Sesuvium portulacastrum is a halophytic species well adapted to salinity and drought. In order to evaluate the physiological impact of salt on water deficit-induced stress response, we cultivated seedlings for 12 days, in the presence or absence of 100 mmol l(-1) NaCl, on a nutrient solution containing either 0 mmol l(-1) or 25 mmol l(-1) mannitol. Mannitol-induced water stress reduced growth, increased the root/shoot ratio, and led to a significant decrease in water potential and leaf relative water content, whereas leaf Na(+) and K(+) concentrations remained unchanged. The addition of 100 mmol l(-1) NaCl to 25 mmol l(-1) mannitol-containing medium mitigated the deleterious impact of water stress on growth of S. portulacastrum, improved the relative water content, induced a significant decrease in leaf water potential and, concomitantly, resulted in enhancement of overall plant photosynthetic activity (i.e. CO(2) net assimilation rate, stomatal conductance). Presence of NaCl in the culture medium, together with mannitol, significantly increased the level of Na(+) and proline in the leaves, but it had no effect on leaf soluble sugar content. These findings suggest that the ability of NaCl to improve plant performance under mannitol-induced water stress may be due to its effect on osmotic adjustment through Na(+) and proline accumulation, which is coupled with an improvement in photosynthetic activity. A striking recovery in relative water content and growth of the seedlings was also recorded in the presence of NaCl on release of the water stress induced by mannitol.

The present study compares the demands for P of the initial nodule formation, and of the later growth and functioning of the nodulated root system in two inoculated lines of common bean (Coco blanc and BAT477). After germination and inoculation, seedlings were divided into two lots. One lot was grown under constant P supply, either 15 (low) or 250 (high) µM P, corresponding to provision of 120 and 2000 µmol P, respectively. In the second, seedlings were cultivated on the same medium supplied with 15 µM P for 24 days after germination, and then with 60 or 250 µM (total provision of P: respectively, 390 and 1530 µmol). Nodule number and biomass were significantly diminished by the low P (120 µmol) treatment, as compared with the other treatments. However, the intrinsic characteristics of the nodules (individual biomass and size, P concentration and efficiency of N fixation) did not depend on P availability. Although the bean line BAT477 was distinguished from the Coco blanc line through higher nodule number, size, biomass, and nitrogen fixation, both lines displayed analogous responses to P availability.

The impact of phosphorus (P) availability on root proliferation, proton efflux, and acid phosphatase activities in roots and leaves was investigated in two lines of common bean (Phaseolus vulgaris): BAT 477 and CocoT. Phosphorus was supplied as KH 2 PO 4 at 0 and 60µmol per plant (0P and 60P, respectively). Under P shortage, the plant growth was more restricted in CocoT than in BAT 477, shoots being more affected than roots. The root area increased significantly at 0P in both lines. Up to 1 week following P shortage, the proton efflux increased in both lines despite a higher extent in BAT 477 as compared to CocoT. Root acid phosphatase activity was significantly higher under P limitation in the both lines, this trend being more pronounced in BAT 477 than in CocoT. This was also true for the leaf acid phosphatase. Regardless of the bean line, higher values were recorded for the old leaves as compared to the young ones for this parameter. Interestingly, a significant correlation between Pi content in old leaves and their acid phosphatase activity was found in P-lacking (0P) plants of the both bean lines, suggesting that acid phosphatase may contribute to increase the phosphorus use efficiency in bean through the P remobilization from the old leaves. As a whole, our results highlight the significance of the root H + extrusion and the acid phosphatase activity rather than the root proliferation in the relative tolerance of BAT 477 to severe P deficiency.

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Abstract. The aim of this comparative research was to determine the chemical composition, antioxidant and antibacterial activities of the methanolic extracts and essential oils (EOs) of Artemisia absinthium aerial parts from five different regions (Bizerte, Zaghouan, Kasserine, Gabes and Tozeur). The polyphenol and flavonoid contents significantly varied (P < 0.05) among the studied regions with maximal contents observed in Zaghouan. Based on the High Performance Liquid Chromatography results, quercetin and isorhamnetin were the main compounds and their percentages were region dependent. The methanolic extract of Zaghouan showed the highest scavenging ability of DPPH (IC50 = 31.46 ± 1.42 µg/mL). A. absinthium EOs from of the different regions were found to interestingly inhibit the growth of both Gram-negative and Gram-positive bacteria strains. The antibacterial effect was strongly related to the organoleptic EO quality. The EO of Zaghouan exhibited an important inhibitory effect with an inhibition zone estimated at 31 mm against Escherichia coli strain. The EO composition was obtained by GC-MS analysis showing the presence of thirty-five compounds. Camphor (49.70 ± 2.34 %) and chamazulene (25.41 ± 0.61 %) were the main constituents. These results suggested that the north regions have a high potential for selecting varieties rich on bioactive volatile and phenolic compounds.   Resumen. El objetivo de esta investigación fue determinar y comparar la composición química, las actividades antioxidantes y antibacterianas de los extractos metanólicos y de los aceites esenciales (AE) de las partes aéreas de Artemisia absinthium de cinco regiones (Bizerta, Zaghouan, Kasserine, Gabes y Tozeur). Los contenidos de polifenoles y flavonoides variaron significativamente (P < 0,05) entre las regiones estudiadas con contenidos máximos observados en Zaghouan. De acuerdo con los resultados de la cromatografía líquida de alta resolución, la quercetina y la isorhamnetina fueron los compuestos principales y sus porcentajes dependieron de la región. El extracto metanólico de Zaghouan mostró la mayor capacidad secuestrante de DPPH (IC50 = 31.46 ± 1.42 µg mL-1). Se descubrió que los aceites esenciales de A. absinthium de las diferentes regiones inhibían de manera interesante el crecimiento de cepas de bacterias Gram-negativas y Gram-positivas. El efecto antibacteriano estuvo fuertemente relacionado con la calidad organoléptica del AE. El AE de Zaghouan exhibió un importante efecto inhibidor con un halo de inhibición estimado en 31 mm frente a una cepa de Escherichia coli. La composición de AE se obtuvo mediante análisis GC-MS y mostró la presencia de treinta y cinco compuestos. El alcanfor (49.70 ± 2.34 %) y el camazuleno (25.41 ± 0.61 %) fueron los principales constituyentes. Estos resultados sugirieron que las regiones del norte tienen un alto potencial para seleccionar variedades ricas en compuestos bioactivos volátiles y fenólicos.