AMP-Activated Protein Kinase (AMPK) Mediates Nutrient Regulation of Thioredoxin-Interacting Protein (TXNIP) in Pancreatic Beta-Cells

Thioredoxin-interacting protein (TXNIP) regulates critical biological processes including inflammation, stress and apoptosis. TXNIP is upregulated by glucose and is a critical mediator of hyperglycemia-induced beta-cell apoptosis in diabetes. In contrast, the saturated long-chain fatty acid palmitate, although toxic to the beta-cell, inhibits TXNIP expression. The mechanisms involved in the opposing effects of glucose and fatty acids on TXNIP expression are unknown. We found that both palmitate and oleate inhibited TXNIP in a rat beta-cell line and islets. Palmitate inhibition of TXNIP was independent of fatty acid beta-oxidation or esterification. AMP-activated protein kinase (AMPK) has an important role in cellular energy sensing and control of metabolic homeostasis; therefore we investigated its involvement in nutrient regulation of TXNIP. As expected, glucose inhibited whereas palmitate stimulated AMPK. Pharmacologic activators of AMPK mimicked fatty acids by inhibiting TXNIP. AMPK knockdown increased TXNIP expression in presence of high glucose with and without palmitate, indicating that nutrient (glucose and fatty acids) effects on TXNIP are mediated in part via modulation of AMPK activity. TXNIP is transcriptionally regulated by carbohydrate response element-binding protein (ChREBP). Palmitate inhibited glucose-stimulated ChREBP nuclear entry and recruitment to the Txnip promoter, thereby inhibiting Txnip transcription. We conclude that AMPK is an important regulator of Txnip transcription via modulation of ChREBP activity. The divergent effects of glucose and fatty acids on TXNIP expression result in part from their opposing effects on AMPK activity. In light of the important role of TXNIP in beta-cell apoptosis, its inhibition by fatty acids can be regarded as an adaptive/protective response to glucolipotoxicity. The finding that AMPK mediates nutrient regulation of TXNIP may have important implications for the pathophysiology and treatment of diabetes

Arabidopsis thaliana tolerates iron deficiency more than Thellungiella salsuginea by inducing metabolic changes at the root level

Several studies have used A. thaliana as a model to identify the physiological and molecular mechanisms underlying iron deficiency tolerance in plants. Here, Arabidopsis thaliana and Thellungiella salsuginea were used to investigate the differential responses to iron deficiency of these two species. Plants were cultivated in hydroponic medium containing 5 or 0 μM Fe, for 10 days. Results showed that rosette biomass was more reduced in T. salsuginea than in A. thaliana when grown on Fe-deficient medium. As a marker for iron deficiency tolerance, the induction of ferric chelate reductase (FCR) and phosphoenolpyruvate carboxylase (PEPC) activities was observed only in A. thaliana roots. In addition, we found that the accumulation of phenolic acids in roots of N1438 ecotype of A. thaliana was stimulated by Fe deficiency. Furthermore, an increase of flavonoids content in the root and exudates was observed under Fe-deficiency in this ecotype. Unlike other abiotic stresses, it appears that iron deficiency effects were more pronounced in Thellungiella than in Arabidopsis. The higher tolerance of the Arabidopsis plant to iron deficiency may be due to the metabolic changes occurring in the roots

Association épisodique d'halophytes stricts et de glycophytes dans un écosystème hydromorphe salé en zone semi-aride

La production de biomasse et le prélèvement d'éléments nutritifs majeurs (N, P, K) dans une parcelle mise hors pâturage en bordure de la sebkha d'Enfidha (100 km au sud de Tunis, étage bioclimatique semi-aride inférieur) ont été suivis au cours de 2 années consécutives, l'une particulièrement sèche et l'autre relativement pluvieuse. Environ la moitié de la biomasse aérienne sur la parcelle correspond à des halophytes pérennes caractéristiques de sols à forte salinité. Au cours de l'année pluvieuse, 40% de la production primaire de l'écosystème sont dus aux espèces annuelles, parmi lesquelles Medicago ciliaris (L) Krock, M polymorpha L, M truncatula Gaertn, et M minima Grufb sont dominantes. La réaction de ces Medicago au stress salin a été étudiée au laboratoire. Au stade végétatif, la production de MS est restreinte par NaCI (110 mM et 160 mM) chez tous les Medicago. Cet effet est lié à une réduction de la surface foliaire plutôt qu'à une baisse de la vitesse d'assimilation nette. Le sel diminue la production de graines en limitant le nombre de gousses, sans affecter le nombre de graines par gousse ni le poids individuel de la graine. La viabilité des graines n'est que très faiblement affectée. En dépit de leur origine (bordure de sebkha peuplée d'halophytes), les Medicago se sont révélés relativement sensibles à la salinité. La dynamique de leur reproduction dépend du maintien de la salinité à un niveau faible. Ces résultats suggèrent que ces plantes exploitent un horizon superficiel moins salé que celui qui supporte la croissance des halophytes. La présence des halophytes pourrait favoriser le maintien d'un horizon peu salé et relativement fertile, occupé périodiquement par les Medicago annuels.Episodic association of strict halophytes and glycophytes in a saline, hydromorphic ecosystem in semi-arid zones. The biomass production and the uptake of mineral nutrients (N, P, K) in an ungrazed area edging the sebkha of Enfidha (100 km south-east of Tunis; semi-arid bioclimatic zone) were studied for 2 successive years; the first year was particularly dry, the second relatively rainy. Half the aerial biomass was produced by perennial halophytes. Annual plants were responsible for a large part of the ecosystem productivity in the second year. Among them, Medicago ciliaris (L) Krock, M polymorpha L, M truncatula Gaertn and M minima Grufb were the dominant species (40% of ecosystem primary production). We studied their response to salinity in controlled culture conditions. Vegetative growth (dry matter production) was reduced by NaCl (110 or 160 mM) in all Medicago species. This effect was related to a reduction in leaf area rather than in assimilation efficiency. The number of seeds produced per plant and per unit biomass was severely reduced in the presence of salt. In contrast, individual seed weight, as well as their germinating power, were only weakly affected. In spite of their origin (edge of sebkha crowded by halophytes), the Medicago species studied appeared to be glycophytic, on the basis of their growth and nutritional responses to NaCl. Their reproduction depended on the maintenance of the salt concentration at low levels. These results suggest that these plants exploit the upper horizon layer, which is less salty than the deeper ones, which support the halophytes. The presence of halophytes might contribute to maintaining a fertile and less salty superficial layer, occupied periodically by annual Medicago species

Effect of salinity on germination, phytase activity and phytate content in lettuce seedling

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699International audienceSeeds of four lettuce (Lactuca sativa L.) varieties (Romaine, Augusta, Vista and Verte) differing in their salt sensitivity were sown at 0 (Control), 50, 100 and 150 mM NaCl. The final germination percentage decreased with the increasing salinity and was annulated at the highest salt concentration in Vista and Verte, the most sensitive varieties. However, in the less sensitive ones, Romaine and Augusta, it was slightly modified at 50 and 100 mM NaCl and then decreased by 50% compared with the control, at 150 mM. The effects of NaCl 100 mM on seedling growth, phytase activities, phytate and inorganic phosphorus contents were studied in Romaine and Vista showing different behaviours towards salinity. Radicle and hypocotyl length and fresh and dry weights were reduced by salt treatment in both varieties. In addition, radicle phytase activity exhibited an increase in Romaine (less sensitive) and a decrease in Vista (more sensitive). In hypocotyl, this activity showed no difference with the control in the two varieties. However, in cotyledons, and during early hours after germination, salinity decreased phytase activity in both varieties whereas in the later hours (72-96 h) this activity reached the value of the control in Romaine. The enhancement of phytase activity was concomitant with an increase in orthophosphate content and a decrease in phytate reserve. These results suggest that salt presence in the medium delays Pi remobilization from phytate stock, but stimulates assimilation of phosphorus more than its accumulation in the organs of the two lettuce varieties

Antioxidative responses of Ocimum basilicum to sodium chloride or sodium sulphate salinization

Soils and ground water in nature are dominated by chloride and sulphate salts. There have been several studies concerning NaCl salinity, however, little is known about the Na2SO4 one. The effects on antioxidative activities of chloride or sodium sulphate in terms of the same Naþ equivalents (25 mM Na2SO4 and 50 mM NaCl) were studied on 30 day-old plants of Ocimum basilicum L., variety Genovese subjected to 15 and 30 days of treatment. Growth, thiobarbituric acid reactive substances (TBARS), relative ion leakage ratio (RLR), hydrogen peroxide (H2O2), ascorbate and glutathione contents as well as the activities of ascorbate peroxidase (APX, EC 1.11.1.11); glutathione reductase (GR, EC 1.6.4.2) and peroxidases (POD, EC 1.11.1.7) were determined. In leaves, growth was more depressed by 25 mM Na2SO4 than 50 mM NaCl. The higher sensitivity of basil to Na2SO4 was associated with an enhanced accumulation of H2O2, an inhibition of APX, GR and POD activities (with the exception of POD under the 30-day-treatment) and a lower regeneration of reduced ascorbate (AsA) and reduced glutathione (GSH). However, the changes in the antioxidant metabolism were enough to limit oxidative damage, explaining the fact that RLR and TBARS levels were unchanged under both Na2SO4 and NaCl treatment. Moreover, for both salts the 30-day-treatment reduced H2O2 accumulation, unchanged RLR and TBARS levels, and enhanced the levels of antioxidants and antioxidative enzymes, thus achieving an adaptation mechanism against reactive oxygen species

Changes in the antioxidative systems of Ocimum basilicum L. (cv. Fine) under different sodium salts

The effects of different sodium salts on some physiological parameters and antioxidant responses were investigated in a medicinal and aromatic plant, Ocimum basilicum L. (cultivar Fine). Plants were subjected to an equimolar concentration of Na2SO4 (25 mM) and NaCl (50 mM) for 15 and 30 days. Growth, oxidative stress parameters [electrolyte leakage, peroxidation, and hydrogen peroxide (H2O2) concentration], antioxidant enzyme activities [ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), and peroxidases (POD, EC 1.11.1.7)], as well as antioxidant molecules [ascorbate and glutathione] were determined. The two salts affected leaf growth rates to the same extent, after 15 or 30 days of treatment, indicating a similar effect of Na2SO4 and NaCl salinity on growth, even if different (enzymatic and non-enzymatic) antioxidant mechanisms were involved in H2O2 detoxification. However, under both salts, the efficiency of the antioxidant metabolism seemed to be sufficient to avoid the deleterious effects of reactive oxygen species (ROS). Indeed, both ion leakage and peroxidation did not change under either Na2SO4 or NaCl salinity. As a whole, these data suggest that a cooperative process between the antioxidant systems is important for the tolerance of Ocimum basilicum L., cv. Fine to Na2SO4 and NaCl salinity