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International audience; The essential oils obtained from Origanum libanoticum Boiss., a plant endemic to Lebanon, were analyzed by GC/MS. Seventy compounds were identified, covering till 99.8% of the total oil composition. All samples were p-cymene and/or beta-caryophyllene chemotype, with variable percentage of other compounds such as alpha-pinene, myrcene, a-phellandrene, limonene, etc. Compared to traditional drying method, lyophilized samples provided the highest essential oil (EO) yields and yields were higher at flowering stage (Chouwen: 0.33% in 2013 and 0.32% in 2014; Qartaba: 0.27% in 2013 and 0.37% in 2014). According to independent components analysis (ICA), date and site of harvest, altitude and drying technique had no effect on the variation of O. libanoticum EO, chemical composition. An annual variation of EOs composition was observed since a particular variation in some major components concentration was revealed monthly and annually between 2013 and 2014.

The essential oils were extracted by hydrodistillation from Satureja cuneifolia, Satureja thymbra, Coridothymus capitatus, Thymus syriacus and Thymbra spicata growing wild in Lebanon. Their phytochemical analysis performed by GC/MS showed that the aforementioned species are characterized either by carvacrol (60.9%) or thymol (54.3%) or by a more or less equal amounts of these two phenols. Assessment of their in vitro antimicrobial activity against Candida albicans and six pathogenic bacteria using the broth dilution method revealed that the tested oils have a broad activity spectrum with minimum inhibitory concentration ranging from 0.1 to 0.8 mg/ml. Among the tested species, S. thymbra EO showed the highest antimicrobial potential whereas T. syriacus showed the lowest inhibitory activity. These results give scientific evidence for the use of those species in the Lebanese folk medicine and lend support to implement them as natural alternatives for synthetic antimicrobials. This article is protected by copyright. All rights reserved.

International audience; AbstractThis study deals with the variation in the yield and composition of Lebanese Origanum syriacum L. essential oil (EO) according to harvesting time, drying methods used, and geographical location. Plant material was harvested twice a month all over 2013 and 2014 from Qartaba and Achkout located at high altitude and from Byblos at low altitude. EOs of the aerial parts were obtained by hydrodistillation. The highest yields were obtained at full flowering stage and slightly reduced after flowering. The GC/MS analysis revealed the presence of 50 components representing 90.49 – 99.82%, 88.79 – 100%, and 95.28 – 100% of the total oil extracted from plants harvested from Qartaba, Achkout, and Byblos, respectively. The major components in the oils were: carvacrol (2.1 – 79.8%), thymol (0.3 – 83.7%), p‐cymene (2.8 – 43.8%), thymoquinone (0.4 – 27.7%), γ‐terpinene (0.4 – 10.0%), octan‐3‐ol (0.3 – 4.9%), caryophyllene oxide (0.2 – 4.7%), oct‐1‐en‐3‐ol (0.3 – 3.7%), β‐caryophyllene (0.7 – 3.2%), cis‐sabinene hydrate (0.1 – 2.8%), terpinen‐4‐ol (0.1 – 2.8%), and α‐terpinene (0.2 – 2.2%). Independent components analysis (ICA) revealed that two groups were discriminated, reflecting compositional differences in the EOs profiles of the Lebanese oregano samples: O. syriacum grown in Qartaba and Achkout belongs to carvacrol chemotype, while O. syriacum grown in Byblos belongs to thymol chemotype. The flowering phase was the most productive period in terms of yield, bringing marked changes in the EO composition by increasing the amounts of carvacrol or thymol, and decreasing those of thymoquinone and p‐cymene.

A soybean cytosolic glutamine synthetase gene (GS15) was fused with the constitutive 35S cauliflower mosaic virus (CaMV) promoter in order to direct overexpression in Lotus corniculatus L. plants. Following transformation with Agrobacterium rhizogenes, eight independent Lotus transformants were obtained which synthesized additional cytosolic glutamine synthetase (GS) in the shoots. To eliminate any interference caused by the T-DNA from the Ri plasmid, three primary transformants were crossed with untransformed plants and progeny devoid of TL- and TR-DNA sequences were chosen for further analyses. These plants had a 50-80% increase in total leaf GS activity. Plants were grown under different nitrogen regimes (4 or 12 mM NH4+) and aspects of carbon and nitrogen metabolism were examined. In roots, an increase in free amino acids and ammonium was accompanied by a decrease in soluble carbohydrates in the transgenic plants cultivated with 12 mM NH4+ in comparison to the wild type grown under the same conditions. Labelling experiments using 15NH4+ were carried out in order to monitor the influx of ammonium and its subsequent incorporation into amino acids. This experiment showed that both ammonium uptake in the roots and the subsequent translocation of amino acids to the shoots was lower in plants overexpressing GS. It was concluded that the build up of ammonium and the increase in amino acid concentration in the roots was the result of shoot protein degradation. Moreover, following three weeks of hydroponic culture early floral development was observed in the transformed plants. As all these properties are characteristic of senescent plants, these findings suggest that expression of cytosolic GS in the shoots may accelerate plant development, leading to early senescence and premature flowering when plants are grown on an ammonium-rich medium.

In this paper we discuss the ways in which our understanding of the nature of the molecular controls of nitrogen assimilation has been increased by the use of non-leguminous and leguminous plants with genetically-altered capacities for ammonia assimilation. Using tobacco or Lotus as model plants, Glutamine synthetase (GS) and glutamate synthase (GOGAT) activities have been altered by stimulating or inhibiting in an organ- or tissue-specific manner the expression of the corresponding genes. In a few selected examples, the physiological impact of these genetic manipulations has been studied on plants grown under different nitrogen regimes. The use of such genetically-modified plants will allow us to better understand the molecular control of this metabolic pathway. It is also potentially of great importance in agriculture if such internal and stable modifications are beneficial in terms of nitrogen use efficiency, thus avoiding an excessive utilization of fertilizers or herbicides (GS inhibitors). Our current knowledge and prospects for future development are explored. Manipulation der NH4-Assimilation in transgenen Nicht-Leguminosen und Leguminosen Das Verstandnis der molekularen Steuerungsmechanismen der Stickstoffassimilation ist durch die Verwendung von Pflanzen mit genetisch veranderter Kapazitat der NH4+-Assimilation betrachtlich gewachsen. Bei den Modellpflanzen Tabak (fur Nicht-Leguminosen) und Lotus corniculatus (fur Leguminosen) lassen sich die Aktivitaten der Glutaminsynthetase (GS) und der Glutamatsynthase (GOGAT) auf Organ-und Gewebsebene durch Stimulierung oder Hemmung der Expression der entsprechenden Gene verandern. Die physiologischen Konsequenzen dieser Genmanipulation wurden an Pflanzen unterschiedlicher N-Versorgung untersucht. Sollten sich solche internen und stabilen Modifikationen der Pflanzen als gunstig im Hinblick auf eine Verbesserung der N-Dungereffizienz erweisen, konnte zukunftig der Aufwand fur N-Dunger und (uber die GS-Inhibierung wirkende) Herbizide reduziert werden. Die Chancen hierfur bedurfen jedoch noch weiterer Forschung.

Our understanding of plant growth in response to nitrogen (N) supply is mainly based on studies of mutants and transformants. This study explored the natural variability of Arabidopsis thaliana first to find out its global response to N availability and secondly to characterize the plasticity for growth and N metabolism among 23 genetically distant accessions under normal (N+), limited (N-), and starved (N0) N supplies. Plant growth was estimated by eight morphological traits characterizing shoot and root growth and 10 metabolic parameters that represented N and carbon metabolism. Most of the studied traits showed a large variation linked to genotype and nutrition. Furthermore, Arabidopsis growth was coordinated by master traits such as the shoot to root ratio of nitrate content in N+, root fresh matter and root amino acids in N-, and shoot fresh matter together with root thickness in N0. The 23 accessions could be gathered into four different groups, according to their growth in N+, N-, and N0. Phenotypic profiling characterized four different adaptative responses to N- and N0. Class 1 tolerated N limitation with the smallest decrease in shoot and root biomass compared with N+, while class 2 presented the highest resistance to N starvation by preferential increased root growth, huge starch accumulation, and high shoot nitrate content. In contrast, class 3 plants could tolerate neither N limitation nor N starvation. Small plants of class 4 were different, with shoot biomass barely affected in N- and root biomass unaffected in N0.

To address the questions of whether allocation of carbohydrates to roots is influenced by ionic form of nitrogen absorbed and whether allocation of carbohydrates to roots in turn influences proportionality between NH4+ and NO3- uptake from mixed sources, NH4+ and NO3- were supplied separately to halves of a split-root hydroponic system and were supplied in combination to a whole-root system. Dry matter accumulation in the split-root system was 18% less in the NH4(+)-fed axis than in the NO3(-)-fed axis. This, however, does not indicate that partitioning of carbohydrate between the two axes was different. Most of the reduction in dry matter accumulation in the NH4(+)-fed axis can be accounted for by the retransport of CH2O equivalents from the root back to the shoot with amino acids produced by NH4+ assimilation. Uptake of NH4+ or NO3- by the respective halves of the split-root system was proportional to the estimated allocation of carbohydrate to that half. When NH4+ and NO3- were supplied to separate halves of the split-root system, the cumulative NH4+ to NO3- uptake ratio was 0.81. When supplied in combination to the whole-root system, the cumulative NH4+ to NO3- uptake ratio was 1.67. Thus, while the shoot may affect total nitrogen uptake through the export of carbohydrates to roots, the shoot (common for halves of the split-root system) apparently does not exert a direct effect on proportionality of NH4+ and NO3- uptake by roots. For whole roots supplied with both NH4+ and NO3-, the restriction in uptake of NO3- may involve a stimulation of NO3- efflux rather than an inhibition of NO3- influx. While only the net uptake of NH4+ and NO3- was measured by ion chromatography, monitoring at approximately hourly intervals during the first 3 days of treatment revealed irregularly occurring intervals of both depletion (net influx) and enrichment (net efflux) in solutions. In the case of NH4+, numbers of net efflux events were similar (21 to 24 out of 65 sequential sampling intervals) whether NH4+ was supplied with NO3- to whole-root systems or separately to an axis of the split-root system. In the case of NO3-, however, the number of net efflux events increased from 8 when NO3- was supplied to a separate axis of the split-root system to between 19 and 24 when NO3- was supplied with NH4+ to whole-root systems.

Soybean [Glycine max (L.) Merrill] plants that had been subjected to 15 d of nitrogen deprivation were resupplied for 10 d with 1.0 mol m-3 nitrogen provided as NO3-, NH4+, or NH4(+) + NO3- in flowing hydroponic culture. Plants in a fourth hydroponic system received 1.0 mol m-3 NO3- during both stress and resupply periods. Concentrations of soluble carbohydrates and organic acids in roots increased 210 and 370%, respectively, during stress. For the first day of resupply, however, specific uptake rates of nitrogen, determined by ion chromatography as depletion from solution, were lower for stressed than for non-stressed plants by 43% for NO3- resupply, by 32% for NH4(+) + NO3- resupply, and 86% for NH4+ resupply. When specific uptake of nitrogen for stressed plants recovered to rates for non-stressed plants at 6 to 8 d after nitrogen resupply, carbohydrates and organic acids in their roots had declined to concentrations lower than those of non-stressed plants. Recovery of nitrogen uptake capacity of roots thus does not appear to be regulated simply by the content of soluble carbon compounds within roots. Solution concentrations of NH4+ and NO3- were monitored at 62.5 min intervals during the first 3 d of resupply. Intermittent 'hourly' intervals of net influx and net efflux occurred. Rates of uptake during influx intervals were greater for the NH4(+)-resupplied than for the NO3(-)-resupplied plants. For NH4(+)-resupplied plants, however, the hourly intervals of efflux were more numerous than for NO3(-)-resupplied plants. It thus is possible that, instead of repressing NH4+ influx, increased accumulation of amino acids and NH4+ in NH4(+)-resupplied plants inhibited net uptake by stimulation of efflux on NH4+ absorbed in excess of availability of carbon skeletons for assimilation. Entry of NH4+ into root cytoplasm appeared to be less restricted than translocation of amino acids from the cytoplasm into the xylem.

In non-nodulated soybean [Glycine max (L.) Merrill cv. Ransom] plants that were subjected to 15 d of nitrogen deprivation in flowing hydroponic culture, concentrations of nitrogen declined to 1.0 and 1.4 mmol Ng −1 dry weight in shoots and roots, respectively, and the concentration of soluble amino acids (determined as primary amines) declined to 40 μmol g −1 dry weight in both shoots and roots. In one experiment, nitrogen was resupplied for 10 d to one set of nitrogen-depleted plants as 1.0 mol m −3 NH 4 + to the whole root system, to a second set as 0.5 mol m −3 NH 4 + plus 0.5 mol m −3 NO 3 − to the whole root system, and to a third set as 1.0 mol m −3 NH 4 + to one-half of a split-root system and 1.0 mol m −3 NO 3 − to the other half

International audience; In a low-input agricultural context, plants facing temporal nutrient deficiencies need to be efficient. By comparing the effects of NOFormula-starvation in two lines of Arabidopsis thaliana (RIL282 and 432 from the Bay-0xShahdara population), this study aimed to screen the physiological mechanisms allowing one genotype to withstand NOFormula-deprivation better than another and to rate the relative importance of processes such as nitrate uptake, storage, and recycling. These two lines, chosen because of their contrasted shoot N contents for identical shoot biomass under N-replete conditions, underwent a 10 d nitrate starvation after 28 d of culture at 5 mM NOFormula. It was demonstrated that line 432 coped better with NOFormula-starvation, producing higher shoot and root biomass and sustaining maximal growth for a longer time. However, both lines exhibited similar features under NOFormula-starvation conditions. In particular, the nitrate pool underwent the same drastic and early depletion, whereas the protein pool was increased to a similar extent. Nitrate remobilization rate was identical too. It was proportional to nitrate content in both shoots and roots, but it was higher in roots. One difference emerged: line 432 had a higher nitrate content at the beginning of the starvation phase. This suggests that to overcome NOFormula-starvation, line 432 did not directly rely on the N pool composition, nor on nitrate remobilization efficiency, but on higher nitrate storage capacities prior to NOFormula-starvation. Moreover, the higher resistance of 432 corresponded to a higher nitrate uptake capacity and a 2–9-fold higher expression of AtNRT1.1, AtNRT2.1, and AtNRT2.4 genes, suggesting that the corresponding nitrate transporters may be preferentially involved under fluctuating N supply conditions.

In plants, water and anion parameters are linked, for example through the integration of nutritional signaling and the response to diverse stress. In this work, Arabidopsis thaliana is used as a model system to dissect the genetic variation of these parameters by quantitative trait loci (QTL) mapping in the 415 recombinant inbred lines of the Bay-0 × Shahdara population. Water, nitrate, chloride, and phosphate contents were measured at the vegetative stage in the shoots of plants grown in controlled conditions. Two contrasting nitrogen (N) conditions were studied, one leading to the complete depletion of the nitrate pool in the plants. Most of the observed genetic variation was identified as QTL, with medium but also large phenotypic contributions. QTL colocalization provides a genetic basis for the correlation between water and nitrate contents in nonlimiting N conditions and water and chloride contents in limiting N conditions. The 34 new QTL described here represent at least 19 loci polymorphic between Bay-0 and Shahdara; some may correspond to known genes from water/anion transport systems, while others clearly identify new genes controlling or interacting with water/anion absorption and accumulation. Interestingly, flowering-time genes probably play a role in the regulation of water content in our conditions.

When NO3 - is maintained at concentrations greater than those required to sustain maximum cumulative uptake by wheat (Triticum aestivum) and nonnodulated soybean (Glycine max [L.] Merrill), the net rate of uptake is not constant but oscillates between maxima and minima. The amplitudes of both the maxima and the minima increase with increases in NO3 - concentration of the solution. To determine if the amplitudes of oscillations decline when NO3 - in solution is maintained at suboptimal concentrations, net rates of NO3 - uptake were monitored daily during 22 d of vegetative growth under controlled environmental conditions for wheat from solutions containing 0.1, 0.25, 0.4, 0.5, 0.8, 1.5, 3.0, and 5.0 mM NO3 - and for soybean from solutions containing 0.05, 0.1, 0.5, and 1.0 mM NO3 -. The amplitudes of variations in daily net rates of NO3 - uptake increased with the increases in concentration of NO3 - in the nutrient solutions. The differences in magnitude of the amplitudes in oscillation, expressed as coeff...

Les agents de solidification influent sur la croissance des pousses du noyer cultivees in vitro. La gelrite a un effet benefique sur l'elongation des explants et la production de bourgeons, tandis que l'agar inhibe la croissance et provoque la maturation des feuilles ou encore des necroses. Les 2 agents de solidification presentent des differences importantes dans leurs teneurs en elements mineraux. Ils alterent la composition minerale du milieu de culture, comme celle des explants (.)

As a part of a project aimed at elucidating the causal relationship between reserve mobilisation and the extent of shedding in Vitis vinifera L., we compared storage and fate of carbon (C) and nitrogen (N) reserves in two varieties differing in their susceptibility to fruitlet abscission. Merlot (susceptible) and Pinot Noir (P. Noir, not susceptible) vines were grown in trenches under semi-controlled conditions over a 3-y period after planting. Mobilisation of stored C and N, distribution of reserve materials within the vines and 15N uptake were followed particularly during the spring growth flush and floral development in the third year. At dormancy, starch levels in the perennial tissues (roots, trunk, canes) were higher in Merlot than in P. Noir. During the spring growth flush, starch level decreased markedly in the roots of both cultivars until early bloom. At that time, starch started to accumulate in P. Noir but not in Merlot. Similar variations were found with total N. Accordingly, 15N analysis showed that translocation of storage N to the annual tissues was nearly achieved at early bloom in P. Noir while it continued until pea berry size in Merlot. In parallel, N uptake increased during the spring growth flush, and it was higher in P. Noir than in Merlot. These results indicate that transition between heterotrophic (root) and autotrophic (leaf) mode of nutrient allocation towards the developing inflorescences occurs earlier in P. Noir. Possible consequences are discussed in relation to the susceptibility of each cultivar to shedding.