A pulse-chase technique involving the in vivo feeding of L-[1-H-3]arabinose to suspension-cultured rose (Rose) cells at 4 d and 9 d after subculture (fast- and stow-growing, respectively) was used to create a population of [H-3]xyloglucan molecules end to follow their subsequent fate. The weight-average relative molecular mass ((M) over bar(w)) of [H-3]xyloglucan freshly deposited in the cell wall was similar to 160 000 and similar to 240 000 in the fast- and slow-growing cells, respectively, The wall-bound [H-3]xyloglucan of both cultures underwent a decrease in (M) over bar(w) of similar to 40 000 during the first 2 d after the pulse-labelling. At the same time, 20-30% of the initially-deposited [H-3]xyloglucan disappeared from the cell wall, and a similar amount appeared in solution in the culture medium. Its failure to remain bound to the cell wall and its low (M) over bar(w) (similar to 39 000) indicated that this soluble extracellular [H-3]xyloglucan was derived from partial degradation of segments of wall-bound xyloglucan that were not directly hydrogen-bonded to microfibrils ('loose ends' and 'tethers'). The possible enzymic basis and biological roles of the degradation are discussed.
- cell expansion
- cell wall