Effect of phosphorus deficiency induced in calcareous soil on plant growth, phosphorus use efficiency and acid phosphatase activity of Medicago truncatula.

Calcareous soils, characterized by a higher pH, are frequent in the North West of Tunisia. Large concentrations of calcium carbonate in calcareous soils result in accumulation of high levels of bicarbonate ions, which complex with phosphate, resulting in phosphorus deficiency (induced P deficiency) for plants. The impact of calcareous soil on plant growth, photosynthetic activity and acid phosphatase activity was explored in two lines of Medicago truncatula: TN6.18 and Jemalong. Calcareous soil significantly restricted shoot growth only in Jemalong (-45 % of the control). When grown on calcareous soil, root length was stimulated, this effect being more pronounced in TN6.18. Under calcareous soil, net CO2 assimilation declined more in Jemalong (-40 % of the control) than in TN6.18 (-20 % of the control). CO2 accumulation was increased in Jemalong (+35% of the control) plants grown in calcareous soil. The acid phosphatase activity was higher in plants cultivated under calcareous soil. This increased phosphatase activity was more pronounced in TN6.18, which showed higher accumulation of Pi in shoots and roots than Jemalolng.  In the light of these results, the present study proposes acid phosphatase as a useful candidate for improving Pi acquisition and utilization under calcareous soil

Effect of intercropping alfalfa on physiological and biochemical parameters of young grapevine plants cultivated on agricultural and contaminated soils

Our research aimed to reveal the capacity of intercropping with Medicago sativa-rhizobia in the amelioration of grapevine growth in agricultural and a Cd/Pb contaminated soils. A local variety of grapevine was cultivated in monocropping and in intercropping with Medicago sativa inoculated or not with its associated rhizobia. Intercropping with alfalfa induced a significant increase in shoot and root biomass of grapevine in the agricultural soil. However, in the contaminated soil, a slight increase in root biomass was observed. Concerning photosynthesis apparatus, we showed that the presence of Cd and Pb in the soil induced a significant decrease in both CO2 assimilation rate and stomatal conductance. Interestingly, intercropping with alfalfa only and with rhizobia alleviate this effect. Similar results are obtained for chlorophyll and carotenoid content. This was associated with a significant decrease in the malondialdehyde level in leaves and roots of grapevine cultivated in intercropping with alfalfa with and without inoculation in the two soils as compared the monoculture treatment. Comparison between treatments revealed also that intercropping with alfalfa induced a decrease in the activities of some enzymes implicated in the defence to the oxidative stress such as catalase and superoxide dismutase. Regarding soluble protein content, it is needed to signal the improvement of this parameter with the intercropping system in the contaminated soil when compared to the monocropping treatment. This work highlights the importance of the use of legumes in intercropping with grapevine as intercrop plant non-competitive for soil nutrient and proving N supply for associated plants.         &nbsp

Effect of increasing zinc levels on Trigonella foenum-graecum growth and photosynthesis activity

Zinc is an indispensable element for the plant growth and the cellular metabolism. However, this mineral element becomes harmful athigh quantities. The effects of high zinc supply on different physiological parameters were investigated in fenugreek. Seedlings were grown in plastic pots filled with inert sand under five ZnSO4 treatments (C: control :1.5 μM Zn; 1mM, 2 mM, 3 mM and 4 mM ZnSO4). Results showed a decrease of 56% to 75% in shoot dry weight and a decrease of 65% to 90% in roots dry weight, relatively to the control. In addition we showed a significant reduction in photosynthetic parameters, with the highest value of CO2 assimilation under 1 mM Zn (3.3 μmol CO2, m-2·s-1) and a lower value under 4 mM Zn (0.5 μmol CO2, m-2·s-1). The concentration of zinc in plant shoot was around two folds the control under 1, 2 and 3 mM Zn and about four folds under the maximal concentration, 4 mM Zn. In roots, we showed a progressive increase of zinc content. Increasing zinc concentration induced a significant decrease of phosphorus concentration in shoot. Fenugreek was mainly affected by zinc excess greater than 1 mM ZnSO4, however at the highest concentration, fenugreek plants exhibited different adaptation strategies

Monopotassium phosphate (KH2PO4) and salicylic acid (SA) as seed priming in Vicia faba L. and Vicia sativa L.

The first experiment was conducted to evaluate the impact of seed priming on germination behavior and seedling establishment in Vicia faba and Vicia sativa, for that, seeds priming was done using SA (100 µM) and KH2PO4. In order to determine the optimal concentration of KH2PO4 for improving germination, different concentrations were used: 25 µM, 50 µM, and 100 µM. The best germination behavior and seedling establishment were obtained with 25 and 50 µM KH2PO4, respectively for Vicia faba and Vicia sativa. Moreover, data showed that 100 µM of SA improved seed germination as well as the seedling establishment for both species. The second experiment was carried out to investigate the influence of seed priming for improving phosphorous (P) deficiency tolerance. To do, seedling obtained from primed and nonprimed seeds were grown in a hydroponic culture system with three different treatments: control (C, medium containing sufficient P concentration: 360 µM KH2PO4), direct phosphorus-deficient (DD, medium containing only 10 µM KH2PO4), and induced P deficiency by bicarbonate (ID, medium containing sufficient P concentration: 360 µM KH2PO4 + 0.5 g L-1 CaCO3 + 10 mM NaHCO3). Furthermore, the role of exogenous SA applied to P deficiency tolerance enhancement was explored. Seed priming or the exogenous application of SA significantly reduced the severity effect of P deficiency. In fact, the pretreated plants were observed more tolerant to P deficiency as reflected from the significant increase in plant biomass, P uptake, and an efficient antioxidant system. Overall, this paper highlights the beneficial effect of seeds priming or the exogenous application of SA in the improvement of plant tolerance to phosphorus deficiency

Genotype-specific Patterns of Physiological, Photosynthetic, and Biochemical Responses in Faba Bean Contrasting Pair to Salinity

To understand the salinity tolerance mechanism in faba bean contrasting pair to salinity (cv. Chourouk as sensitive and cv. Najeh as tolerant), we evaluated the effect of high salt concentration (150 mM NaCl) on the photosynthetic, physiological, and biochemical parameters at short and long term of treatment (1 and 6 days, respectively) in the seedling stage. In general, the salinity affects the growth of plants. High salinity decreased all studied parameters, especially transpiration rate (E), stomatol conductance (gs), net CO2 assimilation (A), and substomatal CO2 concentration (Ci), and dramatic changes was registered in cv. Chourouk compared to cv. Najeh. Chlorophyll contents were also affected by salinity, especially in the sensitive variety. In addition, the synthesis of osmolytes (proline) was determinate, to understand whether the osmotic adjustment is a mechanism used by cv. Najeh to tolerate salt stress. Our research suggests that cv. Najeh should be introduced in a crossbreeding program as an elite salt-tolerant germplasm

Behaviours of Medicago truncatula-Sinorhizobium meliloti symbioses under osmotic stress in relation with the symbiotic partner input: Effects on nodule functioning and protection

Three genotypes of the model legume Medicago truncatula were assessed for symbiotic effectiveness in cross inoculation with two strains of Sinorhizobium meliloti under mannitol-mediated osmotic stress. Symbioses showed different tolerance levels revealed on plant growth, nitrogen-fixing capacity and indices of nodule functioning and protection. The variability of stress response was essentially correlated with performance at non-stressful conditions. Symbiosis attitude depended on bacterial partner, host-plant genotype and their interaction. Plant genotype manifested the highest contribution to symbiotic efficiency indices under osmotic stress, even for nodulation and nitrogen fixation where the bacterial strain effect is highly pronounced. Contrasting (tolerant/sensitive) associations were identified for tolerance behaviours, involving the same plant genotype with different rhizobial strains and vice versa. In nodules, osmotic stress leads to accumulation of oxidized lipids and decrease in total protein and leghaemoglobin contents. Antioxidant responses were manifested as induction of guaiacol peroxidase (POX, E.C. 1.11.1.7) and superoxide dismutase (E.C. 1.15.1.1). POX induction was higher in tolerant symbioses and both enzymes were suggested as contributors to the protection of nodule integrity and functioning under osmotic stress. In conclusion, symbiotic efficiency in M. truncatula-S. meliloti combinations under osmotic stress is determined by each symbiont's input as well as the plant-microbe genotype interaction, and POX induction could prove a sensitive marker of tolerant symbiose

Effect of phosphorus deficiency induced in calcareous soil on plant growth, phosphorus use efficiency and acid phosphatase activity of Medicago truncatula.

Calcareous soils, characterized by a higher pH, are frequent in the North West of Tunisia. Large concentrations of calcium carbonate in calcareous soils result in accumulation of high levels of bicarbonate ions, which complex with phosphate, resulting in phosphorus deficiency (induced P deficiency) for plants. The impact of calcareous soil on plant growth, photosynthetic activity and acid phosphatase activity was explored in two lines of Medicago truncatula: TN6.18 and Jemalong. Calcareous soil significantly restricted shoot growth only in Jemalong (-45 % of the control). When grown on calcareous soil, root length was stimulated, this effect being more pronounced in TN6.18. Under calcareous soil, net CO2 assimilation declined more in Jemalong (-40 % of the control) than in TN6.18 (-20 % of the control). CO2 accumulation was increased in Jemalong (+35% of the control) plants grown in calcareous soil. The acid phosphatase activity was higher in plants cultivated under calcareous soil. This increased phosphatase activity was more pronounced in TN6.18, which showed higher accumulation of Pi in shoots and roots than Jemalolng.  In the light of these results, the present study proposes acid phosphatase as a useful candidate for improving Pi acquisition and utilization under calcareous soil

Inoculation with Efficient Nitrogen Fixing and Indoleacetic Acid Producing Bacterial Microsymbiont Enhance Tolerance of the Model Legume Medicago truncatula to Iron Deficiency

The aim of this study was to assess the effect of symbiotic bacteria inoculation on the response of Medicago truncatula genotypes to iron deficiency. The present work was conducted on three Medicago truncatula genotypes: A17, TN8.20, and TN1.11. Three treatments were performed: control (C), direct Fe deficiency (DD), and induced Fe deficiency by bicarbonate (ID). Plants were nitrogen-fertilized (T) or inoculated with two bacterial strains: Sinorhizobium meliloti TII7 and Sinorhizobium medicae SII4. Biometric, physiological, and biochemical parameters were analyzed. Iron deficiency had a significant lowering effect on plant biomass and chlorophyll content in all Medicago truncatula genotypes. TN1.11 showed the highest lipid peroxidation and leakage of electrolyte under iron deficiency conditions, which suggest that TN1.11 was more affected than A17 and TN8.20 by Fe starvation. Iron deficiency affected symbiotic performance indices of all Medicago truncatula genotypes inoculated with both Sinorhizobium strains, mainly nodules number and biomass as well as nitrogen-fixing capacity. Nevertheless, inoculation with Sinorhizobium strains mitigates the negative effect of Fe deficiency on plant growth and oxidative stress compared to nitrogen-fertilized plants. The highest auxin producing strain, TII7, preserves relatively high growth and root biomass and length when inoculated to TN8.20 and A17. On the other hand, both TII7 and SII4 strains improve the performance of sensitive genotype TN1.11 through reduction of the negative effect of iron deficiency on chlorophyll and plant Fe content. The bacterial inoculation improved Fe-deficient plant response to oxidative stress via the induction of the activities of antioxidant enzymes

Comparative study of local and introduced chard (Perpetual spinach) varieties grown under salt stress. Mehdaoui, M., Mhamdi, R., Mhadhbi, H., Gouia, H., and Debouba, M. (Tunisia)

Unfortunately, many traditional crop germplasms are being abandoned by local farmers and newly introduced varieties are used instead, without any rigorous ecophysiological study regarding their adaptive potential to local environment. In Tunisian arid regions, where salt water is often used for irrigation, a commercial chard (Perpetual spinach) variety Sais has been introduced and is currently replacing an inherited one Arbi of Medenine. In the present work, we aimed to assess the differential response of these two chard varieties (Arbi, Medenine and Sais, Italy) to two salt treatments (7 and 14 g NaCl/l). In both Arbi and Sais shoots, salinity increase led to an endogenous accumulation of sodium and proline associated with a decrease in potassium levels. The lipid peroxidation products (Malondialdehyde, MDA) accumulation in Arbi was considerably greater than in Sais, indicating a higher degree of lipid peroxidation at 14 g/l salt treatment. Salinity stimulated the superoxide dismutase (SOD, E.C. 1.15.1.1), catalase (CAT, EC 1.11.1.6) and guaïacol peroxidase (GPX, EC 1.11.1.7) activities in Arbi shoot, even under severe salt stress (14 g/l). In contrast, these antioxidant enzymes were inhibited by NaCl in Sais shoots. It could be concluded that introduced chard (Sais) exhibited better growth and displayed similar metabolite levels relative to local one (Arbi), but the local chard seems to have stronger antioxidant system that may insure better adaption to water salinity