Effects of NaCl on growth and activity of enzymes involved in carbon metabolism in leaves of tobacco (Nicotiana rustica)

The adverse effects of salt should not be the same in tobacco plants exposed to a permanent and transient high concentration of NaCl in its environment. Experiments were conducted in order to verify the hypothesis of reversibility of NaCl effects. The study of this reversibility is checked by monitoring a number of parameters in pre-stressed plants and then, replaced in normal conditions. Plants previously grown for 30 days on basic medium were treated for 7 days with 200 mM NaCl and then placed back on the basic culture without NaCl for 10 days. The results show that NaCl suppression leads to a resumption of growth with a decrease in the concentration of sodium (Na+) and chloride ions (Cl-). Hence, potassium content (K+) increases gradually in the leaves to reach the level obtained with unstressed plants. At the same time, there is a stimulation of the activities of phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase isoenzymes (NAD, NADP, NADH and NADPH-MDH) and isocitrate dehydrogenase (ICDH) after NaCl had been removed. Along with the boosting of the activity of these enzymes involved in the process of carbon assimilation, there is a gradual decrease in soluble sugars content, suggesting a resumption of the normal activity of photosynthetic assimilation process. All these results verify our hypothesis and can be explained by the ability of the plant to dilute the effects of Na+ and Cl- during the recovering period. An important result of this study is that a transient salinity is not necessarily followed by a significant depreciation in product yield or quality.Keywords: Tobacco, NaCl, reversibility, phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase (MDH), isocitrate dehydrogenase (ICDH

Effects of abiotic stress on the germination of Pennisetum dichotomum

Seeds germination of Pennisetum dichotomum was tested for three alternating temperatures (10, 25, 35°C) at different hydric potentials (0, – 1, – 3, – 7, – 10 and – 16 bar) applied with different concentrations of sodium chloride (0-3-6-12 or 15g/l of NaCl). The highest germination parameters (germination rate, germination percentage) were obtained with no osmotic potential (0 bar) under 25°C. Germination rate decreased progressively with increasing NaCl dose, and the lower value of this parameter was reached with 15g/l of NaCl. Compared to control (0g/l of NaCl) P. dichotomum seeds, the radical length (RL) and the hypocotyl length (HL) of the NaCl-treated ones were severely decreased at 12 and 15g/l concentrations. In another way, seedling growth of P. dichotomum was shown more sensitive than germination seeds to salinity stress.Chaffei Haouari Chiraz, Hajjaji Nasraoui Afef, Gouia Houda, Haouari Ali. Effects of abiotic stress on the germination of Pennisetum dichotomum. In: Ecologia mediterranea, tome 38 n°2, 2012. pp. 17-22

Variations in α-, β-amylase and α-glycosidase activities in two genotypes of wheat under NaCl salinity stress

Two wheat differing in salt sensitivity, was examined for osmolyte contents and activities of α-amylase, β-amylase and α-glucosidase enzymes involved in seeds germination, in absence as well as in presence of  100, 150, 200 and 300 mM NaCl. The inhibitory effects of NaCl differed, depending on the species tested. In wild wheat specie (Triticum monococcum), with reduced germination percentage and lower relative water  content, the   increase in NaCl concentration resulted in the decrease in endogenous level of proline, total soluble sugars and activities of the main enzymes involved in the germination process. In contrast, cultivated  wheat specie (Triticum aestivum) seed in response to salt stress accumulated higher proline and total soluble  carbohydrate concentrations  which improved  their  water  status and the enzyme  activities  involved  in the germination  process. Differential response of the different species of wheat to salt stress is governed by the accumulation of osmolytes in seeds

Biochemical and Physiological Changes in Response to Salinity in Leaves and Roots of Two Durum Wheat (Triticum Durum Desf.) Genotypes

Salt stress is a major abiotic stress that limits agricultural productivity in many regions of the world. To understand the molecular basis of the salt stress response, two wheat (Triticum durum Desf.) cultivars, Karim and Azizi, which are of agronomic significance in Tunisia, were grown under non-saline and saline conditions (100 mM). Leaves and roots of control and salt-stressed plants were harvested after 11 days of salt treatment. Karim cultivar may behave as a typical Na+ include, which compartmentalizes Na+ within the leaf cell vacuoles where it could be used as an osmoticum to lower the osmotic potential necessary for the maintenance of the plant hydric status. While, accumulation of K+ was greater in Karim cultivar compared to Azizi, in both organs, presenting an important manifestation of salinity tolerance. Significant changes in metabolism of antioxidative system were observed, with an increase in protein tyrosine nitration, which indicates that salinity stress induces a nitro-oxidative stress

Exogenous application of salt (NaCl) inhibit antioxidative system in Cd-treated watercress (Nasturtium officinale R. Br.)

International audienceThis research simulates conditions found in metal-contaminated sites also affected by a high concentration of salt. For these reasons, several exogenous doses of NaCl were used to treat Cd-stressed Nasturtium officinale R. Br. We have chosen Nasturtium officinale R. Br which is a hyper accumulator plant of metals (based on literature). Data suggested induction of oxidative stress under Cd treatment and demonstrated watercress's capacity to upregulate its antioxidative defense. Superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (GPX) activities were stimulated by Cd. Supplementation of (100, 200, 300 mM NaCl) simultaneously with 1 MCd to six weeks aged Nasturtium officinale R. Br caused growth inhibition, reduction of photosynthetic pigment contents and a significant increase of Malonyldialdehyde (MDA) and hydrogen peroxide (H2O2) ones in leaves. Increase of NaCl dose reduced Cd tenor in Nasturtium officinale leaves. Moreover, a dramatic lost of antioxidant system efficiency was detected in these plants. Rise of salinity concentration significantly inhibited SOD, CAT, APX and GPX activities in Cd-treated Nasturtium officinale R. Br

Long-term salt stress responsive growth, carbohydrate metabolism, proline and anti-stress enzymes in Nicotiana tabaccum

We investigated the long-term responses of tobacco tissues to salt stress, with a particular interest for growth parameters, proline (Pro) accumulation, and carbohydrate metabolism. Exposure of 17-day-oldtobacco plants to 0.2 M NaCl was followed by a higher decrease in dry matter in roots than shoots with a decrease of both Chlorophyll a and b. Analysis of potassium, sodium and chloral accumulation showed dramatic effect to K+ accumulation especially in shoots, whereas Na+ and Cl- accumulation were strongly increased in shoots with NaCl treatment, but with minor effects in the roots. Salinity stress conditions induced a strong increase in sugar free content in the shoot and root and Pro and 2-oxoglutarate biosynthesis in tobacco tissues. However, salt-stress resulted in significant increase in the activity of NADPH and NADH malate dehydrogenase dependency, particularly in the roots, and this effect was reversed with NADP+ and NAD+-dependent malate dehydrogenase, but the activity of these enzymes was also maintained significantly higher in the absence of NaCl. Significant decreases in NADPH-depend isocitrate dehydrogenase was also observed after long-term salt treatment in tobacco plants. In addition, a gradual increase was observed in the in vitro aminating GDH activity, but the in vitro deaminating activity remained unchanged under salinity stress. These results confirmed thehypothesis that the salinity-generated MDH and GDH induction act as anti-stress enzymes in ammonia detoxification and production of Glu for Pro synthesis.Keywords: Tobacco, carbohydrate metabolism, salinity stres

Response of two wheat genotype to long-term salinity stress in relation to oxidative stress and osmolyte concentration

Effect of long-term salinity stress was studied in wheat, Karim (tolerant) and Om Rabiaa (moderately tolerant) under control and two levels of salinity (100 and 200 mM NaCl). Salinity stress decreased relative water content (RWC), chlorophyll (CHL), carotenoids (CAR), membrane stability index (MSI), and increased hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS), proline, glycine-betaine (GB), soluble sugars, superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) activity in both the genotypes and at all the stages. Salinity induced decrease in RWC, CHL, CAR, MSI, were significantly higher in Om Rabiaa than more tolerant Karim. Karim recorded higher activity of SOD, CAT, GR, as well as contents of proline, soluble sugar, GB and K, and comparatively lower H2O2 and TBARS contents compared with Om Rabiaa. Om Rabiaa also showed higher Na and Na/K ratio. Results show that salinity tolerance of Karim as manifested by lower decrease in biomass is associated with higher antioxidant activity, osmolyte concentration and potassium contents, and lower H2O2, TBARS and sodium contents than Om Rabiaa