Life Sciences Commons^™

Ammonium Chemotaxis In Chlamydomonas Reinhardtii, Gabela Nelson

LSU Doctoral Dissertations

Analysis of ammonium chemotaxis in Chlamydomonas reinhardtii is largely hindered, compared to that of phototaxis, despite equal importance on flagellated microalgal physiology. A major contribution of this shortfall is the lack of proper assay method. We developed a simple Petri dish assay method in which light is homogenously exposed while patterns of the cellular migration are tracked with a function of time. Using the method, new findings were revealed. First, this research presented that a strain lacking the eyespot organelle required for light gradient-sensing exhibits similar chemotactic behavior compared to a wild-type strain, suggesting Chlamydomonas sense an ammonium gradient not …

Spatiotemporal Transcriptome Diversity And Responses To Salinity Tolerance In The Extremophyte Schrenkiella Parvula, Chathura Wijesinghege

LSU Doctoral Dissertations

Schrenkiella parvula is an extremophyte model related to the most widely studied plant model, Arabidopsis thaliana and Brassica crops in the mustard family (Brassicaceae). It can thrive in highly saline environments where the soil is enriched in Na⁺, K⁺, Li⁺, borates, and chlorides. Understanding how this extremophyte can survive high salinity with genomic adaptations can provide insight into developing stress resilient crops in the future. Gene expression of S. parvula in response to salt has been investigated using shoot and root tissue from mature vegetative-phase plants. However, prior studies have not examined the transcript …

The Effects Of Drought And Shade On Bottomland Hardwood Regeneration, Charles Joseph Pell

LSU Doctoral Dissertations

Floodplain forests support a high diversity of tree species adapted to regenerate under fluctuating water and light availability. Regeneration regulates species composition, and shade and flood tolerance influence the likelihood of regeneration. Regeneration failure of shade-intolerant and flood-tolerant tree species commonly occurs in southcentral and southeastern floodplain forests of the United States, also known as bottomland hardwoods (BLHs). In many BLHs reduced flooding has resulted in a dryer floodplain. These changes in flooding are linked to recent shifts in species composition. The mechanisms controlling regeneration in BLHs and these composition shifts are poorly understood. In a controlled germination experiment, I …

The Importance Of Co2 Recapture In The Co2 Concentrating Mechanism Of Chlamydomonas Reinhardtii, Ashwani Rai

LSU Doctoral Dissertations

The aim of this thesis is to investigate the CO₂ concentrating mechanism (CCM) of Chlamydomonas reinhardtii and to develop a quick method for estimating the activity of carbonic anhydrases (CAs). The first project demonstrates that there are two almost identical mitochondrial CAs in C. reinhardtii, CAH4 and CAH5, that help to maintain photosynthesis and minimize the leak of CO₂ generated by respiration and photorespiration. We used an RNAi approach to reduce the expression of CAH4 and CAH5 so that their physiological functions could be studied. RNAi mutants with low expression of CAH4 and CAH5 have impaired rates …

Sodium Mediates Developmentally Plastic Responses In Plants And Herbivores, Luis Santiago-Rosario

LSU Doctoral Dissertations

Sodium plays a crucial role in organismal performance, trophic-level interactions, and eco-evolutionary dynamics. For plants, sodium impacts osmoregulation, growth, and water uptake. For animals, sodium is essential influencing osmoregulatory processes, muscle and neural development, and blood regulation. My dissertation aims to disentangle why sodium mismatch affects resource-consumer interactions and its influence on morphological and behavioral plasticity. First, I identified how sodium impacts plant performance and sodium accumulation strategies. I initially focused my research on understanding how increasing substrate sodium affects plant growth and tissue sodium accumulation strategies in controlled settings using a systematic review approach. I found that saltier plants …

Impact Of New Technologies On Weed Control In Louisiana Rice Production, David C. Walker

LSU Doctoral Dissertations

Field studies were conducted in 2018-2021 at the LSU Agricultural Center’s H.R. Caffey Rice Research Station (RRS) near Crowley, LA, and the Dean Lee Research and Extension Center (DLREC) near Alexandria, LA to evaluate off-target florpyrauxifen movement on soybean. Soybean was treated with florpyrauxifen at the V4-V5 or R1-R2 growth stages. Soybean injury was evaluated at 1, 7, 14, and 28 days after treatment (DAT) and soybean plant height (cm) was recorded at 7, 14, and 28 DAT. At soybean maturity, yield and individual yield components were subjected to regression analysis to describe the relationship between florpyrauxifen rate and soybean …

Investigation Of Arabidopsis Extremophyte Relatives, Schrenkiella Parvula And Eutrema Salsugineum Reveals Different Roads Leading To Salt Stress Tolerance, Kieu-Nga Thi Tran

LSU Doctoral Dissertations

How plants adapt to salt stress has been a central question in plant biology for decades. Yet we have not been able to fully understand the molecular networks and genetic mechanisms underlying this complex trait. Most of the genetic work on salinity stress has focused on understanding salt stress responses in the leading, yet a salt-sensitive model Arabidopsis thaliana. With the recent availability of genomes for wild-relatives of A. thaliana, we can now investigate how naturally salt adapted plants may have evolved modified or novel molecular networks to adapt to salt stress. Therefore, my research utilizes a comparative …

Insights Into Abscisic Acid And Phosphatidic Acid Signal Transduction Dynamics In Arabidopsis Thaliana, Ruth Wanjiru Ndathe

LSU Doctoral Dissertations

Abscisic acid (ABA) is a plant hormone that triggers a signaling transduction in response to drought, salinity, and cold. The core components in the ABA signaling pathway that lead to downstream ABA responses have been identified.

Phosphatidic acid (PA) is a membrane phospholipid that is involved in the signaling pathway for ABA-induced stomatal closure. We tested whether PA is involved in the signaling pathway for ABA-induced gene expression as well, using model plant Arabidopsis thaliana. We selected the RD29A gene which is a canonical drought gene that is induced by ABA. We found that PA is not involved in …

Understanding Potassium Toxicity Stress Responses Of The Extremophyte Schrenkiella Parvula Using Systems Biology Approaches, Pramod Pantha

LSU Doctoral Dissertations

Schrenkiella parvula is an extremophyte model closely related to Arabidopsis thaliana and Brassica crops. Its natural habitat includes shores of saline lakes in the Irano-Turanian region. It has adapted to grow in soils rich in multiple salts including Na⁺ and K⁺. I have investigated the genetic basis for high K⁺ tolerance in plants using S. parvula as a stress tolerant model compared to the premier plant model, Arabidopsis thaliana which is highly sensitive to salt stresses using physiological, ionomic, transcriptomic, and metabolomic approaches. Under high K⁺ stress, root system architecture changes significantly compared to control …

Floodplain Forest Regeneration Dynamics In The Lower Mississippi River Alluvial Valley, Whitney Anne Kroschel

LSU Doctoral Dissertations

Floodplain forest species diversity is driven, in part, by variation in disturbance regime. Flood patterns create heterogeneity in microsite quality from small differences in elevation across a floodplain which, in turn, influence flood timing and duration. Differences in species’ regeneration niches in relation to hydrologic patterns can account for long-term coexistence of various species. In the past century floodplain forests have exhibited a wide range of changes in stand development and species composition as a result of altered hydrology in rivers and floodplains. I evaluated the role of regeneration in floodplain forest systems of the Lower Mississippi River Alluvial Valley …

Functions Of Cdk/Cyclin Complexes In Endoreplication Regulation By The Cdk Inhibitor Siamese, Kai Wang

LSU Doctoral Dissertations

Arabidopsis trichome (leaf hair) is a specialized single cell extended from epidermal cell on the leaves, which is a typical endoreplication and is also known as endoreduplication. Several D-type cyclins were tested to check the cell division in trichome, and the trichome expressing either CYCB1;2 or CDKB2;2 cannot trigger cell division, even if simultaneous expression of CYCB1;2 and CDKB2;2 failed to produce mitosis in trichome. Only CYCD3;1 specifically promotes multicellular trichome. cdkb1;1cdbk1;2 double mutants and sim cdkb1;1cdkb1;2 triple mutants exhibit the phenotype similar to the wild type and very limited cell division respectively. Overexpression of a CDKB1;1 dominant-negative construct that …

The Role Of Chromatin State Transitions In Modulating Early Phosphate-Deficiency Response Genes In Plants, Maryam Foroozani

LSU Doctoral Dissertations

Phosphorus (P) is an essential plant macronutrient vital to fundamental metabolic processes. Plant-available P is low in most soils, making it a frequent limiter of growth. Declining P reserves for fertilizer production exasperates this agricultural challenge. Plants modulate complex responses to fluctuating P levels via global transcriptional regulatory networks. Although chromatin structure plays a substantial role in controlling gene expression, the chromatin-level mechanisms involved in regulating P homeostasis have not been determined.

In this work, I used chromatin immunoprecipitation (ChIP) combined with next-generation DNA sequencing (ChIP-seq) to map the distribution of H3K4me3 in rice (Oryza sativa L.) during both …

The Tripartite Interaction Between Arbuscular Mycorrhizal Fungi, Rice, And Insects, Lina Bernaola Alvarado

LSU Doctoral Dissertations

Losses caused by pests remain an important limitation to achieving high rice yields in the United States. Arbuscular mycorrhizal fungi (AM fungi) are able to modify plant physiology by increasing plant growth or inducing defense responses against insect herbivores. However, studies of the role of AM fungi in agroecological factors, including natural occurrence, plant resistance, soil dependency, and plant tolerance, with specific regards to pests that feed on rice plants have not been conducted before. A three-year study revealed natural occurring colonization by AM fungi on rice roots sampled in four rice-producing areas in the southern United States. Overall, rice-AM …