Flavonoids are a class of plant secondary metabolites that fulfill many functions in planta and also benefit human health. Glucosylation of flavonoids, catalyzed by glucosyltransferases (GTs), help flavonoids perform their important roles. Citrus paradisi (grapefruit) is known to be active in flavonoid metabolism and possesses a variety of secondary product GTs. This research is designed to test the hypothesis that PGT10 is a flavonoid glucosyltransferase. PGT10 was cloned, expressed, purified, and tested for GT activity with a variety of phenolic substrates. Efforts to identify the reaction catalyzed by PGT10 continue. A second project was designed to test the hypothesis that multiple bands obtained by RT-PCR of PGT 5/6 found in root cDNA represented a set of homologous genes. Hypothesis has been confirmed by the homologous fragments found. Additional structural information is presented.

Plant innate immunity is activated upon pathogen attack by recognizing their avirulent (avr) genes by Resistant (R) genes leading to R-gene resistance or host resistance. Another form of innate immunity is non-host resistance that is exhibited by a given plant species to most strains of a microbial species. R-gene resistance activates salicylic acid (SA) that is synthesized from methyl salicylic acid (MeSA) by Salicylic Acid Binding Protein 2 (SABP2). It was hypothesized that SABP2 plays the similar role in non-host resistance also. Growth experiments and non-host related gene analysis experiments were conducted on tobacco plants using P.s tabaci and P.s. phaseolicola that are host and non-host pathogens on tobacco respectively. Tobacco control plant C3 that expresses SABP2 and 1-2 that is RNAi silenced in SABP2 expression were used in this study. Results suggest that SABP2 may not have any significant role in tobacco non-host resistance.

We examined several aspects of nectar production in Campsis radicans to better understand how standing crop is affected and how production affects pollinator visitation. In all experiments, nectar and concentration of flowers were measured and total sugar was calculated. Flowers do not produce additional nectar unless nectar is removed, and it is not resorbed. Volume of standing crop and total sugar fluctuates throughout the day, whereas concentration remains constant. Age and time of day significantly affect regeneration of nectar and sugar. The number of removals did not significantly affect the amount of nectar or sugar regenerated; however, concentration declined significantly after the initial removal. We have established several factors affecting nectar production, although clearly there are other aspects influencing the production of nectar in C. radicans. Focus should be placed on determining the physiological aspects of secretion as well as studying the role that environmental factors have on physiological aspects.

Plants have evolved an efficient mechanism to defend themselves against pathogens. Many biotic and abiotic agents have been shown to induce defense mechanism in plants. Acibenzolar-S-Methyl (ASM) is a commercially available chemical inducer of local and systemic resistance (SAR) response in plants. ASM functioning at molecular level is mostly unclear. This research was designed to investigate the mechanism of ASM action in plants. It was hypothesized that SABP2, a plant protein, plays an important role in ASM-mediated defense signaling. Biochemical studies were performed to test the interaction between SABP2 and ASM. Transgenic SABP2-silenced tobacco plants were used to determine the role of SABP2 in SAR induced by ASM. The expression of PR-1 proteins was used as a marker for SAR induction. Results showed that SABP2 converts ASM into acibenzolar that induces the expression of PR-1 proteins and develops the SAR response in ASM-treated plants.

Experiments were performed to investigate the influence of water availability on the diel patterns of nectar secretion (volume, concentration, sugar production) in male squash flowers as well as to discover what physical component of nectar honey bees use to trigger their time-memory. Squash plants were grown in the greenhouse and in the field under both constant and variable watering regimes. Throughout anthesis, nectar volume and sugar concentration were recorded. In the field, the temporal distribution of arrivals to squash was observed with and without blossoms present. In the greenhouse and in the field, squash flowers exhibit a consistent diel pattern of nectar secretion that does not significantly alter during drought conditions; flowers open just before sunrise (with low volume and sugar and high concentration) and close at midday (with high volume and sugar and low concentration). Honey bees preferentially arrived early in anthesis possibly cueing on either the sugar concentration or the first availability of nectar.

A variety of plants synthesize and store oil in the form of triacylglycerols (TAG) in their seed and nonseed tissues that are commonly used as vegetable oils. In seed tissues, an acyl CoA-dependent diacylglycerol (DAG) acyltransferase (DGAT) and/or -independent phospholipid:DGAT (PDAT) catalyze the conversion of DAG to TAG. In avocado fruit, which stores up to 70% oil by dry weight in mesocarp, it is hypothesized that both DGAT and PDAT are likely involved in TAG synthesis. To investigate, TAG content and composition and transcript levels for the acyltransferases in avocado fruit were quantified by gas chromatography and real-time polymerase chain reaction, respectively. Temporal, tissue-specific and phenotypic comparisons revealed that while DGAT1 gene expression was specifically associated with TAG accumulation, PDAT also correlated with higher levels of polyunsaturated fatty acid; DGAT2 was barely detectable. These studies suggest that TAG biosynthesis in nonseed tissues of avocado involves acyl CoA-dependent and -independent reactions.

No description available.

No description available.

Arbuscular mycorrhizal fungi (AMF) are a category of fungi that occupy virtually all of the Earth's soils. Their role as plant symbionts for nearly all land plants is well documented, where these fungi forms partnerships with plants through the root system. These relationships vary from mutualistic to parasitic and allow the exchange of nutrients between the partners via fungal hyphae that penetrate the cell walls of roots. However, many details of the nature of this symbiosis are not well understood, and the interaction between plants and AMF has been the subject of increased interest recently given the potential benefit to farming systems and natural ecosystems. This study evaluated the variability of mycorrhizal growth response (MGR) to inoculation by the common AMF species Rhizophagus intraradices in a diverse set of wild sunflower species (Helianthus), focusing on how changes in plant traits due to fungal colonization may determine the relative cost or benefit of AMF partnership for wild plants. Results indicate that the overall impacts of AMF colonization on plant growth rate are small, though MGR is correlated with AMF-driven shifts in leaf chlorophyll content. These findings suggest that relative changes in plant growth rate that result from AMF partnership are mediated by plant functional trait.

While pollinators and leaf herbivores have been a focus of research for decades, floral antagonists have been studied significantly less. Since floral antagonists can be as common as leaf herbivores and have strong impacts on plant reproduction, it is important to understand the role of floral antagonists in the ecology and evolution of flowers. I conducted four experiments to better understand the relationship between plants, floral traits, floral antagonists, and other plant-insect interactions. First, I manipulated resources (light and soil nutrients) that are known to have impacts on plants and floral traits to test how they affect floral antagonists and other plant-insect interactions. Plentiful resources increased the proportion of floral antagonists to visit flowers, but also increase tolerance of floral antagonists. Second, I manipulated flower bud gallers, a species-specific floral herbivore that destroys flowers, to test how it affected other plant-insect interactions, floral traits, and plant reproduction. Plants with flower bud gallers tended to have more pollinator visits, but this effect is due to a shared preference by gallers and pollinators for similar plants. Third, I manipulated florivory to examine how it affects subsequent plant-arthropod interactions, floral traits, and plant reproduction. Florivory had systemic effects on other plant-insect interactions, including leaf herbivores, and shifted the plant mating system towards more selfing. Additionally, I tested how several floral antagonists respond to floral attractive and defense traits to understand which floral traits are important in mediating antagonisms. Finally, I manipulated florivory, pollination, and nectar robbing to test for effects of multiple floral interactions on subsequent plant-insect interactions, floral traits, and plant reproduction. There were significant many-way interactions between the three treatments on subsequent plant-insect interactions and reproduction, indicating that the effect of one interaction depends on what other interactions are present. Understanding the role that floral antagonists play in plant ecology can help scientists determine which interactions are most important, and may help determine why some floral traits exist in their current state. Together, this work represents some of the most comprehensive research on the community consequences of floral antagonists, as well as the interplay between floral traits and floral interactions.