Abscisic acid in the xylem: where does it come from, where does it go to?

Abscisic acid is a hormonal stress signal that moves in the xylem from the root to the different parts of the shoot where it regulates transpirational water loss and leaf growth. The factors that modify the intensity of the ABA signal in the xylem are of particular interest because target cells recognize concentrations. ABA(xyl), will be decreased as radial water flow through the roots is increased, assuming that radial ABA transport occurs in the symplast only. Such dilutions of the plant hormone concentration can be compensated in different ways, which help to keep the ABA-concentrations in the xylem constant: (i) apoplastic bypass flows of ABA, (ii) ABA flows between the stem parenchyma and the xylem during transport and (iii) the action of beta-D-glucosidases that release free ABA from its conjugates to the root cortex and the leaf apoplast. The significance of reflection coefficients (sigma(ABA)), permeability coefficients of membranes (P(S)(ABA)) and apoplastic barriers for ABA is discussed.     

The glyoxylate cycle: does it function in the dormant or active bear?

The presence of or induction of an active glyoxylate cycle (GC) in the dormant black bear whose sole source of energy is body fat is an attractive concept which would allow lipid (acetate) to be directed from oxidation via the tricarboxylic acid cycle to many biosynthetic pathways. However, in spite of earlier claims, the present report establishes that isocitrate lyase and malate synthetase, GC marker enzymes, could not be detected in liver or kidney of active or dormant bears; liver peroxisome numbers were similar. The absence of brown fat (by light microscopy) and of the GC enzymes in the dormant bear raises questions about the prior report.     

Calcitonin, an enigmatic hormone: does it have a function?

This editorial presents our view of the status of thyroidal calcitonin (TCT) in mammalian physiology. The discovery of calcitonin (CT) enabled the development of a valuable therapeutic agent but the early experiments most likely misled us with regard to its physiological significance. These early purported roles for TCT, first as an agent important in blood calcium regulation and later as an agent to prevent hypercalcemia, are no longer considered as physiological functions. While large supraphysiological doses of CT have an effect on the morphology and function of osteoclasts, it is unlikely that these effects of CT are important in the normal physiology of osteoclasts or bone remodeling. It is surprising that 38 years after the discovery of TCT there is no consensus as to its role in normal mammalian physiology. This editorial concerns three possibilities with respect to TCT: 1) the hormone is vestigial; 2) the hormone plays a role in water metabolism, ionic concentrations, and/or acid-base balance, actions that may not involve calcium metabolism at all; and 3) TCT acts to store phosphate postprandially on bone surfaces as a labile calcium-phosphate colloid, an action that may provide calcium needed for use in non-feeding periods or to reduce postprandial loss of phosphate when dietary phosphate is limited. Also discussed are recent publications indicating that CT synthesized in non-thyroidal tissues (NTCT) may have paracrine actions.     

First-phase insulin secretion: does it exist in real life? Considerations on shape and function

To fulfill its preeminent function of regulating glucose metabolism, insulin secretion must not only be quantitatively appropriate but also have qualitative, dynamic properties that optimize insulin action on target tissues. This review focuses on the importance of the first-phase insulin secretion to glucose metabolism and attempts to illustrate the relationships between the first-phase insulin response to an intravenous glucose challenge and the early insulin response following glucose ingestion. A clear-cut first phase occurs only when the beta-cell is exposed to a rapidly changing glucose stimulus, like the one induced by a brisk intravenous glucose administration. In contrast, peripheral insulin concentration following glucose ingestion does not bear any clear sign of biphasic shape. Coupling data from the literature with the results of a beta-cell model simulation, a close relationship between the first-phase insulin response to intravenous glucose and the early insulin response to glucose ingestion emerges. It appears that the same ability of the beta-cell to produce a pronounced first phase in response to an intravenous glucose challenge can generate a rapidly increasing early phase in response to the blood glucose profile following glucose ingestion. This early insulin response to glucose is enhanced by the concomitant action of incretins and neural responses to nutrient ingestion. Thus, under physiological circumstances, the key feature of the early insulin response seems to be the ability to generate a rapidly increasing insulin profile. This notion is corroborated by recent experimental evidence that the early insulin response, when assessed at the portal level with a frequent sampling, displays a pulsatile nature. Thus, even though the classical first phase does not exist under physiological conditions, the oscillatory behavior identified at the portal level does serve the purpose of rapidly exposing the liver to elevated insulin levels that, also in virtue of their up-and-down pattern, are particularly effective in restraining hepatic glucose production.     

Which humans behave adaptively,and why does it matter?

There has long been debate about the relevance of evolutionary theory to the study of humans. To many of us, however, the debate has shifted from whether to proceed with an evolutionary approach to how to proceed. Increasingly, it has been argued that studies of the current reproductive function of human traits make little or no contribution to the understanding of the psyche (e.g., Symons 1989). Here, on the basis of arguments about the relationship between an adaptation and an adaptive outcome, and a review of studies that assess current adaptiveness, I argue to the contrary that knowledge of the contexts in which people do or do not behave adaptively provides important information about the nature of the mechanisms that comprise the human psyche. In particular, studies that indicate that people behave adaptively in at least some contemporary environments cast doubt on many nonevolutionary constructions of human nature, and can be used now to distinguish alternative evolutionary constructions that are at odds over many issues pentaining to the human psyche's ontogeny and evolutionary background, especially the extent to which the human psyche is general purpose.     

Vertebrate hox temporal collinearity: does it exist and what is it’s function?

Hox temporal collinearity (TC) is a mysterious feature of embryogenesis. This article is opportune because of a recent challenge to TC’s existence This challenge is examined and the evidence that TC does exist is presented. Its function is discussed. Temporal collinearity is thought to be important because it lays the basis for Hox spatial collinearity and the vertebrate A-P axial pattern. The time-space translation mechanism whereby this occurs is examined.     

Regeneration in the metazoans: why does it happen?

Why does regeneration occur? And why, when it manifests itself, does it do so in some but not all metazoan species? Hence, what are the permissive or inhibitory factors operating behind this phenomenon? When it comes to regeneration, many questions, such as these, remain unanswered. In fact, the problem of animal regeneration has withstood the probing of scientific inquiry for over 250 years and still awaits a satisfactory mechanistic explanation. In this essay, I will review the distribution and the modes of regeneration that are found in the different metazoan phyla. Also, I will re-examine ideas on its evolutionary origins, and discuss its possible relationship to both asexual reproduction and embryogenesis. This endeavor has two objectives. First, to bring forward an interpretation of regeneration which integrates evolutionary and developmental considerations into its discussion. And second, to suggest a comparative experimental approach to this problem that may bring us closer to understanding the molecular basis of this long-standing biological problem. BioEssays 22:578-590, 2000.     

Seed positioning in extruded pellets: does it matter?

Extruded pellets containing activated carbon (AC) can be used to sow native seeds while simultaneously applying herbicide to control invasive species. Incorporating AC in pellets has been demonstrated to protect native seeds; however, there may be unintended detrimental impacts to seedling emergence. We aimed to optimize seed position within pellets to maximize emergence and survival of the perennial shrub Jacksonia furcellata. Seeds were positioned at 2 mm (top), 6 mm (middle), and 12 mm (bottom) within pellets (with or without AC), sown on or below the soil surface, and compared to non-pelleted seeds sown under the soil surface in the equivalent positions (2, 6, and 12 mm depth). Trays were treated with a pre-emergent herbicide (Simazine) or left unsprayed. Emergence (without herbicide) was significantly higher from seeds positioned at the bottom of pellets without AC sown on the soil surface (70%), compared to non-pelleted seeds sown at the bottom (12 mm below the soil surface; 57%). However, emergence was inhibited when seeds were positioned in the middle (6 mm) of pellets with AC (32%). When treated with Simazine, survival was highest from seeds positioned at the bottom of pellets with AC (60%), compared to pellets without AC (15%) and non-pelleted seeds sown at the bottom (12 mm below the soil surface; 15%). Jacksonia furcellata seeds positioned at the bottom of pellets, sown on the soil surface, shows promise to minimize negative impacts to emergence, and maximize herbicide protection. Further testing with additional species is required to refine pellet production (e.g. recipe, extrusion, and shape) for optimal emergence.     

Vesicular transport in capillary endothelium: does it occur?

A revised picture of the organization of endothelial plasmalemmal vesicles is presented. Three-dimensional reconstructions of endothelial segments from frog mesenteric capillaries and rat heart capillaries based on ultrathin serial sectioning have shown that plasmalemmal vesicles are not true vesicles but parts of an elaborate system of invaginations of the surface membrane. The revised picture probably applies to capillary endothelia in general. The absence of free cytoplasmic vesicles implies that vesicular transport is unlikely to occur. A reinterpretation of previous studies of vesicular transport shows that they are equally compatible with the present view that plasmalemmal vesicles are static elements of invaginations of the endothelial surface membrane.     

Drug resistance in Leishmania: does it really matter?

Treatment failure (TF) jeopardizes the management of parasitic diseases, including leishmaniasis. From the parasite’s point of view, drug resistance (DR) is generally considered as central to TF. However, the link between TF and DR, as measured by in vitro drug susceptibility assays, is unclear, some studies revealing an association between treatment outcome and drug susceptibility, others not. Here we address three fundamental questions aiming to shed light on these ambiguities. First, are the right assays being used to measure DR? Second, are the parasites studied, which are generally those that adapt to in vitro culture, actually appropriate? Finally, are other parasite factors – such as the development of quiescent forms that are recalcitrant to drugs – responsible for TF without DR?     

Subfunctionalization: How often does it occur? How long does it take?

The mechanisms responsible for the preservation of duplicate genes have been debated for more than 70 years. Recently, Lynch and Force have proposed a new explanation: subfunctionalization--after duplication the two gene copies specialize to perform complementary functions. We investigate the probability that subfunctionalization occurs, the amount of time after duplication that it takes for the outcome to be resolved, and the relationship of these quantities to the population size and mutation rates.     

Symmetry breakage in the vertebrate embryo: When does it happen and how does it work?

Asymmetric development of the vertebrate embryo has fascinated embryologists for over a century. Much has been learned since the asymmetric Nodal signaling cascade in the left lateral plate mesoderm was detected, and began to be unraveled over the past decade or two. When and how symmetry is initially broken, however, has remained a matter of debate. Two essentially mutually exclusive models prevail. Cilia-driven leftward flow of extracellular fluids occurs in mammalian, fish and amphibian embryos. A great deal of experimental evidence indicates that this flow is indeed required for symmetry breaking. An alternative model has argued, however, that flow simply acts as an amplification step for early asymmetric cues generated by ion flux during the first cleavage divisions. In this review we critically evaluate the experimental basis of both models. Although a number of open questions persist, the available evidence is best compatible with flow-based symmetry breakage as the archetypical mode of symmetry breakage.     

Impact factor in cytopathology journals: what does it reflect and how much does it matter?

B. AbdullGaffar
Impact factor in cytopathology journals: what does it reflect and how much does it matter? Objective: To study the trends of impact factor (IF) in four cytopathology journals. To investigate the factors that might influence IF in cytopathology literature and whether IF has any impact on cytopathology practice. Methods: The IFs of four cytopathology journals were searched from 2005 to 2009. The IFs and their relationships with the types and number of publications, publishers, the official societies, readership, the quality of their contents, the topics covered and the levels of evidence were compared. Results: Cancer Cytopathology (CC) had the highest IF. Acta Cytologica (AC) had the lowest IF, which appeared to be in decline. Cytopathology (C) and Diagnostic Cytopathology (DC) had a slow but steady increase in their IF. Components that might influence these differences could include the category and the society of the journal, targeted readers and certain types of publications. Publishers, the number of publications, the types of topics covered and the levels of evidence probably have no major effect on IF. Conclusions: IF has its own benefits and original applications. IF is a quantitative measure that does not reflect the levels of evidence in cytopathology journals. IF should not be abandoned because it might encourage competition between cytopathology journals, but it should not dictate their contents.     

Sartorial eloquence: does it exist in the paediatrician-patient relationship?

OBJECTIVE--To evaluate children''s and parents'' perceptions of hospital doctors'' attire. DESIGN--Questionnaire study asking children and parents to assign positive and negative attributes to five photographs of a male or female doctor dressed formally and informally. SETTING--Outpatient department, Children''s Hospital, Birmingham. SUBJECTS--203 consecutive child-parent pairs attending outpatient clinics over three months. MAIN OUTCOME MEASURES--Children''s and parents'' preferences, assessed by comparing proportions. RESULTS--70% (286/406) of children and parents rated doctors'' dress as important; more children rated it "very important" (27% (54/203) v 14% (29/203), P < 0.01, 95% confidence interval for difference 5% to 21%). Of the 99 children responding, 44 regarded the man in white coat as most competent (44% v 20% expected by chance, P < 0.01, 34% to 54%) and most concerned (32% v 20%, P < 0.01, 23% to 41%). Children also regarded the woman in white coat as most competent; however, male and female doctors in white coats rated lower for friendliness. Asians and regular surgical attenders preferred doctors in white coats. The man in polo shirt and trousers was rated as most friendly (40% v 20% expected by chance, P < 0.01, 30% to 50%) and most gentle (37% v 20%, P < 0.01, 27% to 46%). The woman in tee shirt and slacks also rated most friendly and gentle; however, both casually dressed doctors rated lower for competence. Parents preferred more casual dress but expressed preferences less strongly, and they poorly predicted which outfits their children preferred. CONCLUSIONS--Children regard formally dressed doctors as competent but not friendly; they regard casual dress as friendly but not competent.     

Bi-site catalysis in F1-ATPase: does it exist?

The mechanism of action of F(1)F(0)-ATP synthase is controversial. Some favor a tri-site mechanism, where substrate must fill all three catalytic sites for activity, others a bi-site mechanism, where one of the three sites is always unoccupied. New approaches were applied to examine this question. First, ITP was used as hydrolysis substrate; lower binding affinities of ITP versus ATP enable more accurate assessment of sites occupancy. Second, distributions of all eight possible enzyme species (with zero, one, two or three sites filled) as fraction of total enzyme population at each ITP concentration were calculated, and compared with measured ITPase activity. Confirming data were obtained with ATP as substrate. Third, we performed a theoretical analysis of possible bi-site mechanisms. The results argue convincingly that bi-site hydrolysis activity is negligible, and may not even exist. Effectively, tri-site hydrolysis is the only mechanism. We argue that only tri-site hydrolysis drives subunit rotation. Theoretical analyses of possible bi-site mechanisms reveal serious flaws, not previously recognized. One is that, in bi-site catalysis, the predicted direction of subunit rotation is the same for both ATP synthesis and hydrolysis; a second is that infrequently occurring enzyme species are required.     

Heterospecific pollen deposition: does diversity alter the consequences?

? In natural communities, plants can receive pollen from multiple heterospecifics as well as conspecifics. However, studies on the effects of interspecific pollen transfer have focused on interactions between species pairs. The potential exists for diverse interactions among heterospecific pollen (HP) grains on the stigma, and for these to affect plant reproduction, alone or in combination with conspecific pollen (CP) loss, but these interactions have not yet been explored. ? We used hand-pollinations to simulate increasing community diversity and CP loss on Mimulus guttatus stigmas. We used pollen mixes of one to three heterospecific donors to determine how species composition and CP load size affect seed production and to characterize the mechanisms underlying fertilization failure. ? Heterospecific pollen deposition reduced M. guttatus seed production and while the effect increased with the number of heterospecific donors, the strength depended on species composition and was independent of conspecific load size. Different types of interactions (additive and synergistic) are hypothesized to underlie the diverse effects on M. guttatus reproductive success. ? Our results suggest that an increase in the diversity of heterospecific donors will not always lead to a greater decrease in fitness because multispecies effects depend on the interacting species.     

Male care in primates: does it ever reflect paternity?

Female mammals have internal fertilization, long gestation, and lactation. These basic facts of reproductive biology have important social consequences. Internal fertilization (accompanied by sperm competition) forces males either to face considerable uncertainty about paternity or to invest heavily in mate guarding. Long gestation increases the benefits of mate desertion for males. And because only females lactate, males have relatively less to contribute to rearing the young. Hence, it is not surprising that male mammals rarely assist their mates in caring for their young: Direct infant care by males occurs in fewer than 5 percent of all mammalian species.^1,2 In fact, many mammalian mothers attack males, even possible father of their offspring.³