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

Abstract

A pulse-chase technique involving the in vive 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 molecular mass (M̄(w)) 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 M̄(w) of ~ 40000 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 M̄(w) (~ 39 000) indicated that this soluble extracellular [3H]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.