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Articles by Mahmoud Mhamdi
Total Records ( 4 ) for Mahmoud Mhamdi
  Faycal Boughalleb , Mahmoud Mhamdi and Hichem Hajlaoui
  Experiments were conducted with lemon (Citrus limon v. Eureka) and orange trees (Citrus sinensis cv. Maltese) to determine the optimum NPK fertilizer rates for young citrus trees in greenhouse and field conditions. Greenhouse nursery trees received 0-0-0, 0-25-50, 25-25-50, 50-25-50 or 100-25-50 mg L-1 of N-P2O5-K2O via drip irrigation. The results showed that increased N rates improved leaf number, shoot length, total leaf area and stem diameter. The optimum tree growth was occurred with 50 and 100 mg N L-1. Results also showed that the percentages of N in the leaves were increased in proportion to the amount of N added while the percentage of P and K were decreased. However, the concentrations of Ca, Mg, Fe, Mn and Zn were unaffected by N rates but the leaf Cu concentration increased significantly. Leaf Mg concentration was increased by the presence of K in the nutrition solution. Form this study, we recommended the use of 100 N-25 P2O5-50 K2O mg L-1 for the good growth of nursery citrus plants in the absence of any possibility of deficiency or excessive accumulation of mineral elements. In the second experiment, two fertilizers mix 180-90-180 and 360-90-180 of N-P2O5-K2O kg ha-1 were applied to young citrus tree in field condition. Increased the level of N had no effect on leaf number and stem diameter in Eureka lemon however shoot length and total leaf area were slightly increased and these increment in growth was higher in Maltese orange.
  Faycal Boughalleb , Hichem Hajlaoui , Mahmoud Mhamdi and Mounir Denden
  The possible involvement organic metabolites and the antioxidative defence system in salt tolerance were investigated in Medicago arborea (L.). Plants were subjected to three salt treatments, 100, 200 and 300 mM NaCl for 60 days under glasshouse conditions. The plant growth, leaf water content, solutes content, H2O2 generation, lipid peroxidation, membranes stability index, phenols accumulation and antioxidative enzymes activities were quantified in the roots and shoots. Increasing concentrations of salinity induced decrease in plant growth in both organs parts, especially in the shoots. In addition both shoots and roots were able to accumulate a large quantity of Na+ whereas the contents of K+ decreased significantly. Total soluble sugars and proline content were increased by salinity but do not seem to play an important role in osmoregulation. Indeed, leaf water content was reduced to 78.9% of the control at 300 mM NaCl, explaining the lower aptitude of M. arborea to adjust osmotically. After stress, the accumulation of phenols and the activities of the antioxidative enzymes were changed and the extent of alteration varied between the shoots and roots. Salt stress impacts in term of H2O2 generation and lipid peroxidation were more pronounced in the shoots than the roots. The relative antioxidative defence capacity in the leaves of M. arborea may be manly attained by the increasing activities of Superoxide Dismutase (SOD) and Catalase (CAT) at lower salt stress whereas at higher salinity the antioxidative defence might be achieved essentially by Peroxidase (POD), Ascorbate Peroxidase (APX) and several metabolites such as phenols and proline. In the roots, the scavenging system might be achieved by SOD, POD and APX activities which showed to participate efficiently in restriction of oxidative damages caused by the H2O2 generation.
  Faycal Boughalleb and Mahmoud Mhamdi
  The possible involvement organic metabolites and the antioxidative defence system in water drought tolerance were investigated in three olive cultivars. About 2 years old olive trees, grown in pots in greenhouse were subjected to increasing Water Deficit (WD) regime (5, 10, 20 and 40 days). After 40 days without irrigation, the biomass production, osmotic potential (Ψs) and turgor Potential (P) were decreased in the three olive cultivars and the lower reduction was observed in Zalmati. Under WD conditions, Chemlali and Zalmati showed a greater accumulation of proline associated with the better maintenance of plant water status and biomass production. Different cultivars developed certain antioxidative defense mechanisms including the accumulation of phenolic compounds and increased antioxidative enzymes activities. However, differences were observed between the three cultivars for these enzymatic and non-enzymatic antioxidants. Zalmati leaves accumulated the larger quantities of phenolic compounds followed by Chemlali which can improve their antioxidant responses. Superoxide Dismutase (SOD) activity was more enhanced in Zalmati than in Chemlali under water stress but was decreased in Chetoui. Catalase (CAT) activity was more enhanced in Chetoui under water stress. The activity of Peroxidase (POD) and Ascorbate Peroxidase (APX) increased under water stress and the higher levels were reached in Zalmati followed by Chemlali. In contrast, Polyphenol Oxidases (PPO) activity decreased under WD conditions in Chemlali and Zalmati, however this reduction was slightly in Chetoui. The lower increase in malondialdehyde content and H2O2 generation suggest that Zalmati was more able to maintain leaf cell integrity than Chemlali, especially Chetoui under severe water stress because of the more efficient osmoprotection and antioxidant defense systems. Thus, the great accumulation of phenolic compounds, the increased activity of SOD and the higher POD, especially APX activity might be linked to the better performance of the antioxidant defense in Zalmati olive cultivar under severe water deficit.
  Faycal Boughalleb , Mahmoud Mhamdi , Hichem Hajlaoui and Mounir Denden
  The effect of NaCl stress on the growth, organic compounds content and antioxidant enzymes activities were investigated in two xero-halophytes Nitraria retusa and Atriplex halimus. Plants were grown in 0-800 mM NaCl for 120 days under glasshouse conditions. Both xero-halophytic species showed positive plant growth for low levels of salinity. Increasing concentrations of salinity from 400-800 mM, NaCl induced decrease in plant growth in the two species, especially in A. halimus. In addition, both species were able to accumulate a large quantity of Na+ and to maintain a higher leaf water content which was probably associated with a greater capacity for osmotic adjustment whereas the contents of K+ decreased significantly, resulting in an increase in the Na+/K+ ratio when NaCl concentrations increased. Organic osmotica was highly involved in osmotic adjustment in A. halimus leaves, especially glycinebetaine. In N. retusa leaves, glycinebetaine, soluble sugar and proline were increased by salinity. The relatively better salt tolerance of N. retusa compared to A. halimus plants may be related to the lower Malondialdehyde (MDA) content and hydrogen peroxide (H2O2) concentration and the increased activity of Catalase (CAT) and Peroxydase (POD) which participate to protect cells from ROS damage. In A. halimus, the higher antioxidant enzyme activities (Superoxide Dismutase, SOD; Catalase, CAT; Peroxydase, POD) play a major role in the restriction of oxidative damages caused by salt stress.
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