Papers by Haythem Mhadhbi
Agronomy
The present study was carried out in order to investigate the behaviour of six faba bean (Vicia f... more The present study was carried out in order to investigate the behaviour of six faba bean (Vicia faba Minor) genotypes (Saber 02, Locale, Baachar, Badii, Chourouk and Najeh) in response to salinity and flooding (hypoxia), either alone or combined, to identify tolerant genotypes and to select efficient faba bean-rhizobia symbiosis under salinity and/or hypoxia conditions. faba bean genotypes were cultivated in three agricultural soils with either low (160 µs/cm) or moderate (1850 µs/cm) salt content and submitted or not to a 30-day long flooding period. Growth parameters and photosynthetic performance were analyzed at the end of the flowering period. At harvest time, the Najeh genotype showed the highest dry mass production in both control and hypoxia conditions (7.90 and 6.75 g/plant, respectively), whereas Saber 02 showed the lowest (3.75 and 2.25 g/plant, respectively). Differences between genotypes were less marked in salinity or combined salinity/flooding conditions. Principal co...
Euro-Mediterranean Journal for Environmental Integration
Crop and Pasture Science
Iron (Fe) deficiency leads to an overproduction of reactive oxygen species (ROS) in plants that a... more Iron (Fe) deficiency leads to an overproduction of reactive oxygen species (ROS) in plants that activate their antioxidant systems to control oxidative burst. In this study, contrasting Medicago truncatula genotypes, A17 and TN8.20 (tolerant) and TN1.11 (sensitive), were grown under Fe deficiency. The superoxide dismutase (SOD: EC1.15.1.1) activity, their isoforms’ coding genes, the copper chaperone expression patterns, and leaf phenolic contents were analysed. Our results showed that Fe deficiency decreases the photosynthetic capacity and plant biomass production with a prominent effect on TN1.11 genotype. The tolerance of A17 and TN8.20 was correlated with a maintenance of Fe content and the photosynthetic apparatus and an increase of Cu concentration compared with the sensitive genotype. We revealed a significant increase of H2O2 in Fe-deficient plants, mainly in TN1.11 sensitive genotype. TN8.20 and A17 tolerance were concomitant with a significant increase of SOD activities (SO...
Notulae Botanicae Horti Agrobotanici Cluj-napoca, 2021
Our research aimed to reveal the capacity of intercropping with Medicago sativa-rhizobia in the a... more 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 interc...
Bacterial and arbuscular mycorrhizal symbiosis are both beneficial for bacteria or fungus and hos... more Bacterial and arbuscular mycorrhizal symbiosis are both beneficial for bacteria or fungus and host plants. The bacterial symbiosis enhances plant growth and productivity and it is beneficial for sustainable agriculture. In fact, rhizobia are soil bacteria that form symbiosis with legumes and help in fixing atmospheric nitrogen by converting into ammonia inside the root nodules. Legumes-rhizobia interaction is specificity controlled by various genetic and molecular mechanisms. Here we review the different components and molecules implicated in this interaction. Moreover, we detailed the genes coding for Nod factor secreted by bacteria and their receptors present on the cell membrane of plant host. The perception of Nod factors by their receptors leads to activate various signaling pathways that involve different transcription factors depending on the symbiotic stage. Nodule inception NIN proteins are crucial for nodulation organogenesis through the activation of target proteins. Fina...
The Plant Pathology Journal, 2021
Fusarium and Rhizoctonia genera are important pathogens of many field crops worldwide. They are c... more Fusarium and Rhizoctonia genera are important pathogens of many field crops worldwide. They are constantly evolving and expanding their host range. Selecting resistant cultivars is an effective strategy to break their infection cycles. To this end, we screened a collection of Medicago truncatula accessions against Fusarium oxysporum, Fusarium solani, and Rhizoctonia solani strains isolated from different plant species. Despite the small collection, a biodiversity in the disease response of M. truncatula accessions ranging from resistant phenotypes to highly susceptible ones was observed. A17 showed relative resistance to all fungal strains with the lowest disease incidence and ratings while TN1.11 was among the susceptible accessions. As an initiation of the characterization of resistance mechanisms, the antioxidant enzymes’ activities, at the early stages of infections, were compared between these contrasting accessions. Our results showed an increment of the antioxidant activities...
Environmental Science and Pollution Research, 2021
Among abiotic stress, the toxicity of metals impacts negatively on plants’ growth and productivit... more Among abiotic stress, the toxicity of metals impacts negatively on plants’ growth and productivity. This toxicity promotes various perturbations in plants at different levels. To withstand stress, plants involve efficient mechanisms through the implication of various signaling pathways. These pathways enhance the expression of many target genes among them gene coding for metal transporters. Various metal transporters which are localized at the plasma membrane and/or at the tonoplast are crucial in metal stress response. Furthermore, metal detoxification is provided by metal-binding proteins like phytochelatins and metallothioneins. The understanding of the molecular basis of metal toxicities signaling pathways and tolerance mechanisms is crucial for genetic engineering to produce transgenic plants that enhance phytoremediation. This review presents an overview of the recent advances in our understanding of metal stress response. Firstly, we described the effect of metal stress on plants. Then, we highlight the mechanisms involved in metal detoxification and the importance of the regulation in the response to heavy metal stress. Finally, we mentioned the importance of genetic engineering for enhancing the phytoremediation technique. In the end, the response to heavy metal stress is complex and implicates various components. Thus, further studies are needed to better understand the mechanisms involved in response to this abiotic stress.
Applied Soil Ecology, 2021
Abstract Plant health largely depends on root-associated microorganisms that inhibit pathogens. E... more Abstract Plant health largely depends on root-associated microorganisms that inhibit pathogens. Enriching the rhizosphere microbiome with beneficial bacteria has a high potential of supporting future sustainable food production. However, the introduced microorganisms often show low activity with a low survival rate. We propose to solve this limitation by co-inoculating beneficial bacteria with protists. Free-living protists are one of the main regulators of bacterial activity in the rhizosphere and can increase the density and activity of pathogen-suppressive microbes. We therefore hypothesized that protist-bacteria interactions may serve to enhance plant protection against soil-borne pathogens. We tested whether co-inoculating beneficial bacteria with protists increases plant protection against Fusarium solani S55, a fungal pathogen causing root rot. We inoculated Vicia faba seedlings with the disease-suppressing bacteria Rahnella aquatilis B16C and Pseudomonas yamanorum B12, alone or in combination with three different bacterivorous soil protists, Rosculus terrestris S14D1, Bodomorpha sp. C10D3 and Cercomonas lenta C5D5. We grew plants in Fusarium-infested soil and recorded the effect of inoculation on disease severity and pathogen density. We demonstrated that introduced bacteria and protists synergistically impact plant health. When introduced alone, both bacteria and protists provided a partial protection against Fusarium rot. Protists further modulated the performance of the bacteria in an idiosyncratic way, with some combinations offering an almost complete Fusarium solani S55 suppression. These results suggest that protists could form the base of a new generation of biological control strategies of soil-borne diseases, either as a standalone inoculant or as an enhancer of beneficial bacteria.
Applied Soil Ecology, 2019
Abstract In this study, the effect of the phyto-pathogenic fungus Fusarium oxysporum on Medicago ... more Abstract In this study, the effect of the phyto-pathogenic fungus Fusarium oxysporum on Medicago truncatula-Sinorhizobium symbiosis performance was investigated. Fusarium oxysporum (KLR13) was inoculated on two genotypes of M. truncatula, one tolerant (Jemalong A17) and one susceptible (TN1.11), in symbiosis with Sinorhizobium meliloti (TII7), Sinorhizobium medicae (SII4) or fertilized with KNO3. Fungus infection reduced significantly biomass production and photosynthetic related parameters of non-symbiotic M. truncatula A17 and TN1.11. Reduction was less pronounced in A17, where a lower accumulation of H2O2 and lipid peroxidation (MDA) in concomitance to high activities of antioxidant enzymes, catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) was detected. In symbiosis, the fungus affected the nodule number and weight and inhibited the nitrogen fixing capacity (NFC), as well as the fructose and glucose contents. Nevertheless, inoculation with S. meliloti and S. medicae alleviated the effect of F. oxysporum on plant biomass production compared to the KNO3 fertilized plants. Moreover, the Sinorhizobium inoculation decreased H2O2 and MDA over-production caused by the fungal infection in leaves of both genotypes. This tolerance enhancing effect was more pronounced in S. medicae-TN1.11 symbiosis, where the relative maintenance of photosynthesis related parameters, growth capacity and NFC performance was concomitant to the induction of SOD and CAT activities and an increase of the sucrose content in leaves. For A17 genotype, both Sinorhizobium strains induced an increase of the proline and sucrose accumulation. In conclusion, F. oxysporum effect on M. truncatula was mitigated when plants were in symbiosis with Sinorhizobium species, mainly Sinorhizobium medicae that alleviated the oxidative stress and enhanced the accumulation of sucrose as energy source in TN1.11 genotype, which attenuates its susceptibility to F. oxysporum infection.
Industrial Crops and Products, 2019
Abstract Biofilm formation by the pathogenic strain Candida albicans (C. albicans) is a crucial v... more Abstract Biofilm formation by the pathogenic strain Candida albicans (C. albicans) is a crucial virulence factor on biotic and abiotic surfaces especially in medical devices. The present study investigated the effects of Cinnamomum verum and Thymus capitatus essential oils (EOs) and their combination with antifungal drugs on the development of biofilm and mature biofilm. The molecular mechanism of action was also investigated. Results showed that C. verum and T. capitatus EOs were broadly effective against C. albicans biofilm formation exhibiting 85.57% and 80.6% inhibition at half MIC values, respectively. Furthermore, they showed 92.79 and 94.46% eradication of C. albicans mature biofilm at 2xMIC values. Moreover, these EOs were able to reduce the production of secreted aspartic proteases by >90% at 0.75xMIC. The antibiofilm potency was improved when EOs were combined with AMB, effectively eradicating C. albicans mature biofilm on central venous catheter (CVC). Transcriptomic analyses indicated that EOs, especially when combined with AMB, down-regulate Ras-cAMP-Efg and MAPK signaling genes. In addition, EOs and their combination with AMB significantly inhibited the expression of adhesion and secreted aspartyl proteinase virulence factor genes. Our results demonstrated that C. verum and T. capitatus EOs and their combination with AMB could provide an effective treatment against C. albicans biofilm on medical devices.
Plant Species Biology, 2019
African Journal of Agricultural Research, 2019
Applied Soil Ecology, 2018
Abstract Legumes (Fabacea) plants are mainly known for their symbiotic relationship with soil nit... more Abstract Legumes (Fabacea) plants are mainly known for their symbiotic relationship with soil nitrogen-fixing bacteria (rhizobia). This symbiosis requires the formation of new root structures called nodules. Besides rhizobia, nodules host several microbial species that may serve to enhance plant growth and disease resistance. In this study, we demonstrate that several endophytic bacteria isolated from nodules harbour plant growth promotion and biocontrol traits. A collection of 120 bacterial strains isolated from Faba bean (Vicia faba) and chickpea (Cicer arietinum) nodules were screened for their ability to inhibit phytopathogenic Fusarium solani on “In vitro” antibiosis tests. Sixteen best effective isolates were selected, identified and sequences were deposited in Genbank. These strains were all isolated from Faba bean nodules. These have the characteristics to produce siderophores and auxin as well as expression of some genes coding the production of the antibiotic compounds as Pyrrolnitrin (PRN), Phenazine (PHZ)… Based on the former PGPR and biocontrol characteristics, three strains; Rahnella aquatilis B16C, Pseudomonas yamanorum B12 and Pseudomonas fluorescens B8P were analyzed for their “In vivo” biocontrol potential in suppressing F. solani root rot of three cultivars of Faba bean under greenhouse conditions. The three strains significantly reduced the pathogen symptom severity. R. aquatilis B16C showed the best protecting potentiality with the three Faba bean cultivars and it is consequently, suggested as biocontrol agent for field application. Then again, our study confirms previous suggestion of legume nodules as untapped suitable source of beneficial microorganisms that can be used to control pathogens in a sustainable way.
Physiologia Plantarum, 2010
Antioxidant responses and nodule function of Medicago truncatula genotypes differing in salt tole... more Antioxidant responses and nodule function of Medicago truncatula genotypes differing in salt tolerance were studied. Salinity effects on nodules were analysed on key nitrogen fixation proteins such as nitrogenase and leghaemoglobin as well as estimating lipid peroxidation levels, and were found more dramatic in the salt-sensitive genotype. Antioxidant enzyme assays for catalase (CAT, EC 1.11.1.6), superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11) and guaiacol peroxidase (EC 1.11.1.7) were analysed in nodules, roots and leaves treated with increasing concentrations of NaCl for 24 and 48 h. Symbiosis tolerance level, depending essentially on plant genotype, was closely correlated with differences of enzyme activities, which increased in response to salt stress in nodules (except CAT) and roots, whereas a complex pattern was observed in leaves. Gene expression responses were generally correlated with enzymatic activities in 24-h treated roots in all genotypes. This correlation was lost after 48 h of treatment for the sensitive and the reference genotypes, but it remained positively significant for the tolerant one that manifested a high induction for all tested genes after 48 h of treatment. Indeed, tolerance behaviour could be related to the induction of antioxidant genes in plant roots, leading to more efficient enzyme stimulation and protection. High induction of CAT gene was also distinct in roots of the tolerant genotype and merits further consideration. Thus, part of the salinity tolerance in M. truncatula is related to induction and sustained expression of highly regulated antioxidant mechanisms.
Plant Growth Regulation, 2012
In the present investigation we studied the role of CaCl2 pretreatment on physiological and bioch... more In the present investigation we studied the role of CaCl2 pretreatment on physiological and biochemical characteristics in faba bean (Vicia faba L.) seedlings subjected to cadmium (Cd) stress. The seeds of faba bean were treated with H2O and 2 % CaCl2 before germination for 6 h. Primed or nonprimed (control) seeds were then germinated under increasing concentrations of Cd (0, 10, 50 and 100 μM) for 21 days. The contents of Cd, soluble protein (SP), malondialdehyde (MDA), total membrane lipid contents, fatty acid composition and the activities of superoxide dismutase (SOD EC 1.15.1.1), catalase (CAT EC 1.11.1.6), guaiacol peroxidase (GPX EC 1.11.1.7), lipoxygenase (LOX) in the seedlings leaves were tested. Exposure of the plants to Cd caused a gradual decrease in the shoot and root dry weight. Seed pretreatment with CaCl2 alleviated the negative effect of Cd on plant growth parameters. The same tendency was observed for the chlorophyll content. The level of lipid peroxidation (as indicated by MDA content) was higher in Cd-treated plants, and remained unchanged in CaCl2-pretreated plants. The same results for the total lipid content, fatty acids composition and SP level were observed. Treatment of plants with Cd drastically decreased CAT activity and caused an increase in both SOD and GPX activity. However, in CaCl2-pretreated plants, CAT activity exhibited a slight decrease under Cd treatment. An increased of SOD and GPX activity in leaves of pretreated plants was also demonstrated. The data suggest that CaCl2 pretreatment may protect faba bean seedlings against Cd toxicity.
Journal of Plant Growth Regulation, 2011
Nitrogen-fixing capacity (NFC) in nodules of four Medicago truncatula lines inoculated with four ... more Nitrogen-fixing capacity (NFC) in nodules of four Medicago truncatula lines inoculated with four strains of Sinorhizobium was assessed, during the plant life cycle, in relation to parameters identified as indices of plant growth, photosynthetic capacity, nodule integrity, and functioning. Differences in duration of the NFC period were observed among symbiotic associations and were correlated with variability on plant biomass production. Senescence appearance and vigor varied in parallel with structural, physiological, and biochemical stability of nodules. Maintenance of a longer high-NFC period was correlated to a higher stimulation of antioxidant enzymes, mainly superoxide dismutase (SOD, EC 1.15.1.1) and guaiacol peroxidase (POX, EC 1.11.1.7), and a consequent longer maintenance of membrane integrity and nodule structure within the first stages of senescence. Salinity and drought stresses interfered with nodule functioning and triggered fast and global nodule senescence, albeit a superiority of nodules having a long high-NFC period. The protective role of POX activity on salt-and drought-stressed nodules was revealed. On the other hand, SOD stimulation was independent of stress application. Another strategy allowing the maintenance of longer NFC in salt-stressed nodules could be the accumulation of starch granules in the senescencefunctioning interface of nodules. This finding is currently under investigation. Interestingly, the symbioses with different behaviors of nodule senescence identified in this work would be useful bases for biochemical, genomic, and proteomic studies dissecting nodule senescence.
Journal of Plant Physiology, 2013
Alternative oxidase (AOX) is the central component of the non-phosphorylating alternative respira... more Alternative oxidase (AOX) is the central component of the non-phosphorylating alternative respiratory pathway in plants and may be important for mitochondrial function during environmental stresses. Recently it has been proposed that Aox can be used as a functional marker for breeding stress tolerant plant varieties. This requires characterization of Aox alleles in plants with different degree of tolerance in a certain stress, affecting plant phenotype in a recognizable way. In this study we examined Aox1 gene expression levels in Medicago truncatula genotypes differing in salt stress tolerance, in order to uncover any correlation between Aox expression and tolerance to salt stress. Results demonstrated a specific induction of Aox1 gene expression in roots of the tolerant genotype that presented the lowest modulation in phenotypic and biochemical stress indices such as morphologic changes, protein level, lipid peroxidation and ROS generation. Similarly, in a previous study we reported that induction of antioxidant gene expression in the tolerant genotype contributed to the support of the antioxidant cellular machinery and stress tolerance. Correlation between expression patterns of the two groups of genes was revealed mainly in 48 h treated roots. Taken together, results from both experiments suggest that M. truncatula tolerance to salt stress may in part due to an efficient control of oxidative balance thanks to (i) induction of antioxidant systems and (ii) involvement of the AOX pathway. This reinforces the conclusion that differences in antioxidant mechanisms can be essential for salt stress tolerance in M. truncatula and possibly the corresponding genes, especially Aox, could be utilized as functional marker.
Archives of Phytopathology and Plant Protection
European Journal of Plant Pathology
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Papers by Haythem Mhadhbi