Littérature scientifique sur le sujet « Odontarrhena »

In the recent treatment of the tribe Alysseae (Španiel et al. 2015), many taxa of the genus Alyssum Linnaeus (1753: 650) were transferred to Odontarrhena C.A.Mey. ex Ledebour (1830: 15). Odontarrhena clearly differs from Alyssum in molecular markers and morphological characters such as a predominantly compound inflorescence and monospermous locules of silicles (versus a usually simple raceme and silicles with two seeds in each locule). A list of accepted species and numerous new combinations of Odontarrhena were recently published (Španiel et al. 2015). However, two species names, Alyssum mozaffarianii Kavousi (2001: 48) and A. baldaccii Vierhapper ex Nyárády (1928: 123), were previously overlooked or misinterpreted and their respective combinations within Odontarrhena were not established. The new combinations are presented here together with taxonomic notes, a new synonym and newly designated lectotypes of four names of Odontarrhena taxa.

A comparative research on the impact of organic amendments on the soil characteristic and uptake of heavy metals, micro and macroelements of Odontarrhena chalcidica has been carried out. Experiments have been implemented in controlled conditions. The serpentine soil used in this experiment was sampled from the vicinity of the village Kazak, Bulgaria. The pot experiment was a randomized complete block design containing 9 treatments and three replications (27 pots). The treatments consisted of a control (no organic meliorants), and compost, vermicompost, biochar and activated carbon (added at 2.5% and 5.0%, respectively, recalculated based on dry soil weight). The application of organic additives to the soil influences the physicochemical properties and leads to an increase in organic matter and the content of macroelements (P, K, Ca and Mg) and trace elements (Fe, Mn, Zn) in the soil. The application of organic additives to the soil affects the uptake of Ni, micro and macroelements by Odontarrhena chalcidica. Plant biomass increased significantly, and there was a clear correlation between the amount of supplement applied and the increase in biomass. Organic additives had a positive effect on yield, influenced by the type of additive and dose. Ni yield was 3 times higher in the variants with 5% compost and 2.5% vermicompost input. The application of biochar resulted in a twofold decrease in Ni yield, while the application of activated carbon resulted in a marginal increase.

The elemental defense hypothesis supports that metal hyperaccumulation in plant tissues serves as a mechanism underpinning plant resistance to herbivores and pathogens. In this study, we investigate the interaction between Odontarrhena lesbiaca and broomrape parasitic species, in the light of the defense hypothesis of metal hyperaccumulation. Plant and soil samples collected from three serpentine sites in Lesbos, Greece were analyzed for Ni concentrations. Phelipanche nowackiana and Phelipanche nana were found to infect O. lesbiaca. In both species, Ni concentration decreased gradually from tubercles to shoots and flowers. Specimens of both species with shoot nickel concentrations above 1000 mg.kg−1 were found, showing that they act as nickel hyperaccumulators. Low values of parasite to O. lesbiaca leaf or soil nickel quotients were observed. Orobanche pubescens growing on a serpentine habitat but not in association with O. lesbiaca had very low Ni concentrations in its tissues analogous to excluder plants growing on serpentine soils. Infected O. lesbiaca individuals showed lower leaf nickel concentrations relative to the non-infected ones. Elevated leaf nickel concentration of O. lesbiaca individuals did not prevent parasitic plants to attack them and to hyperaccumulate metals to their tissues, contrary to predictions of the elemental defense hypothesis.

Due to the high nickel concentrations, serpentine soils provide a very restrictive and selective environment for plant life. Some plants, termed “Ni-hyperaccumulators”, are adapted to live on these heavy-metal-enriched soils without toxicity symptoms. Ni-hyperaccumulators are increasingly important for research on metal tolerance, homeostasis and biotechnological applications. This project aims to investigate nickel accumulation in taxa and populations of Odontarrhena, a genus of tribe Alysseae (Brassicaceae) that includes over 85 species many of which are Ni-hyperaccumulators. Based on a previous systematic study conducted on poorly-known populations of Odontarrhena native to Albania we performed a molecular study to characterize taxa and populations of this genus. To this purpose we used DNA sequencing and the AFLP-fingerprint technique to reconstruct the species phylogenetic relationships and the population differentiation patterns in relation to their distribution, ploidy level, intensity of anthropic site disturbance, altitude, soil type and metal concentration population (Ni, Cr, Co, Ca, Mg). We found significant population differentiation, dominance of within-population variation, no isolation by geographic distance and existence of six genetic groups variously represented across the six taxa possibly due to hybridization especially in disturbed sites. Next, we compared metal concentrations in native Odontarrhena populations from Albania in relation to their soil of origin. We determined the concentration of the most important trace metals (Ni, Co, Cr, Mg, Ca, K, Fe and Mn) in soil, plant roots and shoots of five taxa from 20 different outcrops. We found large differences in mineral element concentrations in soils and also between the plants; shoot Ni concentrations in Albanian Odontarrhena taxa depend on soil Ni concentrations but not on species identity. For O. chalcidica, the most widely distributed species, this “environmental fingerprint” was found not only for Ni, but also for Ca and Mg. After these investigations on native populations from the natural environment, we designed an experimental study in controlled conditions. Plant seedlings of seven taxa and 11 populations of Odontarrhena from serpentine and non-serpentine sites of the Balkan peninsula and Italy were cultivated in hydroponics with increasing NiSO4 concentrations to determine plant growth and Ni accumulation. These plantlets were analyzed to test inter- and intra-specific differences in nickel tolerance and accumulation, in relation to Ni levels in the soils and in wild plants. We found a metal stimulatory effect on growth that was present in the low-dose zone and significantly fitted the Brain-Cousens hormetic model. Taxa showed broad variation in tolerance, with the most tolerant plants requiring the highest Ni concentration for optimal growth. Our data suggested that tolerance is associated with hyperaccumulation ability. Among the obligate and facultative serpentinophytic species of Odontarrhena that have been investigated we found a notable exception, O. sibirica, a facultative serpentinophyte in which accumulation ability was enigmatic from previous studies. We addressed this issue using observational and experimental methods as in our previous researches. We found that Ni-concentrations in the native populations sampled on serpentine soils in Greece were always much lower than the hyperaccumulation threshold. When cultivated together with other Ni-accumulating Odontarrhena species on the same natural ultramafic soil, O. sibirica was the only one unable to accumulate the metal. When grown in hydroponics at different NiSO4 levels Ni-accumulation occurred only at higher concentrations which, however, had a toxic effect. This peculiar combination of Ni-response traits could be the result of a partial evolutionary loss of ability with respect to all other Ni-accumulating congeneric species. For its unique characteristics, O. sibirica could therefore represent a unique model system for further studies on the evolutionary dynamics, physiological mechanisms and genetic control of metal accumulation and homeostasis. In a parallel study, we investigated photosynthesis responses of the same plants using an experimental approach. In non-hyperaccumulator plants, toxicity symptoms to above 10 μg g-1 DW nickel concentrations in soils can include inhibition of photosynthesis, impaired nitrogen assimilation and disturbed enzyme activity. However, there is a complete lack of information about how Ni-hyperaccumulators reconcile that extraordinary amount of metal in their shoots with an efficient photosynthetic activity, or at least on which photosynthetic parameters the excess of Ni impacts less in these plants. We measured Ni effects on growth, root and shoot metal accumulation and several photosynthetic parameters, such as gas exchange, chlorophyll fluorescence analyses and pigments content in three Odontarrhena taxa (two hyperaccumulators, one not) grown in hydroponics and exposed to three NiSO4 treatments. We found that Ni-hyperaccumulators species are photosynthetically more efficient under Ni excess in respect to the non-accumulating species. In fact, Ni treatment in O. chalcidica increased not only the photochemical efficiency of PSII and the CO2 assimilation rate, but also the stomatal conductance. Finally, this project focused on the determination of the activity of the enzyme urease, the only Nimetalloenzyme known so far in plants, in selected Odontarrhena taxa. The hypothesis to test was whether the high basal requirement for this micronutrient in these plants could be linked to a depletion of the Ni cytosolic pool at low external metal concentration, due to hyperaccumulation mechanism and impairing urease activity. To this purpose, enzyme activity and Ni shoot concentration were determined in plants of accumulating and non-accumulating taxa of Odontarrhena cultivated on Ni-rich serpentine soil and on garden soil, as well as in samples of O. bertolonii cultivated in hydroponics at increasing Ni concentrations. Odontarrhena hyperaccumulators showed similar urease activity when grown on both kinds of soils, with no relation between the enzyme activity and the leaf Ni accumulation. Contrarily, clear indications came from the experiment in controlled conditions, where the presence of Ni determined a progressive stimulation, in respect to control samples, of the activity of the enzyme, associated with an increase in shoot metal concentration. A significant relationship was found between the levels of urease activity and the amount of Ni accumulated in the leaves. Therefore, the already known Ni-stimulated growth of O. bertolonii at increasing metal concentrations in the low-dose zone could be explained by a Ni-induced activity of urease, associable to an enhanced nitrogen metabolism, unless other still unknown physiological functions of Ni in hyperaccumulating plants.

La connaissance de la diversité microbienne des milieux ultramafiques est essentielle pour établir le fonctionnement écologique de ces milieux, qui présentent de fortes teneurs en Ni et sont caractérisés par une flore particulière, e.g. plantes hyperaccumulatrices de Ni. La rhizosphère des hyperaccumulateurs comporte une forte proportion de bactéries résistantes au Ni, qui peuvent aussi agir sur la nutrition des plantes et sur les propriétés physico-chimiques du sol. Le premier défi de cette thèse a été de cerner le déterminisme de la diversité bactérienne de la rhizosphère d’hyperaccumulateurs de Ni. Le second a été de tester l'intérêt de souches PGPR (Plant Growth Promoting Rhizobacteria) pour optimiser l'agromine à partir d'interactions entre les rhizobactéries et les hyperaccumulateurs de Ni. La démarche s'est appuyée sur un ensemble de prospections dans deux régions climatiques et sur des analyses de séquençage haut débit. Des tests de cultures de plantes hyperaccumulatrices inoculées ont également été conduits. Les résultats montrent que le déterminisme de la diversité bactérienne est variable selon l'échelle spatiale. A l'échelle mondiale, le type de végétation est le facteur majeur structurant les communautés bactériennes, elle-même contrôlée indirectement par le climat. L’influence directe du climat (température et humidité) sur la diversité est significative mais moindre. A l'échelle d'une région climatique, la physico-chimie des sols ultramafiques structure et détermine la diversité des communautés bactériennes rhizosphériques. Enfin, l'inoculation de souches PGPR fortement bioaccumulatrices de Ni modifie la dynamique du Ni dans le sol, ce qui démontre qu'il existe une compétition pour le Ni entre la plante et la bactérie inoculée. En conclusion, le déterminisme de la diversité des communautés bactériennes rhizosphériques est dépendant de l'échelle spatiale considérée. En outre, le choix de la souche PGPR à inoculer, dans un contexte d'amélioration de l'agromine du Ni, est primordial
Knowledge of the microbial diversity in ultramafic areas is essential to establish the ecological functioning of these environments, which display high level of Ni and are characterized by the presence of particular plants, e.g. Ni hyperaccumulators. The rhizosphere of these plants promotes a high proportion of Ni resistant bacteria that can act on plant nutrition and soil physicochemical properties. The first challenge of this thesis was to understand the bacterial rhizosphere diversity of Ni hyperaccumulators. The second was to test the interest of PGPR (Plant Growth Promoting Rhizobacteria) strains in order to improve agromining based on rhizobacteria and Ni hyperaccumulators interactions. The approach was based on two-contrasted climatic areas prospection and on high-throughput sequencing analyzes. Tests on culture of hyperaccumulator plants inoculated were also conducted. The results show that the determinism of this bacterial diversity is variable according to the spatial scale. On a global scale, the vegetation type, indirectly influenced by the climate, is the major factor structuring bacterial communities. The direct influence of the climate (temperature and humidity) on bacterial diversity is significant but lower. At the scale of a climatic region, the physic-chemistry of ultramafic soils structures and determines the rhizosphere bacterial community diversity. Finally, the inoculation of highly Ni bioaccumulative PGPR strains modifies the Ni dynamic in the soil, demonstrating that there is a competition for this metal between the inoculated bacteria and the hyperaccumulator plant. In conclusion, the rhizosphere bacterial community diversity is dependent on the considered spatial scale. Furthermore, these results emphasize how the choice of the PGPR strain to inoculate is important in order to improve Ni agromining