Trimming and solubilization of xyloglucan after deposition in the walls of cultured rose cells

A pulse-chase technique involving the in vivo feeding of L-[1-3H]arabinose to suspension-cultured rose (Rosa) cells at 4 d and 9 d after subculture (fast- and slow-growing, respectively) was used to create a population of [3H]xyloglucan molecules and to follow their subsequent fate. The weight-average relative molecu lar mass (Mw) of [3H]xyloglucan freshly deposited in the cell wall was ∼160 000 and ∼240 000 in the fast- and slow-growing cells, respectively. The wall-bound [3H]xyloglucan of both cultures underwent a decrease in Mw of ∼40 000 during the first 2 d after the pulse-labelling. At the same time, 20–30% of the initially-deposited [3H]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 Mw (∼39 000) indicated that this soluble extracellular ( 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.