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Poplar Bark Storage Proteins (BSP) are important in storing nitrogen (N) recovered from autumn-senescent leaves, and supply N for spring growth. Plants of Populus tremula x P. alba were transformed with a poplar BSP antisense cDNA fused to a double 35S promoter. Regenerated lines were screened for reduced BSP accumulation in short day photoperiod, and two lines were selected for further studies. Under long-day conditions, both BSP-antisense lines were characterized by larger leaves, longer internodes and slower growth rates, for a net shift in dry-matter partitioning from stem to leaf. Antisense lines also show reduced N concentration in leaf and stem tissue, and altered nitrate uptake. Grafting studies show that these effects on leaf and stem partitioning and N content are determined by the shoot genotype. These results indicate an important role of BSP in long day growth and partitioning. BSP-antisense plants did not show altered Nitrate Reductase activity, as determined by in vivo assay. Wild-type poplar plants were grown hydroponically on solutions of 0 to 30 mM nitrate, and NR activity determined on leaf, stem and root tissue. Leaf activity was >20x higher than root or stem, with the highest activity found in young expanding leaves. NR activity of both leaves and roots increased with N supply. During autumn, BSP-antisense leaves abscised earlier than the untransformed wt. Abscised wt leaves contained a higher proportion of pre-senescent N levels. Comparisons among ecotypes of P. deltoides and among clones of P. trichocarpa x P. deltoides demonstrated genetic variation in both time of BSP induction, and amount of BSP accumulation. In six P. deltoides ecotypes grown at a common site, time of maximum BSP mRNA was inversely correlated with latitude of origin. Eight to ten clones from each of six full-sib families of P. trichocarpa x P. deltoides were screened for SD BSP accumulation. Clonal differences in BSP accumulation were significant in 5 of 6 families, and clones with high BSP levels also had higher total stem N content. These results further confirm the importance of BSP in autumn N resorption. / Graduation date: 2000

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One postulated prerequisite for phenotypic plasticity to evolve in a population is gene flow among its members. To test this hypothesis, I compared the phenotypic plasticity of 3 congeneric nut-sedges (Cyperus: Cyperaceae) that are similar in size, cohabit sandy beaches, yet differ in their reproductive strategies. Cyperus strigosus reproduces sexually by seed, C. dentatus asexually by bulbils, tubers, and rhizomes, and C. esculentus by a combination of sexual seed and asexual rhizomes and tubers. I predicted that C. strigosus and C. esculentus would be most plastic due to their potential for gene migration, while the asexual C. dentatus would be less plastic. Progeny arrays from nine genotypes of each species were grown in a series of eight environments in growth chambers. I measured 15 vegetative and reproductive traits at maturity. Analysis of covariance indicated a plastic response to the environment for all traits as well as genetic variation in phenotypic plasticity for all but vegetative allocation traits. Indices of plasticity for each genotype were highest for C. esculentus genotypes for vegetative traits and for C. strigosus genotypes for reproductive traits. These results support the hypothesis that non-zero gene migration enables the evolution of phenotypic plasticity.

Thesis (Ph.D.) in Biological Sciences--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 146-164).

Thesis (Ph. D.)--University of Oregon, 2004. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 125-142). Also available for download via the World Wide Web; free to University of Oregon users.

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