian desert were obtained by hydrodistillation and were analyzed by GC-FID and GC-MS in order to discern the differences and similarities between the chemical composition of the essential oils of these species. A total of 110 compounds, which accounted for 94.0 – 99.7 % of the total composition of the essential oils, have been identified. The main constituents were viridiflorol (9.6 %) in C. azel, hexadecanoic acid (20.1 %) in C. arich and 9-octadecenoic acid (19.8 %) in C. comosum. Based on their chemical composition, two chemotaxonomic groups may be established: C. azel on one hand, C. arich and C. comosum on the other hand.

Anatomical adaptations of Astragalus gombiformis Pomel. under drought stress

The present study was designed to study the effect of drought on root, stem and leaf anatomy of Astragalus gombiformis Pomel. Several root, stem and leaf anatomical parameters (cross section diameter, cortex, root cortical cells, pith, leaf lamina and mesophyll thickness) were reduced under moderate to severe water deficit (20–30 days of withheld irrigation). The stele/cross section root ratio increased under moderate water deficit. The root’s and stems vascular systems showed reduced xylem vessel diameter and increased wall thickness under water deficit. In addition, the root xylem vessel density was increased in these drought conditions while it was unchanged in the stems. The stomata density was increased under prolonged drought conditions whereas the stomata size was untouched. The leaf vascular system showed reduced xylem and phloem tissue thickness in the main vein under moderate to severe water deficit. However, in the lamina the vascular tissue and the distance between vascular bundle were unaffected. Our findings suggest a complex network of anatomical adaptations such as a reduced vessel size with increased wall thickness, lesser cortical and mesophyll parenchyma formation and increased stomata density. These proprieties are required for the maintenance of water potential and energy storage under water stress which can improve the resistance of A. gombiformis to survive in arid areas.

Anatomical adaptations of the desert species Stipa lagascae against drought stress

Abstract Stipa lagascae R. & Sch. (perennial bunchgrass) is one of the most promising steppic species for arid and desert lands of Tunisia. The present study was designed to study the effect of drought on root and leaf anatomy, water relationship, and the growth of three- month-old S. lagascae plants, submitted to water deficit (5, 10, 15, 20, 30 days of withheld irrigation) and grown in pots in greenhouse conditions. The results show that water deficit treatments reduced the biomass accumulation (MS) and leaf water potential (Ψw) of plants. However, leaf relative water content (RWC) decreased significantly only at severe drought. The root’s anatomical features showed reduced root cross-sectional diameter under water deficit. Conversely, epidermis was unaffected by water stress. Moderate and/or severe water deficit (20-30 days) reduced significantly the cortex thickness, cortical cell size, stele diameter, xylem vessel diameter and the stele/root crosssectional ratio, while the number of cortical cells increased for severe water deficit. The cuticles and mesophyll of S. lagascae was thickened by moderate to severe drought and the entire lamina thickness was increased significantly by 5.8% only after 30 days of water deficit while epidermis was unaffected by water deficit. However, severe water deficit (30 days) decreased the width and the length of the bundle sheath. At the same time, the mesophyll cells size and both the xylem and phloem vessels diameter diminished by 12, 16.8 and 17.5%, respectively. Leaf rolling occurs as a response to water deficit and its level increases as the drought period is progressing in plants while reduced bulliform cells size occurred only at severe water deficit. Our findings suggest a complex network of root and leaf anatomical adaptations such as a reduced vessel size with lesser cortical and mesophyll parenchyma formation and increased leaf rolling. These proprieties are required for the maintenance of water potential and energy storage under water stress which can improve the resistance of S. lagascae to survive in extremely arid areas

Effects of natural long storage duration on seed germination characteristics of Periploca angustifolia Labill.

This study was carried out to evaluate the effect of long-term natural aging on germination ability and several biochemical characteristics regarding soluble sugars and polyphenol matter contents and radical scavenging activity of Periploca angustifolia Labill. (Asclepiadaceae) stored seeds for 1, 3, 7, 10, 11 and 15-years, dry storage compared to freshly collected seeds. The long-term aging caused an important decrease of germination percentage, seed vigor index, seeds’ viability, moisture content and seed vigor except for seeds stored for seven-years. The latter showed the highest percentages of germination and viability, seed vigor index and seed vigor under a 7.3% moisture content when compared to the oldest seeds (15-years old) which presents the lowest moisture content. In our study, aged seeds showed the lowest radical scavenging percentage activity and amounts of polyphenol, keeping free radicals and peroxides at high levels causing thereby seeds deterioration. P. angustifolia seeds undergo a process of after-ripening under the storage conditions, possibly depending on the low, but steady water loss down to an optimal storage water content of approx. 7.3%, thereafter undergoing some deterioration as indicated by reduced amounts of soluble sugars by polyphenol contents and experimentally tested antioxidant activities, which is in line with increased membrane leakages as indicated by increased electrical conductivities of solution from experimentally soaked seeds. Keywords : Periploca angustifolia Labill, polyphenol, germination African Journal of Biotechnology Vol. 12(15), pp. 1760-1768

Physiological, anatomical and antioxidant responses to salinity in the Mediterranean pastoral grass plant Stipa lagascae

Abstract. Soil and water salinity is a major environmental problem in the dry Mediterranean regions, affecting rangeland production. This study investigated the effects of salinity on the wild perennial grass (Poaceae) species Stipa lagascae R. & Sch., a potential forage plant that could be used to rehabilitate degraded rangelands in dry areas. In a laboratory, 3-month-old S. lagascae seedlings were subjected to increasing salt treatments (0–400 mm NaCl) for 45 days. Physiological and biochemical parameters such as leaf water potential (Ψw), leaf relative water content (RWC), proline, total soluble sugars, Na+, K+ and Ca2+ contents, and catalase, ascorbate peroxidase and glutathione reductase activities were measured. Total soluble sugars and proline concentrations increased and Ψw and RWC decreased with increasing salt concentrations. Lower salt concentrations induced a non-significant degradation of chlorophyll pigments. Shoot Na+ content increased with a salinity level, whereas shoot K+ and Ca2+ concentrations decreased and the K+ : Na+ ratio was lower. The salinity threshold, above which S. lagascae showed signs of damage, occurred at 300 mm. Plants have evolved reactive oxygen species (ROS) scavenging enzymes including catalase, ascorbate peroxidase and glutathione reductase, which provide cells with an efficient mechanism to neutralise ROS. The tolerance strategies of S. lagascae to moderate salinity seem to include osmotic adjustment through total soluble sugars and proline accumulation, and highly inducible antioxidative defence. Further investigations are necessary to study the effect of salt stress on distribution of ions (Na+, K+, Ca2+, Mg2+, Cl–, NO3–, SO42–) and osmotic adjustment. Photosynthesis and water-use efficiency parameters could be also useful tools.

Effect of NaCl stress on physiological, antioxidant enzymes and anatomical responses of Astragalus gombiformis

Abstract The current study was carried out to check the influence of the gradient saline (0, 50, 150, 200, 250 and 300 mM NaCl) on Astragalus gombiformis Pomel. plants grown in pots in greenhouse conditions. The results demonstrated that salt levels above 50 mM substantially reduced the biomass accumulation in both roots and especially in shoots. Similarly, higher salinity (100–300 mM NaCl) resulted significant decline in net photosynthetic (–66.2%), transpiration (–80%), stomatal conductance (–87.7%), intercellular CO2 concentration (–78.1%) and chlorophyll a and b contents (–45.7 and –51%, respectively). Also, leaf relative water content (RWC) was reduced significantly with salinity exceeding 100 mM NaCl, while the leaf water potential (Ψw) decreased significantly as salinity rises. Salt stress increases Na+, Na+/K+ and decreases K+ concentrations in all tissues of A. gombiformis. Compensatory, an accumulation of organic osmolytes such as soluble sugars in response to higher salinity (150–300 mM NaCl) was observed, while proline content increased drastically with progressive salinity. The present study reveals that GPX and GR were highly used to protect from NaCl-induced H2O2. APX might to participate efficiently in restriction of oxidative damages under higher salinity (50–150 mM). The leaf anatomy showed an increase in upper epidermal thickness at higher salt level (300 mM), whereas the total leaf thickness and the mesophyll parenchyma area decreased with salinity exceeding 100 mM NaCl. The distance between vascular bundle and the xylem vessel diameter were reduced only at 300 mM. The stomatal density decreased with enhanced stomata size at 200–300 mM NaCl. Based on these physiological, biochemical and anatomical responses to salinity we conclude that A. gombiformis is unable to maintain the ionic homeostasis and to managing ROS stress at high salinity and therefore can tolerate only mild to moderate salinity.