Iron Deficiency Tolerance at Leaf Level in <i>Medicago ciliaris</i>Plants

Iron deficiency is an important environmental factor restricting plant productivity. Selecting tolerant genotypes is one of the possible ways to solve this problem. Many studies reported the effects of Fe deficiency on photosynthesis and anti-oxidative defense system. Yet, there is little information available on the use of these attributes as selective criteria. In the present study, we aim to determine some physiological and biochemical traits conferring Fe deficiency tolerance at leaf level in two lines of Medicago ciliaris. Our results showed that Fe deprivation had a lowering effect on photosynthesis (chlorophyll, photosynthetic electron transport activity and chlorophyll fluorescence) in both lines studied. However, the sensitive line TN8.7 was more affected. Hydrogen peroxide concentration was negatively correlated with the activities of antioxidant enzymes and with the concentration of some non-enzymatic antioxidant. The tolerant line TN11.11 was characterized by a more efficient antioxidant defense system in comparison with the sensitive line TN8.7. The main conclusion of this study is that photosynthesis and antioxidant defense system could be used as physiological and biochemical indicators of Fe deficiency tolerance in Medicago ciliaris plants.

Antioxidant and Antibacterial Properties of <i>Mesembryanthemum crystallinum</i>and <i>Carpobrotus edulis</i>Extracts

The two halophyte plants Mesembryanthemum crystallinum and Carpobrotus edulis (Family: Aizoaceae, Order: Cary-ophyllales), widely used in the traditional medicine, were chosen for this study. There is no much information about the antioxidant and antibacterial activities of the two plants growing in the Tunisian coasts. The most of studies conducted confirmed the responses of these plants to the abiotic stresses. We demonstrate a high antioxidant activity in the two plant extracts by using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) method. The two plant extract also exhibited antibacterial activity by using the minimal inhibitory concentration (MIC) against bacterial strains;Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853) and Staphylococcus aureus (ATCC 25923). The different medicinal properties can be attributed in part to the presence of polyphenolics compounds in the two plant extracts.

Ecophysiological aspects and photosynthetic pathways in 105 plants species in saline and arid environments of Tunisia

In Tunisian arid regions, plant life forms, ecotypes, physiological types and photosynthetic pathways （03, 04 or CAM） remain unclear. Understanding the characters of these plant species could be important for land restoration. A literature survey was conducted for 105 plants species in arid regions of Tunisia. These plant species belong to several ecotypes： halophytes, xerophytes, gypsophytes, psamophytes, xero-halophytes, gypso-halophytes, psamo-halophytes, psamo-xerophytes, xero-gypsophytes and hygro-halophytes. The variation of photosynthetic pathway types in the 105 studied species shows that 56.2% were C3, 41.0% were C4, 1.9% were CAM and 1.0% were C3-CAM. The C3 pathway was more abundant in the halophytes, whereas the C4 one was more common in the xerophytes, gypsophytes, gyp- so-halophytes and psamo-halophytes. The ratio of C3 to C4 species （C3/C4 ratio） was 0.2 in the psamo-halophytes, 0.8 in the gypso-halophytes, 1.1 in the xerophytes, 1.6 in the xero-halophytes, 1.8 in the hygrohalophytes, 2.0 in the psamo- phytes and 3.8 in the halophytes. The annuals were mainly C3 plants whereas most of perennials were C4 ones. The C3/C4 ratio was 1.3 in succulent species and 1.4 in non-succulent species. Thus, succulence seems not to affect the distribution of C3 and C4 pathways within the studied plants. This investigation shows high percentages of C4 plants occurred in Tuni- sian arid regions. However, there were significant differences in their abundance among ecotypes. Basing on C3/C4 ratio, we can find that the abundance of the C4 pathway was in the following order： psamo-halophytes, gypso-halophytes, xe- rophytes, xero-halophytes, hygro-halophytes, psamophytes and halophytes. In Tunisian arid regions, C4 species were most abundant in xerophytes and less abundant in halophytes. In the Chenopodiaceae the number of C3 plants was 13 and the number of C4 species was 20 and in the Poaceae the number of C3 was 23 and the number of C4 was 19 species. Thus, the most C4 proportion was in the Chenopodiaceae and Poaceae species. This confirms the fact that the Cheno- podiaceae and the Poaceae were the leading families that tolerate salinity and aridity.

Kinetics of the Anti-oxidant Response to Salinity in the Halophyte Cakile maritima

The effects of NaCl stress on the activity of anti-oxidant enzymes （superoxide dismutase, catalase （CAT）, peroxidase （POD）, ascorbate peroxidase （APX）, monodehydroascorbate reductase, dehydroascorbate reductase （DHAR）, and glutathione reductase （GR））, anti-oxidant molecules （ascorbate and glutathione）, and parameters of oxidative stress （malondialdehyde （MDA）, electrolyte leakage, and H2O2 concentrations） were investigated in Cakile maritima, a halophyte frequent along the Tunisian seashore. Seedlings were grown in the presence of salt （100, 200, and 400 mmol/L NaCl）. Plants were harvested periodically over 20 days. Growth was maximal in the presence of 0-100 mmol/L NaCl. At 400 mmol/L NaCl, growth decreased significantly. The salt tolerance of C. maritima, at moderate salinities, was associated with the lowest values of the parameters indicative of oxidative stress, namely the highest activities of POD, CAT, APX, DHAR, and GR and high tissue content of ascorbate and glutathione. However, prolonged exposure to high salinity resulted in a decrease in anti-oxidant activities and high MDA content, electrolyte leakage, and H2O2 concentrations. These results suggest that anti-oxidant systems participate in the tolerance of C. maritima to moderate salinities.