Influence de la taille de l’échantillon sur la variation des paramètres hydriques déterminés à partir des courbes-pression-volume

Le potentiel hydrique est utilise en tant que grandeur thermodynamique qui sfapplique a tous les compartiments du continuum sol-plante-atmosphere et qui reagit la circulation de lfeau entre le sol, les racines, les tiges, les feuilles et lfatmosphere. Il est determine par la methode de la chambre a pression de Scholander ; methode simple et rapide qui donne aussi acces a plusieurs parametres hydriques, decrivant lfetat de lfeau dans la plante, a travers une representation graphique ou courbe-pression-volume (CPV). Cependant, certaines procedures experimentales utilisees lors des mesures peuvent augmenter les risques des erreurs, au niveau des resultats, comme lfutilisation arbitraire dfechantillons de tailles variables. Le but de ce travail est dfetudier lfimpact de la variabilite de la taille des echantillons preleves sur les parametres hydriques et de trouver a la suite des solutions pouvant minimiser les erreurs experimentales induites. De ce fait, 12 CPV par jour ont ete effectuees sur des phyllodes (10}0,5 cm de longueur) et des rameaux de 16}0,5 cm de longueur (avec 5 a 6 phyllodes), de plants dfAcacia cyanlophylla Lindl., preleves a lfaube,sous conditions hydriques non limitantes, temoins, (ĵb.-0,2 } 0,1 Mpa) ou stressantes (ĵb = -1,80 } 0,20 Mpa) puis soumis immediatement a saturations (12h, 24h et 48h). Les resultats indiquent qufaussi bienpour les plants temoins que les stresses, la taille de lfechantillon influe significativement leurs parametres hydriques. Le prelevement des rameaux a lfaube, et leurs mises a saturation jusqufa 48h, permettraitdfavoir moins de variations dans le nombre et dans les valeurs des composantes hydriques determines.Mots-cles : taille de lfechantillon, Acacia cyanophylla Lindl., parametres hydriques, courbes pression volum

The Effects of Vapor Gard on some Physiological Traits of Durum Wheat and Barley Leaves under Water Stress

The use of antitranspirants is one method of mitigating water while increasing the yield of cereal crops. Experiments were carried out on a durum wheat (Triticum durum L.) variety (Karim) and a barley (Hordeum vulgare L.) variety (Rihane) to study the effects of Vapor Gard (VG; di-1-p-menthene), an antitranspirant, on two physiological traits at two different growth stages. The study was conducted in a glasshouse under water stress and VG was sprayed twice at three concentrations (5, 7, and 10%) at tillering and stem elongation stages. VG spray reduced the effect of water stress on durum wheat and barley varieties. Leaf water potential (LWP) was significantly increased, albeit at different rates, for the two cereal species. However, no significant change was observed for photosynthetic rate (PR). These results favor the use of VG although more studies are recommended on other physiological traits to strongly support the application of this antitranspirant

Endurcissement à la sécheresse et accumulation de glucides solubles et d'acides aminés libres dans les phyllodes d'Acacia cyanophylla Lindl

Drought hardening, soluble carbohydrates and free amino acid accumulation in Acacia cyanophylla Lindl phyllodes. Two plots of 8-month-old plants of Acacia cyanophylla Lindl grown in the greenhouse have been subjected to two contrasting water feedings. The first was nearly maximum evapotranspiration (D) and the second was D/6. Three plants of each water feeding were subjected to a drying cycle by water withholding after 1, 3, 5 and 13 months in order to allow the emergence of adaptive mechanisms in hard drought. At the beginning of each drying cycle, water potential component had been measured at 1 Pm in order to evaluate the effect of drought preconditioning duration on the D/6 plants. At the end of each cycle, marked by zero turgor, the same measures had been made and the remaining phyllodes were used to determine the concentration of free amino acids, soluble sugars and starch. We noted at the beginning of the cycles that D plants had a slight decrease in osmotic potential and a slight increase in the turgor; these variations seemed to be related to age. The response of D/6 plants varied with the duration of preconditioning. After 1 month, at the beginning of the cycle, their turgor was less than that of D plants. At the end of the cycle, they had a less negative osmotic potential and lower contents of free amino acids as compared to D plants. This suggests that a 1 month preconditioning to D/6 treatment was insufficient to induce hardening mechanisms. After 3 months and at the beginning of the cycles, we noted a higher turgor and a lower osmotic potential in the D/6 plants with an increasing difference in osmotic potential between D and D/6 over time (from 0.15 to 0.47 MPa). At the end of the fourth cycle, D/6 plants maintained a positive turgor at water potentials near -4.50 MPa. The difference of osmotic potential between D and D/6 plants was significant (from 0.40 to 1.60 MPa) and was accompanied by an increasing accumulation of soluble sugars and free amino acids, especially proline. Concomitantly, a reduction in starch concentration was observed. This could in part explain the accumulation of soluble sugars. These results attest to an acquired hardening by D/6 plants subsequent to a preconditioning of more than 3 months. This hardening was expressed at the end of the drying cycles by increasing osmotic adjustment ability over time.Deux lots d'Acacia cyanophylla Lindl cultivés en pots, sous serre, ont été soumis à l'âge de 8 mois à deux alimentations hydriques très contrastées : une dose d'irrigation proche de l'évapotranspiration maximale (D) et D/6. Au bout de 1, 3, 5 et 13 mois, trois plants de chaque lot ont été soumis à un cycle de dessèchement par privation d'eau afin de permettre aux mécanismes adaptatifs de s'exprimer en condition de sécheresse extrême. Au début de chaque cycle, les composantes du potentiel hydrique du phyllode ont été mesurées à 13 heures, afin d'évaluer l'effet de la durée du préconditionnement à la sécheresse sur les plants D/6. À la fin de chaque cycle, marquée par une turgescence nulle, des mesures analogues ont été effectuées et les phyllodes restants ont servi à la détermination des acides aminés libres, des sucres solubles et de l'amidon. Chez les plants D, on a noté au début des cycles une légère baisse du potentiel osmotique et une légère augmentation de la turgescence au cours du temps; ces variations semblent être liées à l'âge. La réponse des plants D/6 a varié selon la durée du préconditionnement. Après 1 mois, leur potentiel de turgescence, au début du cycle, a été inférieur à celui des plants D; à la fin du cycle, ils ont eu un potentiel osmotique moins négatif et des teneurs plus faibles en acides aminés libres en comparaison avec les plants D. Cela semble indiquer que 1 mois de préconditionnement à la dose D/6 a été insuffisant pour induire des mécanismes d'endurcissement. À partir du troisième mois, on a noté, au début des cycles, une turgescence plus élevée et un potentiel osmotique plus bas chez les plants D/6 avec une différence de potentiel osmotique entre D et D/6 croissante dans le temps (de 0,15 à 0,47 MPa). À la fin du quatrième cycle, les plants D/6 ont conservé une turgescence positive à des potentiels hydriques voisins de -4,50 MPa. La différence de potentiel osmotique entre D et D/6 s'est accentuée (de 0,40 à 1,60 MPa) et a été accompagnée d'une accumulation croissante de sucres solubles et d'acides aminés libres, essentiellement de proline. Parallèlement, on a enregistré une diminution de la teneur en amidon qui n'explique qu'en partie l'accumulation des sucres solubles. Ces résultats témoignent d'un endurcissement acquis par les plants D/6 suite à un préconditionnement de 3 mois ou plus. Cet endurcissement s'est traduit à la fin des cycles de dessèchement par une capacité d'ajustement osmotique croissante au cours du temps

Rendement agronomique du blé et de l'orge dans les parcelles associées des jeunes pacaniers à Sidi Mbarek au nord de la Tunisie

Productivity of Wheat and Barley in Plots Associated with Young Pecan in Sidi Mbarek at North of Tunisia. The productivity of two agroforestry associations is studied in the region of Mateur north of Tunisia (bioclimate subhumid). This crop of durum wheat and barley in association with young people aged 8 pecan during unproductive phase (0 to 10 years) to promote the cultivation of this tree to dry fruit in the region, occupy the land and improve incomes of rural populations. The pecans are planted at a density of 5 m x 5 m while wheat and barley are sown on the fly (± 200 plants/m²) in the bands between the rows of pecan (EA), near the pecan (SA) and in field control without trees (TE) with similar soil and climatic characteristics. The results show that the yields of intercropping depend on the location of planting. The yields of durum wheat sown between rows of pecan (8.4 t / ha) and those of the control (8.6 t/ ha) are not statistically significant difference, while yields of corn planted near the pecan (3.5 t/ha) and those of the control (8.6 t/ha) have a very significant difference. The yield of barley sown between rows of pecan (6.2 t/ha), near the pecan (1.9 t/ha) and those of the control (8.6 t/ha) are significantly different. The competition of surface roots of pecan and shading of the branches are pointed in SA as the main cause of declining performance. The pecan coexists easily with winter annual crops because of phenological shift. This system is productive and sustainable when it is practiced beyond 1 m from the pecan

A greenhouse investigation of responses to different water stress regimes of Laurus nobilis trees from two climatic regions

Plants from two populations of Laurus nobilis (Tunisia issued from a semi-arid inland site and Algeria originating from a coastal sub-humid area) were exposed during three months under similar controlled conditions to two stress intensities of permanent stress (60% (S1) and 20% (S2) of Held capacity) or to cyclic water stress, plants being re-watered when the soil moisture dropped to 60% (S11) or 20% (S22) of field capacity. One-year old plants displayed contrasting physiological strategies to cope with water stress. Algeria exhibited a higher decrease in osmotic potential (psi s) in relation to stress-induced proline accumulation. Glycinebetaine accumulated in response to drought in response to permanent stress (Algeria) or cyclic stress (Tunisia). The two populations had similar net photosynthesis (A) but Algeria exhibited higher water use efficiency (WUE) than Tunisia. A drought-induced increase in the apoplastic water content (AWC) was noticed in response to mild stress intensities (S1 and S11) in Tunisia and in response to higher stress intensities (S2 and S22) in Algeria in relation to a stress-induced accumulation of pectin and proportion of arabinose within the pectic fraction. Bulk modulus of elasticity (E) increased in Tunisia in response to permanent drought and in Algeria in response to cyclic stress, as a result of a stress-induced increase in cellulose (Algeria) or hemicellulose (Tunisia). It is concluded that water stress tolerance could be achieved by both osmotic and elastic adjustment in the coastal population which did not exhibit a prodigal water use comparatively to the inland population. Differences between populations are strongly influenced by the kinetics of water stress application. (C) 2009 Published by Elsevier Ltd

Physiological and anatomical adaptations induced by flooding in Cotula coronopifolia

Cotula coronopifolia is a wild annual Asteraceae that grows in periodically-flooded prone environments and seems highly tolerant to periodic flooding. Seedlings of about 15 cm were collected directly from the edge of Soliman sabkha (N-E Tunisia, semi-arid stage) and grown under greenhouse conditions. Two treatments were considered: drainage and flooding. After 56 days of treatment, flooded plants showed a pronounced growth increase. This performance was essentially associated with significant increment in biomass production of both shoots and roots (about 220% of the control). The appropriate response to flooding was also characterized by the ability of the species to maintain its water status under such conditions. Neither water content nor water potential showed a significant variation as compared to those of non-flooded plants. However, transpiration rate decreased slightly but significantly in flooded plants (from 0.86 to 0.64 mmol H2O m–2 s–1). Na+ and K+ concentrations were practically maintained under waterlogging conditions, except a significant increase of Na+ content in roots of flooded plants (157% of the control). These responses were concomitant with maintenance of photosynthetic rate. However, the contents of chlorophylls a and b increased to 167% and 295%, respectively. It seems that the enhancement in these photosynthetic pigments together with a significant improvement in water use efficiency (from 4.66 to 6.07 mmol CO2 mol–1 H2O) allowed to the species to compensate the decrease in photosynthetic rate. At the anatomical level, this species responded to flooding by a significant development of its root aerenchyma (+63%) and an increase in the lignification of its stem xylem tissues (+37%). Based on the presented data, the plant fitness under flooding conditions was a result of dynamic readjustment of several morphological, physiological, and anatomical adaptive traits. Flood requirement together with salt tolerance are responsible for the predominance of C. coronopifolia in a large area in its natural biotope where most plants cannot tolerate interactive effects of flooding and salinity

Composition of fatty acids, triacylglycerols and polar compounds of different walnut varieties (Juglans regia L.) from Tunisia.

The chemical composition (total oil content, fatty acids, triacylglycerols (TAGs) and polar compounds) of six walnuts (Juglans regia L.) cultivars (Lauzeronne, Franquette, Hartley, Local pt, Local gd and Parisienne) collected from Mateur (north of Tunisia) was evaluated. The major fatty acids found in the walnut oils are linoleic acid (60.42-65.77%), oleic acid (13.21-19.94%) and linolenic acid (7.61-13%). The TAG species were mainly composed of trilinolein (LLL), dilinoleoyl-linolenoyl-glycerol, dilinoleoyl-oleoyl-glycerol and palmitoyl-dilinoleoyl-glycerol classes. The results revealed that Local pt variety has the highest level of oil (62.56%), linoleic acid (65.77%) and LLL (33.48%). Significant differences among oil samples were observed, therefore showing a great variability in the oil composition among cultivars.This work has been done as a part of a National Research Project. Part of this work was carried out at ‘Instituto de la Grasa’, Consejo Superior de Investigaciónes Científicas (CSIC), 41012 Sevilla, Spain.Peer Reviewe

Composición química y propiedades térmicas de aceites de nuez de pecana [Carya illinoinensis (Wangenh.) K. Koch]tunecina

International audienceAn investigation on fatty acid, triacylglycerol, tocopherol, and xanthophyll contents and thermal properties of pecan (Carya illinoinensis) kernel oils from two cultivars was carried out. The main fatty acids were oleic acid, followed by linoleic and palmitic acids. The predominant triacylglycerols were OOL, OOO, and OLL (where O stands for oleoyl and L for linoleoyl). Pecan kernel oil is a rich source of tocopherols, mainly γ-tocopherol. Two xanthophylls (lutein and zeaxanthin) were investigated, and lutein was found to be the major one. Thermal behavior was studied by differential scanning calorimetry (DSC). Pecan nut oil displayed melting and crystallization transitions at low-temperature zones. The difference between DSC parameter values provides a path for distinguishing among cultivars. These data promote pecan kernel oil as a potential source of bioactive compounds with nutraceutical properties (monounsaturated fatty acids, tocopherols, and xanthophylls) and reveal, for the first time, the thermal properties of Carya illinoinensis oil.Se llevó a cabo una investigación sobre el contenido de ácidos grasos, triacilgliceroles, tocoferoles, xantofilas y propiedadestérmicas de aceites de nuez de pecana (Carya illinoinensis) de dos cultivares. Los principales ácidos grasos fueron el ácido oleico seguidode los ácidos linoleico y palmítico. Los triacilgliceroles predominantes fueron OOL, OOO y OLL (donde O, oleoilo y L; linoleoilo). Elaceite de nuez de pecana es una fuente rica en tocoferoles, principalmente γ-tocoferol. Se investigaron dos xantofilas (luteína y zeaxantina), la luteína fue la mayoritaria. Los comportamientos térmicos se estudiaron mediante calorimetría diferencial de barrido (DSC). Elaceite de nuez de pacana mostró transiciones de fusión y cristalización en zonas de baja temperatura. La diferencia entre los valores delos parámetros de DSC proporciona un camino para distinguir entre cultivares. Estos datos presentan al aceite de nuez pecana como unafuente potencial de compuestos bioactivos con propiedades nutracéuticas (ácidos grasos monoinsaturados, tocoferoles y xantofilas) yrevelan, por primera vez, las propiedades térmicas del aceite de Carya illinoinensis