No description available.

Citrus paradisi 3-O-glucosyltransferase (Cp3GT, Genbank Protein ID: ACS15351) and Citrus sinensis 3-O-glucosyltransferase (Cs3GT, Genbank Protein ID: AAS00612.2) share 95% amino acid sequence identity. Cp3GT was previously established as a flavonol-specific 3-O-glucosyltransferase by direct enzymatic analysis. Cs3GT is annotated as a flavonoid-3-O-glucosyltransferase and predicted to use anthocyanidins as substrates based on gene expression analysis correlated with the accumulation of anthocyanins in C. sinensis cv. Tarocco, a blood orange variety. Mutant enzymes in which amino acids found in Cs3GT were substituted for position equivalent residues in Cp3GT were generated, heterologously expressed in yeast, and characterized for substrate specificity. Structure–function relationships were investigated for wild type and mutant glucosyltransferases by homology modelling using a crystallized Vitis viniferaanthocyanidin/flavonol 3-O-GT (PDB: 2C9Z) as template and subsequent substrate docking. All enzymes showed similar patterns for optimal temperature, pH, and UDP/metal ion inhibition with differences observed in kinetic parameters. Although changes in the activity of the mutant proteins as compared to wild type were observed, cyanidin was never efficiently accepted as a substrate.

Soil and root microbial communities have been studied for decades, and the incorporation of high-throughput techniques and analysis has allowed the identification of endophytic/non-culturable organisms. This has helped characterize and establish the core microbiome of many model plant species which include underground and aboveground organs. Unfortunately, the information obtained from some of these model plants is not always transferable to other agronomic species. In this project, we decided to study the microbiome of the Nicotiana genus because of its importance in plant physiological and plant-microbe interactions studies. The data obtained was used as baseline information that allowed us to better understand the effect of microbial inoculums on the assembly of the microbiome of the plant. We analyzed 16s rRNA amplicons to survey the microbiome in different plant organs and rhizosphere from four different species. Bacterial strains evaluated were screened for a consistent reduction or improvement in plant growth. Four bacterial strains were tested and used as seed inoculum (Lf-Lysinobacillus fusisormis, Ms –Micrococcus sp., Bs–Bacillus sp., Bc–Bacillus cereus). Bs and Bc inoculants caused plant growth promotion, and in contrast Ms caused retarded growth, while Lf acted as a neutral or non-inducing phenotype strain. Data supported that microbial inoculum used as seed treatment caused systemic changes in the host plant microbiome. Functionality of the inoculum was studied and the response in plant growth was linked to hormonal changes (evaluated in the plant and in the bacterial strains). Gene expression analysis using a genome-scale approach revealed that genes that could possibly be involved in stress response are down-regulated for Bc and Bs treatments and up-regulated for Ms. Flexibility variability of the inoculum was also evaluated to have a better understanding of the main factors involved in the promotion or suppression of growth, and possibly its effect in following generations. In summary, the findings of this project support that the plant functional microbiome responds to exogenous stimulation from abiotic and biotic factors by adapting endogenous hormone responses.

This study lends strong support to the idea that members of Bromeliaceae have undergone a recent adaptive radiation, and therefore show that, at least in part, diversity in the tropics is due to a fast speciation rate and that the tropics can be a "cradle" for new diversification and exploitation of varying ecological niches through the diversification of ecophysiological traits within a lineage.

We explored the seasonal factors that might play a role in triggering germination of Dendromecon rigidaand Ehrendorferia chrysantha.D. rigida and E. chrysantha have been found difficult to germinate using common greenhouse techniques, Keeley and Fotheringham successfully germinated both species after storing their seeds in the field over a year and treating them with smoke. Identifying the specific seasonally changing factors that stimulated germination could have implications for understanding germination requirements for these and other hard-to-germinate chaparral species. Dendromecon rigidaand Ehrendorferia chrysanthaare part of the Papaveraceae family and both are found in the chaparral environment in Southern California. Both species are known to increase in numbers after fire events. Both are believed to have morphophysiological dormancy based on their miniscule embryo and increase in seedling presence after fire events. Climate within the chaparral environment consists of hot, dry summers and cold, wet winters. Storing seeds of D. rigidaand E. chrysantha in the field over winter and spring months resulted in increasing germination for D. rigida seeds that were imbibed in smoke-water. Germination of D. rigidaseeds occurred within six weeks and no further germination was noted beyond that. Ehrendorferia chrysanthaseeds failed to germinate in the field. Lab studies tested effects of stratification at different temperatures (5ºC, 10ºC, 18ºC, 25ºC and 30ºC), stratification for different durations (0, 2, 4, 8, and 12 weeks), heat-shock, and fluctuating moisture and temperature conditions on a weekly time scale, on germination of both species. Of all these treatments the only combination that was effective in germinating seeds of D. rigidaand E. chrysanthawas warm stratification at 30ºC for 8 weeks following smoke-water imbibition. Under these conditions seeds of D. rigidaand E. chrysanthagerminated to 10% and 9.3%, respectively. Further studies on D. rigidaindicated a stratification temperature optimum between 30-40ºC with germination increasing with lack of light. These tested conditions corresponded to the daily peak soil temperatures measured at shallow depth in an area of chaparral inhabited by D. rigida. The period immediately after the first rain event after a fire may provide the chemical cues and warm stratification required to germinate buried seeds in this species.

Plants emit a diverse range of biogenic volatile organic compounds (BVOCs) into the atmosphere, of which isoprene is the most abundantly emitted. Isoprene significantly affects biological and atmospheric processes, but the range of isoprene and BVOCs present in bamboos has not been well characterized. In this thesis I explore the range of isoprene emission found in bamboos and relate it to plant morphological and physiological characteristics. In addition, I measure and relate the entire suite of BVOCs present in the bamboos to their fundamental isoprene emission rate. Interspecific variation in isoprene emission documented in a comprehensive survey of bamboos. Two groups of bamboo species were measured in the greenhouse and the field. Elevated photosynthetic rate was significantly correlated with isoprene emission. In the field, dark respiration rate was highest in bamboos that made the least amount of isoprene. The total BVOC suite was significantly influenced by whether or not leaf-level isoprene emission was present. I conclude that bamboos vary with regard to physiology, morphology, and total BVOC suite and that isoprene emission is correlated with these changes, and introduce the bamboos as a novel system for studying the impacts of isoprene emission.

No description available.

Coastal wetlands store immense amounts of carbon (C) in vegetation and sediments, but this store of C is under threat from climate change. Accelerated sea level rise (SLR), which leads to saltwater intrusion, and more frequent periods of droughts will both impact biogeochemical cycling in wetlands. Coastal peat marshes are especially susceptible to saltwater intrusion and changes in water depth, but little is known about how exposure to salinity affects organic matter accumulation and peat stability. I investigated freshwater and brackish marsh responses to elevated salinity, greater inundation, drought, and increased nutrient loading. Elevated salinity pulses in a brackish marsh increased CO2 release from the marsh but only during dry-down. Elevated salinity increased root mortality at both a freshwater and brackish marsh. Under continuously elevated salinity in mesocosms, net ecosystem productivity (NEP) was unaffected by elevated salinity in a freshwater marsh exposed to brackish conditions (0 à 8 ppt), but NEP significantly increased with P enrichment. Elevated salinity led to a higher turnover of live to dead roots, resulting in a ~2-cm loss in soil elevation within 1 year of exposure to elevated salinity. When exposing a brackish marsh to more saline conditions (10 à 20 ppt), NEP, aboveground biomass production, and root growth all significantly decreased with elevated salinity, shifting the marsh from a net C sink to a net C source to the atmosphere. Elevated salinity (10 à 20 ppt) did not increase soil elevation loss, which was already occurring under brackish conditions, but when coupled with a drought event, elevation loss doubled. My findings suggest these hypotheses for the drivers and mechanisms of peat collapse. When freshwater marshes are first exposed to elevated salinity, soil structure and integrity are negatively affected through loss of live roots within the soil profile, leaving the peat vulnerable to collapse even though aboveground productivity and NEP may be unaffected. Subsequent dry-down events where water falls below the soil surface further accelerate peat collapse. Although saltwater intrusion into freshwater wetlands may initially stimulate primary productivity through a P subsidy, the impact of elevated salinity on root and soil structure has a greater deleterious effect and may ultimately be the factors that lead to the collapse of these marshes.

Medicago is widely used as a forage crop. It is often susceptible to various pathogenic infections and exhibits low growth in drought and extreme climatic conditions. In the current study, a strategy was developed for over-expressing an “Osmotin-Chitinase” gene chimera in transgenic Medicago that could potentially confer resistance to different biotic and abiotic stresses. Seed germination of several cultivars of Medicago (M. sativa ssp. sativa, M. sativa ssp. falcata, M. sativa ssp. caerulea, M. truncatula, and M. Rugosa) was tested to determine the cultivars with good germination rates. Among these, M. sativa ssp. sativa showed an average of 80% germination over a period of one week and was subsequently selected for regeneration and transformation experiments. Different explants (cotyledons, hypocotyls, petioles) were tested for regeneration. Among these, hypocotyl explants showed highest (46.17 %) percent regeneration. Escherichia coli harboring Osmotin-Chitinase (OSM-CHI) gene chimera cloned into binary vector pBTEX with nptII as a selection marker was mobilized in Agrobacterium tumefaciens strain EHA105 which was employed in the transformation of hypocotyl explants of Medicago. Transformed calli were grown on callus inducing medium containing kanamycin for screening. Further screening of the positive transgenics was performed using PCR. Southern hybridization was carried out for further confirmation of successful transformation. Transformed shoots will be grown on the root inducing medium for developing into plantlets which would then be transferred to the green house and later tested for their degree of resistance to various biotic and abiotic stresses.

<p>This dissertation examines issues concerning sap flux scaled estimates of the canopy-averaged transpiration rate of trees per unit leaf area (E_L) and stomatal conductance (G_S), as well as their implications in the water and carbon balance of individuals and stands, with the final goal of an integrated assessment of 11 years of such data from two species (<italic>Pinus taeda</italic> and <italic>Liquidambar styraciflua</italic>) at the Duke Free Air Carbon dioxide Enrichment (Duke FACE) facility. These issues include (1) the effects of allometric relationships and xylem characteristics on the gas phase transport of water from leaves and the hydraulic supply of it, (2) consideration of the hydraulic capacitance in the inference of stomatal behavior from sap flux data and (3) the dynamic modeling of stomatal conductance to environmental drivers using Bayesian techniques. It is shown that a) for resolution of sap flux in conifers at the scale of minutes under dynamic conditions, time constants for both stomatal responses and hydraulic capacitance of sapwood must be considered, (b) nighttime conductance can lead to large errors in rates of sap flux measured under some conditions, (c) variation in allometry between <italic>P. taeda</italic> individuals can lead to different rates of transpiration and carbon assimilation per unit leaf area and that (d) hydraulic time constants for the stems of mature <italic>P. taeda</italic> at Duke FACE trees varied by the stem length considered and were on the order of 30-45 minutes for a 10-m segment. An analysis incorporating all these elements leads to the conclusions that (e) both elevated CO₂ (eCO₂) and fertilization (FR) resulted in proportionally larger reductions in the E_L and G_S of P. taeda as soil moisture decreased with (f) eCO₂ having little to no effect in months of high soil moisture and (g) FR leading to ~14% reduction of GS under high soil moisture in absence of eCO₂, while (h) both eCO₂ and FR led to reduced E_L and G_S of <italic>L. styraciflua</italic> across soil moisture conditions.</p> / Dissertation