Correlates of leaf optical properties in tropical forest sun and extreme-shade plants

Thirteens hade-adaptedr ain forest species were comparedw ith twelve sun-adaptedt ropical forest species for correlates to leaf optical properties (described previously in Amer. J. Bot. 73: 1100-1108). The two samples were similar in absorptance of quanta for photosynthesis, but the shade-adaptedt axa: 1) had significantlyl ower specificl eaf weights,i ndicatinga more metabolically efficient production of surface for quantum capture; 2) synthesized less chlorophyll per unit area; and 3) used less chlorophyll for capturing the same quanta for photosynthesis. The anatomical features that best correlate with this increased efficiency are palisade cell shape and chloroplast distribution. Palisade cells with more equal dimensions have more chloroplasts on their abaxial surfaces. This dense layer of chloroplasts maximizes the light capture efficiency limited by sieve effects. The more columnar palisade cells of sun-adapted taxa allow light to pass through the central vacuoles and spaces between cells, making chloroplasts less efficient in energy capture, but allowing light to reach chloroplasts in the spongy mesophyll. Pioneer species may be an exception to these two groups of species. Three pioneer taxa included in this study have columnar palisade cells that are extremely narrow and packed closely together. This layer allows little penetration of light, but exposure of the leaf undersurface may provide illumination of spongy mesophyll chloroplasts in these plants.

Simulating Forest Shade to Study the Developmental Ecology of Tropical Plants: Juvenile Growth in Three Vines in India

Both light quantity and quality affect the development and autoecology of plants under shade conditions, as in the understorey of tropical forests. However, little research has been directed towards the relative contributions of lowered photosynthetic photon flux density (PPFD) versus altered spectral distributions (as indicated by quantum ratios of 660 to 730 nm, or R:FR) of radiation underneath vegetation canopies. A method for constructing shade enclosures to study the contribution of these two variables is described. Three tropical leguminous vine species (Abrus precatorius L., Caesalpinia bondicela Fleming and Mucuna pruriens (L.) DC.) were grown in two shade enclosures with 3-4% of solar PPFD with either the R:FR of sunlight (1.10) or foliage shade (0.33), and compared to plants grown in sunlight. Most species treated with low R:FR differed from those treated with high R:FR in (1) percent allocation to dry leaf weight, (2) internode length, (3) dry stem weight/length, (4) specific leaf weight, (5) leaf size, and (6) chlorophyll a/b ratios. However, these plants did not differ in chlorophyll content per leaf dry weight or area. In most cases the effects of low R:FR and PPFD were additional to those of high R:FR and low PPFD. Growth patterns varied among the three species, but both low PPFD and diminished R:FR were important cues in their developmental responses to light environments. This shadehouse system should be useful in studying the effects of light on the developmental ecology of other tropical forest plants.

The significance of chloroplast movement in leaves of tropical plants

The purpose of this research project was to contribute to the understanding of chloroplast movement in plants. Chloroplast movement in leaves from twenty tropical plant species ranging from cycads to monocots and varying in shade tolerance was examined by measuring changes in transmittance following 30 min. of exposure to white light at 1000 μmol m−2 s −1 in the wavelength range of 400–700 nm (photosynthetically active radiation, PAR). Leaf anatomical characteristics were also measured. Eighteen species increased significantly in transmittance (Δ T) at this level of illumination. ^ Chloroplast movement was significantly correlated with palisade cell width suggesting that cell dimensions are a significant constraint on chloroplast movement in the species examined. In addition, Δ T values were strongly correlated with values of an index of shade tolerance. ^ To further examine the relationship between palisade width and chloroplast movement, additional studies were conducted with a tropical aroid vine, Scindapsus aureus Schott. Scindapsus plants were grown under three different light treatments: 63% (control), 9.0% and 2.7% of full sunlight. Under these growing conditions plants produced markedly different palisade cell widths. Palisade cell width was again found to be correlated with transmittance changes. In addition, the observed increases in transmittance following exposure to the above illumination condition were correlated with absorbance of PAR. Fluorescence studies demonstrated that chloroplast movement helps protect Scindapsus aureus from the effects of photoinhibition when it is exposed to light at a higher intensity relative to the intensity of its normal environment. Ratios of variable fluorescence (Fv) to maximal fluorescence (Fm ) were higher in plants exposed to high light when chloroplasts moved than in plants where chloroplasts did not. ^ To further explore the role of chloroplast movement, studies were conducted to determine if transmittance changes could be induced in ten xerophytes at (1000 μmol m−2 s−1), as well as two stronger light intensities (1800 μmol m−2 s−1 and 2200 μmol m−2 s −1). Transmittance changes in the ten xerophytes were dependent upon the illumination intensity; nine out of the ten xerophytes changed in transmittance at 1800 μmol m−2 s−1. For the other two intensity levels, only three out of the ten xerophytes tested exhibited transmittance changes, and for two species, a negative Δ T value was obtained at 1000 μmol m−2 s−1 . No relationship was found between cell dimensions and chloroplast movement, although all species had large enough chlorenchyma cells to allow such movements. ^ The results of the study clearly show that in non-xerophytes, palisade cell anatomy is a strong constraint on chloroplast movement. This relationship may be the basis for the relationship between chloroplast movement and shade tolerance. Although absorbance changes are relatively small, chloroplast movement was clearly shown to reduce photoinhibition. ^

Voting with their feet: Migration, partisanship, and party-safe elections in Florida

Political scientists have long noted that Congressional elections are often uncompetitive, often extremely so. Many scholars argue that the cause lies in the partisan redistricting of Congressional districts, or “gerrymandering”. Other scholars emphasize polarization created by a fragmented news media, or the candidate choices made by a more ideological primary electorate. All these explanations identify the cause of party-safe elections in institutions of various kinds. This dissertation, by contrast, presents a structural explanation of uncompetitive elections. My theory is that population composition and patterns of migration are significant causes and predictors of election results in Florida. I test this theory empirically by comparing the predictions from four hypotheses against aggregate data, using the county as the unit of analysis. The first hypothesis is that Florida can be divided into clearly distinguishable, persistent partisan sections. This hypothesis is confirmed. The second hypothesis is that Florida voters have become increasingly partisan over time. This hypothesis is confirmed. The third hypothesis is that the degree of migration into a county predicts how that county will vote. This hypothesis is partially confirmed, for the migration effect appears to have waned over time. The last hypothesis is that the degree of religiosity of a county population is a predictor of how that county will vote. This hypothesis is also supported by the results of statistical analysis. By identifying the structural causes of party-safe elections, this dissertation not only broadens our understanding of elections in Florida, but also sheds light on the current polarization in American politics.

Factors influencing the implementation of substance use prevention programs in elementary schools

Prevention scientists have called for more research on the factors affecting the implementation of substance use prevention programs. Given the lack of literature in this area, coupled with evidence that children as early as elementary school engage in substance use, the purpose of this study was to identify the factors that influence the implementation of substance use prevention programs in elementary schools. This study involved a mixed methods approach comprised of a survey and in-person interviews. Sixty-five guidance counselors and teachers completed the survey, and 9 guidance counselors who completed the survey were interviewed individually. Correlation analyses and hierarchical multiple regression were conducted. Quantitative findings revealed ease of implementation most frequently influenced program implementation, followed by beliefs about the program's effectiveness. Qualitative findings showed curriculum modification as an important theme, as well as difficulty of program implementation. The in-person interviews also shed light on three interrelated themes influencing program implementation – The Wheel, time, and scheduling. Results indicate the majority of program providers modified the curriculum in some way. Implications for research, policy, and practice are discussed, and areas for future research are suggested.^

Molecular studies in gorgonian alloimmunity : search for gene homologs of the immunoglobulin gene superfamily in Swiftia exserta

Humoral and cells surface molecules of the mammalian immune system, grouped into the Immunoglobulin Gene Superfamily, share protein structure and gene sequence homologies with molecules found among diverse phylogenetic groups. In histocompatibility studies, the gorgonian coral Swiftia exserta has recently demonstrated specific alloimmunity with memory (Salter-Cid and Bigger, 1991. Biological Bulletin Vol 181). In an attempt to shed light on the origins of this gene family and the evolution of the vertebrate immune response, genomic DNA from Swiftia exserta was isolated, purified, and analyzed by Southern blot hybridization with mouse gene probes corresponding to two molecules of the Immunoglobulin Gene Superfamily, the Thy-1 antigen, and the alpha-3 domain of the MHC Class I histocompatibility marker. Hybridizations were conducted under low to non-stringent conditions to allow binding of mismatched homologs that may exist between the mouse gene probes and the Swiftia DNA. Removal of non-specific binding (sequences less than 70% homologous) occurred in washing steps. Results show that with the probes selected, the method chosen, and the conditions applied, no evidence of sequences of 70% or greater homology to the mouse Thy-1 or MHC Class I alpha-3 genes exist in Swiftia exserta genome.

Factors Influencing the Implementation of Substance Use Prevention Programs in Elementary Schools

Prevention scientists have called for more research on the factors affecting the implementation of substance use prevention programs. Given the lack of literature in this area, coupled with evidence that children as early as elementary school engage in substance use, the purpose of this study was to identify the factors that influence the implementation of substance use prevention programs in elementary schools. This study involved a mixed methods approach comprised of a survey and in-person interviews. Sixty-five guidance counselors and teachers completed the survey, and 9 guidance counselors who completed the survey were interviewed individually. Correlation analyses and hierarchical multiple regression were conducted. Quantitative findings revealed ease of implementation most frequently influenced program implementation, followed by beliefs about the program’s effectiveness. Qualitative findings showed curriculum modification as an important theme, as well as difficulty of program implementation. The in-person interviews also shed light on three interrelated themes influencing program implementation – The Wheel, time, and scheduling. Results indicate the majority of program providers modified the curriculum in some way. Implications for research, policy, and practice are discussed, and areas for future research are suggested.

Factors affecting the nodulation and growth of tropical woody legume seedlings

This study surveys the occurrence of nodulation in woody legume species in Panamá and Costa Rica, describes nodule and root characteristics, and researches host-bacteria specificity, nodulation potential of soils, and the effects of light, added nitrogen, and rhizobia and VA mycorrhizal fungi inoculation on seedling growth. I examined 83 species in 37 genera and found 80% to be nodulated. Percent nodulated species in the Caesalpinioideae, Mimosoideae, and Papilionoideae was 17, 95, and 86, respectively, with no correlation between nodule morphology and tribal classification. Nodules formed mainly at root branch points which supports epidermal breaks as an important rhizobia infection route. More non-nodulated than nodulated species had root hairs. Several species emitted volatile sulfur-containing compounds, including the toxic compound ethylmercaptan, from roots, germinating seeds, and other tissues. These emissions may have an allelopathic action against pathogens, predators, or other plants. In contrast to the general non-specificity of most legumes for rhizobia, Mimosa pigra L. was highly specific and only nodulated in flooded soils. This species' specificity, combined with a limited occurrence of its root nodule bacteria may limit its natural distribution, but its spread as an invasive weed is facilitated when fill material from rivers is deposited in other areas. ^ An experimental light level of 1.5% of full sun completely inhibited seedling nodulation, as do similar naturally low levels in forest understory. In the forest, trees and seedlings were not nodulated. in some soils with suspected high N content. For six experimental species, added N progressively increased seedling growth while decreasing nodule biomass; at the highest level of added N nodulation was completely suppressed. Species and individuals showed variation in nodule biomass at high N applications which may indicate an opportunity for genetic selection for optimal N acquisition. Rhizobia inoculation had a small positive effect on seedling shoot growth, but VA mycorrhiza inoculation overwhelmingly increased seedling size, biomass, and leaf mineral concentration. In lowland tropical forest, VA mycorrhizal colonization appears indispensable for legume nodulation because of the fungus' ability to supply P in deficient soils. This requirement makes the legume-rhizobia-mycorrhiza association obligately tripartite. ^

Pseudomonas aeruginosa AMPR transcriptional regulatory network

In Enterobacteriaceae, the transcriptional regulator AmpR, a member of the LysR family, regulates the expression of a chromosomal β-lactamase AmpC. The regulatory repertoire of AmpR is broader in Pseudomonas aeruginosa, an opportunistic pathogen responsible for numerous acute and chronic infections including cystic fibrosis. Previous studies showed that in addition to regulating ampC, P. aeruginosa AmpR regulates the sigma factor AlgT/U and production of some quorum sensing (QS)-regulated virulence factors. In order to better understand the ampR regulon, the transcriptional profiles generated using DNA microarrays and RNA-Seq of the prototypic P. aeruginosa PAO1 strain with its isogenic ampR deletion mutant, PAOΔampR were analyzed. Transcriptome analysis demonstrates that the AmpR regulon is much more extensive than previously thought influencing the differential expression of over 500 genes. In addition to regulating resistance to β-lactam antibiotics via AmpC, AmpR also regulates non-β-lactam antibiotic resistance by modulating the MexEF-OprN efflux pump. Virulence mechanisms including biofilm formation, QS-regulated acute virulence, and diverse physiological processes such as oxidative stress response, heat-shock response and iron uptake are AmpR-regulated. Real-time PCR and phenotypic assays confirmed the transcriptome data. Further, Caenorhabditis elegans model demonstrates that a functional AmpR is required for full pathogenicity of P. aeruginosa. AmpR, a member of the core genome, also regulates genes in the regions of genome plasticity that are acquired by horizontal gene transfer. The extensive AmpR regulon included other transcriptional regulators and sigma factors, accounting for the extensive AmpR regulon. Gene expression studies demonstrate AmpR-dependent expression of the QS master regulator LasR that controls expression of many virulence factors. Using a chromosomally tagged AmpR, ChIP-Seq studies show direct AmpR binding to the lasR promoter. The data demonstrates that AmpR functions as a global regulator in P. aeruginosa and is a positive regulator of acute virulence while negatively regulating chronic infection phenotypes. In summary, my dissertation sheds light on the complex regulatory circuit in P. aeruginosa to provide a better understanding of the bacterial response to antibiotics and how the organism coordinately regulates a myriad of virulence factors.

Selective and specific activation of Rab5 during endocytosis of receptor tyrosine kinases

The Rab family of proteins are low molecular weight GTPases that have the ability to switch between GTP- (active) and GDP- (inactive) bound form, and in that sense act as molecular switches. Through distinct localization on various vesicles and organelles and by cycling through GTP/GDP bound forms, Rabs are able to recruit and activate numerous effector proteins, both spatially and temporally, and hence behave as key regulators of trafficking in both endocytic and biosynhtetic pathways. The Rab5 protein has been shown to regulate transport from plasma membrane to the early endosome as well as activate signaling pathways from the early endosome. This dissertation focused on understanding Rab5 activation via endocytosis of receptor tyrosine kinases (RTKs). First, tyrosine kinase activity of RTKs was linked to endosome fusion by demonstrating that tyrosine kinase inhibitors block endosome fusion and activation of Rab5, and a constitutively active form of Rab5 is able to rescue endosome fusion. However, depending on how much ligand is available at the cell surface, the receptor-ligand complexes can be internalized via a number of distinct pathways. Similarly, Rab5 was activated in a ligand-dependent concentration dependent manner via clathrin- and caveolin-mediated pathways, as well as a pathway independent of both. However, overexpression Rabex-5, a nucleotide exchange factor for Rab5, is able to rescue activation even when all of the pathways of EGF-receptor internalization were blocked. Next, the three naturally occurring splice variants of Rabex-5 selectively activated Rab5. Lastly, Rabex-5 inhibits differentiation of 3T3-L1 and PC12 cells through 1) degradation of signaling endosome via Rab5-dependent fusion with the early endosome, 2) and inhibition of signaling cascade via ubiquitination of Ras through the ZnF domain at the N-terminus of Rabex-5. In conclusion, these data shed light on complexity of the endosomal trafficking system where tyrosine kinase activity of the receptor is able to affect endosome fusion; how different endocytic pathways affect activation of one of the key regulators of early endocytic events; and how selective activation of Rab5 via Rabex-5 can control adipogenesis and neurogenesis.

The Road from Emmaus

THE ROAD FROM EMMAUS is a collection of 20 personal and lyric essays that explores the narrator’s role as mother and daughter through a close look at significant life events, including her parents’ divorce, a high-risk pregnancy, the death of her father, talking to her daughter for the first time about sex, and accompanying her daughter to the DMV for a learner’s permit. Through examining familial roles and relationships, the narrator’s longing for home emerges as a unifying theme. The essays in THE ROAD FROM EMMAUS vary in style and tone, from light and funny to serious and probing. The collection is divided into five sections, each highlighting a different aspect of the narrator’s life as she evolves from a child, to a young adult, a mother, and a daughter who must help take care of her aging parents.

Uniquely Identifiable Tamper-Evident Device Using Coupling between Subwavelength Gratings

Reliability and sensitive information protection are critical aspects of integrated circuits. A novel technique using near-field evanescent wave coupling from two subwavelength gratings (SWGs), with the input laser source delivered through an optical fiber is presented for tamper evidence of electronic components. The first grating of the pair of coupled subwavelength gratings (CSWGs) was milled directly on the output facet of the silica fiber using focused ion beam (FIB) etching. The second grating was patterned using e-beam lithography and etched into a glass substrate using reactive ion etching (RIE). The slightest intrusion attempt would separate the CSWGs and eliminate near-field coupling between the gratings. Tampering, therefore, would become evident. Computer simulations guided the design for optimal operation of the security solution. The physical dimensions of the SWGs, i.e. period and thickness, were optimized, for a 650 nm illuminating wavelength. The optimal dimensions resulted in a 560 nm grating period for the first grating etched in the silica optical fiber and 420 nm for the second grating etched in borosilicate glass. The incident light beam had a half-width at half-maximum (HWHM) of at least 7 µm to allow discernible higher transmission orders, and a HWHM of 28 µm for minimum noise. The minimum number of individual grating lines present on the optical fiber facet was identified as 15 lines. Grating rotation due to the cylindrical geometry of the fiber resulted in a rotation of the far-field pattern, corresponding to the rotation angle of moiré fringes. With the goal of later adding authentication to tamper evidence, the concept of CSWGs signature was also modeled by introducing random and planned variations in the glass grating. The fiber was placed on a stage supported by a nanomanipulator, which permitted three-dimensional displacement while maintaining the fiber tip normal to the surface of the glass substrate. A 650 nm diode laser was fixed to a translation mount that transmitted the light source through the optical fiber, and the output intensity was measured using a silicon photodiode. The evanescent wave coupling output results for the CSWGs were measured and compared to the simulation results.

Selective and Specific Activation of Rab5 during Endocytosis of Receptor Tyrosine Kinases

The Rab family of proteins are low molecular weight GTPases that have the ability to switch between GTP- (active) and GDP- (inactive) bound form, and in that sense act as molecular switches. Through distinct localization on various vesicles and organelles and by cycling through GTP/GDP bound forms, Rabs are able to recruit and activate numerous effector proteins, both spatially and temporally, and hence behave as key regulators of trafficking in both endocytic and biosynhtetic pathways. The Rab5 protein has been shown to regulate transport from plasma membrane to the early endosome as well as activate signaling pathways from the early endosome. This dissertation focused on understanding Rab5 activation via endocytosis of receptor tyrosine kinases (RTKs). First, tyrosine kinase activity of RTKs was linked to endosome fusion by demonstrating that tyrosine kinase inhibitors block endosome fusion and activation of Rab5, and a constitutively active form of Rab5 is able to rescue endosome fusion. However, depending on how much ligand is available at the cell surface, the receptor-ligand complexes can be internalized via a number of distinct pathways. Similarly, Rab5 was activated in a ligand-dependent concentration dependent manner via clathrin- and caveolin-mediated pathways, as well as a pathway independent of both. However, overexpression Rabex-5, a nucleotide exchange factor for Rab5, is able to rescue activation even when all of the pathways of EGF-receptor internalization were blocked. Next, the three naturally occurring splice variants of Rabex-5 selectively activated Rab5. Lastly, Rabex-5 inhibits differentiation of 3T3-L1 and PC12 cells through 1) degradation of signaling endosome via Rab5-dependent fusion with the early endosome, 2) and inhibition of signaling cascade via ubiquitination of Ras through the ZnF domain at the N-terminus of Rabex-5. In conclusion, these data shed light on complexity of the endosomal trafficking system where tyrosine kinase activity of the receptor is able to affect endosome fusion; how different endocytic pathways affect activation of one of the key regulators of early endocytic events; and how selective activation of Rab5 via Rabex-5 can control adipogenesis and neurogenesis.

Pseudomonas Aeruginosa AmpR Transcriptional Regulatory Network

In Enterobacteriaceae, the transcriptional regulator AmpR, a member of the LysR family, regulates the expression of a chromosomal β-lactamase AmpC. The regulatory repertoire of AmpR is broader in Pseudomonas aeruginosa, an opportunistic pathogen responsible for numerous acute and chronic infections including cystic fibrosis. Previous studies showed that in addition to regulating ampC, P. aeruginosa AmpR regulates the sigma factor AlgT/U and production of some quorum sensing (QS)-regulated virulence factors. In order to better understand the ampR regulon, the transcriptional profiles generated using DNA microarrays and RNA-Seq of the prototypic P. aeruginosa PAO1 strain with its isogenic ampR deletion mutant, PAO∆ampR were analyzed. Transcriptome analysis demonstrates that the AmpR regulon is much more extensive than previously thought influencing the differential expression of over 500 genes. In addition to regulating resistance to β-lactam antibiotics via AmpC, AmpR also regulates non-β-lactam antibiotic resistance by modulating the MexEF-OprN efflux pump. Virulence mechanisms including biofilm formation, QS-regulated acute virulence, and diverse physiological processes such as oxidative stress response, heat-shock response and iron uptake are AmpR-regulated. Real-time PCR and phenotypic assays confirmed the transcriptome data. Further, Caenorhabditis elegans model demonstrates that a functional AmpR is required for full pathogenicity of P. aeruginosa. AmpR, a member of the core genome, also regulates genes in the regions of genome plasticity that are acquired by horizontal gene transfer. The extensive AmpR regulon included other transcriptional regulators and sigma factors, accounting for the extensive AmpR regulon. Gene expression studies demonstrate AmpR-dependent expression of the QS master regulator LasR that controls expression of many virulence factors. Using a chromosomally tagged AmpR, ChIP-Seq studies show direct AmpR binding to the lasR promoter. The data demonstrates that AmpR functions as a global regulator in P. aeruginosa and is a positive regulator of acute virulence while negatively regulating chronic infection phenotypes. In summary, my dissertation sheds light on the complex regulatory circuit in P. aeruginosa to provide a better understanding of the bacterial response to antibiotics and how the organism coordinately regulates a myriad of virulence factors.