Effect of seed priming with auxin on ROS detoxification and carbohydrate metabolism and their relationship with germination and early seedling establishment in salt stressed maize.

As crucial stages in the plant ontogeny, germination and seedling establishment under adverse conditions greatly determine staple crop growth and productivity. In the context of green technologies aiming to improve crop yield, seed priming is emerging as an effective approach to enhance seed vigor and germination performance under salt stress. In this study, we assess the efficiency of seed priming with indole-3-acetic acid (IAA) in mitigating the adverse effects of salt stress on maize (Zea mays L.) seedlings during germination and early seedling stages. In unprimed seeds, salt stress reduced germination indices, and seedling (both radicle and coleoptile) growth, together with decreased tissue hydration. However, seed priming using IAA significantly improved maize salt response, as reflected by the increased seed germination dynamics, early seedling establishment, and water status. Besides, seedlings from IAA-primed seeds showed a higher activity of α-amylase, resulting in increased sugar contents in roots and coleoptiles of salt-stressed plants. Further, IAA-seed priming stimulated the accumulation of endogenous IAA in salt-stressed seedlings, in concomitance with a significant effect on reactive oxygen species detoxification and lipid peroxidation prevention. Indeed, our data revealed increased antioxidant enzyme activities, differentially regulated in roots and coleoptiles, leading to increased activities of the antioxidant enzymes (SOD, CAT and GPX). In summary, data gained from this study further highlight the potential of IAA in modulating early interactions between multiple signaling pathways in the seed, endowing maize seedlings with enhanced potential and sustained tolerance to subsequent salt stress.

Silicon mitigates salinity effects on sorghum-sudangrass (Sorghum bicolor × Sorghum sudanense) by enhancing growth and photosynthetic efficiency.

The aim of this study was to investigate whether silicon (Si) supply was able to alleviate the harmful effects caused by salinity stress on sorghum-sudangrass (Sorghum bicolor ×Sorghum sudanense ), a species of grass raised for forage and grain. Plants were grown in the presence or absence of 150mM NaCl, supplemented or not with Si (0.5mM Si). Biomass production, water and mineral status, photosynthetic pigment contents, and gas exchange parameters were investigated. Special focus was accorded to evaluating the PSI and PSII. Salinity stress significantly reduced plant growth and tissue hydration, and led to a significant decrease in all other studied parameters. Si supply enhanced whole plant biomass production by 50%, improved water status, decreased Na+ and Cl- accumulation, and even restored chlorophyll a , chlorophyll b , and carotenoid contents. Interestingly, both photosystem activities (PSI and PSII) were enhanced with Si addition. However, a more pronounced enhancement was noted in PSI compared with PSII, with a greater oxidation state upon Si supply. Our findings confirm that Si mitigated the adverse effects of salinity on sorghum-sudangrass throughout adverse approaches. Application of Si in sorghum appears to be an efficient key solution for managing salt-damaging effects on plants.

Silicon (Si) mitigates the negative effects of iron deficiency in common bean (Phaseolus vulgaris L.) by improving photosystem activities and nutritional status.

Silicon (Si) is the second most abundant element in the Earth's crust after oxygen. Its beneficial impact on crop development and yield, particularly under stressful conditions such as iron (Fe) deficiency, has been well documented. Fe deficiency is a critical constraint that limits crop production globally. The objective of this study was to investigate the effects of silicon (Na2SiO3) on common bean (Phaseolus vulgaris L. 'Coco Rose' variety) under iron-deficient conditions. The common bean plants were subjected to six treatments, which included three sufficient iron treatments (50 µM Fe) each paired with three varying silicon concentrations (0, 0.25, and 0.5 mM Si), and three iron-deficient treatments (0.1 µM Fe) each associated with the same silicon concentrations (0, 0.25, and 0.5 mM Si). The results indicate that iron deficiency had a negative impact on almost all the measured parameters. However, under silicon treatments, especially with 0.5 mM Si, the depressive effects of iron deficiency were significantly mitigated. The addition of 0.5 mM Si alleviated leaf chlorosis and improved biomass production, nutritional status, photosynthetic pigment content, photosynthetic gas exchange, and photosystem (PSI and PSII) activities. Interestingly, a greater beneficial effect of silicon was observed on PSII compared to PSI. This was accompanied by a significant augmentation in leaf iron concentration by 42%. Therefore, by enhancing the photosystem activities and nutritional status, among other mechanisms, silicon is capable of mitigating the adverse effects of iron-deficient conditions, making it a successful and effective solution to cope with this nutritional stress.

Seed Priming with Salicylic Acid Alleviates Salt Stress Toxicity in Barley by Suppressing ROS Accumulation and Improving Antioxidant Defense Systems, Compared to Halo- and Gibberellin Priming.

Plants are highly sensitive to various environmental stresses, which can hinder their growth and reduce yields. In this study, we investigated the potential of seed priming with salicylic acid (SA), gibberellic acid (GA3), and sodium chloride (NaCl) to mitigate the adverse effects of salinity stress in Hordeum vulgare at the germination and early seedling stages. Exposing H. vulgare seeds to salt stress reduced the final germination percentage and seedling shoot and root growth. Interestingly, all seed treatments significantly improved salt-induced responses, with GA3 being more effective in terms of germination performance, plant growth, and photosynthesis. SA priming exhibited promising effects on antioxidant defense mechanisms, proline, sugar, and ascorbic acid production. Notably, SA priming also suppressed reactive oxygen species accumulation and prevented lipid peroxidation. These findings highlight the ability of SA to manage crosstalk within the seed, coordinating many regulatory processes to support plant adaptation to salinity stress.

Characterization, Antimicrobial and Anticancer Properties of Palladium Nanoparticles Biosynthesized Optimally Using Saudi Propolis.

Due to their unique physicochemical characteristics, palladium nanoparticles (Pd-NPs) have shown tremendous promise in biological applications. The biosynthesis of Pd-NPs employing Saudi propolis has been designed to be environmental, fast, controlled, and cost-effective. The formation and stability of biosynthesized Pd-NPs by Saudi propolis extract were proved by ultraviolet-visible spectrophotometry (UV-Vis), Fourier-transform infrared spectroscopy (FT-IR), and Zeta potential analysis. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) findings show that the average particle size of Pd-NPs is between 3.14 and 4.62 nm, which is in quantum scale. The Saudi propolis enhanced the antimicrobial activity against B. subtilis, S. aureus, E. coli, K. pneumoniae, and C. albicans. Pd-NPs show effective anticancer activity against ductal carcinoma (MCF-7) with IC50 of 104.79 µg/mL.

Do Specialized Cells Play a Major Role in Organic Xenobiotic Detoxification in Higher Plants?

In the present work, we used a double cell screening approach based on phenanthrene (phe) epifluorescence histochemical localization and oxygen radical detection to generate new data about how some specialized cells are involved in tolerance to organic xenobiotics. Thereby, we bring new insights about phe [a common Polycyclic Aromatic Hydrocarbon (PAH)] cell specific detoxification, in two contrasting plant lineages thriving in different ecosystems. Our data suggest that in higher plants, detoxification may occur in specialized cells such as trichomes and pavement cells in Arabidopsis, and in the basal cells of salt glands in Spartina species. Such features were supported by a survey from the literature, and complementary data correlating the size of basal salt gland cells and tolerance abilities to PAHs previously reported between Spartina species. Furthermore, we conducted functional validation in two independent Arabidopsis trichomeless glabrous T-DNA mutant lines (GLABRA1 mutants). These mutants showed a sensitive phenotype under phe-induced stress in comparison with their background ecotypes without the mutation, indicating that trichomes are key structures involved in the detoxification of organic xenobiotics. Interestingly, trichomes and pavement cells are known to endoreduplicate, and we discussed the putative advantages given by endopolyploidy in xenobiotic detoxification abilities. The same feature concerning basal salt gland cells in Spartina has been raised. This similarity with detoxification in the endopolyploid liver cells of the animal system is included.

Moderate salinity reduced phenanthrene-induced stress in the halophyte plant model Thellungiella salsuginea compared to its glycophyte relative Arabidopsis thaliana: Cross talk and metabolite profiling.

It was shown that halophytes experience higher cross-tolerance to stresses than glycophytes, which was often associated with their more powerful antioxidant systems. Moreover, salinity was reported to enhance halophyte tolerance to several stresses. The aim of the present work was to investigate whether a moderate salinity enhances phenanthrene stress tolerance in the halophyte Thellungiella salsuginea. The model plant Arabidopsis thaliana, considered as its glycophyte relative, was used as reference. Our study was based on morpho-physiological, antioxidant, and metabolomic parameters. Results showed that T. salsuginea was more tolerant to phenanthrene stress as compared to A. thaliana. An improvement of phenanthrene-induced responses was recorded in the two plants in the presence of 25 mM NaCl, but the effect was significantly more obvious in the halophyte. This observation was particularly related to the higher antioxidant activities and the induction of more adapted metabolism in the halophyte. Gas Chromatography coupled with Mass Spectrometry (GC-MS) was used to quantify alcohols, ammonium, sugars, and organic acids. It showed the accumulation of several metabolites, many of them are known to be involved in signaling and abiotic stress tolerance. Moderate salinity and phenanthrene cross-tolerance involved in these two stresses was discussed.

New parameters for a better evaluation of vegetative bioremediation, leaching, and phytodesalination.

Vegetative bioremediation of calcareous sodic and saline-sodic soils is a biological approach for soil desalination by plants. It is based on three main processes: (i) sodium release from cation exchange sites, (ii) its leaching, and/or (iii) phytodesalination (Na(+) uptake by plant roots and its accumulation in shoots). Leaching needs sufficient rainfall and/or adequate irrigation. Thus, under non-leaching conditions, phytodesalination is the only existing process in terms of sodium removal. Several works tried to evaluate these processes; used plants were grown in field, in lysimeters, or in non-perforated pots. The evaluation of vegetative bioremediation, leaching, and phytodesalination was mainly based on plant analyses (including biomass production, sodium accumulation, test culture, and co-culture) and soil analyses (porosity, salinity, sodicity...). Nevertheless, used parameters are not enough to ensure comparisons between results found in different investigations. The present study introduces new parameters like phytodesalination efficiency, yield, and rate as well as vegetative bioremediation and leaching yields and rates. Our study is also illustrated by an estimation of all parameters for several previously-published data from our own works and those of other authors. Obtained results showed usefulness of these parameters and some of them can be extended to heavy metal phytoexraction.

Preferential damaging effects of limited magnesium bioavailability on photosystem I in Sulla carnosa plants.

MAIN CONCLUSION: Magnesium deficiency preferentially inhibits photosystem I rather than photosystem II in Sulla carnosa plants. The effects of magnesium (Mg(2+)) deficiency on growth, photosynthetic performance, pigment and polypeptide composition of chloroplast membranes were studied in the halophyte Sulla carnosa (Desf.), an annual legume endemic to Tunisia and Algeria. The results demonstrate a gradual decrease in biomass production with decreasing Mg(2+) availability in the growth medium. The increase of Mg(2+) deficiency was also associated with a decline of the net CO2 assimilation (Pn) in fully expanded leaves, a decrease in the amount of photosynthetic pigments, and an increase in the lipid peroxidation in plants exposed to decreased Mg(2+) concentrations. Interestingly, while CO2 assimilation already was affected at Mg(2+) concentrations below 1.5 mM, the photochemical efficiency of photosystem II (PSII) declined only in the absence of Mg(2+). In contrast, plants of S. carnosa grown in Mg(2+)-deficient conditions exhibited a significant decrease in photosystem I (PSI) photochemistry in vivo at much higher Mg(2+) levels compared to PSII photochemical activity. The inhibitory effect of Mg(2+) deficiency on PSI photochemistry strongly correlated with significantly lower relative abundance of PSI-related chlorophyll-protein complexes and lower amounts of PSI-associated polypeptides, PsaA, PsaB, and Lhca proteins within the same range of Mg(2+) concentrations. These observations were associated with a higher intersystem electron pool size, restricted linear electron transport and a lower rate of reduction of P700(+) in the dark indicating restricted capacity for PSI cyclic electron transfer in plants exposed to Mg(2+)-deficient conditions compared to controls. These results clearly indicate that PSI, rather than PSII is preferentially targeted and damaged under Mg(2+)-deficiency conditions.

The Halophyte Cakile maritima Reduces Phenanthrene Phytotoxicity.

In a previous study, we showed that the halophyte plant model Thellungiella salsuginea was more tolerant to phenanthrene (Polycyclic Aromatic Hydrocarbon: PAH) than its relative glycophyte Arabidopsis thaliana. In the present work, we investigated the potential of another halophyte with higher biomass production, Cakile maritma, to reduce phenanthrene phytotoxicity. Sand was used instead of arable soil with the aim to avoid pollutant degradation by microorganisms or their interaction with the plant. After 6 weeks of treatment by 500 ppm phenanthrene (Phe), stressed plants showed a severe reduction (-73%) in their whole biomass, roots being more affected than leaves and stems. In parallel, Guaiacol peroxidase (GPX) activity was increased by 185 and 62% in leaves and roots, respectively. Non-enzymatic antioxidant capacity (assayed by ABTS test) was maintained unchanged in all plant organs. The model halophytic plant Thellungiella salsuginea was used as a biomarker of phenanthrene stress severity and was grown at 0 (control), 125, 250, and 375 ppm. T. salsuginea plants grown on the sand previously contaminated by 500 ppm Phe then treated by C. maritma culture (phytoremediation culture) showed similar biomass production as plants subjected to 125 ppm Phe. This suggests that the phytotoxic effects of phenanthrene were reduced by 75% by the 6-week treatment by C. maritima. Our findings indicate that C. maritima can constitute a potentially good candidate for PAH phytoremediation.

Effects of the halophytes Tecticornia indica and Suaeda fruticosa on soil enzyme activities in a Mediterranean Sabkha.

In the present work, we studied the effectiveness of the predominant halophytes of Soliman sabkha (Tecticornia indica and Suaeda fruticosa) to promote soil biological activities and ecosystem productivity. Soil Arylsulphatese ARY, beta-glucosidase beta-GLU, phosphatase PHO, invertase INV, urease URE, and dehydogenase DES activities in Extra- and Intra-tuft halophytes and plant productivity were assessed. Results revealed a high increase of microbial community and ARY, beta-GLU, PHO, INV URE and DES activities (+298%, +400%, +800%, +350%, +320%, +25% and +759%, respectively) in Intra-tuft rhizosphere as compared to Extra-tuft one, which is likely due to the significant decrease of salinity in the rhizosphere of Tecticornia indica and Suaeda fruticosa. Both perennial plants exhibited high productivities (7.4 t dry weight ha(-1) and 2.2 t dry weight ha(-1), respectively) and Na+-hyperaccumulating capacities (0.75 t Na+ ha(-1) and 0.22 t Na+ ha(-1), respectively), reducing salt constraint and favouring soil fertility. This constitutes a promising alternative to enhance productivity in such a salt-affected biotope by offering suitable microhabitat for annual glycophytes.

Phytodesalination of a moderately-salt-affected soil by Sulla carnosa.

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.

OPTIMIZATION OF SALT CONCENTRATIONS FOR A HIGHER CAROTENOID PRODUCTION IN DUNALIELLA SALINA (CHLOROPHYCEAE)(1).

Dunaliella salina (Dunal) Teodor, when treated over 25 d with a wide range of NaCl salinities (0.6-4.5 M), showed its maximal growth potentialities at 1.5-3.0 M NaCl and was able to survive even at 4.5 M NaCl. Sodium concentrations increased significantly at the supraoptimal salinities, reaching up to 5 mmol · g(-1) dry weight (dwt) at 4.5 M NaCl. Interestingly, ability of D. salina to take up essential mineral nutrients was not impaired by increased salinity. As for growth, chl concentrations were maximal in the 1.5-3.0 M NaCl range. Interestingly, carotenoid concentrations increased with the increasing salinity. The highest values of total antioxidant activity (5.2-6.9 mg gallic acid equivalents [GAE] · g(-1) dwt), antiradical activity, and reducing power were measured at 1.5-3.0 M NaCl. As a whole, these results showed that at 1.5-3.0 M NaCl, D. salina produce appreciable antioxidant level. But, once it reaches its growth maximum, a salt addition up to 4.5 M could enhance its carotenoid yield.

Localization of potential ion transport pathways in vesicular trichome cells of Atriplex halimus L.

The secreting glandular trichomes are recognized as an efficient structure that alleviates salt effects on Atriplex halimus. They are found on buds, young green stems, and leaves. They occupy both the leaf surfaces and give them a whitish color. Their histogenesis and ultrastructure were investigated in the third young leaves. They appear in early stage of plant development and its initiation continuous until just the leaf final development state. Each trichome contains two parts; a stalk which has high electron opacity, embedded in epidermal cells, and bears a second one which is unicellular, called bladder cell and has a low electron density. The bladder cell appears as a huge vacuole and the well-reduced cytoplasm which is pushed close to the wall, contains only a few organelles. Concurrently, the use of silver chloride precipitation technique shows that, in secretion process, salt follows a symplasmatic pathway which is consolidated by the presence of numerous plasmodesmata between the stalk cell(s), and the bladder one and the neighboring mesophyll cells. In addition, according to lanthanum-tracer study, salt can be excreted apoplastically. In fact, the heavy element can be transported via endocytosis vesicles, and by Golgi, endoplasmic reticulum, and lysosome (G.E.R.L.) network toward the storage vacuoles.

Sesuvium portulacastrum maintains adequate gas exchange, pigment composition, and thylakoid proteins under moderate and high salinity.

Cuttings of Sesuvium portulacastrum L. (Aizoaceae) were taken from plants cultivated under severe saline conditions. The obtained seedlings were grown on sand and irrigated with nutrient solution over 5 weeks under no (0 mM NaCl), moderate (200 mM NaCl), or high (400 mM NaCl) salinity conditions. A follow-up of gas exchange was performed weekly and pigment levels and patterns of fully expanded leaves were determined after 3 and 5 weeks of treatment. At the end of the 5-week period, immunoblot analysis of the main polypeptides of photosystem I and II was performed with the aim to investigate salt-induced variations in photosystem composition. Net CO2 assimilation rate (Pn) increased under salinity up to 3 weeks of treatment then decreased to reach the value of 0mM-treated plants at the end of the experiment. For stomatal conductance (gs) and intercellular CO2 concentration (Ci), the opposite occurred. These results were concomitant with an increase in practically all pigment levels, mainly under high salinity, with the exception of zeaxanthin. The de-epoxidation index (DEPS index) was much lower under saline than non-saline conditions in the 3rd week, indicating light stress in 0mM-treated plants. At the end of the experiment, this index showed much lower values with no significant differences between treatments, which coincided with no significant differences in gas exchange as well. Protein amounts of D1, CP47, and CP43 did not show noticeable variations with salt treatment, whereas LHCII underwent a slight but significant decrease (-15%) at the highest NaCl concentration. LHCI polypeptides were unaffected by the salt treatments, where conversely, the highest concentration induced a significant decrease in PsaA/B amount (-18%).

Differences in efficient metabolite management and nutrient metabolic regulation between wild and cultivated barley grown at high salinity.

Physiological and biochemical responses of Hordeum maritimum and H. vulgare to salt stress were studied over a 60-h period. Growth at increasing salinity levels (0, 100, 200 and 300 mM NaCl) was assessed in hydroponic culture. H. maritimum was shown to be a true halophyte via its typical behaviour at high salinity. Shoot growth of cultivated barley was gradually reduced with increasing salinity, whereas that of wild barley was enhanced at 100 and 200 mm NaCl then slightly reduced at 300 mM NaCl. The higher salt tolerance of H. maritimum as compared to H. vulgare was due to its higher capacity to maintain cell turgor under severe salinity. Furthermore, H. maritimum exhibited fine regulation of Na(+) transport from roots to shoots and, unlike H. vulgare, it accumulated less Na(+) in shoots than in roots. In addition, H. maritimum can accumulate more Na(+) than K(+) in both roots and shoots without the appearance of toxicity symptoms, indicating that Na(+) was well compartmentalized within cells and substituted K(+) in osmotic adjustment. The higher degree of salt tolerance of H. maritimum is further demonstrated by its economic strategy: at moderate salt treatment (100 mm NaCl), it used inorganic solutes (such as Na(+)) for osmotic adjustment and kept organic solutes and a large part of the K(+) for metabolic activities. Indeed, K(+) use efficiency in H. maritimum was about twofold that in H. vulgare; the former started to use organic solutes as osmotica only at high salinity (200 and 300 mm NaCl). These results suggest that the differences in salt tolerance between H. maritimum and H. vulgare are partly due to (i) differences in control of Na(+) transport from roots to shoots, and (ii) H. maritimum uses Na(+) as an osmoticum instead of K(+) and organic solutes. These factors are differently reflected in growth.

Phytodesalination of a salt-affected soil with the halophyte Sesuvium portulacastrum L. to arrange in advance the requirements for the successful growth of a glycophytic crop.

In the present work, we studied the potential of the obligate halophyte, Sesuvium portulacastrum L., to desalinize an experimentally-salinized soil after the following criteria: (i) decrease in soil salinity and sodicity, (ii) plant biomass capacity to accumulate sodium ions, and (iii) phytodesalinized soil quality (equivalent to growth of a glycophytic test culture of Hordeum vulgare L.). The cultivation of the halophyte on the salinized soil (phytodesalination culture) led to a marked absorption of Na(+) ions by S. portulacastrum roots and their accumulation in the above-ground biomass up to 872 mg plant(-1) and 4.36 g pot(-1) (about 1 tha(-1)). The decrease in salinity and sodicity of the phytodesalinized soil significantly reduced the negative effects on growth of the test culture of H. vulgare. Furthermore, the phytodesalination enabled H. vulgare plants to keep a high water content and to develop a higher biomass with relatively high K and low Na contents.

Effectiveness of compost use in salt-affected soil.

Soil degradation and salinization are two of the utmost threat affecting agricultural areas, derived from the increasing use of low quality water and inappropriate cultural practices. The problem of low productivity of saline soils may be ascribed not only to their salt toxicity or damage caused by excess amounts of soluble salts but also arising from the lack of organic matter and available mineral nutrients especially N, P, and K. Concerns about salinization risk and environmental quality and productivity of agro-ecosystems have emphasized the need to develop management practices that maintain soil resources. Composted municipal solid waste (MSW) was commonly used to enhance soil productivity in the agricultural lands and rebuild fertility. However, their application could be also a promising alternative to alleviate the adverse effects caused by soil salinization. MSW compost, with high organic matter content and low concentrations of inorganic and organic pollutants allow an improvement of physical, chemical and biochemical characteristics and constitute low cost soil recovery.

Iron deficiency tolerance traits in wild (Hordeum maritimum) and cultivated barley (Hordeum vulgare).

Phytosiderophores (PS) are Fe(III)-solubilizing compounds released by Poaceae roots under iron deficiency conditions. Several studies focused on the capacity of these plants to secrete PS as a center of their iron deficiency tolerance, and little information is available on other traits such as root/shoot biomass ratios, iron use efficiency, photosynthetic activity, and iron mobilization capacity that might also contribute to iron deficiency tolerance. In this study, we evaluated some traits other than PS release capacity that could be responsible for differences in iron deficiency tolerance in two barley species, Hordeum maritimum and Hordeum vulgare. Results showed that under iron starvation, biomass production was affected in both species, but H. maritimum kept higher root/shoot ratios due to the distribution efficiency of carbohydrates within the plant and the growth flexibility of its organs. Both species responded to iron starvation by an early release of PS, but they differed in their secretion capacity. In cultivated barley, the PS release rate was 1.5-2-fold higher than that of wild barley. This behavior was also concomitant with no modification in shoot iron concentration of the latter, which may lead to a low stimulation of its PS release as compared to the former. The amount of Fe(3+) mobilized by root exudates was determined at different pH values (between 5.6 and 8.6). Results showed a decrease in the mobilization capacity with the increasing pH, mainly in H. vulgare. At 8.6, it was reduced by 50% in H. vulgare and 30% in H. maritimum. These data suggest that differences in Poaceae tolerance to iron deficiency is attributed not only to PS secretion capacity, but also to carbohydrate distribution within the plant, Fe use efficiency, and root exudates capacity to mobilize Fe(III).

Application of municipal solid waste compost reduces the negative effects of saline water in Hordeum maritimum L.

The efficiency of composted municipal solid wastes (MSW) to reduce the adverse effects of salinity was investigated in Hordeum maritimum under greenhouse conditions. Plants were cultivated in pots filled with soil added with 0 and 40tha(-1) of MSW compost, and irrigated twice a week with tap water at two salinities (0 and 4gl(-1) NaCl). Harvests were achieved at 70 (shoots) and 130 (shoots and roots) days after sowing. At each cutting, dry weight (DW), NPK nutrition, chlorophyll, leaf protein content, Rubisco (ribulose-bisphosphate carboxylase/oxygenase) capacity, and contents of potential toxic elements were determined. Results showed that compost supply increased significantly the biomass production of non salt-treated plants (+80%). This was associated with higher N and P uptake in both shoots (+61% and +80%, respectively) and roots (+48% and +25%, respectively), while lesser impact was observed for K+. In addition, chlorophyll and protein contents as well as Rubisco capacity were significantly improved by the organic amendment. MSW compost mitigated the deleterious effect of salt stress on the plant growth, partly due to improved chlorophyll and protein contents and Rubisco capacity (-15%, -27% and -14%, respectively, in combined treatment, against -45%, -84% and -25%, respectively, in salt-stressed plants without compost addition), which presumably favoured photosynthesis and alleviated salt affect on biomass production by 21%. In addition, plants grown on amended soil showed a general improvement in their heavy metals contents Cu2+, Pb2+, Cd2+, and Zn2+ (in combined treatment: 190%, 53%, 168% and 174% in shoots and 183%, 42%, 42% and 114% in roots, respectively) but remained lower than phytotoxic values. Taken together, these findings suggest that municipal waste compost may be safely applied to salt-affected soils without adverse effects on plant physiology.