Fayçal Boughalleb

Polygonum equisetiforme is a perennial herbaceous plant thriving in the arid regions of Tunisia and widely used in health care and self-medication. The objective of the current study was to investigate the distribution of minerals, phenolic compounds, and antioxidant potentials in various plant parts including the fruit, stem, leaf, and root. The mineral composition was determined using flame atomic absorption spectrometry. The phenolic content of the samples was investigated using colorimetric assays and identified and quantified using HPLC-ESI/MS. The study found that the different parts of P. equisetiforme contain significant amounts of essential minerals such as sodium, potassium, calcium, magnesium, copper, zinc, and iron. The leaf and root extracts had high amounts of polyphenols, flavonoids, and tannins. Through LC-ESI-MS analysis, eleven flavonoids and eight phenolic acids were characterized. The most abundant compounds were gallic acid, quinic acid, catechin (+), and hyperoside. The findings suggest that different parts of P. equisetiforme are valuable sources of essential minerals and phenolic compounds, which can have potential health benefits.

Silybum marianum and Silybum eburneum are wild edible Mediterranean plants used in the human diet. This study presents the initial findings on the phytochemical characterization of Tunisian S. marianum and S. eburneum organs. It examined their mineral, sugar, organic acid, polyphenolic, and seed storage protein contents, as well as their antioxidant potential. In S. marianum, stems had high sodium and potassium contents, while the immature and mature seeds were rich in calcium and magnesium. However, S. eburneum had high potassium levels in stems and high sodium and calcium levels in the flowers. S. marianum showed substantial fructose variation among its organs. Conversely, S. eburneum exhibited significant heterogeneity in glucose, sucrose, and maltose levels across its organs, with maltose exclusively detected in the immature seeds. A notable organ-dependent distribution of organic acids was observed among the two species. Higher levels of phenolic contents were detected in both mature and immature seeds in both species compared to the other plant parts. The seeds possessed higher antioxidant activities than other plant organs. In both S. marianum and S. eburneum seeds, albumins and globulins were the predominant protein fractions. This study brings evidence supporting the important potential of Silybum organs as sources of nutrients with antioxidant properties for producing functional food.

Climate change conditions can strongly influence the kinetics of morphogenetic processes. Our study showed that the total thickness of leaf lamina, adaxial palisade parenchyma, abaxial palisade parenchyma and spongy parenchyma increased significantly during the dry period, especially in August (31.4%, 52.1%, 37.6%, 27.69%, respectively). Moreover, the adaxial and abaxial epidermis becomes thicker during the most dry months (July and August). Likewise, the adaxial cuticle thickness increased during the dry period. The stomata density in the adaxial and abaxial leaf sides is 1.36- and 1.4-fold higher than those recorded during the wet periods. However, the salt glands’ density showed a much greater increase in the abaxial face (+2.4-fold). The bundle sheath size was unchanged under the seasonal environmental fluctuation in the sabkha. The xylem vessels diameter showed a maximum reduction in August (–63.8%). Likewise, the xylem vessels density increased significantly during the dry period. The closer relationship between the anatomical proprieties with soil salinity allows us to conclude that salt stress is one of the most limiting factors for Limoniastrum guyonianum in its natural biotope.

To cope with abiotic stresses, the halophytes use various tolerance mechanisms that are not all known for some species of halophytes. This work aimed to model the responses of two halophytes, Limonium pruinosum and Limonium tunetanum, to changing environmental conditions over a year in Sabkha biotope, Tunisia. Our findings indicated that the model could describe well the seasonal variations of all studied traits over a year in this region (R² > 0.80). The pH, electrical conductivity (EC), and mineral composition (i.e., Sodium [Na⁺], potassium [K⁺], calcium [Ca²⁺], and magnesium [Mg²⁺] concentrations] in the soil significantly varied during the year (P < 0.01). The highest soil Na⁺ concentration was found during the dry period (June–August), which matched with a high Na⁺ content in the aerial parts (i.e., 2455.1 and 3366.0 μmol g⁻¹ SDM in August for L. pruinosum and L. tunetanum, respectively). This accumulation is concomitant with a deficit in nutrients, particularly K⁺ and Mg²⁺ and, to a lesser extent, Ca²⁺. Following these disturbances, both species decreased their photosynthetic activity, water potential as well as the relative water content to a lesser extent, especially in August. To counteract these harmful effects, these species have accumulated organic substances, but in a different way. Indeed, L. pruinosum accumulated sucrose, fructose, and citrate, while L. tunetanum accumulated sucrose, xylitol, citrate, and malate, indicating a major role of these osmolytes in the stress tolerance mechanisms. In both species, the results also showed that all traits were highly correlated with the edaphic variables (i.e., pH, EC, Na⁺, K⁺, Ca²⁺, and Mg²⁺ concentrations) and with temperature as the climatic variable.

Polygonum is the largest genus of Polygonaceae and 5 species are reported in Tunisia. In order to characterized flower, seed, and fruit development in Polygonum, flower and fruit of Polygonium equisetiforme (var. graecum and peyerinhoffi), P. aviculare and P. maritimum, collected from Tunisia, were examined. Flowers are composed of five oblong tepals. P. equisetiforme and P. aviculare have whitish-pink distylous flowers with dimorphism of style, filament and anther height, pollen diameter and stigma size. In contrast, P. maritimum shows white homostylous flowers. The floral vasculature showed that the tepals are inserted in one whorl and their traces arise independently in 3+2 manner. The eight stamens are arranged in a 5+3 manner and the staminal bundles arise independently in the two whorls. The epidermis and endothecium cells width were higher in P. maritimum and the lowest endothecium width was observed in P. aviculare. Polygonum aviculare and P. equisetiforme showed circular pollen with shallow colpi and trilobite pollen shape with deep colpi, while P. maritimum rarely showed shallow colpi. The ovule is anatropous with basal placentation in P. equisetiforme and P. aviculare and apical placentation in P. maritimum. The young seed coat was formed by an endotesta with thick-walled cells, a mesotesta and exotesta with thin-walled cells and a tegmen composed of radially elongated cells. The fruits of the studied species are trigonous with ovate-lanceolate shape. In P. aviculare, the exocarp is thicker compared to the two other species, in P. equisetiforme, the mature exocarp consists of smaller rectangular cells with narrow cavities, and in P. maritimum showed a thinner exocarpIn conclusion, P. equisetiforme and P. aviculare are a typically distylous species from the morphological point of view and we discussed the significance of heterostyly in Polygonaceae. From this first morpho-anatomical study of Polygonum species in North Africa, we can conclude mainly that there is no significant difference between P. equisetiforme var. graecum and var. peyerinhoffi supporting a taxonomic grouping of these two varieties.

Possible Involvement of Organic Compounds and the Antioxidant Defense System in Salt Tolerance of Medicago arborea (L.)