OLD AND NEW WAYS TO PROBE PLANT CELL-WALL ARCHITECTURE

Wall structure has been analysed by a process of careful demolition, i n which chemical extractants are used to remove specific polymers for sugar and linkage analysis, gel-permeation or ion-exchange chromatogra phy, and nuclear magnetic resonance spectroscopy. Sequence-dependent e ndoglycanases cleave certain polysaccharides into oligomers that can b e sequenced completely and give a clear picture of the repetitive unit s used to make fundamental polymers. We have also developed and adapte d new chemical procedures and pulse-labelling techniques to give more information on the ways that wall polymers are subtly modified during growth. In this report, we review these conventional means of carbohyd rate analyses together with newer methods of selective enzymic hydroly sis, separation of large oligosaccharides by high pH anion-exchange ch romatography, and detection of molecular mass of several thousand dalt ons by electrospray mass spectrometry. These new technologies have alr eady given much valuable information about the polymeric building bloc ks, but little information on how these polymers are arranged in space . For this, we adapted new cryopreservation techniques for electron mi croscopy that can image the wall in as close to the in vivo state as p ossible. In addition to defining anomeric linkages and linkage structu res in preparations of native polymers, nuclear magnetic resonance spe ctroscopy can also determine the relative mobility of particular polym ers within the structure of hydrated cell walls. The generation of ant ibodies to particular cell wall epitopes has enabled us to define arch itectural differences among species, among tissue types, and even amon g domains within a single wall. Our awareness of the diversity and com plexity of primary cell wall architecture has driven a search for meth odologies such as Fourier transform infrared and Fourier transform Ram an microspectroscopies, which are suitable for analysis at the single cell wall level.