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Abstract
My dissertation is comprised of dual research in tree biology and biology education. The first part presents my molecular tree biology research which sought to elucidate how sucrose trafficking influences carbohydrate remobilization in Populus. The second chapter focuses on a tonoplast sucrose transport protein (SUT4), a transmembrane protein that facilitates subcellular sucrose transport. By using transgenic mutants and coppicing experiments conducted under contrasting seasons, the study explored how trees allocate, store, and mobilize carbohydrate reserves to sustain growth and protection in an environmentally conditioned manner. The results suggest that carbohydrate reserves were maintained following coppicing and not completely depleted to sustain new tissue growth. The third chapter examined the importance of winter-biased sucrose transporters for carbohydrate allocation, phenology, and biomass accrual in hybrid poplar under a multi-season field trial. Despite their similar winter-biased expression, SUT4 appeared to have a greater role than SUT5 and SUT6 on environmental sensing, leaf area duration, and protective metabolism during the winter for woody perennials. Taken together, the findings highlight an environmentally conditioned role for sucrose transporters in the perennial growth cycle. The second part of this dissertation investigated how mentoring relationships contribute to or hinder STEM graduate student development. The fourth chapter defined and characterized graduate students negative mentoring experiences during their graduate education. The findings suggest that graduate students experience negative mentoring from multiple, interacting levels which hinders their career and psychosocial outcomes. The fifth chapter extended these findings by developing a psychometrically sound scale to measure negative mentoring experiences in STEM graduate education. The work provided rigorous validation evidence in support of the scale to measure these destructive experiences and relate them to graduate student outcomes. Finally, the sixth chapter tested the influence of variables theorized to predict mentorship quality. Despite an abundance of lore, little evidence supported the widely held beliefs that matching based on demographics and career stage promotes higher quality mentorship. The results of this study provided the most robust evidence to date on how to match graduate students and faculty mentors to promote effective and supportive mentoring relationships.