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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.

The effects of water deficit stress on growth, Na+, K+ and osmolyte accumulation in the halophyte species Cakile maritima were investigated. Two Tunisian provenances, Tabarka and Chaffar, belonging to different bioclimatic stages, humid and arid, respectively, were compared. After germination, thirty-day-old seedlings were cultivated for 4 weeks under optimal or limiting water supply, at 100% and 25% of field capacity (FC), respectively. A subset of stressed plants was thereafter rehydrated. The final harvest was carried out after 60 days of treatment. Upon water deficit stress, Chaffar provenance showed significantly lower reduction in biomass production, net CO2 assimilation and stomatal conductance as well as of leaf water content. Leaf malondialdehyde (MDA) content was significantly increased in the two provenances but this effect was more pronounced in Tabarka plants than in Chaffar ones. Several criteria seem to be associated with the relative tolerance of Chaffar to water deficit: a slow growth rate, a greater ability to control photosynthetic gas exchange, a high ability to preferentially allocate photoassimilates to its roots, and a greater capacity for osmotic adjustment ensured by K+ and some compatible solutes such as proline and glycine betaine, but not soluble sugars. The superiority of Chaffar provenance also appeared at the level of its ability to recover after a severe water deficit stress (irrigation at 25% FC only during one month). The data suggest that compatible osmolytes (proline and glycine betaine) accumulated upon water deficit stress play important roles in this halophyte, being involved not only in osmotic adjustment but probably serving also in preservation of the structural and functional integrity at the cellular level during water deficit.

International audience; The effects of water deficit stress and recovery on growth, photosynthesis, physiological and biochemical parameters were investigated in the cultivated Beta vulgaris and in two Tunisian provenances (Soliman and Enfidha) of its wild relative B. macrocarpa. Seedlings were cultivated for 4 weeks under optimal or limiting water supply (respectively, 100% and 25% of field capacity, FC). After 2 weeks of treatment, a lot of stressed plants were rehydrated to 100% FC. In the Control, B. vulgaris was more productive than B. macrocarpa, whereas Enfidha provenance showed the highest biomass production (1.6- and 3-fold compared with B. vulgaris and Soliman, respectively), under water deficit stress. A partial re-establishment of growth occurred in both species upon recovery at 100% FC. The sensitivity of B. vulgaris and Soliman provenance to drought was associated with the disturbance of leaf water status and the sharp decrease in net CO2 assimilation (–66% and –82% as compared with the Control, respectively). On the contrary, the better behaviour of Enfidha provenance was related to its better photosynthetic capacity and leaf relative water content, along with a higher accumulation of amino acids (proline, glycine, and glutamine) implied in the osmotic adjustment. Leaf hexose concentration increased significantly under drought stress in both species whereas leaf sucrose concentration declined only in drought-stressed B. vulgaris and Soliman provenance. Leaf glutamate dehydrogenase activity increased under water deficit in both species despite to a higher extent in B. vulgaris. As glutamate dehydrogenase is implied in catabolism of glutamate to oxoglutarate, it might contribute to provide stressed plants with carbon skeletons.Enfidha provenance of the spontaneous species B. macrocarpa could be used in the marginal arid ecosystems in order to limit the deficit in fodder and to improve the pastoral value of these regions. In addition, this species could serve as a source of genes for genetic improvement to water deficit stress.

Phosphorus (P) is an essential macronutrient for all living organisms. In plants, P is taken up from the rhizosphere by the roots mainly as inorganic phosphate (Pi), which is required in large and sufficient quantities to maximize crop yields. In today's agricultural society, crop yield is mostly ensured by the excessive use of Pi fertilizers, a costly practice neither eco-friendly or sustainable. Therefore, generating plants with improved P use efficiency (PUE) is of major interest. Among the various strategies employed to date, attempts to engineer genetically modified crops with improved capacity to utilize phytate (PA), the largest soil P form and unfortunately not taken up by plants, remains a key challenge. To meet these challenges, we need a better understanding of the mechanisms regulating Pi sensing, signaling, transport and storage in plants. In this review, we summarize the current knowledge on these aspects, which are mainly gained from investigations conducted in Arabidopsis thaliana, and we extended it to those available on an economically important crop, wheat. Strategies to enhance the PA use, through the use of bacterial or fungal phytases and other attempts of reducing seed PA levels, are also discussed. We critically review these data in terms of their potential for use as a technology for genetic manipulation of PUE in wheat, which would be both economically and environmentally beneficial.

Salinity stress reduces plant productivity, but low levels of salinity often increase plant growth rates in some species. We herein describe the effects of salinity on plant growth while focusing on nitrogen use. We treated Trifolium alexandrinum with two nitrogen concentrations and salinity levels and determined growth rates, mineral concentrations, nitrogen use efficiency, photosynthesis rates, and nitrate reductase (NR, E.C. 1.6.6.1) and glutamine synthetase (GS, EC 6.3.1.2) activities. The T. alexandrinum growth rate increased following treatment with 100 mM NaCl in low nitrogen (LN) and high nitrogen (HN) conditions. Salt treatment also increased root volume, intrinsic water use efficiency, and nitrogen use efficiency in LN and HN conditions. These changes likely contributed to higher biomass production. Salinity also increased accumulations of sodium, chloride, and phosphate, but decreased potassium and calcium levels and total nitrogen concentrations in all plant organs independently of the available nitrogen level. However, the effect of salt treatment on magnesium and nitrate concentrations in photosynthetic organs depended on nitrogen levels. Salt treatment reduced photosynthesis rates in LN and HN conditions because of inhibited stomatal conductance. The effects of salinity on leaf NR and GS activities depended on nitrogen levels, with activities increasing in LN conditions. In saline conditions, LN availability resulted in optimal growth because of low chloride accumulation and increases in total nitrogen concentrations, nitrogen use efficiency, and NR and GS activities in photosynthetic organs. Therefore, T. alexandrinum is a legume forage crop that can be cultivated in low-saline soils where nitrogen availability is limited.

International audience; Inorganic phosphate (Pi) and Zinc (Zn) are an essential macro- and micronutrients for plant survival. Control of Pi and Zn content in tissues is of major importance for normal plant growth and development. Zn deficiency typically leads to Pi over-accumulation in shoots (and vice versa), signifying the presence of complex interactions that link the homeostatic regulation of these two nutrients. Despite their primary importance, the molecular bases of these interactions remains poorly understood. Recent research has placed the co-regulation of these two elements at a limiting step in Pi and Zn distribution within plants, e.g. the loading of Pi and Zn into root xylem. In Arabidopsis thaliana, this process mainly involves members of the Phosphate 1 (PHO1 and PHO1;H1) family (for Pi) and the heavy metal ATPases protein (HMA2 and HMA4) family (for Zn). This review examines recent progress in determining the molecular mechanisms that regulate the loading of Pi and Zn into root xylem, by individually describing these specific genes. The first molecular evidence for their signalling crosstalk at this particular step of their transport in plants is also presented, with an emerging role for PHO1;H3. This recent progress is important for biotechnological and agronomic strategies aimed at enhancing Pi and Zn transfer to the aerial part of plants.

International audience; Inorganic phosphate (Pi) and zinc (Zn) are two essential nutrients for plant growth. In soils, these two minerals are either present in low amounts or are poorly available to plants. Consequently, worldwide agriculture has become dependent on external sources of Pi and Zn fertilizers to increase crop yields. However, this strategy is neither economically nor ecologically sustainable in the long term, particularly for Pi, which is a non-renewable resource. To date, research has emphasized the analysis of mineral nutrition considering each nutrient individually, and showed that Pi and Zn homeostasis is highly regulated in a complex process. Interestingly, numerous observations point to an unexpected interconnection between the homeostasis of the two nutrients. Nevertheless, despite their fundamental importance, the molecular bases and biological significance of these interactions remain largely unknown. Such interconnections can account for shortcomings of current agronomic models that typically focus on improving the assimilation of individual elements. Here, current knowledge on the regulation of the transport and signalling of Pi and Zn individually is reviewed, and then insights are provided on the recent progress made towards a better understanding of the Zn-Pi homeostasis interaction in plants.

Inorganic phosphate (Pi) and Zinc (Zn) are essential nutrients for normal plant growth. Interaction between these elements has been observed in many crop plants. Despite its agronomic importance, the biological significance and genetic basis of this interaction remain largely unknown. Here we examined the Pi/Zn interaction in two lettuce (Lactuca sativa) varieties, namely, “Paris Island Cos” and “Kordaat.” The effects of variation in Pi and Zn supply were assessed on biomass and photosynthesis for each variety. Paris Island Cos displayed better growth and photosynthesis compared to Kordaat under all the conditions tested. Correlation analysis was performed to determine the interconnectivity between Pi and Zn intracellular contents in both varieties. Paris Island Cos showed a strong negative correlation between the accumulation levels of Pi and Zn in shoots and roots. However, no relation was observed for Kordaat. The increase of Zn concentration in the medium causes a decrease in dynamics of Pi transport in Paris Island Cos, but not in Kordaat plants. Taken together, results revealed a contrasting behavior between the two lettuce varieties in terms of the coregulation of Pi and Zn homeostasis and provided evidence in favor of a genetic basis for the interconnection of these two elements.

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 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.

The present study was fixed as objective to compare the response to water deficit (33% of field capacity, FC) stress of eight cultivars of Medicago sativa, originating from the Mediterranean basin. Comparison was performed on some key parameters such as growth, relative water content, leaf water potential, MDA tissue content, electrolyte leakage and proline and soluble sugar tissue concentrations. In all cultivars, water deficit stress reduced the whole plant growth, increased the root/shoot DW ratio and led to a significant decrease in leaf relative water content and leaf water potential. In water-stressed plants and for the majority of cultivars, proline and soluble sugar concentrations increased significantly. The Tamantit cultivar originating from Algeria showed the better tolerance to water deficit stress. Some criteria are concomitant with this tolerance: (1) a high biomass production under stress conditions when compared to other cultivars (2) the root preferential development, (3) the better ability to accumulate proline and soluble sugars, and (4) the aptitude to protect its photosynthetic apparatus against the oxidative stress generated by the water deficit stress. Ecotipo Siciliano, originating from Italy was the most sensitive cultivar. The increase of proline and soluble sugars concentrations upon water deficit stress particularly in the most tolerant cultivar suggested their involvement in the osmotic adjustment.Key words: Medicago sativa, intraspecific variability, water deficit stress, osmotic adjustment, MDA.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; Lettuce (Lactuca sativa) is a plant species that shows high accumulation of cadmium, a toxic heavy metal. Lettuce is therefore a good model both for identifying determinants controlling cadmium accumulation in plant tissues and for developing breeding strategies aimed at limiting cadmium accumulation in edible tissues. In this work, 14-day-old plants from three lettuce varieties were grown for 8 days on media supplemented with cadmium concentrations ranging from 0 to 50 microM. Growth, as well as Cd(2+), Zn(2+), K(+), Ca(2+), NO(3)(-), SO(4)(2-), Cl(-), phosphate, malate and citrate root an shoot contents were analyzed. The three lettuce varieties Paris Island Cos, Red Salad Bowl and Kordaat displayed differential abilities to accumulate cadmium in roots and shoots, Paris Island Cos displaying the lowest cadmium content and Kordaat the highest. From the global analysis of the three varieties, three main trends were identified. First, a common negative correlation linked cadmium tissue content and relative dry weight reduction in response to cadmium treatments in the three varieties. Second, increasing cadmium concentration in the culture medium resulted in a parallel increase in zinc tissue content in all lettuce varieties. A common strong positive correlation between cadmium and zinc contents was observed for all varieties. This suggested that systems enabling zinc and cadmium transport were induced by cadmium. Finally, the cadmium treatments had a contrasting effect on anion contents in tissues. Interestingly, citrate content in shoots was correlated with cadmium translocation from roots to shoots, suggesting that citrate might play a role in cadmium transport in the xylem vessels. Altogether, these results shed light on three main strategies developed by lettuce to cope with cadmium, which could help to develop breeding strategies aimed at limiting cadmium accumulation in lettuce.