Mustapha Gorai

Relationship between phenological traits and water potential patterns of the wild jujube Ziziphus lotus (L.) Lam. in southern Tunisia

Background: Ziziphus lotus, wild jujube, is a xerophytic shrub of the Rhamnaceae family widely distributed in arid and semi-arid regions of Tunisia, where it occupies most soil types. Phenological patterns of desert plants are strongly affected by the seasonality of water availability and phreatophytes represent a particularly interesting case for studying such relationships. Aim: This study aims to investigate the relationship between phenological traits and water potential patterns of the wild jujube as a tool for understanding how plants cope with extreme drought. Methods: Phenophases and predawn (Ψpd) and midday (Ψmd) xylem water potentials of wild jujube were studied monthly (Nov 2007–Oct 2008) at Samaâliate and Oued El Hallouf in southern Tunisia. These sites receive164 mm and 191 mm of annual rainfall, respectively, and differ in slope and soil type. Results: The Ψmd decreased progressively and concomitantly with increasing seasonal drought, reaching the lowest values in late summer (down to –3.9 MPa for both sites). Seasonality of Ψpd was less pronounced for plants established in Oued El Hallouf (–2.09 MPa) than in Samaâliate (–2.63 MPa) at the end of the dry season. Wild jujube is dormant from October through to March and mature plants flower in May and produce fruits in August. Conclusions: Our results clearly demonstrate that wild jujube is a drought tolerant species reaching low water potentials during the driest months of summer.

Growth, root colonization and nutrient status of Helianthemum sessiliflorum Desf. inoculated with a desert truffle Terfezia boudieri Chatin.

This study aims to investigate the effects of inoculation using Terfezia boudieri Chatin ascospores (ectomycorrhizal fungus) on growth, root colonization and nutrient status of Helianthemum sessiliflorum Desf. seedlings grown in pots on two-soil types (gypseous and sandy loam). Mycorrhizal seedlings had significantly increased their height and leaf number compared to non-mycorrhizal ones. Regardless of mycorrhizal inoculation treatments, the plants growing on gypseous soil showed higher growth as compared to sandy loam one. It appears that inoculation with T. boudieri changed root morphology, increasing branching of first-order lateral roots of H. sessiliflorum seedlings. The highest root mycorrhizal colonization was recorded in inoculated seedlings on sandy loam soil (89%) when compared to gypseous one (52%). N, P and K concentrations in mycorrhizal seedlings were significantly improved by fungal inoculation. It can be concluded that inoculation of H. sessiliflorum with T. boudieri increased growth attributes and improved plant nutritional status.

Vessel-associated cells in angiosperm xylem: Highly specialized living cells at the symplast-apoplast boundary

BACKGROUND Vessel-associated cells (VACs) are highly specialized, living parenchyma cells that are in direct contact with water-conducting, dead vessels. The contact may be sparse or in large tight groups of parenchyma that completely surrounds vessels. VACs differ from vessel distant parenchyma in physiology, anatomy, and function and have half-bordered pits at the vessel-parenchyma juncture. The distinct anatomy of VACs is related to the exchange of substances to and from the water-transport system, with the cells long thought to be involved in water transport in woody angiosperms, but where direct experimental evidence is lacking. SCOPE This review focuses on our current knowledge of VACs regarding anatomy and function, including hydraulic capacitance, storage of nonstructural carbohydrates, symplastic and apoplastic interactions, defense against pathogens and frost, osmoregulation, and the novel hypothesis of surfactant production. Based on microscopy, we visually represent how VACs vary in dimensions and general appearance between species, with special attention to the protoplast, amorphous layer, and the vessel-parenchyma pit membrane. CONCLUSIONS An understanding of the relationship between VACs and vessels is crucial to tackling questions related to how water is transported over long distances in xylem, as well as defense against pathogens. New avenues of research show how parenchyma-vessel contact is related to vessel diameter and a new hypothesis may explain how surfactants arising from VAC can allow water to travel under negative pressure. We also reinforce the message of connectivity between VAC and other cells between xylem and phloem.

Prediction of auxin response elements based on data fusion in Arabidopsis thaliana

The plant hormone “auxin” is a key regulator of plant development and environmental responses. Many genes in Arabidopsis thaliana are known to be up-regulated in response to auxin. Auxin response factors activate or repress the expression of genes by binding at their promoter regions within auxin response elements (AuxRE) that are key regulatory cis-acting motives. Therefore, the identification of auxin-response elements is among the most important issues to understand the auxin regulation mechanisms. Thus, searching the TGTCTC motif is an unreliable method to identify AuxRE because many AuxRE variants may also be functional. In the present study, we perform an In-silico prediction of AuxREs in promoters of primary auxin responsive genes. We exploit microarray data of auxin response in Arabidopsis thaliana seedlings, in order to provide biological annotation to AuxRE. We apply a data fusion method based on the combined use of evidence theory and fuzzy sets to scan upstream sequences of response genes.