Plant cell walls are the starting materials for many commercial products, from lumber, paper and textiles to thickeners, films and explosives. The cell wall is secreted by each cell in the plant ...body, forming a thin fibreglass-like network with remarkable strength and flexibility. During growth, plant cells secrete a protein called expansin, which unlocks the network of wall polysaccharides, permitting turgor-driven cell enlargement. Germinating grass pollen also secretes an unusual expansin that loosens maternal cell walls to aid penetration of the stigma by the pollen tube. Expansin's action has puzzling implications for plant cell-wall structure. The recent explosion of gene sequences and expression data has given new hints of additional biological functions for expansins.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Objectives To evaluate the extent to which intensive care units participating in the initial Keystone ICU project sustained reductions in rates of catheter related bloodstream infections.Design ...Collaborative cohort study to implement and evaluate interventions to improve patients’ safety. Setting Intensive care units predominantly in Michigan, USA.Intervention Conceptual model aimed at improving clinicians’ use of five evidence based recommendations to reduce rates of catheter related bloodstream infections rates, with measurement and feedback of infection rates. During the sustainability period, intensive care unit teams were instructed to integrate this intervention into staff orientation, collect monthly data from hospital infection control staff, and report infection rates to appropriate stakeholders.Main outcome measures Quarterly rate of catheter related bloodstream infections per 1000 catheter days during the sustainability period (19-36 months after implementation of the intervention).Results Ninety (87%) of the original 103 intensive care units participated, reporting 1532 intensive care unit months of data and 300 310 catheter days during the sustainability period. The mean and median rates of catheter related bloodstream infection decreased from 7.7 and 2.7 (interquartile range 0.6-4.8) at baseline to 1.3 and 0 (0-2.4) at 16-18 months and to 1.1 and 0 (0.0-1.2) at 34-36 months post-implementation. Multilevel regression analysis showed that incidence rate ratios decreased from 0.68 (95% confidence interval 0.53 to 0.88) at 0-3 months to 0.38 (0.26 to 0.56) at 16-18 months and 0.34 (0.24-0.48) at 34-36 months post-implementation. During the sustainability period, the mean bloodstream infection rate did not significantly change from the initial 18 month post-implementation period (−1%, 95% confidence interval −9% to 7%).Conclusions The reduced rates of catheter related bloodstream infection achieved in the initial 18 month post-implementation period were sustained for an additional 18 months as participating intensive care units integrated the intervention into practice. Broad use of this intervention with achievement of similar results could substantially reduce the morbidity and costs associated with catheter related bloodstream infections.
Polysaccharides and proteins are secreted to the inner surface of the growing cell wall, where they assemble into a network that is mechanically strong, yet remains extensible until the cells cease ...growth. This review focuses on the agents that directly or indirectly enhance the extensibility properties of growing walls. The properties of expansins, endoglucanases, and xyloglucan transglycosylases are reviewed and their postulated roles in modulating wall extensibility are evaluated. A summary model for wall extension is presented, in which expansin is a primary agent of wall extension, whereas endoglucanases, xyloglucan endotransglycosylase, and other enzymes that alter wall structure act secondarily to modulate expansin action.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
5.
Growth of the plant cell wall Cosgrove, Daniel J
Nature reviews. Molecular cell biology,
200511, 2005-Nov, 2005-11-00, 20051101, Letnik:
6, Številka:
11
Journal Article
Recenzirano
Plant cells encase themselves within a complex polysaccharide wall, which constitutes the raw material that is used to manufacture textiles, paper, lumber, films, thickeners and other products. The ...plant cell wall is also the primary source of cellulose, the most abundant and useful biopolymer on the Earth. The cell wall not only strengthens the plant body, but also has key roles in plant growth, cell differentiation, intercellular communication, water movement and defence. Recent discoveries have uncovered how plant cells synthesize wall polysaccharides, assemble them into a strong fibrous network and regulate wall expansion during cell growth.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The selection of appropriate solvents into which carbon blacks can be dispersed optimally is important for product manufacture and performance. Molecular-level interactions determine solvent ...suitability but are difficult to measure; existing experimental approaches require slow/expensive tests of dispersion stability. NMR solvent relaxation measurements are shown to be a fast indicator of solvent suitability, with sensitivity to the solvent-particle intermolecular forces making it a reliable proxy for determining optimum dispersibility. A structured approach to relaxation measurements with a selection of both good and poor solvents yields the Hansen solubility parameters (HSP) for the particle surface. Once obtained, suitable solvents (or solvent mixtures) can be selected from a database of HSP values to match the particle interface. The application of the NMR solvent relaxation approach for determining the HSP values is illustrated for a commercially available carbon black. Furthermore, individual solvent relaxation data for two solvents (e.g., hexane and IPA) with a variety of carbon blacks may be plotted against each other to highlight differences in surface chemistry. Using this approach, results are compared, for the first time, with data from inverse gas chromatography (IGC) with a relatively similar outcome. NMR solvent relaxation analysis provides a quick, facile, and cost-effective methodology to identify the replacement of both powder and solvent raw materials.
Graphical Abstract
Data for 479 patients were analyzed to assess the impact of methicillin resistance on the outcomes of patients with Staphylococcus aureus surgical site infections (SSIs). Patients infected with ...methicillin-resistant S. aureus (MRSA) had a greater 90-day mortality rate than did patients infected with methicillin-susceptible S. aureus (MSSA; adjusted odds ratio, 3.4; 95% confidence interval, 1.5–7.2). Patients infected with MRSA had a greater duration of hospitalization after infection (median additional days, 5; P < .001), although this was not significant on multivariate analysis (P = .11). Median hospital charges were $29,455 for control subjects, $52,791 for patients with MSSA SSI, and $92,363 for patients with MRSA SSI (P < .001 for all group comparisons). Patients with MRSA SSI had a 1.19-fold increase in hospital charges (P = .03) and had mean attributable excess charges of $13,901 per SSI compared with patients who had MSSA SSIs. Methicillin resistance is independently associated with increased mortality and hospital charges among patients with S. aureus SSI.
Growing plant cells are shaped by an extensible wall that is a complex
amalgam of cellulose microfibrils bonded noncovalently to a matrix of
hemicelluloses, pectins, and structural proteins. ...Cellulose is synthesized by
complexes in the plasma membrane and is extruded as a self-assembling
microfibril, whereas the matrix polymers are secreted by the Golgi apparatus
and become integrated into the wall network by poorly understood mechanisms.
The growing wall is under high tensile stress from cell turgor and is able to
enlarge by a combination of stress relaxation and polymer creep. A pH-dependent
mechanism of wall loosening, known as acid growth, is characteristic of growing
walls and is mediated by a group of unusual wall proteins called expansins.
Expansins appear to disrupt the noncovalent bonding of matrix hemicelluloses to
the microfibril, thereby allowing the wall to yield to the mechanical forces
generated by cell turgor. Other wall enzymes, such as (1 → 4)
β-glucanases and pectinases, may make the wall more responsive to
expansin-mediated wall creep, whereas pectin methylesterases and peroxidases
may alter the wall so as to make it resistant to expansin-mediated creep.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
It is common for the root/shoot ratio of plants to increase when water availability is limiting. This ratio increases because roots are less sensitive than shoots to growth inhibition by low water ...potentials. The physiological and molecular mechanisms that assist root growth under drought conditions are reviewed, with a focus on changes in cell walls. Maize seedlings adapt to low water potential by making the walls in the apical part of the root more extensible. In part, this is accomplished by increases in expansin activity and in part by other, more complex changes in the wall. The role of xyloglucan endotransglycosylase, peroxidase and other wall enzymes in root adaptation to low water potential is evaluated and some of the complications in the field of study are listed.
PDF
