Effet de l’interaction lumiere-salinite sur l’activite du photosysteme ii des feuilles excisees de maïs

La diminution de la croissance vegetative observée chez nombreuses plantes, soumises au stress salin et exposées à des conditions naturelles d’ensoleillement, est souvent associée à une baisse de leur activité photosynthétique. Cependant les mécanismes de l’inhibition photosynthétique sont encore peu étudiés. Le photosystème II (PS II) est considéré un des facteurs clé dans la réponse de la photosynthèse des feuilles aux stress environnementaux. L’association de la lumière et du stress salin parait avoir des effets synergétiques sur l’activité photochimique du PSII conduisant, ainsi à la photoinhibition. L’objectif de cette etude est de diagnostiquer l’effet de l’interaction lumière- salinité sur l’activité photochimique du photosystème II au cours de la photosynthèse. Le materiel vegetal est constitué de deux variétés de maïs (Zea mays L.) fourrager: Aristo et Arper. Des feuilles détachées de plantes cultivées sur milieu témoin (eau distilée), sont incubées pendant 6 heures dans des solutions salines à différentes concentrations (0, 100, 200 et 300 mM NaCl), soit en absence ou en présence de lumière (1000 μmol m-2 s-1). Puis, leurs teneurs en sodium ont été déterminées. Pour vérifiers’il y’aura récupération de leur activité photochimique, d’autres feuilles qui ont été mises à absorber du NaCl dans une solution de 300 mM à la lumière pendant 4 heures, sont transferees dans de l’eau distillée en obscurité ou en lumière. Les resultants montrent une stabilité du rendement quantique maximal (Fv/Fm) pour les feuilles mises à absorber du NaCl à l’obscurité.Par contre l’éclairement associé avec la salinité engender une photoinhibition qui se manifeste par une diminution du rendement quantique maximal du PSII. Cette photoinhibition, due à une accumulation excessive des ions Na+dans les tissus foliaires, est réversible. En effet, en absence d’un seul des facteurs de l’association lumière-salinité le PSII récupère son activité photochimique.Mots Clés: fluorescence chlorophyllienne, feuillesexcisées, stress lumineux, chlorure de sodium, Zea maysEnglish AbstractThe decline in growth observed in many plants, subjected to salt stress and exposed to sunlight conditions, is often associated with a decrease in their photosynthetic activity. No clear mechanisms of the inhibited photosynthesis have emerged since photosystem II (PS II) is considered to play a key role in the response of leaf photosynthesis to environmental  perturbations. The combination of light and salt stress appears to have synergistic effects on the photochemical activity of PSII driving, and to photoinhibition. The objective of this study was to evaluate the reversible effect of salinity and light interaction on maximal quantum efficiency of photosystem II (Fv/Fm.). In this experiment, detached leaves of two forage maize (Zea mays L.) varieties, Aristo and Arper were placed during 6 hours in solutions of different concentrations of NaCl (0, 100, 200 and 300 mM) and subjected to light (1000 μmol m-2 s-1) or obscurity. Then, their contents of sodium were determined. In order to verify the photo-inhibition reversibility, other leaves which were incubated in a solution of 300 Mm NaCl, during 4 hours were transferred in distilled water and also subjected to light or to obscurity. Results indicate that leaves which had been put to absorb NaCl in obscurity showed no change in maximal efficiency of PSII (Fv/Fm). Nevertheless, light treatment associated with salinity generates a photo-inhibition of PSII manifested by a significant decrease in maximal efficiency of PSII. This photo-inhibition, due to an excessive accumulation of sodium in leaves, is reversible. It is quite sufficient to eliminate only one factor of the association light-salinity for the PSII activity resume.Keywords: Light stress, sodium chloride, Zea may

Influence of water stress on the nutritional quality of peach fruits

Climate change, especially in arid and semi-arid areas, affects the production of fruit trees. In this region, fruit tree production requires an efficient water supply that maintaining safe and stable yields. The aim of this work is to study the influence of irrigation modes on the nutritional peach fruit quality and the control of water stress indicators rates. Our experiment was carried out at the CRRA Sidi Bouzid (Central-West of Tunisia). It focused on four varieties of peach (Prunus persica L), two early varieties (Flordastar (FS) and Early Maycrest (EMC)), a seasonal variety (Rubirich (RUB)) and a late variety (O'Henry (O'H)). Three different irrigation treatments were applied to the experimental plot: full irrigation (T1; 100% ETc), sustained deficit irrigation (T2; 50% ETc) and cyclical deficit irrigation (T3). The contents of total sugar, protein, and proline as well as some bioactive compounds and stress indicators (MDA, H2O2) were quantified in the exocarp and mesocarp of the fruit. The results showed that O’H fruits are the richest in phenolic compounds, as well as they have significant antioxidant activity. While, both FS tissues accumulated more sugar (55.15 and 81.31g/100g in the mesocarp and exocarp, respectively). Protein level was much higher under T2 and T3 treatments compared to the control treatment (T1) in all varieties. Water stress mainly T2 had significantly stimulated the accumulation of proline in the mesocarp of FS (the content increased from 0.61 to 2.1 µmol/100 g MS). In addition, in the four varieties, the cyclic water treatment (T3) has a significant effect on the accumulation of sugar and phenolic compounds. In conclusion, T3 seems to be the most adequate water regime to be applied in semi-arid region, saving water resources and maintaining fruit quality

Pomological evaluation of some genotypes of figs (Ficus carica L.)

In order to enhance some cultivars of fig widespread in the Oasis of Gafsa located in the south of Tunisia (arid bioclimatic stage). Four cultivars of Fig (Ficus Carica L.) were evaluated 'Sawoudi', 'Bayoudhi', ' Mlouki ',' Assal '. The phenolic composition and antioxidant activities of skin, pulp and whole fruit were determinate. In this study the results showed that the total polyphenol contents of Assal cultivar were the highest in the various tissues (190.98-697.94 mg/100g FW). In all cultivars and whatever the tissue examined (whole fruit, peel, and flesh), the flavonoid content varied from 14.71 to 63.92 mg/100gFW). Also, Assal cultivar was the richest with flavonoids in comparison to other cultivars. The ortho-diphenol content varied from 8.21 to 118.62 mg/100g FW. Indeed, the flesh of Sawoudi and Bayoudhi cultivars had the higher ortho-diphenol content. On the other hand, Bayoudhi (flesh) was the more concentrated in anthocyanins which was around 2.8 mg/100g FW. However, the highest anthocyanin content in the peel was registrated in Sawoudi cultivar (0.934mg/100g FW). This cultivar had the most important antioxidant activity (p <0.05) evaluated by the four test DPPH, ABTS, reducing power and phosphomolybdenum. The comparison between the different cultivars has shown that Assal had the highest levels of total polyphenols and flavonoids as well as potential antioxidant activity. The results of the present study suggest that fig skin may be useful as a viable source of natural antioxidants for agri-food applications

Physiological traits, fruit morphology and biochemical performance of six old fig genotypes grown in warm climates “Gafsa oasis” in Tunisia

The study assessed the physiological parameters in leaves and the morphological/pomological traits in fruits of six fig cultivars (Ficus carica L.) – Sawoudi, Bayoudhi, Mlouki, Assal, Zidi, and Mozai – which grow in the arid climate of the Gafsa oasis (in the center of Tunisia). These cultivars are distinguished by different peel colors ranging from greenish, yellowish-brown, up to dark purple. Experiments measured chlorophyll and gas exchange in the plant leaves and various morphological, pomological, and chemical parameters, including phenolic compounds and antioxidant enzyme activities of the peel and pulp. The results showed that the Mlouki and Assal cultivars had the highest rates of photosynthesis (Pn) (10.17 and 10.44 μmol CO2 m−2 s−1, respectively). In addition, the fruits of these cultivars showed the highest concentration of sugar in the peel and flesh, as well as the highest values of solid soluble content (22.23 and 20.83 °Bx, respectively). Mlouki had the highest fruit weight (66 g) compared to the other cultivars studied. As for the acidity of the fruit, Bayoudhi showed the highest values (6.56 g MAE 100 mL−1), while the fruits of Assal and Zidi had the lowest acidity values. Biochemical determinations showed that Sawoudi had important enzymatic activity assessed by catalase (10.64 and 12.08 U min−1 g−1 in flesh and peel, respectively) and peroxidase, while Mlouki and Assal fruits showed the lowest values. The results also confirmed that the fig peel had higher antioxidant enzyme activity than the flesh. It can be concluded that the Mlouki cultivar exhibits superior overall quality with the highest weight and sugar content, while the dark-peeled cultivars (Sawoudi and Zidi) show the highest concentrations of phenolic compounds and antioxidant enzyme activities. The characteristics of these cultivars are in line with consumer demands, and therefore farmers can be encouraged to devote themselves to multiplying their cultivation

Carotenoids, Phenolic Profile, Mineral Content and Antioxidant Properties in Flesh and Peel of Prunus persica Fruits during Two Maturation Stages

Carotenoids and phenolic profile, antioxidant activity as well as concentrations of selected macronutrients (K, N, Mg, Ca and Na) and micronutrients (Zn, Cu and Mn) in flesh and peel of peach fruit were recorded at two harvest dates. Predominant mineral was potassium, followed by calcium, magnesium and sodium. The concentration of most micronutrients was greater in the peel than in the flesh especially in early season. The concentration of most elements in flesh and peel decreased during fruit maturation. Total carotenoids content varied with respect to the cultivar. β-cryptoxanthin and β-carotene were the major carotenoids in both tissues and flesh contain the lowest amounts. Neochlorogenic acid, chlorogenic acid, catechin, epicatechin, gallic acid, rutin, quercetin-3-O-galactoside, cyanidin-3-O-glucoside, cyanidin-3-O-rutinoside, were detected in both peel and flesh, with chlorogenic acid and catechin being the predominant components. Peel extracts showed markedly higher antioxidant activities, when estimated by ABTS or DPPH assays, than the flesh counterparts, consistent with the observed higher phenolic content. Overall, total phenolics levels increased at full ripening stage in both peel and flesh. The results found herein provide important data on carotenoids, phenolic and macro- and micronutrient changes during fruit growth, and emphases peach fruit as a potential functional food

Evaluation of New Cultivars of Plum (Prunus salicina) under Deficit Irrigation in a Semi-Arid Zone of Tunisia

The lack of precipitation influences the salinity of irrigation water. The experiment was conducted in a plum orchard in the Rgueb region. Two water regimes were applied. Stressed trees received 50% crop evapotranspiration (ETc) and the controls received 100% ETc. During the experimentation period, the phenological stages, flowering period and some pomological criteria were surveyed. The different parameters followed confirmed that the Black Star cultivar, with a shorter cycle, was the most resistant to water deficits and salinity. According to this study, it will be strategic to encourage the cultivation of the Black Star cultivar in the semi-arid region of Tunisia

Influence of water stress on the nutritional quality of peach fruits

Climate change, especially in arid and semi-arid areas, affects the production of fruit trees. In this region, fruit tree production requires an efficient water supply that maintaining safe and stable yields. The aim of this work is to study the influence of irrigation modes on the nutritional peach fruit quality and the control of water stress indicators rates. Our experiment was carried out at the CRRA Sidi Bouzid (Central-West of Tunisia). It focused on four varieties of peach (Prunus persica L), two early varieties (Flordastar (FS) and Early Maycrest (EMC)), a seasonal variety (Rubirich (RUB)) and a late variety (O'Henry (O'H)). Three different irrigation treatments were applied to the experimental plot: full irrigation (T1; 100% ETc), sustained deficit irrigation (T2; 50% ETc) and cyclical deficit irrigation (T3). The contents of total sugar, protein, and proline as well as some bioactive compounds and stress indicators (MDA, H2O2) were quantified in the exocarp and mesocarp of the fruit. The results showed that O’H fruits are the richest in phenolic compounds, as well as they have significant antioxidant activity. While, both FS tissues accumulated more sugar (55.15 and 81.31g/100g in the mesocarp and exocarp, respectively). Protein level was much higher under T2 and T3 treatments compared to the control treatment (T1) in all varieties. Water stress mainly T2 had significantly stimulated the accumulation of proline in the mesocarp of FS (the content increased from 0.61 to 2.1 µmol/100 g MS). In addition, in the four varieties, the cyclic water treatment (T3) has a significant effect on the accumulation of sugar and phenolic compounds. In conclusion, T3 seems to be the most adequate water regime to be applied in semi-arid region, saving water resources and maintaining fruit quality

Pomological evaluation of some genotypes of figs (Ficus carica L.)

In order to enhance some cultivars of fig widespread in the Oasis of Gafsa located in the south of Tunisia (arid bioclimatic stage). Four cultivars of Fig (Ficus Carica L.) were evaluated 'Sawoudi', 'Bayoudhi', ' Mlouki ',' Assal '. The phenolic composition and antioxidant activities of skin, pulp and whole fruit were determinate. In this study the results showed that the total polyphenol contents of Assal cultivar were the highest in the various tissues (190.98-697.94 mg/100g FW). In all cultivars and whatever the tissue examined (whole fruit, peel, and flesh), the flavonoid content varied from 14.71 to 63.92 mg/100gFW). Also, Assal cultivar was the richest with flavonoids in comparison to other cultivars. The ortho-diphenol content varied from 8.21 to 118.62 mg/100g FW. Indeed, the flesh of Sawoudi and Bayoudhi cultivars had the higher ortho-diphenol content. On the other hand, Bayoudhi (flesh) was the more concentrated in anthocyanins which was around 2.8 mg/100g FW. However, the highest anthocyanin content in the peel was registrated in Sawoudi cultivar (0.934mg/100g FW). This cultivar had the most important antioxidant activity (p <0.05) evaluated by the four test DPPH, ABTS, reducing power and phosphomolybdenum. The comparison between the different cultivars has shown that Assal had the highest levels of total polyphenols and flavonoids as well as potential antioxidant activity. The results of the present study suggest that fig skin may be useful as a viable source of natural antioxidants for agri-food applications

EFFET DE L\u2019INTERACTION LUMIERE-SALINITE SUR L\u2019ACTIVITE DU PHOTOSYSTEME II DES FEUILLES EXCISEES DE MA\ucfS

The decline in growth observed in many plants, subjected to salt stress and exposed to sunlight conditions, is often associated with a decrease in their photosynthetic activity. No clear mechanisms of the inhibited photosynthesis have emerged since photosystem II (PS II) is considered to play a key role in the response of leaf photosynthesis to environmental perturbations. The combination of light and salt stress appears to have synergistic effects on the photochemical activity of PSII driving, and to photoinhibition. The objective of this study was to evaluate the reversible effect of salinity and light interaction on maximal quantum efficiency of photosystem II (Fv/Fm.). In this experiment, detached leaves of two forage maize ( Zea mays L. ) varieties, Aristo and Arper were placed during 6 hours in solutions of different concentrations of NaCl (0, 100, 200 and 300 mM) and subjected to light (1000 \ub5mol m-2 s-1) or obscurity. Then, their contents of sodium were determined. In order to verify the photo-inhibition reversibility, other leaves which were incubated in a solution of 300 Mm NaCl, during 4 hours were transferred in distilled water and also subjected to light or to obscurity. Results indicate that leaves which had been put to absorb NaCl in obscurity showed no change in maximal efficiency of PSII (Fv/Fm). Nevertheless, light treatment associated with salinity generates a photo-inhibition of PSII manifested by a significant decrease in maximal efficiency of PSII. This photo-inhibition, due to an excessive accumulation of sodium in leaves, is reversible. It is quite sufficient to eliminate only one factor of the association light-salinity for the PSII activity resume.La diminution de la croissance vegetative observ\ue9e chez nombreuses plantes, soumises au stress salin et expos\ue9es \ue0 des conditions naturelles d\u2019ensoleillement, est souvent associ\ue9e \ue0 une baisse de leur activit\ue9 photosynth\ue9tique. Cependant les m\ue9canismes de l\u2019inhibition photosynth\ue9tique sont encore peu \ue9tudi\ue9s. Le photosyst\ue8me II (PS II) est consid\ue9r\ue9 un des facteurs cl\ue9 dans la r\ue9ponse de la photosynth\ue8se des feuilles aux stress environnementaux. L\u2019association de la lumi\ue8re et du stress salin parait avoir des effets synerg\ue9tiques sur l\u2019activit\ue9 photochimique du PSII conduisant, ainsi \ue0 la photoinhibition. L\u2019objectif de cette etude est de diagnostiquer l\u2019effet de l\u2019interaction lumi\ue8re- salinit\ue9 sur l\u2019activit\ue9 photochimique du photosyst\ue8me II au cours de la photosynth\ue8se. Le materiel vegetal est constitu\ue9 de deux vari\ue9t\ue9s de ma\uefs ( Zea mays L. ) fourrager: Aristo et Arper. Des feuilles d\ue9tach\ue9es de plantes cultiv\ue9es sur milieu t\ue9moin (eau distil\ue9e), sont incub\ue9es pendant 6 heures dans des solutions salines \ue0 diff\ue9rentes concentrations (0, 100, 200 et 300 mM NaCl), soit en absence ou en pr\ue9sence de lumi\ue8re (1000 \ub5mol m-2 s-1). Puis, leurs teneurs en sodium ont \ue9t\ue9 d\ue9termin\ue9es. Pour v\ue9rifiers\u2019il y\u2019aura r\ue9cup\ue9ration de leur activit\ue9 photochimique, d\u2019autres feuilles qui ont \ue9t\ue9 mises \ue0 absorber du NaCl dans une solution de 300 mM \ue0 la lumi\ue8re pendant 4 heures, sont transferees dans de l\u2019eau distill\ue9e en obscurit\ue9 ou en lumi\ue8re. Les resultants montrent une stabilit\ue9 du rendement quantique maximal (Fv/Fm) pour les feuilles mises \ue0 absorber du NaCl \ue0 l\u2019obscurit\ue9.Par contre l\u2019\ue9clairement associ\ue9 avec la salinit\ue9 engender une photoinhibition qui se manifeste par une diminution du rendement quantique maximal du PSII. Cette photoinhibition, due \ue0 une accumulation excessive des ions Na+dans les tissus foliaires, est r\ue9versible. En effet, en absence d\u2019un seul des facteurs de l\u2019association lumi\ue8re-salinit\ue9 le PSII r\ue9cup\ue8re son activit\ue9 photochimique