Prospects for a Statistical Theory of LC/TOFMS Data

The critical importance of employing sound statistical arguments when seeking to draw inferences from inexact measurements is well-established throughout the sciences. Yet fundamental statistical methods such as hypothesis testing can currently be applied to only a small subset of the data analytical problems encountered in LC/MS experiments. The means of inference that are more generally employed are based on a variety of heuristic techniques and a largely qualitative understanding of their behavior. In this article, we attempt to move towards a more formalized approach to the analysis of LC/TOFMS data by establishing some of the core concepts required for a detailed mathematical description of the data. Using arguments that are based on the fundamental workings of the instrument, we derive and validate a probability distribution that approximates that of the empirically obtained data and on the basis of which formal statistical tests can be constructed. Unlike many existing statistical models for MS data, the one presented here aims for rigor rather than generality. Consequently, the model is closely tailored to a particular type of TOF mass spectrometer although the general approach carries over to other instrument designs. Looking ahead, we argue that further improvements in our ability to characterize the data mathematically could enable us to address a wide range of data analytical problems in a statistically rigorous manner

Enzymatic investigation of plant cell wall mechanical properties

National audienc

Links between cell wall polysaccharide side chains and mechanicals properties

DREAM - Design and development of REAlistic food Models with well-characterised micro- and macro-structure and compositioNational audiencePlant cell walls are made of interacting networks of polysaccharides (cellulose, hemicelluloses, pectins) and some structural proteins that greatly contribute to cell and organ mechanical properties. Various enzymes remodel these networks with consequences on the wall rheology during cell growth and development. In fleshy fruits, these remodeling together with turgor pressure and spatial organization of cells in tissues determine texture. Fruit genetic, physiology and development modulate the cell wall composite structure and enzyme remodeling and are at the origin of a large range of textures hardly controlled. To date, beside the concurrent pectin degradation and fruit softening, relationships between cell wall assemblies and fruit texture are scarcely known. To establish roles of specific cell wall polysaccharides on the cell wall mechanical properties, spatially homogeneous parenchyma from contrasted texture Golden Delicious (Go) and Granny Smith (Gr) apples were sampled and vacuum infused with enzymes in buffer solution aimed at maintaining and homogenising turgor pressure and limiting oxidation. Glycoside hydrolases (a-fucosidase, a- and ß- galactosidase, a-arabinofuranosidase and combinations of fucosidase and galactosidases) were used to study the impact polysaccharide side chains on parenchyma mechanical properties. The mechanical assay consisted in a sinusoidal deformation in elastic domain at 1 Hz frequency to yield the storage modulus (representing the elastic behaviour) and phase angle (describing the viscous behaviour) of apple samples. The temporal evolution of mechanical properties was measured every hour over 5 h of enzymatic degradation and modelled by second order polynomials. The equations coefficients of the curves described the change in samples mechanical parameters during enzymatic treatments. Comparing the chemical composition and structure of cell wall polysaccharides in treated and control samples assessed the enzyme action. Principal Component Analysis (PCA) was applied on all data to identify relations between specific polysaccharide networks and structures with cell wall mechanical properties. Enzymatic treatments induce modifications of mechanical parameters leading to time dependant modifications in viscous and elastic behaviour. Due to different cell wall polysaccharide compositions and structures, the extent of conversion from elastic to viscous material differed for Go and Gr. In particular, altering ß-galactose decreased storage modulus and increased phase angle for Go, but for Gr, it increased the storage modulus but kept constant phase angle. Altering fucose, decreased storage modulus and increased phase angle for Go and Gr. Altering fucose and ß-galactose simultaneously emphasised fucose induced effects. These results emphasize the key roles of side chains in the regulation of mechanical properties whether directly in changing polysaccharides conformations and interactions or indirectly in regulating endogenous enzymes involved in the remodelling of networks assemblies. With these contrasted effects in Go and Gr, these results illustrate the diversity and complexity of apple cell walls with regard to their role on texture. The experimental framework developed in this study opens the way to explore the functions of cell wall polysaccharide structure on mechanical properties emerging at the tissue scale

Enzymatic investigation of plant cell wall mechanical properties

National audienc

Orders of Magnitude Extension of the Effective Dynamic Range of TDC-Based TOFMS Data Through Maximum Likelihood Estimation

In a recent article, we derived a probability distribution that was shown to closely approximate that of the data produced by liquid chromatography time-of-flight mass spectrometry (LC/TOFMS) instruments employing time-to-digital converters (TDCs) as part of their detection system. The approach of formulating detailed and highly accurate mathematical models of LC/MS data via probability distributions that are parameterized by quantities of analytical interest does not appear to have been fully explored before. However, we believe it could lead to a statistically rigorous framework for addressing many of the data analytical problems that arise in LC/MS studies. In this article, we present new procedures for correcting for TDC saturation using such an approach and demonstrate that there is potential for significant improvements in the effective dynamic range of TDC-based mass spectrometers, which could make them much more competitive with the alternative analog-to-digital converters (ADCs). The degree of improvement depends on our ability to generate mass and chromatographic peaks that conform to known mathematical functions and our ability to accurately describe the state of the detector dead time—tasks that may be best addressed through engineering efforts. [Image: see text] ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s13361-014-0961-5) contains supplementary material, which is available to authorized users

Integrative Mechanobiology of Growth and Architectural Development in Changing Mechanical Environments

Mention d'édition : P. Wotjaszek (ed)Mechanosensitive control of plant growth is a major process shaping how terrestrial plants acclimate to the mechanical challenges set by wind, self-weight, and autostresses. Loads acting on the plant are distributed down to the tissues, following continuum mechanics. Mechanosensing, though, occurs within the cell, building up into integrated signals; yet the reviews on mechanosensing tend to address macroscopic and molecular responses, ignoring the biomechanical aspects of load distribution to tissues and reducing biological signal integration to a "mean plant cell." In this chapter, load distribution and biological signal integration are analyzed directly. The Sum of Strain Sensing model S 3 m is then discussed as a synthesis of the state of the art in quantitative deterministic knowledge and as a template for the development of an integrative and system mechanobiology