Primary cell wall metabolism: tracking the careers of wall polymers in living plant cells


  • Stephen C. Fry

    Corresponding author
    1. The Edinburgh Cell Wall Group, Institute of Cell and Molecular Biology, The University of Edinburgh, Daniel Rutherford Building, The King's Buildings, Mayfield Road, Edinburgh EH9 3JH, UK
    Search for more papers by this author

Author for correspondence:Stephen C. Fry Tel: +44 131 650 5320 Fax: +44 131 650 5392 Email:



  • I. Primary cell walls: composition, deposition and roles000
  • II. Reactions that have been proposed to occur in primary cell walls000
  • III. Tracking the careers of wall components in vivo: evidence for action of enzymes in the walls of living plant cells000
  • IV. Evidence for the occurrence of nonenzymic polymer scission in vivo?000
  • VI. Conclusion000


Numerous examples have been presented of enzyme activities, assayed in vitro, that appear relevant to the synthesis of structural polysaccharides, and to their assembly and subsequent degradation in the primary cell walls (PCWs) of higher plants. The accumulation of the corresponding mRNAs, and of the (immunologically recognized) proteins, has often also (or instead) been reported. However, the presence of these mRNAs, antigens and enzymic activities has rarely been shown to correspond to enzyme action in the living plant cell. In some cases, apparent enzymic action is observed in vivo for which no enzyme activity can be detected in in-vitro assays; the converse also occurs. Methods are reviewed by which reactions involving structural wall polysaccharides can be tracked in vivo. Special attention is given to xyloglucan endotransglucosylase (XET), one of the two enzymic activities exhibited in vitro by xyloglucan endotransglucosylase/hydrolase (XTH) proteins, because of its probable importance in the construction and restructuring of the PCW's major hemicellulose. Attention is also given to the possibility that some reactions observed in the PCW in vivo are not directly enzymic, possibly involving the action of hydroxyl radicals. It is concluded that some proposed wall enzymes, for example XTHs, do act in vivo, but that for other enzymes this is not proven.