Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 86-94). Also available on the World Wide Web.

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Vascular tissues provide both the mechanical support to the plant body and the conducting cells for the transport of water, mineral solutes, hormones and other signaling molecules, amino acids, and sugars. To identify genes that may regulate vascular tissue-specific functions, we isolated xylem, phloem-cambium, and nonvascular tissues from the Arabidopsis root-hypocotyl, performed a genome-wide comparative analysis of tissue-specific transcripts using the 24K Affymetrix Arabidopsis ATH1 Genome Array (24K GeneChip), and identified potential genes that are required for xylem and phloem differentiation or tissue-specific functions. Based on this comparative analysis, two phloem-specific G2-like transcription factors, MYR1 and MYR2, and a xylem-specific NAC domain family member, XND1, were selected for further characterization. Under continuous light, myr2 plants flowered early, while myr1 plants did not differ significantly from wild type controls. However, double mutant myr1myr2 plants exhibited a novel phenotype characterized by elongated petioles, semi-erect leaf orientation, and suppression of lateral shoot outgrowth. These characteristics are reminiscent of yucca, a dominant Arabidopsis mutant with elevated levels of free auxin. Preliminary results indicated that like yucca, myr1myr2 plants were more resistant than wt plants to 5-mT, a toxic tryptophan analog, suggesting that MYR1 and MYR2 may be involved in regulating tryptophan-dependent auxin biosynthesis. Overexpression of any one of MYR1 isoforms resulted in a phenotype that in some cases resembled that observed in the double mutant, indicating that the regulation mediated by MYR1 and MYR2 may depend on formation of specific heterodimers consisting of isoforms of MYR1 and/or MYR2, and that the dimerization was susceptible to disruption both by overexpression and loss-of-function of MYR1/MYR2. Overexpression of XND1 resulted in the absence of TEs as determined from the absence of both secondary cell wall deposition and TE death. Using 3 tissue-specific promoter-GUS lines as genetic backgrounds, we demonstrated that overexpression of XND1 suppressed only TE-specific GUS expression but not phloem-specific GUS expression. Three T-DNA/transposon insertion lines, xnd1-1, -2, and -3, were identified. Under normal conditions, xnd1 did not exhibit significantly different growth and development compared to wild type plants. However, preliminary data indicated that xnd1 plants were ABA and cold hypersensitive. Yeast-two hybrid screening using the N-terminal portion of XND1 as bait identified a novel RING finger protein, At3g62970 that may function as the ubiquitin ligase (E3). These results suggested that XND1 functions as a negative regulator of xylem cell differentiation, and that the regulation mediated by XND1 may be integrated with the ubiquitin/26S proteasome pathway. / Ph. D.

Trace element mobility in bald cypress (Taxodium distichum) was investigated for a suite of elements using cores from century-old trees from a wetland in Humphreys County, Mississippi. Element mobility was determined by comparing the dendrochemistry of decadal increments over the life span of a tree, and by comparing increments of the same age collected from the same tree during two different seasons. Variability within growth increments at the time of sampling was evaluated by comparing cores from the same tree collected at three points around the bole. Of 42 elements analyzed, eight were found above detection limits (As, Ca, K, Mg, Mn, Na, P, Zn). Clear evidence of translocation of P and Mn to the sapwood and K, Mg, and Na to the heartwood was observed. Ca and Zn were found with higher average concentrations in the sapwood, though evidence of translocation to the sapwood was equivocal. Arsenic did not vary significantly through any individual core. Variation in concentration was not found to be significant for any element with respect to year of sampling, season, location in the wetland, or position around the bole. With the exception of As, variation was significant with respect to increment age (decade) and location within the heartwood or sapwood.

This thesis presents the results of an investigation into the uptake and distribution of cadmium (Cd) in two cultivars of potato (Solanum tuberosum L.) shown to contain different concentrations of Cd in the tuber at maturity. An initial glasshouse trial sought to determine whether differences in tuber Cd between these two cultivars resulted from differences in uptake from the soil, or were due to differences in the allocation of Cd to the various tissues within the plant. Total uptake of Cd from the soil did not differ between cultivars, nor did the yield of tubers. However, there were marked differences in Cd distribution within the plant. Most of the differences in tuber Cd concentration could be accounted for by a large (3-fold) retention of Cd in the roots of cultivar Wilwash. The concentration of Cd in the shoots of Wilwash was also higher than of Kennebec, although to a lesser extent than the roots. Further studies were conducted to trace the pathways of Cd uptake and movement within the plant. A split-pot trial, involving long-term growth of potatoes in 109Cd-labelled soil, was undertaken to determine the overall pattern of Cd distribution and the importance of the root system in supplying Cd to the tubers. The root system of the potato plant is different to many plants, in that the main root system (basal roots) is augmented after tuber initiation by roots extending from the stolon and from the tuber itself. The basal roots were found to be the dominant source of Cd to all tissues and accounted for approximately 85 % of tuber Cd. The remaining tuber Cd was sourced directly from the stolon and tuber roots. However, there was no evidence of a direct link between the main (basal) root system and the stolons. Although Cd was found to accumulate in the periderm of the tubers, there was no uptake into the tuber tissue itself. Isotopic studies were undertaken to investigate the short-term movement of newly absorbed Cd in the xylem and the phloem. Cadmium was found to be highly mobile in both the xylem and phloem, with added Cd being rapidly assimilated into all tissues following both root and foliar application. Newly absorbed Cd was rapidly sequestered by the stems when applied to either the soil or to a source leaf, suggesting that the stems may act as a transitional storage pool when rapid turnover of nutrients and other mineral elements is required during tuber bulking. Inhibition of Cd uptake by zinc (Zn), has been proposed as a method for reducing the concentration of Cd in various agricultural crops, including potatoes. The ability of Zn to reduce Cd uptake was found to be highly dependent upon cultivar and on the concentration of Cd in the external medium. Although competition between Zn and Cd was found for cultivar Wilwash when the external concentration of Cd was low, when the concentration of Cd in the external media was high, increasing Zn served to increase Cd uptake. Both synergistic and competitive responses were also noted for cultivar Kennebec. However, the patterns of response were opposite to those evident in Wilwash. The complexity of these interactions highlighted the possible shortcomings in using soil applied Zn to limit Cd uptake by potatoes. / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2004.

Programmed cell death (PCD) refers to a genetically controlled process causing the death of certain cells or tissues. In plants PCD is critical in normal development of for instance xylem vessels. A group of proteins called metacaspases are believed to play a pivotal role in PCD in plants. As Metacaspase 9 have been shown to be upregulated in Populus during xylem maturation this study attempted to identify genes affecting its expression in Arabidopsis thaliana by forward genetics using a reporter line with GFP fused to the promoter of Metacaspase 9 (AtMC9). Ethyl methanesulfonate seed mutagenesis was used to generate mutants resulting in eleven mutant lineages with a GFP expression pattern deviating from that of the reporter line. These mutants fell into two categories; low/no-signal mutants and ectopic expressors. Several of the low/no-signal mutants had longer roots at five to eight days after germination, a time point shown to be critical for metaxylem differentiation. Further studies of their roots would reveal whether the developing xylem is abnormal or not. Deep sequencing provided evidence for involvement of abscisic acid and polyamines in regulation of AtMC9 expression. Sequencing from a low/no-signal mutant suggests that AtMC9 expression might be affected also by disturbed lignin biosynthesis. Rescuing mutant lineages through transformations with fully functional forms of the candidate genes is the next step to experimentally validate that the candidate genes are involved in the observed changes in AtMC9 expression in each of the isolated mutants.

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Dissertation (M.S.)--The University of North Carolina at Greensboro, 2008. / Directed by Bruce Kirchoff; submitted to the Dept. of Biology. Title from PDF t.p. (viewed Feb. 2, 2010). Includes bibliographical references (p. 134-146).

Thesis (Ph. D.)--Institute of Paper Chemistry, 1937. / Includes bibliographical references (leaves 161-164).