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Potassium (K+) deficiency is one of the most abiotic constraints reducing plant growth and productivity. The use of silicon (Si) has been reported to alleviate abiotic stresses in plants. However, data regarding the roles played by this element in mediating K+ deficiency are still scarce. Therefore, the present work was carried out to investigate the possible involvement of Si in mitigating the negative impact of K+ deficiency on cultivated barley Hordeum vulgare L. (var. Rihane). Plants were hydroponically grown either under K+ sufficient nutrient solution containing 3 mM K+ or in K+-deficient medium containing 10 µM K+ without or with Si (1 mM). Shoot growth, shoot water content, leaf osmotic potential, shoot K+ concentration, photosynthetic activity, chlorophyll fluorescence, soluble sugar concentrations, and shoot phenolic compound contents and their antioxidant properties were determined. Results showed that shoot growth, shoot K+ concentration, and gaseous exchange were reduced by K+ deficiency. Photosynthesis decrease was mainly linked to sugar accumulation in leaves. Except for K+ concentration, a beneficial effect of Si was observed. A modulation in the accumulation of polyphenols and their antioxidant capacities has been observed. Overall, the data indicate that the beneficial effects of Si on barley plants grown under K+ deficient medium were mainly due to increased growth and photosynthetic activity but not through an improvement of shoot K+ concentration and phenolic compound accumulation and related antioxidant capacity suggesting a possible use of Si as a fertilizer to correct the deleterious effects of nutritional stress.

Silicon (Si) is a ubiquitous element and the second most abundant after oxygen in the Earth’s crust. Although silicon is not yet listed among the essential nutrients for higher plant growth, its beneficial impact on improving crop development and yield, especially under stressful environments such as iron deficiency, was well documented. Iron deficiency is a major concern for crop production mainly observed in calcareous soils all over the world. The objective of this study was to investigate the effects of silicon on sea barley (Hordeum marinum ssp. marinum) under iron deficiency. Twenty-six-day-old plants of H. marinum were exposed to three treatments, sufficient iron treatment (50 µM Fe), iron-deficient treatment (0.1 µM Fe), and iron-deficient treatment (0.1 µM Fe) combined with silicon application (0.5 mM Na2SiO3). Our results showed that iron deficiency negatively affects almost all measured parameters. However, these depressive effects were significantly mitigated under silicon treatment. Indeed, silicon addition alleviated stress effect on the morphological aspect of plants and enhanced their growth (between + 93 % and + 283 %), water status (between + 57 % and + 58 %), photosynthetic pigment concentrations (between + 129 % and + 200 %), photosynthetic gas exchange (between + 73 % and + 129 %), and both Photosystem I (PSI) and Photosystem II (PSII) functions. However, a greater beneficial effect of silicon was observed on PSI, by comparison with PSII. This was concomitant with a significant increase of iron quantities in both roots and shoots by 153 % and 236 %, respectively. Based on our findings, silicon is able to mitigate the adverse effects of iron deficiency, probably by enhancing iron remobilization. Therefore, silicon application seems to be an effective and successful solution to cope with iron deficiency.

Iron (Fe) is one of the essential nutrients for plant growth which is involved in several physiological functions. Hence, there are intensive efforts to improve plant tolerance to Fe deficiency, by genotypic screening and by the use of adapted physiological tools. The intend of the current study was to explore the seed priming effect with salicylic acid (SA 0.25 mM) and hydrogen peroxide (H2O2 20 mM), either separately applied or combined, on plant growth, nutritional elements status (Fe and potassium K), root acidification and photosynthetic activity in two S. carnosa cultivars (Sidi Khlif and Kalbia) with different tolerance to such constraint. Under unprimed conditions, Fe deficiency decreased plant growth, chlorophyll concentration, in addition to Fe and K contents. Moreover, it affected the photosynthetic activity by inhibiting the net CO2 assimilation rate and increasing the transpiration rate of both cultivars, following a reduced water use efficiency. The changes above described were much less pronounced in Sidi Khlif than in Kalbia. The stomatal conductance increased in Fe-deficient leaves of both cultivars, suggesting that the photosynthesis impairment should be attributed to non-stomatal factors. Interestingly, priming seeds with both agents significantly improved the growth performance and the rhizosphere acidification of deficient S. carnosa plants. However, the D + SA + H2O2 treatment had the most beneficial effect on S. carnosa plant growth. The degree of this stimulation may vary depending on the cultivar, the tissue and the priming agent applied. This could be owing to the photosynthetic performance modulation, leading to more efficient nutrient uptake.

Silicon (Si) plays an important role in providing beneficial effects on plant growth and yield, especially under stressful environments such as salinity. The objective of this work is to study the effects of a fertilizer based on silicon (Na2SiO3 synthesized from Tunisian silica sand) on sea barley (Hordeum marinum Huds.) under salt stress. Due to its forage potentialities, this species presents a very interesting capacity for the rehabilitation of non-productive marginal areas. Forty-two-day-old H. marinum plants were exposed to three concentrations of Na2SiO3 (0, 1, or 2 mM) in the absence or presence of salt (0 or 150 mM NaCl). The examination of the growth parameters, water status, lipid peroxidation, photosynthetic gas exchange, photosynthetic pigment contents, and chlorophyll fluorescence proved that silicon is a great interest support for the remediation of the deleterious effects of salt stress. Therefore, our fertilizer can be considered as an effective solution to cope with salt stress and promote the development of marginal lands. Taking into consideration its high efficiency and its low production cost, this product can compete with other fertilizers.

Plant growth-promoting rhizobacteria (PGPR) are considered as bio-ameliorators that confer better salt resistance to host plants while improving soil biological activity. Despite their importance, data about the likely synergisms between PGPR and halophytes in their native environments are scarce. The objective of this study was to assess the effect of PGPR (

Psammophilic halophytes are subjected in their natural habitats to the interactive effects of salinity and nutrient deficiencies. The aim of the present investigation was to check whether an optimal salt treatment enhances growth and antioxidant responses of the psammophilic obligate halophyte Sesuvium portulacastrum L. Seedlings were grown for 6 weeks on a nutrient medium (C), diluted 50 times (D), or diluted 50 times and added with 200 mM NaCl (DS). Nutrient deficiencies drastically reduced biomass production in both shoots and roots but did not induce a marked oxidative stress as shown by the ‘non-toxic’ levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA). In roots, a marked decrease in catalase (CAT) activity seems to keep a certain level of H2O2 for stress signalling purposes. The detrimental effect on growth was slightly alleviated by the optimal salt concentration in DS treatment. H2O2 and MDA concentrations were higher in DS treatment than in D treatment, but they remained at ‘nontoxic’ levels. The responses of antioxidant enzymes showed the same trend in D and DS treatments but with different magnitudes. Taken together, these results showed that the beneficial effect of salinity on the responses of this psammophilic obligate halophyte to other stresses (i) is limited by the severity of those stresses and (ii) is not mainly based on antioxidant responses.

This study aimed to rigorously investigate and integrate the underlying hypothesis that an enhancing effect of gibberellic acid (GA(3), 3 µM) with increased growth actually leads to a modification of the physiological role of polyamines during salinity stress (NaCl, 100 mM) in fennel. These analyses concern both reserve tissues (cotyledons) and embryonic axes in growth. Physiological results indicate a restriction of germination, growth, mineral nutrition and damages to membranes of salt-treated seedlings. This was partially attenuated in seedlings treated with an interaction effect of GA(3) and NaCl. Peroxidase and catalase activities showed a reduction or an augmentation according to the treatments and organs. The three main polyamines (PA): putrescine, spermidine and spermine were elevated in the salt-treated seedlings. Meanwhile, GA(3) seed priming was extremely efficient in reducing PA levels in salt-stressed seedlings compared to the control. Response of PA genes to salinity was variable. Up-regulation was noted for SPMS1, ODC1, and ADC1 in hypocotyls and cotyledons (H + C) and down-regulation for SAMDC1 in the radicle. Interaction of salt/GA(3) treatment showed different responses, only ODC1 in (H + C) and ADC1 in both radicle and (H + C) were overexpressed. Concerning other genes, no change in mRNA abundance was observed in both organs compared to the salt-treated seedlings. From these results, it could be inferred that the fennel seedlings were NaCl sensitive. This sensitivity was mitigated when GA3 applied for seed priming and applied in combination with NaCl, which resulted in a reduction of the PA content. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-022-01140-4.

Oil field wastewater (produced water) management is a crucial environmental issue due to its hydrocarbons content, heavy metal, and high salinity. In this study, soluble sodium silicate was used, under controlled conditions in laboratory, for treating generated water from a petroleum field situated in Southern Tunisia. The efficiency of soluble sodium silicate (Na2SiO3) in the removal of organic matter and heavy metal from produced wastewater was investigated, the optimization of the proposed process (Na2SiO3dose, agitation speed, and required treatment time). Soluble sodium silicate (SiO2/Na2O = 1) at a dose of 1%, low agitation (50 rpm), and a treatment duration of only 5 min achieved a high removal efficiency for simultaneous removal of chemical oxygen demand(COD) and major heavy metals. The removal yield of contaminant could reach up to 97%. Instantaneous chemical precipitation and adsorption onto calcium silicate are the main processes that yielded a high removal rate of organic matter and heavy metals. Silica and calcium silicate with absorbed contaminants were found to be the two stabilized by-products that could safely be dumped at landfill sites. Sludge by-product was carefully investigated with FTIR analysis, XRD and SEM-EDAX. The silicate-derived component along with co-precipitated calcium carbonate and sodium chloride are the main recognized salts.

Salinity and potassium deficiency are major abiotic constraints affecting plant growth, productivity, and metabolism. The present work was conducted to check whether salinity alleviates, aggravates, or does not affect the effects of potassium deficiency on Sulla carnosa, a salt-tolerant legume common in diverse saline soils. We investigated the changes in plant growth, phenolic compound composition, and antioxidant activity in stems and roots of this species grown hydroponically under different conditions: C, control (complete nutrient solution containing 6 mM K+ and not added with NaCl); KD, K+ deficiency (K+-deficient nutrient solution (60 μM K+) not added with NaCl); C + S, salt treatment (control nutrient solution containing 6 mM K+ and added with 100 mM NaCl); and KD + S, combined treatment between salinity and K+ deficiency (K+-deficient nutrient solution (60 μM K+) added with 100 mM NaCl). Results showed that all treatments applied led to a significant decrease of root and stem growth, with a more marked reduction in plants exposed to the combined stresses, suggesting synergistic effects of salinity and K+ deficiency. In addition, results indicated that both stresses either applied alone or in combination quantitatively or qualitatively modulated phenolic compound accumulation and their antioxidant activities. But a predominance of K+ deficiency effect was noticed, which may be considered as a suitable manipulation for the production of antioxidants compared to the other treatments.

In the present study, the effects of elevated zinc concentrations on germination, physiological and biochemical parameters were investigated in basil (Ocimum basilicum L.). Results indicate that zinc excess (1–5 mM ZnSO4) did not affect germination process, but it drastically reduced vigor index and radicle elongation, and induced oxidative stress. Exposure of basil plants to 400 and 800 µM Zn decreased aerial parts and roots dry biomass, root length and leaf number. Under these conditions, the reduction of plant growth was associated with the formation of branched and abnormally shaped brown roots. Translocation factor 1 was observed for 100 µM Zn suggested the possible use of basil as a phytostabiliser. Excess of Zn supply (> 100 µM) decreased chlorophyll content, total phenol and total flavonoid contents. Additionally, an increased TBARS levels reflecting an oxidative burst was observed in Zn-treated plants. These findings suggest that excess Zn adversely affects plant growth, photosynthetic pigments, phenolic and flavonoid contents, and enhances oxidative stress in basil plants.

Iron (Fe) is one of the essential nutrients for plant growth which is involved in several physiological functions. Hence, there are intensive efforts to improve plant tolerance to Fe deficiency, by genotypic screening and by the use of adapted physiological tools. The intend of the current study was to explore the seed priming effect with salicylic acid (SA 0.25 mM) and hydrogen peroxide (H

Three-year-old seedlings of two Tunisian provenances of cork oak (Quercus suber L.) differing in climatic conditions at their geographical origin were subjected to increasing light intensities. Gaâfour was the provenance from the driest site and Feija from the wettest site. Low-light adapted seedlings from both provenances were exposed to two light treatments: full sunlight (HL) and low light (LL, 15% sunlight) for 40 days. The CO2-response curve of leaf net photosynthesis (An-Ci curve) established under saturated photon flux density was used to compare photosynthetic parameters between leaves subjected to continuous low light (LL leaves) and leaves transferred from low to high light (HL leaves). Transfer from low to high light significantly increased net photosynthesis (An) and dark respiration (Rd) in Gaâfour provenance but not in Feija. After transfer to high irradiance, specific leaf area (SLA) did not change in either provenance. This suggested that the increase in photosynthetic capacity on a leaf area basis in HL leaves of Gaâfour provenance was not due to increased leaf thickness. Only the seedlings from the Gaâfour provenance were able to acclimate to high light by increasing Vcmax and Jmax.

In order to understand the molecular basis of vacuolar H+-ATPase subunits and reveal their possible role in salt and drought tolerance in plant species, a vacuolar H+-ATPase subunit E1 gene (LmVHA-E1) was isolated from the halophyte Lobularia maritima and over-expressed in the glycophyte Arabidopsis thaliana. Q-RT-PCR demonstrated that the expression of this gene was induced in L. maritima in response to salt stress and PEG-induced osmotic stress. The overexpression of LmVHA-E1 in Arabidopsis thaliana conferred high salt and drought tolerance to transgenic plants. Transgenic Arabidopsis plants showed higher seedling survival rates and better antioxidant activities under salt and drought stress. The analysis of ion content and osmotic potentials indicated that under high salinity the transgenic plants compartmentalized more Na+ and showed enhanced osmotic adjustment in the leaves compared with wild-type plants. Accordingly, the higher levels of expression of different stress related genes such as AtNHX1 AtP5CS, AtCAT, AtSOD, AtPOD and AtLEA, indicated higher levels of activities in sodium sequestration into vacuoles, in osmotic regulation and in ROS scavenging of transgenic plants.

Control of K+ and Na+ transport plays a central role in plant adaptation to salinity. In the halophyte Hordeum maritimum, we have characterized a transporter gene, named HmHKT2;1, whose homolog HvHKT2;1 in cultivated barley, Hordeum vulgare, was known to give rise to increased salt tolerance when overexpressed. The encoded protein is strictly identical in two H. maritimum ecotypes, from two biotopes (Tunisian sebkhas) affected by different levels of salinity. These two ecotypes were found to display distinctive responses to salt stress in terms of biomass production, Na+ contents, K+ contents and K+ absorption efficiency. Electrophysiological analysis of HmHKT2;1 in Xenopus oocytes revealed distinctive properties when compared with HvHKT2;1 and other transporters from the same group, especially a much higher affinity for both Na+ and K+, and an Na+–K+ symporter behavior in a very broad range of Na+ and K+ concentrations, due to reduced K+ blockage of the transport pathway. Domain swapping experiments identified the region including the fifth transmembrane segment and the adjacent extracellular loop as playing a major role in the determination of the affinity for Na+ and the level of K+ blockage in these HKT2;1 transporters. The analysis (quantitative reverse transcription-PCR; qRT-PCR) of HmHKT2;1 expression in the two ecotypes submitted to saline conditions revealed that the levels of HmHKT2;1 transcripts were maintained constant in the most salt-tolerant ecotype whereas they decreased in the less tolerant one. Both the unique functional properties of HmHKT2;1 and the regulation of the expression of the encoding gene could contribute to H. maritimum adaptation to salinity.

This work characterized mechanisms controlling cadmium (Cd) tolerance and accumulation in lettuce at both the physiological and genetic levels. These traits were evaluated in 18 Lactuca accessions representing a large genetic diversity. Cd tolerance and accumulation in roots and shoots as well as Cd translocation from roots to the shoot varied independently, and with a significant range of variation. Analyses of F1 progenies of crosses between cultivars with contrasted phenotypes showed that high tolerance to Cd, low Cd accumulation and low Cd root-shoot translocation were recessive traits. Results of analyses of F2 progenies of different crosses suggest that root Cd concentration and root-shoot Cd translocation were under a complex genetic determinism involving at least two loci. This work thus revealed that limiting both Cd accumulation and Cd root-shoot translocation in lettuce is possible and depends on recessive loci. Differences in the ability to accumulate Cd in roots in the long term could not be linked to differences in short-term 109Cd uptake into, or efflux from, roots. In contrast, the cultivar with the highest root-shoot Cd translocation was the same in the long term and in the short term, which suggests that this trait relies on processes that are implemented quickly (i.e. in less than three days) after the start of Cd exposure.

Trehalose (Tre) and salicylic acid (SA) are increasingly used to mitigate drought stress in crop plants. In this study, a pot experiment was performed to study the influence of Tre and SA applied individually or in combination on the growth, photosynthesis, and antioxidant responses of sweet basil (Ocimum basilicum L.) exposed to drought stress. Basil plants were watered to 60% or 100% field capacity with or without treatment with 30 mM Tre and/or 1 mM SA. Drought negatively affected growth, physiological parameters, and antioxidant responses. Application of Tre and/or SA resulted in growth recovery, increased photosynthesis, and reduced oxidative stress. Application of Tre mitigated the detrimental effects of drought more than SA. Furthermore, co-application of Tre and SA largely eliminated the negative impact of drought by reducing oxidative stress through increased activities of antioxidant enzymes superoxide dismutase, peroxidase, and catalase, as well as the accumulation of the protective osmolytes proline and glycine betaine. Combined Tre and SA application improved water use efficiency and reduced the amount of malondialdehyde in drought-stressed plants. Our results suggested that combined application of Tre and SA may trigger defense mechanisms of sweet basil to better mitigate oxidative stress induced by drought stress, thereby improving plant growth.

The response of halophytes to salt stress was investigated by electrical impedance spectroscopy (EIS).EIS can be used to quickly compare between different growth condition and different salinity treatments.EIS is useful to study signaling and short-term responses to salinity.EIS might be applied as a suitable method for assessing salt resistance of plants without damaging effects on tissues. In order to evaluate the reliability and the practical use of the electrical impedance spectroscopy method applied in the area of salt resistance, electrical impedance spectra were compared in the leaves of halophyte plants cultivated under different growth conditions (biotope versus controlled conditions, hydroponic versus sand system cultures) and different salt stress conditions. The kinetic of impedance parameters was also monitored under short term salinity. The spectra of electrical impedance of leaves under biotope and laboratory conditions showed difference in the electrical response of Cakile maritima in the biotope and laboratory conditions. The response of electrical impedance parameters to salinity was also different in the hydroponic system when compared to the soil one, indicating more stressful conditions in solution culture. The amplitude of the curves of impedance spectrometry decreased when plants were stressed comparatively to their controls, with the highest electrical resistance in the presence of 50 and 100mM while the lowest value was at 400mM NaCl. The electrical resistance increased at an early stage after the application of salt stress reaching maximal value 180min later, before it rapidly declined thereafter. The observed peak can translate a signal, that the plant could have received, which triggers a cascade of metabolic reactions allowing the plant to regain its hydro-ionic balance. In conclusion, electrical impedance spectroscopy can be used to quickly compare different growth conditions as well as different salinity treatments. This method can also separate between the osmotic and the ionic phases of the response to salt stress.

Our study aims to assess the implication of WRKY transcription factor in the molecular mechanisms of grapevine adaptation to salt and water stresses. In this respect, a full-length VvWRKY2 cDNA, isolated from a Vitis vinifera grape berry cDNA library, was constitutively over-expressed in Nicotiana tabacum seedlings. Our results showed that transgenic tobacco plants exhibited higher seed germination rates and better growth, under both salt and osmotic stress treatments, when compared to wild type plants. Furthermore, our analyses demonstrated that, under stress conditions, transgenic plants accumulated more osmolytes, such as soluble sugars and free proline, while no changes were observed regarding electrolyte leakage, H2O2, and malondialdehyde contents. The improvement of osmotic adjustment may be an important mechanism underlying the role of VvWRKY2 in promoting tolerance and adaptation to abiotic stresses. Principal component analysis of our results highlighted a clear partition of plant response to stress. On the other hand, we observed a significant adaptation behaviour response for transgenic lines under stress. Taken together, all our findings suggest that over-expression of VvWRKY2 gene has a compelling role in abiotic stress tolerance and, therefore, would provide a useful strategy to promote abiotic stress tolerance in grape via molecular-assisted breeding and/or new biotechnology tools.

In saline biotopes, different mechanisms may contribute to the tolerance of halophytes to high soil salinity and temperature, drought and other abiotic stresses, but their relative responses and their ecological plasticity for a given species remain unknown. In this study, we examined the responses of the salt marsh halophyte Limonium delicatulum to changing environmental conditions of its natural habitats (Sabkha “El Kalbia”, Tunisia). The specific aim of the work was to check whether statistically significant correlations could be established between particular stress response mechanisms (ion uptake, activation of antioxidant systems) and soil parameters and climatic data associated with environmental stress. The results showed that the salinity of the soil increased during the months of June, July and August (dry period), concomitantly with a strong accumulation of salt ions in the aerial parts of the plant. Moreover, the highest antioxidant capacity of this halophyte (enzymes and antioxidant molecules) was reached during the same period of the year. The remaining periods (corresponding to the rainy season) did not show a significant difference in enzymes activities and level of antioxidants, with a minimum observed in the months of January and February. These results show a remarkable effect of salinity in the natural habitat on the activity of enzymes and antioxidant molecules. Other edaphic and climatic factors could also be involved to increase antioxidant capacity, such as nutrient deficiency, temperature and precipitation.

Salt-induced responses of Medicago ciliaris was studied under controlled conditions. Twenty-two-day old seedlings were cultivated for one month in a nutrient medium added or not with 75 mM sodium chloride (NaCl). Our results showed that this species is relatively salt-tolerant since the whole biomass production of salt-treated plants was affected a little (−30%) as compared to the control. The slight salt effect was mainly nutritional and concerned both macro potassium, calcium and magnesium (K, Ca, and Mg) and micro-nutrients iron (Fe). K and Fe uptake efficiencies were more affected than those of Ca and Mg. Nevertheless, M. ciliaris was able to counterbalance this impact by increasing both K and Fe use efficiencies. The enhancement of K use efficiency could be due in part to the plant aptitude to accumulate sodium (Na+) ions within its shoot tissues and to use them for osmotic adjustment. This “includer” behavior allowed M. ciliaris to maintain an adequate water status under saline conditions.

Magnesium deficiency in plants was described on several calcareous soils. Some authors attributed such an induced Mg deficiency to excess calcium, whereas some others attributed it to an influence of carbonate minerals on Mg bioavailability to plants. In this investigation, we attempted to determine which factor is responsible for Mg deficiency in the Fabaceae Sulla carnosa found on several types of soils, including calcareous ones. S. carnosa plants were cultivated on an agricultural soil (control soil) that was either added with 20 % CaCO3 or watered with 100 mM CaCl2. After 1 month of treatment, gas exchange measurements were performed in these plants which were harvested later for dry weight determination, pigment contents, and mineral analysis. Also, some physicochemical properties (pH, EC, and mineral analysis) of the soil were studied. Calcareous treatment showed more detrimental effect on whole plant and shoot growth, leaf area, Mg concentrations in leaves and stems, Mg uptake efficiency, carotenoid concentration, and carotenoid/chlorophyll ratio as compared to CaCl2. By contrast, calcareous treatment increased chlorophyll concentrations, Mg/Ca transport selectivity, and Mg use efficiency. Soil analysis showed that CaCO3 had no effect on soil properties (pH, EC, extractible Mg and Ca concentrations, and Ca/Mg ratio), whereas CaCl2 induced substantial increases in EC (ca. +436 %), Mg (ca. +760 %), and Ca (ca. +354 %) levels and a significant decline in Ca/Mg ratio (ca. −48 %) as compared to control soil. Ca excess was not the main factor inducing Mg deficiency in S. carnosa on calcareous soils. Indeed, Ca2+ concentration did not increase in the soil because of the low solubility of CaCO3. Soil pH and extraxtible Mg concentration were also unaffected by CaCO3 addition, and therefore, they cannot be directly related to Mg deficiency. Hence, one can speculate that bicarbonate ions affect root Mg transporters and/or Mg availability within plant tissues.

The abundance of calcareous soils makes bicarbonate-induced iron (Fe) deficiency a major problem for plant growth and crop yield. Therefore, Fe-efficient plants may constitute a solution for use on calcareous soils. We investigated the ability of the forage legume Sulla carnosa (Desf.) to maintain integrity of its photosynthetic apparatus under Fe deficiency conditions. Three treatments were applied: control, direct Fe deficiency and bicarbonate-induced Fe deficiency. At harvest, all organs of deficient plants showed severe growth inhibition, the effect being less pronounced under indirect Fe deficiency. Pigment analysis of fully expanded leaves revealed a reduction in concentrations of chlorophyll a, chlorophyll b and carotenoids under Fe deficiency. Electron transport rate, maximum and effective quantum yield of photosystem II (PSII), photochemical quenching (qP), non-photochemical quenching (qN) as well as P700 activity also decreased significantly in plants exposed to direct Fe deficiency, while qN was not affected. The effects of indirect Fe deficiency on the same parameters were less pronounced in bicarbonate-treated plants. The relative abundances of thylakoid proteins related to PSI (PsaA, Lhca1, Lhca2) and PSII (PsbA, Lhcb1) were also more affected under direct than indirect Fe deficiency. We conclude that S. carnosa can maintain the integrity of its photosynthetic apparatus under bicarbonate-induced Fe deficiency, preventing harmful effects to both photosystems under direct Fe deficiency. This suggests a high capacity of this species not only to take up Fe in the presence of bicarbonate (HCO3- ) but also to preferentially translocate absorbed Fe towards leaves and prevent its inactivation.

Our study aims to assess the implication of WRKY transcription factor in the molecular mechanisms of grapevine adaptation to salt and water stresses. In this respect, a full-length VvWRKY2 cDNA, isolated from a Vitis vinifera grape berry cDNA library, was constitutively over-expressed in Nicotiana tabacum seedlings. Our results showed that transgenic tobacco plants exhibited higher seed germination rates and better growth, under both salt and osmotic stress treatments, when compared to wild type plants. Furthermore, our analyses demonstrated that, under stress conditions, transgenic plants accumulated more osmolytes, such as soluble sugars and free proline, while no changes were observed regarding electrolyte leakage, H(2)O(2), and malondialdehyde contents. The improvement of osmotic adjustment may be an important mechanism underlying the role of VvWRKY2 in promoting tolerance and adaptation to abiotic stresses. Principal component analysis of our results highlighted a clear partition of plant response to stress. On the other hand, we observed a significant adaptation behaviour response for transgenic lines under stress. Taken together, all our findings suggest that over-expression of VvWRKY2 gene has a compelling role in abiotic stress tolerance and, therefore, would provide a useful strategy to promote abiotic stress tolerance in grape via molecular-assisted breeding and/or new biotechnology tools. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13205-018-1301-4) contains supplementary material, which is available to authorized users.

The growth reduction observed in many plants caused by salinity is often associated with a decrease in their photosynthetic capacity. This effect could be associated with the partial stomatal closure and/or the non-stomatal limitation which involves the decrease in ribulose-1,5-bisphosphate carboxylase oxygenase (RUBISCO) activity. The objective of this study was to explore the mechanisms of inhibited photosynthesis in Arabidopsis thaliana ( Pa-1 accession) under salt stress. Pa-1 seeds grown on a solid substrate for 25 days on standard medium were challenged with 50 mM NaCl for 15 days. Harvests were carried out every five days by separating the rosette leaves and roots. Salt stress reduced growth by limiting the number of the rosette leaves and not their biomass. Accumulation of Na+ and Cl- increased during the treatment period, whereas K+ and Ca2+ accumulation were reduced in salt treatment. RUBISCO and phosphoenolpyruvate carboxylase (PEPC) activities were increased with the age of the leaves to a maximum after 10 days of treatment then later decreased. We concluded that the sensitivity of Pa-1 to salinity may be due to a reduction in number of leaves, in the photosynthetic assimilation with stomatal closure and damage of the RUBISCO and PEPC activities. Keywords : Arabidopsis thaliana , photosynthetic parameters, salinity, ribulose-1,5-bisphosphate carboxylase oxygenase (RUBISCO), phosphoenolpyruvate carboxylase (PEPC). African Journal of Biotechnology Vol. 12(29), pp. 4594-4602

Magnesium nutrition is often forgotten, while its absence adversely affects numerous functions in plants. Magnesium deficiency is a growing concern for crop production frequently observed in lateritic and leached acid soils. Competition with other cations (Ca2+, Na+, and K+) is also found to be an essential factor, inducing magnesium deficiency in plants. This nutrient is required for chlorophyll formation and plays a key role in photosynthetic activity. Moreover, it is involved in carbohydrate transport from source-to-sink organs. Hence, sugar accumulation in leaves that results from the impairment of their transport in phloem is considered as an early response to Mg deficiency. The most visible effect is often recorded in root growth, resulting in a significant reduction of root/shoot ratio. Carbohydrate accumulation in source leaves is attributed to the unique chemical proprieties of magnesium. As magnesium is a nutrient with high mobility in plants, it is preferentially transported to source leaves to prevent severe declines in photosynthetic activity. In addition, Mg is involved in the source-to-sink transport of carbohydrates. Hence, an inverse relationship between Mg shortage and sugar accumulation in leaves is often observed. We hereby review all these aspects with a special emphasis on the role of Mg in photosynthesis and the structural and functional effects of its deficiency on the photosynthetic apparatus.

International audience; The ability of exogenous compatible solutes, such as proline, to counteract cadmium (Cd) inhibitory effects in young date palm plants (Phoenix dactylifera L. cv Deglet Nour) was investigated. Two-year-old date palm plants were subjected for five months at different Cd stress levels (0, 10 and 30mg CdCl2kg(-1) soil) whether supplied or not with exogenous proline (20mM) added through the irrigation water. Different levels of Cd stress altered plant growth, gas exchanges and chlorophyll content as well as water status, but at different extent among them. In contrast, an increase of antioxidant enzymes activities of Cd-treated plants in association with high amounts of proline content, hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS) and electrolyte leakage (EL) were observed. Interestingly, exogenous proline mitigated the adverse effects of Cd on young date palm. Indeed, it alleviated the oxidative damage induced by Cd accumulation and established better levels of plant growth, water status and photosynthetic activity. Moreover, proline-treated plants showed high antioxidant enzymes activities (superoxide dismutase, catalase and glutathione peroxydase) in roots and leaves as compared to Cd-treated plants

Identification de gènes impliqués dans l’accumulation des métaux lourds chez la laitue (Lactuca sativa). 1er congrès International de Technologies Alimentaires et Contrôle Qualité des Aliments

The aim of this investigation was to evaluate the ability of the indifferent halophyte Sulla carnosa Desf. to desalinize a moderately-salt-affected soil. Seeds were sown on a fertile soil added or not with 1.5 g NaCl. kg(-1). Analogous treatments without plantation (control and salinized) were also used. Plant culture was performed under greenhouse conditions in non-perforated pots containing 10 kg soil each and irrigated with non-saline tap water. After 80 days of treatment, shoots were harvested. Soil samples were also collected after division of soil column in each pot into two horizons. Our results showed that salt addition increased electrical conductivity of saturation paste extract (ECe)from 3.3 to 8.4 dS. m(-1) and soluble sodium concentration from 0.32 to 1.15 g. kg(-1) soil in the upper horizon. In the lower horizon however, Na+ concentration was quasi-constant and then ECe was less increased. Plant culture inversed this pattern of sodium accumulation and salinity. Its productivity and phytodesalination capacity in 80 days were 5.0 t DW. ha(-1) and 0.3 t Na+. ha(-1) (24% of the added quantity), respectively. Interestingly, sodium dilution within biomass (41.5-45.6 mg. g(-1) DW) and the non-altered nutrition make this plant suitable for forage as second use after phytodesalination.

International audience; Cadmium (Cd) is a metal pollutant that accumulates in cultivated soils and has detrimental consequences in terms of food safety. Lettuce (Lactuca sativa) can be characterised as having a high capacity to accumulate Cd in its tissues. An analysis of Cd tolerance and Cd accumulation was carried out using two varieties of lettuce ('Divina' and 'Melina'). A wide range of CdCl2 concentrations was used (0.0, 0.1, 0.6, 3.0, and 15.0 mu M CdCl2). The lowest concentration (0.1 mu M CdCl2) stimulated growth, while the two highest concentrations resulted in a reduction in biomass. Cadmium concentrations were found to be twice as high in roots as in shoots. 'Divina' displayed lower concentrations of Cd than 'Melina' in nearly all treatments. A strong negative correlation was observed between Cd concentration and Cd tolerance in the roots and shoots (R-2 > 0.87) of both 'Melina' and 'Divina'. Lettuce grown in the presence of 15.0 mu M CdCl2 had leaf Cd concentrations that were 100-fold higher than the legal maximum level for vegetable products marketed for human consumption, but showed no symptoms of dehydration, chlorosis, or necrosis. This result represents an important alert for lettuce consumers and growers.

The response patterns during water deficit stress and subsequent recovery of two forage species, Medicago truncatula and Sulla carnosa, were studied. After germination and pre-treatment, seedlings were individually cultivated for two months under two irrigation modes: 100% and 33% of field capacity. Measured parameters were plant growth, water relations, leaf osmotic potential, lipid peroxidation, and leaf inorganic (Na+ and K+) and organic (proline and soluble sugars) solute contents, as well as delta-1-pyrroline-5-carboxylate synthase (P5CS) and proline dehydrogenase (PDH) activities. Our results showed that under control conditions, and in contrast to roots, no significant differences were observed in shoot biomass production between the two species. However, when subjected to water-deficit stress, M. truncatula appeared to be more tolerant than S. carnosa (reduction by 50 and 70%, respectively). In the two studied species, water-deficit stress led to an increase in root/shoot ratio and leaf proline and soluble sugar contents, and a decrease in leaf osmotic potential. Enzymatic assay revealed that in the two species, P5CS activity was stimulated whereas that of PDH was inhibited under stress conditions. Despite greater accumulation of proline, sugar, and potassium in leaves of S. carnosa, M. truncatula was more tolerant to water deficit. This was essentially due to its capacity to control tissue hydration and water-use efficiency, in addition to its greater ability to protect membrane integrity. Following stress relief, M. truncatula and S. carnosa showed partial re-establishment of growth capacity.

We aimed at characterizing mechanisms controlling cadmium accumulation in lettuce, which is a food crop showing one of the highest capacities to accumulate this toxic compound. In this study, plants from three lettuce varieties were grown for eight days on media supplemented or not with cadmium (15 μM CdCl2) and containing different concentrations of calcium (0.5, 1, 2.5, 5 and 10 mM Ca(NO3)2). Ourresults show that exposure to cadmium resulted in biomass reduction. The biomass reduction was particularly high at 0.5 mM calcium but supplementation of the medium with increasing calcium concentrations alleviated the toxic effect of cadmium on the growth and water status of lettuce plants. The three lettuce varieties displayed different abilities to accumulate cadmium. Interestingly, increasing the calcium concentration in the medium resulted in a strong decrease in cadmium contents. These results suggest that cadmium uptake in lettuce plants is negatively associated with the presence of calcium in the culture medium, maybe due to a competition between these two cations for binding and absorption sites in roots. In conclusion, the results suggest that fertilization with Ca2+ appears to be a promising strategy for decreasing risk associated with ingesting food crops grown on cadmiumpolluted soils.Keywords: Lettuce, food security, growth, cadmium accumulation, cadmium translocation, calcium

W.Z. was supported by a scholarship from the Tunisian Ministry of Higher Education and Scientific Research (LR10CBBC02), and then by a scholarship from the "Agence universitaire de la francophonie" (AUF). We thank Dr F. Gosti and Dr L. Marques for critical reading of the manuscript, and A. Adiveze, H. Afonso, C. Baracco, H. Baudot, F. Bourgeois, C. Dasen, X. Dumont, C. Fizames, J. Garcia, S. Gelin, F. Lecocq, V. Papy, V. Rafin, G. Ruiz and C. Zicler, for technical and administrative supports.; International audience; Plant Zn/Cd/Pb/Co P1B-ATPases (HMAs) play different roles, among which are the control of metal transport from the roots to the shoot and/or from the cytoplasm into the cell vacuole. Transferring the knowledge acquired on HMAs from model species to HMAs from other species requires one to identify orthologues in these other species. Through an extensive screening of the public sequence databases, 96 plant P1B-ATPases showing orthology to any of the AtHMA1, AtHMA2, AtHMA3 or AtHMA4 isoforms were identified from 32 plant species belonging to 15 botanical families. The number of paralogues within a species varied greatly from species to species, even within a specific botanical family, suggesting that gene duplication events occurred after speciation. The phylogenetic tree gathering the Zn/Cd/Pb/Co P1B-ATPases was strongly structured according to the botanical family to which the sequences could be related to. In particular, no strict orthology relationship links the Brassicaceae HMAs to the non-Brassicaceae or the Poaceae ones. Recent data showed that the sole rice HMA characterised to date displays different functional properties from the Arabidopsis HMAs. Altogether, data suggest that it might be risky to directly transfer the knowledge acquired through the study of HMAs in model plant species to HMAs from other species.

Cadmium is an extremely toxic pollutant causing a great number of diseases. It is a widespread metal which concentration rises in cultivated soils, thus exposing food or feed crops to it and ultimately causing potential major sanitary problems as a consequence of its entry in the food chain. Among the vegetable species used for food, lettuce shows a higher capacity of accumulating cadmium.Our objective was to identify molecular determinants controlling cadmium accumulation in lettuce.We aim at characterizing mechanisms controlling cadmium accumulation in lettuce, which is a food crop showing one of the highest capacities to accumulate this toxic compound.Starting from a phenotypic and transcriptomic analysis of 18 lettuce genotypes representing the genetic diversity of the species, we identified trends linking cadmium and zinc accumulation in roots an shoots, cadmium translocation from roots to shoot, cadmium tolerance, and expression of a dozen of candidate genes proposed to be involved in cadmium transport. A positive correlation linked cadmium accumulation and the mRNA accumulation of an heavy metal efflux transporter. Interestingly, measurements of 109Cd influx in roots and 109Cd efflux from roots revealed that the genotype displaying the least cadmium accumulation could be discriminated from the genotype displaying the highest one by its markedly increased ability to efflux cadmium from the roots to the culture medium. Progeny analysis from crosses between the genotypes displaying extreme performances for cadmium accumulation or cadmium translocation from roots to shoots revealed that these traits could be supported by single genetic determinism.In conclusion, starting from the analysis of cadmium accumulation in a large set of lettuce genotypes, a major determinant limiting cadmium accumulation in this species was revealed, that is the ability to efflux cadmium from the root to the culture medium. A candidate gene has been identified for this function, which paves the way towards the breeding for lettuce with reduced cadmium accumulation in leaves.As a non-essential element for plants, cadmium has been assumed to be taken up by making use of non-specificity of essential elements transporters. Numerous physiological studies have described that cadmium uptake is negatively associated with iron pathway, by competing for absorption sites in roots. The principal candidate for this transport in lettuce is a possible “orthologue” of Arabidopsis thaliana IRT1. In fact, AtIRT1 is a major transporter responsible for iron uptake from the soil, and is known to have a broad substrate range, including cadmium. IRT1-overexpressing A. thaliana plants were then shown to accumulate more cadmium in root tissue. In this work, NCBI sequence libraries were analysed and two lettuce “orthologues” of AtIRT1 were found (LsIRTa and LsIRTb). Cloning “orthologues” of AtIRT1 was carried out for five lettuce varieties. Moreover, LsIRTs expression in plants from 14 lettuce accessions were analysed by PCRQ and were compared to cadmium accumulation in plants. Interestingly, our results revealed that expression of LsIRTa is significantly correlated with root cadmium content. LsIRTa seems to be involved in the control of cadmium accumulation in roots.This result has been supported by tow physiological experiments. The first experiment showed that increasing iron in the growth medium resulted in a strong decrease in root cadmium content. And conversely, the second experiment revealed that root iron content decrease in response to increasing concentrations of cadmium in the medium. These results suggest that cadmium competes with iron for uptake through ion transporters in lettuce root cells. As mentioned above, a candidate gene for this transport has been identified (LsIRTa), which paves the way towards the breeding for lettuce with reduced cadmium accumulation.; Les activités humaines agricoles, urbaines et industrielles, sans cesse croissantes, sont à l'origine d'une contamination de notre environnement par les métaux lourds. Alors que de nombreuses molécules organiques peuvent être dégradées, les métaux lourds ne le peuvent pas et leur concentration augmente régulièrement dans les sols et les eaux. Ceci expose les plantes à des concentrations croissantes de métaux lourds. L’accumulation de métaux lourds dans les plantes présente un risque toxique pour l’Homme, car les plantes cultivées sont le point d’entrée dans la chaîne alimentaire. Par comparaison aux autres espèces, la laitue « Lactuca sativa » a tendance à présenter des teneurs élevées en cadmium, un métal lourd très toxique dont la concentration croît régulièrement dans les sols cultivés pour des raisons environnementales. En termes de sécurité alimentaire, il est donc important de produire des variétés accumulant des teneurs en cadmium réduites, et la laitue est un bon modèle pour débuter ce type d’approche.L’objectif de notre thèse était de caractériser aux niveaux physiologique, génétique, et moléculaire, les déterminants majeurs contrôlant l’accumulation du cadmium chez la laitue. Notre objectif a été décliné en différentes opérations. Tout d’abord une analyse de diversité nous a permis de décrire la capacité d’accumulation de cadmium de 18 génotypes de laitue et de sélectionner des génotypes présentant des performances extrêmes vis-à-vis du cadmium. Ainsi, des génotypes présentant des performances extrêmes du point de vue de la tolérance au cadmium, de l’accumulation de cadmium et de la capacité de translocation du cadmium des racines vers les parties aériennes ont été sélectionnés.Dans une deuxième étape, nos variétés extrêmes pour les caractères d’accumulation de cadmium et de translocation de cadmium des racines vers la partie aérienne ont été utilisées pour développer une approche physiologique. L’objectif de cette approche était de montrer l’origine de leur variabilité afin de comprendre les déterminants physiologiques contrôlant l’accumulation du cadmium chez la laitue.Dans le cadre de cette approche, des expériences d’efflux faites en utilisant du cadmium radioactif (109Cd) ont montré que la variété la moins accumulatrice de cadmium se caractérise par un efflux de cadmium marqué plus important par comparaison aux autres variétés. Cette variété possède vraisemblablement un mécanisme d’efflux plus efficace par comparaison aux autres variétés qui pourraient être le déterminant majeur permettant d’obtenir une plus faible accumulation de cadmium chez cette variété.Notre étude a permis de montrer une forte corrélation positive entre teneur en cadmium et teneur en zinc. Ce qui a permis d’émettre l’hypothèse d’un transport très associé entre le cadmium et le zinc. De même, une corrélation positive entre le niveau de translocation de cadmium des racines vers la partie aérienne et le niveau relatif du citrate entre les racines et les feuilles a été montrée. Cette corrélation suggère que le citrate pourrait être impliqué dans le transport du cadmium.Enfin, notre étude physiologique a permis de mettre en évidence un effet dépressif de l’augmentation des concentrations de fer et de calcium dans le milieu de culture sur l’accumulation du cadmium chez nos plantes de laitue.Ceci permet de penser que l'absorption de cadmium peut se faire d’une manière non spécifique via des transporteurs de fer et/ou de calcium.Dans le but de mieux comprendre les mécanismes impliqués dans l’accumulation du cadmium chez la laitue nous avons élaboré une approche génétique. Cette approchea visé à préciser le déterminisme, simple ou complexe, des caractères d’accumulation de cadmium et de translocation du cadmium des racines vers les parties aériennes. Pour cela des croisements ont été réalisés entre les génotypes les plus extrêmes pour ces caractères. À la suite de ces croisements, les populations F1 et F2 ont été analysées.Les résultats de l’analyse des plantes F1 ont montré qu’on est en présence d’une dominance forte, voire absolue, des caractères qui assurent la sensibilité au cadmium, la forte accumulation du cadmium et la forte translocation du cadmium des racines vers les parties aériennes. De même, pour ces trois caractères étudiés, les plantes F1 issues des deux sens de croisement ont montré un comportement identique vis-à-vis du cadmium ce qui prouve que nos caractères ne sont pas des liés au sexe.Les analyses des plantes F2 pour les deux caractères accumulation de cadmium et translocation de cadmium des racines vers les parties aériennes ont permis de montrer que la distribution phénotypique n’est pas bimodale pour les deux caractères étudiés, indiquant que ces caractères ne présentent pas des cas typiques de monohybridisme. Ces deux caractères sont donc contrôlés par plus qu’un seul gène pour chacun d’entre eux.Dans le but de mieux comprendre les mécanismes impliqués dans l’accumulation du cadmium chez la laitue, nous avons complété les approches d’analyse de la diversité, de physiologie et de génétique par une approche moléculaire. Cette approche avait comme objectif l'identification de corrélations, si elles existent, entre l'accumulation de cadmium dans les racines et/ou les feuilles et le niveau d’expression de gènes candidats décrits chez les espèces modèles comme impliqués dans le contrôle de l’accumulation de cadmium. Cette approche a permis de cloner et de séquencer des fragments d’ADN correspondant à 9 gènes candidats de laitue et d’évaluer le niveau de leurs expressions par PCR quantitative. Ensuite, l’expression de ces gènes a été comparée aux teneurs en cadmium et en zinc mesurées dans les racines et/ou les feuilles.À la suite ce cette étude nous avons pu mettre en évidence une éventuelle implication d’un gène de laitue (que nous avons nommé LsIRTa) dans l’accumulation du cadmium. Ce gène est très probablement un orthologue fonctionnel du gène AtIRT1 qui code un transporteur représentant la principale voie d'absorption du fer par les cellules racinaires d’Arabidopsis thaliana. D’autre part, nos résultats ont montré une corrélation positive entre l’expression d’un autre gène (que nous avons nommé LsPDRa) et l’accumulation du zinc et du cadmium au niveau foliaire, ce gène est donc très probablement impliqué dans l’accumulation de ces deux métaux à ce niveau, ce qui confirme davantage notre hypothèse de transport associé entre le cadmium et le zinc.