Plants respond to wounding and pathogen ingress by synthesizing defence proteins that facilitate wound healing, cell death or provide protection against further pathogen attack. The accumulation of these proteins is mainly due to rapid transcriptional activation of corresponding genes, though preliminary evidence implies that translational control may also have a role in the stress response. This study focuses on the function of <i>Arabidopsis thaliana</i> eukaryotic translation initiation factor 5A (eIF5A) in mechanical wounding and during infection with the phytopathogen <i>Pseudomonas syringae</i>. Recent evidence suggests that eIF5A acts as a nucleo-cytoplasmic shuttling protein that facilitates mRNA translation through selective transport from the nucleus. Three isoforms of eIF5A have been identified and isolated in <i>Arabidopsis thaliana</i>, suggesting that each distinct isoform may be involved in transport of different subsets of mRNA required for a specific physiological event. The analysis in this study revealed that the eIF5A-2 isoform appears to be involved in the signal transduction pathways that result in cell death following virulent infection, systemic acquired resistance and wounding in <i>Arabidopsis thaliana</i>. Transgenic plants with reduced expression of eIF5A-2 were developed using antisense T-DNA insertion. These lines have shown marked resistance to <i>Pseudomonas syringae</i> pv <i>tomato</i> DC3000, exhibiting up to 99% decrease of bacteria <i>in planta</i> and cell death associated with disease. The capacity to effectively limit growth of various pathogens is important for the design of strategies to improve disease resistance in crops. Development of disease-resistant lines allows efficient crop production with reduced reliance on environmentally undesirable toxic agrichemicals.

Multiple pterosaur specimens have revealed details of their soft tissue anatomy, including wing membranes supported internally by strengthening fibres (aktinofibrils), a hair-like integument across their bodies, necks and heads (pycnofibres), elaborate soft-tissue head crests, tail vanes and other structures. These have enabled a more comprehensive picture of them as living animals than skeletal remains alone could, though many aspects of the structure and composition of these soft tissues remain controversial. The histology of pterosaur wing membranes has been a particularly contentious issue, with much debate focused on an alleged portion of wing membrane (DGM 1475-R) from the Lower Cretaceous Santana Formation of northeast Brazil. Initially described as a portion of wing membrane from the proximal wing region by Martill and Unwin (1989), after re-examination of the same specimen Kellner (1996) argued that it represented a piece of body wall. With DGM 1475-R showing features not seen in other specimens of pterosaur wing membrane and being one of the few three-dimensionally preserved portions of pterosaur membrane known, resolving this controversy is key to understanding this important component of pterosaur flight anatomy. In this study, DGM 1475-R was re-examined in an attempt to clarify the identity of its soft-tissues. Interpretation of the humerus and several ribs associated with the soft-tissue tentatively suggests that the specimen represents a thalassodromid pterosaur. A new section was taken through the soft-tissues and acid etched to highlight histological features. Multiple layers were identified within the soft tissue, including an external epidermis and a layer of muscle. The structures between these layers - numerous objects that appear to be fibres larger than the undoubted muscle fibres - are more ambiguous. These were previously identified as aktinofibrils (Martill et al., 1990), but this is considered unlikely due to differences in the shape, density and distribution of the structures when compared to aktinofibrils in other pterosaur wings. Instead, it is tentatively suggested that they represent a further layer of muscle fibres, but this cannot be conclusively proven. Further comparisons were made between DGM 1475-R and a dissected bat wing to find additional diagnostic wing tissues, but they were found to have such fundamental histological differences that such comparisons were of little use. Aktinofibrils are the only known diagnostic features of pterosaur wings, suggesting that their absence in DGM 1475-R argues against the specimen stemming from the wing tissues. Interpretations of pterosaur wing membrane and flight based on DGM 1475-R being wing membrane are therefore suspect.

The metabolic secretions from Aspergillus flavus, aflatoxins. are often found as contaminants of agricultural products used for human and animal consumption. Aflatoxin B1 is the most toxic and carcinogenic of the aflatoxins. A reduction in weight gain has been observed when juvenile animals are fed aflatoxin B1 over an extended period of time. This reduction in weight gain may possibly result from an anemic condition induced by an alteration of iron absorption and/or distribution. The effect of chronic sublethal levels of this hepatocarcinogen on weight gain and the uptake and distribution of 59Fe++ were studied in this investigation. An experimental group consisting of 12 male gerbils was fed an agar-based diet containing 10 ppm aflatoxin B1 and a control group consisting of 6 male gerbils was fed an identical diet which did not contain aflatoxin B1 for a 75-day period. The total mean aflatoxin B1 consumption of the experimental group amounted to 0.170 mg aflatoxin B1/kg of body weight. At the termination of the investigation the mean percent iron absorption of the control and experimental groups was determined. Values of 6.25 and 6.89, respectively, were calculated. The difference between these means was not determined to be significant. At the termination of the investigation the mean weight gain of the control group animals was 36.9 g as compared to 29.8 g for the aflatoxin group. The difference indicated that a significant reduction in weight gain was observed in the experimental group. lt was apparent that neither the physical activity nor diet consumption measured in the investigation affected the weight gain. Pathological analysis indicated that one-third of the experimental animals had liver injury and two of these had toxic hepatitis. The difference in the iron absorption between the aflatoxin group and the control group was not found to be significant but certain trends were observed. Animal number 13. the animal with the highest percent absorption, also had toxic hepatitis. However, contradictory evidence was also present with animal number 16 having toxic hepatitis and a very low percent iron absorption.

<p>Bet-hedging strategies are used by organisms to survive in</p><p>unpredictable environments. To pursue a bet-hedging strategy, an</p><p>organism must produce multiple phenotypes from a single genotype. What</p><p>molecular mechanisms allow this to happen? To address this question, I</p><p>created a synthetic system that displays bet-hedging behavior, and</p><p>developed a new technique called `TrackScar' to measure the fitness</p><p>and stress-resistance of individual cells. I found that bet-hedging</p><p>can be generated by actively sensing the environment, and that</p><p>bet-hedging strategies based on active sensing need not be</p><p>metabolically costly. These results suggest that to understand how</p><p>bet-hedging strategies are produced, microorganisms must be</p><p>examined in the actual environments that they come from.</p> / Dissertation

<p> Black abalone on California&rsquo;s rocky shores are critically endangered due to overfishing, disease, and increasing environmental temperatures. Risk of thermal stress and disease have been found to increase with variation in body temperature (<i>T</i>_b), yet we lack a clear understanding of the temperature regimes experienced by abalone in the wild. I created a mechanistic heat budget model coupled with long-term meteorological records to identify key environmental controls and expected distributions of abalone <i> T</i>_bs in the field. Overall, thermal stress increased with shore height and was highest for abalone on southwest facing moderately sloped surfaces; in contrast, disease risk was mostly high and independent of orientation at all but the lowest shore heights. Mechanistic approaches such as heat budget modeling enhance our ability to quantify physiological risk to individuals, compare ecological conditions across broad spatial scales, and successfully predict consequences of changing environmental conditions through time.</p>

No description available.

During a two—year period, beginning in the summer of 1973 and ending in the summer of 1975, a study was conducted on myxomycete bionta from bark of living trees growing in five widely separated localities within the Atlanta city limits. The objectives of the study were to determine (1) whether bark of living trees is a natural substratum for certain kinds of myxomycetes; (2) whether certain myxomycetes manifest affinities for certain species of trees; (3) whether seasonal variations exist in corticolous myxomycete occurrence; and (4) whether any correlation exists between the distribution of corticolous myxomycetes and tree habitats. Since two earlier studies of limited scope represent the only reports of systematic studies on corticolous myxomycetes of Georgia, a need has existed for more extensive information on this myxomycete bionta of the state. This study was undertaken in order to fulfill that need. To accomplish the objectives a total of 171 trees, representing 12 genera and 21 species, growing in five selected areas within the city limits of Atlanta, were chosen for the study. The genus and species of the trees used were Acer and A. saccharinum, Carya illinoensis and C. ovata, Cedrus deodara, Cornus florida, Diospyros virginiana, Liquidambar styraciflua, Liriodendron tulipifera, Ostrya virginiana, Pinus echinata and P. taeda, Prunus serotina, Quercus alba, Q. falcata, Q. nigra, Q. phellos, Q. stellata, and Q. velutina, Ulmus alata and U. americana. The five different localities used in this study included three relatively undisturbed wooded areas and two open park areas. The localities were (1) a wooded area in the Highpoint section; (2) a wooded hillside in the Collier Heights section; in the Beecher Circle section; and (4) two city parks, namely, Washington and Piedmont Parks. Specific plots were selected within each locality for sampling. Each plot was approximately 15 meters square and contained at least one tree of each species that was to be studied. In two of the localities, viz., Collier Heights and Beecher Circle, fallen debris on the forest floor was periodically examined in the field. Five different techniques were used to create conditions favor able for myxomycete development. These techniques were as follows: (1) a modification of the moist chamber technique originally used by Gilbert and Martin; (This modification involved the gradual soaking of bark pieces in sterile petri dishes by adding small volumes of sterile water intermittently as was absorbed by the bark, This practice reduced the possibility of spores being discarded, as may happen when the method of Gilbert and Martin is used.) (2) the placing of bark samples in polyethylene bags and attaching these bags to the sides of the trees from which they were collected; (Sterile distilled water was added to the bags in order to first saturate the bark pieces and subsequently maintain a high humidity.) (3) the removal of bark samples from trees and the incubation of these samples in petri dish moist chambers that were left in the field at the base of the tree from which the samples were removed; (4) the attaching of large water—filled polyethylene bags to trees at about breast height; (The bags were perforated at the bottom by puncturing the corners and the middle with a few pin holes. This enabled water to slowly drip onto the bark below the bag and consequently keep the trunk in that region continuously moist.) and (5) the periodic examination of undisturbed bark of standing trees with a 1OX hand lens in a search for naturally developing slime molds. Field examinations of leaf litter were also made in order to determine whether myxomycetes that developed in moist chamber on bark samples also developed naturally on plant debris on the forest floor. A total of 46 species of myxomycetes was found during the two years of the study. Forty species of myxomycetes, representing 16 genera, appeared on collected bark samples during the course of the study, and six other species representing six genera were found on field observed leaf litter. The following species of myxomycetes were found: Arcyria carnea, A. cinerea and A. nutans, Badhamia nitens and B. obovata, Calomyxa metallica, Ceratiomyxa fruitculosa, Clastoderma debaryanum, Comatricha elegans, C. fimbriata, C. lurida, C. nigra and C. pulchella, Cribraria minutissima and C. violacea, Dictydium cancellatum, Diderma hemispaericum, Didymium difforme, D. iridis and D. squamulosum, Echinostelium minutum, Enerthenema papillatum, Fuligo septica, Hemitrichia stipitata, Lamproderma scintillans, Licea erecta, L. kleistobolus and L. operculata, Lycogala epidendrum, Macbrideola cornea, M. decapillata, M. martini, M. scintillans and M. synsporos, Metatrichia vesparium, Perichaena chrysosperma and P. minor, Physarum cinereum, P. crateriforme, P. decipiens, P. leucophaeum, P. nutans and P. viride, Stemonitis axifera, S. flavogenita, S. fusca and S. virginiensis. The data from this study shows that some myxomycete species will develop only on bark from living trees, some species develop only on forest floor debris, and some species will develop on bark of living trees as well as on fallen debris. The species that appeared on fallen debris as well as on tree bark were Arcyria carnea and A. nutans, Physarum cinereum, P. nutans and P. viride, Stemonitis axifera and S. fusca. The species that were found on bark from living trees but were not found on fallen debris were Badhamia obvata, Clastoderma debaryanum, Comatricha fimbriata, C. elegans, and C. nigra, Cribraria minutissima, C. violacea, Didymium squamulosum, Licea erecta, L. kleistobolus and L. operculata, Macbrideola synsporos, Perichaena chrysosperma and P. minor, Physarum crateriforme, P. decipiens, and P. leucophaeum. The species of slime molds that were found on forest floor litter but were not found on bark of living trees were Ceratiomyxa fruitculosa, Dictydium cancellatum, Fuligo septica, Hemitrichia stipitata, Lycogala epidendrum, and Metatrichia vesparium. Echinostelium minutum is a ubiquitous species for it was common on bark from living trees as well as on fallen plant debris. Throughout this study variations were noted in the number of species of slime molds appearing on incubated bark samples during different seasons of the year. Echinostelium minutum appeared throughout the year on bark of all trees sampled except Acer negundo, A. saccharinum, Cedrus deodara, and Quercus phellos. Didymium squamulosum was found throughout the entire collecting period, except for the spring of 1974. Except for the summer of 1973, Comatricha fimbriata appeared on bark samples collected each season over the two—year period of study. In some instances a slime mold may have appeared during a particular season in one year and may not have been found the following year during the same season. For example, Arcyria nutans was found during the winter of 1974, but was not found during the winter of 1973. Comatricha lurida appeared during the spring of 1974. Comatricha pulchella appeared only during the winter of 1974 as did Didymium difforme. Some slime mold species appeared only once during the course of the study. Macbrideola cornea and M. decapillata, Physarum cinereum, and Stemonitis axifera, are examples of species that were found once. Based on the data from this study, bark of living trees appear to represent a natural substratum for some species of myxomycetes. Some general affinity is apparent between some species of trees and some species of myxomycetes, depending upon the locality. Also, the appearance of some species of corticolous myxomycetes may vary with the season of the year, and some correlation appears to exist between the distribution of some myxomycete species and tree habitat. Some of the myxomycetes found in this study represent species previously unreported from the state. Those species are Calomyxa metallica, Clastoderma debaryanum, Badhamia nitens, B. obovata, Licea erecta, Macbrideola cornea, M. decapillata, M. martinii and M. synsporos, Perichaena minor, Physarum crateriforme, P decipiens and P. leucophaeum.

No description available.

Exon amplification is a method used to identify regions of DNA that contain transcribed sequences. The large cloning capacity of yeast artificial chromosome (YAC) systems and the inability to isolate large intact DNA from YACs introduce limitations to the exon amplification technique. The feasibility of exon amplification from a mega-YAC clone 2001C6 (CEPH) has been analyzed as a means to isolate transcribed sequences and has been used to produce 10 putative exon sequences from human chromosome 17q21. Six of the sequences showed homology to sequences that were previously published in the GenBANK database. Three of the sequences showed no homology, thereby indicating the isolation of putatively novel sequences. The sequences were radiolabeled and used as hybridization probes on a multiple tissue RNA dot blot. This blot contains RNA isolated from 50 human tissues. Clone E5 produced hybridization signals in fetal liver, fetal spleen and placenta. Clone F12 produced hybridization signals in fetal liver, fetal spleen, placenta and bone marrow. Clone G12 produced hybridization signals in all of the RNAs, indicating a pattern of expression similar to that of a housekeeping gene. These findings contribute to the enhancement of a high density transcriptional map within the q21-q22 region of human chromosome 17.

No description available.