Phytohormone Mediation of Interactions Between Plants and Non-Symbiotic Growth Promoting Bacteria Under Edaphic Stresses

The capacity of rhizoshere bacteria to influence plant hormonal status, by bacterial production or metabolism of hormones, is considered an important mechanism by which they promote plant growth, and productivity. Nevertheless, inoculating these bacteria into the plant rhizosphere may produce beneficial or detrimental results depending on bacterial effects on hormone composition and quantity in planta, and the environmental conditions under which the plants are growing. This review considers some effects of bacterial hormone production or metabolism on root growth and development and shoot physiological processes. We analyze how these changes in root and shoot growth and function help plants adapt to their growth conditions, especially as these change from optimal to stressful. Consistent effects are addressed, along with plant responses to specific environmental stresses: drought, salinity, and soil contamination (with petroleum in particular)

Synthesis and pH- and salinity-controlled self-assembly of novel amphiphilic block-gradient copolymers of styrene and acrylic acid

cited By 31International audienceA novel type of amphiphilic ionic copolymer comprising a hydrophilic poly(acrylic acid) (PAA) block and an amphiphilic poly(acrylic acid)-grad-poly(styrene) (PAA-grad-PS) copolymer block was synthesized using a one step direct nitroxide-mediated polymerization (NMP). A strong influence of the macroinitiator on the values of the reactivity ratios of the co-monomers is confirmed by 1H NMR. The aggregation behaviour of the copolymers in the aqueous medium was studied by small-angle neutron scattering (SANS) and dynamic light scattering (DLS) and by transmission electron microscopy (TEM) in a wide range of pHs and ionic strengths. It has been demonstrated that PAA-b-(PAA-grad-PS) copolymers are soluble in alkaline water at room temperature without the special experimental procedures (addition of co-solvent, heating, etc.) that are usually required for solubilisation of classical PAA-b-PS diblock copolymers. The self-assembly of the PAA-b-(PAA-grad-PS) copolymers into nano-scale aggregates at low/moderate pH and/or high ionic strength was demonstrated by SANS and DLS experiments. The SANS spectra for the copolymer solution exhibit a correlation peak pointing to the formation of micelles with repulsive coronae. TEM images indicate that the micelles have an approximately spherical shape and exhibit a wide size distribution. Our results prove, that in contrast to "frozen" aggregates formed by PAA-b-PS copolymers in aqueous media, the micelles of PAA-b-(PAA-grad-PS) amphiphilic copolymers exhibit "dynamic" pH-responsive properties, i.e. they can reversibly change their aggregation number upon a variation in the pH or salinity of the solution. © 2012 The Royal Society of Chemistry

PH-triggered reversible sol-gel transition in aqueous solutions of amphiphilic gradient copolymers

cited By 36International audienceWe demonstrate the possibility of reversible pH-controlled sol-gel transition in aqueous solution of associating amphiphilic triblock copolymer poly(styrene-grad-acrylic acid)-b-poly(acrylic acid)-b-poly(styrene-grad-acrylic acid), (PS-grad-PAA)-b-PAA-b-(PS-grad-PAA), synthesized via nitroxide-mediated (NM) radical copolymerization. The presence of pH-sensitive co-monomer units of the acrylic acid in the terminal blocks ensures the dynamic nature of the styrene-rich hydrophobic nano-domains which are formed at low pH. At small polymer concentrations the association triggered by lowering the pH gives rise to flower-like micelles stabilized by partially ionized PAA coronae. The pH-controlled association was monitored by DLS-titration and manifested in the evolution of a correlation peak in the SANS spectra. The resulting copolymer aggregates were visualized by TEM, which confirmed the spherical shape of the dense styrene-rich domains. Above the micelle overlap concentration a decrease in pH provokes macroscopic gelation. Here the styrene-reach domains perform as cross-links in the transient network. The pH-triggered sol-to-gel transition is manifested in an abrupt and strong (up to 3 orders of magnitude) increase in the zero-shear viscosity and in a characteristic change in the frequency dependence of the storage and loss moduli. The discovered effect can be used for efficient pH-control of the rheological properties of aqueous solutions. © 2011 The Royal Society of Chemistry

Modelling infrastructure along the value chain from materials to system performance

This paper reports on progress towards the development of an infrastructure to integrate existing modelling tools, and thus allow modelling of the entire solar cell value chain, from initial material parameters to the long term energy yield of complete PV systems. Currently, the infrastructure has been developed and successfully tested from the material to the system level, for three different cell technologies using 13 different programs across 7 European institutes. Input data can be either modelled or experimentally measured. Further work will focus on comparison of the simulation results with experimentally measured system data; defining standard interface protocols to simplify the information transfer; and predicting the yearly energy output for installed PV system

“Struggle” between three switching mechanisms as the underpinning of sleep stages and the pattern of transition between them

Complex systems are occasionally switching between several qualitatively different modes of behavior, even in the absence of external influences. An example of such mode-switching behavior of a complex system is a sequence of changes in sleep stages observed on approximately 90-min interval of sleep cycle. We examined whether relatively stable stages and relatively rapid transitions between them can be linked to the observed markers of underlying processes of sleep–wake regulation. Using data on two napping attempts of each of 28 university students, we described how scores on principal components of the EEG spectrum and rates of transitions between stages can serve as objective markers of interaction between three underlying on–off switching mechanisms that, in turn, can reflect strengths of the mutually inhibiting drives for sleep, wake, and REM sleep. A sequence of transitions between five stages over sleep cycle can be viewed as representing a sequence of episodes of the “struggle” between these three permanently competing mechanisms. Each of typical stage transitions in sleep cycle can be interpreted as a relatively rapid change in state of one or two of these three on–off switchers. It seems that only one of them is capable to maintain the switch on state during a stage with the exception of transient stage 1 sleep during which all switches remain in switch off state. An aim of future research of stages and their transitions during normal and disturbed sleep can be aimed on identification of a switching mechanism involved into a certain disturbance of sleep

The Irrecoverable Loss in Sleep on Weekdays of Two Distinct Chronotypes Can Be Equalized by Permitting a >2 h Difference in Waking Time

Background: Our work/study culture is biased towards the circadian clocks of “morning types”, whereas “evening types” are forced to advance their weekday waking times relative to weekend waking times. Since the experimental research consistently reveals a >2 h difference between these two chronotypes in the positions of their endogenous circadian phases, we hypothesized the necessity to permit a >2 h difference between them in weekday waking times to equalize their irrecoverable loss in sleep on weekdays. Methods: A total of 659 and 1106 participants of online surveys identified themselves as morning and evening types, respectively. The hypothesis was tested by applying a model of sleep–wake regulation for simulating sleep times reported by 245 lecturers of these two types, and by comparison of sleep times of these types among these lecturers and 1520 students. Results: The hypothesis was supported by results showing that, if, on weekdays, an “average” morning type wakes at 6 a.m., the equalization of the weekday sleep loss of the two chronotypes would require the waking time of an “average” evening type to be no earlier than 8 a.m. Conclusions: These results may be implemented in a model-based methodology for the correction of weekday waking times to equalize weekday sleep loss