Showing papers by "University of Arkansas published in 1990"
TL;DR: Dental enamel hypoplasias are deficiencies in enamel thickness resulting from physiological perturbations (stress) during the secretory phase of amelogenesis, and their study has begun to extend into other subdisciplines of physical anthropology.
Abstract: Dental enamel hypoplasias are deficiencies in enamel thickness resulting from physiological perturbations (stress) during the secretory phase of amelogenesis. The results of a wide variety of experimental, clinical, and epidemiological studies strongly suggest that these defects and their associated histological abnormalities (such as accentuated stria of Retzius and Wilson bands) are relatively sensitive and nonspecific indicators of stress. Because of the inability of enamel to remodel, and the regular and ring-like nature of their development, these defects can provide an indelible, chronological record of stress during tooth crown formation. For these reasons, along with the ease with which they are studied, enamel hypoplasias have been increasingly employed as indicators of nutritional and disease status in paleopathology, and their study has begun to extend into other subdisciplines of physical anthropology.
In order to provide the reader with a better understanding of the current issues in this field, we first review normal enamel development, historical advances in the study of enamel developmental abnormalities, and provide a threshold model to help conceptualize the etiology of enamel developmental defects. Specific attention is then centered on extant, fundamental issues in the use of enamel hypoplasias and histological structures as epidemiological indicators of nonspecific stress.
Most enamel hypoplasias are associated with abnormal histological changes (accentuated stria of Retzius or “Wilson” and “Cluster” bands). However, the lack of association of some mild surface irregularities, characteristically seen as thin, perikymata-like surface depressions, with abnormal prism morphology suggests that these surface features may not be evidence of physiological perturbation.
Methods now exist to reliably identify both histological and enamel surface defects. However, further research is needed on methods for determining the size of defects and the epidemiological significance of defect widths and depths. Similarly, the general relationship between the location of enamel hypoplasias and associated histological structures on the one hand, and an individual's age at the time of their development on the other hand, is also well understood. However, better estimates of intra- and inter-population variation in the timing of enamel matrix formation are needed before these defects can reach their full potential as chronometric measures of stresses.
Lack of understanding patterns of differential susceptibility of enamekl to developmental disruption has likely hindered interpretations of the results of a number of past experiments. The seemingly strong pattern of differential suscetibility of enamel to disruption-within teeth and across tooth classes, dentitions, and taxa-may yield a number of significant clues to understanding basic issues in enamel development.
Populations that are exposed to a high degree of undernutrition and disease, from prehistoric to contemporary times, share high rates of linear enamel hypoplasias. While these defects seem to relate to bouts of undernutrition and infection, their specific etiology is still unknown. In the next decade we expect to develop more precise information on the specificity and sensitivity of secretory ameloblaste to disruption. A variety of research directions are suggested for further anthropological study.
708 citations
TL;DR: Mobile genetic elements are useful genetic tools and have been found in most organisms which have been examined and will be used as probe for the identification of the M. tuberculosis complex.
Abstract: Mobile genetic elements are useful genetic tools. They have been found in most organisms which have been examined (for recent reviews see 1). /S900 was isolated from M. paratuberculosis (2) and IS6100 from a M. fortuitum strain (our unpublished results). IS elements have been used as taxonomic markers useful for diagnostic purposes, (2, 3). From a IA. tuberculosis cosmid library constructed in pHC79 (4), an IS-like element, 1S6110, was identified as a repeated sequence, by screening the library with labelled M. tuberculosis total DNA. This sequence (1361 nt) possesses characteristics of IS elements, i.e., inverted (28bp with 3 mismatched bp) and direct (3bp) repeats of the target sequence at its extremities. A search in the EMBL data bank has revealed homologies with IS3411, an insertion element from E. coli (5). Cross-hybridization was observed between 1S6110 and a repeated sequence previously isolated from M. tuberculosis (6). IS6110 has been found in M. tuberculosis and M. bovis but not in any of the other mycobacteria tested (our unpublished data). Therefore, IS6110 will be used as probe for the identification of the M. tuberculosis complex. ACKNOWLEDGEMENTS
476 citations
TL;DR: In this article, a model for understanding ethical behavior in business organizations is proposed, and it is concluded that managers engage in a concentrated effort which involves espousing ethics, behaving ethically, developing screening mechanisms, providing ethical training, creating ethics units and reinforcing ethical behavior.
Abstract: Managing ethical behavior is a one of the most pervasive and complex problems facing business organizations today. Employees' decisions to behave ethically or unethically are influenced by a myriad of individual and situational factors. Background, personality, decision history, managerial philosophy, and reinforcement are but a few of the factors which have been identified by researchers as determinants of employees' behavior when faced with ethical dilemmas. The literature related to ethical behavior is reviewed in this article, and a model for understanding ethical behavior in business organizations is proposed. It is concluded that managing ethics in business organizations requires that managers engage in a concentrated effort which involves espousing ethics, behaving ethically, developing screening mechanisms, providing ethical training, creating ethics units and reinforcing ethical behavior.
373 citations
TL;DR: In this paper, the authors conducted a longitudinal study of over 100 organizations to investigate the relationships among changes in organizational contexts, designs, and effectiveness, using interviews with top managers in each organization.
Abstract: This paper describes assumptions, rationale, and track-offs involved in designing the research methodology used in a longitudinal study of the relationships among changes in organizational contexts, designs, and effectiveness. The basic research question concerns when how, and why do different types of organizational change occur. Given this research question and a desire to develop and test generalizable theory about changes in organizational design and effectiveness, we conducted a longitudinal study of over 100 organizations. Data concerning the changes were obtained through four interviews spaced six months apart with the top manager in each organization. Each interview provided a short-term retrospective event history over the preceding 6-month interval in aggregate, the four interviews provided a 24-month event history for each organization. Additionally, periodic assessments of the state of the organization's context, design, and effectiveness were collected with two questionnaires spaced one year apart. Finally, in each organization, the top manager's personal characteristics were assessed after all other data were obtained. This paper examines the alternatives, advantages, and disadvantages of the research design decisions. With some hindsight, we also offer some suggestions for future researchers with similar goals of developing and testing generalizable explanations of change processes in organizations.
372 citations
TL;DR: The evolution of the atomic state in the resonant Jaynes-Cummings model (a two-level atom interacting with a single mode of the quantized radiation field) with the field initially in a coherent state is considered and it is shown that the atom is to a good approximation in a pure state in a middle of what has been traditionally called the "collapse region".
Abstract: The evolution of the atomic state in the resonant Jaynes-Cummings model (a two-level atom interacting with a single mode of the quantized radiation field) with the field initially in a coherent state is considered. It is shown that the atom is to a good approximation in a pure state in the middle of what has been traditionally called the "collapse region. This pure state exhibits no Rabi oscillations and is reached independently of the initial state of the atom. For most initial states a total or partial "collapse of the wave function" takes place early during the interaction, at the conventional collapse time, following which the state vector is recreated, over a longer time scale. PACS numbers: 42.50.— p, 03.65.— w, 42.52.+x The Jaynes-Cummings model' (JCM) is perhaps the simplest nontrivial example of two interacting quantum systems: a two-level atom and a single mode of the radiation field. In addition to its being exactly solvable, the physical system that it represents has recently become experimentally realizable with Rydberg atoms in high-Q microwave cavities. Comparison of the predictions of the model with those of its semiclassical version have served to identify a number of uniquely quantum properties of the electromagnetic field; indeed, the model displays some very interesting dynamics, and the differences with the semiclassical theory are both profound and unexpected. The JCM would also appear to be an excellent model with which to explore some of the more puzzling aspects of quantum mechanics, such as the possibility (or impossibility) to describe an interacting quantum system by a state vector undergoing unitary evolution; i.e., the socalled "collapse of the wave function. " In the semiclassical version, the atom interacting with the classical electromagnetic field may at all times be described by a state vector evolving unitarily. What happens, however, when it is recognized that the field is itself a quantum system (which leads inevitably to "entanglement" )? This is the question addressed in this Letter. It does not seem to have been addressed before in full generality, although entanglement in the JCM dynamics plays an essential role in a recent measurement-theory-related proposal of Scully and Walther, and preparation of a pure state of the field in the JCM has been the subject of several theoretical investigations and may be close to being achieved experimentally. The resonant JCM interaction Hamiltonian may be written as Ht = hg(~a&(b (a+ a'(b)(a ~ ), ' is a coupling constant (d is the atomic dipole matrix element for the transition, m is the transition frequency, and Vis the mode volume), ~a) and ~b) are the upper and lower atomic levels, respectively, and a and a are the annihilation and creation operators of the field mode, which in the semiclassical theory are simply replaced by c numbers. The solution to the Schrodinger equation for the atom initially in state y(0)).,&,~ =a~a)+ p b) and field initially in state ttt(0))fi iu g„-OC„n) is ~y(t)) = g [[aC„cos(gOn+1 t) — ipC„s+i l(gnawn +1 t)]~ a& +[ — iaC„~sin(gran t)+pC„cos(gran
299 citations
TL;DR: Results indicate that the hydrophobic gramicidins are surprisingly membrane impermeant, a conclusion that was confirmed in experiments in which gA was added asymmetrically and symmetrically to preformed bilayers.
Abstract: Conducting gramicidin channels form predominantly by the transmembrane association of monomers, one from each side of a lipid bilayer. In single-channel experiments in planar bilayers the two gramicidin analogs, [Val1]gramicidin A (gA) and [4,4,4-F3-Val1]gramicidin A (F3gA), form dimeric channels that are structurally equivalent and have characteristically different conductances. When these gramicidins were added asymmetrically, one to each side of a preformed bilayer, the predominant channel type was the hybrid channel, formed between two chemically dissimilar monomers. These channels formed by the association of monomers residing in each half of the membrane. These results also indicate that the hydrophobic gramicidins are surprisingly membrane impermeant, a conclusion that was confirmed in experiments in which gA was added asymmetrically and symmetrically to preformed bilayers.
220 citations
TL;DR: It is concluded that cells of multiple lineages are involved in myeloma--a finding that is consistent with the hypothesis that there is a common primary neoplastic lesion for all hematologic cancers.
Abstract: Multiple myeloma is considered a cancer of mature plasma cells. Recent studies, however, suggest the possible involvement of early B cells and the expression of myelomonocytic antigens by myeloma cells. Using flow cytometry, we searched for evidence of the expression of genes specific for different hematopoietic lineages by tumor cells in bone marrow aspirates from 27 patients with aneuploid multiple myeloma. In addition to features characteristic of myeloma cells, we found evidence of the frequent expression by myeloma tumor cells of the pre–B-cell antigen CALLA (common acute lymphocytic leukemia antigen) (in specimens from 58 percent of patients) and of megakaryocytic (88 percent), myelomonocytic (65 percent), and erythroid (39 percent) surface markers. The proportion of tumor cells expressing the different markers varied among patients, from 2 to 100 percent of recognizable tumor cells. We conclude that cells of multiple lineages are involved in myeloma — a finding that is consistent with the ...
157 citations
TL;DR: A buffered propionic acid (BPA) was added to broiler diets fed in floor pens with litter and had no adverse effect on growth, feed utilization, the abdominal fat of females, or the dressing percentage of males while significantly reducing the abdominalFat for males and increasing the dressing Percentage for females.
142 citations
TL;DR: Flooding did not affect components of leaf water potential indicating that the decreases in P n and g s were not associated with plant water-deficit stress, and Forrest appeared more tolerant to excess water than Essex.
141 citations
TL;DR: Three peptides from the NH(2)-terminus of the ANF prohormone as well as ANF (the COOH-terminus) have either natriuretic, kaliureic, and/or diuretic properties, but the respective ability of each of these peptides to produce these effects varies considerably.
Abstract: The present investigation was designed to determine whether peptides derived from the NH(2)-terminal portion of the 126-amino acid prohormone (pro) of atrial natriuretic factor (ANF) have natriuret...
131 citations
TL;DR: It is concluded that food availability during the nestling stage can limit present reproduction, enhance the likelihood of additional reproduction, or both, in Cactus Wrens.
Abstract: Food limitation of reproduction during the nestling stage was tested by supplementing food only during this stage in Cactus Wrens. Parents offered supplemental food fed their young more (volume per unit time) than unsupplemented parents in 2 yr of experimentation. In 1986, food-supplemented nestlings had greater mass and linear mea- sures, whereas in 1987, most food-supplemented nestlings had greater mass, but not linear dimensions, than their controls. In 1986, survivorship of young both in the nest and during 4-6 wk after fledging, was greater with food supplementation than without. In 1987, sur- vivorship differences were not significant. Food supplementation enhanced annual repro- duction of parents because more food-supplemented Cactus Wrens laid second clutches than controls in 1987, the only year when this was examined. We conclude that food availability during the nestling stage can limit present reproduction, enhance the likelihood of additional reproduction, or both, in Cactus Wrens.
TL;DR: New evidence suggests that both blinks and the alpha rhythm may be controlled by a linked neuroanatomical circuit that begins in rostral pons and involves several subcortical structures as well as the occipital cortex.
Abstract: The activity of a putative marker of central dopamine function, spontaneous eye blink rate is examined in patients with schizophrenia. Chronic schizophrenic patients withdrawn from medication have elevated blink rates which are reduced by neuroleptic medication. Furthermore, neuroleptics reduce the so called “positive” symptoms of schizophrenia and blink rates in a positively correlated fashion. The above findings apply to patients who have normal cerebral ventricles and not those with large ventricles. Taken together, this evidence suggests that spontaneous eye blink rate is a marker of central dopamine activity and that increased dopaminergic activity is a relevant factor in chronic schizophrenic patients who have normal cerebral ventricles.
TL;DR: A modification of Davidson's eigenvalue algorithm, based on the conjugate gradient method, is described, making it practical for very large problems where disk storage is the limiting factor, without the necessity of restarting or discarding some expansion vectors.
Abstract: A modification of Davidson's eigenvalue algorithm, based on the conjugate gradient method, is described. This method needs storage only for a few vectors (five to seven, depending on the implementation), making it practical for very large problems where disk storage is the limiting factor, without the necessity of restarting or discarding some expansion vectors. The convergence characteristics of the modified method are essentially identical with those of the original Davidson method if all expansion vectors are retained in the latter.
TL;DR: In this article, the authors compared the performance of batch, continuous stirred tank and bubble column reactors with strict anaerobe Peptostreptococcus productus as a model organism and showed the effects of increased mass transfer and total pressure on system performance.
Abstract: Anaerobic bacteria may be utilized in the conversion of CO, CO 2 and H 2 in synthesis gas to products such as methane, acetate, ethanol and butanol. Bioreactors for these fermentations are mass transfer limited due to very low gas solubilities. Several reactor designs have been examined for these conversions including batch, continuous stirred tank and bubble column reactors. This paper presents laboratory results for these reactor systems using the strict anaerobe Peptostreptococcus productus as a model organism. Results comparing the performance of these reactors and showing the effects of increased mass transfer and total pressure on system performance are presented are discussed.
TL;DR: Osmotic adjustment was measured in various structures in the temperate grass tall fescue to characterize whole-plant response to water stress and to determine tissues most responsive to intermittent water deficit.
TL;DR: Onda et al. as mentioned in this paper showed that the experimental rotational constants of catechol can be reproduced by a geometry in which the CO bond lengths are 1.409 and 1.395 A.
TL;DR: A successful new rearing technique is employed for isolating specific southern pine beetle/fungal associations and the re-emergence rate of beetles was fastest for P beetles associated with C .
Abstract: The southern pine beetle, Dendroctonus frontalis Zimmermann, was studied in the laboratory to determine the influence of associated fungi on its reproduction. First-generation (P) surface-sterilized beetles associated with mycangial fungi (Ceratocystis minor [Hedgecock] Hunt var. barrasii Taylor or SJB 122) constructed more galleries and laid more eggs, at faster rates, than P beetles not associated with these mycangial fungi. No significant differences occurred among non-surface-sterilized P beetles associated with the phoretic blue staining fungus Ceratocystis minor (Hedgecock) Hunt and mycangial fungi or among progeny of P beetles (F1 generation) carrying mycangial fungi. P and F1 surface-sterilized beetles produced more eggs at a greater density than non-surface-sterilized beetles associated with blue stain, but gallery length and the rate of construction were not different. P and F1 surface-sterilized beetles laid more eggs and constructed galleries faster than surface-sterilized beetles that carried no mycangial fungi. The re-emergence rate of beetles was fastest for P beetles associated with C. minor and significantly slower for fungus-free P beetles, P beetles carrying only mycangial fungi, and F1 beetles, respectively. The F1 generation emerged fastest when associated with both mycangial fungi and slowest when associated with SJB 122, and C. minor var. barrasii or no fungus, respectively. This study employed a successful new rearing technique for isolating specific southern pine beetle/fungal associations.
TL;DR: In this paper, a quantitative measure of structural equivalence of the peptide backbone among gramicidin channels based on functional (single-channel) measurements was developed to determine whether amino acid side-chain substitutions in linear gramICidins alter the structure of membrane-spanning channels formed by the modified peptides.
TL;DR: A new method for double phase conjugation particularly suited to the tungsten bronze crystal strontium barium niobate is reported, which is called the bridge conjugator because the two beams enter opposing crystals and fan together to form a bridge without reflection off a crystal face.
Abstract: In this paper we report a new method for double phase conjugation particularly suited to the tungsten bronze crystal strontium barium niobate. It has also been observed to produce conjugate waves in BaTiO(3) and BSKNN. This new arrangement is called the bridge conjugator because the two beams enter opposing [100] crystal faces and fan together to form a bridge without reflection off a crystal face. Our measurements indicate that the bridge conjugator is competitive with previously reported double phase conjugate mirrors in reflectivity, response time, ease of alignment, and fidelity.
TL;DR: Three experiments were conducted to determine the effects of feeding broilers formic acid (FA) or calcium formate (CF) on performance and microbiological characteristics of broilers.
TL;DR: In this article, the authors summarized research to optimize the performance of some of these cultures, and discussed experimental results and models for several reactor designs, including CSTR and packed columns.
Abstract: Liquid and gaseous fuels may be produced biologically from coal by the indirect conversion of coal synthesis gas. Methane has been produced from synthesis gas using acetate and CO2/H2 as intermediates, utilizing a number of CO-utilizing and methanogenic bacteria. Also, a bacterium that is capable of producing ethanol from synthesis gas through indirect liquefaction has been isolated fron natural inocula. This paper summarizes research to optimize the performance of some of these cultures. These conversions, involving H2 and CO, which are only slightly soluble in the liquid media, may be mass transfer limited, and methods to enhance mass transport are examined. Experimental results and models for several reactor designs, including CSTR and packed columns, are presented and discussed.
TL;DR: In this article, the authors used ab initio geometry trends to refine the empirical force constants and equilibrium geometry in the CHARMM force field for peptides, leading to modifications in the bond stretch, angle bending, and some torsional parameters.
Abstract: Previous 4-21G ab initio geometry optimizations of various conformations of the model dipeptides (N-acetyl N'methyl amides) of glycine (GLY) and the alanine (ALA) have been used to help refine the empirical force constants and equilibrium geometry in the CHARMM force field for peptides. Conformationally dependent geometry trends from ab initio calculations and positions of energy minima on the ab initio energy surfaces have been used as guides in the parameter refinement, leading to modifications in the bond stretch, angle bending, and some torsional parameters. Preliminary results obtained with these refined empirical parameters are presented for the protein Crambin. Results for the cyclic (Ala-Pro-DPhe)2 are compared with those from other calculations. It seems that the dihedral angle fit achieved by the new parameters is significantly improved compared with results from force fields whose derivation does not include ab initio geometry trends.
TL;DR: In this article, a database of quadratic force fields for organic molecules is described, which is based on systematic ab initio calculations, scaled to reproduce the experimentally observed frequencies.
TL;DR: This research evaluated N transfer by white clover, red clover or birdsfoot trefoil, grown with tall fescue at various legume proportions, on a Typic Argiudoll soil in Uruguay.
Abstract: This research evaluated N transfer by white clover (Trifolium repens L.) (WC), red clover (Trifolium pratense L.) (RC) or birdsfoot trefoil (Lotus corniculatus L.) (BT), grown with tall fescue (Festuca aruondinacea Schreb.) (TF) at various legume proportions. Two identical experiments were extablished on a Typic Argiudoll soil in Uruguay, one in 1983 (Exp. 1) and one in 1984 (Exp. 2), and each was evaluated for approximately 2 yr. The soil of the area was a fine, montmorillonitic, mesic, Typic Argiudoll. Transfer of N to TF was estimated by 15 N isotope dilution
TL;DR: P perturbed the cycle during a 30-sec viewing period by immediately forcing an eye to return to dominance whenever it became suppressed, consistent with the existence of a short-term adaptation, or fatigue, process responsible for transitions from dominance to suppression.
Abstract: Successive durations of binocular rivalry are sequentially independent, random variables. To explore the underlying control process, we perturbed the cycle during a 30-sec viewing period by immediately forcing an eye to return to dominance whenever it became suppressed. During this period of forced dominance, that eye’s individual dominance durations were unusually brief, but immediately following the period of forced dominance that eye’s suppression durations were unusually long. However, no long-term change in the sequential pattern of rivalry occurred, and the stochastic independence of successive durations was maintained during and following the period of forced dominance. The same pattern of results was obtained with even longer periods of forced dominance. These results are consistent with the existence of a short-term adaptation, or fatigue, process responsible for transitions from dominance to suppression.
TL;DR: This study was an attempt to document the health status and disease exposure of wild turkeys in Arkansas to aid in managing and preventing the spread of disease agents to wild turkey and other species of birds.
Abstract: Wild turkeys (Meleagridis gallopavo silvestris) trapped as part of a relocation program by the Arkansas Game and Fish Commission were tested for selected infectious diseases and parasites. The 45 birds were trapped at four locations in Pope, Scott, and Montgomery counties (Arkansas, USA). Forty-four blood samples for serology, 27 blood smears and 12 fecal samples were collected. Of the serum samples tested, 20 of 44 (45%) were positive for Pasteurella multocida by enzyme-linked immunosorbent assay (ELISA), 42 of 44 (95%) were positive for Bordetella avium by ELISA, and 15 of 44 (34%) were positive for Newcastle disease virus antibody by the hemagglutination inhibition test. All serum samples were negative for Mycoplasma gallisepticum, Mycoplasma synoviae, avian paramyxovirus 3, avian influenza, hemorrhagic enteritis, Marek's disease, avian encephalomyelitis, laryngotracheitis, Salmonella pullorum and Salmonella gallinarum. Haemoproteus meleagridis was found in eight of 27 (30%) and Leucocytozoon smithi in nine of 27 (33%) blood smears; all smears were negative for Plasmodium hermani. Enteric parasites included Ascaridia dissimilis, Heterakis gallinarum, Eimeria dispersa and Raillietina spp. This study was an attempt to document the health status and disease exposure of wild turkeys in Arkansas to aid in managing and preventing the spread of disease agents to wild turkeys and other species of birds.
TL;DR: One monoclonal antibody (MAb), P5C9, reacted with all test strains of L. monocytogenes, L. innocua, and L. welshimeri but not with any strains of the other four Listeria species or with any of 22 gram-positive or 11 gram-negative species of bacteria when tested in microtiter and dot blot enzyme immunoassays.
Abstract: Eight hundred fifty-nine murine hybridomas were produced from eight fusions, and 27 were characterized for secretion of antibodies reactive to Listeria monocytogenes. One monoclonal antibody (MAb), P5C9, reacted with all test strains of L. monocytogenes (31 of 31), L. innocua (3 of 3), and L. welshimeri (1 of 1) but not with any strains of the other four Listeria species or with any of 22 gram-positive or 11 gram-negative species of bacteria when tested in microtiter and dot blot enzyme immunoassays. Of the other 26 antibodies, 20 reacted with either L. monocytogenes Scott A or V7 and with some or all of the other six Listeria species but also cross-reacted with some or all of the non-Listeria bacteria tested. MAb P5C9 is of the immunoglobulin G1 murine subclass. In Western blot (immunoblot) analyses, this MAb reacted with a single antigen with a molecular weight of 18,500, and it is shared in common with all three reactive species, L. monocytogenes, L. innocua, and L. welshimeri. This antigen was extracted with detergent and appeared to be cell bound.
TL;DR: Analysis of the parameters which contributed to the rise and fall pattern of Pn with leaf age indicated the primary involvement of leaf area expansion, leaf nitrogen, PPFD, and gs·CO2 in this process.
Abstract: Photosynthetic characteristics of field-grown cotton (Gossypium hirsutum L.) leaves were determined at several insertion levels within the canopy during the growing season. Single-leaf measurements of net photosynthesis (Pn), stomatal conductance to CO2 (gs·CO2), substomatal CO2, leaf area expansion, leaf nitrogen, and light intensity (PPFD) were recorded for undisturbed leaves within the crop canopy at 3–4 day intervals during the development of all leaves at main-stem nodes 8, 10, and 12. Patterns of Pn during leaf ontogeny exhibited three distinct phases; a rapid increase to maximum at 16–20 days after leaf unfolding, a relatively short plateau, and a period of linear decline to negligible Pn at 60–65 days. Analysis of the parameters which contributed to the rise and fall pattern of Pn with leaf age indicated the primary involvement of leaf area expansion, leaf nitrogen, PPFD, and gs·CO2 in this process. The response of Pn and gs·CO2 to incident PPFD conditions during canopy development was highly age dependent. For leaves less than 16 days old, the patterns of Pn and gs·CO2 were largely controlled by non-PPFD factors, while for older leaves Pn and gs·CO2 were more closely coupled to PPFD-mediated processes. Maximum values of Pn were not significantly different for any of the leaves monitored in this study, however, those leaves at main-stem node 8 did possess a significantly diminished photosynthetic capacity with age compared to upper canopy leaves. This accelerated decline in Pn could not be explained by age-related variations in gs·CO2 since all leaves showed similar changes in gs·CO2 with leaf age.