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Dans ce travail, l’évaluation des activités antioxydantes, antibactérienne, anti-âge et photoprotectrices ont été effectuées sur les parties aériennes de douze halophytes : dont 6 Tunisiennes et 6 françaises montre une variabilité importante en fonction de l’espèce.Cependant, la fraction MeoH60% se distingue par son activité antioxydante, antibactérienne ainsi que pour l’activité écran pour les deux plantes sélectionnées. Ensuite, les fractions MeOH20%, et MeOH40% présentent une activité anti-élastase et anti-collagénase importante pour Haloxylon articulatum alors que pour daucus carota les fractions MeOH20% et MeOH100% présentent les activités anti-élastase et anti-collagénase les plus intéressantes.L’évaluation du potentiel cytotoxique des fractions sur la viabilité des kératinocytes humains indique une absence de toxicité puisqu’une viabilité de 100% des cellules est obtenue avec différentes concentrations (jusqu’à 100 μg/ml) et différents temps de contact (jusqu’à 24 h) des deux plantes. Toutes les activités biologiques montrées dans cette étude sont expliquées par l'existence de divers composés phénoliques essentiellement: la scopolétine (coumarine aglycone), l’épigallocatéchine, l’esculétine et l’isorhamnétine triglycoside, l’acide caféique, l’acide chlorogénique, la lutéoline et sa forme glycosylé( la lutéoline-3-O-glucoside), enfin l’apigénine libre et sa forme glycosylée. / In this work, the evaluation of antioxidant, anti-bacterial, anti-aging and photoprotective activities was carried out on the aerial parts of twelve halophytes: 6 Tunisian and 6 French shows a high variability according to the species. A screening based on these activities allowed the selection of the two most promising species (Haloxylon articulatum and Daucus carota). A fractionation by adsorption chromatography of their hydroalcoholic extracts was used to specify its antioxidant, antimicrobial, anti-aging and cytotoxic capacities. The results show a high variability between the fractions. The MeOH20% and MeOH100% fractions showed the most interesting anti-elastase and anti-collagenase activities. The evaluation of the cytotoxic potential of the fractions on the viability of human keratinocytes indicates an absence of toxicity since a viability of 100% of the cells is obtained with different concentrations (up to 100 μg / ml) and different contact times (At 24 h) of the two plants.These biological activities were correlated to the presence of various phenolic compounds mainly: scopoletin (coumarin aglycone), epigallocatechin, esculetin , isorhametin triglycoside, caffeic acid, chlorogenic acid, Luteolin and its glycosylate form (luteolin-3-O-glucoside), and finally free apigenin and its glycosylate form.

Many plants are highly sensitive to salt in the soil, and their growth and yield can be greatly hindered by as little as less than 1% salt concentration in the soil. Additionally, soil salinity is a growing issue globally and affects significant areas in Utah. Halophytes are plants that are adapted to grow in saline soils and have been widely studied for their physiological and molecular characteristics, but little is known about their associated microbiomes. Bacteria were isolated from the rhizosphere and as root endophytes of Salicornia rubra, Sarcocornia utahensis, and Allenrolfea occidentalis, three native Utah halophytes. Several strains of halophilic bacteria have been isolated and screened for the ability to stimulate plant growth in saline conditions despite the high salt concentrations. Halomonas, Bacillus, and Kushneria species were consistently isolated both from the soil and as endophytes from roots of all three plant species at all collection times. Of the isolates tested for the ability to stimulate growth of alfalfa under saline conditions, Halomonas and Kushneria strains stimulated plant growth in the presence of 1% NaCl. The same bacteria used in the inoculation were recovered from surface sterilized alfalfa roots, indicating the ability of the inoculum to become established as an endophyte. This raises the question of whether these plant associated halophilic isolates contain genes that aid in plant growth promotion. We are interested in genomic sequencing of our Halomonas and Kushneria strains and performing genomic analysis to determine if there is a difference in genes between plant associated and non-plant associated halophilic isolates. We explored the hypothesis that certain bacterial properties have been selected for to aid plant growth. This was accomplished by performing whole genome sequencing of 26 Kushneria and Halomonas strains, both plant and non-plant associated. These strains came from freezer stocks of previously collected isolates as well as field trips to collect more samples. Halophilic bacteria were isolated from bulk soil, rhizosphere, and halophyte tissues (root and shoot tissues). The non-plant associated (bulk soil) halophilic Kushneria and Halomonas strains aided in determining if there are specific bacterial genes that are expressed in plant associated strains. Whole genome sequencing of the isolates was performed on the Oxford Nanopore platform. The sequence data was then assembled and annotated. The genomes were then included in a genome wide association study was performed. The results from the GWAS show that there is not a significant difference between plant and non-plant associated isolates, disproving our hypothesis. The results also show that few known genes for phytohormone synthesis were present in the pangenome, highlighting the need for further research to determine how these halophilic isolates aid in plant growth promotion in saline soils.

In many arid and semiarid regions worldwide, high levels of soil salinity is a key driver of land degradation, as well as a key impediment to re-establishing plant cover. Combating land degradation and erosion associated with soil salinity requires experimental determination of plant species that can grow in soils with high levels of salinity and can be used to re-establish plant cover. Herein, we evaluated the responses of untested candidate cultivars of two halophytic grass species to high soil salinity: alkali sacaton (Sporobolus airoides Torr.) and seashore paspalum (Paspalum vaginatum Swartz). We evaluated the growth responses of both species in a greenhouse under control (no-salt) and various levels of NaCl salinity (EC 8, 16, 24, 32, 40, and 48dSm(-1)) using Hoagland solution in a hydroponics system in a randomized complete block design trial. At all salinity levels, sacaton grass had a greater shoot height, shorter root length, lower shoot fresh and dry weights, and poorer color and general quality compared to seashore paspalum. The shoot fresh and dry weights of both grasses were greatest at the low to medium levels of salinity, with the greatest response observed at EC 16dSm(-1). At the highest level, salinity significantly reduced shoot fresh and dry weights of both grasses. Because growth of both halophytic species exhibited high tolerance to salinity stress and were stimulated under low to medium levels of salinity, both species could be considered suitable candidates for re-establishing plant cover in drylands to combat desertification and land degradation associated with high levels of soil salinity.

Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv & Cons Biol) / Salicornia tegetaria is an endemic salt marsh macrophyte that is widely distributed in estuaries along the South African coast. The aims of the study were to understand the phylogeography of the species, compare the biomass allocation in two regions and to determine phenological patterns of S. tegetaria between the warm and cool temperate biogeographical regions. The phylogeography of S. tegetaria was studied using the noncoding chloroplast DNA region rpS16 and nuclear rDNA ITS region. Five samples each were collected from eighteen estuaries stretching from Orange River in the Northern Cape to Mngazana Estuary in the Eastern Cape. Above- and belowground biomass was collected and physico-chemical conditions measured at Olifants, Berg and Langebaan Estuaries in the cool temperate, and Heuningnes, Nahoon and Kwelera Estuaries in the warm temperate biogeographical regions. The growth and flowering phenology of S. tegetaria in relation to environmental conditions was investigated in the cool temperate Langebaan Estuarine Embayment and compared to findings in the warm temperate, permanently open Kowie Estuary. The physico-chemical gradient found between the cool and warm temperate biogeographical regions may be useful to study climate change effects on plant species. The comparison of similar habitats in each region may provide insight into how different climate regimes may affect biomass allocation and phenology.

Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv & Cons Biol) / Salicornia tegetaria is an endemic salt marsh macrophyte that is widely distributed in estuaries along the South African coast. The aims of the study were to understand the phylogeography of the species, compare the biomass allocation in two regions and to determine phenological patterns of S. tegetaria between the warm and cool temperate biogeographical regions. The phylogeography of S. tegetaria was studied using the noncoding chloroplast DNA region rpS16 and nuclear rDNA ITS region. Five samples each were collected from eighteen estuaries stretching from Orange River in the Northern Cape to Mngazana Estuary in the Eastern Cape. Above- and belowground biomass was collected and physico-chemical conditions measured at Olifants, Berg and Langebaan Estuaries in the cool temperate, and Heuningnes, Nahoon and Kwelera Estuaries in the warm temperate biogeographical regions. The growth and flowering phenology of S. tegetaria in relation to environmental conditions was investigated in the cool temperate Langebaan Estuarine Embayment and compared to findings in the warm temperate, permanently open Kowie Estuary. The physico-chemical gradient found between the cool and warm temperate biogeographical regions may be useful to study climate change effects on plant species. The comparison of similar habitats in each region may provide insight into how different climate regimes may affect biomass allocation and phenology.

La pollution environnementale constitue un problème majeur pour les écosystèmes naturels et la santé publique. Récemment, la phytoremédiation a émergé comme une stratégie innovante, écologique et à faible coût. Elle consiste à utiliser les capacités des plantes à stocker ou/et à dégrader les polluants. Dans cette étude, des analyses physiologiques, biochimiques et métabolomiques, ont permis de montrer que les halophytes, une catégorie des plantes extrêmophiles, présentent une grande capacité à remédier la pollution engendrée par les Hydrocarbures Aromatiques Polycycliques (HAPs). D'autre part, la salinité modérée améliore leur capacité phytoremédiatrice. Ces résultats apportent de nouvelles données pouvant contribuer à l'amélioration de cette stratégie. / Halopytes, plants naturally adapted to high salt concentrations, have no clear definition, yet. Their cross-tolerance to abiotic stresses was reviewed in this work at the physiological, biochemical, and molecular levels, with a special emphasis on the mechanisms involved in their cross-tolerance to salinity and organic pollutants that could allow them a higher potential of xenobiotic phytoremediation as compared to glycophytes. In our experimental part, we compared in a first step some physiological and antioxidant responses to phenanthrene as well as its accumulation in the two related model plants Arabidopsis thaliana (glycophyte) and Thellungiella salsuginea (halophyte).In a second step, we investigated the effects of moderate salinity on the responses of the two species to phenanthrene considered as model Polycyclic Aromatic Hydrocarbon (PAH) molecule. Obtained results showed an improvement of phenanthrene-induced responses in the two plants, the effect being more marked in the halophyte. This observation was particularly related to higher antioxidant activities and the induction of more adapted metabolism as several accumulated metabolites are known to be involved in signaling and osmotic adjustment processes. In a final step, we studied the potential of the halophyte Cakile maritima to remediate an inert sand (to avoid the degradation of the pollutant by microorganisms or their interaction with the plant) highly contaminated with phenanthrene.

Soil salinity is an increasing problem facing agriculture in many parts of the world. Climate change and irrigation practices have led to decreased yields of large areas of farmland due to increased salt levels in the soil. Irrigation introduces salts to the soil that with time accumulate and threaten crop yield. In arid climates like Utah, the practice of irrigation is especially threatening to salt-sensitive crops including alfalfa (Medicago sativa). Plants that have tolerance to salt are needed to feed livestock and the world's population. One approach to address this problem is to introduce genes encoding salt tolerance into the genomes of salt-sensitive plants through genetic engineering, but this approach has limitations. These limitations include the misinformed public perception of genetically modified organisms (GMOs). Even if the GMO salt-tolerant plants could produce palatable foods, in regions of the world with saline soils incongruous with farming, if consumers refuse to purchase the food then the engineering and upfront costs of production are negated. Another fairly new approach involves the isolation and development of salt-tolerant (halophilic) plant-associated bacteria. Several reports are now available demonstrating how the use of halophilic inoculants enhance plant growth in salty soil. This enhanced plant growth is most likely associated with changes in plant gene expression; however, the mechanisms behind this growth stimulation are not yet clear. Halomonas elongata 1H9, a rhizobacteria native to Goshen UT, has been identified as a plant growth-promoting rhizobacteria (PGPR) when used as an inoculant added to alfalfa seedlings grown in salty soils. Plants grown in the presence of this Halomonas sp. and 1% salt demonstrated an average increase of 2.4x the biomass of alfalfa plants grown without inoculum in salty soils. This suggests that this Halomonas sp. positively influences plant salt tolerance, which raises the question as to how the bacteria stimulate plant growth under these conditions. To identify and characterize plant genes induced by Halomonas elongata, transcriptional analysis was performed using RNA-sequencing (RNA-seq). This analysis identified a variety of differentially expressed genes (DEGs) including transcription factors (e.g. MYB14, GATA transcription factor 9, Ethylene-responsive transcription factors ER017 and ER109) and plant enzymes involved in growth and development (e.g. xyloglucan endotransglucosylase and phosphodiesterase). This was followed by gene validation via real-time quantitative PCR (RT-qPCR), the gold standard for RNA-seq validation, however this process was never successfully completed. Suggestions for next steps are included in the discussion section of chapter 3.

Increasing sea levels and anthropogenic disturbances have caused the world’s coastal vegetation to decline 25-50% in the past 50 years. Future sea level rise (SLR) rates are expected to increase, further threatening coastal habitats. In combination with SLR, the Everglades ecosystem has undergone large-scale drainage and restoration changing Florida’s coastal vegetation. Everglades National Park (ENP) has 21 coastal plant species threatened by SLR. My dissertation focuses on three aspects of coastal plant community change related to SLR and dehydration. 1) I assessed the extent and direction coastal communities—three harboring rare plant species—shifted from 1978 to 2011. I created a classified vegetation map and compared it to a 1978 map. I hypothesized coastal communities transitioned from less salt- and inundation-tolerant to more salt- and inundation-tolerant communities. I found communities shifted as hypothesized, suggesting the site became saltier and wetter. Additionally, all three communities harboring rare plants shrunk in size. 2) I evaluated invading halophyte (salt-tolerant) plant influence on soil salinity via a replacement series greenhouse experiment. I used two halophytes and two glycophytes (non-salt-tolerant) to look at soil salinity over time under 26 and 38‰ groundwater. I hypothesized that halophytes increase soil salinity as compared to glycophytes through continued transpiration during dry, highly saline periods. My results supported halophytic influence on soil salinity; however, not from higher transpiration rates. Osmotic or ionic stress likely decreased glycophytic biomass resulting in less overall plant transpiration. 3) I assessed the best plant life-stage to use for on-the-ground plot-based community change monitoring. I tested the effects of increasing salinity (0, 5, 15, 30, and 45‰) on seed germination and seedling establishment of five coastal species, and compared my results to salinity effects on one-year olds and adults of the same species. I hypothesized that seedling establishment was the most vulnerable life-stage to salt stress. The results supported my hypothesis; seedling establishment is the life-stage best monitored for community change. Additionally, I determined the federally endangered plant Chromolaena frustrata’s salinity tolerance. The species was sensitive to salinity >5‰ at all developmental stages suggesting C. frustrata is highly threatened by SLR.

Scotts Creek Marsh (SCM) is a small coastal wetland ecosystem in Davenport, CA. The vegetation of SCM is dominated by three halophytic zones comprised of saltgrass, salt rush, cattails. The objectives of the study were (i) to investigate the variables that influence the zoning of the three dominant halophyte communities in SCM and (ii) to the test the effectiveness of Indicator of Reduction in Soil (IRIS) tubes to indicate the reduction of S. The study examined the following parameters from April 6 to July 21, 2013: (i) the HGM of Scotts Creek Marsh, (ii) soil oxidation and reduction (redox) conditions, (iii) salinity, and (iii) the effectiveness of Adobe Photoshop CS 5.1 (AP5) to analyze IRIS images. All three halophytes were well suited for anoxic, redox, and saline conditions by utilizing morphological adaptations (arenchyma, adventitious roots) to their root systems. The study concluded that the spatial zoning of the three dominate halophyte species within SCM was most likely due to slight differences in the water levels and salinity. The halophytes within SCM were zoned with saltgrass occupying the areas with the lowest water table and highest EC (26.98 dS/m). The cattails dominated the low average saline areas (9.60 dS/m) near the marsh channels with the highest water level. The salt rush zones had a mild EC level of 15.24 dS/m and intermediate water level. The IRIS tubes that were installed as indicators of both sulfur and iron reduction were effective. The tubes that were withdrawn after the closure of Scott’s Creek all had more than 30% reduction of the Fe3+ paint. The results from the IRIS study indicate that they are effective at recording the reduction of sulfur. The use of AP5 seemed to be an effective tool for analyzing IRIS images. The analyzed data from the study suggests that changes to the HGM of SCM could potentially alter the ecology of the marsh.