INFRARED MICROSPECTROSCOPY - SAMPLING HETEROGENEITY IN PLANT-CELL WALL COMPOSITION AND ARCHITECTURE

The use of probes such as monoclonal and polyclonal antibodies to spec ific cell wall components, at both the light and electron microscope l evels, has demonstrated the diversity in cell wall composition between species, between tissues, between different regions of the cell surfa ce, and even within a single wall. Traditional methods of cell wall an alysis have provided valuable information on wall composition and arch itecture, but, by having to rely on the use of bulk samples, have aver aged out this intrinsic heterogeneity. Fourier Transform Infrared FIR) microspectroscopy addresses this problem by providing chemical inform ation from an area as small as 10x10 mu m of a single cell wall fragme nt or area of a tissue section that has been imaged with a microscope accessory.We have used FTIR microspectroscopy as a powerful and extrem ely rapid assay for wall components and putative cross-links in mure. The spectra are sensitive to polymer conformation, and the use of pola risers in the microscope accessory allows the orientation of particula r functional groups to be determined, with respect to the long axis of elongating cells. The spectra constitute species and tissue-specific 'finger-prints', and the use of classical discriminant analysis may pr ovide 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 ce ll growth and differentiation to be characterised chemically at the si ngle cell level.