bluuebunny/crossref_metadata_2025 huggingface dataset:
Chasing A Receding Zero: Impact of the Zero Threshold Concept on Actions of Regulatory Officials
Authors: Jukes Thomas H.
Published: February 2008

The principle of toxicological threshold was stated in 1564 by Paracelsus as “All things are poisonous, yet nothing is poisonous. Dosage alone determines poisoning.” This principle remains valid, even with consideration of today's public concern with low-dosage effects of compounds that are categorized as carcinogens, mutagens and teratogens. Modern laboratory methods enable detection of increasingly small traces of such compounds in foods. The search for these has been termed “Chasing a receding zero, ” and this quest has been stimulated by statements that no one knows how small an amount of a carcinogen, taken for how short a time, can induce cancer, and that even one molecule of a carcinogen, acting on a single cell, can transform a normal cell into a cancer cell.

This latter proposal is a stochastic impossibility. Every cell contains millions of carcinogenic molecules. Examples are arsenic, cadmium and chromium. In addition, there are estrogens and other steroid hormones present in each cell and needed for normal bodily functions. These substances are regarded as carcinogens because of their effect at high levels on increasing the cancer rate in experimental animals. Obviously, there must be a threshold for this effect. An estimate has been made by Dingman that “a threshold for biological activity exists within a cell at 10, 000 atoms.”

It is also obvious that there is a threshold for deficiencies that induce cancer, such as that of iodine. Iodine deficiency is mimicked by administration of goitrogens, and these are present naturally at low to moderate levels in many common foods.

The threshold principle is stated by Claus and Bolander to be a law of nature, valid in many circumstances, and governing the fact that a causative agent must be present in a quantity exceeding a definite minimum in order to produce the effect.
Dietary and other Modulators of Carcinogenesis
Authors: Rogers Adrianne E.
Published: February 2008

Nutritional or dietary status and interactions between carcinogens and nutrient absorption, storage or metabolism influence carcinogenesis in many experimental animal models and probably in people. Use of dose-response data to indicate a threshold exposure for carcinogenesis must include consideration of dietary and nutritional factors that may alter the dose response. Two models in rats in which there is clear evidence of dietary or nutritional modulation of chemical carcinogenesis are mammary tumors induced by 7, 12-dimethylbenzanthracene (DMBA) or N-nitrosomethyl-urea (NMU) and hepatocarcinomas induced by many compounds. Mammary tumorigenesis is increased by increasing dietary content of some, but not all, fats. The time in tumor development at which fats act varies. Their mechanisms of action are not known but appear to include effects on the hormonal mileu and possibly mammary gland cell turnover and response to hormones.

Hepatocarcinogenesis by chemicals is increased by dietary deficiency of the lipotropes methionine, choline and folate, possibly through alteration of carcinogen metabolism and increased hepatocyte DNA synthesis. The same deficiency induces cirrhosis. In humans, cirrhosis induced by alcoholism, viral hepatitis or unknown factors increases the risk for hepatocarcinoma. Alcohol-induced folate or other deficiency can be a contributory factor in the alcoholics. Infection with hepatitis B virus is increased in alcoholics and in patients with hepatocarcinoma and may be an initiating or modulating factor for tumors.
Implications for the Future: Regulation of Chemicals and Prevention of Cancer
Authors: Kolbye Albert C
Published: February 2008

Lifetime feeding studies, when positive for cancer induction, do not provide information to differentiate between primary and secondary mechanisms of cancer induction. So many factors can influence the ultimate risk of incurring cancer in animals or humans that the observation of an increased incidence of cancer in association with exposure to any particular test substance should not lead automatically to the inference that the substance is a carcinogen per se. An increased incidence of cancer can result not only from exposure to “complete” carcinogens, but also from critical exposures to the following factors: those that decrease biological resistance to other independently occurring cancer risk factors, those that cause toxic hyperplasia, or those that act as classical promoters. Both initiation and promotion are prerequisites to cancer induction. Initiation can result independently from the effects of viruses, radiation, chemical initiators, and aging. For example: endogenously-formed nitrosamines are capable of effecting initiation in hepatic cells. Many non-genotoxic hepatic so-called “carcinogens” appear to be “promoters” of cancer induction rather than complete carcinogens. Hepatic cancer induction can be enhanced by classical promotion phenomena, by toxic hyperplasia, or by selective pressures on cell replication created by hormones. Substantial and consistent exposure doses are required to invoke secondary mechanisms of enhancing cancer induction; these secondary events occur in dosage ranges associated with observable histopathologic effects and thus can be detected and measured. By using combinations of in vitro and in vivo techniques, no-adverse-effect dosage levels can be determined whereby the risks for enhancing cancer induction can be avoided.
Total Quality Approach to Operational Improvements in an Analytical Laboratory
Authors: Gates Gloria A.
Published: February 2008

The Philip B. Crosby Quality Process was selected for use at Lancaster Laboratories mainly because there was a good fit with our culture and existing quality systems. The process was uniformly applicable to both the technical and support areas within the company. The quality process provides a way for each employee to evaluate, measure, and then improve systems in the laboratory. Impelementing the system increases the awareness of all employees toward quality. Improvements were not only measured as a reduction of PONC (price of nonconformance), but as reduction of the “hassle factor” and elimination of barriers to doing it right the first time.
Evaluation of the Safety of Tara Gum as a Food Ingredient: A Review of the Literature
Authors: Borzelleca Joseph F. , Ladu Bert N. , Senti Frederic R. , Egle John L.
Published: February 2008

Tara gum is a potential replacement for locust bean gum for use as a formulation aid, stabilizer, and thickener for food applications. In addition to biochemical and digestibility data, studies assessing the toxicity of tara gum are reviewed. The latter includes three 90-day feeding studies, two in rats and one in dogs; two 2-year feeding studies in rats and one in mice; a 3-generation reproduction study with rats and a reproductive toxicity and teratogenicity study with rats; an Ames reverse mutation assay with five Salmonella typhimurium strains; and a micronucleus test in mice. The feeding studies did not indicate any significant adverse effects attributable to tara gum at the maximum dietary level of 5%. The results of the genotoxicity studies were negative. It is concluded that tara gum meets the scientific standards required for classification as a GRAS food ingredient.
Presenting Toxicology to the Public: The Middle School
Authors: Derelanko Michael J.
Published: February 2008

Toxicologists are being called upon to educate the public about the value of toxicity testing and the important role animals play in this regard. This article discusses the importance of toxicologists educating students in the middle school about the science of toxicology and suggests various ways to convey basic concepts of toxicity, dose response, and animal research to students in these grades. The methods described in this article have been developed and used successfully by the author in making presentations to middle school students.
Influence of cocaine on ruptured intracranial aneurysms: a case control study of poor prognostic indicators
Authors: Vannemreddy Prasad , Caldito Gloria , Willis Brian , Nanda Anil
Published: February 2008

Object

The purpose of this study was to determine whether cocaine use is a significant prognostic factor for outcome measures such as Hunt and Hess grade and Glasgow Outcome Scale (GOS) score among patients presenting with ruptured intracranial aneurysms (IAs).

Methods

The authors performed a MEDLINE/PubMed search for cases of ruptured IAs associated with cocaine use. Fourteen cases from the authors' experience were combined with 50 from a literature review, for a total of 64 cases associated with cocaine use. These 64 cases were compared with 65 cases without cocaine use (controls), which had been obtained from an aneurysm database. Logistic regression analysis was performed to determine significant prognostic factors for a poor Hunt and Hess grade and a poor GOS score, and a general linear model was applied to identify significant factors for these measures among cocaine users.

Results

There were 40 women in each group. The mean age was 32.3 ± 8.1 years in the cocaine group and 49.7 ± 10.6 years in the control group; thus, patients in the cocaine group were significantly younger (p < 0.01). Cocaine was snorted in 21% of cases, smoked in 55%, and intravenously injected or taken in through a combination of routes in 24%. Fifty-one percent of cocaine users and 7.7% of nonusers presented with a poor GOS score (p < 0.01). Fifty-six percent had ictus during cocaine abuse. At the end of a 30-day follow-up, 51% of the patients in the cocaine group had a good GOS score compared with 92% in the control group (p < 0.01). Controlling for the effects of other significant factors, cocaine use had a significant effect on Hunt and Hess grade (p < 0.03) and GOS score (p < 0.01). The odds of having a poor Hunt and Hess grade among cocaine users were 4.2 times greater than those in nonusers, and the odds of having a poor GOS score among cocaine users were 38.8 times greater.

Conclusions

Aneurysms were significantly smaller and ruptured at a younger age among cocaine users compared with nonusers. Although the poor clinical grade was not significantly different between the 2 groups, outcome was significantly worse in cocaine users.
Preoperative visualization of neurovascular anatomy in trigeminal neuralgia
Authors: Miller Jonathan , Acar Feridun , Hamilton Bronwyn , Burchiel Kim
Published: February 2008

Object

The authors report on a novel technique to identify neurovascular compression in trigeminal neuralgia (TN). Using 3D reconstructed high-resolution balanced fast-field echo (BFFE) images fused with 3D time-of-flight (TOF) magnetic resonance (MR) angiography and Gd-enhanced 3D spoiled gradient recalled sequence, it is possible to objectively visualize the trigeminal nerve and nearby arteries and veins.

Methods

Magnetic resonance imaging was performed in 18 patients with unilateral TN using 3 sequences: BFFE, 3D TOF angiography, and 3D Gd-enhanced imaging. The images were imported into OsiriX imaging software; after their fusion, a 3D false-color reconstruction was produced using surface rendering. The reconstructed images objectively differentiate nerves and vessels and can be viewed from any angle, including the anticipated surgical approach.

Results

Fifteen patients were predicted to have neurovascular compression on the symptomatic side (9 arterial and 6 venous compressions). All patients had a vascular structure that was identical in location and configuration to that predicted on preoperative analysis. The 3 patients without predicted compression underwent surgical exploration because they manifested the classic symptoms. As expected, exploration in 2 of these patients revealed no offending vessel. The third patient had a small vein embedded in the trigeminal nerve that was beyond the resolution of the 3D Gd-enhanced study.

Conclusions

Combining BFFE with MR angiography and Gd-enhanced MR images capitalizes on the advantages of both techniques, enabling MR angiography and contrast-enhanced MR imaging discrimination of vascular structures at BFFE resolution. This results in an unambiguous 3D image that can be used to identify the neurovascular compression and plan the surgical approach.
Anatomical study of the trigeminal and facial cranial nerves with the aid of 3.0-tesla magnetic resonance imaging
Authors: Kakizawa Yukinari , Seguchi Tatsuya , Kodama Kunihiko , Ogiwara Toshihiro , Sasaki Tetsuo , Goto Tetsuya , Hongo Kazuhiro
Published: February 2008

Object

Neuroimages often reveal that the trigeminal or facial nerve comes in contact with vessels but does not produce symptoms of trigeminal neuralgia (TN) or hemifacial spasm (HFS). The authors conducted this study to determine how often the trigeminal and facial nerves came in contact with vessels in individuals not suffering from TN or HFS. They also investigated the correlation between aging and the anatomical measurements of the trigeminal and facial nerves.

Methods

Between November 2005 and August 2006, 220 nerves in 110 individuals (60 women and 50 men; mean age 55.1 years, range 19–85 years) who had undergone brain magnetic resonance (MR) imaging for other reasons were studied. The lengths, angles, ratio, and contact points were measured in each individual. A correlation between each parameter and age was statistically analyzed.

Results

The mean (± standard deviation) length of the trigeminal nerve was 9.66 ± 1.71 mm, the mean distance between the bilateral trigeminal nerves was 31.97 ± 1.82 mm, and the mean angle between the trigeminal nerve and the midline was 9.71 ± 5.83°. The trigeminal nerve was significantly longer in older patients. Of 220 trigeminal nerves, 108 (49.0%; 51 women and 57 men) came in contact with vasculature. There was 1 contact point in 99 nerves (45%) and 2 contact points in 9 nerves (4.1%). Contact without deviation of the nerve was seen in 91 individuals (43 women and 48 men), and mild deviation was noted in 17 individuals (8 women and 9 men). There was no moderate or severe deviation in any individual in this series. The mean length of the facial nerve was 29.78 ± 2.31 mm, the mean distance between the bilateral facial nerves was 28.65 ± 2.22 mm, the angle between the nerve and midline was 69.68 ± 5.84°, and the vertical ratio at the porus acusticus was 0.467 ± 0.169. Of all facial nerves, 173 (78.6%; 101 in women and 72 in men) came in contact with some vasculature. Contact without deviation was seen on 64 sides (in 37 women and 27 men), mild deviation on 98 sides (in 57 women and 41 men), and moderate deviation on 11 sides (in 7 women and 4 men). There was no severe deviation of the facial nerve in this series. The proximal length of the facial nerve, interval, angle, and ratio against the age were significantly shorter or smaller in the older individuals.

Conclusions

The findings in asymptomatic individuals in this study will help in deciding which findings observed on MR images may cause symptoms. In addition, the authors describe the variations of normal anatomy in older individuals. Knowledge of the normal anatomy helps to hone the diagnostic practices for microvascular decompression, which may increase the feasible results on such surgery.
Solitary pituitary sarcoidosis with normal endocrine function
Authors: Pillai Promod , Ray-Chaudhury Abhik , Ammirati Mario , Chiocca E. Antonio
Published: February 2008

✓ Sarcoidosis is a multisystemic granulomatous disease characterized by noncaseating epithelioid granulomata that affects the lung in over 90% of patients and the central nervous system (CNS) in 5–9%. Neurosarcoidosis often occurs as multifocal meningeal and parenchymal lesions, and its diagnosis is particularly difficult in the absence of concomitant systemic disease. Hypothalamic-pituitary sarcoidosis occurs in fewer than 10% of patients with neurosarcoidosis and has been previously reported in association with profound endocrinological dysfunction. The authors report the case of a patient with isolated pituitary sarcoidosis who was first evaluated for visual symptoms and showed no preoperative endocrinological dysfunction or evidence of multisystemic or other CNS involvement. To the authors' knowledge, only 1 other such presentation is previously reported in the English literature. Such presentations are diagnostically and therapeutically challenging, and definitive diagnosis requires obtaining a biopsy specimen of the lesion with histological proof of noncaseating epithelioid granuloma, as well as the exclusion of other possible entities.
A stereotactic device for rabbits based on mandibular and cranial landmarks
Authors: Kockro Ralf A. , Giacomelli Rainer , Scheihing Martin , Aschoff Alfred , Hampl Juergen A.
Published: February 2008

✓ The authors have developed a stereotactic device for use in rabbits that uses the plane at the base of the mandible combined with cranial sutures as an anatomical reference. The device was developed for a study designed to evaluate catheters for infection prophylaxis, and this required the implantation of silicone catheters along a reproducible trajectory through the lateral ventricle. Cadaver and atlas studies demonstrated consistent spatial relationships between intracranial structures and the surface plane on which the animals were resting during the surgery. This plane is formed by the 2 mandibular angles and the mandibular tip. The authors developed a stainless steel stereotactic device that uses this mandibular plane as well as the coronal and sagittal sutures as spatial references.

Operations were performed in 60 animals using the stereotactic device, and postmortem dissections of the animals' brains demonstrated 78.6% accuracy of the trajectory within a tolerance of deviation of 5°, and 94.6% accuracy within a tolerance of 10°. The accuracy of the trajectory of the last 18 consecutively operated animals was constantly within a tolerance of 5°. The device can be autoclaved and, since it is relatively simple and inexpensive to build, the authors manufactured 3 identical frames and used them alternately to operate under sterile conditions. The fast and pain-free head fixation minimized anesthesia-related risks. The authors' experiences suggest that the device is suitable for ventricular punctures and, dependant on the individual requirements of accuracy, other procedures that require “approximate” stereotactic guidance especially when a series of animals need to undergo operations quickly.
Pathophysiology and treatment of focal cerebral ischemia
Authors: Siesjö Bo K.
Published: February 2008

✓ This article examines the pathophysiology of lesions caused by focal cerebral ischemia. Ischemia due to middle cerebral artery occlusion encompasses a densely ischemic focus and a less densely ischemic penumbral zone. Cells in the focus are usually doomed unless reperfusion is quickly instituted. In contrast, although the penumbra contains cells “at risk,” these may remain viable for at least 4 to 8 hours. Cells in the penumbra may be salvaged by reperfusion or by drugs that prevent an extension of the infarction into the penumbral zone. Factors responsible for such an extension probably include acidosis, edema, K+/Ca++ transients, and inhibition of protein synthesis.

Central to any discussion of the pathophysiology of ischemic lesions is energy depletion. This is because failure to maintain cellular adenosine triphosphate (ATP) levels leads to degradation of macromolecules of key importance to membrane and cytoskeletal integrity, to loss of ion homeostasis, involving cellular accumulation of Ca++, Na+, and Cl−, with osmotically obligated water, and to production of metabolic acids with a resulting decrease in intra- and extracellular pH.

In all probability, loss of cellular calcium homeostasis plays an important role in the pathogenesis of ischemic cell damage. The resulting rise in the free cytosolic intracellular calcium concentration (Ca++) depends on both the loss of calcium pump function (due to ATP depletion), and the rise in membrane permeability to calcium. In ischemia, calcium influx occurs via multiple pathways. Some of the most important routes depend on activation of receptors by glutamate and associated excitatory amino acids released from depolarized presynaptic endings. However, ischemia also interferes with the intracellular sequestration and binding of calcium, thereby contributing to the rise in intracellular Ca++.

A second key event in the ischemic tissue is activation of anaerobic glucolysis. The main reason for this activation is inhibition of mitochondrial metabolism by lack of oxygen; however, other factors probably contribute. For example, there is a complex interplay between loss of cellular calcium homeostasis and acidosis. On the one hand, a rise in intracellular Ca++ is apt to cause mitochondrial accumulation of calcium. This must interfere with ATP production and enhance anaerobic glucolysis. On the other hand, acidosis must interfere with calcium binding, thereby contributing to the rise in intracellular Ca++.
Neurosurgical implications of osteogenesis imperfecta in children
Authors: Sasaki-Adams Deanna , Kulkarni Abhaya , Rutka James , Dirks Peter , Taylor Michael , Drake James M.
Published: February 2008

✓Osteogenesis imperfecta (OI) is a rare genetic disorder characterized by disruption of normal collagen formation resulting in varying degrees of skeletal vulnerability, ligamentous laxity, and scleral discoloration. Children with OI may suffer from complex neurosurgical problems affecting the brain and spine. The authors sought to determine the neurosurgical implications of OI in a cohort of patients treated at a quaternary care center for pediatrics.

The authors reviewed the case histories of 10 children with OI treated by the neurosurgical service at the Hospital for Sick Children in Toronto between January 1988 and March 2007. The cases of 4 of these children are highlighted in the article. The most common neurosurgical conditions encountered in this cohort included macrocephaly in 5 patients, subdural hematoma in 3 patients, epidural hematoma in 2 patients, and hydrocephalus in 3 patients. Basilar invagination and spinal fractures were observed in 20% of the cohort. Although some patients could be treated nonoperatively, several required craniotomy for clot evacuation, decompression, and spinal fixation for fracture or basilar invagination, and cerebrospinal fluid shunt insertion.

Neurosurgical conditions affecting patients with OI include macrocephaly, the development of an acute intracranial hematoma after often minimal trauma, the development of chronic subdural fluid collections that may require drainage, hydrocephalus (both communicating and noncommunicating), basilar invagination, and subaxial spinal fractures. Surgery may be complicated in some children because of the underlying bone fragility and bleeding diathesis commonly observed in patients with OI.
Intermittent atlantoaxial subluxation caused by a prolapsing neurofibroma
Authors: Kelleher Michael O. , Quarishi Nasir A. , Tan Gamaliel , Guha Abhijit , Massicotte Eric M.
Published: February 2008

✓In this report, the authors describe a unique case of intermittent high cervical cord compression caused by a prolapsing neurofibroma at the C1–2 level. This 21-year-old man with known neurofibromatosis Type 1 presented with a mass between the anterior arch of the atlas and the odontoid peg, causing atlantoaxial dissociation and cord compression. The cervicomedullary compression appeared to be caused in part by the neurofibroma but also by the abnormal alignment and thickening of the ligaments between the clivus and C-2. Preoperative imaging repeated on the morning of surgery revealed that the atlantoaxial dissociation had reduced with relief of cord compression and the lesion prolapsed inferiorly. The authors discuss this unusual lesion and describe the associated operative findings and surgical management.
Thoracic spinal iophendylate-induced arachnoiditis mimicking an intramedullary spinal cord neoplasm
Authors: Hwang Steven W. , Bhadelia Rafeeque A. , Wu Julian
Published: February 2008

✓Iophendylate (Pantopaque or Myodil) was commonly used from the 1940s until the late 1980s for myelography, cisternography, and ventriculography. Although such instances are rare, several different long-term sequelae have been described in the literature and associated with intrathecal iophendylate. The authors describe an unusual case of arachnoiditis caused by residual thoracic iophendylate imitating an expansile intramedullary lesion on magnetic resonance images obtained 30 years after the initial myelographic injection.
Odontoid fracture complicating Jaffe–Lichtenstein disease
Authors: Peltier Johann , Lefranc Michel , Fichten Anthony , Cordonnier Carole , Toussaint Patrick , Desenclos Christine , Le Gars Daniel
Published: February 2008

✓The authors report the case of a 31-year-old man with polyostotic fibrous dysplasia who suffered a traumatic odontoid fracture in an area of a preexisting bone lesion. Conservative treatment was successfully performed. Jaffe–Lichtenstein disease is discussed along with differential diagnoses and alternative methods of treatment.
Relation of ramet size to acorn production in five oak species of xeric upland habitats in south‐central Florida
Authors: Abrahamson Warren G. , Layne James N.
Published: February 2008

This study examined variation in two components of acorn production. Percentage of bearing ramets (stems) and number of acorns per bearing ramet were examined in five clonal oaks in three xeric habitats of south‐central peninsular Florida in relation to ramet size within and between species and vegetative associations. Counts of acorns on two white oaks (Quercus chapmanii and Q. geminata) and three red oaks (Q. inopina, Q. laevis, and Q. myrtifolia) were conducted annually from 1969 to 1996 (except in 1991) on permanent grids in southern ridge sandhill, sand pine scrub, and scrubby flatwoods associations at the Archbold Biological Station, Florida, USA. Percentage of bearing individuals and mean number of acorns per bearing individual increased with increasing ramet size for all species across all vegetation associations. However, in Q. geminata and Q. myrtifolia, acorn production declined in the largest size class (>3.2 m), implying that larger individuals of these clonal species may become senescent. All oak species in sand pine scrub, which had a nearly closed overstory, had lower frequencies of bearing oaks and mean numbers of acorns compared with similar‐sized individuals of the same species in the more open‐canopied southern ridge sandhill and scrubby flatwoods associations, suggesting light limitation. The annual production of acorns by a given oak species was correlated across vegetative associations and annual acorn production of oak species was correlated for species within the same section. Intermediate‐size class oaks contributed the most acorns per unit area, suggesting that stands managed with short fire‐return times will provide fewer acorns to wildlife than stands managed to produce more variable distributions of oak size classes. However, our study suggests that long‐unburned stands, such as those studied here, will maintain relatively constant levels of acorn production as a consequence of ramet replacement within the clones of these shrubby oaks to create a variable distribution of size classes. Of the oak species studied, Q. myrtifolia had the highest acorn production and the smallest acorns, while Q. laevis had the lowest acorn production and the largest acorns, suggesting an allocation trade‐off between acorn numbers and size.
Phylogeny of Stephanomeria and related genera (compositae–lactuceae) based on analysis of 18S–26S nuclear rDNA ITS and ETS sequences
Authors: Lee Joongku , Baldwin Bruce G. , Gottlieb L. D.
Published: February 2008

A phylogenetic analysis of DNA sequences from the internal transcribed spacer (ITS), the external transcribed spacer (ETS), and the 5.8S regions of 18S–26S nuclear rDNA from all diploid species of Stephanomeria and related genera shows that Stephanomeria does not include either Munzothamnus blairii (previously S. blairii) or Pleiacanthus spinosus (previously S. spinosa). Without these two taxa, Stephanomeria is a well‐supported (100% bootstrap), monophyletic group of ten perennial and six annual species. Munzothamnus blairii and Pleiacanthus spinosus, both now considered members of monotypic genera, had been placed in Stephanomeria primarily because they have the same chromosome number as Stephanomeria and similar pollen surface features, but many disparities were ignored in previous classifications. Within Stephanomeria, an unsuspected sister relationship was detected between the montane S. lactucina and coastal S. cichoriacea. A second clade contained all the annual taxa and five of the perennial species. Among the annuals, strong bootstrap support was obtained for the previously recognized relationships between S. diegensis and S. exigua (98%) and between S. malheurensis and its progenitor, S. exigua subsp. coronaria (96%). Among the five perennial species that constitute a clade with the annuals, the recently described S. fluminea was shown to be sister to S. runcinata, and both of them were closely allied to S. tenuifolia and S. thurberi. The clade including the annuals (and five of the perennial species) was subtended by perennial lineages and pairwise divergence values among the annual taxa were much lower than among the perennial taxa as a group (though not too different than among the perennials in the same clade). The annuals probably originated recently within the genus.
Stratified analysis of the soil seed bank in the cedar glade endemic Astragalus bibullatus: evidence for historical changes in genetic structure
Authors: Morris Ashley B. , Baucom Regina S. , Cruzan Mitchell B.
Published: February 2008

Persistent seed banks may provide information on historical changes in the genetic composition of populations. We used stratified sampling of the soil seed bank of Astragalus bibullatus (Pyne's ground plum) to assess levels of temporal variation in population genetic structure and to infer historical changes in the levels of inbreeding and relative gene flow. This species has an extremely limited distribution in the Central Basin of Tennessee, where it is found in open areas and along the edges of cedar glades. Protein electrophoresis was conducted on seedlings grown from seeds that had been recovered from three successive 1 cm thick layers of soil sampled from six sites. Analyses of seven polymorphic allozyme loci indicated that there were substantial levels of genetic differentiation among soil layers and sites. Higher levels of genetic diversity were found in seed than in vegetative populations that had been sampled in a previous study. Seed populations from the uppermost soil layer had higher heterozygote deficiencies, displayed higher levels of differentiation among sites, and had higher private allele frequencies than seed populations from the lower two layers. The change in heterozygosity and distribution of genetic variation among sites for the youngest soil layer is consistent with a pattern of increased selfing, sib mating, and decreased gene flow among populations. These changes in inbreeding and relative levels of gene flow are corroborated by information on historical land use practices in the region and support the hypothesis that loss of appropriate habitat has led to smaller population sizes and a more fragmented distribution of this cedar glade endemic.
Multiple factors contribute to outcrossing in a tropical emergent Dipterocarpus tempehes, including a new pollen‐tube guidance mechanism for self‐incompatibility
Authors: Kenta Tanaka , Shimizu Kentaro K. , Nakagawa Michiko , Okada Kiyotaka , Hamid Abang A. , Nakashizuka Tohru
Published: February 2008

The self‐rejection system of Dipterocarpus tempehes (Dipterocarpaceae), an emergent tree of the lowland tropical forests of Borneo, were studied by means of pollination experiments, fluorescence microscopy of pollen tubes, and monitoring of ovary maturation patterns. Fruit set was higher in cross‐pollinated flowers than in control and self‐pollinated flowers, indicating the existence of pollen limitation and a self‐rejection system. Although the adhesion and the germination of self‐pollen and the growth of self‐pollen tubes were not inhibited, the proportion of cross‐pollen tubes that entered the style was 1.7–2.3 times higher than that of self‐pollen tubes, indicating a partial self‐incompatibility that inhibits self‐pollen tubes from entering the style hollow. These results suggest, for the first time, that self‐incompatibility is caused by a defect of pollen‐tube guidance. We also suggest a threshold effect in number of pollen tubes or late‐acting self‐incompatibility to fully explain the drastic and uniform selection against self‐pollinated flowers before ovary swelling. After that, maternal selection and/or inbreeding depression caused the abortion and delayed maturation of self‐pollinated flowers. The advantages of the self‐rejection process composed of partial early‐acting self‐incompatibility and relatively strong delayed abortion is discussed with respect to the general‐flowering phenomenon in lowland dipterocarp forests.
Changes in the risk of fine‐root mortality with age: a case study in peach,Prunus persica(Rosaceae)
Authors: Wells Christina E. , Glenn D. Michael , Eissenstat David M.
Published: February 2008

Previous studies suggest that younger roots are more vulnerable to mortality than older roots. We analyzed minirhizotron data using a mixed‐age, proportional hazards regression approach to determine whether the risk of mortality (or “hazard”) was higher for younger roots than for older roots in a West Virginia peach orchard. While root age apparently had a strong effect on the hazard when considered alone, this effect was largely due to different rates of mortality among roots of different orders, diameters, and depths. Roots with dependent laterals (higher order roots) had a lower hazard than first‐order roots in 1996 and 1997. Greater root diameter was also associated with a decreased hazard in both 1996 and 1997. In both years, there was a significant decrease in the hazard with depth. When considered alone, age appeared to be a strong predictor of risk: a 1‐d increase in initial root age was associated with a 1.26–2.62% decrease in the hazard. However, when diameter, order, and depth were incorporated into the model, the effect of root age disappeared or was greatly reduced. Baseline hazard function plots revealed that the timing of high‐risk periods was generally related to seasonal factors rather than individual root age.
Host compatibility of the cloud forest mistletoe Psittacanthus schiedeanus (Loranthaceae) in Central Veracruz, Mexico
Authors: de Buen Lorena López , Ornelas Juan Francisco
Published: February 2008

The consequences of the seed deposition of the parasitic mistletoe Psittacanthus schiedeanus were evaluated in a 32‐mo study. We conducted a field seed inoculation experiment to determine variation in seed adhesion, seed germination, seedling establishment, and plant survival to reproduction among five host species and to evaluate whether these post‐dispersal processes explain mistletoe prevalence and specificity at the regional scale. Seeds without an exocarp were inoculated onto branches of individuals of the five most common host species identified in nature in central Veracruz, México. Seed fate was monitored for 2 yr, at weekly intervals for the first 2 mo and at 2‐mo intervals thereafter. The height and diameter of experimental host branches and canopy cover above them were measured to see if these factors affected mistletoe establishment. Significant differences in seed attachment and seed germination were found among host species. Fewer seeds remained attached on experimental branches of Quercus germana than those of Liquidambar styraciflua, Acacia pennatula, and Platanus mexicana. Although significant differences in seed germination were observed among species (significantly greater on A. pennatula), >70% of mistletoe seeds germinated within the first 5 wk on all host species. Towards the end of the inoculation experiment, more mistletoe seedlings survived, grew, and then flowered on Liquidambar styraciflua than on A. pennatula, P. mexicana, Q. germana, or Q. leiophylla. Host branch initial height and diameter did not affect seedling survival, but seedlings survived better on trees where the canopy was more open. Our results suggest that Liquidambar styraciflua is the most compatible host species with P. schiedeanus in central Veracruz. Not surprisingly, Liquidambar is by far the most common host tree for P. schiedeanus in this area as well. We suggest that the observed local specialization is a result of seed dispersal as consequence of bird foraging and territorial behavior, host abundance, and host species compatibility.
Censusing natural microgametophyte populations: variable spatial mosaics and extreme fine‐graininess in winter‐flowering Helleborus foetidus (Ranunculaceae)
Authors: Herrera Carlos M.
Published: February 2008

Little is known about patterns and correlates of variation in microgametophyte populations for naturally pollinated plants, yet this information is critical for evaluating the prevalence and potential evolutionary significance of gametophyte competition in the wild. This paper analyzes spatial and temporal variation in microgametophyte populations (= number of pollen tubes per style) for the winter‐flowering, perennial herb Helleborus foetidus (Ranunculaceae), based on data from 29 populations in three regions of the Iberian Peninsula collected over two consecutive years. Mean size of microgametophyte populations varied significantly at a wide range of spatial scales, including among regions, among populations within regions, among individual plants within populations, among flowers of the same plant, and among pistils of the same flower (H. foetidus flowers are apocarpous). Differences between regions were quantitatively negligible. Differences between populations in the same region were moderate to low, and their sign and magnitude were inconsistent between years. Roughly half of total variance in microgametophyte numbers was accounted for by variation within individual plants, and the largest part of this component was due to differences between the pistils of the same flower. These results reveal extreme spatial fine‐graininess and marked stochasticity in the spatial variation of H. foetidus microgametophyte populations and suggest that opportunities for consistent selection on male gametophyte competitive ability are probably negligible in this species.
Interactive effects of lateral shade and wind on stem allometry, biomass allocation, and mechanical stability in Abutilon theophrasti (Malvaceae)
Authors: Henry Hugh A. L. , Thomas Sean C.
Published: February 2008

The effects of lateral shade and wind on stem allometry, whole‐plant biomass allocation, and mechanical stability were examined for Abutilon theophrasti in a fully factorial glasshouse experiment. Lateral shade from neighboring plants increased stem height by 33% relative to control plants grown individually, despite a decrease in plant dry mass. Intermittent wind decreased stem height by 18% in unshaded plants, but by only 3% in shaded plants. Surprisingly, both lateral shade and wind caused decreases in stem diameter, even with diameter controlled for height, resulting in low diameter : height ratios in wind‐treated plants relative to untreated plants. Under shade, wind‐treated plants had higher root allocation than untreated plants, which allowed wind‐treated shade plants to compensate for a low diameter : height ratio. This did not occur in the absence of shade, where stem tissue density and root allocation of wind‐treated plants did not exceed that of untreated plants. Nevertheless, wind‐treated plants experienced low drag relative to untreated plants due to a lower leaf area. Consequently, stem deflections of wind‐treated plants did not exceed those of untreated plants at any given windspeed. Our results document a complex interaction between shade and wind on plant morphology and suggest that the nature of this interaction is generally that lateral shade acts to reduce or eliminate thigmomorphogenic responses.
Soil seed bank and seed dormancy in wild populations of lima bean (Fabaceae): considerations for in situ and ex situ conservation
Authors: Degreef Jérôme , Rocha Oscar J. , Vanderborght Thierry , Baudoin Jean‐Pierre
Published: February 2008

Seed dormancy and its impact on the soil seed bank for wild Lima bean (Phaseolus lunatus) populations were studied in the Central Valley of Costa Rica. Five populations were selected in contrasted environments. In all cases, distribution of seeds in the soil was limited to 3 cm depth. No innate dormancy was observed but combination of hard seed coat and hilum opening controlled by environmental conditions were responsible for an induced dormancy and the constitution of a persistent seed bank. Breaking of this dormancy was obtained by a brief elevation of temperature from 25° to 45°C. Impacts of this phenomenon concern both genetic and demographic aspects of in situ conservation of the species. Consequences on ex situ conservation are mainly related with the regeneration of the seed collection.
In situ development of the foliicolous lichenPhyllophiale(Trichotheliaceae) from propagule germination to propagule production
Authors: Sanders William B.
Published: February 2008

The vegetative cycle of the foliicolous lichenPhyllophiale, from propagule germination to propagule production, was studied by light microscope observation of thalli colonizing plastic cover slips placed within a lowland tropical forest. Discoid propagules germinated by growth of radially arranged fungal cells and developed directly into lichen thalli. The young lichen comprised a single disc of closely branched, radiating filaments of the algal symbiontPhycopeltis, covered by a network of fungal hyphae extending onto the substrate as a prothallus. The prothallic hyphae incorporated additionalPhycopeltisthalli encountered on the substrate. The phycobiont formed a single layer, with individual algal thalli clearly distinguishable within the lichen. Radial growth ceased at points of contact between adjacent phycobiont thalli. The visible shape of the crustose lichen thallus corresponded to the perimeter of the phycobiont thalli within. Propagules were initiated at points corresponding to the margins of the phycobiont thalli, by vertical reorientation of horizontal algal filaments surrounded by fungal hyphae. The lichenized alga produced intercalary gametangia. Degeneration of propagules unsuccessful in lichen establishment sometimes resulted in free growth of the phycobiont. The alga generally maintained its shape, growth pattern, and reproductive independence within the lichen, while also participating in the formation of unique symbiotic propagules.
Is auxin the repressor signal of branch growth in apical control?
Authors: Cline Morris G. , Sadeski Kevin
Published: February 2008

“Apical control” is the repression of branch growth by a higher dominating branch or shoot. There has been some confusion in the literature concerning the meaning and causal mechanisms of this correlative phenomenon with those of “apical dominance,” which term is often used in a strict sense to connote the repression of the initiation of axillary bud outgrowth by an active shoot apex. Although the term “apical control” is most commonly employed with respect to woody species, this phenomenon also widely occurs in herbaceous plants. Because of the strong evidence for a role of auxin as a repressor signal in apical dominance and partly because of this lack of distinction in terminology, a similar role for auxin in apical control is often assumed in spite of the obvious acropetal auxin transport difficulty and the lack of direct evidence for the acropetal transport of any inhibitor influence. In the present study with the herbaceous Ipomoea nil, it has been clearly demonstrated that while exogenous auxin (1% NAA) strongly restores apical dominance in the Thimann‐Skoog experiment, auxin treatments to decapitated dominant shoots do not, in any observable way, restore apical control in lower dominated branches. Hence, in this fast‐growing species, the hypothesis for the role of auxin as a repressor signal for apical control is not supported.
Variation in floral scent composition within and between populations of Geonoma macrostachys (Arecaceae) in the western Amazon
Authors: Knudsen Jette T.
Published: February 2008

In geonomoid palms floral scent is both an important pollinator attractant and an important factor in reproductive isolation. However, little is known about intraspecific variation in floral scent composition in these as well as in other plants. In this study the level of variation in floral scent composition found within and among five populations of Geonoma macrostachys var. macrostachys in the western Amazon is documented. Floral scent samples were collected using head‐space adsorption and were analyzed by gas chromatography‐mass spectrometry. Most of the 108 compounds recorded were of isoprenoid origin, but only 28 of the compounds were found in all 62 samples analyzed. No differentiation was found between the studied populations, confirming that G. macrostachys var. macrostachys is outbreeding and indicating that the individual populations are part of a metapopulation linked by sufficient gene flow to avoid local differentiation. However, a negative correlation between distance and similarity of floral scent chemistry indicates a case of clinal variation within the distribution area of G. macrostachys. Male euglossine bees are infrequent visitors to G. macrostachys, while other groups of insects are abundant. However, the level of variation and the chemical composition lend support to a suggested importance of male euglossine bees in long‐distance pollen flow in G. macrostachys. Other insect groups are probably important in securing pollination of most flowers with pollen from nearby sources.
Limited seed dispersal and microspatial population structure of an agamospermous grass of West African savannahs, Hyparrhenia diplandra (Poaceae)
Authors: Garnier Lisa K. M. , Durand Jacques , Dajoz Isabelle
Published: February 2008

We studied the microspatial population structure of the perennial tussock grass, Hyparrhenia diplandra (Poaceae), a facultative agamospermous species of West African savannahs. The microspatial population structure of H. diplandra was investigated by choosing two 100‐m2; quadrats at random from which all individuals were mapped. The genotype of every individual was determined using two highly polymorphic microsatellite loci. A chloroplast locus was also used to investigate the role of seed dispersal on the genetic structure of populations. The genetic diversity index (0.85) was high for a clonal species. Significant genetic differentiation over short distances was detected by F statistics, and spatial autocorrelation analyses within both quadrats showed significant isolation‐by‐distance patterns, both with the cytoplasmic locus and the nuclear loci. Some clones formed large patches (up to 5 m in diameter) whereas others were more scattered. However, the genetic differentiation between quadrats was much higher when studied with the cytoplasmic locus than with the nuclear loci, indicating that gene flow via pollen, but not seeds, may frequently occur between quadrats. The maintenance of genetic diversity in this facultative agamospermous species most likely results from several factors, such as low seed dispersal ability, nonnegligible gene flow through pollen, and selective pressures induced by regularly occurring fires in this ecosystem.