Can loaded interface characteristics influence strain distributions in muscle adjacent to bony prominences?

Pressure distributions at the interface between skin and supporting tissues are used in design of supporting surfaces like beds, wheel chairs, prostheses and in sales brochures to support commercial products. The reasoning behind this is, that equal pressure distributions in the absence of high pressure gradients is assumed to minimise the risk of developing pressure sores. Notwithstanding the difficulty in performing reproducible and accurate pressure measurements, the question arises if the interface pressure distribution is representative of the internal mechanical state of the soft tissues involved. The paper describes a study of the mechanical condition of a supported buttock contact, depending on cushion properties, relative properties of tissue layers and friction. Numerical, mechanical simulations of a buttock on a supporting cushion are described. The ischial tuberosity is modelled as a rigid body, whereas the overlying muscle, fat and skin layers are modelled as a non-linear Ogden material. Material parameters and thickness of the fat layer are varied. Coulomb friction between buttock and cushion is modelled with different values of the friction coefficient. Moreover, the thickness and properties of the cushion are varied. High shear strains are found in the muscle near the bony prominence and the fat layer near the symmetry line. The performed parameter variations lead to large differences in shear strain in the fat layer but relatively small variations in the skeletal muscle. Even with a soft cushion, leading to a high reduction of the interface pressure the deformation of the skeletal muscle near the bone is high enough to form a risk, which is a clear argument that interface pressures alone are not sufficient to evaluate supporting surfaces.     

The differential replication of DNA during plant development

The percentage of satellite DNA, as defined by neutral CsCl equilibrium centrifugation, varied in different tissues of a plant. Satellite DNA formed a higher percentage of the genome in meristematic tissues (seed, root tip) than in mature, differentiated tissues (fruit, leaf, cotyledon). The buoyant density of the satellite peak, and in some cases of the mainband, also varied significantly between seed and fruit tissue. This variation in the percentage of satellite DNA was correlated with a difference in the heterochromatin content of nuclei from cucumber root tips and fruit. The fruit contained at least two classes of polyploid nuclei, differing in their heterochromatin content.     

Trubs,but no trianas: filled and empty regions of angiosperm stem length‐diameter‐mechanics space

Discrete plant habit categories such as ‘tree’, ‘shrub’, and ‘liana’ belie continuous variation in nature. To study the evolution of this continuous variation, we gathered data on stem length, diameter and tissue mechanical stiffness across a highly morphologically diverse highland xerophytic scrub on a lava flow in central Mexico. With stem allometric and mechanical data from 1216 segments from 50 species, we examined relationships between stem length–diameter proportions and tissue mechanical stiffness using linear mixed‐effects models. Rather than a series of discrete clouds in stem length–diameter–tissue stiffness space, corresponding to traditional habit categories, the plants of this xerophytic scrub formed a single continuous one. Within this cloud, self‐supporting plants had stems that became predictably longer and tissues that became stiffer for a given diameter increase, and there was no paucity of intermediates between trees and shrubs (‘trubs’). Non self‐supporting plants had a steeper stem length–diameter slope and their tissues did not increase in stiffness with stem size. The area between self‐ and non self‐supporting plants was sparsely occupied as stem size increased. We predict that this ‘empty’ space between lianas and trees is developmentally accessible but of low fitness, meaning that there should be few ‘trianas’ in nature. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 361–373.     

The plant cell nucleus is constantly alert and highly sensitive to repetitive local mechanical stimulations

When mechanical stimulation is applied to a plant cell, the nucleus usually shows oriented movement to the site of stimulation (as a defensive response). Former researchers have revealed that applying mechanical pressure to plant tissues could line up cell division plane. A proposal, therefore, was put forward that cells inside plant tissue could receive mechanical signals from their growing neighbors to adjust their nuclear position and thus regulate the orientation of their dividing plane in order to form characteristic morphology of plant organs. To explore nuclear capacity and sensitivity to rapidly changing signals, multiple mechanical stimulations were applied to the same plant cell at intervals, either locally or at distance. The results revealed that the nucleus was highly sensitive to mechanical stimulations. It responded quickly to both local and distant stimulation by showing oriented movement toward the stimulation site. The nucleus was able to respond immediately to a second stimulation (no time lag) by starting up a second oriented movement toward the new signal; the completion of nuclear oriented movement to a first site of stimulation was not necessary for startup of a subsequent movement track to a second stimulation site, regardless of whether the second stimulation was applied ahead of or behind the moving nucleus. The nucleus responded to a second stimulation without loss of velocity, whether or not it was in a resting or moving state. This novel finding favors the proposal that growing tissues adjust the location of nuclei in cells by varying mechanical pressures; they thus control cell division according to a plan whereby organs and their constituent tissues develop in an orderly, specified manner. It appears that the enhanced sensitivity of plant cells to mechanical pressure is necessary not only in response to the external environment, but also to the developmental microenvironment inside the tissues.     

Mechanical stress acts via katanin to amplify differences in growth rate between adjacent cells in Arabidopsis

The presence of diffuse morphogen gradients in tissues supports a view in which growth is locally homogenous. Here we challenge this view: we used a high-resolution quantitative approach to reveal significant growth variability among neighboring cells in the shoot apical meristem, the plant stem cell niche. This variability was strongly decreased in a mutant impaired in the microtubule-severing protein katanin. Major shape defects in the mutant could be related to a local decrease in growth heterogeneity. We show that katanin is required for the cell's competence to respond to the mechanical forces generated by growth. This provides the basis for a model in which microtubule dynamics allow the cell to respond efficiently to mechanical forces. This in turn can amplify local growth-rate gradients, yielding more heterogeneous growth and supporting morphogenesis.     

Posture control and skeletal mechanical acclimation in terrestrial plants: implications for mechanical modeling of plant architecture

Self-supporting plant stems are slender, erect structures that remain standing while growing in highly variable mechanical environments. Such ability is not merely related to an adapted mechanical design in terms of material-specific stiffness and stem tapering. As many terrestrial standing animals do, plant stems regulate posture through active and coordinated control of motor systems and acclimate their skeletal growth to prevailing loads. This analogy probably results from mechanical challenges on standing organisms in an aerial environment with low buoyancy and high turbulence. But the continuous growth of plants submits them to a greater challenge. In response to these challenges, land plants implemented mixed skeletal and motor functions in the same anatomical elements. There are two types of kinematic design: (1) plants with localized active movement (arthrophytes) and (2) plants with continuously distributed active movements (contortionists). The control of these active supporting systems involves gravi- and mechanoperception, but little is known about their coordination at the whole plant level. This more active view of the control of plant growth and form has been insufficiently considered in the modeling of plant architecture. Progress in our understanding of plant posture and mechanical acclimation will require new biomechanical models of plant architectural development.     

Cytometry and flow cytometry of 4',6-diamidino-2-phenylindole (DAPI)-stained suspensions of nuclei released from fresh and fixed tissues of plants

Cytometry and flow cytometry were used to study characteristics of fluorescence of the DNA-DAPI complex in nuclei released from different fresh and formaldehyde-fixed pea ( Pisum sativum L. cv. Lincoln) tissues. The two methods of isolation are compared and discussed as well as their possible use for quantitative analysis of DNA in plant tissues. With fixed tissues it is possible to obtain a number of nuclei sufficient for the flow cytometric analysis, even using small amounts of plant tissue.     

Mechanical properties of the endophytic ovipositor in damselflies (Zygoptera, Odonata) and their oviposition substrates

Damselfly females use their ovipositor valves to saw aquatic plants in order to insert their eggs into the plant tissues. Stiffness of the plant substrata is therefore an important parameter for oviposition substrate choice by females. Using a force transducer combined with a motorised micromanipulator, the bending stiffness of the ovipositor at the axial compressional load was studied in seven European damselfly species and compared to the local stiffness of seven preferred plant substrates. The puncture force of tested plant samples ranged from 105 to 1500 mN, and their local stiffness ranged from 208 to 1776 N/m. The bending stiffness of the ovipositor was estimated as 173-409 N/m depending on the damselfly species. Using original and literature data, a significant positive correlation between mechanical properties of the ovipositor and preferred oviposition substrates was demonstrated. Possible behavioural adaptations to overcome high stiffness of plant tissues during oviposition are discussed.     

The influence of gravity and wind on land plant evolution

Aspects of the engineering theory treating the elastic stability of vertical stems and cantilevered leaves supporting their own weight and additional wind-induced forces (drag) are reviewed in light of biomechanical studies of living and fossil terrestrial plant species. The maximum height to which arborescent species can grow before their stems elastically buckle under their own weight is estimated by means of the Euler-Greenhill formula which states that the critical buckling height scales as the 1/3 power of plant tissue-stiffness normalized with respect to tissue bulk density and as the 2/3 power of stem diameter. Data drawn from living plants indicate that progressively taller plant species employ stiffer and lighter-weight plant tissues as the principal stiffening agent in their vertical stems. The elastic stability of plants subjected to high lateral wind-loadings is governed by the drag torque (the product of the drag force and the height above ground at which this force is applied), which cannot exceed the gravitational bending moment (the product of the weight of aerial organs and the lever arm measured at the base of the plant). Data from living plants indicate that the largest arborescent plant species rely on massive trunks and broad, horizontally expansive root crowns to resist drag torques. The drag on the canopies of these plants is also reduced by highly flexible stems and leaves composed of tissues that twist and bend more easily than tissues used to stiffen older, more proximal stems. A brief review of the fossil record suggests that modifications in stem, leaf, and root morphology and anatomy capable of simultaneously coping with self-weight and wind-induced drag forces evolved by Devonian times, suggesting that natural selection acting on the elastic stability of sporophytes occurred early in the history of terrestrial plants.     

Comparison of small-scale methods for the rapid extraction of plant DNA suitable for PCR analysis

We present results from a comparison of six methods for rapid DNA extraction from leaf and other plant tissues. We have used samples from six plant species in our study, including both crop species and their wild relatives. The success of the methods is assessed by PCR of the DNA using conserved primers, and the applicability of the different methods to particular species and tissues is assessed. The speed, reliability, convenience, and potential for further improvement of the methods are also discussed.     

Mechanical signalling,calcium and plant form

Calcium is a dynamic signalling molecule which acts to transduce numerous signals in plant tissues. The basis of calcium signalling is outlined and the necessity for measuring and imaging of calcium indicated. Using plants genetically transformed with a cDNA for the calcium-sensitive luminescent protein, aequorin, we have shown touch and wind signals to immediately increase cytosol calcium. Touch and wind signal plant cells mechanically, through tension and compression of appropiate cells. Many plant tissues and cells are very sensitive to mechanical stimulation and the obvious examples of climbing plants, insectivorous species as well as other less well-known examples are described. Touch sensing in these plants may be a simple evolutionary modification of sensitive mechanosensing system present in every plant. The possibility that gravitropism may be a specific adaptation of touch sensing is discussed. There is a growing appreciation that plant form may have a mechanical basis. A simple mechanical mechanism specifying spherical, cylindrical and flat-bladed structures is suggested. The limited morphological variety of plant tissues may also reflect mechanical specification. The article concludes with a discussion of the mechanisms of mechanical sensing, identifying integrin-like molecules as one important component, and considers the specific role of calcium.     

Spontaneous and lectin-induced redistribution of cell surface receptors on embryonic chick neural retina cells.

The mobility of plant lectin receptors in the plane of the membrane is examined for cells prepared from embryonic chick neural retinas by a variety of procedures. Cells liberated from the intact tissue by trypsin treatment followed by mechanical dissociation are able to redistribute their receptors into 'caps' both spontaneously and in the presence of a multivalent lectin. These cells, dispersed by trypsinization, upon repair in culture for a suitable period of time lose their ability to redistribute lectin receptors. Cells dispersed by mechanical means without prior trypsin treatment are unable to undergo 'cap' formation. In addition, cells within intact tissues are also unable to redistribute their lectin receptors into 'caps.' Based on these observations we propose that within solid tissues which have assumed their characteristic architecture, cell surfaces are immobilized, and that this phenomenon may be a critical parameter in determining the potential of a cell to undergo morphogenetic rearrangements.     

Carnitine is associated with fatty acid metabolism in plants

The finding of acylcarnitines alongside free carnitine in Arabidopsis thaliana and other plant species, using tandem mass spectrometry coupled to liquid chromatography shows a link between carnitine and plant fatty acid metabolism. Moreover the occurrence of both medium- and long-chain acylcarnitines suggests that carnitine is connected to diverse fatty acid metabolic pathways in plant tissues. The carnitine and acylcarnitine contents in plant tissues are respectively a hundred and a thousand times lower than in animal tissues, and acylcarnitines represent less than 2% of the total carnitine pool whereas this percentage reaches 30% in animal tissues. These results suggest that carnitine plays a lesser role in lipid metabolism in plants than it does in animals.     

Cyclic mechanical strain regulates the development of engineered smooth muscle tissue.

We show that the appropriate combinations of mechanical stimuli and polymeric scaffolds can enhance the mechanical properties of engineered tissues. The mechanical properties of tissues engineered from cells and polymer scaffolds are significantly lower than the native tissues they replace. We hypothesized that application of mechanical stimuli to engineered tissues would alter their mechanical properties. Smooth muscle tissue was engineered on two different polymeric scaffolds and subjected to cyclic mechanical strain. Short-term application of strain increased proliferation of smooth muscle cells (SMCs) and expression of collagen and elastin, but only when SMCs were adherent to specific scaffolds. Long-term application of cyclic strain upregulated elastin and collagen gene expression and led to increased organization in tissues. This resulted in more than an order of magnitude increase in the mechanical properties of the tissues.     

植物生长抽梢期和气候因子对株高生长影响

利用西双版纳热带植物园的热带植物物候观测资料和气候资料,通过对热带植物株高生长偏差、生长抽梢期和气候因子的分析,探讨了三者的关系。结果表明,热带植物生长抽梢期变长不一定影响株高生长,而且与株高生长偏差的关系也小于气候因子与株高生长偏差的关系。同时,热带植物生长抽梢期对气候因子和株高生长偏差之间关系的贡献很小。因此,可以认为热带植物的生长期对植被生产力的促进作用较弱。     

Mathematical modelling of the cellular mechanics of plants

The complex mechanical behaviour of plant tissues reflects the complexity of their structure and material properties. Modelling has been widely used in studies of how cell walls, single cells and tissue respond to loading, both externally applied loading and loads on the cell wall resulting from changes in the pressure within fluid-filled cells. This paper reviews what approaches have been taken to modelling and simulation of cell wall, cell and tissue mechanics, and to what extent models have been successful in predicting mechanical behaviour. Advances in understanding of cell wall ultrastructure and the control of cell growth present opportunities for modelling to clarify how growth-related mechanical properties arise from wall polymeric structure and biochemistry.     

Species-common antigen of connective tissues.

Collagen-free extracts were prepared from bovine, porcine and canine hyaline, elastic and fibrous cartilages, articular capsule, tendon, aorta, cortical bone and regenerating articular surfaces. The extracts were investigated with antisera to bovine nasal septal cartilage, dog articular cartilage and non-collagenous protein fraction of bovine cortical bone. Immunodiffusion, immunoelectrophoresis, and immunohistochemical methods were used. In the different supporting tissues of the three animal species a common antigen, probably of proteoglycan origin, was demonstrated. The finer differences in antigenicity between the different tissues are probably due to the variations in proteoglycan composition of the given supporting tissues. Owing to the wide-spread occurrence of the antigen, the authors suggest the term "species-common connective tissue antigen" instead of the "species-common cartilage antigen" used so far.     

Internal structure of developing aucuba fruit as a defence increasing oviposition costs of its gall midges Asphondylia aucubae

Abstract. 1. Damage to juvenile plant tissues can cause reductions in fitness. Therefore, plants are expected to have evolved various defences for juvenile organs; however, so far, little attention has been paid to mechanical defence, as they have been considered to constrain the growth of juvenile organs. This study revealed that the dioecious tree Aucuba japonica uses mechanical defences to protect young developing fruit from the gall midge Asphondylia aucubae. 2. Young fruit of A. japonica have a hard layer of endocarp covering the integument. Midges oviposit on the surface of the integument, where larval chambers are later formed. The endocarp gradually becomes cracked as the embryo sac develops. 3. Oviposition by the midges is successful only when the ovipositors happen to pass through cracks in the endocarp. Thus, to successfully lay eggs, midges must insert the ovipositor repeatedly. This should decrease the fecundity of the midges, and subsequently their infectiousness, because their adult lifespan is short and they do not consume food during this time. 4. Expansion of the cracks in the endocarp simplifies oviposition over time; however, the embryo sac continues to grow, increasing its volume relative to that of the ovule. This appears to deplete available space and tissue used in the construction of larval chambers, gradually making the fruit less susceptible to midge attacks. 5. The temporary nature of this defence should prevent it from constricting the growth of young fruit. This exemplifies a novel strategy for a mechanical defence of young developing plant tissues.