Pollen tubes and the physical world

The primary goal of our previous opinion paper (Winship, L.J. et al. (2010) Trends Plant Sci. 15, 363-369) [1] was to put two models for the control of pollen tube growth on the same theoretical and biophysical footing, and to then test both for consistency with basic principles and with experimental data. Our central thesis, then and now, is that the biophysical and biochemical mechanisms that enable pollen tubes to grow and to respond to their environment evolved in a physical context constrained by known, inescapable principles. First, pressure is a scalar, not a vector quantity. Second, the water movement in and out of plant cells that generates pressure is passive, not active, and is controlled by differences in water potential. Here we respond to the issues raised by Zonia and Munnik (Trends Plant Sci. 2011; this issue) [2] in the light of new evidence concerning turgor pressure and pollen tube growth rates.     

Exploiting the effects of high hydrostatic pressure in biotechnological applications

Applying hydrostatic pressure to biological systems and processes can alter their characteristics. In addition to its use as a basic research tool for investigating the kinetics and thermodynamics of biological systems at the molecular level, the application of pressure is also being used to modify the properties of biological materials to preserve or improve their qualities. This article reviews the principles underlying the observed effects of applied pressure on biological systems, and discusses current and potential application of pressure in biotechnological processes.     

Trunk, abdomen, and pressure sore reconstruction

LEARNING OBJECTIVES: After reading this article, the participant should be able to: 1. Describe the principles of wound closure, torso reconstruction, and pressure sore reconstruction. 2. Outline standard options to treat defects of the chest, abdomen, and back and pressure ulcers in all anatomical areas. 3. Manage and prevent pressure ulcers. SUMMARY: Chest wall reconstruction is indicated following tumor resection, radiation wound breakdown, or intrathoracic sepsis. Principles of wound closure and chest wall stabilization, where indicated, are discussed. Principles of abdominal wall reconstruction continue to evolve with the introduction of newer bioprosthetics and the application of functional concepts for wound closure. The authors illustrate these principles using commonly encountered clinical scenarios and guidelines to achieve predictable results. Pressure ulcers continue to be devastating complications to patients' health and a functional hazard when they occur in the bedridden, in patients with spinal cord injuries, and in patients with neuromuscular disease. Management of pressure ulcers is also very expensive. The authors describe standard options to treat defects of the chest, abdomen, and back and pressure ulcers in all anatomical areas. A comprehensive understanding of principles and techniques will allow practitioners to approach difficult issues of torso reconstruction and pressure sores with a rational confidence and an expectation of generally satisfactory outcomes. With pressure ulcers, prevention remains the primary goal. Patient education and compliance coupled with a multidisciplinary team approach can reduce their occurrence significantly. Surgical management includes appropriate patient selection, adequate débridement, soft-tissue coverage, and use of flaps that will not limit future reconstructions if needed. Postoperatively, a strict protocol should be adapted to ensure the success of the flap procedure. Several myocutaneous flaps commonly used for the surgical management of pressure are discussed. Commonly used flaps in chest and abdominal wall reconstruction are discussed and these should be useful for the practicing plastic surgeon.     

Thermodynamic and functional characteristics of deep-sea enzymes revealed by pressure effects

Hydrostatic pressure analysis is an ideal approach for studying protein dynamics and hydration. The development of full ocean depth submersibles and high-pressure biological techniques allows us to investigate enzymes from deep-sea organisms at the molecular level. The aim of this review was to overview the thermodynamic and functional characteristics of deep-sea enzymes as revealed by pressure axis analysis after giving a brief introduction to the thermodynamic principles underlying the effects of pressure on the structural stability and function of enzymes.     

Investigation of the effect of high hydrostatic pressure on proteins and lipidic membranes by dynamic fluorescence spectroscopy

Dynamic fluorescence spectroscopy brings new insight into the functional and structural changes of biological molecules under moderate and high hydrostatic pressure. The principles of time-resolved fluorescence methods are briefly described and the resulting type of information is summarized. A first set of selected applications of the use of dynamic fluorescence on pressure effects on proteins in terms of denaturation, ternary and quaternary structure, aggregation and also interaction with DNA are presented. A second set of applications is devoted to the effect of pressure and of cholesterol on lateral heterogeneity of lipidic membranes.     

First principles study of the electronic structure and optical properties of chrysene under pressure

Structural parameters, electronic and optical properties of chrysene have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first principles density functional theory. The pressure dependence of the electronic band structure, density of states and partial density of states of chrysene were presented. Meanwhile, the complex dielectric function, refractive index, absorption coefficient, reflectivity, and the extinction coefficient are calculated and analysed. According to our work, we found that the optical properties of chrysene undergo a red shift with increasing pressure.     

Pressure and life: some biological strategies

All biological processes of life on Earth experience varying degrees of pressure. Aquatic organisms living in the deep-sea, as well as chondrocytic cells of articular cartilage are exposed to hydrostatic pressures that rise up to several hundred times that of atmospheric pressure. In the case of marine larvae that disperse through the oceanic water column, pressure changes might be responsible for stress conditions during development, limiting colonisation capabilities. In a number of biological systems, life strategies may be significantly influenced by pressure. In this review, we will focus on the consequences of pressure changes on various biological processes, and more specifically on animals living in the deep-sea. Revisiting general principles of pressure effects on biological systems, we present recent data illustrating the diversity of effects pressure may have at different levels in biological systems, with particular attention to effects on gene expression. After a review of the main pressure equipments available today for studying species living naturally at high pressure, we summarise what is known concerning pressure impact during animal development.     

An Impasse in Plant Water Relations?

Balling and Zimmermann [Planta 182 (1990), 325–338] used a pressure probe to measure directly negative pressures in the xylem of transpiring plants. They obtained data that challenge the standard framework that plant physiologists use when thinking about plant water relations, and, most notably, found a substantial discrepancy between their measurements of xylem pressure and of leaf water potential measured with a Scholander pressure bomb. Their data are critically examined and it is shown that most of them can be accommodated within the established principles of plant water relations. In particular, there are several reasons, consistent with the established principles, why leaf water potential and xylem pressure may differ.     

Challenges in teaching the mechanics of breathing to medical and graduate students

The mechanics of breathing has always been a difficult topic for some medical and graduate students. The subject is very quantitative and contains a number of concepts that some students have trouble with, including physical principles such as pressure, flow, volume, resistance, elasticity, and compliance. Apparently, present-day students find the subject more difficult than students of 20 years ago. A possible reason for this is that the teaching of elementary physics in high school and college is now given less emphasis, whereas other topics, such as molecular biology, receive a great deal of attention. Another factor may be that many of us grew up building radios and other such devices, whereas modern students tend to plug in an electronic unit with little idea of its function. Some examples of misconceptions of present-day students who have taken our course are given. To help the weaker students, we now include a primer at the beginning of our handout for the course that covers simple physical principles. Examples of some of the most difficult concepts for students are given.     

Piezotolerance as a metabolic engineering tool for the biosynthesis of natural products

Thermodynamically, high-pressure (>10's of MPa) has a potentially vastly superior effect on reactions and their rates within metabolic processes than temperature. Thus, it might be expected that changes in the pressure experienced by living organisms would have effects on the products of their metabolism. To examine the potential for modification of metabolic pathways based on thermodynamic principles we have performed simple molecular dynamics simulations, in vacuo and in aquo on the metabolites synthesized by recombinant polyketide synthases (PKS). We were able to determine, in this in silico study, the volume changes associated with each reaction step along the parallel PKS pathways. Results indicate the importance of explicitly including the solvent in the simulations. Furthermore, the addition of solvent and high pressure reveals that high pressure may have a beneficial effect on certain pathways over others. Thus, the future looks bright for pressure driven novel secondary metabolite discoveries, and their sustained and efficient production via metabolic engineering.     

Biomechanical model of the xylem vessels in vascular plants

BACKGROUND AND AIMS: The xylem, or water transport system, in vascular plants adopts different morphologies that appear sequentially during growth phases. This paper proposes an explanation of these morphologies based on engineering design principles. METHODS: Using microscopic observations of the different growth stages, an engineering analysis of the xylem vessels as a closed cylinder under internal pressure is carried out adopting pressure vessel design concepts. KEY RESULTS: The analysis suggests that the xylem vessel structural morphology follows the 'constant strength' design principle, i.e. all of the material within the wall of the xylem is loaded equally to its maximum allowable stress capacity, and the amount of material used is therefore systematically minimized. The analysis shows that the different structural designs of the xylem vessel walls (annular, helical, reticulate and pitted) all quantitatively follow the constant strength design principle. CONCLUSIONS: The results are discussed with respect to growth and differentiation. It is concluded that the morphology of the xylem vessel through the different phases of growth seems to follow optimal engineering design principles.     

Designing and engineering evolutionary robust genetic circuits

Background  

One problem with engineered genetic circuits in synthetic microbes is their stability over evolutionary time in the absence of selective pressure. Since design of a selective environment for maintaining function of a circuit will be unique to every circuit, general design principles are needed for engineering evolutionary robust circuits that permit the long-term study or applied use of synthetic circuits.     

Model analogues in the study of cephalic circulation

Simple laboratory models are useful to demonstrate cardiovascular principles involving the effects of gravity on the distribution of blood flow to the heads of animals, especially tall ones like the giraffe. They show that negative pressures cannot occur in collapsible vessels of the head, unless they are protected from collapse by external structures such as the cranium and cervical vertebrae. Negative pressures in the cerebral-spinal fluid (CSF) can prevent cerebral circulation from collapsing, and the spinal veins of the venous plexus can return blood to the heart in essentially rigid vessels. However, cephalic vessels outside the cranium are collapsible, so require positive blood pressures to establish flow; CSF pressure and venous plexus flow are irrelevant in this regard. Pressures in collapsible vessels reflect pressures exerted by surrounding tissues, which may explain the observed pressure gradient in the giraffe jugular vein. Tissue pressure is distinct from interstitial fluid pressure which has little influence on pressure gradients across the walls of major vessels.     

Water pumping and analysis of flow in burrowing zoobenthos: an overview

Burrowing animals maintain contact with the water above the sediment by pumping water through a tube system and therefore measurements of water pumping rate of burrowing animals is of crucial importance for the study of many processes both within and above the sea floor. This review deals with the measuring of water pumping and the analysis of flow generated by burrowing deposit- and filter-feeding zoobenthos in order to determine the type of pump and mechanisms involved, flow rate, pump pressure, and pumping power. The practical use of fluid mechanical principles is examined, and it is stressed that not only the pump pressure that a burrowing animal can apply is of interest for assessing the energy cost of pumping, but also the distribution of excess pressure along its burrow is of importance for assessing the seepage flow of oxygen-rich water into the sediment surrounding the burrow because this bioirrigation exerts a considerable effect on the chemistry and microbiology of sediments. Dense populations of burrowing filter-feeding zoobenthos also interact with the water above the sediment interface and this is reflected in the development of phytoplankton concentration profiles above the filter-feeding animals. In stagnant situations the near-bottom water may be depleted of food particles, depending on the population filtration rate and the intensity of the biomixing induced by the filtering activity. But moderate currents and the biomixing can presumably generate enough turbulence to facilitate mixing of water layers at the sea bed with the layers above where food particle concentrations are relatively higher. Following a brief summary of types of burrowing benthic animals, common methods for measuring pumping rates are described along with examples. For estimating the required pump pressure, biofluid mechanical theory for flow in tube–pump systems is summarised (elaborated in Appendix A). Specific examples are given to illustrate general principles and to give an idea of typical values of flow rate, pressure drop and power involved. Finally, some flow effects generated by burrowing animals in and above the sediment are described.     

On the principles of the vascular network branching

We propose an explanation of Murray's law without applying the minimality principles. The model deals with a "delivering" artery system of an organ that is characterized, first, by the space-filling embedding into the organ tissue and, second, by the uniform distribution of the blood pressure drop over it. The latter assumption is justified using the available physiological data and the idea about conditions needed for perfect self-regulation. Based on the two statements we get Murray's law, and so, demonstrate that it can be also regarded as a direct consequence of the organism's capacity for controlling finely the blood flow redistribution over peripheral vascular networks.     

Domestication and the behavior-genetic analysis of captive populations

Captive environments are believed to produce behavioral changes in animal populations that may limit our ability to generalize back to natural populations. These behavioral changes are thought to be associated with one or both of the following: (a) changes in frequencies of genes or gene complexes due to the effects of inbreeding or to changes in selection pressure; (b) changes in development of the phenotype due to the effects of changes in environmental variables. Inbreeding leads to increase in homozygosity, that may result in developmental anomalies because of a breakdown in developmental homeostasis. Changes in selection pressure may disrupt coadapted gene complexes that have evolved in the wild. Often, domestication is believed to result in individuals that are “degenerate”; i.e. inferior to individuals in the wild. However, this notion has received no empirical support. In fact, if phenotype changes do occur under domestication, these are usually quantitative, not qualitative, in nature. We suggest that the study of the domestication process may reveal evolutionary principles that would be difficult to discover in other ways, and the zoological parks may be ideal situations for such research.     

Hemodynamic diagnostics of epicardial coronary stenoses: <Emphasis Type="Italic">in-vitro</Emphasis> experimental and computational study

Background  

The severity of epicardial coronary stenosis can be assessed by invasive measurements of trans-stenotic pressure drop and flow. A pressure or flow sensor-tipped guidewire inserted across the coronary stenosis causes an overestimation in true trans-stenotic pressure drop and reduction in coronary flow. This may mask the true severity of coronary stenosis. In order to unmask the true severity of epicardial stenosis, we evaluate a diagnostic parameter, which is obtained from fundamental fluid dynamics principles. This experimental and numerical study focuses on the characterization of the diagnostic parameter, pressure drop coefficient, and also evaluates the pressure recovery downstream of stenoses.     

Isolation and Identification of Antitumor Prineiple Maytansine,Maytanprine and Other Constituents from Gymnosporia diversifolia

The potential antitumor principles, maytansine and maytanprine were isolated from the overground parts of Gymnosporia diversifolia for the first time. The method of separation was modified by application of dry column chromatography, low pressure column chromatography and other separation techniques. Besides, six known compounds were also isolated and identificated as dulcitol, friedelin, β-amyrin, β-sitosterol, kaempferitrin and kaempferol-7-O-rhamnoside respectively. The latter two flavonoids were not reported in this genus before.