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Maize (Zea mays) root quiescent center (QC) cells deteriorate during hypoxic treatment, halting root growth. Over-expression of the Phytoglobin1 ZmPgb1.1 is known to alleviate these effects through the retention of the auxin flow along the root profile required for QC specification. To elucidate QC-specific hypoxia responses and whether ZmPgb1.1 exercises a direct role on QC stem cells, we performed a QC functionality test. This was done by estimating the ability of QCs to regenerate a root in-vitro in a hypoxic environment. Hypoxia decreased the functionality of the QCs by depressing the expression of several genes participating in the synthesis and response of auxin. This was accompanied by a decrease in DR5 signal in oxygen deprived QCs and a consequent suppression of QC markers and genes of jasmonic acid (JA) synthesis and signaling. Over-expression of ZmPgb1.1 mitigated all these responses. Through pharmacological alterations of auxin and JA (through 1-Naphthaleneacetic acid and methyl jasmonate, respectively), it is demonstrated that both compounds are required for QC functionality under hypoxia, and that JA acts downstream of auxin during QC regeneration. A model is proposed whereby the ZmPgb1.1 maintenance of auxin in hypoxic QCs is determinant for the retention of their functionality, with JA supporting the regeneration of roots from the QCs.

Plant responses to salinity and herbivory have been primarily studied separately. However, in natural settings, plants are affected simultaneously by several factors. Because of an overlap in signaling pathways between plant responses to salinity and to herbivory, responses to one factor could be enhanced or lessened by exposure to the other. To investigate the interaction of the responses to these two stress factors, four cultivars of hybrid poplars (Populus) were used to determine if salt tolerance affects resistance to insect herbivory by Orgyia leucostigma. Hybrid poplar seedlings in hydroponics were exposed to 0, 50, and 100 mM NaCl for either two- or three-week treatment periods. Salt exposure resulted in decreased leaf photosynthesis, transpiration, and stomatal conductance, while chlorophyll fluorescence, chlorophyll a, lignin, phenolic compounds, proline, and glycine betaine content of leaves were not affected by salinity. Jasmonic acid (Ile) was found to increase in Walker cultivar at the lowest salt concentration but was not affected at the highest salt concentration. Elemental composition varied between the four cultivars, as noted between leaves that expanded either prior to or during salt exposure at the highest concentration. This included increased nitrogen (Only in Can Am and Okanese pre-salt treatment leaves) and phosphorus (Only in Assiniboine and Walker post-salt treatment leaves), while calcium contents decreased regardless of leaf age/position on the plant. Sodium content increased regardless of leaf age/position on the plant of all cultivars at 50 mM NaCl except for Okanese plants. Constitutive and induced resistance to herbivores, estimated from leaf disc feeding assays were not significantly affected by salinity despite changes in the nutritional value of salt-exposed leaves (cultivar dependent: increase or decrease in total soluble carbohydrates, decrease in proteins, and increase in Na/K ratio). These results suggest that feeding

To examine the function of phytoglobin 2 (Pgb2) on seed oil level in the oil-producing crop Brassica napus L., we generated transgenic plants in which BnPgb2 was over-expressed in the seeds using the cruciferin1 promoter. Over-expression of BnPgb2 elevated the amount of oil, which showed a positive relationship with the level of BnPgb2, without altering the oil nutritional value, as evidenced by the lack of major changes in composition of fatty acids (FA), and key agronomic traits. Two key transcription factors, LEAFY COTYLEDON1 (LEC1) and WRINKLED1 (WRI1), known to promote the synthesis of fatty acids (FA) and potentiate oil accumulation, were induced in BnPgb2 over-expressing seeds. The concomitant induction of several enzymes of sucrose metabolism, SUCROSE SYNTHASE1 (SUS) 1 and 3, FRUCTOSE BISPHOSPHATE ALDOLASE (FPA), and PHOSPHOGLYCERATE KINASE (PGK), and starch synthesis, ADP-GLUCOSE PHOSPHORYLASE (AGPase) suggests that BnPgb2 favors sugar mobilization for FA production. The two plastid FA biosynthetic enzymes SUBUNIT A OF ACETYL-CoA CARBOXYLASE (ACCA2), and MALONYL-CoA:ACP TRANSACYLASE (MCAT) were also up-regulated by the over-expression of BnPgb2. The requirement of BnPgb2 for oil deposition was further evidenced in natural germplasm by the higher levels of BnPgb2 in seeds of high-oil genotypes relative to their low-oil counterparts.

The historical occurrence of hydroelectric development in northern Manitoba has resulted in disturbed areas without vegetative cover within the boreal forest. These disturbed areas exhibit conditions detrimental to restoration, including compacted soil lacking in nutrients, and organic matter and possessing low water-holding capacities. Northern climate conditions and short growing seasons further inhibit recovery potential. The study objective was to develop a strategy for encouraging self-sustaining native plant communities on borrow areas in northern Manitoba. Using fertilizer and mycorrhizal inoculations, seeding, transplants and cuttings were carried out using locally sourced plant species. Soil nitrogen, phosphorus, organic matter content, pH and electrical conductivity were analyzed for differences among treatments and the surrounding undisturbed forest to determine the impacts of material extraction on the land. Plant number, height, leaf area, chlorophyll fluorescence, chlorophyll a + b and total proteins as a proxy for stress were used to determine plant suitability for revegetation. Additionally, the height of trees planted by Manitoba Hydro and monitoring of the natural revegetation were performed over the duration of the experiment. Results of this study show transplantation as the most effective planting method due to the lower survival of seeds and cuttings. Successful establishment of Fragaria virginiana and Rubus idaeus transplants was observed. Inorganic fertilizer application resulted in increased leaf area and height of some species. Soil nutrients were significantly higher in fertilized plots although no significant differences were identified in the number or stress of plants between treatments. Differences in soil nitrogen, phosphorus and pH were found between the borrow pits and undisturbed forested areas. Inoculation with Oidiodendron maius increased survival of transplanted Vaccinium uliginosum and Vaccinium vitis-idaea. Natural revegetatio

UV-B and UV-C can damage DNA by generating DNA photoproducts such as cyclobutane pyrimidine dimers (CPDs), pyrimidine 6-4 pyrimidone (6-4 PPs) and its Dewar isomers (Dewar PP). These DNA photoproducts inhibit DNA transcription and replication, and cause mutations. Thus, DNA photoproducts must be repaired. Plants use two different mechanisms to repair these DNA photoproducts: light-dependent repair via photolyase and light-independent repair via nucleotide excision repair (NER). The NER mechanism in plants is similar to that elucidated in yeast and mammalian models. In yeast systems, the global genomic NER (GG-NER) damage recognition complex RAD7/RAD16/ELOC/ CUL3 recognizes the damaged DNA in the non-transcribed regions of the genome. The mammalian Elongin A/B/C/CUL5 /RBX2 and the yeast Elongin A/C/CUL3/RBX1 complexes target the large subunit of the lesion stalled RNAPII on the transcribed strand for ubiqitination and degradation. Arabidopsis has two RAD16 homologs: AtRAD16 and AtRAD16b. In this thesis, I characterized the role of AtRAD16 and AtRAD16b in plant UV tolerance and growth using loss of function and gain of function analysis. Atrad16 and Atrad16b null mutants exhibited increased UV sensitivity, early flowering time and short silique length. AtRAD16 overexpression increased UV resistance, and YFP-tagged RAD16 is localized in the nucleus. In addition, AtRAD16 physically interacts with AtRAD7, all these results indicate that the role of AtRAD16 in GG-NER is conserved with its yeast counterpart. I also identified Arabidopsis ELOA homolog, ELOA, and characterized the role of both Arabidopsis ELOA and ELOC homologs in plant UV tolerance and growth. Ateloa and Ateloc null mutants exhibited increased UV sensitivity in seedlings and adult plants. AtELOA was found to physically and genetically interact with AtELOC. AtELOA is nuclear localized, whereas AtELOC localized in the nuclei and the cytosol. ELOA overexpression increases hypocotyl UV resistance and ELOA/ELOC

Barley (Hordeum vulgare L.) is the most susceptible cereal species to excess moisture stress. Waterlogging-induced hypoxia causes major physiological changes that disrupt the photosynthetic machinery of seedlings. The signaling molecule nitric oxide (NO) regulates numerous metabolic processes but increases to toxic levels during hypoxia. Phytoglobin1 (Pgb1) functions as a NO-scavenging hemeprotein that influences hypoxic stress responses such as ethylene-mediated adaptations and nitrate use. This study demonstrated that overexpression of HvPgb1 maintains photosynthetic rate in barley during waterlogging, but also confirms previously reported decreases in physiological performance during normoxic (control) conditions. Foliar ethylene was found to decrease in waterlogged wild type (WT) but remain unchanged in the HvPgb1-overexpressing line [HvPgb1(OE)]. It is proposed that ACC from the hypoxic root mobilizes to the shoot, where it induces HvPgb1 activity and nitrate generation. Foliar nitrate was measured as well and showed a significant increase in leaves of waterlogged HvPgb1(OE) plants, while remaining unchanged in waterlogged WT leaves. These changes were associated to a putative increased in the levels of polyamines. Finally, HvPgb1 expression was measured from a group of selected waterlogging-tolerant and susceptible genotypes. A sharp increase in gene expression was seen in the leaves of waterlogged tolerant genotypes, thus positioning HvPgb1 expression as a potential molecular marker for waterlogging tolerance in barley.

Reclamation and revegetation of boreal sites disturbed by oil exploration depend on the availability of topsoil salvaged on-site during the disturbance. For successful reclamation, current regulations require the salvaging of enough soil to attain at least 80% of the original topsoil depth. However, salvaged topsoil at many sites is often insufficient to achieve the 80% topsoil replacement depth (TRD80) required for successful reclamation in western Canada. We tested organic amendment effects on reclamation success of wellsites reclaimed with insufficient salvaged topsoil to a level similar to the mandatory TRD80. Two main studies were conducted to examine (i) soil responses and (ii) vegetation responses to 50% topsoil replacement depth without organic amendment (TRD50) or amended with either peat (PTRD50) or biochar (BTRD50), relative to the TRD80 treatment, following wellsite reclamation at Cold Lake, Alberta. Soil properties results showed that both amendments improved topsoil properties. Peat-amended plots showed a 113% increase in total Kjeldahl nitrogen concentration relative to the mean of other treatments, while biochar produced significantly greater potassium concentrations in TRD50 relative to peat-amended plots. Vegetation responses to insufficient topsoil depth and organic amendment application showed an increase in native species, graminoid and woody species richness while non-native and forb species richness decreased across all treatments 5 yr after reclamation. Tree growth was greater in the peat amendment and the TRD80 treatment than in the TRD50 and the biochar treatments. Peat and biochar improved soil properties of disturbed boreal sites reclaimed with insufficient salvaged topsoil to a level suitable for successful restoration. However, in the revegetation study peat improved vegetation establishment and plant community development while biochar showed no benefits on vegetation variables. Overall, the peat treatment (PTRD50) produced similar veg

Fusarium head blight (FHB) is an important fungal disease of wheat predominantly caused by Fusarium graminearum. FHB infection in cereal crops leads to yield loss and decreased grain quality due to accumulation of mycotoxins such as deoxynivalenol. Many highly FHB resistant wheat cultivars are tall and are prone to lodging. Application of plant growth regulators (PGRs) to tall cultivars with the highest level of FHB resistant could prevent wheat from lodging and overcome the negative association between shorter plants and FHB susceptibility. The objectives of this study were to investigate the effect of PGRs on FHB infection and anther retention in spring wheat cultivars. Two commercially available PGRs, Manipulator™ and Ethrel™, were applied to five spring wheat (Triticum aestivum L.) cultivars which differed in height, FHB resistance level and semi-dwarfing alleles. Results from this study showed Ethrel™ reduced plant height under field and controlled environments conditions. Under field conditions, PGRs did not influence anther retention and FHB infection in spring wheat. In contrast, in controlled environment conditions, Manipulator™ decreased anther retention, while Ethrel™ increased anther retention. Treatment with Manipulator™ showed conflicting results on the accumulation of F. graminearum DNA in the spike. The Ethrel™ treatment showed that accumulation of F. graminearum DNA is genotype specific. Overall, the performance of PGRs on height, anther retention and FHB infection were influenced by environmental conditions.

Soybean production is negatively affected by certain morphology related factors such as the occurrence of short lowest pod height which results in stubble losses since the pods lower than the reach of the combine cutter are lost during harvest. Therefore, it is necessary to develop strategies that can promote the elongation of lower internodes such that the first pods can be set at a harvestable height. Plant hormones such as gibberellins (GA) and cytokinins play important roles in regulating stem elongation through promoting cell elongation and cell division, respectively. Therefore, plant growth regulators (PGRs) containing GAs and cytokinins can promote internode elongation and therefore the height of lowest pod bearing nodes. Using a soybean cultivar characterized by a short lowest pod height, this thesis investigated the effects of GA and/or cytokinin based PGRs, applied as a seed treatment, on enhancing the elongation of lower internodes and thereby lowest pod height. The findings show that the GA based PGR was effective in increasing the lengths of lower internodes and height of the lowest pods. In order to gain insights into the molecular basis of GA metabolism in the regulation of pod heights, this thesis examined the expression patterns of GA biosynthetic and catabolism genes in lower internodes of three different soybean cultivars with contrasting pod heights. The results indicate that the three cultivars exhibit differential expression patterns of the genes analyzed.

In the nitrogen-fixing clade, only 10 out of 28 plant families retain the nitrogen fixation trait. It is thought that the nitrogen fixation has been lost repeatedly since it evolved. Exploring the potential abiotic and biotic factors that trigger the loss of nitrogen-fixing traits is critical to understanding the evolution and ecology of plants. I designed three studies to examine how nitrogen-fixing plants respond to N deposition, different levels of CO2, herbivore damage, and less-effective symbionts. For the first study I grew three nitrogen fixers (Alnus incana ssp. rugosa, Alnus viridis ssp. crispa, and Alnus rubra) and their close non-nitrogen fixing relatives (Betula pumila, Betula papyrifera, Betula glandulosa) at ancient (1600 ppm) or present (400 ppm) CO2 over a range of soil N levels, equivalent to 0, 10, 50, and 200 kg N ha-1 year-1. I found nitrogen-fixing plants were less competitive as soil N increased compared with non-N fixers, but at ancient CO2 levels nitrogen-fixing plants are at an advantage at higher soil N levels. The seconded study explored the interaction between Alnus incana ssp. rugosa and Orgyia leucostigma under ambient (400 ppm), future (800 ppm), and ancient (1600 ppm) CO2. Herbivores preferred to feed on nodulated plant leaves grown at 400 ppm and 1600 ppm when given a choice, compared with non-nodulated leaves. At 800 ppm CO2 nodulated plants accumulated more total phenolic compounds in response to herbivore damage than plants in the non-Frankia and non-herbivore treatments. The third study examined if Alnus spp. can select against less-effective symbiont via partner choice or sanctioning. In a co-inoculation experiment, host plants could not prevent the less effective sp+ Frankia from entering roots when inoculated with a mixture of effective (sp-) and less effective (sp+) Frankia. When plant roots were inoculated with sp+ Frankia and exposed to Argon to induce Frankia cheating, specific nodule mass was not reduced. However, Argon-t

Plant growth-promoting bacteria (PGPB) are a heterogeneous group of soil microbes that confer beneficial effects to plants. Recent interest in sustainable and organic agriculture has highlighted the potential uses of PGPB as agricultural adjuncts. Currently, PGPB are used to increase crop yield and productivity. Substantial work has been done on the active metabolites secreted by PGPB that drive plant growth. However, little is known about their effects on the global transcriptome of the host plant. P. chlororaphis PA23 is a gram-negative bacterium that has shown great potential as a plant growth promoting agent. Using a combination of next-generation RNA sequencing and bioinformatic analyses, the mechanisms that underlie P. chlororaphis PA23 induced growth in Brassica napus seedlings were investigated. The results showed that P. chlororaphis modulates plant phytohormone signaling systems resulting in elevated expression levels of genes associated with photosynthesis and root hair development. Next, the scalability of P. chlororaphis PA23 as an agricultural adjunct with a Glycine max field study was investigated. An increase in soybean pod set following P. chlororaphis PA23 treatment was observed, suggesting plant growth-promoting activity under field conditions. To determine the effects of P. chlororaphis PA23 on the microbial communities found in the soil, a combination of marker-based sequencing and bioinformatic analyses were utilized. Here I report that the addition of P. chlororaphis PA23 does not alter the bacterial or fungal species diversity. Furthermore, I report that the community composition within the rhizosphere does not change in response to P. chlororaphis PA23. This research provides the necessary information for the development of P. chlororaphis PA23 as an agricultural adjunct and lays the foundation for multi-year field studies that integrate the utilization of P. chlororaphis PA23 as a PGPB.