Walid Zorrig | Centre de Biotechnologies de Borj-Cédria (original) (raw)

Papers by Walid Zorrig

In the present study, the effects of elevated zinc concentrations on germination, physiological a... more 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 ZnSO 4) 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 and bioconcentration 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.

Salinity and potassium deficiency are major abiotic constraints affecting plant growth, productiv... more 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.

Oil field wastewater (produced water) management is a crucial environmental issue due to its hydr... more 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 (Na 2 SiO 3) in the removal of organic matter and heavy metal from produced wastewater was investigated, the optimization of the proposed process (Na 2 SiO 3 dose , agitation speed, and required treatment time). Soluble sodium silicate (SiO 2 /Na 2 O = 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.

In order to understand the molecular basis of vacuolar H +-ATPase subunits and reveal their possi... more 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.

One of the best alternative disposals of sludge sewage is through the soil-plant system as a fert... more One of the best alternative disposals of sludge sewage is through the soil-plant system as a fertilizer. Sludge sewage is both an environmentally and economically sound way of recycling nutrients which are beneficial for plant nutrition. A field experiment using four doses (100, 200, 300 and 400 t ha-1) of an urban sludge was carried out to study the effect of its application on growth, photosynthesis and ion accumulation in Medicago sativa (an important forage crop species) in order to check its usefulness as a safe fertilizer. Results showed a positive effect of the amendment on growth, CO 2 assimilation, stomatal conductance and transpiration rate as well as Ca, Mg and Fe acquisition, especially at 200 t ha-1. For metals accumulation, data showed that up to 300 t ha-1 , sludge presented no risk of contamination. Hence, we suggest that, up to 300 t ha 1 , this amendment is suitable for agriculture.

Iron (Fe) is one of the essential nutrients for plant growth which is involved in several physiol... more 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 2 O 2 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 CO 2 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 rhizo-sphere acidification of deficient S. carnosa plants. However, the D + SA + H 2 O 2 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.

Magnesium nutrition is often forgotten, while its absence adversely affects numerous functions in... more 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 (Ca 2? , 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.

Silicon (Si) plays an important role in providing beneficial effects on plant growth and yield, e... more 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 (Na 2 SiO 3 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 Na 2 SiO 3 (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.

Control of K + and Na + transport plays a central role in plant adaptation to salinity. In the ha... more Control of K + and Na + transport plays a central role in plant adaptation to salinity. In the halophyte Hordeum mariti-mum, 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 oo-cytes 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.

JOURNAL OF PLANT NUTRITION, 2016

Salt-induced responses of Medicago ciliaris was studied under controlled conditions. Twenty-two-d... more 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 (NaC) 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.

Changes in the antioxidant defence systems were investigated in many aromatic and medicinal plant... more Changes in the antioxidant defence systems were investigated in many aromatic and medicinal plants grown under salinity; however, no study is available about its effects on Solanum villosum Mill. In this study, we investigated the response of S. villosum to sodium chloride (NaCl), especially the impacts of NaCl on secondary metabolites production (phenolic compounds , carotenoids, and glycol-alkaloids). For this purpose, a hydroponic culture experiment was conducted on seedlings subjected to 0, 50, 100, or 150 mM NaCl. NaCl affected the growth of S. villosum in terms of plant height and dry weight, however, it increased the water content of the leaves. Although leaf Na + concentration was significantly increased under salt stress, the leaves K + , Ca 2+ and Mg 2+ concentration were enhanced and/ or not significantly affected. The adaptation of S. villosum to NaCl stress was also reflected by the maintain of chlorophyll levels under different NaCl treatments. Additionally, leaf caffeic acid, lutein, and beta-carotene contents were considerably increased under 100 mM NaCl treatment, along with the up regulation of some related phenolic (phenylalanine ammonialyase and flavonol synthase), and carotenoid genes (phytoene synthase 1, phytoene synthase 2, and b-lycopene cyclase). The leaf contents of β-solamargine and α-solasonine also increased significantly with increasing salinity. The present study is the first to through some light on the medicinal quality of S. villosum that would be quite helpful for production of secondary metabolites under salt-stressed conditions.

In order to evaluate the reliability and the practical use of the electrical impedance spectrosco... more 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 halo-phyte plants cultivated under different growth conditions (biotope versus controlled conditions, hydro-ponic 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 100 mM while the lowest value was at 400 mM NaCl. The electrical resistance increased at an early stage after the application of salt stress reaching maximal value 180 min 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... more 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.

This work characterized mechanisms controlling cadmium (Cd) tolerance and accumulation in lettuce... more 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 109 Cd 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.

Three-year-old seedlings of two Tunisian provenances of cork oak (Quercus su-ber L.) differing in... more Three-year-old seedlings of two Tunisian provenances of cork oak (Quercus su-ber 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 photo-synthesis (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 saline biotopes, different mechanisms may contribute to the tolerance of halophytes to high so... more 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 .

Agrochimica, 2017

Summary. – Sesuvium portulacastrum plants were grown on soils with increasing electrical conducti... more Summary. – Sesuvium portulacastrum plants were grown on soils with increasing electrical conductivity of the saturation paste extract (ECe: 3.7, 10.1, 12.6, 15.5, 23.3, and 38.1 dS m-1). Results showed a high productivity over a wide range of salinity levels with an optimum (4.4 t DW ha-1) at 15.5 dS m-1. Plants maintained an adequate shoot water content and non-affected Ca and Mg statuses even at the highest salinity level (38.1 dS m-1). S. portulacastrum cultivation on NaCl-added soils significantly decreased ECe and soluble Na concentration due to its high phytodesalination capacity and rate. Thus, S. portulacastrum is highly productive and can extract high sodium amounts from soil with 10.1 ≤ ECe ≤ 23.3 dS m-1 and 1.2 g kg-1 soil ≤ soluble Na concentration ≤ 2.6 g kg-1 soil. Nevertheless, the highest phytodesalination capacity and rate were obtained at about 15.5 dS m-1 and 1.9 g soluble Na kg-1 soil.

• The abundance of calcareous soils makes bicarbonate-induced iron (Fe) deficiency a major proble... more • 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 caro-tenoids 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.

The ability of exogenous compatible solutes, such as proline, to counteract cadmium (Cd) inhibito... more 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 30 mg CdCl 2 kg À 1 soil) whether supplied or not with exogenous proline (20 mM) 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 (H 2 O 2), 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.

Agrochimica, 2016

Summary. – The aim of the present work was to determine the impact of Mg deficiency on K and Ca n... more Summary. – The aim of the present work was to determine the impact of Mg deficiency on K and Ca nutrition in the pastoral legume Sulla carnosa. Plants were grown in the presence of 1.50, 0.05, 0.01, or 0.00 mM Mg2+ during 3 (medium-term treatment) or 5 weeks (long-term treatment). After 3 weeks of treatment the optimum of growth was observed at 1.50 and 0.05 mM Mg2+, while with a long-term treatment the optimum was found only at 1.50 mM Mg2+. Gas exchange measurements decreased with decreasing magnesium concentration, and the optimum was recorded in plants grown in complete nutrient solution (1.50 mM Mg2+). Cotyledon Mg reserves and Mg use efficiency played a principal role in S. carnosa tolerance to the stress. Antagonisms between major cations were also noticed, mainly between Ca2+ and Mg2+, K+/Mg2+ antagonism being much lower. This antagonism depends on plant species, cation ratios, and treatment period.

JOURNAL OF PLANT NUTRITION, 2016

Agrochimica, 2017

Agrochimica, 2016