Abstract
Lateral expansion of the third internodes of pea epicotyls was evoked by treatment with either 2,4-dichlorophenoxyacetic acid (2,4-D) or ethylene gas. During growth, 2,4-D enhanced and ethylene inhibited the deposition of xyloglucan and cellulose in the cell wall, with the result that the wall framework (ghost) from ethylene-treated swollen tissue was much thinner than that from 2,4-D-treated. The level of activity of xyloglucan synthase, alkali-insoluble beta-glucan synthases, and endo-1,4-beta-glucanases were all enhanced by 2,4-D treatment but not by ethylene. Both 2,4-D and ethylene treatments led to increased osmotic potential in the swelling tissues. Accordingly, swelling after 2,4-D treatment was accompanied by xyloglucan degradation, concomitant with substantial net synthesis, but swollen tissue as a result of ethylene treatment was characterized by walls whose integrity was weakened by relatively low levels of newly deposited polysaccharides rather than by the degradation.