Influence of Water Stress on Seed Germination Characteristics in Invasive Diplotaxis harra (Forssk.) Boiss (Brassicaceae) in Arid zone of Tunisia

Diplotaxis harra (Forssk.) Boiss (Brassicaceae) has a wide ecological and geographical amplitudes in Tunisia and grows under a variety of environmental conditions. A laboratory experiment was performed to evaluate the effect of water potential on seed germination and recovery responses after transfer to distilled water. The germination responses of seeds at 15°C in complete darkness were determined over a wide range of PEG-6000 solutions of different osmotic potentials: 0 to –1 MPa. Greatest germination was obtained in distilled water (71%), and increases in osmolality of solutions progressively inhibited seed germination, less than 10% of the seeds germinated at –0.8 MPa. No germination was observed for the treatment of –1 MPa. The rate of germination decreased as osmotic potential decreased. When seeds were transferred to distilled water after 20 days of water stress, the recovery of germination increased with an increase in pretransfer PEG-6000 treatments. Seeds subjected to high osmotic potential had higher recovery percentages. ÂÂ

Micropropagation of Helianthemum lippii L. var Sessiliforuim (Cistaceae) an important pastoral plant of North African arid areas

Helianthemum lippii L. is a perennial, little brush distributed in sandy regions of southern Tunisia as well as of Mediterranean basin. It presents an important ecological, economical and pastoral interest. All these characteristics encourage us to try the in vitro propagation because it is a feasible alternative for the rapid multiplication and the preservation of plants. A very high frequency of sprouting and shoot differentiation were observed in the primary cultures of nodal explants of H. lippii on MS medium, without growth regulators or with a lower concentration of 6-benzylaminopurine (BAP, 0.5 mg L-1 or 1.0 mg L-1 BAP). In vitro proliferated shoots were multiplied rapidly by culture of shoot tips on MS medium free or with BAP (0.5 to 2.0 mg L-1) which produced the greatest multiple shoot formation. BAP had a positive effect on multiplication and on growth, but a concentration that exceeds 2.0 mg L-1 decreased the growth. A high frequency of rooting (71%) with development of healthy roots was observed with shoots cultured on MS/8 medium hormone-free. After in vitro rooting, and transfer to soil, a number of plantlets suitable for reintroduction in nature were produced.Key words: Helianthemum lippii, axillary buds, micropropagation, plant conservation

Factors influencing seed germination of medicinal plant Salvia aegyptiaca L. (Lamiaceae)

AbstractSalvia aegyptiaca is a xerophytic perennial herb belongs to the Lamiaceae family commonly used for medicinal purposes. Laboratory experiments were carried out to assess the effects of temperature and salinity on seed germination and recovery responses after transferring to distilled water. Temperatures between 10 and 40°C seem to be favourable for the germination of this species. Germination was inhibited by either an increase or decrease in temperature from the optimum (30°C). The highest germination percentages were obtained at 0mM NaCl; however, the increase of solution osmolalities progressively inhibited seed germination. The germination rate decreased with an increase in salinity for most of tested temperatures, but comparatively higher rates were obtained at 30°C. Salt stress decreased both the percentage and the rate of germination. An interaction between salinity and temperature yielded no germination at 300mM NaCl. By experimental transfer to distilled water, S. aegyptiaca seeds that were exposed to moderately saline conditions recovered and keep their ability to germinate mostly at low temperatures. At 300mM NaCl, germination recovery decreased with increasing temperature and it was completely inhibited at 40°C

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, germinationAfrican Journal of Biotechnology Vol. 12(15), pp. 1760-176

Screening of Antiradical and Antibacterial Activities of Essential Oils of Artemisia campestris L., Artemisia herba alba Asso, & Thymus capitatus Hoff. Et Link. Growing Wild in the Southern of Tunisia

The present study was conducted to evaluate in vitro antibacterial and antiradical activities of essential oils extracted from air-dried leaves of Artemisia campestris Artemisia herba alba and Thymus capitatus growing wild in the southern of Tunisia. The principle compounds of Artemisia campestris oil were b-pinene (45.8%) and a-pinène (12.5%), the major constituents of Artemisia herba alba oil were β-thujone (30.0%) and α-thujone (25.7%) whereas the Thymus capitatus oil was mainly composed of  carvacrol (68.8%) and p-cymène (11.1%). The determination of the antiradical activity by DPPH method showed that Thymus capitatus oil exerted the highest activity with (0.15 µl/ml), followed by Artemisia herba alba (1.0 µl/ml) and Artemisia campestris (2.09 µl/ml). The screening of the antibacterial activity against seven bacteria using the disc diffusion method showed that Thymus capitatus oil strongly inhibited the growth of all bacteria studied (20 - 30 mm) except Pseudomonas aerogunosa which was resistant to all oils. The two other oils exhibited moderate and weak antibacterial activity. These results show and confirm that Thymus capitatus possesses strong antiradical and antibacterial activities, and therefore it could be used as a natural preservative ingredient in food and/or pharmaceutical industries

Facteurs influençant la germination des graines de Cleome ambyocarpa Barr. & Murb. (Capparidaceae) dans le Sud tunisien

Cleome amblyocarpa Barr. & Murb. is an annual herb in the family of Capparidaceae. It is abundant in sandy environments, and the gravel and stony grounds in Tunisian arid areas. Laboratory experiments were carried out to assess the effects of temperature (10 to 40° C) on seed germination in complete darkness. The osmotic stress simulated by NaCl at different concentrations (0 to 200 mM) or polyethylene glycol 6000 (PEG-6000) at different osmotic potentials (0 to -1 MPa) was evaluated at the most suitable temperature found. Greatest germination percentage and rate of germination were obtained at 25° C, but germination was inhibited by either an increase or decrease in temperature from the optimal temperature. The increase in osmolality of solutions induced by NaCl or PEG progressively inhibited seed germination. At 150 mM NaCl or osmotic potential of -0.6 MPa, germination was completely inhibited. There was a decrease in the rate of germination as osmotic stress was intensified. These findings suggest that C. amblyocarpa was able to tolerate well osmotically- and saline-stressful habitats of the arid ecosystems during germination stageCleome amblyocarpa Barr. & Murb. est une plante herbacée annuelle de la famille des Capparidaceae. Elle est abondante dans les environnements sableux, les sols secs et pierreux, ainsi que les alluvions de gravier dans les zones arides tunisiennes. Des expériences conduites au laboratoire ont été effectuées pour évaluer les effets de la température (10 à 40° C) à l'obscurité. Le stress osmotique simulé par le NaCl à différentes concentrations (0 à 200 mM) ou le polyéthylène glycol 6000 (PEG-6000) à différents potentiels osmotiques (0 à -1 MPa) a été évalué à la température optimale trouvée. Les meilleurs pourcentages et vitesses de germination ont été obtenus à 25° C, mais la germination est inhibée au-dessus et en deçà de cette température. L'augmentation de l'osmolarité des solutions induites par le NaCl ou le PEG inhibe progressivement la germination des graines. À 150 mM NaCl ou un potentiel osmotique de -0,6 MPa, la germination est complètement inhibée. On assiste à une diminution de l'indice de germination au fur et à mesure que le stress osmotique est accentué. Ces résultats suggèrent que C. amblyocarpa semble bien tolérer la salinité et la sécheresse des écosystèmes arides durant la phase germinative

Adaptive responses to drought of two Retama raetam subspecies from Tunisia

[EN] Aims: The survival and ecological distribution of plants in arid habitats are mainly conditioned by water availability and physiological adaptations to withstand drought. In the present study, we have compared the physiological responses to drought of two Retama raetam (retama) subspecies from Tunisia, one of them living under the desert climate (subsp. raetam) and the other one growing on the coast (subsp. bovei). Methods: To physiologically characterize the two R. raetam subspecies, and to elucidate their main mechanisms underlying their tolerance to drought stress, parameters related to seed germination, growth, photosynthesis (net photosynthetic rate, intracellular CO2 concentration, transpiration rate, stomatal conductance and water-use efficiency) and accumulation of osmolytes (proline, glycine betaine [GB] and soluble sugars) were determined in 4-month-old plants subjected to stress for up to 1 month. Important Findings: Drought significantly inhibited germination, growth and all the evaluated photosynthetic parameters. Plants of R. raetam subsp. bovei were severely affected by drought after 3 weeks of treatment when photosynthesis rates were up to 7-fold lower than in the controls. At the same time, proline and GB significantly accumulated compared with the irrigated controls, but much less than in R. raetam subsp. raetam; in the latter subspecies, proline and GB increased to levels 24- and 6-fold higher, respectively, than in the corresponding controls. In summary, the population living in the desert region exhibited stronger tolerance to drought stress than that adapted to the semiarid littoral climate, suggesting that tolerance in R. raetam is dependent on accumulation of osmolytes.Dhikra Zayoud's stay in Valencia was supported by a grant from the Tunisian Ministry of Higher Education and Scientific Research.Gil, R.; Zayoud, D.; Ouerghi, Z.; Boscaiu, M.; Vicente, O.; Neffati, M. (2021). Adaptive responses to drought of two Retama raetam subspecies from Tunisia. Journal of Plant Ecology. 14(3):527-540. https://doi.org/10.1093/jpe/rtab007S52754014