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 popu- lation 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 /Ww 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 /Ww (~39 000) indicated that this sol- uble extracellular (3H)xyloglucan was derived from par- tial 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.