Oxylipin dynamics in Medicago truncatula in response to salt and wounding stresses

Multiple stresses are becoming common challenges in modern agriculture due to environmental changes. A large set of phytochemicals collectively known as oxylipins play a key role in responses to several stresses. Understanding the fine‐tuned plant responses to multiple and simultaneous stresses could open new perspectives for developing more tolerant varieties. We carried out the molecular and biochemical profiling of genes, proteins and active compounds involved in oxylipin metabolism in response to single/combined salt and wounding stresses on Medicago truncatula. Two new members belonging to the CYP74 gene family were identified. Gene expression profiling of each of the six CYP74 members indicated a tissue‐ and time‐specific expression pattern for each member in response to single/combined salt and wounding stresses. Notably, hormonal profiling pointed to an attenuated systemic response upon combined salt and leaf wounding stresses. Combined, these results confirm the important role of jasmonates in legume adaptation to abiotic stresses and point to the existence of a complex molecular cross‐talk among signals generated by multiple stresses.     

Flat medial-lateral conformity in total knee replacements does not minimize contact stresses.

The potential for wear in UHMWPE components for total knee replacements can be reduced by decreasing the stresses and strains arising from tibial-femoral contact. The conformity of the articular surfaces has a large effect on the resultant stresses, and components that achieve flat medial-lateral contact have been assumed to produce the lowest stresses due to their perfect conformity. We computed the stresses arising from curved and flat contact on a half-space using two-dimensional, plane strain elasticity solutions and finite element analyses to compare the performance of curved and flat indenters. These indenters were represented by a polynomial so the profiles could be continuously varied from curved to flat. Curved contact resulted in maximum stresses at the center of contact, while flat contact produced maximum stresses at the edge of contact. In addition, three contemporary tibial configurations (flat-on-flat, curved-on-flat, and curved-on-curved geometries) were analyzed using the finite element method with nonlinear material properties. The maximum contact stress, von Mises stress, and von Mises strain were lowest for the curved-on-curved model. The other configurations resulted in higher contact stresses, von Mises stresses, and von Mises strains. The perfect conformity arising from flat contact did not reduce the contact stresses in the UHMWPE component. The tensile stresses, however, were lowest for the flat-on-flat geometry compared with the other two configurations. Relating these distinct differences could prove useful in interpretation of data from simulator and retrieval studies.     

Thermal stresses in frozen organs

An analysis was performed to determine the thermal stresses in the solid region of an organ frozen so that a constant cooling rate is imposed on its outer surface. The analysis shows that at the instant the water freezes at a certain location in the organ, compressive azimuthal stresses develop in the region close to the change of phase front. The compressive asimuthal stresses decrease and become tensile at that location as the change of phase front propagates further. The radial stresses are always compressive. It is hypothesized that those stresses might induce mechanical damage to the cellular components of the organ. The analysis shows that the magnitude of these stresses is a function of the material properties and the product of the outer surface cooling rate and the square of the outer surface radius.     

miR398在植物逆境胁迫应答中的作用

MicroRNA (miRNA)是一类新型的调控基因表达的小分子RNA, 它作为基因表达的负调控因子, 在转录后水平调节靶基因的表达。miRNA参与调控植物的生长发育, 并在多种非生物与生物胁迫响应中发挥重要作用。miR398是第一个被报道的受氧化胁迫负调控的miRNA。它通过负调控其靶基因Cu/Zn过氧化物歧化酶(Cu/Zn-superoxide dismutase, CSD)的表达, 在多种逆境胁迫响应中扮演重要角色, 如调节铜代谢平衡, 应答重金属、蔗糖、臭氧等非生物胁迫, 以及参与应答生物胁迫等。文章综述了miR398在多种逆境胁迫响应中重要的调节作用及miR398自身的转录调控。     

Evaluation of residual stresses due to bone callus growth: a computational study

Mechanical environment in callus is determinant for the evolution of bone healing. However, recent mechanobiological computational works have underestimated the effect that growth exerts on the mechanical environment of callus. In the present work, we computationally evaluate the significance of growth-induced stresses, commonly called residual stresses, in callus. We construct a mechanobiological model of a callus in the metatarsus of a sheep in two different stages: one week and four weeks after fracture. The magnitude of stresses generated during callus growth is compared with the magnitude of stresses when only external loads are applied to the callus. We predict that residual stresses are relevant in some areas, mainly located at the periosteal side far from the fracture gap. Therefore, the inclusion of these residual stresses could represent a significant impact on the callus growth and predict a different evolution of biological processes occurring during bone healing.     

Least-squares matrix correlations between stump stresses and prosthesis loads for below-knee amputees

Stump stresses were correlated to prosthesis loads for two unilateral, below-knee amputees over a range of flexion-extension angular adjustments. Normal stresses on the patellar tendon and gastrocnemius were related to the axial force and flexion-extension moment of the prosthesis via a matrix equation. Elements of this matrix, influence factors calculated by least-squares algorithms, identified the contributions of each time-dependent load component acting to produce the time-dependent normal stresses. The flexion-extension angular sensitivity of the way these sagittal plane loads combined to produce normal stresses was included in the matrix equation via a first-order Maclaurin series. Highly favorable correlation coefficients between empirically measured and theoretically predicted stump stresses were calculated. This demonstrated that, in future studies, using an influence-factor matrix holds promise for quantifying sensitivities of normal stresses of the stump to multiple adjustments in prostheses.     

Salt and Drought Stresses Induce the Aberrant Expression of microRNA Genes in Tobacco

Drought and salinity stresses significantly altered microRNA (miRNA) expression in a dose-dependent manner in tobacco. Salinity stress changed the miRNA expression levels from a 6.86-fold down-regulation to a 616.57-fold up-regulation. Alternatively, miRNAs were down-regulated by 2.68-fold and up-regulated 2810-fold under drought conditions. miR395 was most sensitive to both stresses and was up-regulated by 616 and 2810-folds by 1.00% PEG and 0.171 M NaCl, respectively. Salinity and drought stresses also changed the expression of protein-coding genes [alcohol dehydrogenase (ADH) and alcohol peroxidase (APX)]. The results suggest that miRNAs may play an important role in plant response to environmental abiotic stresses. Further investigation of miRNA-mediated gene regulation may elucidate the molecular mechanism of plant tolerance to abiotic stresses and has the potential to create a miRNA-based biotechnology for improving plant tolerance to drought and salinity stresses.     

Factors influencing first-year medical students' perceptions of stress

This preliminary report from an ongoing longitudinal study of students at both Tufts and Harvard medical schools examined the relationship between premedical school demographic and stress variables and the numbers and types of stresses reported by students in open-ended interviews conducted during their first year of medical school. Analyses showed that the general categories of "medical school stresses" and "social stresses related to medical school" accounted for about two-thirds of the total number of stresses mentioned. The overall distributions of stresses across general categories were remarkably similar in all student groups studied, although significant differences were found between students from different background groups on a number of the specific types of stress. No significant differences were found between groups as to those reporting a high total number of stresses. There did appear to be differences in the degree to which students felt affected by the stresses they reported, suggesting the need for additional data on the meanings of different stresses for different students and the ways in which they cope with them.     

Shear effects on failure of hollow trees

It is shown that bending stresses in a non-cracked hollow trunk can never explain failure. Consequently, stem breakage due to bending stress cannot be primary failure. It is shown by field studies and simple theoretical assessments that the initiation of a longitudinal shear crack is primarily responsible for failure. Due to cracking, the bending stresses increase and failure by bending happens as secondary failure. As a result, bending theory of a non-cracked closed circular pipe is inappropriate to describe failure of hollow trees. In the appendix is shown the reason for high shear stresses at the tree base and why the shear stresses increase more due to hollowness than to bending stresses.     

Residual stresses at the stem-cement interface of an idealized cemented hip stem

During the operation of total hip arthroplasty, when the cement polymerizes between the stem implant and the bone, residual stresses are generated in the cement. The purpose of this study was to determine whether including residual stresses at the stem-cement interface of cemented hip implants affected the cement stress distributions due to externally applied loads. An idealized cemented hip implant subjected to bending was numerically investigated for an early post-operative situation. The finite element analysis was three-dimensional and used non-linear contact elements to represent the debonded stem-cement interface. The results showed that the inclusion of the residual stresses at the interface had up to a 4-fold increase in the von Mises cement stresses compared to the case without residual stresses.     

An in vivo method for measuring turbulence in mechanical prosthesis leakage jets

This work introduces a method for the in vivo measurement and analysis of turbulence within the leakage of a mechanical heart valve. Several analysis techniques were applied to ultrasound measurements acquired within the atrium of a pig, and error associated with these techniques was analyzed. The technique chosen applies cyclic averaging to mean and maximum velocity measurements within small, normalized phase windows to calculate Reynolds normal stresses in the direction of the ultrasound beam. Maximum shear stresses are estimated from these normal stresses using an analytical technique. The stresses observed were smaller than those reported from previous in vitro simulations.     

The effect of the interface on the bone stresses beneath tibial components

It was proposed that the stresses in the layer of bone immediately beneath a tibial component are an important determinant of fixation durability. Using finite element analysis, (ANSYS), the stresses were determined as a function of the amount of bone resection, the localization or completeness of implant-bone contact, and the interface material. The model was of two-dimensional sagittal slices consisting of quadrilateral elements (1 mm) with a range of seventeen material properties determined by CT scans. Typical prosthesis designs shifted the center of pressure more centrally rather than posteriorly, and thus increased anterior bone stresses. Resection up to 10 mm could actually decrease bone stresses due to an increase in bone surface area as long as complete coverage was obtained. A cement interface or direct metal on bone produced identical stresses. However a 1 mm complian: interface significantly reduced stresses in regions of high elastic modulus gradient. For rigid interfaces, the contact can be irregular, which leads to areas of over and understressing of bone. These conclusions have implications related to implant design.     

Evolution in stressful environments. I. Phenotypic variability, phenotypic selection, and response to selection in five distinct environmental stresses

Considerable debate has accompanied efforts to integrate the selective impacts of environmental stresses into models of life-history evolution. This study was designed to determine if different environmental stresses have consistent phenotypic effects on life-history characters and whether selection under different stresses leads to consistent evolutionary responses. We created lineages of a wild mustard (Sinapis arvensis) that were selected for three generations under five stress regimes (high boron, high salt, low light, low water, or low nutrients) or under near-optimal conditions (control). Full-sibling families from the six selection histories were divided among the same six experimental treatments. In that test generation, lifetime plant fecundity and six phenotypic traits were measured for each plant. Throughout this greenhouse study, plants were grown individually and stresses were applied from the early seedling stage through senescence. Although all stresses consistently reduced lifetime fecundity and most size- and growth-related traits, different stresses had contrasting effects on flowering time. On average, stress delayed flowering compared to favorable conditions, although plants experiencing low nutrient stress flowered earliest and those experiencing low light flowered latest. Contrary to expectations of Grime's triangle model of life-history evolution, this ruderal species does not respond phenotypically to poor environments by flowering earlier. Most stresses enhanced the evolutionary potential of the study population. Compared with near-optimal conditions, stresses tended to increase the opportunity for selection as well as phenotypic variance, although both of these quantities were reduced in some stresses. Rather than favoring traits characteristic of stress tolerance, such as slow growth and delayed reproduction, phenotypic selection favored stress-avoidance traits: earlier flowering in all five stress regimes and faster seedling height growth in three stresses. Phenotypic correlations reinforced direct selection on these traits under stress, leading to predicted phenotypic change under stress, but no significant selection in the control environment. As a result of these factors, selection under stress resulted in an evolutionary shift toward earlier flowering. Environmental stresses may drive populations of ruderal plant species like S. arvensis toward a stress-avoidance strategy, rather than toward stress tolerance. Further studies will be needed to determine when selection in stressful environments leads to these alternative life-history strategies.     

Stresses applied for the re-programming of plant microspores towards in vitro embryogenesis

Microspore embryogenesis is the most commonly used method to produce doubled haploids. It is based on the ability of a single haploid cell, the microspore, to de-differentiate and regenerate into a whole plant after being exposed to stresses, such as low or high temperatures, carbon starvation and colchicine. Some stresses such as temperature treatments and carbon starvation have been used with success in many plant species, whereas others such as colchicine had limited application in a few species. Reports on the application of whole plant treatments with feminizing agents on inflorescences and buds are scarce. Furthermore, the technical means to apply some stresses such as γ-irradiation are not readily available. Recently, novel stresses such as pH, inducer chemicals, carrageenan oligosaccharides and heavy metals were reported to induce microspore embryogenesis. It remains to be seen, however, whether these stresses are effective in a wider range of species. Finally, pretreatment of cultured cells with high concentrations of 2,4-D efficiently induces somatic embryogenesis in several species (carrot, alfalfa). However, reports on the use of this particular chemical stress are not available in microspore embryogenesis. The paper presented here gives an overview of various stresses and mechanisms of action of these stresses in inducing microspore embryogenesis.     

Pseudomonas putida modulates the expression of miRNAs and their target genes in response to drought and salt stresses in chickpea (Cicer arietinum L.)

MicroRNAs are small non-coding regulatory RNA molecules that play an important role in the modulation of gene expression during various environmental stresses. Pseudomonas putida RA, a plant growth promoting rhizobacteria (PGPR) colonizes the root surface of plants improving their growth and development during abiotic stresses modulating the expression of stress-responsive genes; however, the impact of RA on stress responsive-miRNA remains elusive. The present study was an attempt to delineate the role of PGPR in modulating stress responsive-miRNAs in a tolerant desi chickpea genotype exposed to drought and salt stresses. The existence of variable expression patterns of individual miRNAs and their target genes under these stresses at different time points indicate a distinct miRNA-mediated perception and response mechanisms operating under these stresses in the presence or absence of RA in chickpea.     

Contact stress transients during functional loading of ankle stepoff incongruities

Cartilage deformation demonstrates viscoelastic behavior due to its unique structure. However, nearly all contact studies investigating incongruity-associated changes in cartilage surface stresses have been static tests. These tests have consistently measured only modest increases in contact stresses, even with large incongruities. In this study, an experimental approach measuring real-time contact stresses in human cadaveric ankles during quasi-physiologic motion and loading was used to determine how stepoff incongruities of the distal tibia affected contact stresses and contact stress gradients. Peak instantaneous contact stresses, in ankles with stepoffs between 1.0 and 4.0mm of the anterolateral articular surface, increased by between 2.3 x and 3.0 x compared to the corresponding intact ankle values. Peak instantaneous contact stress gradients in stepoff configurations increased by between 1.9 x and 2.6 x the corresponding intact configuration values. Anatomic reduction of the displaced fragment restored intact contact stresses and contact stress gradients. Intact and anatomic configurations demonstrated a heterogeneous population of low-magnitude, randomly oriented contact stress gradient vectors in contrast to high-magnitude, preferentially oriented gradients in stepoff configurations. Peak instantaneous contact stresses may be important pathomechanical determinants of post-traumatic arthritis. Abnormal contact stress gradients could cause regional pathological disturbances in cartilage stress and interstitial fluid distribution. Measuring contact stresses and contact stress gradients during motion allowed potential incongruity-associated pathologic changes in loading that occur over the complete motion cycle to be investigated.     

A step towards understanding plant responses to multiple environmental stresses: a genome‐wide study

In natural habitats, especially in arid areas, plants are often simultaneously exposed to multiple abiotic stresses, such as salt, osmotic and heat stresses. However, most analyses of gene expression in stress responses examine individual stresses. In this report, we compare gene expression in individual and combined stresses. We show that combined stress treatments with salt, mannitol and heat induce a unique pattern of gene expression that is not a simple merge of the individual stress responses. Under multiple stress conditions, expression of most heat and salt stress‐responsive genes increased to levels similar to or higher than those measured in single stress conditions, but osmotic stress‐responsive genes increased to lower levels. Genes up‐regulated to higher levels under multiple stress condition than single stress conditions include genes for heat shock proteins, heat shock regulators and late embryogenesis abundant proteins (LEAs), which protect other proteins from damage caused by stresses, suggesting their importance in multiple stress condition. Based on this analysis, we identify candidate genes for engineering crop plants tolerant to multiple stresses.     

Combinatorial Interactions of Biotic and Abiotic Stresses in Plants and Their Molecular Mechanisms: Systems Biology Approach

Plants are continually facing biotic and abiotic stresses, and hence, they need to respond and adapt to survive. Plant response during multiple and combined biotic and abiotic stresses is highly complex and varied than the individual stress. These stresses resulted alteration of plant behavior through regulating the levels of microRNA, heat shock proteins, epigenetic variations. These variations can cause many adverse effects on the growth and development of the plant. Further, in natural conditions, several abiotic stresses causing factors make the plant more susceptible to pathogens infections and vice-versa. A very intricate and multifaceted interactions of various biomolecules are involved in metabolic pathways that can direct towards a cross-tolerance and improvement of plant’s defence system. Systems biology approach plays a significant role in the investigation of these molecular interactions. The valuable information obtained by systems biology will help to develop stress-resistant plant varieties against multiple stresses. Thus, this review aims to decipher various multilevel interactions at the molecular level under combinatorial biotic and abiotic stresses and the role of systems biology to understand these molecular interactions.     

Left Ventricular Stresses in the Intact Human Heart

A set of stress differential equations of equilibrium is presented for a thick prolate spheroid which is the assumed shape for the left ventricle. An analysis for the stresses in the ventricular wall indicates that maximum stresses occur at the inner layers and decrease to a minimum at the epicardial surface, a result that is partially validated by experiment. Simple expressions are available for the evaluation of maximum stresses which occur at the equator and are suitable for small laboratory-oriented digital computers employed in the clinical evaluation of patient status. The surprising result is that Laplace's law yields practical values for mean stresses in thick-walled ventricles.