Infrared microspectroscopy: Sampling heterogeneity in plant cell wall composition and architecture

Abstract

The use of probes such as monoclonal and polyclonal antibodies to specific cell wall components, at both the light and electron microscope levels, has demonstrated the diversity in cell wall composition between species, between tissues, between different regions of the cell surface, and even within a single wall. Traditional methods of cell wall analysis have provided valuable information on wall composition and architecture, but, by having to rely on the use of bulk samples, have averaged out this intrinsic heterogeneity. Fourier Transform Infrared (FTIR) microspectroscopy addresses this problem by providing chemical information from an area as small as 10×10 μm of a single cell wall fragment or area of a tissue section that has been imaged with a microscope accessory. We have used FTIR microspectroscopy as a powerful and extremely rapid assay for wall components and putative cross‐links in muro. The spectra are sensitive to polymer conformation, and the use of polarisers in the microscope accessory allows the orientation of particular functional groups to be determined, with respect to the long axis of elongating cells. The spectra constitute species and tissue‐specific ‘fingerprints’, and the use of classical discriminant analysis may provide the opportunity for correlating spectral features with chemical, architectural or rheological wall properties. Spectral mapping of an area of a specimen allows the morphological features resulting from cell growth and differentiation to be characterised chemically at the single cell level.

Flooding tolerance and cell wall alterations in maize mesocotyl during hypoxia

“…The appearance of methyl esters in mesocotyl with constriction ( Figure 4E) based by the peak presence in 1,740 waves cm -1 (Perlin & Casu, 1995) was detected, fact that did not occur when mesocotyl from normal tissue ( Figure 4A) and translucid ( Figure 4C) were analyzed. This fact was also noted by McCann et al (1997), that studied tobacco cell walls during cellular division and expansion, and the methyl esterification of functional groups from carboxylic acid from pectic fraction. This alteration remove the negative charge used for cross linked with calcium.…”

“…After trituration and homogenization, a reading was made, in infrared range to obtain the infrared spectrum with Fourrier Transformation (FTIR). The qualitative interpretation for different carbohydrate groups was realized according to McCann et al (1997).…”

Macromolecular biophysics of the plant cell wall: Concepts and methodology

“…The absorption spectra generated (figure 2) are similar to those obtained in a conventional spectrometer but, even as just a means of obtaining spectra, the microscopy mode has considerable advantages [32]. Cell-wall samples prepared as KBr discs in a conventional spectrometer give good spectra but because the cell walls are finely ground and dispersed, information on polysaccharide orientation is not preserved.…”

“…In microscopy, this is not a problem. Polarised IR microscopy ( figure 3) also has the advantage that an oriented spectrum can be obtained from a single cell wall with the radiation beam passing up through it at right angles [32]. When a larger area of tissue section is viewed in the same way in a conventional spectrometer, some of the cell walls are vertical, parallel to the beam.…”

Wood production, wood technology, and biotechnological impacts

“…The application of FTIR microspectrometry to primary plant cell walls for studying their heterogeneity and architecture was reviewed by McCann et al (1997) and Dokken et al (2005), including spectral fingerprinting of cell walls and their component molecules, characterising the structure and orientation of macromolecules, and functional chemical group mapping of a sample area. Defining the distinct differences of the complex cell walls of tracheids, vessels and fibres of woody plants requires however further investigation and necessitates comparative FTIR analysis of herbal and woody plants.…”